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Discussion Starter · #1 · (Edited)
I recently bought a 2005 KLR 650 (stock) that had been sitting all winter and barely ran (ran fine before parked). Cleaned the carbs and put new gas in and started right up! Took off on it and after 10 min of riding it started to cough and seemed like it was running out of gas upon acceleration. I pulled over and it idled fine. Got moving again and it was fine through a few gear changes, got back up to speed and then same problem. If I go 1/4 throttle or less it has no problems but as soon as I get into it it wont rev. My max speed at is like 40 mph. If I turn on the enricher I can then max out a little faster but still wont rev right.
I checked petcock and have good flow from there, mixture screw is 2 turns out, floats are correct height, carb has been cleaned multiple times, and gas cap vent rebuilt/ran with cap open. None of that made any difference. The symptoms are leading me to believe that fuel is getting to pilot jet but, there just isnt enough fuel getting to the bowl for main jet to draw on. Like maybe it fills up but slowly so when I am at a light or stopped it catches up, but then one Im going it can no longer keep up. Everything I check though seems to point to it getting a constant healthy flow of fuel and when I open the bowl drain theres still a bunch there!
2 other things that may be of note:
If I shut off the petcock, take the fuel line off the carb and look down it while the bike is running, the gas stays at a steady height and then it will drop as the fuel is used a bubble will come back up. Maybe thats normal but I would have thought it would have been a steady decrease with no bubbles. I checked the clear vent tube and it is clear.
Once it ran fine with no issues. rode for a few hrs and didnt stutter at all. Also once it was giving me the normal problem and I puled over and tapped the carb with a wrench thinking the floats maybe stuck closed and it fixed it! Rode for 30 min or so home after with no problems. However next time I took it out it was back to its sorry ways and that trick has never worked again.
Any of yall had this happen or have any ideas?
 

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2014.5 KLR650
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Possibly a clogged gas cap vent ... try running with the cap loose ...
 

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Discussion Starter · #4 ·
Possibly a clogged gas cap vent ... try running with the cap loose ...
Forgot to add it, but I also rebuild gas cap vent and when that didnt work, tried running with cap open. Still not good.
 

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2013 KLR 650/692, 2017 HD Electraglide Ultra
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The only thing that could cause that behavior is the carb. You may think you cleaned and reassembled it, but something still ain’t right. See Tom’s video about cleaning and adjusting the CVK.
 

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The symptoms are leading me to believe that fuel is getting to pilot jet but, there just isnt enough fuel getting to the bowl for main jet to draw on. Like maybe it fills up but slowly so when I am at a light or stopped it catches up, but then one Im going it can no longer keep up.
The pilot jet is very high up inside its tower by quite a bit as compared to the main jet, that lives at the very bottom of the float bowl near the drain screw.

You could attach a drain hose to the float bowl drain and Confirm that the fuel tap, float needle and drain screw can flow at least 3 gallons per hour / 6.4 ounces per minute. That is enough fuel flow for 35mpg at 105 mph running WOT on the main jet.

Have you removed the fuel tap from the fuel tank & cleaned the screens with aerosol carb cleaner or soaked the entire fuel tap in Pine-Sol.
 

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2013 KLR 650/692, 2017 HD Electraglide Ultra
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Because you can get better running by adding enrichment, and taking off the fuel cap doesn’t make a difference, I don’t think it’s a fuel flow problem, but as PDW suggested, it’s easy to check for fuel flow from the carb drain. So do that.

If that flows well, then make sure you got the carb diaphragm seated in the groove of the carb body. Otherwise, I think you still have some blockage of the main jet system.
 

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My bet is a severely damaged throttle slide diaphragm, leaking vacuum so badly that it won't lift the side at all.
So with out the slide lifting with proper vacuum, the engine will only rev to about 3000 rpm.

Will probably need to purchase a throttle slide & diaphragm assembly from 1990's Harley Davidson Sportster to save about 60% price.
 

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Discussion Starter · #9 ·
My bet is a severely damaged throttle slide diaphragm, leaking vacuum so badly that it won't lift the side at all.
So with out the slide lifting with proper vacuum, the engine will only rev to about 3000 rpm.

Will probably need to purchase a throttle slide & diaphragm assembly from 1990's Harley Davidson Sportster to save about 60% price.
I just took the carb off and cleaned it (AGAIN) and that did not fix the problem so im convinced that is not a blockage or anything. I looked carefully at the slide and diaphragm and it all appeared fine, but now im thinking maybe a pinhole that only exposes itsself after the rubber heats up or something. Also noticed the decel valve diaphram is noticably worn and I'm certainly backfiring on deceleration, so that further confirms the rubber in the carb isnt 100%.
1990 Sportster will fit it? Brilliant, thanks for the tip!

The pilot jet is very high up inside its tower by quite a bit as compared to the main jet, that lives at the very bottom of the float bowl near the drain screw.

You could attach a drain hose to the float bowl drain and Confirm that the fuel tap, float needle and drain screw can flow at least 3 gallons per hour / 6.4 ounces per minute. That is enough fuel flow for 35mpg at 105 mph running WOT on the main jet.

Have you removed the fuel tap from the fuel tank & cleaned the screens with aerosol carb cleaner or soaked the entire fuel tap in Pine-Sol.
Yep I took the petcock off and cleaned the whole thing!
 

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Discussion Starter · #10 ·
My bet is a severely damaged throttle slide diaphragm, leaking vacuum so badly that it won't lift the side at all.
So with out the slide lifting with proper vacuum, the engine will only rev to about 3000 rpm.

Will probably need to purchase a throttle slide & diaphragm assembly from 1990's Harley Davidson Sportster to save about 60% price.
Well I replaced the slide diaphragm and rode 30 min on the highway at 80mph with no issues. Then got off the highway almost home and it started again. Same exact problem. VERY annoying.
 

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Check the float bowl atmospheric air vent hose from the upper LH side of the carb does not have any obstruction in it.

I have seen some roughness on the face of the plastic carb tops and some warpage of those caps that can cause vacuum leakage.

Also check the underside of your air filter box for a melted hole from exhaust gas leaking from the exhaust Joint.
 
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I had wonky issues with running at throttle - turned out that the paper element fuel filter would not feed enough juice at highway speeds.

So - are you running a filter in the fuel line?
 
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Discussion Starter · #13 ·
I had wonky issues with running at throttle - turned out that the paper element fuel filter would not feed enough juice at highway speeds.

So - are you running a filter in the fuel line?
I am not running an inline fuel filter and the stock petcock filters are clean and flowing great!
 

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Discussion Starter · #14 ·
Check the float bowl atmospheric air vent hose from the upper LH side of the carb does not have any obstruction in it.

I have seen some roughness on the face of the plastic carb tops and some warpage of those caps that can cause vacuum leakage.

Also check the underside of your air filter box for a melted hole from exhaust gas leaking from the exhaust Joint.
Vent hose is clear, at one point in its life it got melted a bit and I trimmed it shorter, but other than that its all good.

I took the cap off and it was nice and smooth and as far as I could tell it was flat. I did go out of my way to clean it really well and maybe I can now go a little faster before I have problems??? also maybe I just want to believe that... lol.

No melted holes in the airbox.

Thanks for all your suggestions! I was hoping to get this going cheap, but I think im ready to just get a new to me (used) carb and be done with it. Or hopefully be done with it. This is rediculus! It feels so close to running well and yet so far away too. haha
 

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Damn. 30 minutes later it starts acting up again. Well, at this point, I’d probably be looking for another carb too. Just remember that the “new” carb will have its own problems. When you get it, make sure it has the STOCK jets in it. That way you start with known characteristics. And then clean the corn syrup crap out of it throughly, yadda, yadda…
 

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at higher rpm the vacuum pulses are faster and shallower which affects leaking diaphragm in the petcock.
I will disagree. The faster/shallower vacuum pluses will keep the fuel tap diaphragm open 'better' than at near idle speeds.
 

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disagree all you want, he's probably sucking fuel through the vacuum line and the fuel tap is barely opening. Hence the odd symptoms


the other things that could be related,
coil going when it heats up
worn FUEL nozzle (needle jet) (one of the only wear items in a CV carb) , causing a rich mixture and consequently a misfire when the engine reaches operating temp (High mile bike)
plugged air jet
dirty air filter
low compression

all these will cause a mid range miss.


probably the fuel tap, nearly half of them older than 4 years are leaking around the center post that goes through the diaphragms.


30235


I will disagree. The faster/shallower vacuum pluses will keep the fuel tap diaphragm open 'better' than at near idle speeds.
 

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Discussion Starter · #19 ·
vacuum fuel tap failing. at higher rpm the vacuum pulses are faster and shallower which affects leaking diaphragm in the petcock.

convert to vacuum less free here

www.facebook.com/MegaCityPerformance/photos/a.244136713802978/345362043680444

or here
Ive tried pulling over when this problem starts and then removing the fuel line with the bike held at full throttle and stuttering and it still is a solid stream of gas just like when it is first starting up and running fine. Also when I remove the fuel line while its having issues there is still plenty of fuel in the line to the carb so i've pretty much ruled that out. Ill look into the other things you mention if the new carb doesn't fix it as well as go to the vacuumless system just to rule any issues with that out. New-to-me carb comes in today so fingers crossed that takes care of it!
 

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you're not accounting for the raw fuel getting sucked in through the vacuum line, which was the Whole point of my post.

I don't think you're running out of fuel, you're Flooding, potentially.

obviously its an educated guess, i'm not there to troubleshoot it . I've seen it before and about half the fuel taps out there more than 4 years old leak raw fuel into the intake tract through the vacuum line, to varying degrees.

piss poor design



Ive tried pulling over when this problem starts and then removing the fuel line with the bike held at full throttle and stuttering and it still is a solid stream of gas just like when it is first starting up and running fine. Also when I remove the fuel line while its having issues there is still plenty of fuel in the line to the carb so i've pretty much ruled that out. Ill look into the other things you mention if the new carb doesn't fix it as well as go to the vacuumless system just to rule any issues with that out. New-to-me carb comes in today so fingers crossed that takes care of it!
 
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