Help with Mid-Throttle Stumbling

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Help with Mid-Throttle Stumbling

Post  shane3 on Tue May 19, 2015 4:25 am

2001
68s
175 main
comp needle 3rd slot
cut out carb restrictor plate
air box unrestricted and side panel drilled (factory foam filter)
exhaust drilled but previous owner cut off spark arrestor so its basically just the stainless tip
Elevation 500ft

Starts up and idles fine, but idle is highest when screwed all the way in. Runs fine up until 3500-4000 rpm then bucks and sputters. If I go full throttle I can get past the sputtering and it runs ok, but still not as much power as it should. Plug is black and sooty. If I run it with choke half on, symptoms are worse. Running with air filter and side cover off doesn't help. If I turn off petcock, symptoms go away until it stalls.

I cleaned the carb, set valves, lowered float to 18mm.

I'm going to remove the petcock and check for flow tomorrow.

Any other ideas?
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Re: Help with Mid-Throttle Stumbling

Post  Mauser on Tue May 19, 2015 7:58 am

Won't be fuel flow problems she is running mega rich, try raising the clip up bit to lean her out in fact try heron position 1.....
Anyway who are you ?

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Re: Help with Mid-Throttle Stumbling

Post  BuRP on Tue May 19, 2015 8:35 am

Needle & Seat do actually close off the fuel flow?
Besides, std floatlevel + 1mm (= 19mm total?) is the level you should adhere too to prevent pi$$ing when on a sidestand. And, as always, check valveclearance first...
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Re: Help with Mid-Throttle Stumbling

Post  shane3 on Tue May 19, 2015 11:24 pm

Turns out, it was just running really rich.  Moved the needle to the first groove and it runs good.  I just thought it was strange to be that far off from what it seems like most people run.  

Do you think cutting the intake manifold coupler as opposed to buying the nice smooth oem one has anything to do with it?  Either way, I ordered one so I will see if that changes anything.

I am a big car guy but completely new to bikes so I really appreciate the help!

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Re: Help with Mid-Throttle Stumbling

Post  Mauser on Wed May 20, 2015 8:04 am

Wow my advice worked....that's scary lol.....to be honest for what the intake manifold costs (Carb Isolator) as we call it I wouldn't bother.
Bit strange how the bike has been uncorked but someone forgot the carb isolator ? as for jetting check out our sites guide....
http://www.xr650r.co.uk/service/jetting/jetting.shtml

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Re: Help with Mid-Throttle Stumbling

Post  shane3 on Sat May 23, 2015 9:07 pm

I put in the new carb isolator and still have to use the first slot on the comp needle to get it to run well. I also have the 68s pilot and idle is highest when it is all the way in. I also installed a uni filter.

Do these setting seem really strange for sea level and 90 degrees?

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Re: Help with Mid-Throttle Stumbling

Post  BuRP on Tue May 26, 2015 12:01 pm

Yes - all you mention points to super rich running.
You better find the reason for this, and my wildest but bestest guess would be the airfilter - new UNI you say?
Take it out, fold it into a fresh clean kitchen towel, and squeeze all oil out which you can.... and then put it back (fwiw, this is how a foam filter must be oiled, nothing more).
Any improvements perhaps?
If so set the clip back to where it was, it's in the wrong place plus - and zero offense to anyone - it makes a too small difference to notice but for top-end runs, in other words it did change almost nothing.
If not I'd leaktest the needle & seat assy - does it actually really seal off the fuel flow? Could be that while running vibrations cause it to leak ie the 'effective' floatlevel is a lot higher... and that will cause rich running!
You've got some work cut out bru, get cracking! BRP smile
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Re: Help with Mid-Throttle Stumbling

Post  shane3 on Fri May 29, 2015 3:16 pm

So, I was just cleaning my carb again and had a question about these holes.

The one on the bottom right seems to be clear and spraying carb cleaner in comes out at the needle jet.

The others seem to be be blocked (spraying carb cleaner in just sprays back). Are these all supposed to be free?

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Re: Help with Mid-Throttle Stumbling

Post  Zoro on Fri May 29, 2015 4:14 pm

Yeah they should all flow through, they're the air bleeds.
Try some compressed air if you have it available.
Watch the carby cleaner with rubber diaphragm on the fuel cut off valve. Good chance it will ruin the rubber.
I have blocked the vacuum port that actuates that valve, not needed imho.
Make sure the tiny holes on the sides of the emulsion tubes (where the jets screw in) are clear also.

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Re: Help with Mid-Throttle Stumbling

Post  Chris_w_65 on Tue Aug 18, 2015 7:51 pm

Nice motard shane3. Do you get chain rub on your rear tyre? What size rear tyre do you have on there?
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Re: Help with Mid-Throttle Stumbling

Post  shane3 on Wed Aug 19, 2015 2:36 pm

Thanks! I have a 150 on the rear and it was rubbing a lot. I used a grinder and shaved off about 8mm off the tire which helped.
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Re: Help with Mid-Throttle Stumbling

Post  Chris_w_65 on Wed Aug 19, 2015 2:56 pm

shane3 wrote:Thanks!  I have a 150 on the rear and it was rubbing a lot.  I used a grinder and shaved off about 8mm off the tire which helped.  

Why use a grinder, the chain does a good job Very Happy
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