just put the 4bbl on and buttoned her up. after a bunch of cranking to prime she fired right up and purred like a kitten. I run into the problem I had before.... It pops BAD thru the carb once it warms up for a few minutes. if i "Blip" the throttle at any position POW. if I slowly raise the throttle its fine. once or twice when it backfired the throttle jumped up and stayed there till i touched the throttle again. My timing I think is high. it should be around 8 right? depending on what port I'm in on the carb for the vacuum advance i can get it to run at 8 degrees at idle but when i get on the gas it jumps way up. (off scale) I'm also using the old timing mark on the harmonic balancer If Im in the other port the timing seems even more advanced. here is a pic of the ports i've tried. what one is correct? current or the one with the white cap? Nate oh btw this is a 70 carb with an electric choke I added.
first dont time it with a vacume to the pull off on the distributer. I always use a mechanical timing only and skip the vacume part. next if the bushing in the distrib is missing it will allow the engine to rev up and over advance the engine. look under the swing weights under the rotor. make sure the springs are weak so that at lower rpm the motor gets full advance early then power time it to about 32 degrees at about 2500 rpm. You will need a good dial timing light to get this done. Skip the vacume line its only purpose is supposedly for gas mileage. (I bet it wont be any worse without it either) Set the points to 29 degrees on the dwell if your running them also. One more thing , at idle put your hand over the carb and see if the rpm changes (raises) if it does you have a vacume leak and that also may be your problem Hoping the carb is good it should run fine (Im also not a fan of the electric choke but its not my car) Good luck...
Also one more thing I know this is so simple but double check the plug wires positioning to be sure they are correct... simple stuff kills you trust me!!
so if i advance the dial timing light to 32 the mark on the crank would be at zero or really close. my 2 bbl did the same thing pop thru the carb. just before i pulled it. it is also a points car. oh... how do you set the two screws at the base of the carb? I turned them both equally and they didnt seem to do anything constructive. makes me wonder if my valve timing could be off. I did put a new timing chain in it a while back. and then the timing was off one tooth, before I pulled the timing chain, but it ran fine for about 2-3 months like it is now correctly timed though I'm not sure what direction the timing chain was off. I just did the wires but i'll check for a 3rd time.
yes thats correct might be a cam problem yes That means the carb is not in the idle curcuit anylonger and the timing needs to be better first then work on adjusting carb
hmm.... hmm... pulled vacuum advance. Timing still at 8. Timing smoothly rises a lot from there (don't have a decent timing light to really tell.) cam appeared fine when I had intake manifold off. I can play with main idle screw (near throttle linkage.) and makes large diffrence. it only has this problem when warmed up. its also not missing at all just when it pops
I've said this before, but the only time my car has ever backfired through the carb was in a lean condition... and boy was that exciting. 2ft flame... looked like a hot air balloon... Im lucky I didnt burn up my engine... let alone my garage! Good luck getting it sorted out :TU:
I would tune it by ear or feel and see what happens. get it running and rev the engine up and turn it back in fourth till it sounds the best the back a tad. DO that till it reve's fast and doesn't pop. When the timing light fails, ear tuning works great. Some guy do the power brake the car with a buddy turing the cap back n fourth under the hood for best under load timing and sound/feel. Matt uzzled:
Nate, It sounds like it is running lean to me. It runs ok when the choke is on, then when it warms up, you have a problem. I would say vacuum leak. Buy a vacuum gauge, they are cheap and an indispencable tool for any mechanic. Put the gauge on the passenger side nipple on the carb. At idle fully warmed up in neutral, with a stock cam, you should see about 18". If it has a cam the reading will be lower (13-16). While you have the gauge connected, spray a little gumout around the carb gasket. If you see the gauge go up, you've found your vacuum leak. Also check to see if your accelerator pump is working. With the engine off, look down the primary side of the carb, and jab the throttle open. You shoud see a stream of gas shoot out and hit the primary venturi on both sides. IMHO, any street car should have a vacuum advance. It enhances gas mileage and throttle response. That being said, if you have a quick mechanical advance curve, you can get into pinging if the vacuum advance doesn't fall off fast enough. If you buy the Crane adjustable vacuum advance, you can adjust it so that doesn't happen. It also comes with some nice springs for your advance weights. The ignitionman uses this unit in his distributor builds, but he limits the advance to 8 or 10 degrees in a different way then Crane uses (it's a much better way). If you e-mail him, he will send you pictures of the method he uses. Hope that helps.
I'm an IDIOT! I'm such an Idiot. Ok well I'm much happier now that I figured it out. I would have callled myself retarded but that wasn't the problem. It seems that 8 cylinder engines when you swap the firing order of cylinder 7 with 5 they tend to backfire up the carb. who woulda thunk it. don't check once dont check twice check thrise. anyways... I'm getting about 16 inches of vacuum. checked for leaks none found. its time to play now... :Brow: I wonder if I drove about 8000 miles on this engine like that... I last did the wires in Florida b4 i bought it. or some idiot changed them when I had it parked outside at my apartment trying to be funny..... Thanks to everyone who responded. :beer: Nate
Glad I told you to double check !! Its the simple stuff that you find you screwed up on ... well I do anyway.....:TU:
the hose with the green arrow is plugged on my carb...it went to the charcoal canister. this is a 1970 carb as well.
which green arrow, there are 2?? Neither one should go to an emissions canister. One is ported spark advance(dr. side), the other is full manifold vacuum. I think the canister went to the air cleaner.
white cap the one with the white cap is the one i used for vacuum advance. its also closer to the size of the diaphram. and made the timing at idle actually correct. did the full vacuum go up to the air cleaner for the heat riser? yea its fine now but what now craps out? the water pump died. and i have the short one... :ball: Nate
The canister hose on my car goes to the drivers side green arrow:grin: It's rotten to hell, so I guess I better buy a new one before I put the heads back on the car. I can't wait to get this thing running. Nate - You're going to love burying the pedal and hearing (feeling) the secondaries open up:Brow: :Brow: :Brow:
Glad it was only two switched wires. Reminds me of a time.... I had a 350 SBC that I put a small cam in about 8 years ago. Little did I know....I installed the distributer 180 off...... Fired it up and ran for about 2 seconds...POW!!! Believe it or not, it exploded both mufflers, and blew a valve cover off the engine! Pulled all 4 bolts right through the cover. Scared the crap right out of me! :shock: :shock: ...why do I admit to these things? :gt: ou:
yea she pulls really well now. I think I need to loosen up the secondary spring just a tad though. I also need to verify that I'm getting full pull out of the cable linkage. The car ran awesome all I did was drop the carb on connect the linkages. cranked it and it roared to life. the transition between primary and secondarys is extremely smooth now too. (thinking spring may help there) Nate
