Terrible running while warming up

[Heathx4]

Any suggestions given these symptoms, before I start digging around?

Engine is carby straight 6 L28 on PULP, with manual choke. Starts fine with choke out, but starts to run rough after 15 seconds or so. Then deteriates and hardly runs while warming up. Once at operating temp, runs smooth as.

While warming up, it wont idle (usually manages to idle with the choke out, probably just because that opens the throttle a bit. Really sounds like it is missing when you hit the go pedal. Revs wander. Uneven running. Then, when actually driving it (that is, when applying a load) it'll try to accelerate, choke, stutter, pop and ping, jerk and generally make an arse of itself. I can save it by hitting the clutch, or if not going up a hill, by backing the accelerator off.

What does that sound like? Methinks maybe sparkies aren't delivering hot enough spark to ignite fuel in a cold cylinder. I guess that means either plugs are dirty, or charge to plugs is weak.

Points, dizzy cap, recently replaced, carby recently rebuilt.

[Toy80Diesel]

Any suggestions given these symptoms, before I start digging around?

Points, dizzy cap, recently replaced, carby recently rebuilt.

I had an MQ years ago with this same motor.
When you put the dizzy back in, it can enter in a few directions, as it sort of screws into place of the gearing. I had this problem when i undid the oil pump at the bottom of the engine to replace a gasket, as there is a long shaft from the oil pump to the dizzy. And from the bottom this shaft slips out and you need to re-align the dizzy. I did this by putting the motor back to TDC, and setting the dizzy point to spark cylinder 1. If I can do it, you can do it.

It sounds like the dizzy is out by one notch or so. I would check this first. Then check the carby and any vacuum leaks etc.


Just my 2 cents hope it helps.

[dumbdunce]

maybe a vacuum leak? these things are notoriously difficult to diagnose. the carbies on those motors are famous for wear in the throttle butterfy spindles, which causes a vacuum leak under various conditions and variance in the mixture.

also stretch in the timing chain can cause the cam to be retarded, there is 3 positions on the cam sprocket from memory 4 degrees apart so you can tune the cam timing to some degree. there should be a picture in your manual for checking the cam timing, there is a window with a notch in the cam sprocket.

as suggested, check your ignition timing then start hunting for a vac leak. could even be as simple as a clogged fuel filter although that will usually show up even when the engine is up to temp.

good luck!

[Maxtd5def]

Don't anything about these engines, but

What do your spark plugs tell you? Lean or rich? And is there a difference between them? Are Nos 1 & 6 running lean, or 3 & 4 rich?

Do these things have a hot spot under the carb to assist warmup? Is that not getting water in for some reason?

Regards
Max P

[shakes]

I've sent you a PM because i dont know the rules for advertising other forums on here.

My first guess would be your dizzy cap isnt sealing moisture out 100% or... just go find an electronic dizzy anyway!
Simon

[dumbdunce]

I've sent you a PM because i dont know the rules for advertising other forums on here.

My first guess would be your dizzy cap isnt sealing moisture out 100% or... just go find an electronic dizzy anyway!
Simon

true this may or may not solve the problem but L series motors benefit enormously from electronic ignition, especially when starting and cold. the EFI L series motors from skylines, Z cars etc all have an electronic dizzy with built in igniter module that is a complete bolt in and a doddle to wire up, available from wreckers for around $50 - $100 for the whole shebang including the coil.

[Heathx4]

Thanks for all the responses guys. Answering a few q's:

It sounds like the dizzy is out by one notch or so. I would check this first.

I didn't actually take the dizzy off the shaft when I had it apart - I don't see how it could have moved a notch. Of course, it could be stretched. Might have to learn how to check this. Ignition timing is cool, just need to borrow a light.

What do your spark plugs tell you?

1, 2, 3 were dry, 4, 5, 6 were fairly wet. Cleaning them up hasn't seemed to make a lot of difference.

Do these things have a hot spot under the carb to assist warmup? Is that not getting water in for some reason?

Mmm, quite possibly - there are pipes running around the bottom of the carb. Who knows whether they're working right. That would kinda explain the symptoms.

I've sent you a PM. ...just go find an electronic dizzy anyway!

Cheers. Yeah, I think I've seen enough evidence to finally start looking for EFI, or at least elec. dizzy. Grr...

Anyway, had a bit of a play and couldn't get it any better. Everything superficially looks okay. I had a thought though - when I originally posted about the problem I had just got to work and the symptoms were the worst they've been. When I left work 5 hours later, the symptoms were *almost* non-existant. When I start the car the temp gauge slowly climbs to just shy of 3/4, then falls to 1/2 where it never budges while running. I thought the 3/4 point might be when the fan switches to "on" (it is viscous coupled) but maybe that's not right. Just had this crazy thought that water ever "switches" at that time also changes the behaviour of the car - from running like a dog's breakfast to smooth as.