G2 idle and running issues - with videos!

[Janet]

I'm probably wrong again but here are my views, not in any particular order.

Firstly, and possibly a bit important, from a previous thread back in August, Ben's bike is a 1967 G2CSR. Therefore his carb should be the same as my 1964 model, ie a 389/82, not a 376/99. This means that jet sizes, slides, or whatever need to be checked in line with that. I believe the float itself is the same for both versions. Although I'm used to the barrel shaped floats, mine is also a plastic one. I've no idea whether or not it was changed by any previous owner, but knowing two of the three, I doubt it. As Ben says, if it works, why change it.

Regarding the choke mechanism, I think what Duncan was saying is that a manual adv/ret lever has been used in lieu of the original choke lever and, I suspect, fitted to the opposite handlebar, hence working in the opposite direction.

If I understand correctly, what Clanger is referring to when he says 'the gearbox input shaft "sealing" plate on the rear of the primary case' is the two discs on either side of the rear case around the hole that the shaft comes through. These are fixed together and slide across to allow the gearbox to move for adjusting the primary chain. I have no idea whether or not they have a felt seal within them as I've never had a reason to break them apart but I don't have one on either side. There is a oil seal the fits into the gearbox case behind it.

Relating to the fibre washer under the banjo, how on earth am I ever going to learn these things if people keep changing them every 50 years or so?

[SPRIDDLER]

Let's go back to your first post:

It starts after 9 kicks with the choke applied,.......
I fiddle with the idle screw to see where it is and find it is fully wound in. Winding out a fraction causes the bike to stop.
........Later, nothing has changed except the engine has warmed up a bit. When I stop holding a fast idle with the throttle or revving it, the idle is very slow and the engine stops.

.......Any suggestions for a happier idle when warm?

I presume by 'idle screw' you mean the horizontal Pilot jet screw, not the near vertical slow running adjusting screw which merely raises or lowers the throttle slide for tickover adjustment.
Your prime problem is one of starting (9 kicks with choke on) and tickover. I have never found it necessary to use my choke, except in very cold weather and then just about half choke. Just a carb tickle and no choke normally.

The Pilot screw regulates the air flow to the Pilot jet. Unscrewing it increases the air flow.
Your Pilot screw should not be wound fully in, (seriously over-richening the starting mixture), so it is not surprising that when th'engine has warmed up th'engine slows and stops. The approx. correct position for the Pilot screw is one and a half turns open.

This would suggest that you have an air leak on the intake side. Either at the carb/head interface or due to a worn or incorrectly assembled carb.

In your video the zorst sounds very 'splattery' (e.g. not crisp) so there may be a zorst leak as well, but the splattery zorst sound may be the acoustic effect as it's partly in the garage or the camera microhone.

You must start by sorting the Pilot screw issue (it is only the Pilot jet and throttle slide cutaway that influence starting and slow running mixture) and then the four-stroking issue may disappear. Is the Pilot jet (the jet, not the screw) fully screwed home with a fibre washer fitted to the jet cover?
With the rich starting (Pilot wound right in and choke on) and four stroking the plug will (should) have become pretty fouled. A new one would be desirable as today's plugs, once badly fouled, should be considered scrap as they do not respond well to cleaning.

[SideValve]

Just out of curiosity - is the advance/retard working ok?

[Ozmadman]

I'm probably wrong again but here are my views, not in any particular order.
If I understand correctly, what Clanger is referring to when he says 'the gearbox input shaft "sealing" plate on the rear of the primary case' is the two discs on either side of the rear case around the hole that the shaft comes through. These are fixed together and slide across to allow the gearbox to move for adjusting the primary chain. I have no idea whether or not they have a felt seal within them as I've never had a reason to break them apart but I don't have one on either side.

You learn something new everyday!!! I was unaware that that riveted circular plate was free to "slide" to allow gearbox adjustment!! mine appears fixed as any adjustments I have made seems to make the shaft slightly off centre to the plate. There is a felt washer in there though which you can buy as a spare part but impossible to replace unless you either take the plate off, sandwich the felt between the two parts and rivet back or as I did, cut the seal thickness down by half and force it into the space

[Duncan]

Regarding the choke mechanism, I think what Duncan was saying is that a manual adv/ret lever has been used in lieu of the original choke lever and, I suspect, fitted to the opposite handlebar, hence working in the opposite direction.

Thanks for clarifying Janet that's exactly what I meant.

[cbranni]

Is the G2 running ok now?....................I like a happy ending

[borrop01]

Hi, this comment has been a tremendous help, Just trying to start my 14CS after a 5 year rebuild.
Can anyone give me a lead at to the running problem. The engine will start on the first kick, very difficult to make Rev and then dies. I can't get it running long enough to try adjusting mixture or air jet which is one and a half turns out. Carb not fitted with rebuild kit yet.How should I progress from here. Peter.

[SideValve]

Personally, I'd start by quickly checking the timing and that the auto-advance are ok. I doubt its the problem but its easy enough to check and you'd kick yourself if you spent time and money chasing a carb problem that wasn't there.

Then I'd start on the carb.
First I'd check the float, float level and that petrol is able to flow.
Then I'd make sure all the jets are clear and are the right size and the needles in the right slot.

Are you tickling it to get it to start 1st kick? If it starts ok tickled (i.e. enriched) but then won't pick up, perhaps the float is set too high, the flow is restricted, the jet too small or the needle too low.

If it starts ok from cold without any tickling perhaps its the opposite, i.e. set too rich for normal running.

Does it restart again after stopping?

[borrop01]

Many thanks for your input, Peter. I will recheck the ignition. This engine has fixed cam timing and the book says 32'btdc I have reduced the compression from 11.5 down to 8.7 using a road piston to give increased engine life ( I thought) and I have set the timing , with luck, to 1/4" btdc my calc could be suspect ! is any on this any help. The carb is stamped 376/99 which is the wrong one, road bike again. The book says 376/276. jets now are 180. 25. .106. 31/2 slide. Petrol seeping from throttle adjusting screw and pilot air adjusting screw. Hope I have explained the facts ok seems too much petrol around carb. After tickle petrol will leak from tickle hole and engine will start. Thanks again, Peter.

[borrop01]

Hi, Peter, Just had it running.I was able to set a fast tickover and altering mixture but settled for 11/2 turns out as before, Ran well, guite evenly for about 4/5 minutes and then just stopped. Nothing else has been altered. Peter.