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XR500R Loading Up When Twisting Throttle

14 posts in this topic

I have a just restored 84' XR500R that is loading up/lagging when you twist the throttle open quickly. I have dipped, blown out,checked jets, and made specified adjustments to the carburators. The manual I have for this bike doesn't cover These two possible issues, carberators (2-carbs) sincronization, or diagnosing CDI timing advance. Please some suggestions?

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dual setup you said right? or single?

usually that is a jetting issue if you are sure you have no clogged or dirty carb jets or passages but i would be curious to all the jetting specs to help out more. Whats pilot, main, all the rest and any mods to the engine. Also is this fresh new fuel or some old stuff that was sitting in the tank while rebuilding.

WELCOME TO TT!!!!

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My mistake, I responded with information for my CR125 jetting by accident.

The jets on the XR500R is 135 mian jet Primary carb, 108 main jet secondary carb, and on both have 58 for slow jet. Again sorry for the mixup in information.

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im not a dual carb master but 58 pilots seem like they may be a little rich, are those needles in the carbs adjustable also? Where is your air screws in the carbs also?

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I have the needle at 3rd groove and air screw(primary carb has the only air screw) at 2.25 turns out.

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Even if the bike is completely warmed up and jetted perfectly, it will bog if you wack the throttle at low RPMs. This is because the carbs are not pumper carbs, so when the throttle is opened suddenly, there's a lot of air and not enough fuel... it takes a brief moment for the fuel to start flowing through the main jets and needle jets and get the proper mixture. (Pumper carbs don't have this problem because they squirt raw fuel into the ventui when the throttle is suddenly opened.) Just get used to rolling it on gradually, like from idle to WOT in about 3/4 second. You'll eventually get used to it and not notice the bog hardly at all anymore. Or try this (one of my favorite things to do on the 500): with the bike in 2nd gear, lay on just a bit of throttle and get the motor spinning up to about 3000 rpm (~15 mph). Now wack the throttle. Rips good, eh?

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It sounds like your carb is set up right, and your jetting is stock. I own both and 83 and 84 XR 500. Both are dual carb set ups but only the 83 is syncranizable ( honda stopped using the dualies i believe in 87 or 88). I used to live at sea level and my 84 was a wheelie machine, i now live at 6500 ft and the thing still rips it (its ca plated and smokes my buddies KLR 650). The issue i believe lies in your stator. Even if a bike is stored bad oil fries stators. I also own a coulple of XR 600s an 85 and 86. My expierence with my 85 was the stator. The bike started in about 3 to 4 kicks cold, ran great but bogged when i went past half throttle, i changed jets at least 7 times with no improvement. I replaced my stator from a parts 500 i had and no more bogging even when i get on it quick. Stators can measure within spec and still not function properly. My new problem is on my 86 600, it only bogs under load uphill through rough terrain when i am past half throttle. I believe this is an electrical problem also. I think new stators could solve both our issues. Just my 2 cents.

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I have a just restored 84' XR500R that is loading up/lagging when you twist the throttle open quickly. I have dipped, blown out,checked jets, and made specified adjustments to the carburators. The manual I have for this bike doesn't cover These two possible issues, carberators (2-carbs) sincronization, or diagnosing CDI timing advance. Please some suggestions?

I'm sure you can feel in the throttle when you open the second carb. How does it run till then?

reason I ask... My secondary carb needle and seat stuck on me a while back. So there was no gas getting to the secondary carb. Ran great till I hit the second carb, then it fell on it's face.

I know it's a really simple explanation. Check the simple stuff first. Yes it may be jetting, but make sure to start at square one.

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DGXR is right. Even with everything perfect, a big-bore 4-stroke without a pumper carb will bog if you snap the throttle open hard from a low RPM.

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Stock jetting "84 XR500R:

Main jet primary carb: 135

Main jet secondary carb: 108

Pilot jet: 55

Pilot screw opening: 1 1/8 turns out from closed

Needle position primary carb: clip in 4th groove

Needle position secondary carb: clip in 2nd groove

Float level: 20.0mm (.79")

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...on my R to L carb swap i wus have'n sum bogging issues even after it wus jetted perfectly...ended up raising the needle to the 5th clip position and it helped a lot...it's worth a try.

when i get bored and in need of a project i'll probably upgrade to the honda race needle...

:thumbsup:

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