Still running rough and backfiring

'77 GTB, Pertronix ignition, Hemi wires with no extenders.

So, thought I had found the rough running problem with a missing center contact in the distributor cap. Had a spare, so checked out all the wires and put the car back together.

Still running rough and backfiring. Tweaked timing a little and now backfiring at idle. Won't pull past 6000 rpm.

So, I am thinking two different possibilities.

1) Carb is acting up and I will need to rebuild all the carbs.
2) Timimg belt slipped a tooth. Which I have no idea how to check.

Or, should I just bite the bullet and take it to a specialist. Not totally ready to give up but almost want to cut my losses and sell as is.

 

On point 2, open up the inspection port on the top of the flywheel bell housing. Turn the engine over by hand until the flywheel is at top dead center compression. There should be a mark like this 0|I and you set it at the | mark. Then open up the two valve covers to inspect the assembly timing marks on the four cams. They should all line up with their marks on the cam caps.

On point 1, was there any work done to the carbs before you got here?

The pertronix, is that a point/condenser eliminator? Are there pick up points for that to work?

 

Did you use a timing light? What is your advance at idle and at 5000? According to the manual you should be at 33 deg +- 1 at 5000 RPM.
Check to make sure your advance is working - set a timing light up, check timing at idle and make sure it advances when RPM increases.
Did you happen to introduce a vacuum leak while working in there? The servo vacuum hose and check valve run right through there.

If your timing belt slipped a tooth it / they are either really worn or there is very little tension. You should be able to check that by removing the wheel and wheel well and inspecting the belts.

 

I am going back to basics. Will check the cams alignment and pull plugs again. Did just adjust idle mixture so may have gotten some dirt in a jet. I will also check float levels.

 

Replace the plugs. Don't clean. Replace. Fire it up and immediately give it an Italian tune up. Drive it like hell with some full wot runs. Don't dilly dally around with trying to get it to idle, putting on your driving gloves, or taking a selfie. Just get in and drive it. When you get back don't let it idle just shut it down quick. If it's still giving you problems pull the plugs and read them. Report back.

 

Update #2.

I made some marks on the cams and seals when I did the timing belts this past spring. I can see three of the four marks with the belt covers on and all three line up with #1 at TDC. So, I am pretty sure that the belts have not slipped a tooth. This backs up the compression check.

So, tomorrow I will reset the timing. And the. Receive and go from there.

The strange thing is that the car was running well two weeks ago. Then, a week later, all the problems started.

 

I ran NGK 5 ES plugs in my 77 and they ran great. They are hotter and less prone to rich fouling. Set the pertronix at 7*BTDC at 1000 rpm. Used a Bosch blue coils and the red extenders. Use the Birdmans carb set up process. Good luck

 

In an effort to keep it simple.

When was it last running right?

What did you do since then?

Jumping a cam belt tooth??? FWIW- I've never head of that happening.

 

Use a timing light, don't work in the dark.
As Cls said here check timing first on both banks....check all are firing....then plugs.....then check the carbs. Without method one tends to go round in circles on the money-go-round...
Regards Bell

 

Very good advice. Tonight she gets retimed (if I have time, LOL).

Plugs are currently BPR7IEX. May replace them with something a bit hotter. Coils are the Pertronix Flamethrower II units. I will recheck ohms on them as well. No extenders since I am running the Hemi plug wires.

I may do a carb rebuild anyway. I get some surging at idle and suspect that the throttle shaft bearings are leaking air. Time for sealed bearings.

 

Just some thoughts:

Backfiring generally means that you have fuel but it's not igniting or igniting at the wrong time. Ignition system or valves/valve timing (Had it happen in a Bugeye and had bent rocker arm adjusters)

Running rough could be bad fuel, or ignition problems.

Factory setup worked. Well. You would not be the first on here to have running problems caused by after market parts that are "better than stock".

Aslo since you "checked all the wires" it's not at all uncommon to put the wrong wire to the wrong plug. I .. I heard of someone who may have done that once after only 40 years of car mechanic-ing, probably wasn't me but could of been.

Best of luck!

 

My 2 cents, I would go after the distributor caps and wires. If it was running great before, timing doesn't just change on its own. I agree it is good to know where you are but I don't think it is the source of your problem. I am just saying this because my caps and rotors went to hell not that long ago.
Good luck

 

What did you do to the carbs. did you touch the mixture screws or just the idle stops. Did you touch the air screws or adjust any of the linkage. Check the timing 1st and take it from there. If ignition is good then backfire could be the air mixture screws. By the way I think the 7's spark plugs are to cold and you will foul them out. Also check your chokes and make sure they are closed.

 

I have been to this movie before. Try simple before complex. replace plugs and give it an Italian tune up. See my last post.

 

Thanks for all the advice guys. Too tired and cold to work on it last night. May squeeze in some work tonight but got to vote first. Probably later this week.

 

You have an ignition issue. With it not wanting to rev well beyond 6k I would say your Pertronix might not be playing friendly any more. I be seen this happen. Replace with points and make certain dwell is correct.

Make certain the distributors on each bank are where they need to be in terms of splines and flywheel marks. Each bank uses different marks.

 

That is what I am afraid of. Pertronix said that they could check out the ignitors if I send them back to them. Just such a PITA to remove the distributor and pull all the Pertronix components.

I would rather not go back to points so I may step up to the Electromotive XDI setup that Nick Forza sells.

Edit: My dream setup would be higher compression, new cams and either TWM or Jevney throttle bodies in conjunction with coil on plug. I converted my 496 big block Corvette over to FAST XFI and the drivability improvement was amazing.

 

Why not diagnose what you have?

 

What I have right now is the Pertronix MR-183 setup. I called Pertronix and there is no test that the owner can do to confirm functionality of the system. So, I would have to remove all the components and send them cross country to see if there is an issue.

Personally, I would love to figure out a way to use the Nick Forza 58x wheel to trigger an MSD LS box (that lets you change ignition curves in software) firing 8 separate LS coils. Only issue is figuring out a cam sync signal.

 

The MR183 is pretty simple. Maybe that's your point of failure, but I would guess not.
There are a lot of people here who could walk you through some troubleshooting if you post some more information.

I would suggest posting your timing numbers, at least advance at idle and 5k. When I installed my MR183 I ended up having a problem with the mechanical advance in my distributor, we can easily rule that out by checking your advance.

You should also verify your timing marks are accurate by checking TDC at cylinder 1 by removing the #1 spark plug and checking that when piston is at TDC it corresponds with the timing marks on your cams, balancer, and flywheel.

 

Steve, I hate to state the obvious but what color were the plugs? Rich, lean, good? All the same? Did you sniff them? Also, if it's backfiring at idle, have you tried watching for a consistent spark on each cylinder (with a timing light or an extra spark plug?) You might be able to isolate it to one cylinder so can then check wires, plugs of any offending cylinder(s). If the sparks are too fast, film and watch in slow motion (iphone 5S and newer or an app.)

If the compression test was good, the plugs were all the same and the right color, and you can't see a spark drop out at idle, it could be a sticking valve that didn't show up with the compression test. Run the engine for a minute and put a wet finger on each exhaust tube (or an IR thermometer if you have one.)

cheers, derek

ps does your distributor drive have the plug (part 112547) fitted to stop oil getting into the distributor?

 

I didn't read through the whole thread, but I had a misfire/ back fire issue and it was two of the plug extenders were bad. Simple and cheap fix. worth checking.

 

Guys, lots of good comments.

So far;
- Checked coils. Ohms look good and match up.
- Reset mixture screws. Screwed them all in and reset at 3 turns out. Car seemed to like that setting before.
- Picked up 8 new BPR5ES plugs at Advance. Need to gap and install them.

Other notes:
- Cams have plugs in them. GTB had plugs starting with engine 00848 per the Ferrari bulletin. My engine is 02237.
- Plugs all look a little sooty but not fouled. #5 did look a little cleaner and smelled a bit of gas.

Next is to get the new plugs in and recheck the timing. I also swapped back to my old distributor caps from th Superformance units I had installed. I was looking at the caps and rotors from AW Italian ($447 for the set, ouch).

 

If you have checked the timing and both banks are good, my guess is a bad plug wire or extender, or one coil. Even if a coil has the correct resistance, it may be arcing somewhere.

 

+1

This is a very backwards thread. The very first things to check for a misfire would be the above, plug wires, extenders and coils.