NC30 Running On 3 - Compression Results

[alexwitham]

Front right cylinder doesn't want to be giving me any power still, sigh.

Back 2 cylinders and front left are 190PSI, 'problem' cylinder is 170. Few drips of oil have it up to 180. According to the Haynes, all cylinders are within spec. Coincidental that the problem cylinder is lower?

Thanks to arsey30 for the loan of the compression tester, going to be doing some other troubleshooting checks and reporting back. Fingers crossed it's carbs or a tight shim as I don't fancy dropping the motor and doing rings/reboring.

[alexwitham]

Got the bike up to temp when on choke, turned the bike off and let the headers cool. Turned the bike on with no choke so its idling at 1200rpm, no heat on problem cylinders header however with a few revs up to about 5-6k it heats up considerably which is promising.

Going to take the carbs off and check out the pilot circuit and see if there's something blocking the circuit.

I'll report back.

[alexwitham]

Fuck I stink of petrol fumes and wd40.

[CRM]

Alex, you checked valve clearances ?

[alexwitham]

I'm doing that next, as it's got a leaky rocker so may as well do the carbs/fit new gasket and check valves too.

[Variablevalves suck]

Ye mate, no good doing a comp test unless the valves have been done.

[alexwitham]

The valves were done 0 miles ago, before I bought it, apparently.

[porndoguk]

Alex, have you swapped carbs from your bike to confirm is isnt the carbs? Could also be a faulty coil or cdi thats only intermittant.

[johnnie5]

compresssion is ok imho

i think your prob is with the carbs

[Neosophist]

The valves were done 0 miles ago, before I bought it, apparently.

The compression sounds fine on all four.

I take it you've checked the obvious like.

Vaccum take off screw in place (this will only cause a mild air-leak and not stop it running)
Swapped plugs around to isolate defective plug (a visible spark isnt a guarantee it will run)

Is the plug getting wet? (if the balance screws are WAY off, even a clean pilot circuit won't help as there wont be any suck to pull fuel in)

Cracked the drain screw on the carb to make sure theres fuel in the float?

with the airbox off pour a little fuel directly into the non running cylinder and see if it fires up.

Regarding the valves, get in there and check them, there is a chance the seller was having you on, or if they have been done they could have been done wrong.

Blow through the small holes in the carbs pilot circuit with compressed air after a good cleaning.

im sure youll get to the bottom of it.