Help with GQ starting troubles from cold

[simy]

Engine is a TB42. I got it back from the mechanic who said everything is fine. Started it this morning cold and it was running on 5 cylinders and stalling bad and black smoke everywhere, it had never done this before. I called the mechanic who came out to my work and revved the crap out of it and said it was a fouled spark plug.

I'm really lost on where to go from here. The main problem is it revs high on startup (1500-2000rpm) and runs really rough, almost stalls then revs back up, runs on 5 cylinders. Once it's warm it runs like a dream, no problems at all. The mechanic said the auto choke is fine and not sticking, and he can't pinpoint anything else wrong. Plugs, leads and pertronix are only 10,000km old
Oh, it's not LPG.

Any ideas? Could it be the pertronix or the coil? If it was these it wouldn't run well once warm right?

[krbrooking]

Not sure bout what could be wrong with your rig mate but by the sounds of it you need a new mechanic. Just a thought could be injectors, if it was a fouled plug why did he not change it/them.

[Lieney]

If the coil was faulty, the whole lot would be affected, not just missing on one cylinder.
Get a working spark plug (not from your car but same / similar type) and cut the bent bit next to the electrode off. Disconnect the HT lead from one of the spark plugs and connect it to the 'Test plug'. Cutting the bent electrode bit off increases the distance the spark has to jump, replicating the inside of the combustion chamber when under compression.
Use this to test each lead to each plug by earthing the body to the engine.
You want to crank it, but not start it, so you can remove a relay for the fuel system to prevent it from starting.
If the spark at the end of a lead is nice and clear and consistent, then that lead is good.
Do it to all 6.
Check the dizzy cap for tracking (carbon build-up) inside and any cracks or lines. This can cause the spark to run down the cap and earth, instead of the HT lead.
Check all injector electrical connections to ensure they are functioning.
Make sure each injector is firing by using an LED test light on the wiring. It should flash each time it is active.
Not sure if the choke is auto or manual or how it functions but that would be the other idea.
I'd consider checking the inlet, air filter and possibly manifold for carbon build-up and also the blow-by to see if there are other contributing issues

[simy]

If the coil was faulty, the whole lot would be affected, not just missing on one cylinder.
Get a working spark plug (not from your car but same / similar type) and cut the bent bit next to the electrode off. Disconnect the HT lead from one of the spark plugs and connect it to the 'Test plug'. Cutting the bent electrode bit off increases the distance the spark has to jump, replicating the inside of the combustion chamber when under compression.
Use this to test each lead to each plug by earthing the body to the engine.
You want to crank it, but not start it, so you can remove a relay for the fuel system to prevent it from starting.
If the spark at the end of a lead is nice and clear and consistent, then that lead is good.
Do it to all 6.
Check the dizzy cap for tracking (carbon build-up) inside and any cracks or lines. This can cause the spark to run down the cap and earth, instead of the HT lead.
Check all injector electrical connections to ensure they are functioning.
Make sure each injector is firing by using an LED test light on the wiring. It should flash each time it is active.
Not sure if the choke is auto or manual or how it functions but that would be the other idea.
I'd consider checking the inlet, air filter and possibly manifold for carbon build-up and also the blow-by to see if there are other contributing issues

Thanks mate, it's doing my head in even more now. I left it for 5 hours and just started it, it was perfect. First time its started like that in months. I gave it a proper flogging this afternoon, im wondering if it's blown out the gremlin as i never drive it hard, even when out bush, just idles up everything. Will report back in the morning when i crank it over again, if it plays up its going to be a big weekend.

[GQ TANK]

With a pertronix its got to be a carby.

High rev sounds like the autochoke need adjustment.

How do you know its running on 5 cyclinders?

Could it be valve stem seal (do the tb42 have these) - I would pull the plugs and see if any are foled?

[simy]

The thing is it wasnt all that bad until the mechanic adjusted stuff on wednesday. Now it does this crazy chugging and engine sounds like its about to die and revs like its running on 5. The chugging missing sound. I'm wondering what the mechanic could have done to make this start happening as it wasnt happening before. But this is only happening about one in ever 3 cold starts. I've checked the auto choke and it seems fine

[GQ TANK]

I would take it back to the mechanic - he done something to make it play up

I had a problem on my rb30 with the EF alt i had fitted. The alt would not kick in on start - would kick in 100 metres down the road.

The truck would run bad - missing wanting to stall etc until the alt kicked in - next time it does it have a look at the battery metter on the dash - what level?

[simy]

Mechanic came out yesterday at work when it wouldn't go and told me that it was a fouled plug and not something he has done. im really not sure, here in canberra there is a carby specialist 45 minutes out of town, im thinking a drive out there might be worth it. Not going to pick it up until it is fixed.

The mechanic fitted a kill switch as well, wondering if this has something to do with it

[mudnut]

Sounds similar to my Rb30 after it backfired (MY FAULT). It turned out to be the choke break diaphragm, had a small tear in it. Don't know if the tb42 has the same set up though.

[pearcey]

There is a small spring in behind the fast idle cam and if its fitted in back to front it jams the fast idle cam.If it is incorrect the choke wont open properly and the carby will flood and the motor will stall and possible sound like its on 5 cyls. It`s very hard to fit correctly with the carby on the car but can be done. But it is easy to fit on back to front. I know it`s hard to find some one who has a lot of carby knowledge these days but try and find someone who specializes in carburation