Well after 15 years under a tarp, the 91 is running again. New plugs, oil, all filters, carbs removed, drained and cleaned. Idles right around 1100-1200 and sounds great. Now here's the problems: 1) it blows a good amount of smoke once its warmed up, seems more blueish than white, 2) compression is kind of concerning: cylinders 1 and 3 are around 115-120psi, cylinders 2 and 4 are around 150-155psi.

I didn't adjust the mixture on the carbs, because I didn't want to mess with them, so maybe its running rich. I also notice some oily "sludge" on top of the pistons looking through the spark plug hole...I'm guessing from the 15 year slumber. Maybe that's what's producing the smoke when the motor warms up?

Any ideas or suggestions?

 

Good work mate. Could the oil sludge you mentioned be burning off. Piston rings all good ?
Again well done. Just finished my 89 initially flames the works, now she's roaring like the old days.

 

Congratulations on getting her running again. Low compression could be stuck piston rings. Could require pulling head and cylinder to get access to the rings to free them.

 

If you give it a good run and then recheck the compression you'll get an indication of where you're heading.

If there's no change to your original readings, you're looking at a top-end rebuild.

If the low compression cylinders are improving, you might be out of jail.

Good luck.

 

Thanks for the tips...I thought compression should be checked with the motor still warm? And what's a compression number that's "too low"? Manual says it should be between 149 and 206. So, is anything under 149 a concern? Anything under 139? 120? Where's the line?

Thanks!

 

It's not so much what the number is, but that they are significantly different. They should all be around the same.

 

Oops...yes, check compression when hot. I've corrected my previous post.

Now, where's the line....basically no cylinder below the minimum, and preferably all cylinders at about the same pressure.

If your readings don't change after a run, you've struck out on two fronts, minimum and consistency across the four pots.

If the smoke abates and you can ride it, go ahead. Basically you'll have an underpowered CBR, and eventually it won't want to start from cold.

 

I'm good...dumbass that I am, I forgot to leave out all the plugs during the test. Once I did that, my readings were good...all 160 to 170 PSI. Idles right at 1200, and smoke seems to have subsided. Now on to the brakes...thanks everybody!

 

I love it when you find a "self fixing" problem! Best kind to have! Hope you don't get too much snow in the next few days and can go for a proper ride!

 

Result, bet there isn't one of us that haven't done something similar in the past!!!