Advice request - Keihin FCR mods

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robs ss

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I'm about to try a modification on my pair of Keihin FCR 35s and am wondering if anyone else has done this before - and is willing to offer advice.

The slow fuel mixture screw on these is hidden up a vertical hole toward the front of the bowls.
Given that adjustments should be made with engine at operating temp (hot!), fiddling with a screwdriver up these ports is uncomfortable to say the least.
I have bought a couple of "extended" mixture screws from the Australian Keihin agent with the hope that the adjustment can be made as easily as changing the idle speed.
They advised me, however, that they were made for the MX versions of FCRs and that "slight" drilling will be required on my bowls to allow them to fit - it appears that the vertical ports need to be opened by about 0.5mm.

Anyone done this before and have any sage advice?

Cheers
Rob
 
That small a difference in size should be very easy. The drill may want to auger in like a lag bolt. Be careful, hold it securely, feed slowly.
 
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I would not do that with a hand drill without a stop collar on the drill bit to prevent the bit from getting near the threads. When a drill bit augers into soft metal, it moves forward quick using a hand drill. It is harder to stop the drill bit from moving forward than you might think if you don't go in perfectly straight with a hand drill. A jig for holding the bowl at the right angle and a drill press would be handy as well.
 
Since the threaded portion is the same would it be possible the file the adjuster diameter slightly?
 
Since the threaded portion is the same would it be possible the file the adjuster diameter slightly?
Thanks - I'll consider that option - have to pull the carbs off then bowls to have a look
 
Do you know someone with a good drill stand or a mill? Clamp the float bowl down securely and I would think either would give you the control on speed and depth that you need. I wouldn't trust myself to do it with a hand drill.
 
I’d do it with a hand drill, bowl upside down on a pc of wood, held down with my foot. Hold on to the drill like you mean it.
 
Thanks for the advice! I thought I'd post progress to maybe help others.
I pulled the carbs off today (had to put leaner needles in)
Anyway, what I found was the is minimal risk of getting it wrong as the threaded part is in the carb bodies - see central hole in bottom of photo - below jet.
IMG_0270.jpg

..and the hole/passage in the bowls are exactly that, a simple hole - just a tad too small - now out to 6.5mm Just had to avoid cutting into the o-ring gasket channel.
Again - see matching holes central/lower
IMG_0269.jpg

So I should have been right to replace the existing, short slow running adjusters with the new, flash, longer ones - shouldn't I?
IMG_0272.jpg

Fits through the bowls okay...
IMG_0271.jpg

But when I went to screw the new ones into the bodies, one of them started to get "tight" before fully seated - so I stopped, removed and measured them.
I don't know if you can see it in the bottom photo - but the small diameter tip on the LH one is larger OD than the RH one.
The RH one is 0.85mm, same as the short ones I pulled out.
The LH one is 1.04mm - so lucky I didn't force the issue.

So, I put the short ones back and I'll have a talk with Mr Keihin Australia on Monday!

One other issue I noted is the numbered "handles" at the base of these units will foul the float-bowl drain plugs. Can be fixed, but still a bit annoying
 
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Good to know it was much easier to drill the holes out than my negative thought process thought it would be.

Too bad about the needle ends being different diameters, and the knob being too large. Give em hell about the different diameter needles. The knob is obviously because the product is for a MX carburetor.

That stock short screw is way the heck up in there. I can see why you want to replace it. Even if not hot, it would be a PITA to deal with.
 
Hi there,
If you wish to know everithing about FCR, go on the web:
Keihin FCR tuning version 3.3 by Patrick Burns
Yves
 
Hi there,
If you wish to know everithing about FCR, go on the web:
Keihin FCR tuning version 3.3 by Patrick Burns
Yves
Thanks for the suggestion Yves - I do have that.
It's quite a difficult process for a newbie to these carbs, isn't it?
 
There has already been a benefit from opening out (to 6.5mm) those holes in the float-bowls.
While I can't yet use the extended idle mixture screws, the "screwdriver" I have been using is now much easier to use. It used to be a pain to get it to locate and fit into the slot - now it's a breeze.
I would thoroughly recommend anyone with FCRs to open out these ports even if you're not going to use extended mixture screws.
BTW - my "screwdriver" (below) is simply a plain hex bit, ground down to fit into the old hole size. The numbers (printed tape) help me to keep track of adjustments.
Advice request - Keihin FCR mods
 
Thanks for the suggestion Yves - I do have that.
It's quite a difficult process for a newbie to these carbs, isn't it?
Do it step by steb, it is a difficult process, it's take time becouse only for idle you have a pilot jet, a pilot fuel jet and a pilot air jet, follow the instructions from Patrick Burns, sometime you have to change the pilot jet and adjust the pilot air jet to ritch the ideal idle
Good luck
Yves
 
Good job Rob catching the mismatch screws. They do look different color like from different batches. I have fcr's on 2 bikes and curious what keihin tells you. What bikes want or need bigger or smaller tip?
 
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