SOHC.co.uk Forums > CB500/550

Fuel draining but carbs not overflowing

<< < (2/3) > >>

Orcade-Ian:
Did you check for any increase in oil level?  It seems a shame to disturb the top end and barrels - quite apart from the expense of seals/gaskets - have you had it running before and if so, was there any suspicion of all not being well?  I would be inclined to change the oil (the missing fuel could have ended up there) remove the plugs and then crank it over for a while until you get oil pressure, refit the carbs and enjoy it!

Ian

Outrunner:
Ian, there was petrol in the oil, now drained, still not sure how it got there.

Yes it has been running

As far as I know, the bike has only done 18000 miles, the compression is on the low side, max 90 - 130psi with the throttle wide open, so we are going to have a look at the valves and rings.

Orcade-Ian:
The fuel got into the oil from open inlet valve(s) and washed the bore(s).  Does the compression improve after a small squirt of oil down each bore?  If you haven't already started dismantling, it might be worth trying a run - no need to fit all the airbox and stuff for a quick test - just the carbs.

Ian

Outrunner:
The compression was around 90 dry and 130 with the squirt of oil when I tried it a while ago

Murf:
If your comprehension tester has a longish hose between the fitting that screws into the spark plug thread and the pressure gauge, this can add more volume to the cylinder and have the effect of decreasing the compression ratio thus causing a lower compression reading. The smaller the cylinder volume the bigger the effect.  So just something to look out for.   You could do a leak down test which would give you an indication if the valves or rings were leaking.
 I would say there is always going to be some valve leakage on an old engine.
Checking for relatively even compression readings across all cylinders might be more relevant in checking the health of the engine.  Check you have no tight tappet clearance as a first step.

Navigation

[0] Message Index

[#] Next page

[*] Previous page