I HAVE RECENTLY BOUGHT AN NC 30 RACE BIKE TO RACE NEXT SEASON, THE BIKE WAS BOUGHT AS A RACE BIKE BUT STILL NEEDS A GOOD SOUGHT.
aFTER TEST RIDING IT AROUND THE ESTATE I THOUGHT THE BIKE FELT GUTLESS COMPARED TO MY LAST 400 RACE BIKE WHICH WAS A cbr TRI ARM , i even had an nc30 on the road 20 years ago and if my memory serves me well was a lot better than this.
I decided i needed to do a compression test first so after removing the insides from an old spark plug i thread tapped the plug to take the 12mm compression tester hose, i used ptfe tape and it has a tight seal. I did the test on a cold engine the rear cylinders were 149 and 144, the front cylinders 133 and 138.
I know these are fairly low, under the minimum mentioned in the haynes manual. As i have adapted a plug for the compression tester will this method still give the same result as a specific 8mm hose fitment? I was hoping it may be a little lower as the valve on the tester hose is further away from the cylinder as its threaded into a spark plug carcass, i can only hope.
Also if this reading is accurate( i will do again with a drop of oil in the cylinders) is this going to be a problem, what is the safe minimum?
I was hoping with a gf racing ram air box re jetted etc to achieve what i had with my cbr which was about 62bhp, is this still achievable with compression results that low?

Any Advice greatly appreciated.

Thanks

If the hose has no leaks and is re enforced and does not bulge...it could be 5 miles long.
It would just take a long time to reach maximum pressure.

I give engines one half stroke of an oil pot trigger per cylinder.
You know the small oil pot types.
If you are nervous put a good shot in and spin over with a rag over the plug hole then insert the gauge and test.
The cylinder does not need to be full of oil...only coated to seal rings.
If the valve clearances are too small it is impossible to gain full compression as some valves will never fully close.

Cheers for info. When i made the adapter i decided to use an oring to help seal the adapter into the plug hole, i decided to try again without the seal and rely on the plug sealing washer and this gave better results the oring had the opposite affect it was causing a poor seal, im now getting 168 on the rear cylinders and 158 on the fronts so at least im within haynes acceptable tolerances.
I will do the valve clearances to be on the safe side, i usually squirt about 10ml of oil down the plug holes when testing the rings ill try this but im fairly happy with those readings, i think thats good enough to carry on with the rest of the project, im sure i will be asking more questions throughout this project, thankfully i have 6 months to sort before the start of next season.
Cheers

carbs held wide open during compression test? can take time if you have sticking cv slides

Hi,

i compression tested it with the carbs off, will this make a difference? i thought as its measured on its compression stroke and the inlet valves and exhaust valves are closed that it wouldn't make any difference.

Cheers

yep, shouldnt make much of a different then.

does seem low though, carb balance scres connected?