Dead at 6000 RPMs

[Guest]

Saltymonk brought his bike over today (1980 GS1000G) and I thought his woes were carb related. After having the carbs off many times and even switching all the jets into a rack I had that I knew were good it still hit a brick wall at around 6000 rpms.
I put pods and a Dynojet kit in the carbs and he has a V&H 4-1. I've come to the conclusion it is not fuel related. We tried big mains small mains and everything in between and same exact issue. I took off the valve cover to check the cam chain and the timing and recocked the tensioner. Still same problem.
The cam chain has 80,000 miles on it and it has alot of play back and forth and it is loose in spots. Is this a sympton of a bad cam chain or possibly the ignition. It has new Dyna coils but is running with the old igniter and trigger.
The bike takes off like a bat out of heck even with full throttle until that certain point and hits a brick wall. It did this with a stock airbox and stock pipes and now after $200 in new jets and filters. :?

 

[Nessism]

No personal experience but I've heard about ignitor issues causing the symptom you describe.

 

[doctorgonzo]

If it is the igniter, no way I'd replace it. I'd just get the Dyna S. I replaced the igniter on mine (to the tune of $287.00 US) when I first got the bike and no way I'd do it if I had it to do over.

 

[Bizcocho]

Hi Chef,

This sounds a little like my no-power-at-speed problem. I used the ideas you and others gave me to check out the spark: Switching 1 & 4 spark plug wires to see if the high-speed miss followed, checking coil primary voltage, switching coils. Maybe these would help you determine if it is the ignitor. (in my case the ignition proved to be OK.) I too have read on this forum that the ignitor can cause this type of problem.

A kink or other subtle restriction in the fuel supply can do it, too.

Good luck,

~Rich

 

[Sandy]

I had the same sort of thing happen with my GS1000. It fell flat at around 7,000 rpm at full throttle no matter what gear I was in. After much carb rebuilding, etc I swapped out the coils, turns out one of the coils was weak and not capable of reliable spark at higher RPM. Drove me nuts because it sure seemed like carburation. If backed out of it a bit it would pull making me think it was the main jet but when you give more it fuel it also requires more spark which the coils couldn't produce. Much head banging over that one.](*,)](*,)

 

[salty_monk]

That sounds like my symptoms but these are Dyna green 3ohm's fitted less than 18months ago. I bought them new. I have had this bike to rev to red line before with same ignition setup but not for a while. Switching from stock to Dyna greens made no diff to bike performance (I did it to replace wires that were brittle & cracked, got one stuck in one of the old coils when trying to pull them out).

We did a compression check, Bill was reading the gauge but I think it was about 130 & all the same. Valves are in spec & timing was good but that chain is loose.

We finished up with the 170 DJ jets & it runs pretty good up to 7000, seemed to run better in the mountains at +4k ft so I think maybe it's a little lean on the jet or needle.

Back here at sea level this morning (Baco is +400ft) I seem to be getting good performance but I get increased popping on decel & it also pops (sounds like from the air box not from the pipe) if I open the throttle too quickly.

I think first thing is to get a tight chain in it.... Then I can play with the jets again.

I'm not averse to trying a dyna S in it... if it make no difference I can always put the stock back in & keep it as spare for my 78 when I get round to that upgrade.....

It was great for Bill to help me out & confirm that I'm not mad - I had tried a bunch of settings with a stock airbox before this with no real luck so at least us still having no success proves I'm not crazy, everything I though was in spec actually was :lol:

Dan

 

[Dave8338]

me tinks...

me tinks...

Valve timing.....if there is that much slop in the chain, it is likely that your valves are almost "floating" as a hydrolic valve will do at higher RPM's. Add to that the weakened valvesprings from havng done 80K an I'm putting my money on te valves. Also...you mentioned that you've heard "popping" in the intake, another sign of mis-aligned valves at te higher RPM range.

 

[salty_monk]

Seems I need to get a new cam chain in it then & go from there... thanks.

Dan

 

[Dave8338]

That would be a good start! :?

 

[salty_monk]

Would the stretched chain cause it to retard as RPM's increased? Just out of interest....

Dan

 

[Guest]

Valve timing.....if there is that much slop in the chain, it is likely that your valves are almost "floating" as a hydrolic valve will do at higher RPM's. Add to that the weakened valvesprings from havng done 80K an I'm putting my money on te valves. Also...you mentioned that you've heard "popping" in the intake, another sign of mis-aligned valves at te higher RPM range.

i was thinking exactly the same thing... loose camchain + old valve springs
i wouldnt push the bike hard before attending to these

 

[Guest]

Would the stretched chain cause it to retard as RPM's increased? Just out of interest....

Dan

i think so

theres a test you can do without removing the chain (at least you can do so on an 850) - the service manual calls for a maximum length/span of 20 chain "rings" (hm, that doesnt sound like a proper name for it, hopefully you know what i mean )

 

[Nessism]

I seriously doubt the problem is the cam chain. It would be rattling around making tons of noise long before any driveability issues showed up.

Dan, I just bought a Dyna S (DS3-2 model) off a guy in the For Sale forum. I think it will fit your bike. You are welcome to try it so see if it helps. Should be here in a few days (hopefully). Let me know.

Ed

 

[Guest]

I seriously doubt the problem is the cam chain. It would be rattling around making tons of noise long before any driveability issues showed up.

Dan, I just bought a Dyna S (DS3-2 model) off a guy in the For Sale forum. I think it will fit your bike. You are welcome to try it so see if it helps. Should be here in a few days (hopefully). Let me know.

Ed

I am torn between the cam chain and the igniter.

 

[salty_monk]

Ed,

I saw that, beat me to it! Yes please! That would be a great test if it would work. I think we can probably rig it enough for a test without stripping everything else out.....

I will certainly get a new cam chain too. I'm happy that it has good compression.

All the timing marks line up & there are 20 pins between the marks, it's not a tooth off.

Dan

 

[tkent02]

I am torn between the cam chain and the igniter.

If a cam chain was that worn it would retard the cams, if anything that should be better for high RPM, should move the powerband up...
I agree there would be all kinds of noise before any issues with how it runs.

Valve springs going soft, could let the valves float, but that is a LONG way below the redline RPM. I think it would take years for this problem to progress as far as not running correctly down at 6,000 RPM.

Never seen springs cause this, have ridden some GSes with a ton of miles and years on them. Could be possible I guess. Especially if the engine has gotten really hot, enough to weaken the springs more than most?
In cars, valves floating has a distinct feel to it, kind of a fluttering sort of thing, like every power stroke its at a different throttle position.

So exactly what happens at 6,000?
Is it just like hitting a rev limiter at 6,000?
Does it start misfiring?
Switch off like a kill switch?
Just get less powerful as if you closed the throttle?
Does it happen at partial throttle as well as wide open?
Is it the same in any gear?
Up or down hill?
If you hold it in this RPM of the problem, then do a plug chop, what do you see?

Is the fuel flow adequate?

 

[Guest]

Ed,

All the timing marks line up & there are 20 pins between the marks, it's not a tooth off.

Dan

the test i was referring to calls for a measurement between those 20 pins (can do it on 10 pins as well) and tells you if the camchain is stretched beyond acceptable or not

 

[Guest]

If a cam chain was that worn it would retard the cams, if anything that should be better for high RPM, should move the powerband up...
I agree there would be all kinds of noise before any issues with how it runs.

Valve springs going soft, could let the valves float, but that is a LONG way below the redline RPM. I think it would take years for this problem to progress as far as not running correctly down at 6,000 RPM.

Never seen springs cause this, have ridden some GSes with a ton of miles and years on them. Could be possible I guess. Especially if the engine has gotten really hot, enough to weaken the springs more than most?
In cars, valves floating has a distinct feel to it, kind of a fluttering sort of thing, like every power stroke its at a different throttle position.

So exactly what happens at 6,000?
Is it just like hitting a rev limiter at 6,000?
Does it start misfiring?
Switch off like a kill switch?
Just get less powerful as if you closed the throttle?
Does it happen at partial throttle as well as wide open?
Is it the same in any gear?
Up or down hill?
If you hold it in this RPM of the problem, then do a plug chop, what do you see?

Is the fuel flow adequate?

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.

 

[Guest]

i imagine you would have thought of this but just in case ...

automatic cam chain tensioners can get stuck and cause a loose camchain, it pays to have the tensioner checked, cleaned, lubricated

 

[Guest]

i imagine you would have thought of this but just in case ...

automatic cam chain tensioners can get stuck and cause a loose camchain, it pays to have the tensioner checked, cleaned, lubricated

I pulled it off and checked it out. It's OK.