G11 ... little problem with the carb (I hope)

ianrichards · Post by **ianrichards** » Mon Sep 08, 2008 6:46 pm

Novice question ... but we all have to start somewhere

I have just got a 1957 G11 which seems to have a little problem (I hope).
Here's the scenario:
All fine on the flat and going down hills, open the throttle to go up a hill, all still OK and then after a while it seems to lose a bit of power, which then picks up again.
I thought the clutch was slipping, but I have been told that it is probably the carb that needs adjusting.
Is this so ?
I don't want to alter anything until I'm sure that that is where the problem lies.
TIA
Ian

GSAX1 · Post by **GSAX1** » Mon Sep 08, 2008 11:04 pm

Could be a fuel starvation problem, depends on the exact symptoms. Give us more info please. Does it pick up when you close the throttle, or by itself? Does it go better/worse when you close the choke slide? Does this problem ever occur on level ground, at high speed? Are you sure it's not overheating? Checked your ignition timing?

What carb do you have, and what settings?

Michael

bjork · Post by **bjork** » Mon Sep 08, 2008 11:14 pm

Have you checked for fuel tank vent blockage as well?

ianrichards · Post by **ianrichards** » Tue Sep 09, 2008 9:06 am

Thanks for the response, as soon as this heavy rain stops I will take the bike out and check.
Regards
Ian

ianrichards · Post by **ianrichards** » Sun Sep 14, 2008 6:28 pm

Right then, nice weather today and to the G11 out for a ride.
Eventually got the problem to appear again.
... going up a hill, open the throttle a bit and the trouble starts. It feels as though there is a loss of power, keep the throttle just the same and the syptoms continue. Off the throttle a bit ... open up again and the problem disappears. I have checked the vent in the fuel cap and that is fine.
Mmmmmmmmm ... any ideas ???
TIA
IanEdited by - ianrichards on 14 Sep 2008 5:28:46 PM

AJSOWNER · Post by **AJSOWNER** » Sun Sep 14, 2008 11:04 pm

It sounds very much like fuel starvation. When opening the throttle more fuel is drawn into the engine; if the fuel delivery from tank to carb is restricted the fuel level in the carb falls causing a weakened mixture resulting in the lack of power that you describe. When you close the throttle less fuel is used than is being delivered with the result that the fuel level in the carb rises back to normal and power returns.
Try taking the fuel pipe off the tap and watch the flow of fuel as you turn the tap on (use a suitable container). If it is a dribble, you will need to unscew the tap and check for debris on the gauze filter attached to the tap or maybe a blockage internal to the tap (empty the tank first or remove the tank and tilt is so that the tap is above the fuel level!)
If that seem OK remove the banjo connection to the carb and check for debris blocking the filter there.
I use an in-line filter in the fuel pipe and it is amazing the amount of rubbish that collects there even though the tank seems clean internally.
happy biking!

Duncan · Post by **Duncan** » Sun Sep 14, 2008 11:26 pm

Ian, probably not this but how old is your fuel? A friend recently emptied/blended half a tank of very old fuel in to his bike to use it up and noticed a marked lack of power in the top end of the throttle range while lower settings were unaffected.

paul knapp · Post by **paul knapp** » Mon Sep 15, 2008 3:03 am

Ian, what you're describing is a 'flat spot', possibly caused by too lean a setting in the carburettor somewhere.
Do you have the correct carburettor for the year? AMAL 376/58
I would be looking at the slide number, it should be a 376/4, with needle position in the 3rd. slot from the top. Also the pilot jet should be a 30, with main jet a 260. Carburettor bore 1" dia.
When the 'loss of power' occurs, does it come back if you close the choke slide gradually?

Paul

clive · Post by **clive** » Tue Sep 16, 2008 8:06 pm

How about a bit of rust etc in the trap under the main needle jet. Open up to full throttle and it gets sucked up to partially cover the hole to the main jet. Throttle back and the bit of muck falls back allowing a gradual build up of speed again. Clean out the bowl under the jet and if there are any bits in it that may be the problem.