HIGH RPM'S

[uknowme2goog]

I have 1980 XS 650 and recently... only when i am in gear and the rpm's get so high tothe point were i have to change up to the next gear the engine will start to lose power and or sputter and makes a poping sound.
If i shift to the next high gear it rides great again... why do i lose power at high rpm's?

 

[nj1639]

Depending on the RPM it could be when the slides/diaphrams take over.

 

[uknowme2goog]

ok...can you explain that in more detail and how do i fix it?

 

[nj1639]

Pre-face with "No expert on carbs here" but what I understand and have experienced is that you have an idle circuit, a mid-range circuit and then lift off when the slides come into effect. For years it seems, I've been running primarily at the top of the mid-range, hardly going over 4k RPM, rarely getting the slides fully taking over....and I may be full of shit, dunno, but if the diaphragms have holes in them they can fail and you wouldn't notice untill you were in the upper range of RPM's5K?

 

[nj1639]

http://www.amckayltd.com/carbguide.pdf

 

[rebel542]

It's called a rev limiter. Easy to hit in first but not so much the other four gears. Enjoy your bike. Hope this helps.

 

[Scrambled]

Sounds like you are just reving past the powerband , you don't need to redline every shift , once you get past a certain RPM you actually lose power.

 

[uknowme2goog]

I am far from redlining the bike in each gear... However, i should be able to push the bike a little in each gear without the poping/sputtering from the carbs.....

sounds like a few people are saying i need to have the carbs adjusted??

 

[Scrambled]

Maybe, could be an air leak or an exhaust leak or a combination of a few minor things needing adjustment. What do your plugs look like ? Are you running rich or lean ?

And you don't have to be right in the red before you start losing power , it all depends on what has or has not been done to the bike and if it is tuned properly .

 

[uknowme2goog]

hmmmm ok..the bike is not stock , is now a bobber..... u can see that in my profile picture..

the bike hasa set of drag pipes.... once the bike is warmed up there is very little poping from the exhaust......the plugs are good....they turn black but dry after a few months of weekly driving.. the bike is kick start only so i like the bike to kick by the second try... explain what u mean by a air leak? the bike runs good....no leaks, ides fine

 

[Scrambled]

Air leak is air getting in around the carb holders or another problem is with pod filters that don't fit right or have a lip in the rubber where they go on the intake. Another air leak problem is the exhaust leaking at the manifold. Both of those things cause performance problems and both cause some popping , pinging and power loss.

You say your plugs are black, so that means a rich condition = too much fuel not enough air . You may still have an air leak or airflow problem and a rich mix.

 

[weekendrider]

If you have an opening/crack/gap (on purpose or otherwise) under throttle the pressure is pushing the exhaust out. When you decelerate cool air can be pulled in the opening and the result of the cool air hitting the hot exhaust gases can cause popping.
Decel popping can also be caused by a lean condition with the fuel.
As far as running out of power at a low rpm you might want to read about the relation of pipe size and length to the power band range.

 

[Scrambled]

He is running out of power at HIGH RPM , going past the power band with a bike that is out of sync.

 

[weekendrider]

What is high? I didn't see any numbers. I do know some think running these at a constant 5K is off limits let alone touching the red line.
The vibrations only go away above 6K.

 

[jd750ace]

If it's got stock coils they could be taking a crap too. Tends to make them not want to run above about 4500-5K, at least in my limited experience.

 

[Purplezinger]

I have 1980 XS 650 and recently... only when i am in gear and the rpm's get so high tothe point were i have to change up to the next gear the engine will start to lose power and or sputter and makes a poping sound.
If i shift to the next high gear it rides great again... why do i lose power at high rpm's?

What is the RPM when you shift?

 

[lakeview]

Rev limiter is only a function on Fuel Injection bikes, no? If I understand correctly on these non-computerized engines the "rev limiter" is mechanical failure.

 

[gabecustom]

not so, my 07 v-star had a "fuel cut" rev limiter on its carbs.. till i took it off and replaced it with a eliminator kit. extra 500 rpms..

i will say this, it sounds like carb tuning to me.

 

[XSLeo]

Those carbs on your V-star Are $2000 dollar carbs and have a bunch of electrically controlled components. Almost fuel injection.
But yes It does sound like carb tuning. I suggest he read the carb guide.
If he has access to a factory manual it has a very good description of how the carbs work.
I have the Factory book for the 74 to 77 models. if you can find one at biker.net download it.
You will find copies over at the The XS650 Garage USA too. Also the later books.
A carb isn't a complicated device, but it does take a bit of study to understand just how they work. The Factory books descriptions will help you understand them.
Leo

 

[gabecustom]

I'm not going to argue with you on that, times change and so does the technology.
Question for you though, bs34's.. am i correct in saying the needle jet is a press fit? and when re-jetting for uni pods, will i need to change the needle jet?