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Old 09-02-2012, 07:43 AM   #16
LukasM
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Quote:
Originally Posted by Maineroot View Post
OK- that makes sense. And what would be the solution to this?

Jetting specs are above. Let me know if any of this looks out of whack.
I gave you some recommendations above.
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Old 09-02-2012, 07:51 AM   #17
DefyInertia
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Never once used the choke on my 00 640 with 41 FCR....just squirt and start.
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Old 09-02-2012, 08:27 AM   #18
Cruiser
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Do yourself a favor and get an adjustable leak jet.. that way you can adjust the acc pump squirt with a screwdriver quick and easy without even getting off the bike. Well.. if your flexible that is.. I had this on my sxc and found the sweet spot for offroad and on to maximize MPG on road and fun off.. adjusted correctly it would stand on one wheel anytime I wanted..
I miss that bike...
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Old 09-02-2012, 08:37 AM   #19
Maineroot OP
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Quote:
Originally Posted by LukasM View Post
I gave you some recommendations above.
I have never had a rich setting do anything else but cut out or stutter.

I was wondering if this was more of a function of the A/P squirt length and timing.

Thoughts?
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Old 09-02-2012, 12:14 PM   #20
Luke
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For the accelerator pump, replace the diaphragm with a honda or yamaha part. That'll cut the amount of squirt down to reasonable levels. See here:
http://www.advrider.com/forums/showp...81&postcount=6




All your jets/settings are richer than what I use, but I've got a different head on the motor than you, which may matter.

A hanging idle is supposed to be caused by a lean condition; either jetting, or a vacuum leak. Did you stuff the fcr into the stock carb boot or replace it with the SXC boot? It could also be a leaky choke valve. Maybe swap the correct one back in to test.
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Old 09-02-2012, 07:41 PM   #21
Maineroot OP
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I'm not happy about having to take off the carb again to set up the A/P timing- but if that is what it takes, looks like that is what I'm going to have to do!

I am using the stock carb boot. It fits perfect- I got lucky and got an FCR with the bell housing. I am using the FCR choke that came with the carb.

The symptom is more of a running on when letting off (closing) the throttle. In my research, it appears that the symptom could quite possibly be the extended squirt reported of the stock A/P.

I'm not sure I can view this with the carb still installed in the bike except possibly using a mirror looking through the intake with the filter removed.

I will test the squirt duration and report back.


Quote:
Originally Posted by Luke View Post
For the accelerator pump, replace the diaphragm with a honda or yamaha part. That'll cut the amount of squirt down to reasonable levels. See here:
http://www.advrider.com/forums/showp...81&postcount=6




All your jets/settings are richer than what I use, but I've got a different head on the motor than you, which may matter.

A hanging idle is supposed to be caused by a lean condition; either jetting, or a vacuum leak. Did you stuff the fcr into the stock carb boot or replace it with the SXC boot? It could also be a leaky choke valve. Maybe swap the correct one back in to test.
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Old 09-03-2012, 02:53 AM   #22
Droptarotter
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Quote:
Originally Posted by Maineroot View Post
I'm not happy about having to take off the carb again to set up the A/P timing- but if that is what it takes, looks like that is what I'm going to have to do!

I am using the stock carb boot. It fits perfect- I got lucky and got an FCR with the bell housing. I am using the FCR choke that came with the carb.

The symptom is more of a running on when letting off (closing) the throttle. In my research, it appears that the symptom could quite possibly be the extended squirt reported of the stock A/P.

I'm not sure I can view this with the carb still installed in the bike except possibly using a mirror looking through the intake with the filter removed.

I will test the squirt duration and report back.
No one is happy about taking this carb out.....it's a PITA!!
Do it anyhow, have the float bowl full of fuel and look down the carb and count the length of time the fuel squirts into the venturi as you open the throttle wide!

Now you will either have a time span the fuel squirts into the venturi or an eye full of fuel, so maybe I should have stated to look into the carb from the filter end!

What you want to see is about a 1 second squirt time instead of the 3 seconds a stock FCR comes with!

You will either have to adjust a screw, bend some tabs or install a different AP diaphragm , depending on what year of carb you have to get the correct squirt time.

That carb might have to come off quite a few times to get the jetting correct, but it will be worth the effort once you get it dialled in.

Cheers
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Old 09-03-2012, 10:39 AM   #23
Maineroot OP
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Instead of removing the carb to test- I was able to take my iphone and put it in the intake of the airbox and record the A/P squirt duration.

I have a very clear video of this.

It looks like it is aimed correctly, and the duration is correct- around 1 to 1.5 sec.

Next step is to adjust the jetting as recommended to lean it out up top- dropping the main jet a size and test.

Cheers
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Old 09-03-2012, 12:05 PM   #24
Droptarotter
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Quote:
Originally Posted by Maineroot View Post
Instead of removing the carb to test- I was able to take my iphone and put it in the intake of the airbox and record the A/P squirt duration.

I have a very clear video of this.

It looks like it is aimed correctly, and the duration is correct- around 1 to 1.5 sec.

Next step is to adjust the jetting as recommended to lean it out up top- dropping the main jet a size and test.

Cheers
What a great idea!
Thanks!
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Old 09-04-2012, 03:02 AM   #25
Cruiser
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another great time saving trick with the iPhone!! That is great!
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04 KTM exc-ds!-its street legal,really officer it is! well..
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Old 09-08-2012, 07:14 AM   #26
Maineroot OP
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Here is the video of the A/P squirt timing.

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Old 10-31-2012, 01:59 PM   #27
Maineroot OP
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Still running like crap

I got the bike back together after doing a bunch of mods.

Took it out for a spin today.

SAME SYMPTOMS.

Will not start unless you crack the throttle several times (preloading the carb with fuel) with the choke on.

Then it will immediately die. After about 5 or 6 times of this it gets warm enough that it will run on its own- but you have to baby the throttle or it will die.

Took the choke off and adjusted the idle knob so it won't die then went around the block.

After you let off the throttle- it runs on to about 3K until it settles down to idle. Bike was run for about 15 min- and the same symptoms.

SO:

Maybe a clogged pilot jet (due to hard starting)

Incorrect needle position (hard starting/ running on)

Incorrect main jet?

Making me think I want to rip this thing out and start over! Driving me nuts.
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Old 10-31-2012, 03:09 PM   #28
gunnerbuck
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Quote:
Originally Posted by Maineroot View Post
I got the bike back together after doing a bunch of mods.

Took it out for a spin today.

SAME SYMPTOMS.

Will not start unless you crack the throttle several times (preloading the carb with fuel) with the choke on.

Then it will immediately die. After about 5 or 6 times of this it gets warm enough that it will run on its own- but you have to baby the throttle or it will die.

Took the choke off and adjusted the idle knob so it won't die then went around the block.

After you let off the throttle- it runs on to about 3K until it settles down to idle. Bike was run for about 15 min- and the same symptoms.

SO:

Maybe a clogged pilot jet (due to hard starting)

Incorrect needle position (hard starting/ running on)

Incorrect main jet?

Making me think I want to rip this thing out and start over! Driving me nuts.
From what you describe it is running very lean off the bottom, a few things come to mind that could be the cause:

-Check the fuel pump vacuum hose where it bends to slip over the intake manifold bung... If the hose seal at this point is cracked or loose air may get past it and go directly into the intake causing the lean symptoms you describe...

- Pop the pilot jet out and make sure the pilot fuel passageways are clear..

- Make sure all fittings and boots are tight and not allowing air to pass...

- If still not correct try going 2 sizes larger on the pilot jet...
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Old 10-31-2012, 06:46 PM   #29
dnrobertson
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While you have the carby off, check the float height.

Should be 9mm on most FCR IIRC.

I bought and installed one of these:

http://www.innovatemotorsports.com/products/MTXL.php

I find it useful to see the AFR.

I know many on this board think they are crap, but we can't all afford dyno time.
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Old 11-04-2012, 11:17 AM   #30
Maineroot OP
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2012 450sx fcr 41 mx

I got hold of a 2012 450SX FCR 41 from the fine gents at Munn Racing.

There is no "bell" housing on the intake side of the carb- so it was a loose fit into the airbox boot.

Slid right in. Cranked down on the hose clamps. Hooked up the throttle cables.

Rejetted it as per the specs above. Cranked it to fill the float bowl.

Blipped the throttle twice, and it fires right up.

Purrs like a kitten. Pulls like a freight train. Roll on wheelies are no problem.

Problem solved with a fresh swap.
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