New carb on 351C problems!

porkchop3k · Jan 14, 2009

Well I just got my new 770 Holley Street Avenger on my Cleveland yesterday, but it wont run. It has an electric choke. It will run while the choke is engaged but it will not stay running once the choke lets off unless I stay on the gas, but once I let off the engine dies. Im getting good pressure and there are no vacuum leaks or anything. So I guess I am running too lean? I am just throwing that out there and making sure before I go tinker with the fuel mixture. Also if I run the idle higher it still will not want to idle. So am I real lean. I had no problems with my old carb except it did not have a choke on it, but it did run pretty rich. Also would a hotter spark plug help out? Any ideas? Thanks, Rob

D.Hearne · Jan 14, 2009

porkchop3k said:
Well I just got my new 770 Holley Street Avenger on my Cleveland yesterday, but it wont run. It has an electric choke. It will run while the choke is engaged but it will not stay running once the choke lets off unless I stay on the gas, but once I let off the engine dies. Im getting good pressure and there are no vacuum leaks or anything. So I guess I am running too lean? I am just throwing that out there and making sure before I go tinker with the fuel mixture. Also if I run the idle higher it still will not want to idle. So am I real lean. I had no problems with my old carb except it did not have a choke on it, but it did run pretty rich. Also would a hotter spark plug help out? Any ideas? Thanks, Rob

Before screwing with the carb's adjustments, first set the initial spark timing. That needs to be around 10-14* BTDC. Once that's set, then complely close the throttle shaft, then adjust the screw till the linkage just starts to move. If it still won't idle at this point, then try adding some fuel via the mixture screws. If it still won't idle, then I suggest finding someone who's familiar with carbs to help you. Also I suggest tying the choke open so as to eliminate it from the tuning equation. I personally completely remove the SOB, it's not needed if your ignition's in tune and the outside temps are 20*F and above.

RUSTYNUT · Jan 15, 2009

Sounds like a vacuum leak to me. Like stated above DON'T start doing anything crazy to the carb. All aftermarket carbs usually come set up good enough to get your car running. You might also check that the mixture screws are both set at one and half turn from closed as a starting point. Unlike many of the hard core racers, I like a well adjusted choke on my street cars. You might be wishing you got the 670cfm carb unless this a racing set up. Holley has a pretty good web sight on tunning tips. If you are new to holley carbs you may want to get a good book on tunning holley carbs. It help you from making alot of expensive and time wasting mistakes.

Edster · Jan 18, 2009

Most folks that have come to me w/ similar troubles w/ a Holley have screwed the idle air mixture screws all the way closed. The screws are located (at least used to be) in the side of the metering block.

blu2u · Jan 18, 2009

I understand you don't feel that you have a vacuum leak, but a good way to test for it, is to spray carb cleaner with a quick, short, burst at different locations. If there is the smallest leak detected, you will hear your idle speed change. Second step, would be to adjust timing, and adjust air mixture screws.

porkchop3k · Jan 18, 2009

I was looking at it yesterday and there was a vacuum cap that was falling apart on the manifold, so I am going to replace that and double check anywhere else there could be any leaks.. But it ran with the old carb on there but it ran rich and it was not the easiest thing to get started up. The carb I have on there now is brand new and I have not messed with the fuel mixture screws. So i am thinking timing could be an issue also. Thanks for the help so far. I will let you know how it goes.

RUSTYNUT · Jan 18, 2009

The set ups that were given you are the way it should have been set from the factory. Some times guys at the factory are having a bad day and screw up. I have seen speed shops playing with new carbs, showing people how to adjust them. Do they get put back the way they are supposed to be?
I remember having gas station job in high school. In the days the had service bays instead of soda machines. The mechanic, (a very good one) had a pinto with the same issue you are having. Put on a new carb, dizzy, control box, plug wires, plugs, fuel pump. After two weeks turned out that the 10 buck carb spacer had a rusted out hole in it. Tought me to always check the simple stuff first. And yea, the owner of the shop charged the customer for all the time and stuff. Never trusted shops since.

jcp123 · Jan 19, 2009

We had nothing but driveability problems on our Street Avenger that my Dad had on his Cleveland. Turns out the dudes who rebuilt the engine didn't bother to do any jetting and it was running a bunch of sizes too lean on the jets. Eventually got it to a dyno shop where it got tuned properly, and it ran like a raped ape for two weeks before going downhill again.

New carb on 351C problems!

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