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Last winter I rebuilt the engine in my 1972 350/200 MT. I had the block punched out .030 over and installed LT1 flat top pistons, a mild cam, and changed the ignition to electronic. The engine runs well but I have not been able to get the Rochester tuned properly, even after a rebuild. I was thinking of changing to a Holley LT1 carburator.I would greatly appreciate any suggestions here? I use the car as a driver but it is fairly original and I intend to restore it someday. The current carburator is not the original one.
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What do you mean you can't get the carb "tuned". Is there a cold start problem? A hot start problem? Does is stumble? Surge? Do you think it's the idle mixture, the off idle calibration, or the main or power circuit.
The Q-jet is a good carb. If you can't make it work, you'll probably have the same problems with a Holley.
Also, what's a "mild cam". Do you know the manufacturer and model and basic timing specs?
Duke -
Re: Give us more info!
The car is very hard to start when left setting even overnight I have to pump the gas pedal several times before it will fire. It always takes at least two tries to get her to run. Once running I had to set the idle at 1000 RPm to keep it running smmoth. I played with the idle screws but there doesn't seem to bee much difference until I run the screws either in several turns or out several turns. maybe it's just my inexperiance with carburation. I replaced the carb filter with a check valve filter thinking the fuel was being pulled back down the fuel line. As I said before I installed 30 over pistons which are flat top LT1. I put in new hydraulic lifters and the following cam. It is a Federal Mogul CS-1095R, cam lift .3000 intake .307 exhaust.Valve lift .450 int. .460 exh., .050 duration=224 both exh. and int.. I hope this gives you enough info. The reason for my interest in the Holley was that I thought the Rochester was not suitable for the higher compression of the new pistons and I needed more air/fuel flow. I thought maybe the Holley would give me this. If I stay with the Rochester I would like to replace the one on the car with the correct model. Can you or anyone tell me wher I can locate such.Comment
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Re: Give us more info!
The cam sounds like the FM reproduction for the L46/L82 cam. I can't find the original thread, so I don't know the year or engine of your car, but in some cases the same carburetor was used with both base, and HP or SHP engines, so the calibration is probably not to far off the mark.
I suspect that the insensitivity to idle mixture adjustment may be because of dirt in the carburetor. They have very small air bleeds that are critical to the idle and off idle mixture. Since it's hard to cold start the choke mechanism may be dirty and sticky.
I would suggest a thorough overhaul of the carb including soaking everything in a strong carburetor cleaner and carefully setting all adjustments at the correct specifications as a first step.
The pistons and camshaft have nothing to do with the type of required carbuetor. Your Q-jet probably flows about 750 CFM. It's just a matter of having a clean properly function carburetor including all the subsystems, and then perhaps a bit of recalibration.
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