Shop rebuilt '75 auto 350 and installed cam, pistons and perfomer manifold - since I am running headers it opens up both ends. I know the Qjet is the preferred carb, so sent mine to Lars overhaul. Engine installed and idle is horrific - hold hand over primaries and it idles right up. Searched for leak - none found. Sent carb back to Lars to ensure it was good and he ran it on a couple cars and found carb ok. Took vette back to builder and he changed carb to an Edlebrock and says it runs fine now. Go figure?! In searching Edelbrock site I think there are some performers that a Qjet cannot be installed on. Could it be the intake??

Thanks for your input!

BTW - Lars does great work and is a great communicator. I am 110% sure the carb is not the issue.

 

Is the new Edelbrock a spread bore or a square bore? If it is a spread bore (#1901 through 1904) then there is very little differnce between it and the Quadrajet except jetting. If it is a square bore, did they install an adapter plate on the manifold when then changed carbs? If not you have the potential for a vacuum leak at the base of the carb.

Mike

 

No adapter installed. The more I read the more I think I have an intake issue. If I install an adapter I am not so sure I'll get hood clearance. I'm down to 1/2 as it is now.

 

The gaskets for the Qjet series are widely varied and will cause vacuum leaks if the wrong one is installed. Carefully make sure the one you use matches the carb.

 

I have an early Qjet on my 2101 performer, works great

 

My Qjet hasn't been "tuned by Lars" <yet>... but it runs great on my 2101 performer...

 

Same here

 

The Performer was made to run with a Q-Jet so you should have no compatibility problems. I would look to the intake and vacuum system for problems. First, did the shop mill the heads or the deck on the block? If they did, depending on how much material was taken off you may have a problem with the angle of the intake vs. the angle of the intake ports on the heads. You should be able to find this by spraying some WD 40 around the intake ports with the engine running. If the engine idle changes you have a leak. Also make sure you are using the correct gaskets on the intake. Edelbrock has some specific recommendations for intake gaskets to prevent leaks. Look on their site or get in touch with them. Make sure you have the correct carb gasket. My 74 has a rather thick gasket which not only seals but acts as a heat insulator, something you need to prevent fuel percolation. If all this checks out then I would disconnect all the vacuum lines and plug the connections to see if the vacuum system is causing a leak. If the engine idles and runs right with everything disconnected you will have to reconnect each system and troubleshoot it until you find the leak. If the vacuum system is not the cause of the problem then look to the distributor installation. Make sure you have it installed correctly and that the timing is set to specs. Also make sure the timing drops back at idle and advances under acceleration. If the weights in the distributor stick you will be way overtimed at idle. I'm betting that the problem area is with the intake to head seal but this should give you a good roadmap for troubleshooting. Good luck.

 

 

Performer 2101 and a Q-Jet on my 74 with no issues.

 

Bobbyg75 have you checked your QJet's choke & fast idle settings?

 

Did Lars drill out/enlarge the idle restrictors? If this is a 1975 Q-jet, there are restrictors in the idle passages (ensures lean mixture for emissions). If you installed a cam with a longer duration than stock, you will have less vacuum at idle than a stock L48. The vacuum will be to low to pull sufficient fuel through the idle restrictors. There may also be an off-idle flat spot or slight "bucking" from the lean conditions. Resrictors need to be drilled out with extra long drills (carb must be off with air horn removed) using a hand held drill vice. These are small holes, about 0.035", and should be increased in small increments (0.002" to 0.004"). You wouldn't have these issues with an older, pre-emissions Q-jet because the resistor is larger to begin with.