Surging

[mjpchief]

I've looked all through the carb section and found nothing about surging. At 50 mph I get a slight surge. Engine pulls fine at all rpms but when running a steady 50 mph I have this surge. Any ideas. This is a '75 650B. Everything stock. 24000 miles.

Thanks in advance.

 

[5twins]

You might be a little lean in the midrange. Where is your needle set? Stock setting is 4th slot from the top. Your timing may also be off slightly. That can cause a surge in the midrange while cruising.

 

[mjpchief]

Not sure on the needle. I think it's in the middle groove. Will check the timing today. Thanks 5twins.

 

[mjpchief]

Not sure on the needle setting. I think it's in the middle slot. Will check it and the timing today. Thanks 5twins

 

[mjpchief]

Points where closed up to about .009. Reset them to specs and waiting on rain to quit to ride it.

 

[5twins]

If the points had closed up then that changed the timing. Gapping them properly could put the timing back where it belongs but it's best to check it anyway. You can't be sure you've re-gapped the points to exactly what they were when you originally set the timing.

 

[mjpchief]

Checked the timing and I think it's right. Used to work for the Yamaha dealer years ago and I'm kind of retraining myself now. It's good to have someone looking over my shoulder. Thanks 5twins.

 

[angus67]

You might be a little lean in the midrange. Where is your needle set? Stock setting is 4th slot from the top. Your timing may also be off slightly. That can cause a surge in the midrange while cruising.

so.. would he drop the needle a slot, or? My 2003 suzy marauder is doing the same. I stepped down the pilot on the front carb(don't know if you know these bikes) and it seemed to smooth it out alittle, but still there. Drop the needle?

 

[5twins]

No, I would say you want things a bit richer. Surging, if not timing related, is usually a sign of being slightly lean. Your Marauder I'm assuming has fixed needles. Maybe you could shim them richer (higher) with a washer?

 

[mjpchief]

Finally no rain. Took the bike for a ride and found no surge and bike is running like it has a new life. Setting the points was what it needed. Probably will not mess with needles yet. The bike starts better and there is no hesitation on take off. Makes it a pleasure to ride again. Thanks again for the help 5twins.

 

[5twins]

You probably don't need to mess with the needles. It was a timing problem, plain and simple. The points wore closed, that changed the timing a little, and that caused the surging.

Years ago I had an early 500 Kawasaki triple. It surged cruising in the midrange. Since it had electronic ignition that was fixed, I never thought about a timing check. I figured it was just the nature of the beast. When I finally did take a look at the timing, I found it off slightly and that there was a very small adjustment range. I dialed it in and the surging went away.

 

[angus67]

now of course I got rid of the fixed needles as soon as I got it(03 marauder) what kinda meathead do you think I am?lol. No really, though. richer eh? Ill pick up the needle one slot.

 

[jd750ace]

Usually that low a speed is fixed with a one step richer pilo. Why only step the pilot down on one cylinder? I realize the bike has differential jetting like the dual carb Shadow 750, but if you are not tuning with an AFR gauge on each pipe it sure seems it would be easy to get lost. One step up on the pilot or a half step on the needle helps the upper low speed range equally it seems, but i've found that the pilot size increase is generally the most sure change. I've shimmed a needle to fix a 50mph surge, and found it still there at 40, before the needle starts playing into it. If you ride it like you stole it, you'll probably never notice.