Zerocyde

So, I'm trying my hardest to learn the carb. It's been about 3 weeks with the new engine in and I'm getting great performance so far, but a few weird issues. Here are 3...

1. First off, my mechanical advance seems to only be about 16 degrees. Is that normal? I plugged the vacuum, set the idle timing to 10 advanced, and then held the rpms at about 3000 and it showed like 26 advanced.

2. What should I idle at? I've been keeping it at a hairs breath under 1000. It holds at about 750 when cold until it warms up. It's a 355 with a 670 street avenger, thumper cam, and pro comp 3003a heads. (64cc / 210cc). I believe these are the numbers on the cam...

Valve Setting: Intake - Hyd, Exhaust - Hyd
RPM Operating Range: 1900 to 5600
Cam Grind Number: 283THR7
Duration Advertised: Intake - 283, Exhaust - 303
Duration @ .050'': Intake - 227, Exhaust - 241
Valve Lift: Intake - .511, Exhaust - .497
Lobe Sep. Angle: 107°

3. I'm getting serious desiling, the hotter the engine, the worse it is. Forgot to turn the fan on today and it was at about 190 when I got home. Took about 10 seconds for the desiling to stop. My first idea is to drop some seafoam in the carb, but first I wanted to ask if maybe the weird timing issue is at fault and not a carbon build up.

Thanks a million for any help guys!

camaronewbie

1) yes, that's about normal. to get higher total timing, the mechanical advance needs to advance farther and faster - thsi is accomplished with a combo of lighter springs and heavier weights in the distributor - requires a spring/weight kit - several places make them, pretty sure Mr. Gasket is one, I'm sure there are other brands, as well as being available from your dist manufacturer.

2) I'm no idle expert, but that doesn't sound too high, and certainly not too low. Mine isles warm at about 800, and about 950 cold. There should be a fast idle screw that you can adjust onm the linkage for the cold idle, as well as a regular idle screw for the warm idle.

3) 10*BTDC might be a tad low. Mine is set at about 14* BTDC. The way it was explained to me ... You want your 3000rpm timing to be about 34-36* - to get that, you have to set your initial up higher (like you stated, you only get another 16 mechanical advance). BUT - without lighter springs/heavier weights, your mechanical will not advance far enough fast enough to reach the 'magic' 34-36 total timing WITHOUT getting detonation from having the initial timing set too high. So I was told to advance timing higher in like 2 degree increments, and take a WOT run - if no pinging then adavnce another 2 degrees ... until you get pinging at WOTY, then come back down 2 degrees.

So, for me, I ended up with no pinging at 15* initial, but had pinging at a 16* initial (at WOT), so I came back down to 14*. You want a 2 degree safety margin because the human ear cannot hear lower levels of detonation. So for me, at 14* BTDC initial, I get about 29* total at 3000 rpms.

Not sure if it's just me or not, but I could also swear I obtained a tad more vacuum at a slightly higher initial timing - I don't have any monster cam, but it certainly made a difference in my braking when I bumped my timing up some. Of course once you get that timing adjusted, you'll have to readjust idle again.

Hope that helps! Good Luck!

Zerocyde

Awesome info once again camaronewbie. I think I know what's wrong, I've been hearing a weird noise ever since I set the timing at 16. It sounds almost like a rocker that's too lose, but not quite. Is that pinging? I'm not sure what pinging sounds like. Though, I hear this noise at idle, not at WOT.