jerry750 0 #1 Posted May 22, 2012 Hello, Just became a member and looks like I came to the right place for any answer for a problem I need. I have a 1988 520HC with a 60" Deck and a 20hp Onan. I am having a couple issues and need some help. First I have a vacuum issue when idling the vacuum gauge will fluctuate between 5 and 10 but when I open up the throttle and put it under load the vacuum drops to below 2 and it will not run. so my question is where is the most likely place on these engines to develop a vacuum leak, carb gasket, intake manifold I am not sure where to look, also I have noticed when running fuel filter is only about 1/4 full and fuel is spraying out of carb. Could these 2 issues be linked (vacuum & fuel) or are they 2 separate problems. I have read that stuck float, or gas in the float will cause the spewing. I just need pointed in the right direction So any comments suggestions and guidance is greatly appreciated. Thanks Share this post Link to post Share on other sites
Save Old Iron 1,563 #2 Posted May 22, 2012 Jerry, the "spewing" and low vacuum could be related. Is the gas spewing UPWARD out of the carb? If it is, a stuck valve or valve area damage could be causing the pressure produced on the compression and exhaust cycles of the engine to be blown upward into the intake manifold. Of course both these pressure cycles should be contained within the cyclinder by the exhaust and intake valves being closed. If either is stuck open or damaged, gas could be blown upward out of the carb. If the gas is spewing DOWNWARD into the manifold, sure, a stuck float or damaged gasket inside the carb could over run the carb bowl and drain into the manifold - but in this case, the vacuum would not be lowered significantly. Compression on either cyclinder can be checked by removing the spark plug - inserting your finger over the hole - turning the engine over and feeling for both the compression and vacuum cycles. If both cycles are weak, check the valves / head gaskets, etc. Share this post Link to post Share on other sites
jerry750 0 #3 Posted May 22, 2012 Now it seems to me that the gas was going more downward and the amount spraying downward was causing like a big gas vapor cloud coming out the top. Does that make any sense? Thanks for the info it was very helpful, now to start doing some investigating. Share this post Link to post Share on other sites
jerry750 0 #4 Posted May 23, 2012 Ok took everything off this thing today, intake manifold, exhaust manifold, tore carb apart and cleaned it thoroughly( it actually wasnt that bad). Took valve covers off left side looked really good and they were pretty much set correctly. The right hand side on the other hand was a little different story exhaust valve was way off I didnt check it but had to be pretty close to 20 to 22 thousandths the intake side was set too close at around 2 thousandths. I set the exhaust to 13 thousandths and the intake to 5. The biggest issue I seen and am not sure how much of a problem this is and im gonna try to explain this. Inside the port of the intake valve right side looking out toward the valve the outer wall looks as if something had really pressed against it hard cause part of the lip is rolled back into the housing. Now it doesnt seem to affect anything and before I took it apart I pulled the plugs and checked the compression and exhaust with my finger and it seemed to be pretty stout, I had to leave the project before I got it all back together so tomorrow evening i'm gonna try and get it back together and fire it up. Hopefully all is good. If anyone has any suggestions bout something I did or should have done please let me know before I put it back together. Thanks for reading Share this post Link to post Share on other sites
jerry750 0 #5 Posted May 24, 2012 Well fired it up this evening, ran alot better for awhile but vacuum still around 2 when load is put on then it started blowing gas up through the carb.and ran like crap. Is this a valve issue? maybe something i missed? Any input would be greatly appreciated. Thanks Jerry Share this post Link to post Share on other sites
