hollywood6

My '67 has a rebuilt 289 in it. Carb is a 4 barrell Holly.

It is stumbling out of the gate but runs great once past that. I have added a 1" spacer between the carb and the intake but that did not do it. I have changed the squirters/nozzels from a 31 down to a 28 but still no change....

The timing has all been set properly to spec.

Help??????

I do not know what to try next??? A larger nozzel???

Thanks

67mustang302

Define stumbling? What's the engine setup and what's the timing and plugs/gap? Does it bog and get lazy or kind of sputter and then slowly pick up till it's fine? Or does it just fall flat like it tries to stall out and then suddenly pick up and take off? The former is typically too rich, the latter is typically too lean, for the pump shot. When you changed squirter sizes how did it effect how the car performed? What pump cam is in it? What do the plugs look like, is it running rich or lean?

hollywood6

The squirter change did little to nothing, worse if I had to really say.

It tries to stall if I gun it but if I feather it I can get through then gun it and be ok. From a dead stop, if I gun it, it will want to stall. If I am already cruising and gun it, it is ok too.

67mustang302

What pump cams are in it? Try a larger cam or a larger squirter. Sounds like it may be too lean.

hollywood6

Ok, I'll try a larger one. One of the shade tree mechanics I work with said to replace the eccellerator pump, what do you think??

67mustang302

It doesn't need to be replaced unless it's leaking or damaged so that it isn't delivering fuel properly. I wouldn't listen a whole lot to other people about carbs when they can't specifically say why you should do something(and even then take it with a grain of salt). Most people just don't really understand how they work.

Try a cam that delivers more fuel or has a more aggressive rate, if that helps but doesn't solve the issue, then use a larger squirter. The next size up on a Holley from a 31 is a 35 I think. Quickfuel sells a 32 and a 34.

urban_cowboy

Stumbles and bogs are mostly caused by too much fuel or not enough (i.e. dead rich or lean). Without an AFR gauge, it is hard to diagnose and tweak the accelerator circuit. I would put your squirter (nozzle) back to stock size and change the pump cam position or curve to something that will give you more fuel earlier. Larger squirters (nozzles) will cause fluid to enter the carb faster for a given throttle position but does not change the amount of fuel entering the carb for a given throttle position and going too large can cause atomization issues. The pump cam will change the amount of fuel that enters the carb. Try changing the pump cam position and/or pump cam first. Here is a link to the different cam colors and curves. Let us know what cam color and position you are currently on so we can help you pick a new one to got with.

http://www.carbdford.com/tech/Holley20PumCams.gif

hollywood6

Unless it is a really faded out Red, it was pink and the screw was set up in the center of 3 hole positions. I tried them all with no success.....

Please help..

thanks

kalli

i know what 67mustang302 says with the fall flat on your face and then turn into a rocket when you floor it from idlish. that is too lean a pump shot. had the same problem once