RedZ85 Posted January 31, 2006 Share Posted January 31, 2006 Im using an Edelbrock AVS carb. 650CFM. the engine idles well however, under load it seems to backfire out of the carb...which is consistant with a lean situation. I also noticed that compared to the holley (670 CFM) its lacking power. Is this just because the edelbrock isnt satisfying the engines fuel needs? What fuel pressure should i have goin into the carb? Engine specs: Chevy 355 10:1 compression 6000 RPM limit Quote Link to comment Share on other sites More sharing options...
GAZRNR Posted January 31, 2006 Share Posted January 31, 2006 You should have a steady 6 PSI at the carb inlet. Do you have an inline fuel pressure gauge & adjustible fuel pressure regulator? Have you done a plug check yet to verify the lean condition? Have you changed out any other parts or is this a new problem? I am running a 1406 performer carb and could have run it right out of the box after adjusting the choke. I wanted to tinker with it some to get it where the motor responed a little better. My understanding is your carb is easier to adjust on. After you set the fuel pressure and check the fuel filter, I would look to vacume leaks, electrical problems, crossed spark plug wires and proper timing before I would start tuning on the carb. Also, verify that you are getting a full squirt from the accelerator pump. Then write down everything you do and track your changes. Quote Link to comment Share on other sites More sharing options...
desert dog Posted January 31, 2006 Share Posted January 31, 2006 Buy the adjustable kit for the AVS carb. It comes with all the different step springs. It sounds like the step springs on the rods are not strong enough, and the signal to enrichen as the throttle blade is opened is not happening... Quote Link to comment Share on other sites More sharing options...
BrandonsZ Posted January 31, 2006 Share Posted January 31, 2006 1806 AVS 650. It should not be backfiring because of wrong needles, and springs if you have the stock ones in there on a 355. I noticed several things with mine. 1. I had to return the first one because the "adjustable vacuum secondaires" were nothing more than a flap which opens a via engine suction which helps with transition from primary to secondary opening (they overlap quite a bit so I bet this is more of a bandaid than anything else. If that flap is not freely moving, I.e. you push it with your finger and it sticks where you pushed it, then you need that fixed. That might explain "less power". 2. Backfiring in the carb could be lean OR rich! The idle jets of this carb are huge! In fact my 350 idle couldn't be set below 800. The primaries sealed tight but the idle jets were letting so much air/fuel in that the engine idles at 800 minimum. These have a direct and very noticeable effect on light throttle performance (up to 1/4 pedal). I could get mine to backfire when I inadvertantly did not set the idle jets correctly. This should fix your prob. Adjust base timing to 6BTDC, remove vac advance plug ALL vac leaks and make sure the bolts are tight and verify you actually have a gasket, set idel to 600-800. To set the idle jets: 1. Adjust the timing if necessary such that your engine runs 600-800rpm steady and still gives yourself some adjustment with the idle screw. 2. Turn one idle mixture screws in (clockwise) until the RPM drops 50, readjust idle to same as before and do it again for the other one. (each side seperately). You're done. If it drops immediately you're too lean go to step 3. 3. Turn one idle screw out (counterclockwise) and the rpm will rise, adjust the idle in 50prm incriments back to baseline until turning the screw out does not add to RPM. Then repeat for the other side. 4. Turn one idle mixture screw in until the rpm drops 50. Reset idle to base and adjust the other side till it drops 50. You're done. 5. If you still have trouble, you may need to get the adjustment kit and try different needles and seats and springs. It is VERY easy to do small changes because the needles are accessable from the top of the carb through some simple plates that bolt on. 6. If you tried different settings and it still fails you could call edelbrock technical (see their website), they will help if you are patient and can get anything but a busy signal. But if you try often you'll get in. This is most likely a timing problem, but something could be wrong with your valvetrane also. ALSO MAKE SURE YOUR SPARK PLUG WIRES ARE CORRECTLY ROUTED!!! Quote Link to comment Share on other sites More sharing options...
desert dog Posted February 1, 2006 Share Posted February 1, 2006 Check that answer I gave. I forget not everyone lives 1 mile above sea level... We have to change jets in EVERYTHING, and it is guaranteed that any spring in a carburetor will be the wrong tension... Quote Link to comment Share on other sites More sharing options...
BrandonsZ Posted February 1, 2006 Share Posted February 1, 2006 Check that answer I gave. I forget not everyone lives 1 mile above sea level... We have to change jets in EVERYTHING, and it is guaranteed that any spring in a carburetor will be the wrong tension... Don' sell yourself short, there's nothing wrong with what you said. Personally I'd try to adjust the idle mixture first, and get the timing right before changing springs. A richer mixture would tend to effect how timing is felt, and might very well be the fix for this problem. He might have crazy cams and hugely ported heads, I don't know. Quote Link to comment Share on other sites More sharing options...
RedZ85 Posted February 2, 2006 Author Share Posted February 2, 2006 Don' sell yourself short, there's nothing wrong with what you said. Personally I'd try to adjust the idle mixture first, and get the timing right before changing springs. A richer mixture would tend to effect how timing is felt, and might very well be the fix for this problem. He might have crazy cams and hugely ported heads, I don't know. Its a pretty mild engine. 64 cc heads, Comp 256 grind cam, 10:1 compression, Edlbrock AVS 650 carb... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.