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Discussion Starter · #1 ·
I have a Kawasaki fh680v which is giving me fits. Starts and runs great when its cold and will run for hours without missing a beat until you shut it off. then it starts lightly popping back thru the carb and fuel then pools in the filter base. The work I have done to it is as follows:
Compression test 50psi on cyl 1 and 10 on cyl 2
Leakdown test 10% on cyl 1 and 20% cyl 2
For both of these I put new pistons, rings, all valves, pushrods and gaskets. Now compression is 100psi on both cylinders and leakdown is 10% on each.
Installed 2 new coils just to eliminate that possibility
I replaced both heads just because, well why not this far into it.
I swapped carbs with a known good one and this problem still persists. The only thing internally I havent replaced is the cam. It seems like a timing issue with the popping thru the intake but it doesnt do it when sitting overnight. Flywheel key and flywheel are fine and the crank and cam are timed correctly.

What am I missing here? I have 40+ years of working on small engines and I have never had any engine give me this much trouble.
 

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Welcome to the forum cdsand. I’m sure someone smarter than me will be along to help soon!


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until you shut it off. then it starts lightly popping back thru the carb
so does it do that when you turn the key to "off"?... and it doesnt actually turn off - it keeps running but all that stuff happens?....

Or do you actually turn it off... and then when you restart it 2 or 3 minutes later, it runs like crap?....

makes a difference as to what could be the problem.....
 

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I think your having a vapor lock or heat soak issue if I'm reading your post correctly(You shut it down then go to restart and the problem occurs). That would explain why after sitting overnight it starts and runs fine. I'd check fuel supply and make sure it's got good flow when hot. Also check the fuel line routing to make sure it's not close to something that'll boil the fuel in the line. It's really the only thing that fits what you describe happening.
 

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Discussion Starter · #5 ·
It can run for hours or just 1 minute. doesnt matter. Once I shut it off and immediately go to restart it is when it occurs. New fuel, have tried it with fuel cap off and still same issue. Fuel flow is where it should be and the fuel pump is working correctly. I just tried it this morning, it fired right up, I ran it for 2 minutes, shut it off, tried to restart and it pops thru the carb.
 

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Discussion Starter · #6 ·
so does it do that when you turn the key to "off"?... and it doesnt actually turn off - it keeps running but all that stuff happens?....

Or do you actually turn it off... and then when you restart it 2 or 3 minutes later, it runs like crap?....

makes a difference as to what could be the problem.....
It does it when I go to restart the engine immediately after I shut it off. Its not dieseling
 

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hmmm.. weird....

I guess I have a few questions.... you said you had 10PSI on one Cyl. and 50 on the other... this tells me you were running on 1-cyl., as there is no way that the 10PSI cylinder was running at all.
Then you said you installed new stuff including valves.. but then you replaced the heads after?.... did you check compression after the new heads - of those valves (heads) are old?...
you did a lot of work to that engine - the only thing that's not replaced is the block, starter, and ignition....

sounds like a float problem, or fuel cut-off problem....does the hot-start popping clear up after a few minutes?... does it blow lots of smoke on hot start up as if running way too rich?...

I am thinking the carb fuel boils and pushes into the intake..... or the anti-afterfire solenoid is not working (if your engine has one).... The anti-afterfire solenoid is a device that shuts OFF the fuel at the carburetor to prevent the engine from receiving fuel after the ignition switch is shut OFF. This is particularly important for when the engine is hot and fuel in the carb "could" boil.

Now the next question is - why would the fuel boil?... I presume this never happened before - so what's changed?... cooling fan is broken?.. plugged?... etc....

One last question.... you said fuel pools in filter base - well that can;t happen unless there is liquid fuel squirting up (back pressure) through the carb and into the filter assembly....
are you sure that liquid you are seeing is not oil coming from the block breather tube?... did you check your oil level?.. if you had 10PSI compression - that engine was "WORN OUT"... meaning other stuff is probably worn out as well... is there fuel leaking into the oil pan (implies float valve not working on carb)?....
 

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Discussion Starter · #8 ·
hmmm.. weird....

I guess I have a few questions.... you said you had 10PSI on one Cyl. and 50 on the other... this tells me you were running on 1-cyl., as there is no way that the 10PSI cylinder was running at all.
Then you said you installed new stuff including valves.. but then you replaced the heads after?.... did you check compression after the new heads - of those valves (heads) are old?...
you did a lot of work to that engine - the only thing that's not replaced is the block, starter, and ignition....

sounds like a float problem, or fuel cut-off problem....does the hot-start popping clear up after a few minutes?... does it blow lots of smoke on hot start up as if running way too rich?...

I am thinking the carb fuel boils and pushes into the intake..... or the anti-afterfire solenoid is not working (if your engine has one).... The anti-afterfire solenoid is a device that shuts OFF the fuel at the carburetor to prevent the engine from receiving fuel after the ignition switch is shut OFF. This is particularly important for when the engine is hot and fuel in the carb "could" boil.

Now the next question is - why would the fuel boil?... I presume this never happened before - so what's changed?... cooling fan is broken?.. plugged?... etc....

One last question.... you said fuel pools in filter base - well that can;t happen unless there is liquid fuel squirting up (back pressure) through the carb and into the filter assembly....
are you sure that liquid you are seeing is not oil coming from the block breather tube?... did you check your oil level?.. if you had 10PSI compression - that engine was "WORN OUT"... meaning other stuff is probably worn out as well... is there fuel leaking into the oil pan (implies float valve not working on carb)?....
I replaced the head because the exhaust valve seat sounded like it was loose when I manually pushed the valve in and released it. I peened around it as far as the contour of the head would allow and it somewhat eliminated that dead sound but with that and there being some wear in the valve guides I just replaced the head.
As for the fuel pooling in the filter base, yes its fuel, not oil.
As for the compression......the current compression on both cylinders is 100psi. The cylinders were within specs and not worn egg-shaped so I installed new piston assemblies. The ONLY internal components not replaced are the cam and crank.
If this were a fuel issue the engine would start, or at least attempt to fire without popping thru the intake, when starting fluid is introduced but it doesnt. It spits it back out and will occasionally ignite it leading me to believe there is a timing issue or a leaky intake valve but with all new valves and new heads it seems the valves should not be the issue.
 

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so on hot restart it doesnt even start?... sounds like maybe valves are getting hung up?... oil problem?... this engine is forced oil lube - did you confirm the pump works?....

by the sounds of the wear and tear you described (worn valve seats etc), that engine may be just plain old worn out and BER (beyond economic repair). There comes a time in every engine's life, where that's the case. then you chuck everything except the block, and rebuild....

100PSI on fresh rings etc is not that great. 80-90PSI is the minimum required for the engine to run. How did it even run at 50 and 10?... maybe your compression tester gauge is a bit off.....
 
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