Mopar Muscle Association UK

OK so I don’t know a great deal when it comes to motors. The car has generally run fine, I was having a few niggles last year with her being a bit fussy for the first few miles, which I put down to the auto choke being over enthusiastic. I had to put her in the garage for propshaft UJ’s and whilst there I asked the guys to remove the choke flap, a mistake I think as she ran like sh*t afterwards, probably to do with the redundant vacuum /piston thingy that’s part of the choke assembly.

Then all the Covid stupidity started and I took the chance to do some floorpan work and general tidying up, so she wasn’t used for months. When I went to fire her up recently, she was awful, not idling without some revs, spitting flames back out of the carb and backfiring badly. My first thoughts were timing or vacuum leak, I checked the dizzy is firmly mounted and can’t have moved and the carb was all sooted up and needed the choke fixing, I went that way.

I stripped, cleaned and rebuilt the carb with all new bits and properly removed the auto choke, blocking off the piston vacuum port and making up a manual cable. I’ve just refitted all that and there is a definite improvement, no more flames and idling better, but still really lumpy and randomly backfiring quite loudly.

So, with apologies for the essay, I was hoping to call on the wisdom of the group as to what to be looking at next ? I could accept the rough running as she’s not turned a wheel in months, but the backfiring is a concern….

What is the Ignition timing set at?

I have no idea She's always run fine, was set up by Keith Dunnuck racing, who was a friend of the previous owner before she shipped, I've been assuming (maybe naively) that if the dizzy hasn't moved that it's wherever it needs to be...

have you put the wrong oil in,and wiped the cam

Last oil change was done at Alders automotive, I can' remember what they used, but they know what they are doing and although it seldom needs any, I use a high zinc classic car oil to top up.

You really need to get a handle on the Ignition timing, both full advance, Static, and then the rate of advance.

It is a pre-requisite for setting up an engine correctly.

See if there is anyone local with a Dial back Timing light.

Yeah, OK I'll have to get someone to have a look at it for me. It'll have to wait for a month now as I have zero funds left.

I am sure a local club member will help you out...

Just a thought - does it have a vacuum advance canister on the dizzy ?
If so is plugged back to the right port on the carb given that you have had it off ?

If its wrong it will pull advance oddly and can easily produce bangs and backfires as stuff moves about when it shouldnt.
You can always plug it at the dizzy end (just put an airtight cap over the vac can input) to eliminate. (Dont forget to plug carb end either).

So timing stuff (and air leaks in the vac system) would be my first check.

Lots of good advice here Dom. Definitely check the timing and for vacuum leaks, but could be rich or lean fuelling, or a burnt/bent valve. Is the backfire through the carb or exhaust?

Sounds like you can trace it back to the garage work, so did they mess with anything other than the choke flap? e.g. did they try and 'tune out' the rough running.

Any evidence of fuel dribbling down the carb throats? Float levels correct? Mixture screws not all the way in or out? Accel pump working normally? If it's a Holley check the power valve. I know you said you rebuilt the carb, so I don't mean to patronise.

Where in Sussex are you? I have a timing light, vacuum gauge, compression tester etc. if you'd like me to pop over some time?

Thanks guys, The vaccum hose is correctly fitted, ( I photographed everything before I removed the carb and double checked it against the Edelbrock you-tube how to videos), I have a new dizzy cap on order though as the contacts looked a bit pitted.

All the carb bits I'm reasonably confident about, float settings etc as per instructions, I measured all the setting screw positions with a digital caliper before stripdown and reassembled to the same place. It does run better since the carb rebuild, just not well.

I dumped the car on Alders with no notice, as one of my UJ's collapsed and I had to get it recovered, so they were keen to get it out of the way. I think they just took of the choke flap and gave it back to me in a bag with the screws, nothing else.

Adam, I'm on the outskirts of Uckfield if you're ever passing nearby, I work from home so I'm nearly always here with the kettle is on. If that's anywhere near you let me know and I can pm you some contact numbers

Hi Dom. Adam is probably a bit closer to you, but I'm in Bexhill and have a timing light etc. if needed.

Thank you, I'll bear that in mind

Dom66 wrote: ↑Wed Jul 08, 20 4:59 pm Adam, I'm on the outskirts of Uckfield if you're ever passing nearby, I work from home so I'm nearly always here with the kettle is on. If that's anywhere near you let me know and I can pm you some contact numbers

I'm in Newhaven Dom, so not far away. I have a busy month ahead of me, but if things go according to plan, I should have plenty of time from mid August on.

Your new dizzy cap may have fixed it by then, but If you're still using a points ignition, I'd recommend converting to electronic. It's very hard to set the dwell on a V8 if there's any play in the dizzy shaft. That could be the problem.

Thank you, I'll keep checking the easy stuff, leads plugs etc and see how we go. She had a contactless distributor and the (early 70's ?) chrome box ignition module fitted at some point.