Almost Dying - 4 valve

[Freelancer]

Greetings my fellows,

Trying to work out whether this is a problem with the bike, the pilot(me) or if it is even a problem at all.

The when:
When slowing hard from 3rd gear or higher and rpm's are 5k or higher.
Braking hard, roll off throttle all the way, clutch pulled in preparing for downshift and slow corner.

The Symptom:
Bike dies or almost dies when throttle is rolled off and clutch is pulled.
Bike starts right back up as clutch is released.

Doesn't always do this. Happens more often when I've been riding for 30+minutes at hwy speed.

Things it is not:
-Fresh fuel pump & filter
-Throttle bodies are synchronized
-Fresh plugs and wires

Possible causes:
-Old battery?
-Old intake tubes(cracked/leaking)?
-Rider error(improper downshifting technique)? Getting older :oldguy:, maybe time for refresher MSF courses.
-Time for more thermal paste under ignition module?
-Other?   ____________________________



Ideas and suggestions will be much appreciated.

Thanks,
Freelancer

[Scott_]

How well does it idle when you get stopped.

[TimTyler]

Check your valves.

[Freelancer]

How well does it idle when you get stopped.

Idles fine, though after riding at a fast clip for a while, the idle occasionally seems to be about 50 rpm higher than normal. Then will drop down to normal after riding around town.

Check your valves.

Valves checked last oil change. All within tolerance, though 2 exhaust valves will probably need shimming in next 10k-15k.Also, air filter is new.
 The bike just had the big 75k  service where everything is gone through. Also have new 4-hole injectors, which helped this a little. Also, made the girl peppier and smoother.


Thanks for the replies and suggestions, I hope that you guys can help me figure this little puzzle out.
 In the meantime, I've adjusted my riding technique to where I don't slam the throttle shut.  Instead, I either roll of gently(slower) or don't roll of completely when braking and downshifting during fast paced riding.

Later,
Freelancer

[The Mighty Gryphon]

It may be possible that one or more lower throttle body bushings are leaking slightly.  Not enough to disrupt the idle mixture, but closing the throttle at 5k rpm can create a lot of vacuum that could pull enough air to lean out the mixture.

[bocutter Ed]

Mine did that this spring, after sitting for 4 1/2 months with 'no-corn' in the tank (full). Did it at lower revs than yours but cleared up after a couple of tanks.

[TimTyler]

Mine did that this spring, after sitting for 4 1/2 months with 'no-corn' in the tank (full).

Right on. Try a bottle of HEET.

[Scott_]

Or some Seafoam.....

[Freelancer]

It may be possible that one or more lower throttle body bushings are leaking slightly.  Not enough to disrupt the idle mixture, but closing the throttle at 5k rpm can create a lot of vacuum that could pull enough air to lean out the mixture.

This sounds very plausible, Thanks! I, will check this on the next oil change/service.

Mine did that this spring, after sitting for 4 1/2 months with 'no-corn' in the tank (full). Did it at lower revs than yours but cleared up after a couple of tanks.

Right on. Try a bottle of HEET.

Or some Seafoam.....

Thanks for the suggestions guys. :) .....Tho I don't think this is an issue this time. The girl was doing this before the new paint job, at which point, she got a different (clean) tank, pump and filter.


Also, one other thing I've noticed. When riding at 3k-3.5k rpm (4th gear 45mph)the bike sounds a little rough(occasional miss). I can't tell if it is lean or loading up, tho the plugs look fine. Accelerating into 4k and up, she gets smooth and comes on really strong....like my old FJ1200 strong.

I know, shift to 3rd gear for 45mph, yeah yeah.... :).

Am thinking that Gryphons' idea about a possible vaccum leak at the throttle body mounting bushings is a good place to start.

When I do the next service, I'll let you guys know if that is the fix.

Thanks guys,
Freelancer

[Scott_]

You don't have to wait till the next service to check for vac leaks.
Get some carb cleaner with the 6" nozzle extension tube and listen for idle changes when checking the bushings, hoses, etc...
Would not be surprised if you find the lower intake rubber o-rings are dried and leaking, especially if they are still original. Or as Gryph suggested the bushings between the intakes and throttle bodies.
I've replaced the intake o-rings on both my '95 and '97 as pre-emptive when I was replacing all the other 20yr old rubber hoses and bits.

[Freelancer]

I'll check in the next day or two. Probably won't tear into it until the next service seeing as it will be coming up soon.

Also, just thought of this. I will check the vacuum tube covers on the throttle bodies. If they are leaking, I'll fix immediately if they are leaking.
Even if the vacuum tube nipples are the problem I'll still replace the gaskets and mount tubes(bushings?) at the next service.

Any other advice will still be appreciated.

Thanks,
Freelancer