Uneven idle when warming up

[CJG]

I'm afraid my car is still stubbornly refusing to "just idle"!

 

I've replaced the coil (Flamethrower), rotor arm (Martin Jay's red one), distributor cap, leads and plugs (NGK). Oh, and there's an "Ignitor" module fitter, so effectively, the whole ignition system is new. Timing was adjusted when the Ignitor was fitted, the coil and other components were added later.

 

On starting cold, the engine runs just fine (but it seems to need two or three attempts to get going). After about a minute or two, it starts to idle lumpily (sounds like it's on two cylinders), but this smooths out to a normal, regular idle after a mile or two, when the engine is at its operating temperature of 85 degrees. There is still occasional popping on the overrun, but nothing like as bad as it used to be before the ignition system was fixed (sounded like gunshots!).

 

The front two plugs are clean, the rear two slightly black. My first thoughts are carburettor synchronisation or ignition timing (or perhaps an air leak which opens up when the block gets warm, then closes when the manifold has reached operating temperature?). I've had both compression and emissions checked, and they are fine.

 

Finally, I've noticed that when I have both the headlamps (H4 conversion) and Kenlowe electric fan on at the same time, sometimes the ignition light glows dimly at low speeds. Does this mean that the original dynamo (it's a positve earth car) isn't up to the job, or might need some TLC?

 

Regards,

 

CJG

[Brian-Northampton]

Hi,

 

Have you made any attempt yet to sychronise your carburettors??

 

From what you describe on the cold start, it sounds like they are well out of balance when the choke is pulled out - this is also the most ignored part of carburettor tuning. What carbs are you running? If you were running SUs I'd suggest that you visually ensure that when the choke cable is pulled to the extent that the jet is lowered, that both jets are pulled down at the same time - usually just a job of slackening/turning/tightening linkages. Next, once the engine is at operating temperature, pull the choke out a small amount for fast idle only (not pulling the jets) - check the manual for the distance and recommended RPM as I don't have it to hand. Then synchronise the throttle butterflies using the FAST IDLE screws rather than the normal idle screws. I've found it to be these fast idle settings that will give the exact symptoms you describe from a cold start.

 

I've no experience of Strombergs if you have those................ but I would guess there would be similarities.

 

It does also sound like you need to tune/sych the carbs for normal operation too - the plugs should all be a uniform brown colour. When you say one set is sooty - sounds like it's too rich, the other plugs are 'clean', what does that mean? If they have traces of white on them, then they are too lean.

 

Hope that helps,

Best of luck,

Bri.

[Steve Priest]

I had a similar problem so just thought I'd mention it. The problem turned out to be the choke sticking open on one of the carbs. When the choke was released the jet on the second carb was tight in the last few millimetres and failed to return all the way home. Consequently that carb ran rich after the choke was used. Turned out that the jet was very slightly bent. Fitting a new jet solved the problem.

 

Just as an aside I recommend using a Colortune to get the mixture set up correctly. Tried mine for the first time at the weekend and the idle is now much much smoother than I was ever able to get it before.

 

Steve

[CJG]

Just got the car back from a comprehensive tune-up. The diagnosis: not enough oil in the carbs, an air leak at the inlet manifold and one carb too rich, the other too lean.

 

She runs beautifully now, and idles evenly at 800 rpm. However, at idle, the ignition warning lamp glows dimly (the car has been fitted with "Ignitor" electronic ignition). Should I be worried about this, or is this just a "quirk"?

 

Regards,

 

CJG

[RogerH]

Hi CJG,

are you using the original dynamo or an alternator.

If on a dynamo then it sounds normal(ish).

if an alternator then it probably shouldn't be glowing.

What condition is the battery in.

 

Roger

[CJG]

The battery is about 6 months old (Bosch), but the car is running on its original dynamo. Oh, and the Kenlowe has been on more or less permanently, due to the sweltering temperatures here.

 

Regards,

 

 

CJG

[RogerH]

....thats the cause then - kenlowe = 20amps(ish) dynamo = 28 amps flat out

on tickover you haven't got enough amps so the battery comes on line = red light