Concentric running rich on A10 plunger

[muskrat]

G'day owain.
Are you sure the auto advance is working? Or if manual your moving the lever the right way? 3,1/2 slide should be OK, I wouldn't go any bigger.
Cheers

[berger]

 muskrat a friend of mine sussed that mine had been timed without the auto unit being held at full advance. in those days I knew nothing, a bit like present day, but once set up she blew the pipes out of the head and that was more nowadays shes on K2FC but going back to orwains what came first ? the mag replacement or the running problem that he has now

[kiwipom]

Yeah back in the day I just got t.d.c. On firing stroke then the fag paper release and that was that, knew nothing of wedging auto advance open, seemed to work from memory, cheers

[owain]

The original problem was that it was running super rich. I was running a .280 main jet in my concentric carb. Replaced it with a .160 and the plugs were brown and the bike started spluttering when the engine got hot. Replaced it with a .200 main jet now but the engine still splutters when I give it gas or if I'm putting the engine under load e.g. going uphill.

I've just resit the timing. I didn't set the auto-advance in fully advanced when I did it (I did do this last time though). My reasoning was that if it was too retarded before then I'll defo advance it now...

It seems that it's now advanced too much though as I'm just getting loud pops out of the exhausts!

[Greybeard]

...I'm just getting loud pops out of the exhausts!

It will do that if the timing has been swapped left to right. I know, cos I did that recently   

[RDfella]

owain - if it's too advanced, she'll kick back on the kickstarter.

[owain]

Righto, a quick update. I resit the timing. 11/32" BTDC with the auto advance sprocket wedged into full advance. Went for a ride. Same symptoms (Stuttering and spluttering with anything over 1/4 turn of the throttle). So I put the choke on so that the choke was fully lowered to richen the mixture...Cured the symptoms instantly.

So I can rule out ignition. Back to what the carb fix would be. Needle position lowest and possibly smaller cut-away I suppose.

[Triton Thrasher]

Throttle cutaway has little effect past 1/4 throttle.

To enrich the mixture at 1/4 to 3/4 throttle, raise the needle.  That is, put the clip in a lower groove in the needle.

Also check there is no water in the float bowl or anything obstructing the main jet.

[JulianS]

Are you still using the 930/11 carb?

It is quite an early one. The design of the needle, needle jet and jet holder were changed in 1969 to improve running and it could be that your carb has a mix of old and new design parts which are not interchangable.

Service sheet gives details.

[owain]

Thanks. Good advice there as well Julian. I'll check to see whether any parts are getting mixed tomorrow. Just snapped off a cheap petrol whilst trying to the remove the carb  . Another part for the list 

[owain]

Update: I removed and dismantled the carb and believe I found the problem. The needle jet had vibrated loose and was sitting free of the needle jet holder. I coated the thread in loctite and reinstalled the jet.

I guess the smart decision would be to leave the needle position in the middle notch (as it was before) and see if that solves the problem.

[Triton Thrasher]

That’s unusual, although the main jet holder sometimes falls off.

Hope you can get the needle jet off when it needs to be replaced.

[Guy Wilson]

My main problem with running rich is that I don't ride for long enough...My regular trips are around town and rarely more than 3 or 4 miles in total a day.. I do need to address it though, but I need a longer ride and the time to do first..

[muskrat]

G'day Guy.
For short rides (3-4 miles) she would be only just getting to operating temp. Try one or two grades hotter in the plug. NGK's lower # for hotter, Champs the other way.
Cheers

[Guy Wilson]

thanks Muskrat! good advice!
Guy