Need motor head help

[Gill-T]

Engine 305 V8 with Rochester Quadrajet carb.    Been trying to chase a Gremlin in my engine.  When I try to hole shoot and hit the gas my engine starts to bog when I hit 3000 RPM.  Can't go over 20 mph.  Also, when trolling if we try to throttle down too much it starts to sputter and can konk out.

 

So far this year I have had two different mechanics .....

 

Replace spark plugs

Carb rebuild

Cap and Rotor replaced

Anti-siphon gas valve replaced on tank

Checked for blockage on gas vent tube

New fuel filter at start of season

Gas is high octane non-ethanol

Fuel pump replaced

 

with the flame arrester off the choke plates are in the upright correct position when it starts to bog.

 

Any other ideas of where I should be looking?

Edited September 9, 2015 by Gill-T

[bout time]

Did anyone check compression in all the cylinders? Possibly have a bad cylinder? Just a guess.

[sszoldra]

Sounds like it's starving for fuel. Check the fuel pump pressure, or just replace the pump. Chevy pumps are cheap and easy to replace.

[quality time]

Check for water in gas. I've had it a few times. Put a sample in glass jar. If it looks cloudy or you have droplets in the bottom of the jar you my have water. I'm lucky that I have a drain on my carb bowl. I always catch it in a jar to see if that is the issue. Wes 

[rolmops]

What is sounds like is timing. As you increase speed, the timing should advance just a bit. It is a very easy check which you can easily do yourself,

Check your timing at 700,1500,2000,and 3500 and see if it is according to the book. if it does not advance after 3000 than you should advanve your timing possibly  at 700 ( if you have electronic ignition and check with a shunt) . With electronic ignition the advance is more  than with points so bear that in mind.

Edited September 8, 2015 by rolmops

[bulldog63]

had the same problem ended up bad distributor [ under the rotor ]  i was getting shocked touching the coil

[Gill-T]

Sorry I forgot to add the fuel pump was the last thing replaced.  No water in fuel.

Edited September 9, 2015 by Gill-T

[fishfearme]

I agree sounds like a timing issue. But the easiest thing to check would be compression to rule out any mechanical issues. I had a truck 305 that just ate camshafts.

[Xxx]

If it's a points distributor, check the timing at 700 rpm should be at 8*BTDC and to check the advance it should advance with more rpm up to 26* at 3000 rpm. Take cap off and make sure there is no play in the distributor shaft, meaning back and forth not up and down, look at cap make sure the rotor isn't scrubbing against the cap contacts. Will look shiny or smeared from the rotor cap against the cap if all checks out I had a coil go bad on me would run but act kind of like yours. I was told to use a Bosh brand coil, not a aftermarket such a a high fire or other brands. Good luck if you need specs I have a Seloc manual, years 64-86. And like others stated could be a cam going bad also, but that wouldn't be a intermittent thing that would be continuous thing. You would be getting a poping back through the carb.

[geezer]

On my little 120 I/o been having similar issues. Was your carb rebuild mostly a clean up and replacement parts or was it a full blown in the tank/sonic cleaning. My carb had to have passages cleaned with some kind of skinny things pushed through the passages, some kind of little ball thing was frozen in place. Probably not giving a mechanic's explanation but what I learned is that not all carb rebuilds are the same.

[Chas0218]

Engine 305 V8 with Rochester Quadrajet carb.    Been trying to chase a Gremlin in my engine.  When I try to hole shoot and hit the gas my engine starts to bog when I hit 3000 RPM.  Can't go over 20 mph.  Also, when trolling if we try to throttle down too much it starts to sputter and can konk out.

 

So far this year I have had two different mechanics .....

 

Replace spark plugs

Carb rebuild

Cap and Rotor replaced

Anti-siphon gas valve replaced on tank

Checked for blockage on gas vent tube

New fuel filter at start of season

Gas is high octane non-ethanol

Fuel pump replaced

 

with the flame arrester off the choke plates are in the upright correct position when it starts to bog.

 

Any other ideas of where I should be looking?

Does it sputter at the higher rpm? Sounds like the timing is too retarded.

[rolmops]

This may be completely different, but did you go over the lower unit and gear to make sure there is nothing wrong on that end?
 It can also be that one bank or maybe even one cylinder is not firing because of bad wiring between distributor and plug.

And then there is the coil which may seem fine when tested cold,but may be defective when it is hot.

Edited September 11, 2015 by rolmops

[RSF]

1) Check the airfilter, can you see light through it?

4) Check that the timing-advance (under distributor plate isn't stuck from lack of lubrication).

2) Check Choke Butterfly as it may be partly closed preventing enough air down the throat on hole-shot and above a certain amount of RPMs.

3) Change the PCV

[GAMBLER]

I just had the same issue and my water separator filter was full of water.  I had it replaced and the issue is gone.  It was new in the spring.  The filter was dumped into a glass jar and was 99% water.  A missing gasket on my gas cap was the culprit for the water intrusion! 

[cyrility]

You would think that living in Rochester you could find a good quarajet guy. They did have a soft cam problem. Most io's are accessible on the front to replace the cam without pulling the motor. It usually doesn't run well at ant rpm.

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