My first guesses are it is running quite lean and or there could be an air leak causing a lean situation.
I'd look for the obvious first such as any hose that might attach to the carb or intake. Cracked or otherwise poor condition?

Otherwise it may well be the carb needs a full rebuild. Just some initial thoughts.

 

Thanks for the reply. There is no air leaking that is obvious. The tractor and everything on it are in 'near new' condition and having checked everything over I see nothing like that out of order. I'm pretty confident the issues are carb related one way or another.

 

I've got 4 thoughts off the top of my head:
1. Remove the bowl on the carb and see if it's still clean. You could have debris in your fuel line getting passed the filter.
2. Run some sea foam in your gas.
3. Check operators manual for correct fuel...premium?
4. Have you tried adjusting the carb idle mixture?

 

Thanks for the reply.
1. I will remove the bowl again but expect it should be clean as I cleaned and flushed all lines prior to re-fitting.
2. I have Briggs and Stratton stabiliser in the fuel already, but will try to get some seafoam and give that a go. I'm in the UK and thats not a very common product here but I do see it on eBay.
3. The fuel I am using is UK super unleaded 98 RON - equivalent to US octane 91, or the highest grade pump fuel available. I have always used that in my garden equipment even though the octane is higher than recommended and have never had a problem.
4. No, but I am starting to think that this could be the key. I see just 1 adjusting screw on this carb. I will give that a go tomorrow.

I will also report back in case this thread helps anyone else!

 

Angus, I'm glad to hear you use a fuel stabilizer. I'm not familiar with the B&S, but here in the states we have StaBil...and others...and I'm a firm believer in using it. That said, putting fresh fuel...and now knowing you've got a stabilizer...is a good reason for re-examining your bowl. The fresh gas plus the stabilizer may (???) break up some deposits in your tank, lines, and carb that were chemically attached and merely flushing may (??) not have removed them.
SeaFoam. Do you have any marinas, or any place that deals with boats, near you? SeaFoam was VERY popular in marine use. It's basically a detergent additive that break down deposits in your fuel system. I've never had fuel problems, so I don't have any hands on experience, but I've heard nothing but good reports on its results.
I'm thinking that you already know how, but I'll just give you a quick lesson on idle mixture adjustment:
Warm engine and idle down to the lowest/slowest position it will run smoothly. Turn mixture screw slowly until rpm changes or engine sputters. Turn screw in opposite direction, counting the number of turns, until rpm again changes or engine sputters. Turn screw back 1/2 the total number of turns. If all the way in or all the way out doesn't change anything, carb is probably shot!
Best of luck, Bob

 

Brilliant help, thank you. For info here is the B&S stabiliser I use: https://www.ebay.co.uk/itm/BRIGGS-S...DDITIVE-fuel-fresh-measuring-cap-/362454524408?_trksid=p2349526.m4383.l4275.c10
I found seafoam on Amazon so have ordered a couple of bottles and will start using that in the future.
Thanks again!

 

Hmmm. I looked at the JD parts catalog for the X155R tractor...not much info there! No reference to an idle mixture screw, only idle adjust screw & spring. I'm thinking you ARE correct in that the screw with the spring only control the position of the throttle plate and not the mixture.

Sooo, I'm down to 2 conclusions/scenarios: you're not getting fuel or you're getting to much air!

Fuel: It's possible there's still "something" inside the carb that didn't come out when you cleaned it. There're small passages inside and nearly impossible to clean. A possible remedy is get a can of carburetor cleaner that you can dunk the entire carb in...dismantled that is. Don't use the spray cleaner...yet! Letting the carb soak for a day may loosen something, but no guarantees!

Air: Here's where the spray carb cleaner comes into play...BUT be VERY careful, this stuff burns! Get engine running and spray a quick burst into top of carb, rpm should increase and then idle back down (without touching throttle control). If rpm doesn't change, carb cleaner doesn't burn and no good for this. Try same thing with starter fluid...a short spray into running engine and rpm increases. Once you have this change of rpm, spray short burst around all gaskets...one gasket at a time. If rpm changes, that gasket is leaking and sucking fluid into cylinder and firing it. Spray around throttle shaft in carb also...they do wear and suck in air.

I have only one more REALLY odd ball thought: the carb has a "high altitude main jet! It's listed in the JD parts catalog but I have no idea how to tell a std jet from a high altitude jet. Thinking about this though, it could make sense! Less/thinner air at altitude you'd want less fuel. If you have less fuel (at or near sea level) you'd want less air (achieved by applying choke!)

Other than those thoughts, no other constructive ideas! Bob

 

Yup, screw is idle speed control and not idle mixture. Bob

 

If you've got everything back together, try the spraying before dismantling...again!...and dunking. Also, oil on the felt washer(s) around throttle shaft may help (dark brown ring below screw in last pic). Bob

 

All good advice, thanks again. I will give this a go tomorrow. I know that the carb cleaner burns as I sprayed a touch of it in the intake to get the engine started after the last time I took the bowl off, so it will be good for testing with.

My gut is telling me that the carb is either damaged or as you suggest still blocked up inside. I am looking at getting a replacement but struggling to find one. The part number I wrote down off the old one is 897722 - 602401 - 7625, but searching with that number does not bring anything up - perhpas I wrote it down incorrectly? The engine number is 4055-77-0280-B1 but again I'm not finding a carburettor searching with that number either. I hope I can find the Briggs and Stratton carb as I found the John Deere one (I called my local service centre) and they gave the number AM135089 but the price they quoted me was frankly ridiculous, something like £270 (USD $350!!!!) so I thought it best to search for the B&S instead!

I am definitely going to strip the carb again and this time clean it like you suggest, by soaking it overnight, BUT, again my gut is telling me best to just replace the carb before wasting too much more time.

Anyway, thanks again for the help, and I wll report back with tomorrows findings.

 

Hang on, I found the B&S part number for the carb after searching with the engine number:

https://www.repairclinic.com/PartDetail/Carburetor/699807/1645114?modelNumber=405577/0280-B1

So, it's a 699807 I need to get.

 

Quick video i took earlier today after the 2nd carb clean and fitting new filters and spark plugs. The engine was fully warmed up here. You can see / hear that with the ening will surge at idle and not idle smoothly until the choke is partly engaged. Next you can hear that when the engine is run at speed there is a 'sweet spot' with the choke that allows the engine to run smoothly. 100% choke, engine bogs down, 0 choke engine sounds rough like it is running lean, 75% choke runs sweet, but I don't think the full power is there so I will definitely get to the bottom of this until I am happy!!

 

The carburetor your showing is pretty much a general purpose carb used by Briggs. Look at the carb and you'll see a model number on it. Go to Amazon, search for the model number and buy a new carb. I've picked up three of those in the past 6 months for anywhere between $35 and $90. Replace the carb and be happy.

https://www.amazon.com/s?k=briggs+and+stratton+carburetor+699807&ref=nb_sb_noss_2

Here's on for $38;

https://www.amazon.com/YunStal-6998...?keywords=briggs+and+stratton+carburetor+699807&qid=1556827744&s=gateway&sr=8-4

 

Got it. I found the correct one on Amazon and have ordered it. Cheers!

 

Super. Good luck and let us know how you make out with the replacement.

 

Well, it took a while to get to me but the new carburetor arrived today, so I fitted it and tested the tractor. GOOD NEWS - the choke issue is gone! The engine will start with a bit of choke (as expected), then after a few seconds the choke gets turned off and it runs well (again, as expected). I cut some grass to test things out, it was all good with the tractor fully under load, but when the PTO was disengaged I became aware that the engine was 'surging' or 'pulsing', basically searching and not running at steady RPM's. This only happens at high RPM, the idle is in fact very steady.... Again, when the PTO is engaged all is good. I'm kind of stumped again so currently I have the old (original) carb fully stripped and in a cleaning bath and I will rebuild it with the repair kit I also bought (which arrived today too) and will probably fit this back on tomorrow to see if any difference is seen with it's performance.

I can't help but think these Nikki carbs (which have no mixture adjustment on them) are a bit of a pain, as if they are not working correctly there is not much that can be done. I'm also thinking that the replacement carb I got, which was a Chinese made copy might not be of the best quality as well!

Any comments?

 

Angus, Don't bad mouth the Chinese quality ...yet! I could be (??) as good or better than US made or it could also be pure crap! Only time will tell.

Not mainland China, but a company I worked for used a facility in Taiwan. Many/most of out tolerances were +/- 0.005". Upon inspection of parts, we seldom found .0005" from the nominal size. We demanded quality and we got quality. The parts were well within the specs of our drawings and where 1/3 of the cost...delivered to our door!

BUT, these were parts made to our specs. If a Company ...Chinese, Russian, German, or US... makes a part to THEIR standards, it can be anything! To me, a large problem would be not knowing what company is making the parts. Company "A" could be making excellent parts, Company "B", pure garbage. When you order on-line you've no clue if the parts are from Company "A" or "B". If you got them from "A" and recommend them, the next person to order may get "B".

Bottom line, you may get/have a good part that'll last for years and years or junk that will fail in a year or two. Bob

 

Very good points indeed!

 

OK, so to end off my story, here is what happened.
To sum up: Original carb after fuel cleaning, service etc - engine was running well but only with lots of choke. Replacement brand new carb, worked well but engine was constantly surging / revving low to high when not under load. Next step, rebuild original carb completely with the new repair kit and re-fit. Result, engine was running very well, with no choke needed , however, this time the surging issue remained unless the tractor was under load - this was strange as it was not previously there with this carb... Anyway, I cut some more grass and everything was going OK until I became aware that the rpm had dramatically increased, like full throttle! So, I took the tractor back to the shed to investigate. After examining how the throttle lever was constantly in the wide open position at all times I deduced that the governor must have failed. My testing of the external components of the governor proved this - there was absolutely zero resistance on the governor shaft while running the engine and manually operating the throttle.......
So.... I took the engine off the tractor, removed the sump and saw that the governor was broken up, with some damage to some of the governor cog teeth as well. I have no idea how this happened, but I'm thinking the failure was coincidental to the carb work I had done, and *perhaps* the 'surging' I was seeing was an early sign it had started to fail. Anyway, I cleaned the broken metal from inside the engine, cleaned everything up, inspected the shaft that the governor slides on (it appeared perfect), ordered a new sump gasket, PTO oil seal, rocker gaskets and new governor, and a few days later when they arrived fitted them to the engine, then re-fitted the engine. Guess what? - she's up and running again, completely perfectly this time! I set the governed idle and high (non load) revs as per the B&S manual using my laser tacho, and everything is totally perfect now – no surging, excellent power and performing like new. Quite an adventure but at least it's perfect now and can do it's job like it was meant to!
Here’s some pics:

 

:thThumbsU Nice job! Now your next adventure might be to change oil in your Tuff Torq T40 hydrostatic transaxle. 118 hours is a good time for first oil change. You've proven you know your way around a toolbox. Dropping the transaxle will be a piece of cake!

 

Well, at 130 hours I did the oil service on my Tuff Torq K46 transaxle. Easy enough job with the rear of the tractor raised as high as possible. I removed the sump from the transaxle while I had it on the bench and stripped most of the internals out of it to thoroughly clean everything. No sign of any wear at all to be honest but there was a bit of sludge / debris on the dirty side of the filter and a few very small metallic particles. I toyed with the idea of fitting a drain plug on the sump to make future changes easier, but as it is really not that hard to pull the transaxle and having it on the bench allows opening and cleaning I decided against it. Anyway, on a very positive note, I really didn't think anything was wrong with the transmission on my tractor but it always took a long time to start moving in reverse when I pressed the pedal, also it was very slow in reverse. I thought that was normal but after this oil change it is noticeably quicker to engage reverse and also considerably faster when moving in reverse too, so I'm quite happy about that!



For info, on the X155R the removal is as follows: Lift rear of tractor and place high on axle stands. Place a 3rd axle stand directly below the transaxle just touching it. Remove the single bolt on the rear plate just below the chute which allows you to open an inspection hatch. Remove both rear wheels. Unbolt the 1 bolt that holds a metal rod which passes from one side of the tractor to the other just below the transaxle pulley. I’m not 100% sure what this rod does, but if not removed it prevents the transaxle from dropping. Next, unbolt the 6 bolts securing the transaxle to the tractor and gently lower until supported by the axle stand. Next, remove the belt through the open inspection hatch. Finally, gently lower the transaxle until it can be carried off for cleaning.

There are many online guides for the stripping and oil change etc so I wont cover that here, but it is very easy really. The only thing that confused me was 'bleeding' the system after adding the new oil. All I did was operated the transaxle shaft for around 5 minutes with my drill while moving the lever for forward and aft. I could not get the driveshafts to turn on the bench, but as soon as the unit was re-fitted and operated it immediately worked, so i can only assume that my drill work must have bled and primed it well.