Hello Everyone,

It's the time of year that I'm going to be getting the car out and on the road again. Last season I ended on a sour note. Misfiring at high RPMs, and a lousy carb that I ended up sending back to Summit.

However, I have the bug again to try and get the car running right and back on the road. I am currently purchasing a new carb, and will want to get that high RPM misfire figured out.

At about 3 - 3.5 thousand RPM and above I start to get bad misfiring. I'm pretty confident after the help from people on this forum and asking around that this is due to bad timing.

Does anyone on here have a good write-up on how to go about adjusting timing? This is something I've never done before, but would like to fix myself. My uncle had sent the initial timing when he helped my put the motor together. However, he is in Florida until May!

Thank You!

The car is a 68 442, 400G block. Thanks!

 

I wonder if the misfiring (or at least some of it) was due to this lousy carb?

You may have some other issues in the ignition. When was the last time the eginie had a full tune-up (points, plugs, cap, rotor, wires)?

As for timing, what type of distributor do you have? If it's the original distributor, then all you should need to do is set the initial timing to the factory spec.

This brings up the topic if tools. Do you have a timing light? And if it's a points style distributor, do you have a dwell meter?

 

At 3,000-3,500 is when your engine should be making max torque which is when you make max cylinder pressure and in turn that's when you need max spark. I'm pretty sure your not getting very good spark.

So like LoganMiller68 said, let's start with what kind of distributor do you have?

Ray

 

There are several possibilities for your misfire, a weak coil, bad points and/or condensor, a worn distributor, failing plug wires, cap, or rotor arm.
If you don't get the timing right you will never get the carburettor properly tuned.
You will need a timing light, and to check your timing properly you need to know what the advance curve for your distributor should be.

Roger.

 

It might help us to know what your current timing and dwell (if you have points) settings are? What is your timing at idle with vacuum disconnected and what rpm. What is it at 3000-3500 rpm with vacuum disconnected and then with it connected? Does it advance any past 3500 RPM?

 

Thanks guys for the info. I should be getting the new carb today, and tomorrow will be getting the timing light. So tomorrow I'll report back with what info I find getting the car together and running.

One interesting thing that was brought up to me by a friend yesterday, that I guess I must have over-looked previously, could it possibly be a vacuum issue?

These are all things I'll have to test. Thanks everyone!

 

Sounds like ignition and not the carb

 

Yeah. That was my thought as well. I've just bought a new carb because I needed a new one in general. This issue has been present with any carb I've borrowed and put on the car, so I know it isn't carb related.

 

Do you have an HEI conversion in it? Like Pertronix, etc. or maybe a real HEI?

Ok, now I understand the carb part of this.

 

No HEI.

 

I would start by checking your dwell and set it to spec. Then adjust the timing. You also need to check the secondary side of the ignition. Cap, rotor, wires, spark plugs. Sounds like you have a cross fire happening at higher rpm or just a bad plug(s), wires, etc.

 

I did replace plugs and wires before putting her away for the winter, and that didn't solve the issue. Possibly cap or rotor. I haven't checked those yet.

 

So points, right?

 

Yes, correct

 

What plugs did you use? I have experienced a misfire issue with a Chevy engine once and went through a lot of other parts and repairs before replacing the plugs again with better ones to cure the misfire. AC Rapid Fire plugs did the trick in the Chevy.

 

They were AC/Delco's I know for sure, but which ones I don't know. I'm going to be pulling them all tomorrow to look them over and check gaps.

 

Good place to start. Come back with brand, model number and describe their condition and we'll go from there. Maybe they're a bit fouled.

 

And points and condenser, and be sure to adjust the dwell angle. Incorrect dwell could cause the miss.

 

Hey Guys,

Sorry for the delay in getting back with everyone. It's been a very busy past few days as my wife and I bought a new house!

Anyways, back to the matter at hand. I pulled all the plugs (that had less than 100 miles on them) and realized a couple of them had fouled. I checked gap and they were all at 0.60! They were supposed to be pre-gapped and I must have not double checked them before putting them in!

I popped all new ones in, gapped properly and the misfiring is completely gone! She revs beautifully now.

Thank you everyone for you help!

 

Always check the gap. Plugs that fit these cars are never pre-gapped. With a factory points ignition, they should be at 0.030. BTW, what were they fouled with? What color were they?


Oh, also: congrats on the new house! Hope this doesn't mean the car goes back into storage.

 

Nope, new house has a nice attached garage, so I can look at her every morning! lol

Yeah. It's definitely a mistake I will not make again. I gapped all the new ones to .030

 

Plugs do come gapped from the factory, however maybe not correctly and the box might have been dropped. Your dwell needs to be set to 30 degrees, then your timing set to 10 degrees before tdc @1250 rpm, then idle turned down to500-550 rpm, and your plugs should be gapped at .035

 

Timing was all set. Gapped all the plugs between .03 and .04.

After driving around for a few minutes and letting everything get up to temp I finally opened her up and ran her through the revs. Ran like a dream and pulled harder then I ever remembered. Very happy with it!

 

Everywhere else says to gap the plugs at 0.030 with factory points ignition. Have you found 0.035 to be more effective?


And pardon me, I should have said plugs don't come RELIABLY gapped from the factory. To the extent that I've never installed a set that didn't require some adjustment. Sounds like Mr. Miller might have got hold of set of platinum plugs which are frequently pre-gapped to large (0.060!!) apertures.

 

Jackie - I've always used .035 on all my V8 points cars over the years. We run into the statement that plugs come pre-gapped all the time and usually they are gapped wrong. It only takes 10 minutes to go through them and make sure. I was told this also as a teen and learned from experience.

LM68 - Glad it's running well and your happy with it.