Engine won't rev

[phil23fair]

I'm trying to get an imported Indian GP150 ready for MOT so I can get it registered before I start restoration. As a result I want to spend as little as possible getting it together. Everything is working fine now except I cannot get the engine to rev.
It has standard 6 volt points ignition. The points gap is 0.4mm and timing at tickover is 19 degrees BTDC. The carb is a 22mm Jetex, The pilot is 45 and the starter jet is 50 but I cannot say what the atomiser and main jet are because they aren't marked but I'm guessing they are the original ones by the looks of their condition compared to everything else. I believe the slide is a 7895-2 because it has a cutout. The spark is good but once running when I try to open up the throttle it sounds like it is bogging down and cuts out. The exhaust is a standard GP150 exhaust but very beaten up and the drive side oil seal was gone when I got the scooter and so it is probably pretty clagged up although the exhaust is not smoking on tick over.
I have replaced the piston rings and compression is good and the piston arrow faces the exhaust. Having read on here that some pistons have been marked incorrectly I wondered if I had put it in upside down. I haven't taken the barrel right off but slipped the barrel forward and the cutouts in the barrel skirt match those on the piston so I'm guessing the piston is right way up but am open to being corrected. The piston ring pegs sit either side of the exhaust port.
Any ideas please.

[tony]

If you can borrow a carb and try. I think it's blocked possibly

[camel]

throttle cable snapped!!!

[mick1]

Carb' most likely. Try it without the bellows (could be blocked filter). What happens when choke is turned off, does turning choke off and on affect the rev's (if not could be stuck)......tell us if you sort it, always nice to know.

[phil23fair]

Throttle cable is OK. I'm running it open mouthed at the moment. when I fitted the filter and bellows it bogged down even more. I need the choke to start it but if I leave it on it bogs down and stalls. I've blown through the jets and they seem clear. I've just drained the tank and taken out the fuel tap and that all seems OK. If the exhaust was really clagged up would the back pressure cause the problem I'm having?

[mick1]

Hmmmm.....try drilling a hole in the bottom of the exhaust (10mm) see if that makes any difference. Should be easy to patch up for mot

[victor]

I had recurring carb related problems on my Vespa until the other day. Random problems that indicated dirt but with clean jets. Took it off, boilt it for 20 minutes in lemon juice which is acid and just removes any kind of dirt. The juice was black when done with loads of junk floating and on the bottom of the pot. Girlfriend wasn't happy but made me buy a temporary pot at the pound land before starting fortunately because if not I'd have slept in the garage by now


Lemon boiling the carb by wheredowegonowbutnowhere, on Flickr

Will become all grey and with a sandy feeling afterwards though, like when it came out the sand mould

[phil23fair]

Problem sorted - it was the condenser breaking down. I temporarily wired a condenser between the green and earth outside the stator and instant response to throttle

[dapper]

Problem sorted - it was the condenser breaking down. I temporarily wired a condenser between the green and earth outside the stator and instant response to throttle

Then make it permanent,as it's more accessible than having to take the flywheel off, you muppet