'77 450 SEL (K-Jetronic system): Running rich????

[bobboyer5]

Here'smy question:

I've never adjusted the mixture screw. However, I believe that car is running very rich. why? when started after sitting overnight, acceleration response is fine - even with heavy foot. However, gradually, car stumbles and loses power after a while. But only when I depress accelerator quite a bit. Not with a light touch. Additionally, there is a lot of dry black soot inside tailpipe. no oil or grease. And car does not smoke (only has 64K on clock).

no problem with idle.

Is this a symptom of running rich? I.E., that after a while, too much fuel is drowning the plugs and spark cannot keep up with fuel?

Should I adjust mixture screw?????

thanks!!!!!

[bobboyer5]

One other factor to consider when analyzing my description above:

I reside in hot, hot south florida. The probelm, upon reflection, began about a week after my last oil change (in May). I had them put in 10W-30 at the time. Before,m I had been running 10-40. My oil color( I've only done 1500 miles since change) is still rather light, not dark by any means).

Do you think my hesitation/poor running after warm-up might be related to oil weight/viscosity? Should I change, in my limate, to 20-50?

Or is that irrelevant to my situation?

Do not adjust the mixture screw unless you have a CO tester. If you don't own one then take the car to a garage which does and let them adjust it until the CO is in spec.

You should be using a multigrade oil of between 10w40 and 15w50 in the engine.

Poor performance under hard acceleration could be a factor of many things but an overrich mixture will give oil black smoke.

Adam