Difficult to start

[solomonheckler]

Hi all,

To introduce myself: I'm an English fells living in Eastern Finland. I'm a motorcycle mechanic in Joensuu working on everything from Vespas to Triumph Rockets with everything in between. I recently bought, imported and registered a 1991 C3 with low mileage, I've renovated a few bikes recently including a 1987 h***a CBR250R Hurricane, a 1995 TZR 125 4FL, a 1990 Yamaha R1-Z 250 and a 1988 TZR250. The C3 was an impulse buy, never thought I would get to own one but now super happy that I do.

I just finished servicing and getting my C3 sorted, but it still has a bit of an issue when starting.

Is it usual for these to be a bit temperamental?

If I give some choke, maybe half, it fires up after a few kicks but then the revs don't really raise high enough. If I give any throttle it dies. Easy enough to start again but I have to tweak the choke a bit, less choke, a bit of throttle, kick start it again, more throttle, less choke etc. etc. Once it's warm it's fantastic, it's just the starting issue. Carbs were totally serviced, new vales, jets, slow jets, properly cleaned. New spark plugs. Fresh fuel (actually 98 octane Russian fuel with no ethanol). I also fitted Jollymotos.

The only thing that I didn't change were the reeds, there were already carbon reeds fitted which have no gaps or spaces. I have some new stiffer reeds if needed but I don't think this is the problem.

Any advice would be great.

Thanks in advance.

[JanBros]

How did you set the air screw's ? standard is way to lean, I only turn them out +/- 3 quarter of a turn. standard is 1 and a half turn (from memory).

[solomonheckler]

Thanks for your reply.

Air screws set standard. I'll change them and maybe fit the new reeds at the same time.

I'll keep you posted.

G

[Gerrit]

The carbon reeds are most probably the standard reeds, so if they are OK I wouldn't replace them.

[solomonheckler]

Yeah that seems to be better. I'll get it on our Dyno next week and test it.

G

[Bertie_Mollie]

I've found clearing the hole in the brass insert in the float bowl helps starting.

Maybe have a poke and see if it is partially blocked.

Cheers,

Andrew

[solomonheckler]

I also noticed that the left cylinder was cooler than the right, so I took the carbs off again and rechecked both.

Left carb idle jet was new and clear but the tiny hole to the throat was partially blocked. I washed it, rinsed it with carb cleaner, blew it with the air gun, and eventually cleared it out.

Unbelievable difference, choke works like expected now, all good.

The idle jet fuel flow was working but not enough fuel was squirting out of the jet, more like dribbling.

Anyway, all good, just need the winter to come and go and then to the road. Minus 9 Celsius right now, not a bad test for the start circuit tomorrow.

[solomonheckler]

So now she's idling fine on both. But when I first start the left cylinder doesn't warm as quick as the right.

When warm the choke works perfectly, but it's reluctant to raise revs on cold start.

Any ideas?

Fuel tap is working fine, I wondered if it was something to do with vacuum from carb? Since it is that side that is colder.

[mellorp]

I own lots of 2T twins and most of them fire up on 1 cylinder before the 2nd one chimes in after a few seconds. Think of the engine as two 125's bolted together that mirror each other, except 1 side runs the ignition and the other the primary gear.

Once warm if it runs OK I wouldn't worry too much. You may have to alter the jetting on 1 side to get the optimum carburation. Maybe 1 size different on the main jet.

[Binetta Steve]

I own lots of 2T twins and most of them fire up on 1 cylinder before the 2nd one chimes in after a few seconds. Think of the engine as two 125's bolted together that mirror each other, except 1 side runs the ignition and the other the primary gear.

Once warm if it runs OK I wouldn't worry too much. You may have to alter the jetting on 1 side to get the optimum carburation. Maybe 1 size different on the main jet.

Totally agree with the above my C3 Kr1s allways fired up on the RHS cylinder first. This was both before and after an engine rebuild and having had both carbs ultrasonically cleaned and re jetted. The coil fires both cylinders every time as its a wasted spark. I spent ages smoothing the fuel line pathway, thinking it was that.

But after 30/ 15 secs both chimed in and on running and doing a simple plug chop both mixtures were the same.

Its just a two stroke characteristic don’t worry and get some studs in those tyres and shred the minus 9 weather

[solomonheckler]

Thanks for straightening me out and saving me a load of time. I'll stick to my MTB for winter biking though, don't want to gravel rash my KR now it's finished. I've not dynoed it with the new Jollymotos but hope to soon. I'll post the results when done.

Cheers fellas