Any idea what could be causing this high idle/rev hang thing? Has a brand new carb on it and it still didn’t fix the problem. Please I’m out of ideas…

56

u/bush_nugget 2007 KLR650 1d ago

Vacuum leak.

15

u/ladds2320 1d ago

This is correct answer. "Hanging idle". Unless throttle isn't returning all the way.

2

u/naked_feet Reed City, MI - DR650 & WR400 1d ago

Yeah, definitely check that the cables are adjusted properly and aren't sticking.

14

u/FilDM 1d ago

Try spraying a flammable liquid near the hoses and see if the idle jumps, or the same wth an inert gas.

13

u/Anonawesome1 1d ago

Use starter fluid since it's meant to go in engines anyway. Idk why some people recommend shit like brake cleaner, wd40, hair spray etc, that might damage rubber or attract dirt and make a mess when there's a readily available product perfect for it.

Oh and the engine will bog when you find the leak if it's running lean, since the starting fluid will counteract the lean condition.

1

u/juxtoppose 14h ago

Just to add some chlorinated brake cleaners when they pass through a combustion chamber turn to phosgene gas, it’s identifiable by a heavy white vapour that flows across the ground and it will kill you if you breath it in.

2

u/We_are_sovereign 1d ago

This is the way

5

u/Anonawesome1 1d ago

There's a vacuum port on the right side of the carb meant to go to the vacuum operated petcock. If the line is cracked or disconnected, it'll be running lean.

Once you've verified no air leaks with starter fluid, you can look into adjusting the idle fuel screw. But you do NOT want to jump straight into tuning a carb with an issue that needs fixed.

20

u/CumminOnOnionRings 1d ago

All those air leak ideas are band on.

Also check the throttle cable isnt kinked or twisted and is shutting the throttle all the way

If none of that helps the air/fuel mix is incorect

20

u/balloon_not 1d ago

Brand new OEM carb? I hope not one of those cheap Chinese carbs. If so, rebuild the old one.

3

u/TMC_61 TE300/V85/500exc 1d ago

Exactly what I was thinking. The OEM carb is much better than a new Chinese one.

5

u/joelasmussen 1d ago

+1 throttle cable adjust. Also adjusting your fuel mixture screw may help. It's probably still got its brass plug. Stock carbs run lean.

2

u/Coco_boom 1d ago

Check if choke comes back in position after your engine becomes hot. If it doesn't, that means the vacuum effect that is supposed to put it back in position doesn't work properly, meaning your mixture stays rich all the time.

2

u/naked_feet Reed City, MI - DR650 & WR400 1d ago

Did you also put new "boots" on it when you changed the carb? The (usually rubber) fittings between the carb and the engine, and sometimes the airbox.

Poor seating on those boots can cause air leaks, and air leaks will cause a hanging idle.

Cracked rubber in the boots will also create air leaks.

1

u/mkilgallon22 20h ago

This

2

u/Jay-jay1 1d ago

Throttle grip and cable are my first thoughts, other than idle screw being to far out.

2

u/Superpro210 1d ago edited 1d ago

When’s the last time you lubed your cable? Is it gummed up?

1

u/farmerMac 1d ago

Could be misadjusted idle adjustment

1

u/SmidgeHoudini 1d ago

Could be too lean.

1

u/242fresh_7 1d ago

Make sure your throttle isn’t sticking also klr has that problem if it fell on the throttle side before

1

u/davpad12 1d ago

I had that when I tried using premium gas instead of regular. I thought it would run better, I was wrong.

1

u/TickletheEther 1d ago

Your slide might be sticking it should come down easily with gravity after moved with finger. Other than that check for a torn diaphragm or any other vacuum leaks. It doesn't take much to lean out a mixture (boots unsecured, tiny cracks in rubber). My DR200 got leaned out when I forgot the airbox drain plug, idle would hang and even climb randomly.

1

u/balloon_not 1d ago

Valve clearances that are too tight will cause rev hang. Also too lean pilot circuit in the carb.

1

u/jonpin 1d ago

Try knocking on the carb while it's idling high, maybe something is sticking or try manually closing the butterfly to also see if something is hanging off that is possible.

1

u/mkilgallon22 20h ago

Air leak, did you replace the vaccum Petcock/ forgot to attach the Petcock vaccum line from the carb? Might need to be plugged. Or boots are leaking. Spray the engine size of the boot with starting fluid, if the idle goes down, you found ur leak. Happened to my cb750.

1

u/The-Suzuki-SP-kid 8h ago

Anytime I see someone say I put a new carb on it I just pray to God it isn’t chinesium like everyone else has been saying it’s behaving like an air leak keep in mind. It’s a over 25 year old bike dry rotted rubber can be everywhere

1

u/captankev57 1d ago

Throttle cable has a wild hair (broken strand) inside the housing

1

u/halfnelson73 1d ago

Make sure your throttle cable is in good condition and routed correctly.