Engine's missing at lower rpm's

[Ratbird]

I was testing my car out and missed a powershift from 2nd to 3rd. It revved to about 6K, but that shouldn't be a problem in and of itself. Anyway, I drove about a mile back to town and when I came to a stop I noticed the motor was missing a little. I don't know if this is related to the rev, but thought I should mention it.

If I drive it at low RPMs it misses, but if I get it up to wide open throttle it runs fine.

I pulled a plug (#8) and noticed it was black. I decided to go through all the plugs one at a time to see if a fouled plug was the problem, it wasn't. I noticed that plugs from cylinders 4, 8, and 1 were blackish, I think the others were OK color wise. Another thing I notice is that the primary side of my Edelbrock 1407 is a little black too. Is this an indication that I have my idle set too rich?

I decided to listen to each side of my exhaust, they are independent sides with cheap little 18 inch glass packs. I couldn't really tell anything sound wise, but when I put my hand over the exhaust I noticed the drivers side felt noticeably cooler than the passenger side. I have no idea if this means anything, it's just a rookies observation.
 
Any advice on what to look at next? Or even a troubleshooting flow chart type process?

I took pictures and will up load a few of the carb and the plugs here in a bit.

thx in advance for any thoughts.

Dave J
 

[Ratbird]

Here are some pix, these are #8 and 7.

[Ratbird]

and number 6 and 5.

[Ratbird]

One from the passenger side head.
And the carb. Hope you can see that the primary side is a little black compared to the secondaries.

[My427stang]

I'd check your wires for resistance and look close at the ends make sure a crimp didn't go bad or didnt break where it the wire folds over.

Maybe bad wire on that pass side plug and maybe on the chalky one on number 7 too, but I'd start with that wet pass side plug

[fastback 427]

To add to what Ross said, maybe swap the order of plugs. Put a bad one in place of a good one and see if it cleans up. Also if the plugs are out a quick compression test wouldn't hurt.

[lovehamr]

That greasy one from the passenger side would make me look long and hard.  In the pic it looks like oil fouling, not fuel.  Is the junk on it oily?  If so, it's not a carb or ignition problem.  How old are the valve seals?  How about the rings?

[Ratbird]

The motor has about 1000 miles on it, it was completely rebuilt and has been just great. I have notice that all the plugs threads are oily. The plugs and piston tops look mostly flat, sooty black. That along with the carb looking blackish makes me think it's rich. I turned the idle screws in a 1/4 turn, I'll check the color again after 100 miles or so.

The only plug that looked a little shiny is the last one which is number 4. I'm going to replace that plug, and the wire with one from my old stock wires and see how it acts.

The last thing I had really worked on before this started was the vacuum advance and the full in timing. It is set to be all in at about 2.2K rpm to 2.5K rpm. It ran great like this for a few hundred miles. I guess I could check the timing again in case something slipped.

I'll post what I find in a little bit.

thx everyone!

[Ratbird]

I pulled the number 4 and 3 plugs and noticed that the top of the piston in #3 was a little shiny. I used a dull screwdriver and scrapped the top of the piston - it was a tad oily. So I changed out both those plugs and wires. Now it runs about the same, but it pops (like a small backfire) every once in a while in first gear.

Last night I moved the "pump" lever on the carb from the middle hole to the bottom hole. This may be delivering more gas as I first apply the throttle, and thus, may be causing the little backfire/spurt. I'm going to move it to the opposite hole and see if that does anything.

Dave

[Ratbird]

When it rains it pours.
Testing it out and the overflow tank seam sprung a leak. Spent the last couple of hours cleaning that up, (trying) to solder it up, but it still leaks. Soooo, I got to fix that before I can work on the miss.

Not sure I should change the subject, but does anyone have an alternative to these expansion tanks? I've had nothing but trouble with this thing since I got the car. One guy on the T-bird site told me he used e-poxy to coat the entire thing! Seems to me that wouldn't bond to well with the brass and solder.

Dave   

[fe66comet]

I have repaired some amazing stuff with JB weld. It has held up to some pretty high temps for me, you just have to clean it well first and scuff it up.

[TCSOHC]

Hi Dave,
Take your overflow tank to a Radiator repair shop, should be an easy repair for them & you’ll be back on the road in no time

Cheers,
TC

[Ratbird]

JB weld didn't do it. I've decided to try to remove the expansion tank altogether. I ordered parts but haven't received them yet.

Meanwhile, I was thinking and reading online. The Edel1407 manual advises to set the fuel pressure to be at 5.5psi. 6psi is maximum to use.

I completely forgot that I just replaced my fuel lines with 3/8inch lines. I also upgraded my fuel pump to one with a 3/8 inch inlet. The fuel pump spec sheet says it should be a minimum of 5.5 to a maximum of 7 psi. Being that the car misses at lower rpms, but runs fine at higher rpms, could too much fuel pressure be the problem? I'm thinking I'll order one of the Edelbrock fuel pumps that they recommend for my 1407 at 5.5psi.

I'll google how to test the fuel pump pressure, hopefully that's not too hard to do.

Dave 

[machoneman]

Adding a temporary "T" fitting to the pressure side of your pump is really the only way how to do it. By the look of those plugs, you're way too rich yet it's often hard to tell if leaner jetting would help. 7 to 7.5 btw is race carb & race engine territory and only for 1/4 milers. Track cars runs less than 7 usually.

Try it.....but I'd take a different approach.  5.5 to 6.5 is more than enough for a street engine. If the pressure is o.k. I'd yank that carb and beg, borrow or steal another for testing. Why? If the problem still exists, it's an ignition, coil, wiring or other non-gas related issue and you'll eliminate one big variable mighty quick.

[Ratbird]

That's an excellent idea Bob. It could eliminate a lot of unnecessary troubleshooting. Now I wish I hadn't sold the old autolite 4100! Hopefully today or tomorrow I can get the new expansion replacement set up on it and be able to start troubleshooting the "miss" part again. Meanwhile I'll try to track down a carb.

thx, DAve