Rochester carb dogs at 2000RPM

[fishnboat]

I have a 1987 bayliner with a 350 chev engine. We replaced the engine a few months ago, and all was good with the speed (up to 45mph) then it started running rough (after 8 hours on new engine). I have replaced the water-fuel separator, fuel filter at the carb, replaced the dist. cap, rotor, and condensor. It runs great at idol (650 rpm). As the rpm increases to 2000, it starts running rougher. In fact, above 2000 rpm, it seams to not increase any speed. I have observed the accel. pump, and it appears to be working properly. I suspect the secondary air intake not opening fully, but I really do not know carbs... The carb is a Q-jet by rochester, and I do not know of any work that has been done on the carb prior. Any information, suggestions, hints or comments would be great... I am trying to not have to rebuild this carb if I can help it...

 

[Whet_Spot]

Re: Rochester carb dogs at 2000RPM

I have a 87 Wellcraft 350 merc did the same thing, it was the Thunderbolt Ignition module. If you have a timing light hook it up and run the boat up to where it starts acting up and see where the timing is, I would think at 2000 rpm it should be around 14 degrees BTC or approx.

 

[Alrobot]

Re: Rochester carb dogs at 2000RPM

Unbolt the Q-jet, put it in the recycling bin, bolt a Holley 4160 Marine Carb on. Trouble should be over...

 

[fishnboat]

Re: Rochester carb dogs at 2000RPM

Whet_Spot -<br /><br />I will look into it tonight, thanks for the idea...<br /><br />I like the idea of trashing the Q-jet, however, funds would need to be aquired to do that...<br /><br />Signed, <br />no money...

 

[Alrobot]

Re: Rochester carb dogs at 2000RPM

Ebay is a wonderfull place, check it out...

 

[fishnboat]

Re: Rochester carb dogs at 2000RPM

Thanks to all who responded, it turned out to be the dwell settings in the distributer. As the engine speeds up, the dwell made the timing differencial increase which is why it started running very rough... <br /><br />Again, thanks!