Need Advice, Blow by at carb on Fx801v engine

help solve problem

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rrh

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Just purchased the mower with a blown engine. original owners ran it out of oil and wiped out the connecting rods and crank. I went ahead and installed new rings, rods, crank and of course seals and gaskets. I honed the block and before assembly. I did however assemble the block using assembly lube to ensure lubrication when first start. Anyway, getting to the point. The engine fired up fine but there is a lot of blow by through the carb. is won't rev up high and sounds like the timing is off. I tripled checked the timing marks on the crank vs the cam during assembly. I did notice the timing mark on the crank is a small arrow not a dot like the original crank. All parts were purchased from Kawasaki. Can anyone give me some advice on where to start or what to check.
 

mhavanti

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While you had the heads off, did you check the valves for sealing with some very light liquid such as toluene, gasoline, naptha, etc.? Did you grind the valves and seats and then make sure they were seating and sealing?

If the engine got hot enough, the valve springs may also have become annealed and lost 20% or more of their energy.

Here is how you can make a compression tool to hold the valves up while you replace valve springs. Break out the electrode and ceramic of a spark plug that fits the head. It can be any plug as long as it has the correct size threaded area and seating area. Whatever you air quick connect you use, place it against the spark plug base, weld it to the spark plug.

Then screw it into the spark plug hole, also, remove the hose to the fuel pump from the valve cover(s), place compressed air into the cylinder to test blow by from both the carb and oil filler tube. This will tell you if you have a valve leak and you will get some blow by out of the oil filler tube and valve covers as rings can't completely seal a cylinder.

Have fun and good luck,

Max
 

rrh

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I lapped the valves in using lapping compound, got a good ring on the seats there is about 3/16" wide lap looked really good. Also I forgot to mention when the motor was running I pulled off the crankcase breather hose (the one that plugs into the bottom of the carb. No Blow by. I didn't check valve leak by liquid test (my bag). and I didn't touch the carb during this rebuild. I have a compression tested so I can check the compression (just purchased it). I do that this weekend. I really hate to go back into the engine but may have to.

Thanks for your reply and advice
 

mhavanti

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rrh,

If you have a valve seat 3/16" wide, you're more than likely going to have a blow by. You only want 1/16" seat width as it will widen as it begins to wear in way down the road. It can seal much better and much less likely to grab any carbon from the fuel cooled engine in a narrow seat as the valves open and close they have a tendency to self clean. Wider the seat area, more likely you also need a stronger valve spring.

Do your compression check, you might also check the spring pressures on the seat as well as at full valve opening.

Do the compression tests first.

Max
 

rrh

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Again I'm sorry about mis information. My valve seats are more like 3/32" not 3/16" I typed the larger by mistake. I'll do a compression check this weekend. The one thing that stanks out to me was the comment about the exhaust seat moving when worn. I'll do another leak test before I come back with my findings. again thanks for the helpful advice.

RRH
 

mhavanti

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rrh,

Sounds good. Would like to see you back up to snuff soon.

Max
 

bertsmobile1

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While you had the heads off, did you check the valves for sealing with some very light liquid such as toluene, gasoline, naptha, etc.? Did you grind the valves and seats and then make sure they were seating and sealing?

If the engine got hot enough, the valve springs may also have become annealed and lost 20% or more of their energy.

Here is how you can make a compression tool to hold the valves up while you replace valve springs. Break out the electrode and ceramic of a spark plug that fits the head. It can be any plug as long as it has the correct size threaded area and seating area. Whatever you air quick connect you use, place it against the spark plug base, weld it to the spark plug.

Then screw it into the spark plug hole, also, remove the hose to the fuel pump from the valve cover(s), place compressed air into the cylinder to test blow by from both the carb and oil filler tube. This will tell you if you have a valve leak and you will get some blow by out of the oil filler tube and valve covers as rings can't completely seal a cylinder.

Have fun and good luck,

Max

Alternate method is to feed about 3' of thin rope into the plug hole then wind the piston up to compress the rope against the head.
 

mhavanti

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Bert,

Always more than one way to skin a cat.

Max
 

geelee

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think cam is out of time, pull 1 valve cover and plug . slowly rotate engine by hand. on the stroke that's not compression as the piston come up to top dead center one valve will close and other will open . this should happen right at top of stroke, if not cam is out of time
 
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