bad tickover - she just wont idle - desperate!

[bixdog]

Greetings!

It's been ages since I posted, mostly because my 1988 R4 GTL has been running wonderfully for two years now.

Then she sat up for about a month in the middle of a Portugal winter, so we're talking lots of rain, but not too cold. She started up just fine, but as the thread title says, she craps out if I don't rev the engine hard, or have the choke pulled way out (which revs the engine hard). She runs fine on the highway, but dies at every traffic light. huge pain.

So I went through all the usual stuff. I've replaced the entire ignition system, except for the coil, gonna do that next, but no change with an older spare coil I had, and also the entire ignition system was replaced only two years ago.

Then I attacked the carb - did the wd40 spray, which is kind of inconclusive because I have to rev her high to keep running at all. Pulled the carb, checked and cleaned everything, seems okay. Checked the breather hoses, nothing obvious there. I had a guy come by with a carb he had for sale, whacked it on, basically the same thing - she just wont idle.

The carb mount gaskets were not in the best shape, will order new ones, but I made some improvised gaskets from gasket paper, not a long term nor high temperature solution but should at least rule out air leakage at the mount no?

Turning the mixture screw all in or all out seems to have no effect what so ever.

I just don't get it. She was running like a charm. I'm still driving her around, but only when I absolutely have to, and only when most of the drive is straight highway. So there has been plenty of new petrol run through the system as well.

I am absolutely desperate, I need this car to run! Any ideas?

Thanks,

John

 

[Cyprus Andy]

I hope you get it sorted and get some help on here as mine is the same !! Been stood for a year in a garage in the dry and will only run with 1/4 choke on but when you pull up and go to neutral the engine is raceing away.
Maybe they dont like being left for any length of time ???
Good luck John !

 

[Cornish4]

Hello John, it could still be air being sucked in somewhere causing a weak mixture, or maybe just a jet blocked. I think a carb strip down is called for as the car has been standing a while. Good luck, regards Brian.

 

[Bobble]

Hi, i had a similar problem a while ago with my 1986, try the small bypass pipe that goes from the top of the carb
(and it goes into the rocker box top also) to the base of the carb at the back (near the manifold), that had a small split
(perished with the heat) on mine therefore it was sucking air, took me quite a while to find the leak but it runs fine now.
good luck.

 

[tim1casa]

Take off the float chamber and make sure that the float is moving up and down freely. I found that mine was sticking in the up position, so no fuel was getting through at times. In fact my carb is such a problem I am waiting for a second hand one being brought over from France.

 

[angel]

Turning the mixture screw all in or all out seems to have no effect what so ever.

Check carefully that the idle circuit in the carb is not blocked in any way. Pay particular attention to the idle jet itself. This one is the smallest bore in the whole carb, so it's the first to clog especially if the car has not been started for some time.

Use a carburettor cleaning aerosol, WD-40 is not suitable for this job.

 

[bixdog]

Thanks for your replies! I'm still in a bad way. I striped down the carb, new gaskets and other bits, cleaned everything, made sure no jets were clogged (poked needles and wires through everything) all seems fine though she still wont idle. Nothing I do seems to have any effect what so ever. I have to think it is the idle jet as she just seems starved for fuel at idle. Don't forget I also swapped in another carb at one point, to no effect, so this suggests it is not the carb at all.

Something I noticed, it used to be (when she was running perfect) that after a cold start, choked off for a few seconds, the choke light on the dash would come on, so I'd push in the choke, the light goes off, and after about a 20 second warm up, she was good to go. Now, the choke light never comes on at all. Is this an indication of something? What/where is the choke light sensor, and what determines if it is lit up or not?

So if it is not ignition (complete replacement), not an air leak, not a clogged jet, not a leaking manifold gasket (also fairly new), what can cause this behavior???

Still desperate!!

John

 

[Cyprus Andy]

burnt valves ?

 

[mojobaby]

It really does sound like it's got an air leak. I had exactly the same symptons as you and found that my carb wasn't bolted down properly, so air was being sucked into the system. You'll find that if the inlet manifold isn't bolted tight enough where it joins the cylinder head, or if that gasket is damaged, you'll get the same symptoms.
What sort of carb do you have? Automatic choke?

 

[mr-reno-139]

Have you tried blocking the rubber pipe that goes to the inlet manifold with an m8 bolt to see if that makes a difference as the rubber hose should have a restrictor to create a small vacuum on the rocker cover breather circuit
you may be missing this part allowing too much air and stalling due to weak mixture

 

[bixdog]

yeah it sure seems like an air leak, and i have tried all above, but i'll go through it all again before i dig into the valves. uggghhh - she was running so fine.

 

[bixdog]

okay i really don't think it is an air leak. plugged up everything (again), no change. btw it's a zenith 28 carb, manual choke. and i also tried another zenith 28 carb to no effect, though perhaps at that moment there were other bits not quite right that could have caused the idle problem, though i find it unlikely. the header gasket is a couple years old max, changed it myself, looks fine on the outside.

are there other symptoms of burnt valves that might warrant pulling the head? again, she runs fine on the highway.

how can i be absolutely sure the idle jet is not clogged? is there a test other than poking wires through and seeing where they come out?

 

[mojobaby]

I have the same carb and there's a fuel filter at the top that you could check as well. I've never taken mine out because I've never had a problem.
I'm surprised that when you turned the idle jet in and out, it made no difference. It's really very noticeable on mine. The idle jet has a small washer that could be your problem
I bought a can of carb cleaner and I sprayed it into every hole that I could see and made sure that it came out the other side.

However, it sounds like you've covered all your bases. 90% of my problems are electrical and I always go to my distributor first. Last week my engine was hiccuping(missing) and I adjusted the gap on my contact points and it solved the problem.

The only other thing that I can think of is your fuel pump but I'm not sure how to check that its working correctly