Re: Timing a modified bike
Posted: Sat Nov 17, 2018 11:30 amToday was successful. I did 35 ish miles on a run around the country. I believe the problem is solved and perhaps I was barking up some wrong directions along the way... 
First however I did a service, as it has now been a year since this has been done.
New 80/90 mineral oil,
7 grade NGK spark plug
Double checked timing.
Routed the electronic ignition extra wire smartly.
I did also change the carb-cylinder manifold for an original manufacture one. The reproduction I had on there was cracked and I thought perhaps was influencing idle running. I'm not entirely sure that it made a difference however.
Timing was on point however. Pretty much the perfect 22degree BTDC.
I travelled for an hour in variable traffic conditions with only one thing bugging me- the lumpy idle. Otherwise perfectly fine.
On the way back from a stop however it got very windy and the bike was being rather over-cooled. Not to mention the sub-par piston meant that it was easily out of puff. Yet, no issues other than the above mentioned.
When I got back home I decided that the lumpy idle is likely the carburettor. After all, it had been sitting for around 8 months unused, and unstarted. I cleaned it through all channels as thoroughly as I could, and made note of the pilot screw and idle adjustment screw too.
The original adjustment for pilot jet was 1 and 1/4 turns from in. I messed around with it and the bike seemed to behave better with around 5/8ths of a turn from in. A leaner condition, and the idle seems fairly stable and crisp when pulling that throttle tube. Idles at around 1200-1300rpm, clutch in. The original manual states "About 1 revolution open", even though the Haynes states 2-2.5 turns.
No matter how much I tried, through purposeful poorly kicked starts, I could not get the bike to go backwards! And, even after a stop in the wind- and the cylinder had cooled down significantly, the bike didn't go backwards when I was unaware that the choke would need to be applied.
So that's it basically. I believe the bike is 'fixed'. Lovely powerful induction noise too!
I will have to just 'use' the bike and see how everything goes. There is an impending MOT test at the end of the month for it, even if it did only do 800 miles
I must add that my next step is to assign certain things to the bike. For a start, I do want to put the points back on the bike after the bike has been through a successful test phase of running. I want to see whether the points really were chatting and causing any backwards running, or whether it was the original compression issue at fault- and nothing to do with the ignition. We shall see..
I also obviously need to re-instate the 300cc piston. But I need to purchase some new rings first, as I broke one.
I should think that I will include the 2mm base gasket on installation.
Thanks everyone for your help. I've missed the bike, and I've missed the longer swingarm and 18inch rear wheel
Feels more 'stable' than the 251
First however I did a service, as it has now been a year since this has been done.
New 80/90 mineral oil,
7 grade NGK spark plug
Double checked timing.
Routed the electronic ignition extra wire smartly.
I did also change the carb-cylinder manifold for an original manufacture one. The reproduction I had on there was cracked and I thought perhaps was influencing idle running. I'm not entirely sure that it made a difference however.
Timing was on point however. Pretty much the perfect 22degree BTDC.
I travelled for an hour in variable traffic conditions with only one thing bugging me- the lumpy idle. Otherwise perfectly fine.
On the way back from a stop however it got very windy and the bike was being rather over-cooled. Not to mention the sub-par piston meant that it was easily out of puff. Yet, no issues other than the above mentioned.
When I got back home I decided that the lumpy idle is likely the carburettor. After all, it had been sitting for around 8 months unused, and unstarted. I cleaned it through all channels as thoroughly as I could, and made note of the pilot screw and idle adjustment screw too.
The original adjustment for pilot jet was 1 and 1/4 turns from in. I messed around with it and the bike seemed to behave better with around 5/8ths of a turn from in. A leaner condition, and the idle seems fairly stable and crisp when pulling that throttle tube. Idles at around 1200-1300rpm, clutch in. The original manual states "About 1 revolution open", even though the Haynes states 2-2.5 turns.
No matter how much I tried, through purposeful poorly kicked starts, I could not get the bike to go backwards! And, even after a stop in the wind- and the cylinder had cooled down significantly, the bike didn't go backwards when I was unaware that the choke would need to be applied.
So that's it basically. I believe the bike is 'fixed'. Lovely powerful induction noise too!
I will have to just 'use' the bike and see how everything goes. There is an impending MOT test at the end of the month for it, even if it did only do 800 miles
I must add that my next step is to assign certain things to the bike. For a start, I do want to put the points back on the bike after the bike has been through a successful test phase of running. I want to see whether the points really were chatting and causing any backwards running, or whether it was the original compression issue at fault- and nothing to do with the ignition. We shall see..
I also obviously need to re-instate the 300cc piston. But I need to purchase some new rings first, as I broke one.
I should think that I will include the 2mm base gasket on installation.Thanks everyone for your help. I've missed the bike, and I've missed the longer swingarm and 18inch rear wheel
Feels more 'stable' than the 251