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loss of power at high rpms

  • Thread starter Thread starter justarider
  • Start date Start date
J

justarider

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I have been riding my 85 gs700 for a few weeks now and its been running fine.

Just yesterday I went onto the freeway and tried to get my speed up. When I get to high rpms it feels like the throttle is cutting out or something and I lose power then as the rpms come down I regain power. It creates a very unpleasnt ride and I can barely get to 70 mph.

Also as I was coming into a stop sign after I got off the freeway I pop'd into first gear and released the clutch to fast and the engine just died on me. when I started it, it died right off. I restarted and the engine felt very weak, could barely drive. After a few mins of driving like this the engine seemed to recover.

I have driven it at 80+ with none of these problems before.

I put to much oil in before but the mechanic said it was ok. but oil leaks when I park more so after driving at high speed. Sometimes covering the gearbox, and once i had oil on my boot after freeway driving at high speed. is it possible that my air filters are just dirty?

any ideas and tips on what is wrong would be appreciated.

thanks
 
Last edited:
I've been haveing this trouble just yesterday and today. WTF??

No power and bogging. It was fine two days ago. I think I need to check my compression.

It started to smell rich yesterday. Can the carbs goof up on their own? I used ATF on the filter when I cleaned it last week. Could it be that it cleaned the air TOO much and plugged?
 
justarider,

your problem sounds like fuel flow into the carbs. Check your petcock. Check the fuel hose for any place where a bubble could get trapped. Check that your gas tank cap can vent air properly. These bikes have a vacuum operated petcock which requires engine vacuum from carb #2 (you should see the hose going to the petcock). Check that the vacuum petcock is operating correctly by sucking on the vacuum hose and checking the fuel flow. You should taste no gas (no leak into the vaccum hose).

The petcock has a fine screen attached to it. Drain the fuel from the tank (using a long hose and setting the petcock to PRIME) and remove the petcock. Clean the screen of any particles. Be careful its fragile, just shoot some carb cleaner at it.

That's all I can think of right now.

It could be the problem is something totally unrelated but I would start with the above stuff and work my way closer to the motor from there. If the fuel flow checks out then the next place to look it the carbs and the electrical.

-D.
 
Billyboy,

it's a good idea to check compression every 5k miles or so. Just so you know where you stand and how things are progressing. Keep a record of it in your shop manual along with the tappet clearances and your record of oil changes and anything else your do (you are keeping a careful record of this aren't you? :)

Running rich is usually a carb problem. Check your spark plugs for carbon/soot deposits. If the plugs are clean then, check you fuel delivery system (see the above posting) and your electrical system (using your voltmeter). Start with these.

-D.
 
OK. Checked my compression. All good. 110 - 125.

HOWEVER...

Did a chop test. #4 plug is shiny ??? WTF does THAT mean? It's hot, pipe is hot. Somethings fishy.

Maybe timing?
 
Ok. Today I dumped my oil and put in new oil. Also tried to clean the one filter that was covered in oil. After all this I took it for a spin and noticed that I seem to lose power around 5-6k rpms but once I got past 6 it ran fine. although I only tested this in 2nd and 3rd gear as I was only on side streets. I also noticed that now that I don't have to much oil it is alot easier to shift gears, which is great cause I had a hard time shifting into neutral while stopped at lights, etc.

I have heard the opinion that I just have some bad fuel so I got some fuel system cleaner and plan to use it once my tank is empty(almost) and buy some better gas.

I have a question about the cleaner I bought it at autozone and the directions say add to an almost empty tank and fill up to 21 gallons. now see'ing as I only have a few gallon tank should I use the whole thing(less then a quart) ?

thanks.
 
Billyboy said:
OK. Checked my compression. All good. 110 - 125.

HOWEVER...

Did a chop test. #4 plug is shiny ??? WTF does THAT mean? It's hot, pipe is hot. Somethings fishy.

Maybe timing?
Click to expand...

Plugs come out clean sometimes even if the cylinder is working fine. Over time I would expect some tan deposits to build up on the insulator but the metal parts may be shiny for a long time.

So if the bogging happens at open throttle (RPM is not an issue with carbs so much as throttle position) then you either have too little fuel getting to the carbs (problem with petcock, hoses) or the carbs are having trouble sending the available fuel into the motor (clogged jets, clogged float valve, sticky slider).
 
You are not running an aftermarket inline fuel filter spliced into your 5/16th fuel line, are you? It is definitely 5/16 ID fuel line, yes?
 
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