Causes of misfire / stuttering at around 68 mph?

[gimpy limp]

I'm getting some stuttering if I give medium to hard throttle at around 68mph but all through-out the rest of the rev range the bike runs great at any other speed. It doesn't idle rough or pull away bad and it starts first time every time so not sure what this could be? I've only noticed it the past 4 / 5 days.

Has anyone ever had those symptoms from the early stages of a (head) gasket starting to give up maybe?

Other than that I tightened up the head bearings again the other week (I think before I noticed this misfire) and may have yanked something loose as the handlebars went back to do it.

Other than that does it sound like the carbs need fiddling with or the air filter maybe? Can the carbs alter themselves like that without me touching them?
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-=[Sam/b]=- cx500's the only way to travel, we do it in style just like jimmy saville
msn addy - [email protected]
https://pre-auto.com/cx500/rat_and_survival_gallery_2006

[firefox]

when my bike (ped) was backfiring it was the airfilter it had come away, also it caused it to splut and jump about.

[gimpy limp]

my mistkae its not a misfire (Theirs no backfiring) it just stutters and theirs a major powerloss at 70.

I just tried 70 in third to see if it does it any where in that rev range and it went straight up to 70 in third smoothly without a stutter.

It's a strange powerloss, once you reach 70 as your still climbing it stutters then if you back off a tad then slowly accellerate you can reluctantly get up to 75, it does that again then you can get up to 80.


____________________
-=[Sam/b]=- cx500's the only way to travel, we do it in style just like jimmy saville
msn addy - [email protected]
https://pre-auto.com/cx500/rat_and_survival_gallery_2006

[WavyGravy]

could you have trapped a fuel line? sounds like fuel starvation to me
____________________
1975 CB125s, 1991 GN250, 1990 Ducati Paso 906
"Don't wake him up - He's got insomnia - He's trying to sleep it off"

[WavyGravy]

jeez just after i posted that i saw you saying it happened at 70 regardless of gear, fuel must be ok then, is there any sort of vacuum line between carb and electronics?
____________________
1975 CB125s, 1991 GN250, 1990 Ducati Paso 906
"Don't wake him up - He's got insomnia - He's trying to sleep it off"

[TheDonUK]

I am at a far worse stage than yourself with my 500, any attempt at accelerations gives me the same as you, it will chug along at nissan micra speeds all day long but try to give it any and chugachugachuga chuga... My air filter is filthy, replacing that on monday or tomorow with some sort of bodge, maybe clean the filter. and some new spark plugs....

[gimpy limp]

worth giving it a go tomorrow with the air fiters off to narrow that down maybe?

I have to do almost 200 miles each way next week along the motorway mostly so it's not ideal timing, looks like i'll have to do it in 60 all the way

I just had a nosey at the fuel filter but it's so small it's hard to tell if it's dirty (its been on their around 7/8 months without a problem). I think it's fine though nothing obvious.

I did just notice the headlight keeps flicking on and off as I turn the handlebars so I think i've half yanked out a wire when i done the head bearings so it's possible i've trapped something else.
____________________
-=[Sam/b]=- cx500's the only way to travel, we do it in style just like jimmy saville
msn addy - [email protected]
https://pre-auto.com/cx500/rat_and_survival_gallery_2006

[gimpy limp]

[Nath]

How old is the airfilter? When I got my bros400 it would do a similar thing if I took it to high revs, but changing the airfilter made it better. Now my airfilters getting a bit long in the toothe again, it feels like it's got a bit worse (thought truth be told I never normally rev the bike that high as it's got no power at the redline).
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Hard livin', hard luck.

[gimpy limp]

possibly pretty old I think, it's one of those aftermarket cone things that i'm told don't do as good a job as the genuine filters
____________________
-=[Sam/b]=- cx500's the only way to travel, we do it in style just like jimmy saville
msn addy - [email protected]
https://pre-auto.com/cx500/rat_and_survival_gallery_2006

[mr.z]

mr haynes says...

"poor running or lack of power at high speeds"

weak spark at plugs or erratic fireing (section 12)
ht lead insulation failiure, my be completely unnoticeable at lower speeds

fuel/air mixture incorrect
air bleed holes blocked, clean carbs
main jet blocked
reduced fuel flow (cold be the tank breather hole?)
vaccumdiaphram split

compression low (compression test)
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>RidingSkills<->Tech Tips<->MyBikes<

[WavyGravy]

the hollow tube going into ignition box tells the ignition box what curve to choose when advancing the ignition, basically it allows the engine to fire at the right moment to do what youve asked it via the throttle, if the ignition cant advance then the bike will bog down, dont know whether your bike has one or not though,
____________________
1975 CB125s, 1991 GN250, 1990 Ducati Paso 906
"Don't wake him up - He's got insomnia - He's trying to sleep it off"

[WavyGravy]

If the bike was mine i'd run it at the speed it bogs at for a short distance and kill ignition and pull up, remove a plug and sniff it, if it reeks of unburnt fuel you know the problems electrical, it'll also look a bit blackened, if its a light tan colour and no smell of fuel then you know its a fuel starvation issue.
____________________
1975 CB125s, 1991 GN250, 1990 Ducati Paso 906
"Don't wake him up - He's got insomnia - He's trying to sleep it off"