[jeremie]

Not sure what is wrong. Ran fine last year when i put it away for the winter got it out for summer my 400 won't stop back firing. Anyone know what might be the problem?

 

[tfgaasch]

Depending on when it is backfiring (when you shut it off or all the time). First thing I would probably do if it was doing it all the time is rebuilt the carb, next I would look at the governor might not be advancing/retarding spark correctly. Hope that helps.

 

[mikeduwe]

Lean running will cause backfiring, so if the carb is dirty or plugged that could be it.

Ignition timing should not have changed over the winter, but fuel could have gone bad.

 

[trapperjohn]

Do a compression test, you may have a sticking valve.

 

[jameszmcnelley]

HI Jeremie, from your description, I agree with Ron also. compression test will also tell you which side. if its a sticky valve you can trickle ATF into the carb while its running. that process will generally clean up the valve stems. may take an hour or two depending on condition. you can also add lucas fuel additive to the tank at the same time. if its the exhaust valve it may take a little longer to free up.
I once started a 39 Plymouth 6 cyl. flat head that had been sitting 30+ yrs. 56,000 original miles. fired up on just 3 cyls. eventually!! took me 2 days and several gallons of fluid but she cleared right up and was still purring like a kitty 6 months later when I sold her. got her from the proverbial little old lady who bought her new and said she was running fine, when she parked her. good luck, J.Z.M.

 

[sreynolds]

Mine was doing that and I found that the factory settings for the carb were bunk. I have to have 2 MORE turns on the screws to clear up the problem. I don't know why, but wondering if boring the engine block oversize would effect that. I doubt it is due to a faulty carb rebuild.........

Another issue/another time I had was the governor advance. It was trashed and would go in and out of proper ignition time.

 

[jdalchemist]

Jeremie,
Engine problems often appear after winter storage due to a bit of condensate moisture corrosion and/or mouse activity. All of the member suggestions need to be considered as a cause for engine backfiring. There are other causes as well. One comes to mind that would be simple to check. A capacitor that is open or not properly grounded will cause a K532 to run poorly with backfiring. Try cleaning the connections and use an ohmmeter if possible. If troubleshooting from the member suggestions does not solve the problem, please provide some more details about backfiring (upon start-up? upon shut-down? low speed? high speed? with acceleration?).
Harold

 

[grandpajay]

I found the same issue as Scott. To really fine tune the high speed jet, I did that in winter. It's the only chance I have to get the Kohler to grunt a little. It's just loafing when mowing. Jay

 

[wmgeorge]

IF it ran fine last fall the timing did not jump nor did the carburetor adjustment change by its self over the winter! Got either bad gas or the carb needs to be cleaned, or both. Back fire is either running lean or valve problems... usually.

Adjusting the screws is just compounding the problem

 

[69project]

Is it back firing while running or as you shut it down? If it's as you shut it down then check and see if the anti-dieseling solenoid is hooked up. That wire likes to fall off.

If the backfiring is while it's running then I agree with the above suggestions and would also suggest to take a look at the fuel system to see if something is restricting fuel flow.

 

[jeremie]

Thanks for the info. It is back firing all the time. Going to try to mess with it this weekend.

 

[mikeduwe]

Fuel, valves, or ignition timing...

But ignition timing should not have changed unless you sheered the flywheel key or something came loose in the ignition systme.

 

[sreynolds]

Just a thought....have you adjusted the valves lately??? Even if it is a new engine, you still have to go inside and adjust them after you operate it awhile.

I do not use the OEM ignition system, so I can't comment on any problems I have had w/that.

 

[wmgeorge]

You weren't running Ethanol blend and left it in all winter?? If that's the case, remove and drain the tank, replace fuel filters and plan on cleaning the carb, maybe more than once.

 

[motiv8]

Jeremie,
Are you calling an exploding noise happening out the exhaust as "backfiring". Many people have that incorrect. It's really when the fuel "fires back" thru the intake and carburetor. If your noise is out the exhaust then I'd suspect the condenser being faulty which usually causes burned, sticky or dirty points. Sometimes a sticky valve or weak valve spring can do that. MMO in fuel is good. All the other suggestions are valid. I just hadn't seen these yet. David

 

[jeremie]

Finally checked compression left side 85 right side 125. What it is doing is making popping out of the exhaust under 1/2 throttle and wont idle. Higher speed runs fine no popping. Looks like lots of junk in fuel tank going to pull it and clean it out.

 

[wmgeorge]

And after you clean the tank out and install a new fuel filter plan on cleaning the carb.
After you get it running redo the compression test, any sticking valve might be free after running for a while.

 

[hankvc]

Jeremie, if you are getting snap-crackle-pop noises out the exhaust, odds are on that your ignition condenser is on the way out. Replace it and see if that solves the problem.

Technically, popping out the exhaust is "after-firing," which describes what's actually happening. I think of "backfiring" as popping back through the intake and carburetor.

Hank

 

[wmgeorge]

He Said: Looks like lots of junk in fuel tank going to pull it and clean it out.

Let him solve one issue at a time. You guys have him jumping from one thing and another. Do you suppose the condenser just went bad setting for 6 months.... sure, maybe. But stale fuel and dirt in the tank are something that needs to be done no matter what.

 

[jeremie]

Pulled tank and cleaned it. Wow was there junk packed in screen in shut off valve. Took carb off and cleaned. The long needle looks not centered in hole looking from bottom with bowl off. Not sure if that would cause running issues? No more popping out exhaust. Cant get it to idle runs little rough at low speed.