Got any more ideas? Please?

[Roa, Greg]

>> It will run good for a few seconds, then I'll get a stumble, then good for a second or two,
>>and another stumble.  Then it will run good for a second, and stumble twice quickly.  After
>>this quick stumble, it will run good for a few seconds, then the cycle starts again (always
>>the same pattern).
>
>Assuming an MC engine.
>
>Two possible causes:
>
>a) Is the rubber crankcase breather hose (side of the block, behind the warm-up regulator)
>collapsed?
>
>b) Crank rear oil seal letting air in when crankcase achieves vacuum and resealing when revs
>drop and vacuum disappears?
>
>Both would be diagnosed by constricting the hose that runs round the back of the head to the
>metering head plenum chamber.  Progressively squeeze it with a clamp and see if the symptoms
>change just before you close it completely.
>
>--
>  Phil Payne
>  http://www.isham-research.com
>  +44 7785 302 803

Yes, it's an MC engine.

I checked the breather hose again, and pulled it off to reverify for leaks.  Looks good, and isn't too soft.  I've not seen it collapsing while the engine is running.

As far as the crank rear oil seal, it does squeal for a split second when the car is started, but then stops.  Vacuum as shown on a mechanical gauge varies less than 1" Hg while idling, so I don't believe that it is allowing much if any air in.  I read about -18" Hg on my gauge at idle.

Didn't try clamping off the line yet, as I didn't have the proper pliers handy.  I'll try that this evening.

I'm swapping out the coil tonight, as I have a spare.  Not sure if that will help anything, but it's a minimal amount of work.

Also will be checking control fuel pressure tonight to look for any abnormalities.

Are there any problems that a low resistance reading between the terminals on the fuel pump regulator electrical connection would cause?  I noted that it is below spec, but I believe that it shouldn't make any difference when the car is warmed up.

Thanks!
Greg Roa
Cincinnati, OH
86' 4kcsq x2
87' 5kcstq
93' 90CS
83' 944