[WrongDoug]

So I have my Craftsman Franken-Tractor that I picked up for free about two weeks ago up and running. It has a 16.5 HP Briggs number 313777-0134-E1.

It had a blown head gasket, a bad magneto and carb issues. I replaced the head gasket, adjusted the valves to .004" (some say .003" others .005", I think you're splitting hairs but .004" shouldn't cause issues), replaced the air filter and spark plug, replaced the magneto and replaced the carburetor with an aftermarket Nikki style one from Amazon. I also adjusted the throttle linkage to factory spec.

Now it starts and runs, but rough. It runs pretty good with the throttle set all the way down, but with the throttle in the fast position, it surges and backfires and eventually will stall. If you move it to the choke position (one lever for choke and throttle) it will run much better but still surges very bad. Then if you drive it up a hill (put a load on it) it seems to stop surging. Turning the mixture screw in or out does virtually nothing.

Not sure if the aftermarket carb is just junk, or if I need to look at something else. Any help would be appreciated.

 

[WrongDoug]

I watched this video-

https://youtu.be/Sf7Ld2Yd2VI

And I did what was shown. It ran maybe ever so slightly better when I reamed the jet out to about .023", and again ever slightly better when I went to the next size up (.028"), so I went up one more size to .034" and now it's runnings similar to where I started. Surging and backfiring, running really rough with the throttle in the fast position, runs about perfect in the slow position, and runs okay but surges badly when in the choke position.


Anyone?

 

[TobyU]

I watched this video-

https://youtu.be/Sf7Ld2Yd2VI

And I did what was shown. It ran maybe ever so slightly better when I reamed the jet out to about .023", and again ever slightly better when I went to the next size up (.028"), so I went up one more size to .034" and now it's runnings similar to where I started. Surging and backfiring, running really rough with the throttle in the fast position, runs about perfect in the slow position, and runs okay but surges badly when in the choke position.


Anyone?

Stay away form Youtube!! Every video I see is either the hard way or the wrong way.
Only problem with drilling out jets is ---well there is two----
1: usually it is not too small..it is dirty or the "idle" circuit is clogged causing surge at full rpms. AND
2: you can't go back smaller without buying new jet and you usually go too large on 2nd or 3rd adjustment.


31 series are about the most common out there and carbs are readlity available from as little as 18.25 on ebay.
They usually work fine.

The mixture screw is the low speed or idle mixture and will basically have no affect on full rpms.

Surging, hunting, and backfiring/popping are signs of lean. Burbling and rolling are signs of rich mixture.


Valve must NOT be adjusted at TDC. They must be at least about a 1/2 inch past TDC comp stroke. Did you do them this way?

The spec is intake .003-.005 and exhaust .005-.007 no matter what anyone says. You can look it up by googling "Briggs and stratton spec sheet"
It will run at .004 on exhaust but it is too tight and exhaust valve get hotter than intakes and exhaust seats and guides often slip and pop out on these 31 series ones and a valve cools when it is closed so .007 is better than .005 or .004 since out of spec. The wider gap in this case keeps valve closed for a wee bit longer.

Probably not you running issue though but for long term a light .004 or spot on .003 is best for intake and a loose .006 or spot on .007 is best for exhaust.
They do get wider as they wear and I often see them at .012 and more.


You could have an intake or vacuum leak.
You can spray carb cleaner or wd-40 around the intake and carb outside to see if speed changes.

I usually test for lean by folding a shop towel and holding up to carb or air cleaner throat to slightly but consistently restrict the air flow. A lean one will smooth out and speed up usually when you do this.

You can try a new plug and run a few minutes to read it to make sure it is not too rich now and sooting up plug.
Are you certain the choke it opening all the way?
The carbs on those have a habit (mainly old ones though)of sticking in closes position until you flick them open with finger unless they vibrate back open.


You said it gets better with load or hill...load from blades too? Hill can be fuel level in bowl leaning.
New carb should be ok...but you how should works...especially with new cheap stuff today.
Nikki design is a lot more annoying inside than walbro but they get the job done.

 

[WrongDoug]

I watched this video-

https://youtu.be/Sf7Ld2Yd2VI

And I did what was shown. It ran maybe ever so slightly better when I reamed the jet out to about .023", and again ever slightly better when I went to the next size up (.028"), so I went up one more size to .034" and now it's runnings similar to where I started. Surging and backfiring, running really rough with the throttle in the fast position, runs about perfect in the slow position, and runs okay but surges badly when in the choke position.


Anyone?

Stay away form Youtube!! Every video I see is either the hard way or the wrong way.
Only problem with drilling out jets is ---well there is two----
1: usually it is not too small..it is dirty or the "idle" circuit is clogged causing surge at full rpms. AND
2: you can't go back smaller without buying new jet and you usually go too large on 2nd or 3rd adjustment.


31 series are about the most common out there and carbs are readlity available from as little as 18.25 on ebay.
They usually work fine.

The mixture screw is the low speed or idle mixture and will basically have no affect on full rpms.

Surging, hunting, and backfiring/popping are signs of lean. Burbling and rolling are signs of rich mixture.


Valve must NOT be adjusted at TDC. They must be at least about a 1/2 inch past TDC comp stroke. Did you do them this way?

The spec is intake .003-.005 and exhaust .005-.007 no matter what anyone says. You can look it up by googling "Briggs and stratton spec sheet"
It will run at .004 on exhaust but it is too tight and exhaust valve get hotter than intakes and exhaust seats and guides often slip and pop out on these 31 series ones and a valve cools when it is closed so .007 is better than .005 or .004 since out of spec. The wider gap in this case keeps valve closed for a wee bit longer.

Probably not you running issue though but for long term a light .004 or spot on .003 is best for intake and a loose .006 or spot on .007 is best for exhaust.
They do get wider as they wear and I often see them at .012 and more.


You could have an intake or vacuum leak.
You can spray carb cleaner or wd-40 around the intake and carb outside to see if speed changes.

I usually test for lean by folding a shop towel and holding up to carb or air cleaner throat to slightly but consistently restrict the air flow. A lean one will smooth out and speed up usually when you do this.

You can try a new plug and run a few minutes to read it to make sure it is not too rich now and sooting up plug.
Are you certain the choke it opening all the way?
The carbs on those have a habit (mainly old ones though)of sticking in closes position until you flick them open with finger unless they vibrate back open.


You said it gets better with load or hill...load from blades too? Hill can be fuel level in bowl leaning.
New carb should be ok...but you how should works...especially with new cheap stuff today.
Nikki design is a lot more annoying inside than walbro but they get the job done.

Thanks for the reply Toby. The carb I'm using is an aftermarket Nikki style carb that I bought online for about $20. That is why I reamed out the jet. I figured with it being a brand new carb, it isn't dirty, especially since I sprayed it out with carb cleaner each time after I reamed it.

I am aware surging is a sign of a lean condition.

I adjusted the valves with one all the way open, and one all the way closed. That is how I was taught to do them on a car. Should I do it differently?

I did test for vacuum leaks by spraying carb cleaner around everywhere on the intake.

I currently have a brand new spark plug in it, I just installed it before making these adjustments. I can pull it and check it.

I have checked and visually verified the choke is opening all the way.

It seems to get better with a load on it when driving around and especially under a heavier load like up a hill. I have no mower deck for this machine so I couldn't tell you if engaging the blades would help or not.

 

[WrongDoug]

Toby, I readjusted the valves as per your suggestion. I adjusted them about 1/2" down from TDC on the compression stroke. I set the exhaust to about .006-.007" and the intake to about .003-.004". I can't tell any big difference in the way it is running. Here is a video of it running and you can see how it runs with the choke engaged and how it coughs and sputters with the choke off. I hope this helps display the symptoms a little better.

https://youtu.be/wOkGlj0kLZg

 

[Forest Gump]

You need to re-check your valve setting like Toby says (with piston at 1/4 inch past TDC on compression stroke) (this is the way the cam is ground for valve settings to be correct due to compression release on the intake valve) backfiring is a indicator the valves need to be checked and maybe corrected.

If this does not make it go:

Make sure you are not using a gas filter that restricts the gas flow. If gravity fed gas use a Red briggs filter, not a white filter or remove any filters for a test run.

Make sure the anti backfire solenoid pintle is retracting all the way.

Also on the Nikki carb, the adjustable jet is for the low speed idle area. (on some carbs the low speed jet setting will also slightly affect the High speed smoothness) Set the idling real low with the idle screw and then start with the jet at about 1 1/2 turns out and adjust the jet for fastest and smooth idle then adjust idle speed up to normal with the idle screw and slowly tweak the jet to best idle smoothness (usually only 1/4 turn from 1st setting, then advance throttle to medium fast speed and if not smooth try just a slight tweak of the idle jet again (1/4 turn) If the engine idles smooth and gets rough at high, it's most likely a lean condition. Do like Toby says try using hand over carb intake and adding a slight choke.

If you will search around on-line you can find a free download for a Briggs single cylinder OHV engine SERVICE Manual.

Also take what ya see on you tube with a grain of salt or a shot of whiskey or both.

 

[Tractor-Holic]

Might want to ensure the valves are opening to the full amount,it isn't uncommon for a camshaft lobe to wear down on newer Briggs engines..

If an exhaust valve isn't fully opening ,exhaust will back up in the cylinder and try to escape thru the intake valve next time it opens,causing it to spit back or backfire..

If the intake valve does not fully open it'll lack power and run lean,that too can cause backfiring and missing..

Making the fuel mixture richer will tend to mask these symptoms to a degree,but the higher the rpms go the more the valves not opening fully will make it misfire and spit back or backfire..

 

[WrongDoug]

In response to the last two messages-

Thanks, first of all.

I did readjust the valves correctly.

I have verified the shut off solenoid is opening and closing fully.

I have a red Briggs and Stratton fuel filter on it.

I'm pretty sure the valves are opening and closing fully, it's pretty easy to see the rockers move up and down.

 

[Forest Gump]

I did not see your video before I posted awhile ago.

It appears to maybe be starving for fuel (or too much air)

I would check that plastic carb intake manifold between the carb and the engine very close for a crack and also make sure the gasket's (o-rings are good at both ends of the plastic manifold. I really suspect if you do not see anything indicating a air leak you have a bad carb. You say the carb jet does not have any response no matter where it's jet set. They are usually critical to a good idle at 1-2 turns out. Your engine rpms are so fast that the L jet is not going to respond very critical, because the engine is using both the High and the L jet. Mostly the H fixed jet at the speed it's running in your video..

Appears maybe I heard the engine die from lack of gas (ran out of gas) at the end of the video. Remove the red filter and blow backwards through the filter and catch the expelled stuff in a white paper towel and see if you see any trash and also take off the gas cap and blow back through the fuel line towards the tank using low pressure air AFTER removing the gas cap. Also on that type plastic gas tank take the cap off and look INSIDE the tank at the fuel outlet hole, I've seen pieces of the black gas cap seal break off on those type and fall into the tank and restrict the fuel outlet hole. Leave the gas cap off when testing.

I suspect a bad CHINA CLONE carb and since you have been taking the carb apart it's too late for a warranty return/refund.

 

[WrongDoug]

Thanks for the reply Forrest.

Well I have some excellent news. I decided to take one last crack at removing the stripped out brass nozzle in my original walbro carburetor. I figured I had nothing to lose even if I destroyed the carb. So I hammered a torx bit into the brass and was able to spin it out with a 1/4" impact driver. The threads were a little chewed up but running the new nozzle in and out a few times seemed to straighten them back out. I cleaned all the shavings out with carb cleaner very thoroughly, and installed a new nozzle, new jet, new needle and seat, new bowl gasket and solenoid gasket, and then installed it on the tractor.

Sure enough, it fired right up, idles smooth in the slow position and the fast position. No backfiring or surging. Seems to be running very good. Hopefully it stays that way, lol. I only ran it for maybe a minute or two because it's raining now, but I think the cheap Chinese carb was definitely the issue.

I did accidentally bend the choke plate a bit when I chucked the carb in the vise, but i straightened it out and filed the edge down a bit and it seems to be functioning okay. I will get a video of it running as soon as this rain clears up. Thanks to all who responded! Very much appreciated!

Stripped out nozzle that was such a bugger to get out-
View attachment IMG_20190630_170407980_1562345914057.jpg

Rebuild kit I used-
View attachment IMG_20190630_170345194_1562345945694.jpg

 

[WrongDoug]

Well the rain let up just long enough for me to start it up and get a video of it running. You can see that the governor is still working the throttle a little bit, but not nearly as much as before. Also I don't have to have the throttle in the full choke position to keep it running. It stays running throughout the range of the throttle lever and runs as smooth on fast as it does on slow.

I'm going to replace the o-rings on the intake anyways and I'm also going to replace the fuel hose and put a new genuine Briggs fuel filter on it (it has a cheap aftermarket one on it now). I'll probably also add a fuel shutoff valve so the crankcase doesn't fill with gas in case the needle and seat ever fail again. Let me know what you guys think. Thanks everyone!

https://youtu.be/nBpzQnJwc5o

 

[Forest Gump]

couple things from experience:

You done good. Yes add a fuel shutoff between the gas tank and the filter, that way you can check clean the fuel filter every once in awhile with the gas flow off and always check the oil level before starting the engine after it's been not run for awhile (4 hours or more) and if the oil level is high smell and suspect oil contamination.
gas contamination of the oil sump will eventually happen with those type rigs and you will also forget to turn off the petcock every once in awhile. The way that mainifold connects to the engine is a direct shot and you most likely won't even see a drip of gas on the shop floor as a heads up needle /seat has flooded the sump.

Also if you will keep a eye open and get yourself a set of hollow ground gunsmith screwdrivers, they are really good for use as carb jet tools when needing to remove the tough stuck brass jets. Wal mart has them sometimes for $20 a set.

Also If it every gets to slightly running rough again, don't panic, just turn off the petcock and remove the bottom bowl nut and drain the gas from the bowl and re-install the drain leaving the bowl on the carb. Just a little bit of water will sometimes get to the bowl and upset the apple cart again. This is faster than trying to use gasoline additives to immediately cure the pain in the carb. (the water most likely comes from the gas can being used as a refill)

I prefer the Walbro carb's, but the Nikki usually get's er dun, but not always with the China clone carbs.

 

[TobyU]

Thanks for the reply Forrest.

Well I have some excellent news. I decided to take one last crack at removing the stripped out brass nozzle in my original walbro carburetor. I figured I had nothing to lose even if I destroyed the carb. So I hammered a torx bit into the brass and was able to spin it out with a 1/4" impact driver. The threads were a little chewed up but running the new nozzle in and out a few times seemed to straighten them back out. I cleaned all the shavings out with carb cleaner very thoroughly, and installed a new nozzle, new jet, new needle and seat, new bowl gasket and solenoid gasket, and then installed it on the tractor.

Sure enough, it fired right up, idles smooth in the slow position and the fast position. No backfiring or surging. Seems to be running very good. Hopefully it stays that way, lol. I only ran it for maybe a minute or two because it's raining now, but I think the cheap Chinese carb was definitely the issue.

I did accidentally bend the choke plate a bit when I chucked the carb in the vise, but i straightened it out and filed the edge down a bit and it seems to be functioning okay. I will get a video of it running as soon as this rain clears up. Thanks to all who responded! Very much appreciated!

Stripped out nozzle that was such a bugger to get out-
View attachment 2384937

Rebuild kit I used-
View attachment 2384939

This is why I tell customers I would rather clean out a factory carb than to buy a new cheap quality one. Even the briggs new ones are cheap quality.

 

[WrongDoug]

Forest, Thanks for the suggestion on the screwdrivers. I will be sure to grab a set next time I'm at Walmart. I too prefer the walbro style carbs. If the china clone would've worked, I'd have left it alone, but I'd still have been happier with a rebuilt Walbro. I just like the brass needle and seat over the all plastic design of the Nikki.

Toby, I'm an auto repair technician so small engines are an area of interest for me but definitely not my area of expertise. Still I understand the idea of fixing something old being better than buying cheap new. Brake calipers come to mind. In most cases I'd rather rebuild a customer's used brake caliper than replace it with a brand new one from the auto parts store just because I've seen so many fail. Sometimes aftermarket parts work fine, somtimes they are big no, and other times they are a total shot in the dark. Either way I'm glad I've got this one up and running again and I'm going to start hoarding these walbro LMT 5-4993 carbs when I find them.

As for the newer Briggs carbs, I see a Nikki option and another one, "Ruixing"? The Ruixing carbs look very similar to Walbros. Wonder if they are clones themselves?

Thanks for all the help everyone!

 

[Forest Gump]

This is why I tell customers I would rather clean out a factory carb than to buy a new cheap quality one. Even the briggs new ones are cheap quality.

I have several OEM carbs that I have rebuilt and saved that people had removed/replaced.

Few years ago I started using a heated type Ultrasonic cleaner for small engine carbs instead of the carb liquid cleaners. I had originally bought the USonic for cleaning brass hulls when reloading.
The Ultrasonic is really good for carbs, just toss the carb in, do not be concerned about removing the plastic or rubber pieces. On the really bad looking carbs I usually just leave all the jets, etc in place until the sonic has heated them and broke up some of the rust and gunk and the jets will come out easier.

 

[Forest Gump]

Forest, Thanks for the suggestion on the screwdrivers. I will be sure to grab a set next time I'm at Walmart. I too prefer the walbro style carbs. If the china clone would've worked, I'd have left it alone, but I'd still have been happier with a rebuilt Walbro. I just like the brass needle and seat over the all plastic design of the Nikki.

Toby, I'm an auto repair technician so small engines are an area of interest for me but definitely not my area of expertise. Still I understand the idea of fixing something old being better than buying cheap new. Brake calipers come to mind. In most cases I'd rather rebuild a customer's used brake caliper than replace it with a brand new one from the auto parts store just because I've seen so many fail. Sometimes aftermarket parts work fine, somtimes they are big no, and other times they are a total shot in the dark. Either way I'm glad I've got this one up and running again and I'm going to start hoarding these walbro LMT 5-4993 carbs when I find them.

As for the newer Briggs carbs, I see a Nikki option and another one, "Ruixing"? The Ruixing carbs look very similar to Walbros. Wonder if they are clones themselves?

Thanks for all the help everyone!

Midway USA reloading has the really good gunsmith screwdriver sets and they have some really good sales on them every once in awhile. The hollow ground screwdrivers have flat sides and are not as likely to ruin a carb jet or a tough to remove screw. Sign up for their on-line sales ads.
The Wheeler brands are really good and reasonably priced. The larger priced sets have large selection of different sizes screwdrivers heads, allen and torx heads and are good quality stuff in a nice case. I sometimes have to drive a torx head down into a stripped out allen head to get a removal.

Here is a link to Wheeler sets at midway.
https://www.midwayusa.com/s?targetL...1&userItemsPerPage=48&persistedItemsPerPage=0

 

[TobyU]

A lot of people use the ultrasonic but I think a lot of people just feel better when the entire carb body comes out all nice and clean but that's unimportant as far as the engine running correctly. I have never even use in ultrasonic cleaner and I clean these things out pretty much every day. Even on Sunday and the 4th of July. The key for many people who don't work on these all the time is knowing where the jet is. Many people take off the bowl and spread out the carpet cleaner and think they have cleaned it out when I really have that anything flush some fresh gas into the bowl. I always run wire through the Jets along with spraying with carb cleaner and strong compressed air. Some people only use carb cleaner and compressed air and this is where they run into some difficulties but that was still usually get clean enough.
Hondas are one you have to be careful about. Often you can clean out the main jet and they will still surge. Same way with the Chinese ones but the Chinese ones will be fine after you pull off the plastic Idle Jet and run a wire through that. Hondas have a similar with a metal screw but there are three tiny holes in the Smooth Bore of the carburetor closest to the engine side that often need to have a little crooked wire stuck in there and blown out well. This is only on about 20 to 30% of them that are clogged up and not running to start with.
This is a situation where an ultrasonic cleaner would probably get that clean the first time but you would have to remove the carb from the machine to do this. You must realize that I have about 50 mower's to fix at any given time and work on a 3 to 4 weeks backlog. I need to do these things as quickly as possible so 95% of the time I do not remove the carburetor to clean it out. I dropped the bowl and do it all from there. This is why I really like the older Briggs & Stratton. I can drop the bowl clean out the jet spray off the float and put it all back together without ever even removing the air cleaner assembly or even taking out the air filter. This is often only a five to seven minute job.
Now on a Honda or a Chinese one you have to take the bowl off which is nice and one regard because normally the gasket stays up in there and does not fall off whereas the briggs falls off about 10 to 15% of the time. You then have to unscrew the Jet and tap it to get the jet and the emulsion tube.
Sometimes you have to push the tube down from the inside or reach up in the center of it with a wire to pull it out. This is all a bit harder to do with the carburetor still on the machine but it still allows me to do the repair in a shorter amount of time. I tell people all the time that I'm quite weird I would rather work harder for a shorter. Of time and to work easier for a longer. Of time. If you take the carburetor off and put it on your nice clean workbench on a white towel or paper towel for everything is super simple and easy to get to, this will be at least a 20-minute repair if not 30 to 45. Plus, anytime you take a Honda carburetor off you take a chance on a gasket leak. Hondas have between 2 and 5 gaskets on them and you should never remove a Honda carburetor and less you have extra gaskets just in case.

 

[WrongDoug]

So I changed out my fuel line and filter and added in a shutoff valve. I got the hose at O'Reilly's and the filter and shutoff at TSC. Part number for the fuel filter (Red, 150 micron, for applications w/o fuel pump) is 298090S and part number for the shutoff is 698183. I'm going to continue to use the Sta-Bil 360 additive as it is relatively inexpensive when used at the recommended dosage. Hopefully these maintenance items will help prevent future carb issues.

I also changed the oil again and changed the oil filter this time too. I think I've done 3 short interval changes to try to flush out all the gas that was in the crankcase. Probably overkill but that's the way I like to do things. I used Tractor Supply's Traveller brand 10W30 full synthetic as it was dirt cheap at $3.50 a quart! That's cheaper than Walmart! I also used a Wix oil filter that is larger (and less expensive) than the original Briggs filter. The Wix number is 51348 or 1348 for the NAPA Gold equivalent.

View attachment IMG_20190707_172818126_1562535691947.jpg

 

[Forest Gump]

This may have already been mentioned:

Keep a heads up and check the oil level each time before you start the engine, even if you have turned off the petcock and keep a heads up for any oil level increase especially if you notice that you forgot to turn off the petcock during storage. Operating the engine with thinned out contaminated oil will usually ruin a crankshaft/rod fast. If you use the tractor very much you will eventually forget to turn off the petcock every once in awhile. (murphy's law)

Those type gravity flow carb systems will always eventually erratically when you least expect such seep through the needle/seat during storage and the engine runs ok when being operated with a seeping needle/seat because the engine is vibrating enough to seat the needle and the engine is consuming the gas. (all operating ok when running but intermittently leaks into oil sump at rest) It's a direct shot into the engine the way the carb and intake is mounted and no external leaks seen on those type carbs. I suspect the main reason the factory does not install a petcock is it would cost an additional few cents (and they can maybe sell additional replacement engines and carbs) and the owner/operator would not use a petcock until after the fact.:tango_face_surprise

 

[WrongDoug]

This may have already been mentioned:

Keep a heads up and check the oil level each time before you start the engine, even if you have turned off the petcock and keep a heads up for any oil level increase especially if you notice that you forgot to turn off the petcock during storage. Operating the engine with thinned out contaminated oil will usually ruin a crankshaft/rod fast. If you use the tractor very much you will eventually forget to turn off the petcock every once in awhile. (murphy's law)

Those type gravity flow carb systems will always eventually erratically when you least expect such seep through the needle/seat during storage and the engine runs ok when being operated with a seeping needle/seat because the engine is vibrating enough to seat the needle and the engine is consuming the gas. (all operating ok when running but intermittently leaks into oil sump at rest) It's a direct shot into the engine the way the carb and intake is mounted and no external leaks seen on those type carbs. I suspect the main reason the factory does not install a petcock is it would cost an additional few cents (and they can maybe sell additional replacement engines and carbs) and the owner/operator would not use a petcock until after the fact.

The leaking needle and seat is what started all of this. I may have previously mentioned I picked up this tractor for free a week or two ago from a guy who said it didn't run and had all kinds of problems but couldn't say exactly what kind of problems, other than he just wanted to get rid of it.

So when I got it home I smelled the oil before doing anything else, and it reeked of gas. So I drained it out and it was thin like water. Fortunately I don't think anyone ran it with the gas in the oil, because I pulled the cylinder head to replace the head gasket which was bad and the cylinder bore looked pretty good.

But I will be extra cautious about checking the oil for gas before starting it up and I'm going to make a habit of using the petcock everytime I shut it down for more than an hour or so. I don't have any attachments for this machine so it won't see a lot of use just yet, but I'm hoping to find a mower deck and a bagger so I can cut grass with it.