Carburetor Backfiring
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Junior User
Joined: Oct 2015
Posts: 84
Likes: 0
From: Socal
Carburetor Backfiring
Hi there I have a ford 390 with autolite 2100. It has not been that long ago since I have rebuilt it. But it seems I have been having bad luck with this carb. It backfires when I give it gas aggressively and starts popping under load, so I got to give it gas and slowly release the clutch so it wont die. I have already set the adjustment screws to 2 1/2 and still does it. I thought it was the accelerator pump so I adjusted it to the far hole on diaphragm linkage and second hole before the top one on the other end (the one that has several holes). But still no luck
. Maybe a new carb?
. Maybe a new carb?
Logistics Pro
Joined: Aug 2015
Posts: 4,093
Likes: 14
From: Lind, WA- Eastern WA
I have that carb on my 69, with a 360. I think your linkage is setup the same as mine too. But the rebuild kit said to start with the screws adjusted to 1 1/2 turns. I'm guessing that you have checked all the other "tune up" stuff too. Like checking for vacuum leaks (hoses), setting the points, cleaning/replacing plugs and wires, dist cap/rotor, setting the timing. How old is the gas in the tank? Is this a daily driver? I'm not a tune up expert, by any means, but some of the others on here will reply soon.
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
Put a vacuum gauge on it, report back. Sounds like you might have an intake valve issue. You have checked carburation, seems to always be the first thing that gets attacked when there's a drivability issue, could be in the vacuum advance too.
Postmaster
Joined: Nov 2015
Posts: 2,769
Likes: 7
From: O-O-O-Oreilly's
I have been having a very similar problem, if not the identical one. I replaced my distributor with a $45 reman unit and no more backfiring. Yours could be worn and causing your dwell to freak out.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Cut to the chase! First thing, I'd do is a compression test. It sound like the classic brunt exh. seats. If cyl. are all good above 125lbs & up .
Check for a dizzy for shorting condensor/wire or broken frayed ground wire any loose connections at terminals ends.
Check for a bad dizzy lead from coil to dizzy. Check volts going to coil. Also remove all spark plug wires from dizzy cap & check for any corrosion in any & all coil center high voltage wires.
Orich
Check for a dizzy for shorting condensor/wire or broken frayed ground wire any loose connections at terminals ends.
Check for a bad dizzy lead from coil to dizzy. Check volts going to coil. Also remove all spark plug wires from dizzy cap & check for any corrosion in any & all coil center high voltage wires.
Orich
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
Also check the timing chain. Put a timing light on it and rev to about 1500 RPM. Watch to see if the timing mark advances smooth or bounces around.
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Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
Tpp bad more people don't own a vacuum gauge and know how to use it. It is absolutely the best tool and the first thing you should use when there is a drivabilty issue.
I check timing chain slop by rocking the crank by hand. Line it up on tdc and rock the crank back and forth. Use a breaker bar on the harmonic balancer bolt if you need to. You can feel the slack in the timing chain. If it is more than 8 degrees of slop, it's time to replace the timing set. I'd probably replace it if there was 6. A new standard single row timing set that has been run it will have 2-3 usually
I check timing chain slop by rocking the crank by hand. Line it up on tdc and rock the crank back and forth. Use a breaker bar on the harmonic balancer bolt if you need to. You can feel the slack in the timing chain. If it is more than 8 degrees of slop, it's time to replace the timing set. I'd probably replace it if there was 6. A new standard single row timing set that has been run it will have 2-3 usually
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