holly 2X4 tuning

ERA 626 · #1 (**permalink**) 10-25-2002, 09:56 PM

I Just started my FE on the run stand.
I have (2) holly 570 cfm BJ/BK carbs on a fomoco med riser intake.
The carbs seem to be poping & backfiring can any body advise me on how to tune these?
You can view my gallery to see the motor...
or you can go here http://www.gessford.com/quotes/image...roneERA428.htm
Mike

ERA 626 · #2 (**permalink**) 10-26-2002, 10:37 AM

mr0077 · #3 (**permalink**) 10-26-2002, 01:31 PM

mrmike, sounds like you maybe have a large air leak or a missing plug (check the rear of the manifold). I'm going through the same learning curve you are...just got mine installed, but mine fired up and ran great, no popping or backfiring. If no air leaks (try spraying WD40 around the manifold and watch for a change in how the motor runs), I would dial in the float level first, idle speed second, then adjust idle mixture one carb at a time, then repeat the mixture adjustment, looking for highest and best idle. Be sure you have similar air flows through each carb, and the carbs are set for a low idle speed before you try to set the idle screws. A rough way to get similar air flows is to back each idle speed screw out until it's off the throttle stop, then turn in until it just starts opening the throttle (do both carbs); now turn both screws the same amount (1/4 turn or so), start the motor and set the idle speed, turning both screws the same amount. If you have chokes, make sure the chokes are fully open before doing any of the above except maybe float level.
Kountzecobra gave me some good advice awhile back...put each carb on a known good motor, one at a time. Run it in, do the jets, accelerator cams, float levels, idle speed and mixture, etc. Get each one right, then bolt them on your motor. You're gonna have a lot of variables in this project, and doing the tuning on a known motor one carb at a time will eliminate a lot of them. Good luck!

ERA 626 · #4 (**permalink**) 10-26-2002, 01:43 PM

MR077,
Thanks!
OK I think I understand how to adjust the Idle speed screws, but I do not understand how to adjust idle mixture.
Also how do I set float levels and where should it be...?
I adjusted the timing to about 10 degrees advanced at idle and it seemed to help.
Mike

Lubrecon · #5 (**permalink**) 10-26-2002, 02:50 PM

Increase the initial timing to about 12-14 degress BTC. The poping and backfiring should go away.

ERA 626 · #6 (**permalink**) 10-26-2002, 02:55 PM

Luberecon,
That is exactly what I did... And the results are great!!! Thank you! I am learning
Also I have spoke with a few guys about the synthetic oil subject and they all seem to agree with you!
Mike

kountzecobra · #7 (**permalink**) 10-26-2002, 03:27 PM

Mike, check this out: www.bob2000.com/carb.htm