B4 Stalls Randomly...

[hangin_biposto]

... when I pull in the clutch. This is not a consistently occurring problem however it happens most often after longer rides at higher revs. The bike runs great otherwise; it fires up and idles well enough, has plenty of power,  and it never seems to do it when shifting up - only when I'm downshifting to initiate slow turns or stops.

VW_NUT will probably chime in with the more technical tidbits as far as what we have done to the bike, but it's running the proper spark plugs, the coils/wires were swapped to see if that was the problem (used parts were installed) the rectifier was swapped just in case (again used) the carbs are synched nearly perfect, he's put the multimeter to it a bunch of times with no luck, we're pretty sure the jetting is decent (factory pro kit installed), good battery... blah blah... you name it.

He is getting very frustrated as he's not sure where else to look to eliminate this incredibly annoying problem, and it is unsettling to me because I am a new rider and have enough to worry about without having to get my bike running again mid corner.

Can anyone give us a laundry list of things to check to see if there's something we're missing? As I said, VW_NUT has been the one wrenching on it and he's now scratching his haid as to what should be checked.

*sigh*

[andrewsw]

does it stumble/stall when hot, idling, and blipping the throttle? or is it *only* when you are downshifting your way to a stop?

you say randomly... you aren't able to to it reliably? it's not repeatable at whim?

Does it happen with other riders? or just you? (nothing personal, sometimes people cause things and don't realize it...)

I find my idle situation is a little flaky after a hot run. Sometimes it will idle high (like a lean surge), sometimes it will idle low, or fluctuate around. Usually a throttle blip and a few seconds of settling will put it all right.

[pmackie]

I'm not familiar with the B4, but it likely has a clutch switch that needs to be released before the engine will turn over when starting.

It's possible that this switch is acting up, and occasionally cutting the power when you start to pull the clutch in. Maybe look at cleaning or replacing this switch. (Same goes for the sidestand switch, just in case it acting up under vibration.)

Just a thought...

[interfuse]

Check and adjust your clutch. I have a feeling it's dragging and causing the bike to stall at low revs... There are a few ways you can test. Pull the clutch and push the bike in gear it should have the same resistance as pushing in neutral. If it has more resistance then the clutch it dragging. You can also put the bike on the center stand, then pop it into first with the clutch held to see if the rear wheel turns freely.

Is ever difficult to find neutral when hot? it's a tell tale sign of a dragging clutch... or if the bike jumps forward when starting in gear or pulls forward in first if you don't apply the brakes at a light.

I hope this is what's causing you're problems because it's an easy fix. Cheers.

[Banditmax]

I used to get this too. What i did was installed a hotter thermostat which seemed to help it. But this was after fitting new coils, reg/rec, cam chain and (used)cams. Have you got an inline fuel filter by any chance? Sometimes after some hard riding the float bowls can get emptied out etc.

[VW_NUT]

Ok,  Problem only happens after riding the bike for a while.  You have to ride for at least 20 minutes to get it to happen.

The bike has had the carbs cleaned and rebuilt and synched, hotter 195 t-stat, new plugs, idle is @1700, new battery, russel inline fuel filter, and new (used) gs 500 RR.

I first thought the idle might be too rich, but the plugs are very clean.

I don't believe its the clutch because the bike will idle just fine with the clutch in once it's running again. 

Basically the bike stalls when you pull the clutch in to downshift at a light, or stop for the light.  When you pull the clutch in it dies.  I've found its happens a lot less if you let the revs come down natuarally and pull the clutch in at the last second.  I won't always do it, but it doesn't usually do it cold unless its the first stop of the ride and thats just becasue the bike is still cold.

I really don't think it's carb related as the jetting feels very good.  (I can post a pic of my plugs if that helps). 

[tomacGTi]

Have you tried bypassing the clutch switch itself?

If you go into the bird's nest of the headlight bucket, you can just make the connection closed always by plugging the wires into one another. At least there you can see if it's the switch giving you problems.

If it's intermittant, I'd check the coil connections, the pickup on the starter side case and inspect all the wires for possible breaks. Could be that when things open up due to the heat, it shuts off the connections.

Weird though because theoretically, the bike would buck and bounce otherwise.

Maybe that's why I'm attracted to this bike so much, it reminds me of my VW with all the little quirks and niggles. (chest pains)

http://forum.svrider.com/showthread.php?t=81570

Something I came across in the SV forums.

[VW_NUT]

Yea it never hiccups other than when coming to a stop.

It does seem worse if you are just cruizing at a light throttle which is why it happens to hangin_biposto because she is a new ridier.  Which is why I though it might be loading up, but like I said earlier the plugs are pretty clean.

This is very much like an old vw.....  Good analogy...

[hangin_biposto]

I have a bitch of a time finding neutral, but VW_NUT never had an issue so I think that may be operator error 

[andrewsw]

how are the other clutch diagnostic? Do you need the brake when in gear with clutch pulled? With engine off, in gear clutch pulled, is it harder to push than when in neutral?

I wouldn't count out fuel. Maybe you're a little rich on the pilot jets or a/f screw. Is the problem better or worse when fully warmed up versus cold?

How about when you blip the throttle at idle? or rev it up to about 5 or 6 grand, let it run for a couple of seconds and then let the throttle snap shut, how does it behave?

A

[VW_NUT]

It's worse when fully warmed up.  I am going to lean out the fuel screws and see if it stalls again.  Thanks for all the info guys!

[PitterB4]

I'm interested to hear how you make out.  I'm having very similar symptoms with my ZX6R.  It sounds like a combination of your problem and Andrew's.  Every once in a great while after a long, steady run, it will stall when I pull in the clutch.  Much more frequently I have a low or inconsistent idle that is is fixed by a quick blip.  It's worse when warm.  I've also developed a really cool backfire when I run WFO to 7500/8000 and then close the throttle.  I leaned out the screws once and didn't notice a lot of difference.  Maybe I'll go a little further.  I can't believe a stock bike with a slip-on would be rich with out some other contributor, though. 

[andrewsw]

why lean out the mixture when popping? I thought popping was a symptom of being lean. Leaning the mixture would just make it worse?

I'm prepared to be educated on that though.

I'm beginning to think that these issues can be a combination of lots of things (duh). See my other thread about pilot jets and lean surge for more of my symptoms...

Regardless of all that though, I'm of the opinion that this random stalling OP sees is a carb issue. Yeah, maybe the plugs aren't fouled, and maybe they look clean, but that doesn't mean there's not some little glitch in the carbs that's causing it.

That idle is a little high and might be masking other problems. You could be rich on the a/f screws but good on the pilot jet and just the difference in rider behavior is highlighting it for one and not the other.

Plus lots of riders do lots of little things, like lightly blip the throttle on decel without realizing it. VW_NUT could be doing all kinds of stuff that hides or compensates for the problem without realizing it. hangin_biposto, without years of developed habits just doesn't do these things and consequently finds all kinds of little problems.

I would recommend that you first get the idle set a little more sanely, down closer to 1-1,2 k revs, and then start playing with a/f mixture. If you're running that higher idle, you maybe aren't running as much on  the a/f screw as you think you are.

Any other changes to the carbs that we don't know about? mains, needles, needle jets, float level etc.

[PitterB4]

why lean out the mixture when popping? I thought popping was a symptom of being lean. Leaning the mixture would just make it worse?

Because I don't think it's lean popping...  it's an actual backfire.  It's worse when warm, unlike lean popping.  And leaning out the jets was more to help the occasional low idle/stalling. 

[VW_NUT]

Leaned the fuel screws out a 1/4 turn, and took it for a ride.  No stalls, however, when I pulled the clutch in a few times I got the stumble for a second that takes a few seconds to recover from.  The idle dips to say 800 rpm for 2 or 3 seconds and then recovers to 1500.  Not sure what causes it.  Seems to happen most when cruising at light throttle between 4-7K, happens less when you are really hammering.

I can't lean it out any more because any more and it will bog out at low throttle.  0-1/8 throttle.