I recently noticed while cruiseing the if I keep the car in 3rd gear and press the gas lightly the car starts breaking up around 2500-3000 rpms. If do a full throttle in third gear it never happens i guessing becuase the secondaries and kicking in. I have 73 primary jets in it now should I step up the primary a couple sizes ?

 

Either that or higher # PV.

 

Well the pv is already a 4.5 so I think im good there. I will step the primarys up to 75's and see what happens.

Since I got you on this thread I will share something with you I think you will get a kick out of. I recently met Barry Grant at the Syracuse Nationals car show and he gave a bit of advice for tuning a carb. He said never use a vacum gauge to tune. Who ever came up with it and made it general knowledge and put it into a magizine has probably been dead along time and his idea of tuning should go right out the door with him. Tuning with a vacum gauge is BS and the best way too tune is just smelling and seeing how rich you really are.

 

i disagree with the vacuum guage coments. You need to know vacuum to accurately tune the p.v. circuit. When you are cruising flat lighly on the throttle and it breaks up its lean. tell us more about your combo. Possibly need to fine tune the idle mixture screws and notch richer as when low speed cruising your on the idle circuit.

 

I'm not argeeing or disaggreeing with the commet I just posted it because I thought it was funny and others might get a kick out of it.

The idle screws are 3/4 out all the way around and the butterflies are set at about .030 open front and back. I put in larger idle air bleeds to lean out the very bad rich idle I had. Replaced all .070 idle air bleeds with .071 and it helped a little. So thats where in at with carb. It runs very well I just noticed it breaking up about a week ago and it only breaking up around 3000rpms light throttle. Under that and its fine.

 

Sounds too low. 6.5 is pretty typical, and works well in most combos. Unless you have a pretty hefty cam, you shouldn't be using one that low.

A wide-band O2 sensor is best, but a vacuum gage is better than your nose.

 

I've been told I have a pretty big cam for a 355. I dont have vacum worth a crap either. Here's the cam card tell me what you think.

http://www.lunaticamshafts.com/Produ...d=1781&gid=245




Right now Im just adjusting the idle by the eye and tears factor.

 

If you are not getting any steady cruise surging, you shouldn't touch the primary jets.

A 5.5 PV will probably cure your symptom.