XR650R stock carb headaches


16 replies to this topic
  • big bore

Posted August 09, 2008 - 08:47 PM

#1

Flat spot in acceleration on this 650R that I bought last month. When your in gear except 1st, you suddenly go wide open throttle, the bike accelerates but at a certain revs it coughs for a few seconds as it works it's way through that rev range. eg 4th gear slow revs, give it full throttle and it when it gets to the bad rev range it coughs and splutters. Once your past that bit it goes OK right to the top of the revs.

So I pull the carb just to see what jetting it has.
Stock carb, uncorcked
175, 3rd notch, 65S pilot

So I lean the needle by 1 clip position(2nd notch now) and put it all back togther. Now the bike revs a bit higher at idle on it's own. I'll stop at the lights and the idle rises and stays high. It drops toi normal when I snap the throttle but rises again after 2 seconds.


1. What is causing the flat spot.
2. Why is my idle revving up on it's own

Can I rule out the new needle position for causing the idle problem. I have given the pulling cable 1-2mm of freeplay and the returning cable about 1mm of freeplay

  • big bore

Posted August 09, 2008 - 09:23 PM

#2

OK I've sorted out the flatspot. I removed the stock(already drilled) exhaust tip and rode bike with no exhaust tip and no more coughing/flat spot in mow revs full throttle.

But what is more worrying is the new high idle. It's like the bike has 2 different idles depending on how it feels altough the hiher idle seems to be dominant :D . I am thinking it is fuel mixture because when I snap the throttle the idle drops back down to normal (like it was before I pulled the carb). :banghead: :) :worthy: .....:banghead: .....:ride:

arggghhhhhh

But the idle problem can very well be mechanical. Just hoping someone has sorted it out in the past and will chime in with some advice.


I actually had this idle problem on my 97 XR600R. After the workshop put a new cam chain in it I got the bike back this same problem. Although the 600 hangs much higher and is almost dangerous. Wether or not the workshop touched the carb on the 600 I donknow, but I was almost going to buy a new slide (flatside carb on the 600). Still not sure what it is. But I would like to sort it out on the 650 as it is my baby ATM.

  • eastreich

Posted August 09, 2008 - 09:56 PM

#3

A hanging high idle is an indicator of a lean condition. IMO this is a problem with your slow circuit, not something mechanical. It has been a long time since I have had the stock carb on my 650R, but even at 7000 ft I never varied from a 68S pilot with the big round slide Keihin.

Try working with your air screw to correct the high idle. Turning the air screw in will fatten up the slow circuit. If you can correct the hanging idle by turning in the airscrew, count the total turns out of the screw from the bottoming out point. If you are equal to or less than one turn out, you need to increase the size of the pilot. Proper adjustment of the slow circuit should allow the air screw to be set between 1.5 and 2 turns from bottomed out for proper idle.

  • big bore

Posted August 09, 2008 - 10:14 PM

#4

A friend just suggested that it could a leak from the air boots not being on correctly. Will check that but want to know a few other things to try before I take the seat and big tank off again.

Just to clarify EASTREICH, the idle goes high on it's own, not when I rev it. It creeps up and stays up and never comes back down. If I snap the throttle it comes back down to normal for a second or two, then goes back up again. It was fine this afternoon before I pulled the carb, all I did was lean the needle 1 clip.

  • scalejockey

Posted August 09, 2008 - 10:24 PM

#5

A 175 ? That's pretty fat.are you at sea level? A 170 might clean up the jetting.
As far as the high idle check the float level and air jet.Or the pilot might be partialy plugged.

  • big bore

Posted August 09, 2008 - 10:51 PM

#6

Yes at sea level. But that cough problem is not gone but I know what is is now. (rich main jet)
------------
So, that idle problem is fixed now at the moment. I'm not counting chickens though (before they're hatched).

The carb boots were on properly and clamps done up snug(ish). I tightened them a fair bit more and the idle problem was gone when I did a short 5 min test ride.

So Eastreich was right about the lean condition. Maybe check your air boot clamps and jet the idle alittle richer for those with hanging idle problems. I still have the normal hanging idle that you expect from XR's but the annoying really high creeping idle is gone. Although the removal of the exhaust tip on and off didn't effect idle, guess that would affect more at hgiher engine speeds (mainjet).

I will put in a 68S pilot jet next.

Which one is the idle fuel screw? Think there are 2 screws on the right side not including the idle speed screw on the left side.

  • big bore

Posted August 09, 2008 - 11:43 PM

#7

http://www.factorypr...ch/carbtun.html

read point 3

"3. Then, adjust the BEST Float Height for BEST FULL THROTTLE / LOW rpm (many Honda's excluded because floats are not adjustable) -
You should be able to apply FULL THROTTLE at LOW RPM in TOP gear without ANY misfire of bogging or stumble......."


Sounds like the problem I have that was fixed when I rode with no exhaust tip.

Would I have to raise or lower the float fuel LEVEL ?

  • big bore

Posted August 10, 2008 - 02:34 AM

#8

OK third post in a row.

I'm now trying to work out if I need to adjust the float level(I'm guessing lower fuel level) or go a smaller main jet.

The flat spot with WOT in low revs, went away when I rode it with NO exhaust tip on the stock cannister.

hmmmm main jet or float level :)

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  • Kenzo

Posted August 10, 2008 - 05:42 AM

#9

ur pilot is too small causing the hanging idle and a lean condition...

...hell i run a 65s on my L with the R carb swap and wud assume the R wud need more fuel than my L...

check the pilot and adjust the fuel screw per this thread http://www.thumperta...ad.php?t=327405

the R boys shud chime in but at least a 68s or 70s is my guess for the proper pilot jet...

and make sure EVERYTHING has been done per the uncorking instructions here http://www.4strokes....da/650rmods.asp

and here http://www.4strokes....nda/uncork_brp/

:)

  • big bore

Posted August 11, 2008 - 02:25 AM

#10

Bike is well and truely uncorcked except the stock baffle is drilled out.
175 3rd clip, B53E needle, 65S pilot

I don't really want to touch the float level unless it's recommended because I've never played with the float before.

  • phyjy

Posted August 11, 2008 - 02:47 AM

#11

Hey mate!!!
From oz myself, get the 68s pilot first and work from there.
I reckon your main jet is a little to high depending on the temp/elevation where you are.
If you apply full throttle from low/medium revs for 2 secs, say in 3rd gear, and then slightly back the throttle off and if it coughs then it could be two reasons....restricted air flow or main jet too big.
Have you got an after market air filter??

  • big bore

Posted August 11, 2008 - 09:45 AM

#12

[quote name='phyjy']Hey mate!!!
From oz myself, get the 68s pilot first and work from there.
I reckon your main jet is a little to high depending on the temp/elevation where you are.
If you apply full throttle from low/medium revs for 2 secs, say in 3rd gear, and then slightly back the throttle off and if it coughs then it could be two reasons....restricted air flow or main jet too big.
Have you got an after market air filter??[/QUOTE]


No.

I posted this in the jetting forum and Burned saidthat because it's not a pumper carb it will always bogs with WOT from idle, no matter what the jetting.

Then how come the problem goes away when I ride with no exhaust tip (leaning it out).

  • Kenzo

Posted August 11, 2008 - 11:56 AM

#13

I posted this in the jetting forum and Burned saidthat because it's not a pumper carb it will always bogs with WOT from idle, no matter what the jetting.

Then how come the problem goes away when I ride with no exhaust tip (leaning it out).




i had the same issue on my R to L carb swap...first u gotta get the jetting right...i wud try the 68s & 170/172...install a good foam air filter and set ur fuel screw...then see how it runs

also check what happens if u remove the airbox cover...

then if u still have the off idle bog (i had the same issue) the typical way to minimize it is to lower the needle clip to richen the mixture...it is correct that without a pumper there can be a hesitation but it can be reduced to a non-issue with the proper tunning and controlling ur right hand a little better...

ur probably getting the bog from being way too rich on ur main jet and removing the tip gives it the air it needs...ether extreme, too rich or too lean can cause the problems

:)

  • phyjy

Posted August 11, 2008 - 04:59 PM

#14

Kenzo has it in a nut shell....get your jetting right to what he quoted.
Do lap around the street without your airfilter and see how it responds.
Don't work from your exhaust and work back, get the basics right.

I live in Perth, at sea level, have a 2005 xr650r, 168main, 68s pilot, exhaust tip drilled out. To tell you the truth I could even drop the main down to a 165!
Reason being, I at times can find a certain parameter where it does a slight cough telling me the fuel flow's too rich.People will probaly say that 168/165 is too lean...but I read my spark plug and it could'nt be any sweeter:thumbsup:

Some good advice I got:
"tune the main jet until engine performs best at wide throttle,
tune the pilot jet for best idle & super small throttle openings,
tune needle for best steady partial throttle"

  • J_T

Posted August 11, 2008 - 07:21 PM

#15

I don't know OZ weather...but Humidity has an effect as well as sea-level. at 300MSL and 80% humidity and 90-95F temps in the summer it ran well and even better in the winter! I ran 175 68s as well as the same needle you have (But don't remember anymore the clip position) I'd buy the pilot jet and a 172 as well a good foam airfilter (not K&N) and I know you will have what you need to get it spot on! Swap the air filter and the pilot jet first and leave the main in the package...if it fixes it...return the main jet...or swap it out as well to curb your curiosity if your 175 is the best jet?

  • big bore

Posted August 11, 2008 - 07:36 PM

#16

My buddy has the same bike and jetting but he has a staintune header and muffler on it and doesn't have the problem.

The 175 is the recommendation in Honda's letter to the dealers (along with the other uncorking mods) for when they uncorck XR650R's for the customer. And me being at sea level, the 175 (with the proper uncorking mods), should be correct. But I will try a 172.

I have the stock tip drilled but I have ordered the proper HRC style tip for $40 delivered off ebay - which should give that tiny bit extra airflow.

  • drtrider145

Posted August 11, 2008 - 08:08 PM

#17

just a suggestion but take the fuel line off and make sure your petcock is not plugged and or your vent is venting , same problem high crazy idle and after about 5-8 min of riding high idle and conk out and stall then I realized I have my race bike fuel cap on my trail bike tank , race bike has a vent in the tank and not on the cap and the trail bike has a vent on the cap and not in the tank , changed caps bang back in business good luck





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