Compression Test Advise.

[beemeerr11]

Hi,

I have pulled the carburators off the bike, as the bike was sitting for over 8 months before I got hold of it, (possibly longer as the history is unkknown)and when I put fuel in the bike to start it, the bike started, although fuel started pouring out everywhere from the air filter cover, after removing the Carby's they need a good clean and the floats were stuck. Now I want to do a compression test, the speedo reads 33,000Kms and if the compression figures are high, it will give me more insentive to restore the bike properly, knowing the bike still has good life left in it.
Am I wasting my time doing the compression test with the carby's off the bike and the engine cold? Or will I do it and assume I can add a bit because of this?

Over to those knowledgeable on this site.

Cheers
Lou

81 XS1.1

[Crazcnuk]

Doing the test w/o carbs is fine, you won't have to hold the throttles open!

Cold is ok, too, but will give you slightly lower readings than if the motor was hot.

Since you had the motor started, there should be enough oil on the cylinder walls to give you a good reading.

[beemeerr11]

Doing the test w/o carbs is fine, you won't have to hold the throttles open!

Cold is ok, too, but will give you slightly lower readings than if the motor was hot.

Since you had the motor started, there should be enough oil on the cylinder walls to give you a good reading.

Is there somewhere that shows what standard compression should be?

How do these figures compare:- remember there is no oil in the engine, all measured in PSI

Cylinders 1:- 150 2:- 140 3:-125 4:-130

Then I added a squird of WD40 into the chambers and got this

1:- 175 2:- 165 3:- 160 4:- 160

[DGXSER]

Spec is 142 psi +/- 10% with maximum 10% variance between cylinders. This is with the bike warm, WOT. If you are doing this with dry cylinders you will see low numbers. The rings need the oil to seal, that and you really do not want to keep cranking the engine dry, even not running it is not good for the seals or the bearings. JMHO.

[Crazcnuk]

Those readings are a little high, as per DG's numbers. However, they are within the +/- 10% variation.

The first readings were all over, likely due to a lack of oil.

There are a couple of things that could account for the high readings, big bore kit, high compression pistons, too much oil in the cylinders...

What's interesting is that the high to low variation stayed the same both times with a slight jog between 3 and 4.

[petejw]

Hey Beemeerr,
Check your valve gap clearances, if there out
thatl make a difference to your readings.