Rough midrange

[suntennis]

You have determined that the problem is mixture or fuel. A lean mixture can be caused from a number of things. If the carb float level is low, this will cause the fuel mixture to be leaner. You said you rebuit the carb, did you check the float level?

[38plymouth]

You have determined that the problem is mixture or fuel. A lean mixture can be caused from a number of things. If the carb float level is low, this will cause the fuel mixture to be leaner. You said you rebuit the carb, did you check the float level?

I left it where it was from when it was rebuilt. It does not seem to move up very much, maybe I better check it. Thanks for the idea.

[james49ply]

you stated that you put headers on the engine, when you change the exhaust flow and reduce back pressure it allows the engine to breathe better, this will cause a lean condition, this is evedent as you close the choke and it runs better. you will have to change the main fuel jet, find the size that you have now, and go a step or two larger, this is a trial and error process. find where the engine rus best and you have it licked. you will have to test the engine with normal load on it, which means a lot of test driving. testing in nuetral will not give you correct mixture, you must have a load on the engine.

[38plymouth]

you stated that you put headers on the engine, when you change the exhaust flow and reduce back pressure it allows the engine to breathe better, this will cause a lean condition, this is evedent as you close the choke and it runs better. you will have to change the main fuel jet, find the size that you have now, and go a step or two larger, this is a trial and error process. find where the engine rus best and you have it licked. you will have to test the engine with normal load on it, which means a lot of test driving. testing in nuetral will not give you correct mixture, you must have a load on the engine.

Actually it doesn't matter what I do with the choke now, it runs rough wide open or partially closed. I'm frustrated.

[james49ply]

I am thinking different causes here,

1: if you have a dwell meter attach it and watch the dwell, it should only change a degree at best when the engine rpm raises. if it varies at idle or at higher rpm, the distributer shaft is worn.

2: check valve clearance, you can do it cold if you like, I run my lady cruising araound 60-65. the book wants an additional .001 for high speed running, so I set mine at .013 cold, both intake and exhaust, when hot they are at the correct reading.

3: compression, did it run OK prior to Fenton head? head torqued to specs and retorqued when hot?

4: vacuum leak in the intake area, gakets at the block, carb, etc. you put split system on, are you using stock intake? if so I would look close at the manifold, may have a crack in it somewhere around the heat riser area. isolate the top of the carb ( put a 'stack' on it ) and use brake cleaner spray, and sray on short pops at all gasketed areas, engine rpm will show if you hit a leaky spot.

Try these suggestions, if that dosen't find the problem, post and I'll put my thinking cap back on for you:D

Edited September 17, 2010 by james49ply

[38plymouth]

Man after everything I did to fix this it ended up being something very simple. My float was set way to low, I'm surprised it ran at all. The last time I rebuilt the carb I used a new needle and seat. I didn't recheck the float because I figured it wouldn't change. The new seat way different inside and the needle stuck out farther causing the float to barely move. I replaced the seat and set the float and now it runs great. I went on a 20 drive last night and it ran better than I can ever remember.

[james49ply]

Glad ya gotter running good again. seems that the hardest ones to find are the simple ones. Run the ol gal and let her have some fun cruisin.

[P-12 Tommy]

Take a look under the hood after dark with the enigne running. If you can see blue sparks jumping around the spark plug wires, it time for a new set. Tractor supply has 6 clinder universal sets for tractors for under 20 bucks. Several folks are running them with good results.

Check the wire in the distributor that connects the coil terminal tot he points. Some time the insulation will wear allowing it to ground against the body of the dizzy when the breaker plate moves. Also from all the flexing over the years, the wire strands can fatigue within the insulation either breaking the circuit or causing less current flow through the remaining strands.

Also is your breaker plate moving freely and effecting spark advance.

Yesterday I was out and about and out of nowhere the P-12 wouldn't start. It just cranked and cranked. Then it started right up. Then I went to take off and it quit. Hmmm... I checked the carb and it's getting fuel. Pulled the coil wire and got a healthy spark. I managed to get it started and made it home. (I was 10 miles from the house) I pulled the dizzy out and low and behold... that pesky short dizzy wire inside was broken. Must of been hangin' by a thread enough to get home. Made a new for now. Runs great now. Phewww! I want to buy the right wire for it.

Tom

[Jim Yergin]

Tom,

Fortunately your car has a good personality. Lets you know something is wrong but gets you home to let you fix it.

Jim Yergin

[P-12 Tommy]

Well, I spoke too soon! Went out to take the car for a ride and it wouldn't start right away. When it did start it seemed to run ok 'till I drove it. Mashing the gas at full throttle and it was breaking up big time. I popped the hood and started my check around. Took the airhorn off the carb and checked the adjustment on the float. Was ok. Getting plenty of fuel. Still getting a good spark at the coil wire. I also put a test light on one side of the points and got a flash of light everytime the points closed. Pulled the dizzy again and checked all the wires again. Nothing broken. Does that short wire have to be a certain type of wire? Braided with cloth cover? Like on one of Capt. Freds pictures? The wire that broke before was a homemade one. Looks like 16 ga. It ran fine with it up to the other day. Rechecked the points. Still at .20 thousands. When it idles warmed up I checked the timing by vacuum and had 19 and a half lbs. Seems to run ok 'till I drive it. It's never run like this since I've had it. I'm thinking that little wire is possibly causing all this crap. BTW... I've used the search and read up on all the threads on the dizzy. I'm just stumped.

Tom

[Joe Flanagan]

Tom, if you move the breaker plate in the distributor by hand, does that small wire touch anything, like the side of the distributor housing?

[Young Ed]

When you replaced the wire did you reuse the same screws? I've heard of people having issues with using too long of a screw.

[P-12 Tommy]

Joe, Nothing touches when I move the plate. Ed, I reused the same screws.

Tom

[Jim Saraceno]

Is it possible it is not the ignition but the fuel? Have you already determined you are getting proper fuel delivery?

BTW... you can buy new jumper wires for you distributor at NAPA if you are at all concerned about the one you have now.

[P-12 Tommy]

Jim, It looks like I'm getting proper fuel delivery. I'm gonna try NAPA on that wire. If that doesn't do anything, then I'll change the condenser. It's weird that I found a broken wire and fixed it, then it still does the same thing.

Thanks, Tom

[JIPJOBXX]

You might just get a new whole braker plate assembly. I bought one on E-Bay and it was new old stock. Cost somewhere around 20 dollars and well worth the money as that wire your talking about was already mounted. All I had to do was changed out the plate assembly and set the points. Walla! no problems.

[P-12 Tommy]

It wouldn't hurt I guess. Thanks Jon!

Tom

[greg g]

not really, if the original wire was broke or shorting against the body, when the breaker plate moved it cause an inturuption of the ground signal to the coil causing a miss. If the wire is thick enough to keep the breaker plate from rotating properly, the lack of timing signal could mimick the symptoms.

Edited May 4, 2011 by greg g

[P-12 Tommy]

Good point Greg! Makes sense to me. BTW... I found 2 NOS breaker plate kits with all the goodies on E-bay. I bought both for $33.00 plus shipping.

Tom

[P-12 Tommy]

Well guys..... I got both breaker plates I bought on E-bay. I put one in a spare dizzy and put the other in mine. I'm happy to report that it runs really good now after I warmed it up and redid the timing and took it for a nice run. At times I floored it in spurts and it didn't miss a beat! So it's good for now. Thanks for everybodys help.

Tom

[Jim Yergin]

That's good news Tommy.

Jim Yergin

[P-12 Tommy]

Thanks Jim. How's your woody runnin'?

Tom

[Jim Yergin]

Thanks Jim. How's your woody runnin'?

Tom

Seems to be running well. I had to replace a leaking rear inner axle seal on the passenger side but that went OK. Still have to get the O/D to work but have not had the time to work on it. My son wanted to have his 240Z back on the road in time for his senior prom so that took priority. We did it so now I can get back to my car.

Jim Yergin