Broken Fuel needle

[Anonymous]

My wife and I are going on a road trip and supposed to be leaving tomorrow. Her bike (78 GS750 Mikuni Carbs) was fouling plugs, so I adjusted the fuel needles and now all are good except #2. I pulled the carbs and found the fuel needle was broken off! Worse yet it is stuck in the hole (really stuck). I didn't think I ever seated it that hard, but something broke it. Anyway, I would like to know if there is any way to get it out, where I should find a new needle, and what can I do for a temporary fix? I don't know too well how carbs work. Can I adjust it so that cylinder pulls more vacuum? Is it still getting gas, because it is fouling (black powdery carbon)? Thanks in advance. Is it safe to take the bike on a 1500 mile trip with one cylinder not up to par?

 

[hoyterb]

Caballo I rode mine for a few thousand miles with two broken off needles.It is a pain to get the broken tip out I got a rack of carbs.You could try a VERY small needle to push out the tip from the inside of the carb.It affects idle mostly.If you get the tip out I have a needle I'll give to you FOC.
good luck and have a good trip hoyterb

 

[Anonymous]

Hoyterb,

Thanks for the offer! My plug keeps fouling. Did that happen to yours as well? Will the bike still start easily? I mean. it's only one plug, but I wonder if i should replace every once in a while or what. I also though about raising or lowering the Jet needle, but i guess that will affect the whole range, not just idle. There are 2 holes into the venturi from the fuel needle. The closest to the cylinder is the one that is clogged of course. The other is not opened until throttle is engaged, therefore, as you say, it will mostly be affect at idle. So I see it isn't a huge deal, but I would still like to keep the plug from fouling. And I am wondering how it will affect the synch, which I have yet to set. Maybe I should synch with the throttle a little high?

Thanks again.

 

[Anonymous]

I think I figured out why the plug is fouling. I thought that because it was getting less gas that it should read lean on the plugs, not foul them. Now I think I know the reason, tell me if I am wrong. I synchronized these carbs a while ago. When doing so at idle (when no gas can get through the clogged hole) It read a low vacuum. After adjustment, it would have then pulled much more gas then needed when the throttle was open, fouling the plugs. Does this make sense!?!

 

[earlfor]

Caballo

When you add throttle, the slides raise which increases air volume and intake area which results in a decrease in vacum. You use more fuel because of an increase in flow not because of an increase in vacum. Once you're above idle rpm and cruising around, the engine is running on the mains and adjusting the pilot and airscrew will be useful only for very slight "tweaking". If the plugs are burning black, its much more likely that you have worn seals, worn needles, needles set too high or the float level too high. Adjusting the pilot will not have a noticable effect on black burning plugs. Having a pilot screw broken off isnt anything to worry about. It may make the bike need to be warmed up a few minutes longer, but thats probably all you will notice. Once youre running at rpm above idle, the engine isnt running off the pilot anyway and the carb will function as normal. Everything still will work as before on the carb, but you will be missing aproximately the 0% to 25% range on it.

Earl

I think I figured out why the plug is fouling. I thought that because it was getting less gas that it should read lean on the plugs, not foul them. Now I think I know the reason, tell me if I am wrong. I synchronized these carbs a while ago. When doing so at idle (when no gas can get through the clogged hole) It read a low vacuum. After adjustment, it would have then pulled much more gas then needed when the throttle was open, fouling the plugs. Does this make sense!?!

 

[Anonymous]

Hey great news about the broken pilot screw. I guess I have a few things to check out then. The floats are all even when measured with carbs apart. I would bet you might be right about the needle height though. When I first tore them apart (a long time ago) I didn't keep track of which slide went to which carb. As I recall one was set different from the others. I will have to check. Thanks for the great advice!!!