[bob9909]

Hey, was hoping someone could point me in the right direction here
Been having some issues with my sierra. Feels like sometimes when I start it up cold, it is like a cylinder is not firing. The car will be lumpy, wont want to idle, wont rev properly and will spit out heaps of crap out the exhaust. I have forgotten to reconnect a spark plug lead once or twice and this feels exactly like that, down a cylinder. It never really had any issues like this before I started messing around with it :S

It seems to run fine for the most part, once it is warmed up and driven a bit it is good, some days it even starts perfect from cold. I don't think it is the carby as I had all that fixed and was working good.

I started having troubles again after re timing the engine the other day, though I have tried setting it back to 8btdc and it is not much better, I've only got it set on 9-10 at the moment. Still it seems to start fine a lot of the time and then sometimes it doesn't want to go. It blows a lot of smoke on start up when it is having issues, and other times only very little :S

Sticking the timing light on all the leads shows that they are all sparking, but the points are pretty warn down in the cap and have a build up of white powder.

It is the inconsistency of it that confuses me, I'm going to re check the pressure in the cylinders. Last time I checked I thought the numbers were a bit low but they were all close.

Can anyone point me in the right direction? do you think it might be the electrical system? or the engine itself?

Cheers guys

[Scrawny]

What did you have done to the carby? Sounds like a choke thing to me

[bob9909]

After rebuilding the carby I loosened the choke as it wouldn't idle properly when cold, had all those issues already and unless the screws have loosened themselves they were all good, but I don't think it feels the same as that

I'll go check it out though

[whincup]

bob9909 wrote:

but the points are pretty warn down in the cap and have a build up of white powder.

start here. even if its not the problem (which it most likely isnt) it should be done anyway. they dont cost much...

[Scrawny]

whincup wrote:

bob9909 wrote:

but the points are pretty warn down in the cap and have a build up of white powder.

start here. even if its not the problem (which it most likely isnt) it should be done anyway. they dont cost much...

What he said. You can just flick that stuff off the points with a flat blade screwdriver, might pay to replace the cap and rotor if you can.

[bob9909]

Cheers, will look into fixing that, just noticed something else, if when idle I just barely touch the accelerator it will die, and if I accelerate slowly while idle the revs will drop real low for a quick second before shooting up. Is this normal? can't say I have noticed it before.

[Scrawny]

That's usually a sign of the accelerator pump not working. When the engine is off, take the hat off the top and look down the throat. Pull on the cable and you should see a squirt of fuel come out

[bob9909]

Ok, cheers, that was an easy fix, had the accelerator pump screw just a little too tight and it wasn't responsive to the really soft changes in acceleration.

But still worried about the intermittent start up issues, I will play around with the choke some more, but would that really cause it to act so bad, It was working great after I fixed the choke last time and unless it loosened itself I don't understand why I should have problems with it now, especially intermittently. Or why it would through so much crap out the exhaust (the kind of gunk you get when one of the cylinders isn't going)

Thanks for the advice so far guys, will keep working on it

[Scrawny]

That crap is unburnt fuel. On start up would point to choke, maybe comin on too much?

[FullyZooked]

Fasten the choke open by any means for a test, rubber band on lever.
This will cross that off the list.

Poor idling and black smoke is typical for a partially/blocked idle circuit. Easy check is to start cold with carb hat off. Look down the primary throat and make sure the mains aren't fuelling on idle. You should see no fuel ontop of the butterflys.