Help: Bike sputtering/stalling when moving from a stop

[keeena]

Could any of you guys shed some light on this new problem I'm having?

During my last ride my bike started stalling / sputtering when moving from a dead stop. When the clutch is partially engaged, the engine starts to sputter out and lose power to the point of stalling. Its not the normal load when a clutch begins to engage...its more than that. My friend said it sounded like something was up too - said the engine just didn't sound good when moving from a stop. I stalled the bike a few times because of this (I've been riding for years...yes I know how to ride)

To ride it now I have to over-compensate the throttle a bit to keep it from stalling. But even when I do this it still feels strange when engaging the clutch. The clutch seems to work perfectly fine in other gears. It just happens when I try to engage 1st gear at lower RPM (a normal start from a stop). I noticed that the problem seemed to get better when the bike was cold. The problem first started happening after a lot of riding w/ no stopping. Oil level is fine, but I it is due for a change.

Any ideas as to what this could be? I'm thinking it has to be clutch or tranny related. My carbs are tuned well and fuel filter is new, so I don't think I have issues with fuel delivery.

[hohum]

When was the last time the carbs were synched?

Cheers,
Chris

[SSearchVT]

Does the bike run OK once you are moving?

Check to easy stuff first, air filter, plugs (for both tightness and condition), plug wires etc. After that look at the carbs for a stuck float, bad needle and seat, etc...

Good Luck...

[stoinkythepig]

When my bike did this it turned out to be a bad plug wire (actually the 5K ohm resistor inside one of the boots). It was only prevalent when the engine was under load AND the RPMs were low. Try getting it into high gear soon and bogging the motor a bit to see if it'll do it in other than first gear. At higher RPMs my bike apparently made enough ignition voltage to overcome the excess resistance in the plug boot and it ran OK (but not perfectly) What kind of bike is it?

[keeena]

Carbs were synchonized late last year (sept?). I pulled them off in the winter and checked the bowls like I usually do, but didn't resync again since I didn't separate the carbs. Filter is A-OK too. Bike runs fine once I'm moving.

Stoinky - Thats interesting that you mention bogging the motor while in high gear but low RPM. I actually did do this while I was riding, and I remember that it seemed to bog down more than it should've. I'll check the plugs and wires. Anything special to look for? I'm not an engine guy, but I do know the basics of what to look for (like gap, fouling, wire resistance, etc...).

The bike is a '97 ZX7R.

[stoinkythepig]

Originally posted by keeena
Carbs were synchonized late last year (sept?). I pulled them off in the winter and checked the bowls like I usually do, but didn't resync again since I didn't separate the carbs. Filter is A-OK too. Bike runs fine once I'm moving.

Stoinky - Thats interesting that you mention bogging the motor while in high gear but low RPM. I actually did do this while I was riding, and I remember that it seemed to bog down more than it should've. I'll check the plugs and wires. Anything special to look for? I'm not an engine guy, but I do know the basics of what to look for (like gap, fouling, wire resistance, etc...).

The bike is a '97 ZX7R.

Similar igntion system to my Concours. Check the resistance of each plug wire and cap assembly. They should all be the same plus or minus 10% or so. You may find one that's reading infinite resistance. That would be the culprit. If they all read OK cold, hit them with a heat gun and test again. Many times these things will fail only when hot.

Any chance the bike was in the rain for a long time? Maybe water found it's way down one of the spark plug wells and caused corrosion or got hot enough to boil and then popped a spark plug boot off a bit. Seen that happen too.

The pulser coils can fail under heat and cause a similar problem but my money's on the ignition wires.

Assuming I'm right:

You may be able to open the caps up and repair them. Often they have a fuse-shaped resistor and a spring keeping pressue on the resistor. A little carbon build up in the there can cause enough localised heat to ablate/erode the spring quite quickly. The springs I've seen happen to be about the same size and shape as a ball point pen spring so you could theoretically pull a "McGyver" and fix the bike with nothing more than asacrificial ball point pen. Look inside the spark plug end of the cap for a brass, slotted, and hollow screw. Take it out with a flat bladed screw driver and you should get access to the resistor and spring if it's there. Might need to tap it abit to get them to fall out. You might just get a resistor and a small pile of dust that used to be the spring.