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Discussion Starter · #1 · (Edited)
Having a little issue with the pair 39mm FCRs on the 660, figured I'd ask the smartest collective group of fellas I know.

I seem to have a problem with the raptor stuck wide open. The throttle cable was 5 years old and in pretty rough shape so I replaced that since it was sticking open at the thumb lever.

Obviously that didn't do the trick, now it's sticking at high throttle despite the thumb throttle being at the resting/closed position. Thinking the slides were the problem I pulled off the air cleaners, only to find that the slides move up and down with the use of the throttle and the WOT issue occurs even when the slides are closed.

This has me thinking I have an air leak in the intake (I'm using a trinity) or a carb issue that I don't fully understand. Any thoughts Raptorforum? It's time for a good cleaning anyway so I'll be tearing into the carbs as soon as I get around to ordering the replacement parts. Just looking for some ideas or perhaps an obvious issue I've overlooked. I haven't spent a great deal of time troubleshooting this since I replaced the throttle cable.
 

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Having a little issue with the pair 39mm FCRs on the 660, figured I'd ask the smartest collective group of fellas I know.

I seem to have a problem with the raptor stuck wide open. The throttle cable was 5 years old and in pretty rough shape so I replaced that since it was sticking open at the thumb lever.

Obviously that didn't do the trick, now it's sticking at high throttle despite the thumb throttle being at the resting/closed position. Thinking the slides were the problem I pulled off the air cleaners, only to find that the slides move up and down with the use of the throttle and the WOT issue occurs even when the slides are closed.

This has me thinking I have an air leak in the intake (I'm using a trinity) or a carb issue that I don't fully understand. Any thoughts Raptorforum? It's time for a good cleaning anyway so I'll be tearing into the carbs as soon as I get around to ordering the replacement parts. Just looking for some ideas or perhaps an obvious issue I've overlooked. I haven't spent a great deal of time troubleshooting this since I replaced the throttle cable.


So you're saying the slides are working properly with the thumb throttle now "WOT issue occurs even when the slides are closed. " ?
To determine this did you remove the air filters, start the bike, blip the throttle and the RPMs stayed up after the slides returned to their normal position? If yes, then you must be pulling air from the intake side or the head gasket.
 

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When you tear the carbs off look at the carb boots for tears. Their will also be a number on the lip of the boot. It is a Mikuni Carb boot part number. Right that down so you can order a pair of carb boots if need be.

Dennis kirk is where I got mine for my boss racing intake on my banshee. They were like 15 bucks each.


I also had a problem with my FCR's racing at Idle with the ez pull spring. It wouldn't go all the way down unless you let them slam shut. I ended up putting the stiff spring back on. I did buy them used and I might just need to install new slides and polish the bores so they are nice and smooth.
 

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Discussion Starter · #4 ·
So you're saying the slides are working properly with the thumb throttle now "WOT issue occurs even when the slides are closed. " ?
To determine this did you remove the air filters, start the bike, blip the throttle and the RPMs stayed up after the slides returned to their normal position? If yes, then you must be pulling air from the intake side or the head gasket.
Yes, slides appear to be operating just fine. Took the air cleaners off and opened and closed the slides using only the thumb throttle with the bike off. Turned bike on, bike is instantly at WOT while looking at closed slides, blip of throttle moves slides up then back down with no change in revs of engine, still revving to the moon. Raptor is stuck at WOT, you can turn the key and start it up and without touching the throttle or anything else it's instantly at WOT now. It used to just stick there.

When you tear the carbs off look at the carb boots for tears. Their will also be a number on the lip of the boot. It is a Mikuni Carb boot part number. Right that down so you can order a pair of carb boots if need be.

Dennis kirk is where I got mine for my boss racing intake on my banshee. They were like 15 bucks each.


I also had a problem with my FCR's racing at Idle with the ez pull spring. It wouldn't go all the way down unless you let them slam shut. I ended up putting the stiff spring back on. I did buy them used and I might just need to install new slides and polish the bores so they are nice and smooth.
Good info on the boots, I was worried I'd have to go hat in hand to trinity and give them some ridiculous sum for the boots or a whole new intake if I have a tear. I will check DK out in that eventuality. I have the 1.2 spring on there, I would call it the "easy pull" as it's the weaker spring sudco carries. But I've been running it for about 5 years on these carbs so I'm not suspecting it right away, especially with the slides appearing to work properly.
 

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A tear in the boot would give it plenty of air, but what has me curious is where is the fuel coming from?

I would double check that everything went back together correctly, and that the new cable is long enough (and adjusted correctly) to allow the slides to go COMPLETELY down. One way to verify this would be to adjust the idle speed screw and watch the slides move.
 

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Discussion Starter · #6 ·
A tear in the boot would give it plenty of air, but what has me curious is where is the fuel coming from?
That's the question that is perplexing me as well, I can only assume it's somehow getting it through the idle circuit?

I would double check that everything went back together correctly, and that the new cable is long enough (and adjusted correctly) to allow the slides to go COMPLETELY down. One way to verify this would be to adjust the idle speed screw and watch the slides move.
I am planning on tearing down the carbs for a rebuild anyway, they've sat around a little while but the bike was running fine back in January. The sticking throttle issue happened in Feb and I replaced the cable last month, but had to reinstall a decomp mechanism and I did a clean out of the oil system so it took a while for me to get around to putting everything back together. The idle screw on my fcrs has never actually worked (doesn't come up far enough to engage the throttle wheel where I need it to), I've always used the cable itself to adjust the idle speed. When I pull the carbs I'll see if the fully closed position I think I'm seeing is actually fully closed, or if they just look like it and are hung up in some way.
 

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The idle screw on my fcrs has never actually worked (doesn't come up far enough to engage the throttle wheel where I need it to), I've always used the cable itself to adjust the idle speed. When I pull the carbs I'll see if the fully closed position I think I'm seeing is actually fully closed, or if they just look like it and are hung up in some way.
I have to admit I'm not familiar with the Mikunis-Can you reach the throttle wheel to force it closed? It might be worth a try to close it after starting the engine to see if it will drop to an idle.
 

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Discussion Starter · #8 ·
These are aftermarket Keihin FCR Sidedraft carbs, not the OEM mikuni bsr carbs.

The throttle wheel is outside the carb body, and appears to be returning to the desired minimum position.
 

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Does it ever return to normal idle, or always stay way up in the RPM's? Does it start up and immediately go to high RPM, or only when you've blipped the throttle?

If it is just taking a long time to return, could it be a vicious version of 'hanging idle' due to too lean in the pilot circuit? What happens if you turn the fuel screws out a half turn each? Any change?

The FCR's have accelerator pumps, don't they? Any possibility of a tear in the accelerator diaphragm? This could allow unexpected air and fuel to pass into the carb throat even when the slides are down.
 

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Discussion Starter · #10 ·
No ramping up or down, hit the start button and it's at wot throttle and stays there.

Acc pump is where I'm focusing on next, for now going to. Double check leaks with the tank and carbs off. The bike.
 

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If you had a tear in your accel pump diaphragm, you'd most likely see fuel spitting out of the top of the boot that goes around the rod that pushes it down. The FCR's that are on the g/f's Honda had a bad diaphragm, didn't affect the way the motor revved, just left a small puddle on the floor.
 

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Just out of curiosity, you're not using a vacuum operated petcock off another quad (like an LTZ) are you? I recently had a friends LTZ with exactly your symptoms - I traced it to a leaking diaphragm in his vacuum petcock where fuel and air was being sucked thru the vacuum line from the petcock straight into the intake manifold.
 

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Most defiantly a cracked MAIN JET.
PULL YOUR MAINS...INSTALL NEW ONES NICE AND EASY.

when you put them in to tight they will split. causing fuel to dump into motor while the slide and needle are closed.

just revs to the moon like its choked to high...cause it basically is. slides closed with a wide open main=tons of vacuum and tons of fuel!!!
 

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Ive seen this happen a lot when switching jets.
Sometimes it can be difficult to get the broken jet out.
full rebuild kit will defiantly fix your problem.
new jets and a new needle(make sure if the needle has three positions it is in the right one) recheck your throttle cable adjustment.
 
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