Please need help, changed head Gasket, now it cranks but won't start

Slimoo

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  • / Please need help, changed head Gasket, now it cranks but won't start
Hello Everyone,

I am new here and looking for guidance/suggestion with a problem that has been bugging me all summer. Last fall, I bought a used Husqvarna with a 21HP Briggs Vtwin OHV. The mower worked fine but was leaking oil. I changed the sump gasket but I noticed that it was still leaking oil and burning it on the exhaust. Seeing spring coming fast I decided to change the head gasket that I thought as the culprit. Apart for the oil leak, my mower ran just fine before the head gasket removal except maybe for a slow crank when starting the engine. My valves and rods seem ok, no bend or unusual wear. I used the "screwdriver in the spark plug hole" technique to find my dead center and reassemble valves and I adjusted them according to specs (on the bright side, the engine cranks much better than before) but the engine did not start. I noticed a lot of gas being pushed out of the exhaust each time I cranked. I thought I smelled gas in the oil so I changed it completely and started all over again. Same thing, gas in the exhaust and ultimately in the oil. I took my carburetor out and cleaned it out, the float was working fine and the needle was not the problem. I checked my spark plug and electricity was passing by, I checked the air filter\, I checked the fuel pump, all checked out. I used some starting fluid to try to get a combustion but nothing. Any suggestion help would be much appreciated. I had a working mower all winter which I tried to getting in shape for the summer. As a result, I've been mowing 1 acre with my push mower for the past 3 months :laughing:.

Thanks
 
Last edited:

bertsmobile1

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  • / Please need help, changed head Gasket, now it cranks but won't start
The float valve is not cutting off the fuel.
The fuel level rises then overflows through the bowl vent ( which now has to be inside the carb ) .
This fuel flows down the manifold and fills the cylinder , trickles past the rings &e ends up in the sump.
So first problem is to fix the carb.
crank the engine without the float bowl on & hold the float up so it is horizontal.
In this position it should stop the fuel flow.
If you have to push it up any higher then the needle &/or seat requires replacing.
Check the carb gasket, some times they overhang the edge and foul on the float, preventing it from rising high enough to stop the fuel supply.
Double check the pushrods it is possible to cross them over and also possible to have the pushrod sitting on the edge of the cam follower not in it.
Both valves should sit at the same height and both cylinders should be the same.

Change the oil.
When it is running, change the oil after about 1/2 hour and the oil filter as fuel diluted oil will damage the engine.
If the oil is too thin you can not get enough compression in the cylinder for the engine to fire.
 

Slimoo

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Joined
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  • / Please need help, changed head Gasket, now it cranks but won't start
The float valve is not cutting off the fuel.
The fuel level rises then overflows through the bowl vent ( which now has to be inside the carb ) .
This fuel flows down the manifold and fills the cylinder , trickles past the rings &e ends up in the sump.
So first problem is to fix the carb.
crank the engine without the float bowl on & hold the float up so it is horizontal.
In this position it should stop the fuel flow.
If you have to push it up any higher then the needle &/or seat requires replacing.
Check the carb gasket, some times they overhang the edge and foul on the float, preventing it from rising high enough to stop the fuel supply.
Double check the pushrods it is possible to cross them over and also possible to have the pushrod sitting on the edge of the cam follower not in it.
Both valves should sit at the same height and both cylinders should be the same.

Change the oil.
When it is running, change the oil after about 1/2 hour and the oil filter as fuel diluted oil will damage the engine.
If the oil is too thin you can not get enough compression in the cylinder for the engine to fire.

Thank you for taking the time bertsmobile1, I'll check all the above this weekend and see if I make any progress.
 
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