Is it an air leak?

[wax]

I have just been out for a ride on my reed-valves rapido 250. Very nice it is too. Pulls well from no revs and is a pleasure to ride, up until a point.......

After about 2 miles, the revs start to climb and it seems to lean-up. At this point I put the choke on and tootle home. This has happened a few times now, at around the 2 mile mark in the journey. Does this sound like an air leak? I was told that the LTH manifold rubbers were suspect, so I sealed that with loctite, but the problem continues. Could something be expanding and causing an air-leak? I am at a loss as to where to start looking.

Any help or suggestions would be appreciated.

[mick1]

Spray an aerosol (easy start, carb cleaner, etc) around the suspect area.......if the revs change you know the aerosol spray is being sucked into the engine, which will confirm an air leak.

[Darrell Taylor]

did u change the carb jetting from piston port settings to reed valve settings or has it only ever been a reed motor?

what carb and jetting u running

after 2 miles are you just starting to open it up or reaching a longer stretch of road and just starting to load up the motor

[wax]

I purchased the motor from a good mate of mine. It was 'slung' together by AF rayspeed. It did 2 miles before nipping up on him. I sent it to Harry Barlow for a check over and rebuild, with an upgrade to reed valve.

I popped over to sunny Leicester for Harry to jet it up for me and all seemed well. I just don't think it got fully upto temp on the road test.

Is it more likely to be on the intake side rather than the exhaust side of things?

[wax]

All the miles have been tootling around town so far. No open throttle as yet. I thought it might be a dodgy carb, so I swapped the main jet, atomiser, needle and pilot from my Vespa to check, but it's still the same. Both are phbh 28mm.

it starts great, then runs great after the choke is turned off, then it all goes Pete Tong.

[Darrell Taylor]

give harry a shout as he may put his finger straight on it or do a leak down test for ya
the phbh 28 what main jet/pilot jet/atomizer/needle /slide etc

[phil23fair]

I had a similar problem on my Rapido 250. It turned out to be a leaking mag flange gasket.

[fastfrog]

After about 2 miles, the revs start to climb and it seems to lean-up. ... This has happened a few times now, at around the 2 mile mark in the journey. Does this sound like an air leak?
Any help or suggestions would be appreciated.

classical crank seal issue....

[Mag]

or blocked breather in the fuel cap

[fastfrog]

+1