[(username)]

Hi,

I own an old Scotts S1742 which I repowered with a B&S 15hp. It is not an Intek, it's an old Commercial & Industrial which came out of a Troybilt. The engine started and ran fine before I removed it from the Troybilt. Now that it is in my Scotts, it is hard to start. The engine needs to crank for about 30 seconds before the first ignition, and then another 30-45 seconds of cranking with intermittent sputtering before it will stay running. I need to start it at low idle, let it warm up for about 30 seconds, and then slowly bring the throttle up to operational speed.

- I tried adjusting/tightening the valves, it has made no difference.
- I tried tweaking the carburetor a few times. It is currently tuned well, but I have it running a smidgen on the rich side just to keep the engine from burning up.
- The choke is useless. If I try to use the choke, the engine simply will not start. I just leave the choke off.
- I believe the carb is the one which came with the engine, although I can't recall since I did the swap over a year ago.
- The troybilt had a choke which was separate from the throttle. The scotts had one of those setups where you could choke it by pushing the throttle all the way up. I couldn't really get it to work the same after swapping, so I installed a separate choke cable and lever, which I bolted onto the side of the steering column.

Once the engine is running, it runs very well. If the engine stalls while hot (e.g., running out of gas), then I have to set the idle low again to make it start, but it does not need to crank a lot like when it is cold.

Any ideas?

 

[steddy]

My guess might be that the choke isn't FULLY closing. Observe without the air cleaner installed to verify. Also, try disconnecting the choke cable and operating the choke manually while cranking.

 

[tomw0]

What a combo of symptoms. The need for a lengthy crank cold is indicative of lack of fuel in most cases. The hard start warm, and need to set at idle speed, indicates that it may also be lacking fuel as a wide open throttle plate will try to pull fuel ... that may not be there, so it won't even fire, as the mix is too lean.
I would check for a good flow from the tank by removing the fuel line from the carb, and catching the flow in a proper container. You should get full-tube flow of gas if it is gravity fed. No restrictions. If you have a clean fuel line, filter, and you get a slow feed, you might have a too-restrictive fuel filter. I have read that pumped system filters are more restrictive than gravity fed, but don't bet your paycheck.
Any way, you should get a full-diameter flow in either case. If you get that, then pull the float bowl and check that the float will drop properly, and there is not crud in the float valve.
One other thing is that an engine with valves adjusted too close may be difficult to start hot. The clearances close up, and may not allow good valve seating. If you ask around here, you can get instructions on valve adjustment. I think Walter has them available via email. Crankshaft to be at 1/4" past TDC to adjust OHV engine valves, from readings.
Does the installed carburetor have an adjustable 'main jet', or is it fixed? Most are fixed anymore. The idle mix is still adjustable on a lot. The idle mix is used as a 'transition' mix for the engine to accelerate to operating rpm without misfire, FWIW. If too lean, you will likely get stumble and hesitation as you advance the throttle to operating speed.
tom

 

[grattone]

What is the relationship between the fuel tank and the carburetor ? Did the old engine use gravity feed or fuel pump ? Just a thought, I have seen engine swaps that have had such problems.

 

[(username)]

The engine used to have a fuel pump which ran off of the crankcase breather. I removed it because the Scotts is gravity fed. That is something which actually made me wonder, but I didn't think it would matter to the engine, because the fuel tank setup seemed to be the main reason for the pump. The Scotts has an elevated tank which is directly behind the engine, the Troybilt had a tank under the seat which was level to the engine, hence the need for a little pump.

I have drained the fuel tank a few times now for different reasons, and it has a good flow. I will try taking the fuel filter off, though, to see if that will make a difference.

The carb was cleaned before the engine swap, and the starting issues began immediately. I don't think it is a dirty carb.

 

[B440]

Gotta see how much fuel flows out of the fuel line right at the carb. You may want to replace the fuel line if the flow is just a trickle.

I would put the pump back on; Having the fuel pump is a nice feature even when the engine can be gravity-fed because you don't have to worry about a leaky float needle and dumping fuel into the crankcase.

 

[(username)]

I am fairly certain that the pump is long gone. I have a bunch of parts sitting around, but I'm not about to start digging through them just to fix a hard start. After all is said and done, the mower runs well and does what it is supposed to do; this issue is low on my list, it's just a nuisance and not a serious problem.

All of your suggestions regarding the fuel line are intriguing though. The fuel filter is new, I put it in about a year ago. Now that you mention it though, I've seen crap at the bottom of the fuel tank from time to time, like little dead spiders and various bits of small debris.... the opening for the fuel out is very small, about 1/8", I wonder if something could have made its way into there and started messing things up.

 

[mower-obsessed]

Carburetors fed by a fuel pump usually have smaller needle valves and seats then gravity fed fuel systems because the fuel is under pressure, where as the gravity fed system uses larger orifices as to allow the fuel to flow more freely. If there was a fuel pump originally, I would either install it on the new set up, or get a carb kit that includes the needle and seat for a gravity feed fuel talk.

 

[(username)]

I am thinking that it is indeed a fuel delivery issue, because when it first starts, the engine putters very weakly for about 15-30 seconds, and then it suddenly starts to rev up. You guys are probably right, the engine is fuel starved and has trouble drawing fuel until the carburetor has generated enough vacuum.

Perhaps if I could implement a primer bulb....

Part of me wants to say that I swapped the Scotts carburetor onto it, though. So it should have a setup for gravity feed already.

 

[38racing]

My experience with the pump inlet is that starting is fine because bowl will be full from sit time. Engine may cut out under load because fuel supply cannot keep up due to smaller inlet. I agree that engine may not start unless choke is fully closed.

 

[(username)]

OK,

I will take the air housing off and verify if the choke is closing fully.

 

[Tom-machinery-idiot]

I've actually run across one or two fuel filters with just enough resistance to flow so they do not allow for gravity feed. I have removed the fuel inlet hose, no flow. Cover the open tank filler neck with my mouth and blow in some pressure and get a trickle. Replace the filter with a different one and it works fine from then on.