3 replies to this topic

[jakejakejake1]

Hi everyone,
Just changed the head over on my car from a 12g295 to the standard 998 head due to a burnt valve seat,
and being an idiot i somehow managed to not tighten up 3 of the valves after resetting the valve gaps, and the car wouldn't start (obviously haha),
now i have sorted that the car starts up, but idles very badly.

Symptoms:
If idle speed is anything below about 1200 rpm, the car shuts down, the revs decrease to zero over about a second or two, so not an immediate stall.
The exhaust is loud and seems to be blowing a lot of air out, and the air is pulsing, kind of like when I used to pull the choke out before.
The idle mixture is ok according to gunsons colour tune
Also at one point it did backfire out of the carb, but that was before I advanced the timing a little, no more carb backfires after a little advance.

I didn't risk driving the car as I don't know how it will react under load, so I don't know if its down on power or anything.

Now I hope I didn't do any damage when trying to start the car with the valve gaps not done on three of the valves, the car was turning over fine with no odd noises which is why it took me a while to find the problem.

What could be causing this bad idle?

Thanks, Jake

[longbridge4life]

I'd be intrested in the outcome to i have similar problems,car won't start now and chugging if it tries...fingers crossed someone has an idea! I'm starting today by re doing the valve adjustments and checking the coil/ignition. I'll let you know if i have any success.

[jakejakejake1]

I think the head gasket has gone, because removing the HT lead from cylinder three makes no difference to the idle, and removing from cylinder 4 makes little difference.
Using Gunson's Colourtune, it seems that no fuel is igniting in 3, as you can see the spark, but nothing else. And in 4, you can see both the spark and a weak fuel mixture burning, occasionally not burning at all.
The spark seems to be fine in both cylinders, but the not-burning of fuel leads me to believe that the head gasket has gone between 3 and 4.
Does this sound about right? I can't think of any other reasons for there to be no burning in the cylinders.

Jake

[jakejakejake1]

Another update!
Been back out to investigate vacuum leaks after finding a thread about a similar problem, found that the brake vacuum take off was loose, reconnected this up and set mixture as best I could by ear (going by idle speed) and the car seems much, much better. The leak alongside a weak mixture was meaning that the fuel wasn't igniting.
Colourtune indicates that all cylinders are now burning fuel, but the idle is still a bit lumpy. I will do compression test soon to make sure the HG is ok.
In its current state it drives quite well, been up and down the street a few times and its as fast as it ever was :)