The bike hadn't really been used for 3 0r 4 years, although it had been started and run and MOT'd every year and was just ridden, briefly, and Mot'd when I bought it.
Fresh fuel, clean air filter, new plug, test ride. Starts, idle's and picks up perfectly, but after 1/4 throttle the motor 4 strokes badly and won't rev up, coughs, splutters, doesn't backfire. If you short shift through the box then it's fine but open throttle further and no go. Rode for about 12 miles hoping it would clear, no better, no worse.
Thinking this was a fuelling issue, not unlikely, having been stood for so long I stripped and cleaned the carb very thoroughly (it wasn't bad), paying attention to the diaphragm nozzle and the internal filter. Back together, no better. Ran on a separate fuel supply, no better.
Bike went perfectly for a very brief time, when I ran it without the air filter of air box cover on, I thought I had cured it but when I put it back together and ran it again the problem reoccurred! Was this a red herring? Or did I disturb some wiring under the seat or near the side panel. I am now beginning to believe this could be an electrical issue.
If nothing else has been changed on the bike, it's usually fuel blockages. I would check the main jet again, ream it out with a bit of copper wire. At wider throttle openings, it is the main jet that has the most influence on running.
Of course a loose wire or fouled spark plug might cause "stumbling" at higher revs/more vibes, so worth checking too.
Good luck!
-- Edited by mossproof on Sunday 2nd of August 2020 10:07:14 AM
If nothing else has been changed on the bike, it's usually fuel blockages. I would check the main jet again, ream it out with a bit of copper wire. At wider throttle openings, it is the main jet that has the most influence on running.
Of course a loose wire or fouled spark plug might cause "stumbling" at higher revs/more vibes, so worth checking too.
Good luck!
I will go through the carb again and check this, thanks.
Yes, stumbling or stuttering is a good description of what it does so more stuff to check on the electrics side.
Cheers
-- Edited by mossproof on Sunday 2nd of August 2020 10:07:14 AM
Anything above 1/4 throttle causes it. I have only ridden on the road so far and the problem is still there when you run the engine static on the bench and on a auxiliary fuel supply. Really feels like a fuelling issue but I went through the carb so thoroughly I started to doubt that. I will probably bypass the side stand and clutch switch just to eliminate that potential problem.
Cheers
Kev
-- Edited by Kev on Sunday 2nd of August 2020 09:27:06 PM
