Compressiontest........I´m getting confused

[BigBoreSwede]

Hello there.

I did a compressiontest on my tracker with 750 cyl.

I did like this:
Run the engine warm, took out the sparks, mounted the compressiongauge in the left and the i n the right plughole (not at the same time of course)

Ignition OFF, throttles wide open (orginal carbs) and started to kick.
First kick = 50psi
Second = 90
Third = 120
Fourth = 155-160
Should it be like that?? The bike is not easy to kick but with a little jump on the pedal and it fires up nice and easy.

I don´t have any info about what type of piston etc. is put into the engine, just that´s a 750 kit mounted on it...........or maybe not


Thanks guys/BigBoreSwede

 

[Travis]

Depending on how good of a kick you are getting, that sounds reasonable. Just keep kicking it until you get your highest reading.. It should only go so high.

 

[grizld1]

Yep, that's how it's done; you keep pumping until you reach the maximum pressure the cylinder will deliver. Your numbers won't be very meaningful unless you know the displacement and compression ratio of the engine, but if you the read same or close numbers on both sides, that's a good sign. More than 10% difference between cylinders indicates a problem.

 

[BigBoreSwede]

Ohhhh....very well then. It seems ok then. Thanks!

Is there anyway from the outside to indicate if the cyl is a 750. Maybe I have been fooled since many guys seems to have a BIG problem kickstart a 750. I mean, you can´t just "kick"-start it, you have to "jump" it but it´s not too hard.

/BigBoreSwede

 

[Travis]

Aren't the cc numbers cast into the cylinders somewhere?

 

[BigBoreSwede]

Actually I haven´t looked that closed. Nothing obvious for sure because I have been lookin for the numbers. Maybe it´s located somewhere with bad access?!

 

[gggGary]

I'm on the same page the 78 I got running last night is supposed to have an "850" kit but I also am getting compression arround 165 I considered bringing it around to BDC on compression. loosen the valves fill the cylinder with oil have a funnel hooked to the spark plug hole and bring it up to tdc, mark top and bottom oil levels on the funnel and measure how many cc's of oil it displaced. I guess you could go back and forth a few times to get fairly accurate. then do it to a 650 it should be a fairly large difference? 50 cc in the case of a a 750 kit I guess. 375 instead of 325? Anyway an idea.