Engine Problem

[AirAg]

This is my problem, I have a 4 cylinder GPU cont. (PE90) with the bigger jugs(I believe the 0-470). I was told producing 150 hp at 2700 RPM, 68 x 34 stick, one mag, two barrell holley carb with a ported manifold. My problem is that when I step on the gas, it seems like it is lagging behind, like starving for fuel. However when I slowly accerate, it runs fine. I just put the new carb setup on thinking it would help, but it still lags like it performed with the one barrell zenith. So I wouldnt think the carb is the problem since both do it. This is what I know. I do have an air leak, on all four cylinders, where the intake pipes go into the heads. I know this because when I changed the carb around, all the heads had water inside when i pulled the intake pipes off. Could this be the main problem? I always heard that if you had any type of air leak going into your heads, it wouldnt run. But mine runs fine as long as you dont step on the gas all at once. Any advice? Or could it be that my prop is too big for that motor to sling? Will sling it at 2700. Thanks for the help guys

 

[c chardt]

this is right out of the book. LOW POWER OR SPEED
a.check propeller for track,balance and pitch
b. check spark plugs,wires,condensors,coils.
c. check for air leaks at all connections of carburetor and intake manifold
d. check for full opening of throtle valve.
e. check for unrestricted flow of fuel to carburetor inlet for proper operationof carb.
f. check cylinder compression and valve action
g. check carb air temp

 

[c chardt]

found another one ENGINE FAILS TO ACCELERATE PROPERLY
A. motor not sufficiently warm
B.spark plugs fouled by long idling
C. high float level
D. worn intake valve guides and piston rings.

 

[Daddy Dave]

I know this sounds crazy - but take a look at the fuel hose barb coming out of your fuel tank. I had one of those - all my few reamaining hairs are gonna fall out - problems like you describe. Looked at all of the listed steps above and - no luck.

Then I took the fuel barb loose from the tank elbow and - walla - it had an internal check valve and it was clogged with what looked like angel hair pasta. Cleaned it out and my baby went back to running like it was supposed to.

 

[kb27_99]

Check all the basic stuff first.

*Compression
*Timing
*Fuel Pressure
*Plugs (Are they showing signs of rich or lean?)


Just because you bolted up a new carb doesn't mean that it is tuned to that particular engine.

You mentioned that you are aware that you have an air leak. With an air leak in the intake system it is almost impossible to tune the carb. Until the air leak is fixed you may never get it right, and you may burn a hole in a piston or two in the process by running to lean. I fought with a ZZ4 350 for a couple of hours with the same symptoms, found a vacume line plug on the back of the carb dry rotted. Changed it out, adjusted the squirter cams and almost eliminated the lag.


Just my 2cents, Kevin

 

[Anonymous]

Have you checked the accelerator pump in the carb. I have also heard a leak on the intake side could lean out the fuel mixture.

 

[AirAg]

After I stopped the air leaks and cleaned out the plugs, the engine has alot more get up and go. May try to mess with the carb alittle more but I am happy with the performance now. Thanks for all the replys