R90/6 Starting Problems

[Owen Snell]

Having trouble starting the R90/6. I've set the valves (3 of 4 were tight) and changed the float bowl gaskets as the choke did not seem to be effective. Now, if I put on choke it seems to be over fuelling as I sometimes get a backfire after turning it over. The battery is good and fully charged, so it turns over OK but does struggle against the compression sometimes - the bike has had head work done and may be higher than standard compression. Any hints gratefully accepted.

 

[Rob Farmer]

Points Gap? Struggling against the compression would suggest the ignitions advanced.

 

[Owen Snell]

Points Gap? Struggling against the compression would suggest the ignitions advanced.

Electronic ignition that I have never looked at! I suppose I will have to start digging.

 

[Kenny]

.....maybe worth taking the rocker covers off and checking the valves are opening and closing correctly - turning over manually. Maybe a sticking valve? Does she run OK when hot ? As Rob says but you appear not to have altered the points/timing etc. Even worth changing the spark plugs.

 

[Rob Farmer]

I sold a 90/6 to RichC a couple of years ago. It had an early Boyer electronic ignition fitted (Black Box) typically not long after I sold the bike to Rich the ignition packed in. You'll find the later micro digitals work so much better than the early ones.

 

[Owen Snell]

.....maybe worth taking the rocker covers off and checking the valves are opening and closing correctly - turning over manually. Maybe a sticking valve? Does she run OK when hot ? As Rob says but you appear not to have altered the points/timing etc. Even worth changing the spark plugs.

Valves opened and closed fine when I was setting them. Runs and starts OK hot - turns over so much faster too. Did the plugs (twin plug head) a week ago. After doing plugs and valves it started fine. Then I did the carb balance. Maybe that screwed it up on the carbs?

I set idle screw out 1 turn and set idle on the stop. It seemed that the idle screws didn't make any difference to the idle speed, so left at 1 turn. Adjusted choke cable on one side as well as a bit tight - the choke cables are screwed into the top of the adjuster, not floating like on the throttle. Is this right?

 

[Owen Snell]

I sold a 90/6 to RichC a couple of years ago. It had an early Boyer electronic ignition fitted (Black Box) typically not long after I sold the bike to Rich the ignition packed in. You'll find the later micro digitals work so much better than the early ones.

Boyer Bransden fitted in 2000, just found entry in maintenance book. Is this the potentially dodgy 'black box'?

 

[Rob Farmer]

Boyer Bransden fitted in 2000, just found entry in maintenance book. Is this the potentially dodgy 'black box'?

Could be. The ignition box is generally mounted on the frame tube above the airbox.

I'm not saying it's definitely the issue but it could be.

 

[Owen Snell]

OK, so left it on a fast charge for a few hours and tried again. Reset the idle screws to 1 turn to make sure correct (1 was a bit out) and then started it with no choke. It started straight away, although it would not keep going without choke. Down for its MoT now it's running and will look at the carbs more closely when it's back - doesn't seem to be spark related anyway.

 

[Owen Snell]

Update now I've been running regularly for a few days. When adjusting the choke cables, I noticed one was slightly 'on' at rest and once this was sorted, the idle was very slow. I took the tops off the carbs, checked the diaphragms and that the slides were free then reassembled. The throttle and choke cables were set up very carefully, idle set and balanced at idle and at 4000 rpm. Now the starting is much better, some choke and it goes. Hopefully all of the minor stuff done has resolved the problem.