[deere2940]

Alright guys, I am in need of your expertise. I recently restored my John Deere 316, rebuilt the 341aqs Kohler, cleaned and rebuilt carb. Started it up, ran great, went to mow with it, and after about an hour, it started to run lose horsepower and run rough. Now it seems (as I try to troubleshoot) after warming up at full throttle for about 8-10 minutes, it goes back to having little horsepower, running rough, and what sounds like a crack or snap occasionally.

I plan to try the "SeaFoam treatment" tomorrow on the carb.

Could it possibly be the coil? That is one of the few things I didn't replace.

 

[shivelyt]

Welcome to WFM, Benjamin,
Yes, it could be the coil. It could also be the condenser or possibly an exhaust valve sticking if the carb is set too lean. Try setting the carb a little on the rich side and see if that stops it.
Tom

 

[woodpecker41]

Benjamin is the carburetor a Kohler or a Walbro made carburetor? As Tom said I would replace the condenser first. They act up after they heat up when they are going bad and give similar symptoms. Roger

 

[deere2940]

To tell you the truth, Im not certain about the carb make. I got the rebuild kit from Deere for the Original carb, but their diagrams and Kohlers diagrams weren't decisive.

Perhaps I will replace the coil and condenser and give it the SeaFoam treatment Ive been reading so much about, and see what happens.

 

[deereman84]

Bejamin-

There are a couple easy ways to tell the carb make. If it has 1 adjustment screw, it is a Walbro. The Carter and some Walbro had 2 screws but only Walbro ever had 1. You can also look in the throat of the carb. There will be a number in the top of the throat. If it is a Carter carb, it should be a 30.

 

[hankvc]

Jeremy, if you are getting snap-crackle-pop in the exhaust, nine times out of ten, its the condenser.
I'd also check the condition of the ignition points and regap them.

Also, remember that on these small engines, a lot of problems that seem to be "fuel" are actually coming from a fouled spark plug. Put a new one in there before fussing with the carburetor.

Are you running ethanol gas? Can you get ethanol-free in your location? All of us here running small engines are now buying ethanol-free high-test, now that it's available locally.

Hank

 

[deere2940]

Well, after a new condenser and two Seafoam carb treatments, it seemed to run a bit better, but then when it got warmed up, it went back to the misfire every few seconds, and snap-crackle-pop whenever I adjusted the throttle.
I put in a new spark plug when I redid the engine, I have yet to put the new coil on. I will also check the points again when I find my feeler guage.

It runs like a top for the first 10-20 minutes, but after she gets nice and warm, I lose horsepower, it misfires, and any load the governor is trying to compensate for, it snap-crackle-pops.

Ive been running ethanol gas. It seem to run fine on it before I rebuilt it.

 

[deere2940]

It has two adjustment screws. high/low

 

[deere2940]

New coil, same problem

Ben

 

[shivelyt]

Ben,
After all you have done, I'm betting on a valve sticking. Before the engine is warmed up, open the adjustment screw on top of the carb at WOT until it starts running rough. Screw it back in until it starts to smooth out and see if that makes anty difference. If it does, you will have to remove the head and valve and ream it out as described in the tech manual.
Tom

 

[knottyrope]

my tiller did the same and it was the condenser that was bad

 

[deere2940]

Tom- No change. Even when it was cold, after 2 1/2 turns it didn't seem to affect the engine at all no matter how far out I turned it.

I checked point gap, its .020 and the plug is .035

when it cools down a bit, I will remove the head and take a look.

This time I timed it. Full throttle with mower running, it took almost exactly 10 mins before it lost power and started clicking.

The valves I didn't do anything with when I rebuilt the engine, they seemed good.

 

[deere2940]

Got the head off. There is a little carbon, not much. checked the gaps on the valves, and everything looks good.

Is there any way of checking for a sticky valve when the engine is cool and opened up?

 

[knottyrope]

can you look at the points while engine is running?

if yes is there a big spark on the points or just barley a spark? if a big spark then your condenser is most likley bad

 

[deere2940]

Ill look again, but I just put a new condenser on yesterday, I even located it on the coil bracket, appose to the base of the bracket next to the engine.

 

[knottyrope]

ok I didn't see you post that.

possible your valve lash is too tight on the exhaust valve and you are losing compression when hot as the valve stem grows when hot

 

[deere2940]

Well, Im at a loss. Sitting in the shop, with the mowing deck engaged, it will last about 8-10 minutes at full throttle. Then if I back it down to an idle (with deck still going) it will sit and pur like a kitten. I let it pur (cool down) for a few minutes, then I can take it up full throttle again for a few more minutes.
I don't have a tach, but temps on the head by the plug are around 400 degrees when it happens.

If the valve is possibly sticking, would it pur smoothly as soon as I back the throttle down?

Ben

 

[knottyrope]

400 seems a bit high

it might be running too lean or you have cooling fins plugged

 

[shivelyt]

Backing the screw out 2 1/2 turns with no change sounds like carb problems or possibly sucking air somewhere. Check the carb bolts to see if they are loose. Also check how much play is in the throttle shaft.
Tom

 

[deere2940]

I just did a compression test, and it read just under 90 psi.