MaH

I posted this a couple of weeks ago but unfortunately nobody seemed able to come up with the answer.

My 80 (1988 1.8 carb) really hates winter.

It'll drive fine for a while, then it'll start to jump and jerk around. You can feel the power blipping through the wheels and the gearstick wobbles as well. When it's doing this I have two options. One being to stop, turn the engine off and wait a couple of minutes by which time it'll be fine. Or carry on driving and get the revs up above about 3500, so it drinks petrol and means no gear changes! Sometimes when it does this the engine will just stall. It has occasionally stalled at junctions without any warning at all.

When it's doing this it's almost impossible to get the revs up. You can floor the accelerator and get almost no response.

It'll do this about every 8 minutes. The sheer fact that it's so regular leads me to think it's an electrical fault. Possibly a capacitor somewhere. But this is where I'm stuck. Where in this beast are all the electronics? I can't be bothered with dismantling all the panels if I'm not going to be in the right area.

I'm pretty good with electronics so if someone could either point me to the right section of the car or just tell me what's causing this I'd be eternally grateful!

Just so you know what I've tried already...

Replaced the distributor and HT leads / plugs.
Changed all the fuel/air filters.
New battery (the old one died anyway!)
and general cleaning up of all the electrical connectors.

MikTip

Sounds like a fuel pump on its way out! Or the associated relay.

TIREGUY

Your car has a carb? Chk to make sure the preheat for the air intake is working. Years ago I had a Datsun 510 that would do close to the same thing your describing in the winter, what was happening is the carb would ice up. When you stopped the car, the heat from the engine would eventually melt the ice and things would be fine again. Just a stab in the dark. Goodl luck

Seattle Scott

there is sailboat engine called an Atomic, these ice up a lot. Maybe there could be some hints there.

We haven't had carbs in the USA for so long we are probably not a real good resource.

Have you tried running the car without the air cleaner and cover? Maybe you could and then go look at the carb if the problem happens. I think iceing is easy to see in the carb throat. Don't really know, I have only heard about it.

Seattle Scott

Have you asked Honest John? http://www.honestjohn.co.uk/

MaH

I might try running it without the air cleaner/cover. Though I think this would be a rather bad idea as I don't want a carb full of crap!

It's not always that cold though when it does it. The air temperature's probably around 6-7 degrees (centigrade) today and it started mucking me around. Well, I'll try (because I think the auto-selector's broken!) forcing the air intake onto the warm air position. It can't hurt can it?!

Then if that fails I'll try the fuel pump idea. Though I would've though that'd have an affect all year round. Not just in the winter.

Cheers guys, I'll buy you a beer next time you're in England!

Seattle Scott

Your not going to hurt the engine running without an air filter for a little while, say an hour to do a good test?

You said the diverter to feed warm air into the carb is broken? This is the tube that goes frrom the air cleaner inlet to a warm engine area, like the exhaust manifold? There is a butter-fly valve in there? Forcing that open would be a good test too.

According to some posts I see on ultra lights the ice chips going into the carb cause "jumpy" engine operation. (You are trying to burn some water).

An ultra light is a small 15-40 HP single person plane in America.

MaH

Ok, I thought it'd do more damage running it without the filter than that.

The pipe's fine running from around the engine to the filter housing. It's the butterfly valve that's stuck shut. So all cold air flows up. I'll try wedging that open with something and post back in a few days to tell you the results! If it solves the problem it may just stop me from buying a new car! I suppose if it solves the problem I should buy a new selector unit as well!

Cheers
Mark

Seattle Scott

If it is iceing, I think it may disappear pretty quick so you will need to be quick.

Also removing and driving without the air filter may change things so it doesn't happen.

The butterfly "hot air" valve in American cars was open when the engine was cold to allow the carb to get hot air. After the engine / valve warmed up the valve would close and only cold air would go to the engine.

Please post your results, especially sucessful ones.

MaH

Hi guys,

First of all. I took apart the hot/cold air selector last night. Looks like the PO had removed the vacuum line to it, so no auto switching! Not having any spare pipe to fix it (I need to test the temp sensor as well) I just (with a bit of ingenuity and wire!) managed to tie the flap in the half open position. So now it's taking half cold half hot air in. This morning (a lovely misty cold morning, love the British weather!) it ran better than it has all of this winter. Almost as nicely as it does in the warm weather of summer.

Looks like you guys may have fixed my problem! I just need to go out and buy a Y adaptor and some vacuum hose and I should be away! Assuming of course that the little pump thing (don't know what it's official name is!) that moves the flap isn't broken. It seemed to hold alright last night when I was fiddling with it.

Well, looks like I won't be forced to sell the car after all. Quite glad, it's a lovely car otherwise.

Thanks a lot, if it goes wrong again I'll be posting back screaming my head off!!

Cheers,
Mark