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Post by dazzz on Apr 18, 2017 11:24:44 GMT
Check the spring on the idle screw , I never noticed that my carb never had one and it was adjusting itself while the throttle was open then it when you come to a halt is was revving it's tits off , made me scratch my head for a couple of times until I noticed it. New spring job done. Hopefully it's something silly like that.
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Post by leon on Apr 18, 2017 11:39:53 GMT
Thanks lads I've calmed down a bit since yesterday, and am in the shed investigating.
I've checked the throttle screw Spring Dazzz and all seems ok.
Inlet manifold seems to have plenty of clearance from the frame Triffid, frame has been hacked in the past to make room for a different manifold.
Found some old threads on here, I'm thinking either as simple as a weak mixture or possibly an air leak either at carb or manifold. I've not had carb off today but float bowl looked fine last time I looked at it the other week when I changed main jet.
Don't think it's throttle cable catching as when it's in gear throttle works as normal
It only happens once it's fully warmed up - yesterday I kept pulling the carb in periodically to check whether it over revved. Was fine till 7 miles in.
One other thing though, about 500 yards before it over revved it lost power in 4th up a slight hill and cut out, I pulled clutch and coasted to a stop. Waited a minute, then it started 2nd kick.
Could it be related?
Thanks
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Post by leon on Apr 18, 2017 11:41:03 GMT
Ps mixture was at 1.5 turns out. 19/19 carb.
Also idle adjust was on near highest idle to give me a reliable idle. After a mile or so I adjusted it down a notch once engine warmed up a bit.
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Post by leon on Apr 18, 2017 18:00:32 GMT
Carb was a bit loose, and fuel had leaked from the manifold. Hopefully that's the issue.
I remember I went over a couple of nasty potholes before the problems started, maybe the carb got knocked against the inside of the frame as the engine pivoted up over the bumps. It was tight when I refitted it last week. Will refit it again a try another test ride when I get a minute. Might have to try get a bit more clearance from the frame.
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Post by dazzz on Apr 18, 2017 18:17:34 GMT
Have you got the felt manifold gasket to carb ? That could be the problem if old / missing ?
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Post by leon on Apr 18, 2017 18:45:55 GMT
Yeah I've got it. It's a year old but new in miles, if that makes sense. Will check its seated properly.
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Post by henri on Apr 19, 2017 6:30:22 GMT
sounds like carb maybe caught inside of frame or manifold did on a pothole , theres a few types of manifold an the wrong one can move carb over so it can catch on inside engine side .another thing is to open the clamp an make sure both sides sit over the manifold whilst carbs off .otherwise it can slip off one side when you tighten an seem tight but not really be doing much .H
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Post by leon on Apr 19, 2017 7:47:48 GMT
Yeah hopefully H, will take carb off and check there's no movement on the manifold before refitting, and check clearance round it.
Will check clamp before tightening as you suggest, cheers.
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Post by triffid on Apr 19, 2017 7:56:34 GMT
hope it all comes good leon, is it an old shocker on the rear? If carb is catching going over bums you might need to renew rear shock.
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Post by leon on Apr 19, 2017 10:29:12 GMT
Cheers. The guy I bought it off said it was new, but then he said a lot of stuff.....
Not sure how to check whether its still good having nothing to compare it too, but it seems ok, I just ploughed through three consecutive potholes in a row cos I was a)trying to move my keyring out the way of the speedo to see how fast i was going and b) trying to check behind me in my legshield mirror that had vibrated out of position.
Comedy of errors really.
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Post by triffid on Apr 19, 2017 11:36:22 GMT
lol
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Post by leon on Apr 23, 2017 19:59:21 GMT
Removed and remounted the carb, tightened the clamp just to the point that the carb didn't move (am aware of the risk of over tightening) but 3 miles into another test ride it started to rev it's nuts off again.
Pulled over and stalled it, and waited 25 mins for it to cool down. Checked carb and that was still secure. I'd started off with the mixture screw at 2 turns out. I screwed it out to 2.5 turns, started it up and the idle was nice and low. After about 500 yards of riding pretty slow (20-30 mph) on the flat/downhill, I could hear the idle had risen when I pulled the clutch in. I stopped and gave the mixture screw another half turn and the idle dropped nicely. Then 500 yards later at home the idle had risen again. (Not screaming, just a faster idle)
Think I'm gonna bite the bullet and get it looked at, I think I've gone as far as I can on my own.
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Post by snails on May 10, 2017 15:07:44 GMT
I know that feeling where you just want to give up, or throw money at it or just wish some scooter fairy godmother would descend from the sky and fix everything. I admire how far you've got.
Just out of interest, on the carb your using does unscrewing the idle richen or weaken the mixture?
I'd still be tempted to see if you can replicate these symptoms when the scooter is not moving. Then you would hopefully be able to rule out it being something like a bad shock absorber..might piss the neighbours off admittingly.
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Post by leon on May 10, 2017 15:27:52 GMT
Yeah I can't afford to get it fixed professionally so it's just sat in the shed at the moment, I've not looked at it for a couple of weeks. Will get round to it when I can be bothered again.
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Post by triffid on May 11, 2017 8:07:57 GMT
could be head/barrel/manifold leaking once warmed up as this wouldn't show when cold but once metal heats up it moves. See if there is any evidence of oil around head and barrel then check cylinder nuts are tight. Otherwise I am as stumped as you.
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Post by leon on Aug 6, 2017 19:20:26 GMT
A little update. After the last mishap above I eventually took it back out and had a heat seize near the end of an actually enjoyable and uneventful run, which has been detailed in the Technical section (air leak at the head).
Having stripped the top end and cleaned up the piston and barrel I got it all back together. Today, after receiving a new inlet gasket from Rob Vinrouge, I fitted the manifold and managed to do a pressure test without any signs of a leak.
I then started it up and it runs pretty well. I sprayed carb cleaner on all the relevant joints. Had two false alarms - at one point when I sprayed at the base of the barrel the engine died, but I realised that I'd run out of petrol in the tube I was using for fuel. I also thought it was running really rich and bogging, so was about to swap the 50 idle for a 45 when I noticed the choke cable outer had got caught, meaning the choke was out. Sorted that and it seemed to run well at 1.5 turns out on the air screw.
So once again I'm at the point of refitting the engine and taking it for a test run. Will it run right at last? Stay tuned for the next episode of this epic(ally cackhanded) project..
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Post by leon on Aug 8, 2017 10:03:36 GMT
Ran the engine on the stand for a bit last night to get it warmed up again, then re-torqued the head bolts. Seems to be running a little rich but I'd rather start with that for my test rides and work down than the other way around after my experiences running lean....
Engine probably going back in at the weekend.
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Post by leon on Aug 11, 2017 15:38:38 GMT
Engine is back in. Might just be my optimistic nature but I think it sounds better than before, revs don't seem to hang like they used to. I've set it richer than before and am getting blue smoke for the first time, am very wary of running lean after all the palaver I've had! Had a quick go up the street to check gears select ok, will take it for a run round the block at the weekend and book MOT asap. I haven't painted the new engine door yet but I quite like it black.
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Post by dazzz on Aug 11, 2017 17:52:11 GMT
Well done leon , hope you have some happy trouble free miles now.
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Post by terjee on Aug 12, 2017 0:01:00 GMT
On my 19mm there was something strange with the clamp, the carburetor got tight but loosened after a bit of driving. In the end I was mad and tightened it so much that I thought the treds smoke, found out that it would not go through the treds in the new clamp. After I got screwed through it the problem is solved. I had top gasket leak to, use wurth 250 special silicone on top gasket, just a little.
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