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Loss of power around 5-6k RPM

  • Thread starter Thread starter exzachtly1
  • Start date Start date
E

exzachtly1

Guest
I don't know if this is carb related, but I've recently finished a full carb rebuild, finally got it back on and connected to the airbox (I was having trouble with this part :-\\\) and took it for a 20 mile ride just now to check out how it was running.

Things seemed good! The idle was pretty consistent, ran well, etc... until I finally got brave enough to rev it to around 6k RPM (new rider!). I noticed that around this mark the bike loses lots of power - basically bogs down and stops pulling. So I'm looking for a place to start diagnosing this.

So far, I have set the float heights to spec on the carbs, eliminated (i think) all air leaks, mixture screws set to 2.5 turns out, new spark plugs, new air filter. Also, the bike already has an aftermarket ignition system on it, installed by a previous owner.

I have not tested the voltage yet but just got a multimeter in the mail yesterday to do that with. Maybe tomorrow I will check things out to be sure I'm getting good voltage everywhere. I'm not totally clear on the condition of the charging system and battery since the bike is new to me.

Any tips are appreciated.

EDIT: Here is a link to the issues I was having with the airbox. Unfortunately I do not know if this issue existed before the carb cleaning / airbox fiasco since I didn't ride it this hard until now. Hope this helps - I'll get a new pic of the final result in this thread ASAP.
 
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Hate to say this but probably still a airbox issue. Can you edit in a link with your original airbox problems so those not familiar with original problems can chime in? I'm thinking you are getting extra air between the holes in airbox to boots.
Might be wrong on this but considering original problems that would be my first guess.
 
Crankthat said:
Hate to say this but probably still a airbox issue. Can you edit in a link with your original airbox problems so those not familiar with original problems can chime in? I'm thinking you are getting extra air between the holes in airbox to boots.
Might be wrong on this but considering original problems that would be my first guess.
Click to expand...

Updated. Also updated the other thread - just FYI I did seem to get them connected pretty well now, I don't think it is having any erratic idle anymore at least. But you're right, maybe it is still the same issue causing these symptoms.
 
kdo58 said:
try riding with petcock on prime.
Click to expand...

I'll try this as soon as this darn rain goes away. The petcock could be gunked; it is very hard to turn. This would probably tell me for sure if it's in need of replacement.
 
You do have an intact air filter element in place ? your petcock is signaling replacement time!
 
tom203 said:
You do have an intact air filter element in place ? your petcock is signaling replacement time!
Click to expand...

Yes, I replaced the air filter with a UNI foam filter only a few weeks ago. I took care not to over oil it. I am beginning to suspect the petcock as well... where is the cheapest place to buy a replacement? Z1? OR would it be wiser to pull the petcock off and inspect it to see if a rebuild is a viable solution?
 
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Went for a 20 mile ride today with the petcock on PRIME. This made no difference in the power issues :cry:

Seems to struggle around 4.5-6k RPM depending on what gear I'm in. Just loses power and sputters. Could this have to do with the mixture screw settings?? They're at 2.5 turns but I haven't fiddled with them yet since it seems to be running and idling OK aside from this issue.
 
There is still a leak somewhere, as someone said already I guarantee you it's at the airbox. Add some weather stripping to the top of the airbox lid and the air filter. Did you put on new carb boots and o-rings when you did the carbs? Is the exhaust stock?

It sounds like it's hitting a flat spot which means it's running lean, you may have to bump up the size of the mains depending on why it's lean. If it's an airleak you just need to fix it, if its because of aftermarket parts then adjust the mains.
 
Toasty said:
There is still a leak somewhere, as someone said already I guarantee you it's at the airbox. Add some weather stripping to the top of the airbox lid and the air filter. Did you put on new carb boots and o-rings when you did the carbs? Is the exhaust stock?

It sounds like it's hitting a flat spot which means it's running lean, you may have to bump up the size of the mains depending on why it's lean. If it's an airleak you just need to fix it, if its because of aftermarket parts then adjust the mains.
Click to expand...

I did new o-rings, but not intake boots. The boots seem OK to me. The exhaust is stock and there is a leak in the rusty crossover pipe, could that cause this issue? I plan to address this by cutting out the rusty crossover and replacing it with new sections of pipe, I just haven't gotten around to that yet. No aftermarket parts that I'm aware of and jets are all standard size. My airbox looks like this, I only see one place I could add weather stripping which is on the lid to the filter housing. I'll look into doing that.
 
exzachtly1 said:
Went for a 20 mile ride today with the petcock on PRIME. This made no difference in the power issues :cry:

Seems to struggle around 4.5-6k RPM depending on what gear I'm in. Just loses power and sputters......
Click to expand...
It takes alot of fuel flowing thru petcock to refill carbs as revs/power goes up- If your petcock is gunked up, it might not deliver even in prime spot. Get a new one and eliminate the petcock as a problem.
Personally, I doubt the need for gasket on airbox lid- air is flowing thru openings, so a little more shouldn't hurt . BUT, the lid should hold the filter element tight against its base - you need a good seal here.
 
Ordered petcock from z1 today, should be here Tuesday. Will post back with results!

Planning to order all new boots and clamps for both sides too... Just waiting a bit since this will not be cheap.
 
Well, I installed a new petcock but it is still exhibiting the symptoms. Seems like it might be slightly better but it's hard to tell... I'll have to take it for a longer ride this weekend and see. I'm glad I installed a new one though... it's amazing how much easier the handle on this one turns.

I guess it's time to turn my attention back to the other suggestions in this thread. I think I will order new airbox boots and clamps next time I get paid to get that ruled out. Intake boots will have to wait, but I doubt they're the issue. They really seem OK.

Could this maybe be a carb problem? I'm thinking of inspecting the floats again to make sure I got the float levels right, and double checking the slide diaphragms. Though if those are messed up I'm not sure what the heck I'll do.

It seems that it doesn't do it in first or second gear as bad, but it bogs noticeably in 3rd, 4th, 5th somewhere between 4 and 6k RPM.
 
I had a faulty stock igniter on a 1000G that displayed similar symptoms. Chased it for ages thinking it was fuel related....

Maybe your aftermarket ignition is doing the same... What ignition does it have on it?
 
exzactly1 said...
"Seems to struggle around 4.5-6k RPM depending on what gear I'm in"

Could be ignitor or maybe the timing advance is stuck- remove signal generator cover and see if weights move freely.
 
salty_monk said:
I had a faulty stock igniter on a 1000G that displayed similar symptoms. Chased it for ages thinking it was fuel related....

Maybe your aftermarket ignition is doing the same... What ignition does it have on it?
Click to expand...

I'm not sure how to tell. The coils and wires are yellow; I can take a picture later maybe if that would help. Would it be printed somewhere on there?

salty_monk said:
Did you adjust the valves yet? Always good practice...
Click to expand...

I have not done this yet. It's on my list. You're talking about the clearances right?

tom203 said:
exzactly1 said...
"Seems to struggle around 4.5-6k RPM depending on what gear I'm in"

Could be ignitor or maybe the timing advance is stuck- remove signal generator cover and see if weights move freely.
Click to expand...

Is there a tutorial on the bikecliff site for this? I'm totally new to doing anything with the ignition system so I might need some more guidance here.

Thanks guys.
 
Add one more thing to your check list:
Make sure your needle jet's spacers/washers are in proper sequence. Pay particular attention to placement of thick plastic washer (#7) and thin metal washer (#36). Mine were swapped and caused the 5K rpm stumble you speak of... basically allowing needle to "flutter" under roll-on. You'll need ring pliers with long tines to remove the circlip (#10) to disassemble slides and thus check needle jets.

Hope this helps.

2150_11.gif
 
Interesting, thanks Frank. I'll check that too next time I have the carbs off. I have not messed with those myself but perhaps another owner did.
 
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