Mystery engine issue i cant solve

[Squirrel Master]

So I adjusted the vales. The exhaust was actually within spec but the intake was a bit loose. I was surprised at how much the rockers wiggle around when not depressing the valve. I originally thought it was the exhaust valve but after actually checking tolerances I was wrong. The Intake was allowing up to .007. That doesnt seem too out of wack so I dont know if its going to suddenly make the engine run perfect. As far as the coil, I pulled the spark plug and reattached the boot, placed it against the engine and cranked it over. It seems to spark just fine. HOWEVER, the boot had a good size tear in it and I was being shocked while holding the boot. Obviously not good and maybe we found our issue... That being said, I've electrical taped the boot just to test it. I was thinking the charge was jumping to another part of the engine since the wire is routed so close to everything. Now once the silicon on the valve cover cures this evening I'll try to start it again and we will see if the problem is fixed. Fingers crossed but I'm guessing the valve being slightly out of tolerance and the spark plug boot crack isnt the main problem... Hopefully I'm wrong...

 

[Scrubcadet10]

You did adjust the intake down tighter, right? Max spec for the intake is .005"

 

[Squirrel Master]

You did adjust the intake down tighter, right? Max spec for the intake is .005"

Yes. its right at .003. The .004 drags in and out between the rocker and the valve. And the .005 wont go in at all. So withing spec. We got it back together and its still not wanting to run perfect. We had a hard time getting it started but after it finally started running and warmed up, it ran halfway decent at 2.5 turns out on the carb screw. He rode it around a bit and then parked it. We are going to try again tomorrow on a cold engine. It has a dancing idle. Its constantly going up and down and not running smooth. We fiddled with the carb screw but it seems happiest at 2.5 turns out. But again, really hard to get started when cold, backfires still when starting and wont idle right. We are both getting pretty annoyed with it at this point. The mower and engine havent seen much use. Everything appears to be in great shape but the damn thing wont run right. I electrical taped and then heat shrinked the spark plug boot. But i dont believe the coil/wire is an issue. It sparked well and never missed a fire when we were testing it. If we still cant get it to run right tomorrow, its a compression test and then off to the repair shop. We are running out of ideas. Lastly, does anyone have the spark plug gap handy? He did the plug himself and gapped it to match the old plug he pulled out. But the mower has run like crap since he bought it so maybe the last guy gapped it wrong?

Any thoughts? Im trying to help my neighbor out. He's retired, helped me out a few times and is a super nice guy. He's already dumped a bunch of parts into it and a shop probably wont be cheap. I feel bad that i havent been able to fix it for him. Thanks in advance and thanks to everyone who has chimed in.

 

[Scrubcadet10]

Get some WD40 in a trigger spray bottle, saturate the area around where the carburetor mounts, while the engine is running. If it blows white smoke or the engine starts running worse, there is an intake gasket leaking sucking in excess air causing it to run lean and surge.
I generally gap plugs to .030"
Will need the engine model number to look up the correct gap.

One thing i failed to mention is have you checked the flywheel key? It is possible for them shear slightly where it makes it run bad, without no starting at all.

 

[JohnFrancis]

Hello everyone!

(Pictures attached)

I'm trying to fix my neighbors mower for him. He just got a used Ariens zero turn with a Briggs motor. Its in great shape but we cant get the motor to run right. Below is the list of new parts we've put on...

- new carb set to factory specs
- fuel pump
- fuel filter
- spark plug
- filter
- oil and filter
- air filter

The mower is near-impossible to start when cold. The choke/throttle has to be all the way OFF and it backfires through the muffler and carb constantly until it warms up all the way. It WILL NOT start with the choke/throttle up even a little bit. If we can even get it started, once it warms up it runs halfway decent but not perfect. We've fiddled with the carb adjustment screw a lot and nothing seems to make it any better, only worse. We're running out of parts to replace and ideas to fix it. Hence, the forum post. Any ideas or suggestions would be greatly appreciated!

Please let me know if you have any questions or need any additional details. Thanks in advance everyone!

I’ve had a number of similar problems with aftermarket carbs. Usually with oversized main jets and/or fuel float adjustment way off.

 

[cdanon76]

Does this engine have points or a condensor?

 

[cdanon76]

Get some WD40 in a trigger spray bottle, saturate the area around where the carburetor mounts, while the engine is running. If it blows white smoke or the engine starts running worse, there is an intake gasket leaking sucking in excess air causing it to run lean and surge.
I generally gap plugs to .030"
Will need the engine model number to look up the correct gap.

One thing i failed to mention is have you checked the flywheel key? It is possible for them shear slightly where it makes it run bad, without no starting at all.

Why trigger spray and not aerosol can? I don't want to find out the hard way!! All I have is aerosol cans right now.

 

[Scrubcadet10]

Why trigger spray and not aerosol can? I don't want to find out the hard way!! All I have is aerosol cans right now.

I do it like that since the propellant is flammable.

 

[Gord Baker]

Hello everyone!

(Pictures attached)

I'm trying to fix my neighbors mower for him. He just got a used Ariens zero turn with a Briggs motor. Its in great shape but we cant get the motor to run right. Below is the list of new parts we've put on...

- new carb set to factory specs
- fuel pump
- fuel filter
- spark plug
- filter
- oil and filter
- air filter

The mower is near-impossible to start when cold. The choke/throttle has to be all the way OFF and it backfires through the muffler and carb constantly until it warms up all the way. It WILL NOT start with the choke/throttle up even a little bit. If we can even get it started, once it warms up it runs halfway decent but not perfect. We've fiddled with the carb adjustment screw a lot and nothing seems to make it any better, only worse. We're running out of parts to replace and ideas to fix it. Hence, the forum post. Any ideas or suggestions would be greatly appreciated!

Please let me know if you have any questions or need any additional details. Thanks in advance everyone!

Sounds like it is flooding. Carefully remove float and needle and wipe tip clean. Allow fuel to flow.
Check emulsion tube holes and the very tiny one on the bottom of the bowl jet at top of threads if it has one.

 

[Squirrel Master]

Get some WD40 in a trigger spray bottle, saturate the area around where the carburetor mounts, while the engine is running. If it blows white smoke or the engine starts running worse, there is an intake gasket leaking sucking in excess air causing it to run lean and surge.
I generally gap plugs to .030"
Will need the engine model number to look up the correct gap.

One thing i failed to mention is have you checked the flywheel key? It is possible for them shear slightly where it makes it run bad, without no starting at all.

model number.. 21B807 0130 B1. I believe the type number is 90223ZA.

Above is the model and type number. I'll try the WD40 spray this evening and see if I can detect a leak. The thing with the carb is that it ran crappy with the original carb. He replaced it with a new one (aftermarket) and it ran EXACTLY the same. So I don't believe the carb itself is to blame. I could be wrong but that sounds unlikely. An intake leak does seem more plausible.

I haven't checked the flywheel key. I'll give the WD40 a go first and then move on to the key if there isn't an intake leak.

The engine doesn't have points. Just an ignition coil.