[matfan]

Hi Guys,

I'm having some issues with my sierra (standard 1.3). It's running like a dog at the moment and it's got me fucked.
It's symptoms are as follows

High idle 1500-2000
Dead spot at low rpm - You have to rev the shit out of it and slip the clutch to get off the mark or it stalls. It's especially bad when cold.
Revs stay high briefly after backing off the throttle
Occasional dieseling

I've removed and cleaned the idle solenoid and checked for proper function and it seems ok
Throttle spring is all good
Secondary functions perfectly
Choke operation is perfect
All air lines are attached and in good working order
unscrewing the idle adjuster does nothing, screwing it in raises the revs
timing is spot on (8 advance with pulp)

One thing of note (or maybe not) is that if you spray carby cleaner or wd40 etc down the primary the revs rise. From memory, it normally bogs down with extra fuel being sprayed down it's throat which leads me to believe it's running too lean. I mean I have no idea what I'm talking about but it's an observation non the less.

Does anyone have any ideas??

[Jackson]

matfan wrote:

unscrewing the idle adjuster does nothing, screwing it in raises the revs

Do you mean the idle RPM screw or the idle mixture screw, if you mean the idle rpm screw then your accelerator cable needs adjusting as it is holding the accelerator on a bit at idle, probably the high idle.

matfan wrote:

One thing of note (or maybe not) is that if you spray carby cleaner or wd40 etc down the primary the revs rise. From memory, it normally bogs down with extra fuel being sprayed down it's throat which leads me to believe it's running too lean. I mean I have no idea what I'm talking about but it's an observation non the less.

You must be using shit as fuel for it to like carby cleaner, usually they die if you don't rev it before you spray it in.

RIch or lean rich or lean, I always get confused and half the symptoms of one are symptoms of the other so whip ya plugs out and match it to the pictures below.
Either way your carby is probably just dirty as on the inside and needs a clean.

[matfan]

Jackson wrote:

matfan wrote:

unscrewing the idle adjuster does nothing, screwing it in raises the revs

Do you mean the idle RPM screw or the idle mixture screw, if you mean the idle rpm screw then your accelerator cable needs adjusting as it is holding the accelerator on a bit at idle, probably the high idle.

I mean the idle rpm screw. The accelerator cable has slack in it and the throttle seemed to be closing properly. What's the best way to set up the idle mixture? I can't get to it with the carby on the manifold.

Jackson wrote:

matfan wrote:

One thing of note (or maybe not) is that if you spray carby cleaner or wd40 etc down the primary the revs rise. From memory, it normally bogs down with extra fuel being sprayed down it's throat which leads me to believe it's running too lean. I mean I have no idea what I'm talking about but it's an observation non the less.

You must be using shit as fuel for it to like carby cleaner, usually they die if you don't rev it before you spray it in.

RIch or lean rich or lean, I always get confused and half the symptoms of one are symptoms of the other so whip ya plugs out and match it to the pictures below.
Either way your carby is probably just dirty as on the inside and needs a clean.

Shit, I didn't think to check the plugs.. although saying that, it runs fine once you're up to speed, if it is just the idle mixture then am I correct to assume that the plugs wouldn't really tell the story? I'm only ever use premium fuel and regularly check/change the fuel filters (one near the carb and one near the tank)

[JrZook]

If it ain't a vacuum leak then it just sounds like the classic case of a blocked idle jet. You might be able to clear it by revving it up and smothering the carb intake with your hand to pull the crap through. Otherwise its strip down, clean and put a kit through it

[buzbox]

Yep, as what's said above, or the lazy way is to spray with carby cleaner, wack a bottle of fuel cleaner int he tank, fill it with premium fuel and hit the freeway.

[matfan]

It's a strange one, I stripped the carb and put a kit through it about 10k kms ago, the fuel pump was replaced at the same time so none of the membrane should have failed yet, I only ever use pulp, I haven't messed around with any settings and the idle solenoid is clean and functioning perfectly.

Does anyone know the correct way to set idle mixture? Even something along the lines of x revolutions from tight would be a good start.

[JrZook]

Kit quality has become pretty shit these days. I have put a few kits through carbs in the past only to have issues a few days later again. This was due to the fibers in the gaskets coming apart and again blocking the idle jet.

If you haven't messed with the idle mixture screw then you shouldn't have to play with it. You have other issues to sort first. On the idle mixture topic think a base line to start with was around 2.5-3 turns out. Tune by leaning it out until it starts to stumble or run rough and richen by ~1/4 turn.

[matfan]

Cheers for that JrZook, I think I'll strip it down and clean it tonight, I may even have a spare carb kit lying around!