FCR Wear Plate replacement misery...


replaced my wear plate (again) today with the remanufactured unit from ebay US.

This time using a brand new seal from BR special tuning.

Bike was running fine in the morning with the old wear plate.

After installing the new wear plate and seal and firing the bike up, the idle was way higher than before, and when coming off the choke the bike would idle OK for a bit but then always end up stalling.

I took it out for a ride like this anyway, and it rode fine, but under decelleration it popped and banged so much more than before, and then stalled.

Which leads me to the conclusion that my idle mixture when using the new wear plate is so lean the bike idles much faster but then if you set the idle somewhere more reasonable it will stall due to how lean it is.

Now I have put the old wear plate back in, but with the new seal and to be honest the bike runs perfectly, but haven't tested it from very cold. So will give that a go first thing tomorrow.

I am a doughnut though, went and left the fecking throttle stop screw off, so carb off for about the 10th time in the past week tomorrow, getting quite fast at it now!

So I think I'll be sending the throttle wear plate back to the US for a refund and forget about all of this unless I get further problems with low throttle running, then I'll fork out for a genuine plate.





New plate in upside down?

Nope, definitely in the right way (square end down).

Must be something different about the plate itself

What do Eddie et al think about these symptoms? I've contacted the seller of the plate to ask him if he's had any similar issues...

think I'll just send it back to him and be done with it.

Did you put a micrometer on the plate and compare thickness? Was the throttle wheel fully returning to the idle stop (no binding)?

No I didn't. I have a pretty decent vernier caliper which I could have used but nevermind!

The throttle wheel was free.

Right spoke to the seller and he said he had to adjust the idle speed on his bike (same as I experienced) but said his mixture screw was left untouched.

My mixture was perhaps a little lean anyway as I had a fair bit of popping on deceleration, and I have since richened it out 1/4th of a turn which has reduced it a lot.

I'm thinking perhaps my mixture was a little lean, and this leaned it out even further and I just needed to tweak the fuel screw from 2 turns out to 2.5 turns out?

I was wondering what Eddie may think about the effects of this wear plate if I put it back in and tune my pilot mixture to suit it, how it would affect the bike through the rest of the throttle range?

What is the verdict?



Fuel screw is for idle only.

I assumed... you had installed the new plate, messed with the idle speed and fuel screw. These are normal things that often have to be done when you replace a part like the release plate.

I 'messed' with the idle speed, i.e. I adjusted it to something more reasonable.

But at a lower RPM it would stall, think it was too lean as I said.

I didn't realise I would have to adjust the mixture and am just asking you guys who are in the know if this is normal and whether I should have to adjust it or not.

I've since wound it out 1/4th of a turn and it is popping less (with the old wear plate), I think its running fine at the moment but am keen to replace the plate.

Does it sound sensible to try the new plate with another 1/4th of a turn on the fuel screw so it will be 2.5 turns out as we know the other plate runs lean?

I am fully aware the pilot screw is for idle... I just wanted to know if the throttle wear plate would affect my main jet circuit etc.



I'll try and shed some more light on this situation, and would also welcome any opinions on the wear on my slide wheels? One of them appears to be much newer than the rest as the raised disc in the middle of the wheel hasn't worn flush like the rest of them? The one that appears to be new always falls off as it's not as tight as the others, it's the one without the hole all the way through it - is this because the others have all worn through to the point the hole is showing?

Do these wheels cause issues? Shall I replace them too?

anyway, pics:







First, you are over anlyzing this. Your old release plate is worn out. You install a new one. You adjust the fuel screw and the idle speed. Done Do not arbitraialy do this or they, adjust things for a reason.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

The wheels rarely wear, but the cab body does. Do you have deep grooves from the slide wheels?

Hi William

Thanks for detailing the procedure of adjusting the idle mixture, I have read up on this and to be honest I'm just going on guess work as it's nearly impossible to adjust the mixture with the engine running without an extended fuel screw?? Or can you get a very small screw driver bit in there?

Do you not think my wheels look worn?

Not checked the carb body wear out - if that's worn then it'll never be perfect.



Yeah, I doubt yu can access it with a driver other than a specialized tool like the Motion Pro 90 degree one.

Wheels appear ok but you have to measure them and compare to new to see how worn they are.

You are right about the carb body. Some have epoxied the grooves but it is a hard job and a point of realization has to come when you are throwing too much good at a whole lot of bad. Reasons to shy away from most used carbs.

OK well I'm going to give this one more go. I'll put the new plate and seal back in this weekend, and I've ordered an R&D FlexJet screw which bolts up to the side of the carb by the idle knob, could be a neat solution for setting the mixture (I hope).

Will tune the bike to the new wear plate and report back :smirk:




Thanks for your help with this - I persevered yesterday and fitted the R&D fuel flexi fuel screw and the new wear plate and seal.

Tuned the bike up as you described and got the lowest smoothest idle.

Then took it to the dyno to do a power run and check the AFRs, my pilot circuit was a tiny bit rich so he adjusted that for me, but the rest of the AFRs are nearly perfect right through the rev range



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