i need carb help please, anyone.77 351modified

88jeepster

88jeepster

Jesus, Jannette & Jeeps for Life!
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Feb 16, 2012
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Hey guys. put in Brand New 351 Modified in 77 F250 2WD Manual for customer, new vacuum advance distributor, and gas tanks, lines, pump, the works basically to restore it, long tube headers too but no exaust yet>>but do have some 5ft pipes on it just temporarily for running adjusting purposes. First time to crank, fired right up and followed the valve cover specs of 12BTDC. She runs and idles and cranks right up every time BUT no matter where I put the timing with timing light, it still backfires out the exhaust and doesn't rev past 3K or so without chocking/backfiring. any ideas. Everything is new but the carb which only has 18K original miles and after sitting for 15 years, it started right up so wouldn't think the carb was bad. I just can't seem to get the timing right. I've tried putting it at 6-7 ish as a friend told me and seemed not as good so I advanced it more to like 15ish and runs better or at least accepts throttle better but still not past 3k. I don't know carbs at all or timing really well. I keep getting told to not use timing light to adjust timing but go by sound and feel but do I do that with vacuum advance off or on? any help would be awesome. last thing to do before I can give him the truck and get moving into my new home and shop. thank you guys.
 
is the harmonic balancer new & correct for the motor? old, used balancers tend to have the ring spun out of position, making the timing marks useless. for using a timing light, the vacuum advance should be plugged off, by ear, whatever works best
 
yeah everything is new and the motor was matched exactly with numbers and stuff so think good there. ok so next question and i'm gonna be called out like a idiot on this one but that's ok i'm here to learn with this carb/timing light stuff. I have a timing light that's digital and I don't know proper way to set it maybe. do I leave the digital number on timing light at 0 or do I move it up to 12.0? it goes up in .1, .2 etc all the way to 50.0? so If I want 12btdc, do I put timing light to 12.0 and the balancer at 12btdc or leave the light at 0 and put balancer at 12btdc? I feel so stupid right now but new territory for me. thank you.
 
If you want it at 12 put the light at 12 and you should be reading the balancer at 0. You can also do it the other way but most factory balancer do not measure past 12-15. Honestly I'd try putting some moe timing in it and see if that helps.
 
well damn, i'm stupid. vacuum is disconnected. I put the light at 12 and put the pointer at 12 so maybe that's the problem. so is my timing light called a "dial back to zero" light. I hear that's not good for beginners (obviously with my case) but do I just leave it at 0 on the light from now on and just go by the balancer marks. thanks dude.
 
Leave the light on 12 and match with the 0 on the crank. Right now it will have 24* of timing in it. The best way to do it is by ear. Just mess around with timing until you find it's happy place. Some engine like a lot some do not. The 302 in out 76 Ford has 29-32* degrees can't really remember.
 
ok thank you. and do I need to do anything with checking the "total advance" timing or no and does that mean my light is a dial back or just a digital regular timing light
 
Yes advance but try back at 12 first or what ever factory spec is. Being a stock motor other than headers it should be happier there.
 
You will need to check to make sure that the mechanical advance is working yes. Basically it like chasing the line. Continue to increase the rpms steadily while increasing the timing light. It should increase steadily until it maxes out.
 
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