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Dead at 6000 RPMs

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chef1366 said:
I pulled it off and checked it out. It's OK.
Click to expand...
i thought as much, chef, but you never know when you have a problem it's sometimes easy to overlook something simple :-s
good luck troubleshooting [-o<, i'm watching the thread with interest
 
Today it was doing the same thing but not at 6,000rpm, much earlier in the rev range & pretty much at all throttle positions.
Better in high gear than low gear....

Dan :)
 
chef1366 said:
Not fuel related. Did the dance.
It is almost like a rev limiter. Just doesn't want to climb over 6-7. Fine till that point even at wot. Reminds me of a governor I had on a moped when I was a kid.
If a bad cam chain would move the powerband up I'm leaning towards a bad igniter but the chain was worn. LOTS of back and forth play.
Click to expand...

It won't be the stretched cam chain or weak valve springs causing these symptoms. Stock springs last forever with stock cam lifts. I'm still running the original springs in my 850.
When the motor peaks out at 7000rpm, does it miss or completely die. If it dies, try backing off the throttle until it runs normally and then snap the throttle open again and see if it pulls cleanly up to the same rpm. If it does, you can rule out fuel starvation. If not, you need to recheck the fuel supply, to and through the carbs.
If it's acting like a governor, there won't be much missing, just a sudden power drop, and refusal to rev higher.
 
salty_monk said:
Today it was doing the same thing but not at 6,000rpm, much earlier in the rev range & pretty much at all throttle positions.
Better in high gear than low gear....

Dan :)
Click to expand...
I bet at this point with a weak spark your plugs are fouled.
 
Could be.... I just thought about the test we did on the coils... No volts at either connection pointd with the ignition on to either coil terminal...

Anyone know if that's normal or should there be a permanent live 12v to them with the ignition on?

Cheers,

Dan :)
 
Switched out his old carbs with my old 34s. Switched out the jets. Still the same issue. Even cut his new fuel line shorter so no hills to climb.
If you let off the throttle till it runs good and hit it hard it does climb to that same rpm.
He does have the original petcock but he said it flows good.
 
hehe we tested it when you left it switched on prime remember ;) :lol: no way it can be drinking at that rate! :D
 
salty_monk said:
Could be.... I just thought about the test we did on the coils... No volts at either connection pointd with the ignition on to either coil terminal...

Anyone know if that's normal or should there be a permanent live 12v to them with the ignition on?

Cheers,

Dan :)
Click to expand...
kill switch "on", there should be permanent live at the coils (there is on mine anyway)
 
49er said:
Stock springs last forever with stock cam lifts. I'm still running the original springs in my 850.
Click to expand...

hi 49er

not sure how long "forever" is, but mine were shot at less than 90k kms
i would think the wear would also depend on how hard you push them

however, in this case it doesnt seem to be the issue
cheers
 
uh... kill may well have been off, it was late by that time. I can double check that easy enough though.

I have Dyna Suppression wires fitted to dyna greens, stock igniter & NGK B8ES plugs from Z1.

Maybe it is the igniter...

Dan :)
 
I may get a Dyna S or use Ed's that he offered earlier to test it out. I can always use a Dyna S on my 78 if that's not the issue.

Ordered a new Cam chain today, split type with a master link.

Dan :)
 
psyguy said:
hi 49er

not sure how long "forever" is, but mine were shot at less than 90k kms
i would think the wear would also depend on how hard you push them

however, in this case it doesnt seem to be the issue
cheers
Click to expand...

Hi Ivor
Mine hasn't exactly been parked in a monastry the last few years!
It's done 83ks now, and sees 10k on the tacho, off and on.
It's obvious when the springs are sad. You'll never forget the sound of valve bounce once you've experienced it. :) Then it's time to replace the springs. I guess you decided to changed yours after measuring their free length. That's the recommended guideline.
Cheers
 
49er said:
I guess you decided to changed yours after measuring their free length. That's the recommended guideline.
Cheers
Click to expand...
i see what you mean, they would last past their factory specified service limit before they actually cause any damage
yes, i changed them after measuring free length, better safe than sorry kind of approach
 
psyguy said:
i see what you mean, they would last past their factory specified service limit before they actually cause any damage
yes, i changed them after measuring free length, better safe than sorry kind of approach
Click to expand...

Valve springs are one of the most forgotten items during top end rebuilds. In most stock applications, they can be overlooked, without dire consequences. Once you fit high lift/high overlap cams, you need to fit matching springs. Those who dont, risk spring bind causing serious cam and spring coil damage.
My springs were still in the middle of the suggested free length range.

Just checked your 850's pic again. How are you finding the Cycleworks 4-1 slash pipe?
The baffle on mine started to rattle when cold. I removed it last week and drilled some extra holes to improve the upper mid range. It's only marginally noisier than before, the exhaust note, not the rattle!
 
I would put this down as ignition only, especially after reading that the usable RPM range has dropped.

You might look at the ignition rotor and be sure it is not a bit bent, which would make its movement eccentric and at higher RPMs that could cause the effect you mention.

I notice someone already suggested a plug check. This might tell you if a coil was failing.

If the others check out, you need an ignitor.
 
It's happening at pretty much all RPM's now so I guess it's failing & plugs are likely fouled. I will check it out asap. Want to check I have good voltage at the coils etc, maybe run some tests on the ignitor from the Clymer manual.

Thanks again,

Dan :)
 
Last edited:
Well this explains something I think.... at the coils I have 9.5V at 3 of the connectors & 1.5v at the other (engine off, ignition & kill switch on).
At the battery I have about 11.5v (because the headlamp is on by default on my bike, it's fully charged as I charged it last night).

Now to find out where I'm losing all those volts (would explain why number 3 plug is fouled whilst the others are clean...)

I think I should also have 12v (or the same as the battery) at the other points too... can anyone confirm?

Guess I'm going to have to chase my way through that part of the loom & see what I find.

Dan :)
 
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