antsZRS

Hey guys. I am in the process of tuning my carb.
It's a holly 670 street avenger.4150

My problem is that when I get on it at WOT. At about 4000 rpm it startles for a bit than it jumps. Does this mean I need bigger jets or smaller jets in the secondaries?

Any advice will be greatly appreciated! Plz help.

7989camaros

Have you done a rebuild on it or has it always been this way? You can try to adjust the clearance of the accelerator pump cam this operates the squirters, should be .014" clearance with a feeler gauge. If you have a rebuild instruction sheet it will show you this procedure. Also the back secondary butterflies have a set screw only visible with carb off, the butterflies need to be cracked open slightly it explains this on the sheet also. I built mine to the sheet specs and added a couple degrees of timing and it did fine.

blackbmagic

Is it vacuum or mechanical secondary? It sounds to me like the secondary jet might be dumping to much fuel instead of a long straight shot through the power band. Or you might also have to much clearance on the secondary accelerator pump. U loose gas until it hits. Adjust your clearances and try and see if you get a full shot of fuel throughout the throttle range.

antsZRS

yes the carb has been rebuilt. i shall check the accelerator pump clearance hopefully sometime this week. i need to upgrade to a bigger squirtor as well.

it is a vacuum secondary carb.

blackbmagic

Like I said you might actually have to go to a smaller jet. It still dumps the same fuel just over a long amount of time. Its possible you dump to much at once which makes it bog down until its able to use it. Bigger isn't always better especially with carbs.

If you take a look at my setup I had a 750mech double pumper and a vic jr on the same setup as I do now. It would bog down low and pick up fast if I didn't launch it right or pushed it too hard off the line. I took the 750 off and replaced it with a 650 and a different pump/jet setup. I also replaced the big single plane with a performer and I have my performance back off the line with no bogs.

antsZRS

well what size cam do you have. i sort of figured that since im running a decent size cam. that i will need a bigger size jets/ squirtors.

i havent tried anything yet blackmajic. but when i do. ill let you know how it goes. thanx for your imput.

im running a lunati voodoo 504/525 with a 110 LSA

pancherj

Are you saying you floor it from a stand still and at 4000RPM it begins to stumble? Or, are you driving along at 4000RPM and then floor it and it stumbles? Clarify the situation and maybe we can narrow down the places you should be looking to fix this.

antsZRS

Well from a dead stop. It's bogs right off idle. Which is why I believe I need a bigger squirtor. Than it jumps hard really hard until about 4000 rpm it bogs again. So I was thinking I needed bigger secondary jets. But black magic suggested trying a smaller jet for the secondaries.