xr650r jetting question...I am confused...

I posted before about having a bit of "stumble" or hesitation if I rolled on the throttle when going slow in 2nd gear, not whacking it open but quick enough as if you want to pull the front wheel up. When the rpms go up (above 3/4), the hesitation goes away, it is only evident at a certain point in the throttle range.

bike is uncorked with a full yoshimura offroad and a uni-air filter with a couple of holes in the side cover with the round vents installed.

The plug looks good, maybe a bit dark (rich) (chocolate brown, dark tan).

Since I got the bike used and it started no problem (1st kick normally) and ran really well (minus the hesitation) I did not want to mess with anything that ain't broke.

Anyway, I got around to pulling the carb and this is what I have

Main: 158

pilot: 65S

needle is 4th from the top, needle is stamped B53F (is F possible or am I reading wrong)

fuel mixture is 1.5 out

I am pretty much at sea level or a 1000' ft typically in the pacific north west.

What confuses me:confused: is the indications are that I might be a bit rich but my jets indicate that it should be almost lean given how the bike is set up ?? or am I reading things wrong. I have read the jetting guides and it appears I am quite far off the normal 175, 68s setup that is normally talked about.

I have had recommendations to go one bigger on the main, that would bring me to a 160 ?? but this seems reverse to my logic as wouldn't this make it richer

any ideas ??

thanks,

matthew

Yeah that sounds like crazy lean jetting for your setup. When you're checking the plug are you killing the engine with the kill switch while your travelling down the road at a good speed? If not I don't think the plug color is giving you an accurate picture of what's going on. With that setup and altitude you should be 68s or 70s with a 175, 178, 180 main. Here's the jetting guide I used:

http://www.xr650r.us/jetting/

Don't worry about the plug just jet for runability. I think your way lean.

From all indications, as you guys have pointed out, my bike should be way, way to lean. It seems like a bit of leap to from a 158 to 175 and a 65S to 68S.

I will give it a try.

could the fact that my needle is 4 th from the top be compensating for the small main ??

This makes me doubt my plug reading skills ??

thanks

matthew

From all indications, as you guys have pointed out, my bike should be way, way to lean. It seems like a bit of leap to from a 158 to 175 and a 65S to 68S.

I will give it a try.

could the fact that my needle is 4 th from the top be compensating for the small main ??

This makes me doubt my plug reading skills ??

thanks

matthew

Go with the 68S, and 175 main, then re check the needle. B53E is the needle you want, in the 3rd position to start. :)

Go with the 68S, and 175 main, then re check the needle. B53E is the needle you want, in the 3rd position to start. :)

thanks, this is what I ordered today, I will give it a try.

What I did find out was that one of the little panels in the airbox that was supposed to be removed during the uncorking process was still in place. I had just assumed when the previous owner uncorked it, that this piece had been removed. Not sure if this alone could make the difference and allow it to run richer, I can't figure out why you would take one of the panels out but not the other. The side panel is drilled with the two uni-vents at these two locations though..

thanks for all the input

matthew

Needle should be 3rd clip (middle) while dialing in the main jet. I would go with the 175 Main and 68s as the first combo.

B53D is the stock needle. B53E is the HRC needle. Not sure what a B53F is.

Only go to a 70s pilot jet if you can't get it to start easy. Make sure to get the Honda "S" jet instead of a regular one. This affects off-idle response.

I bet your bike bogs when you whack the throttle open in neutral with the small main jet. The baaaaaaaaaaaawooooom sound.

thanks, this is what I ordered today, I will give it a try.

What I did find out was that one of the little panels in the airbox that was supposed to be removed during the uncorking process was still in place. I had just assumed when the previous owner uncorked it, that this piece had been removed. Not sure if this alone could make the difference and allow it to run richer, I can't figure out why you would take one of the panels out but not the other. The side panel is drilled with the two uni-vents at these two locations though..

thanks for all the input

matthew

If the PO did not remove both plugs on the air box and only had a 158? main jet in. There is a good chance the intake manifold could still the stock one. You may want to check the intake manifold. Also I found running a 175 main jet at 6000 ft is a little to rich for a stock uncorked 650r.

That was the next thing I checked, it is the correct intake manifold (it is round and not D shaped)

thanks

If the PO did not remove both plugs on the air box and only had a 158? main jet in. There is a good chance the intake manifold could still the stock one. You may want to check the intake manifold. Also I found running a 175 main jet at 6000 ft is a little to rich for a stock uncorked 650r.

Problem solved...

installed the 68S pilot and 175 main with the B53E needle. Bike fired right up.

adjusted the pilot screw to about 1.5 turns out.

No more sputtering in 2nd when I open the throttle quickly. Seems to be a little more responsive.

Only thing I noticed if I am riding along at speed in 5th (about 3/4 throttle) and quickly add power I get a "little" ping (almost like detonation). Not sure if I should go one bigger on the main or up the octane (was running on 87 octane) at the time.

Matthew

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now