oscillation

[chaklid]

1979 xs 1100sf, 45ks
ran perfect up until lately: as i ride along suddenly it loses power as if no fuel in a couple of cylinders. at standstill and idle i purrs along fine; whipping the throttle wide open the engine responds flawlessly.

i disassembled the carb, inspected EVERYTHING on it; checked plugs, air leaks, connections, timing e.t.c. lately, i discovered when i throttle up to around 2-3k and hold the throttle there the engine oscillates; in other words it simulates a constant throttling up and down, but without me doing so!!!!


So, what is up with that?? i am pretty experienced with these machines: I two indetical xs1100s and '72 honda 450. I know my stuff. there are a few more things i want to try, however, one of you may have quicker idea-- help me out guys

THANKS

[boyat68]

chaklid:

Sounds to me like your Pilot Jets are not functioning properly. These jets support the RPMs from idle up to about 4000 where your mains cut in due to the lifting action of your diaphragm. If your pilots are getting clogged or a pilot screw has fallen out and allowed your jet to fall down in the bowl, then from 1100 to 4000 RPMs will be affected.

[The Lorax]

I read about something like this in another post somewhere. gas tank vent may be plugged starving it of fuel. Someone who knows what the hell I'm babbling about, help me out here. open the gas cap when it happens, is that fixes it, it has something to do with the gas tank vent. I'm thinking that's what it sounds like, but I really haven't got a clue as to what I'm talking about. Your issue reminded me of one I've read about on a few occasions. Have a nice day and ride safe. also, check your petcocks and fuel delivery as well, if one of the lines is kinked, it might starve one bank of fuel giving you the 2 cylinders losing fuel symptom. just a thought.

[TopCatGr58]

Hey Chaklid,

Check your PU coil wires, see the tech tips for the how to. The dropping 2 cylinders is a common symptom for this. The oscillating can be variations in the vacuum advance rotating the timing plate causing flexing of the wires to where 1 PU coil drops out dropping 2 cylinders, revs slower, timing plate rotates wires then reconnect and firing on all 4 again, rpm goes back up, etc.!!
T.C.