Advice from you Holley Guru's - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 4 (permalink) Old Sep 17th, 02, 07:38 AM Thread Starter
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Location: Regina, Saskatchewan, Canada, Earth
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I have a brand new Street Avenger 750 on my newly assembled 355, 10.32:1 comp., Edelbrock 64cc Alum heads, Preformer RPM Air Gap,280H comp Cam. So far the engine has only seen the dyno(406hp 410 tq) so should see 420 of each once rings are seated in.
My concern is we had trouble getting the secondaries to fully open. We went from the original silver spring to the yellow spring to shortening the yellow to stretching the shortened yellow (pulled it inside out) to get the best results. But still not completely opening. There was no obstruction in the linkage or gasket interferance that I could see.
Now I have talked to my speed shop guy and he said some guys are doing this: If has a check ball in place in the secondary pot they are removing it. If no check ball, but a small hole instead, they are drilling it back out to 1/4 inch. Wouldn't this just cause faster rate of opening or would it help pull them open further? I suspect I would have to go back to a heavier spring to counteract the faster opening. Kind of 2 steps ahead and 1 step backward. Is this ball or small hole not the backfire protection they talk about?
We also talked about the tiny ports in the actual venturies, but once fooling around with them the damage is permanent and I don't want to go there.
Do you have any other hints as to what the problem could be? Or is this situation just the carb only giving what the engine needs or is calling for?
Sorry for all the questions but the motor is now in the car and I am just waiting for my rad to be finished (going from a 3 to a 4 core & 2" wider). Then I plan on running it a bit (can hardly wait). This is in a '68 Camaro, 3000 stall, with 4.11. It will mostly be on the street but will hit the track to see what it is capeable of, when unleashed. Thanks again for any info you can provide. Barry from Regina, Sask. Canada
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post #2 of 4 (permalink) Old Sep 17th, 02, 08:19 AM
DjD
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Not a guru by a long shot but have played with holleys a bit. Don't think you can get a 750 street avenger, I believe it's a 870, 770 or a 670. Not overly important though. The reason your secondaries don't open all the way will most likely be too much carb for your mill. That's how vac sec carbs work and why they are considered forgiving...

Don't remove the check ball it's there to insure the sec's close when you take your foot out of it (safty first)!! Side note: The backfire protection uses a ball and spring, but is part of the power valve circuitry in the bottom of the main body of the carb. Modifying the various springs doesn't work well as you'll have no idea of the resulting spring rate. The springs are color coded so you can scale the changes from one spring to the next. You can download tuning help from the holley web site if you don't have a book already and it tells you based on CID what spring should do and under what rpm. I also don't recomend drilling the check ball orfice or modifing the venturies that feed it as it is designed to flow a certain amount and making it bigger isn't gonna help.

The one mod I have heard of that may help is to put a groove in the check ball seat so the ball doesn't completly block the orfice when the ball is sitting on the opening.

The bottom line is you have a new, well thought out carb and at most you should have to do is tuning with the parts that are designed to be adjusted or replaced. Most of the tuning should have been worked out on the dyno. At least proper jetting and such. Accell pump squirters and cams can be changed to over come off idle stumble but usually the vac sec are opening too soon and a spring change there should be looked into first.

Sounds like a sweet little mill Barry, let us know how she does if you get her to the track.

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...Dennis
"The '69, the '96 & the club"
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post #3 of 4 (permalink) Old Sep 17th, 02, 08:44 AM Thread Starter
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Thanks a mill Dennis. You are right it's a 770 I don't know why I keep referring to it as a 750. Thanks again for the quick response and the good info. Luv you guys and this site. Barry
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post #4 of 4 (permalink) Old Sep 19th, 02, 09:40 AM
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Do NOT remove the secondary check ball - it's there to "soften" the opening rate of the secondaries; without it, they will "snap" fully open immediately, and you'll have a "bog" you can't tune out.

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