Club 80-90 Forums

Hi All,
I've been on and off trying to diagnose an intermittent soft misfire on my CU 2.0l Aircooled and I have noticed that when using a timing strobe the mark seems to jump around at mid-high rpm. Now, I'm presuming that this is not normal and in which case would it give the symptoms of a soft missfire/lack of power when accelerating?
A picture speaks a thousand words so hopefully, a video will speak even more.....

https://youtu.be/uZTZTwqH-_M

Melvin

Did you have the vac pipes connected?

bigherb wrote:Did you have the vac pipes connected?

Hi Bigherb,

Yea, Both pipes were connected.

Melvin

That's the reason then, without the engine under load the vac advance will bounce about.

bigherb wrote:That's the reason then, without the engine under load the vac advance will bounce about.

Bugger, I was hoping you'd say that my dizzy was shot and replacing it would fix my problem

Thanks so much for your advice though, back to the drawing board for me......

Cheers
Melvin

melvin wrote:Thanks so much for your advice though, back to the drawing board for me......

Not really. Just repeat the test with vac disconnected and plugged. If it still bounces around, it tells you more info. Is the idle control unit disconnected and plugs joined?


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Re-run the test with the vac pipes disconnected - that way you are testing the basic distributer and centrifugal advance only.

Righto, test re-done with vacuums disconnected and plugged and the Idle Control Plugged together, it seems to be operating correctly, which is nice, but doesn't help me

https://youtu.be/7v7xN-ilO8g

Melvin

Well it does help, you have at least eliminated the dizzy , Sherlock Holmes style

Can you describe what you mean by a soft misfire a little more ?

Well, I will try an explain....
Under acceleration, you can feel a soft mss fire, not a backfire or a harsh miss but more of a gentle shake of the engine, as if a cylinder didn't fire, passengers can hardly feel it but you can when you are the driver. It happens every second but not rhythmically, more randomly, but it is a constant missfire. Once you are up to speed and you ease off the throttle you don't really feel it. The van itself starts well, and idles fine, although if you look at the engine when it is idling you can see a slight random shake.
The compression is good on all cylinders (9bar), I have replaced the coil, check the leads for resistance, the spark plugs look a nice golden brown although cylinders 1 and 4 (I think they are the numbers, they are the ones closest to the flywheel) are a bit carboned up around the outer edge of the plug.
The timings is all good and correct, (it was running really bad before as it had a DG Dizzy on it and I could never get it timed right, till I found out it was the wrong one!)
Fuel FIlter replaced, carb stripped and cleaned.
Power is a bit poor, uphill is a struggle dropping to 35/40 sometimes, but this is hard to judge, maxes out on the flat at about 55/60, but I have had another CU Aircooled and it had a lot more poke than this, although it had twin webbers on it, this is running a completely standard setup.

Can't think of anything else to mention, but if I do I'll add it to my post.......

Any words of wisdom/experence would be greatful

Melvin

You've done a fair bit of elimination so far

It does sound as if the van is down on power. My CU hasn't been on the road in my ownership, so hard for me to compare directly, but my DF/DG hybrid camper with full interior etc will pull 70+ on the flat, lots less on the hills of course. I have no idea what power it is giving, but I would guess around 65, so a bit less than a CU should.

Is there any difference in feeling between light acceleration and full throttle. Is full throttle clean, or is there a similar misfire ?

melvin wrote: carb stripped and cleaned.

Melvin

Carb? do you only have one?

937carrera wrote:You've done a fair bit of elimination so far

It does sound as if the van is down on power. My CU hasn't been on the road in my ownership, so hard for me to compare directly, but my DF/DG hybrid camper with full interior etc will pull 70+ on the flat, lots less on the hills of course. I have no idea what power it is giving, but I would guess around 65, so a bit less than a CU should.

Is there any difference in feeling between light acceleration and full throttle. Is full throttle clean, or is there a similar misfire ?

It is there all the time but the harder you push the more you notice it, I suppose when cruising its less bothersome as you are already going the speed you want to, when accelerating it feels like the miss is holding back the engines potential

Melvin

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bigherb wrote:

melvin wrote: carb stripped and cleaned.

Melvin

Carb? do you only have one?

Sorry forgot my plural, twin Solex's[GRINNING FACE WITH SMILING EYES] is what it's running!

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bigherb wrote:

melvin wrote: carb stripped and cleaned.

Melvin

Carb? do you only have one?

Carbs need balancing?