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Discussion Starter #1
Just replaced cylinder head gasket . New Head and valves . I cannot reduce idle below 1600RPM. No adjustment for idle mixture, fixed. Runs fine ,but backfires and have to choke it to shut down. suggestions please
Thank You,
Bob
 

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Why did you replace the head? Idling too fast - what about the idle speed screw? If you can close the butterfly completely you may have a vacuum leak. Did you have the butterfly out? If so, it may not be oriented correctly.
Why would you have to choke it to shut down? Does the ignition kill not work?
Backfiring during operation? Lifters may need to bleed down, or could be valve not seating or improper mixture (too rich/lean), stale or water in the fuel. Even spark plug gap can affect it's operation.
 

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Discussion Starter #3
The head where the head gasket blew out had piece of the head broke off. Butterfly was not removed. kill switch works. there is no adjustments to mixture , just idle speed. If I turn idle speed down it will shut down if rpm is lower than 1600rpm. Fresh gas. spark plug gapped at .040 per manual.
 

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So you are saying it only runs if above 1600 RPM but backfires only then. How do you choke it down after it back fires?

Or does it backfire when you use the kill switch? Or turn down the idle speed?
 

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Discussion Starter #5
After cutting the lawn and engine is hot ,when I use kill switch it wants to keep running so I choke it and it shuts down. It would shut down just with kill switch by only after backfiring. If i back out idle speed screw It will shut down below 1600 RPM without the key switch.
 

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How long will it keep running with the kill switch engaged before it backfires?

And how long are you waiting before you choke it down - so it will not back fire.

Is there a fuel line shut off valve?
 

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If it continues to run with the ignition cut-off, it's dieseling. The only way that can occur is if it's over-heating. You have something else going on here.
 

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Discussion Starter #8
How long will it keep running with the kill switch engaged before it backfires?

And how long are you waiting before you choke it down - so it will not back fire.

Is there a fuel line shut off valve?
when it started backfiring , i turned key back on and choked it to shut it down.
 

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Discussion Starter #9
How long will it keep running with the kill switch engaged before it backfires?

And how long are you waiting before you choke it down - so it will not back fire.

Is there a fuel line shut off valve?
no shut off valve. I was wondering if a ful solenoid valve could be added to current carb.
 

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It would be easier (maybe) to insert a manual one in the fuel line and use it to shut down with. The back fire is from fuel/fumes leaking into the muffler and igniting. Or worse the overheated block. This doesnt fix your primary issue but gets rid of the back fire.

But, then it doesnt ever backfire when you choke it down though - right?
 

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Discussion Starter #12
It would be easier (maybe) to insert a manual one in the fuel line and use it to shut down with. The back fire is from fuel/fumes leaking into the muffler and igniting. Or worse the overheated block. This doesnt fix your primary issue but gets rid of the back fire.

But, then it doesnt ever backfire when you choke it down though - right?
If I let it idle (1600rpm) for about a min. ,choke it and turn key switch off, no backfire. Need to get it to idle lower. I have another Kohler, same carb, will not idle either. I think, for some reason they are running lean.
 

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Let's try a different approach. Can you physically move the throttle link or plate toward idle, and have it slow down below 1600? I'm looking to see if the throttle bell-crank can be moved to contact the crack screw (idle speed screw).
Since it worked ok before, perhaps you have a linkage problem, or need to do a static governor setting.
As I said before, I think you have something else going on here.
 

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Discussion Starter #14
Let's try a different approach. Can you physically move the throttle link or plate toward idle, and have it slow down below 1600? I'm looking to see if the throttle bell-crank can be moved to contact the crack screw (idle speed screw).
Since it worked ok before, perhaps you have a linkage problem, or need to do a static governor setting.
As I said before, I think you have something else going on here.
I did a static check of the governor and it is ok. Right now I have idle speed screw turn in to keep it at 1600 RPM. if I back it out much lower it will just die.
 

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Let's review. Did it idle before you replaced the head? If so, then ask yourself, what changed? This is what I ask of mechanics and users alike, as something may have been mis-installed; a procedure may have been done incorrectly resulting in a new problem; an underlying problem may have become worse (like a cracked carb. insulator etc.); or a problem may exist with the replacement part. Sometimes taking a break a day or two allows you to look at it with "new eyes."

I still think you may have a vacuum or even compression leak. Try spraying carb. or brake cleaner around the carb. mounting area while looking for an RPM change. Take care not to hit the throttle shaft, as that will result in a false-positive. This could even be a carb. mounting gasket issue allowing a leak.

A leak-down test isn't easy, and while that may be necessary in the end but let's keep looking first.
 

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Discussion Starter #16
Let's review. Did it idle before you replaced the head? If so, then ask yourself, what changed? This is what I ask of mechanics and users alike, as something may have been mis-installed; a procedure may have been done incorrectly resulting in a new problem; an underlying problem may have become worse (like a cracked carb. insulator etc.); or a problem may exist with the replacement part. Sometimes taking a break a day or two allows you to look at it with "new eyes."

I still think you may have a vacuum or even compression leak. Try spraying carb. or brake cleaner around the carb. mounting area while looking for an RPM change. Take care not to hit the throttle shaft, as that will result in a false-positive. This could even be a carb. mounting gasket issue allowing a leak.

A leak-down test isn't easy, and while that may be necessary in the end but let's keep looking first.
I'll be back on it this week
 

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Although very rare on non-"push" mower engines where blade-impact doesn't occur, severe back-fires or extreme shock-load situations could potentially partially or fully shear the flywheel key, resulting in out-of-time ignition. This would actually explain both the over-heating and refusing to idle, albeit a far shot. But then, mechanics do run up against this type of gremlin from time to time...your least thought cause turns out to be the culprit. I've seen bent/sheared flywheel keys on an Exmark Explorer, Snapper riders, even 2-strokes so it has to be considered at one point or another when you're pulling your hair out. But an out-of-time engine will often have starting issues, such as kicking back, or hard to start so if you have either symptom...

I bring this up as I don't know the circumstances leading up to the cyl. head damage...shock-load, piston impact etc. could have occurred, but then I wasn't there.

I've seen some problems be caused by the least likely suspect, so everything is fair ground when you've covered all the "normal" bases.
 

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Discussion Starter #18
Although very rare on non-"push" mower engines where blade-impact doesn't occur, severe back-fires or extreme shock-load situations could potentially partially or fully shear the flywheel key, resulting in out-of-time ignition. This would actually explain both the over-heating and refusing to idle, albeit a far shot. But then, mechanics do run up against this type of gremlin from time to time...your least thought cause turns out to be the culprit. I've seen bent/sheared flywheel keys on an Exmark Explorer, Snapper riders, even 2-strokes so it has to be considered at one point or another when you're pulling your hair out. But an out-of-time engine will often have starting issues, such as kicking back, or hard to start so if you have either symptom...

I bring this up as I don't know the circumstances leading up to the cyl. head damage...shock-load, piston impact etc. could have occurred, but then I wasn't there.

I've seen some problems be caused by the least likely suspect, so everything is fair ground when you've covered all the "normal" bases.
I, had that thought about the flywheel key and I actually started to take flywheel off to check, then had second thoughts. Today I slowed idle down as far as I could without it stalling. I'm going to bite the bullet and remove the flywheel and check the key. It does start ok
 

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Discussion Starter #19
JUST GOT BACK ON IT. TOOK CARB OFF TO CLEAN AND INSULATOR BLOCK ALMOST FELL APART. DON'T HOW i MISSED THAT. ORDERED NEW . I WILL GET BACK TO YOU ALL AFTER i REPLACE IT. THANK YOU
 

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Discussion Starter #20
Replaced insulator block. I know that was bad(cracked and burned). Did a leakdown test, passed with flying colors. I decided to look at flywheel key. Glad I did. Sheared and two magnet were on stator. replaced key and cemented magnets back. Running great.
THANKs guys you made me think. Thanks again to you all for the input
 
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