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Hey all,

 

I have got some carb trouble. 

 

I have been riding around my 2001 xr650r on roadtrips for about a year. Mostly up in northern california in the winter where its cold. With my FCR41 ive always had the issue where if i leave the petcock on, it wont start due to flooding. The bike runs great, just I have to turn off the petcock when doing ANYTHING.. like stopping to piss .. ANYTHING.

I was on a recent trip through Arizona and Nevada a few weeks back and noticed that it was running super super hot. It was 115F outside, but the bike hit 250F on the vegas strip. Ive got a TT Vapor on there, so I am monitoring the water off the block. I have engine ice in it and a 1:8 cap.

I figured with these two issues, its time to mess around with the carb.

I pulled it apart and found that ive got a 160 main jet, 55 pilot jet and an OCEMP jet needle. The Needle clip was on 3/7 (from the top of the needle).

So I set the needle clip to 5/7 and adjusted the float a tad leaner (its supposed to be 9mm).

I also set the fuel screw to 2 turns out.

Put it back together and MAN, the mid range really picked up. It also seemed to run a little cooler (around the 175F range).

Problem is that when i roll off the throttle it bogs down to about 900RPM and then dies. If i keep on the gas, it does just fine.

additionally, when on hills, it dies when i get to a stop on a hill (san francisco). Thinking that this is the float.

 

Can anyone steer me in the right direction about the bogging and dying on hills when the throttle is off? It did not do this before the adjustment of the needle, float and fuel screw.

 

I read that 55 is pretty rich for a pilot jet on this carb/bike. Seems most people run 45-48 pilot jet. My main is also pretty lean looking at 160 when most seem to be up in the 175-185 range.

 

Thoughts?

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Jetting will have a minimal effect of engine temps. Low speed/low air flow through the radiators, stuck thermostat will.

Set the float to OEM specs, do not deviate.

Select the pilot jet based on response from the fuel screw. The bike should stall just at or a little before closing the fuel screw and idle best at 1.74 turns from closed, +/- 1/2 turn. If the bike runs with the fuel screw closed, try a smaller pilot jet.

If the bike seems to flood with the bike off and the petcock open, either the float is set too high or there is corrosion/debris/wear at the float needle seat.

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x2 on float height.

And I agree 55 being big but thats not the first time Ive heard a 650r with an fcr that big of pilot. So I would screw mixture screw all the way in to see if it still runs. 

 

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Yeah, so the float height is set as best as I can tell at the stock 9mm. Following the guide best as I can laying the carb on the side and slowly bringing the float bowl down to where it just cuts the flow and doesn't compress the spring.

When my fuel screw is all the way in, the bike still runs. So sounds like Ive got too big of a pilot.

I tested my thermostat in some boiling water, and it works as expected. I was doing some single track in hollister outside san francisco a few weeks ago and at 7am it was 70F outside and the bike was running consistently at about 209-220. Just seems to be really high temps. Find myself always racing just to keep from overheating.

Anyone have any good guides on setting the float? I want to make sure I am doing this exactly right. 1mm of tolerance is quite.... fine.

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Don't know anything about the FCR on the XRR because I run a stock carb, but from what I could find a 42-45 pilot and 172-175 main sounds about right?  I would also recommend getting a new float needle, they wear and are cheap.

As for the temps, mine will get hot running tight single track, you just gotta keep moving, preferably in 2nd.  Mine actually runs cold in the winter on the road, so I cover 1 rad with cardboard, but single track in summer, hot!  You could mount an electric fan on 1 rad with a switch?

Edited by PeteN

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I adjusted the fuel screw to 1 turn out (pilot must be too rich) and moved the clip to 3/7 and it seemed to perform a lot better. No bogging anymore. 

I am going to drive it from San Francisco to Belden, CA tomorrow (200 mile drive in 100F weather) and see how it does with the heat.

Hopefully it does ok!

Ill report back

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On 7/16/2017 at 6:08 AM, Charles L'Abri Anderson said:

Anyone have any good guides on setting the float? I want to make sure I am doing this exactly right.

If you want to get pedantic with adjusting the float, they do make a tool for it.

IMG_5314.JPG

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On 7/16/2017 at 6:08 AM, Charles L'Abri Anderson said:

Yeah, so the float height is set as best as I can tell at the stock 9mm.

What bike is your FCR41 off of?  Factory Manual for my FCR-MX from a 2008 CRF450R says it should be 6mm.  But those changes were probably made to the 2007-2008 carbs only.  

IMG_6424.PNG

Edited by CongoXR650L
Correction
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have you thought of putting a vacuum fuel pump i have the same problem with my cv carb i have  a lot of work done to the the motor and it still seem to starve for fuel at time. Have you seen anyone with a vacuum pump on there build. Will start new thread about it . 

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