Mopar Muscle Association UK

Hi All,

Been a long time since I have been online, took a notion to do a masters last year and didn't realise it would take over my life so I haven't done anything with the car really. Anyways its nearly summer break and I want to get the most out of the car over the summer.

When I bought the car it was pinking and had the odd backfire (exhaust side), when I got a timing gun on it it appeared to be advancing way to much mechanically, the amount of advance was too high, I think it was going tup to 50* IIRC. I got the FBO limiting place and set the timing to 18* with 16* mechanical disconnected the vacuum.

Anyways she seems to start and run ok, revs up ok under light throttle snap the throttle open and she back fires through the carb every time. I rebuilt the card and tried every accelerator pump cam along with 35 squirters to no avail.

I installed an AEM AF meter, and have the idle set a on the rich side, about 12.5/1. Still backfiring and leaning out.

If i set the advance by RPM, she seems to like about 30* initial and doesn't seem to backfire as much, this seems which seems way too much. I just recheck the TDC against the mark on the balancer and she hasn't slipped.

Shes a 383 with holley 750 vac. Also got new leads, plugs, cap and rotor. no matter what I do I can't get rid of the backfire.

I think I've covered all the basics of what I've done, any suggestions, I don't know anyone with a carb that I can swap out.

Happy to give anyone a call at this point to talk through everything I've done.

I'm sure there will be someone along who knows better than I do but what manifold does it have? Dual plane is the way to go apparently. Does the engine have a thermostat in it? Gets warm enough? Fuel filter not restricting flow?

Dual plane weiland intake.

I think the flow is fine, I got an intake o take the 1/8 fuel pressure gauge I had but it's not working. I need to pick a new one to be sure,

Engine get plenty warm, I've done near everything I can think of timing wise. I'm going to drill the old cap tonight and see if I need to phase the reluctor. Failing that I think it's a case of getting a new carb to try.

Getting a known good one is the problem

Sounds like it needs more accelerator pump, or rather a larger squirter, had to put a 38 on a cleveland to get it right once.

I take it you've checked the pump arm adjustment?

Checked pump, arm and all the cams I have. Considered upgrading to the 50cc pump, 35 seemed big on a 383 for what I've read.

I checked the phasing tonight and it was spot on. I reconnected the vacuum to the dissy and the phasing advances a little. She didn't seem to pop through the carb though snapped her open and little. She Popped through the exhaust couple times, but I think that might be down to the old cap and rotor missing, now and then the light stopped working for a second

I was working in the garage so I couldn't run her for long without killing myself, but this does seem to be an improvement, she's still leaning out on the gauge though.

Anyone got a 38 squirter??

I always work backwards from 34 Degrees fully advanced.
Then the fun starts to get enough timing in at idle.

I have a problem on the Coronet engine and that LOVES lots of advance and I will probably have to lock the timing out at 34 degrees, and then work out a "Starter Saver" mechanism to avoid starter motor premature failure. Easy with an MSD Digital 6.

The motor will always tell you what it wants...

Thanks for the replies guys. I'm gonna try her with the vacuum back on and take her out see how she behaves. I set it back to 18 initial tonight, I didn't measure how much the vacuum brought in but it looked to be plenty. I set advance on the gun to 18 and she jumped way back up onto the make shift timing tape I put on her.

I'm determined to get this all sorted for the summer. I'll keep you posted, might order a 38 squirter too

Have you trimmed that fuel filter? Cut the smaller sections off the ends and run a drill up the bore - they can cause a restriction.

Has the carb been set up at all? Have you set the float levels? That is one of the basics that you can do.
If all the ignition side is correct and you follow Petes instructions you shouldn't be far out.
To be honest, just playing with the dizzy with the motor running should get you in the drivable ball park. If not, look at the fuel side. What are the plugs looking like at idle?
I know you're using an AF gauge but don't be too reliant on it

Hi miles,

I set the floats, after I replaced the needle. plugs were fouled up a bit, I put this down to my running the idle a bit on the rich side.

Haven't thought of trimming the filter, I just threw in there temporarily after putting the carb back onabd the issue was there before.

I'll double check all on the carb later.

Is the valley pan (below intake) sealed correctly? If that is sucking air it could cause some of the problems your having,. I though such backfires were due to leanness, so check for vac leaks.
The BB boys on here have mentioned this issue before I think.

Where's the link to Dave R's carb and timing bible?

have you got the vacuum hose plumbed into the ported vacuum?

that's the slightly higher small pipe into the carb above the throttle plates

Dave

Mines plumbed to ported vacuum..

Haven't checked the valley pan at all.

Dizzy vacuum is ported, only reconnected it last night as I wasn't using it.