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I put a set of FCRs on today with K&N pod filters, no airbox. For the first time I hear this nasty rattle at low revs. It disappears gradually between 3500-4000 RPM. Sounds like its coming from the cylinder head.

It might of been there before, muffled by the airbox. But I've rin the motor before with the tank ouff and never noticed anything.

It has me worried enough that I want to check the valve adjustment, but I just don't have the time to do it before I leave for my next track outing on Sunday. At the same time I don't want the ruin the motor on the track.

It's past the deadline to cancel the track. If I can't find a buyer for my slots I could (nervously) take my street bike.

Thoughts?

Kontoboy

I'll jump on the worst case senario. You dropped something in there whilst changing the carbs. Could have been a washer. I REALLY REALLY hope it isn't.

I'd take the street bike and find out what the problem is before more damage occurs. But that is thinking from worst case.

That's one of my fears too. I wasn't missing any parts/fasteners and I kept the inlets covered when I had the carbs off the bike, but I can't say for sure it didn't happen.

It sounds like the Ducati Desmodeci valve train.

Thanks

Kontoboy

Non vacuume carbs are really sensitive to sync. What this means is if you are a bit off...the power pulses are not uniform from 1 thru 4 and you hear the gears in the primary making noise.


Sync them carbs!!!

But you already knew this...

Jim,

I can't tell you what a relief it is to hear that might be all it is. Yes the carbs do need to be sync'd--I had the slides out so I know they are off, probably way off.

Unfortunately, no sync tool--I'm looking into getting my hands on one quickly without getting robbed.

(I did read on the Factory Pro site that you could use a small drill bit to mechnically sync them--I didn't bother.) If I can't get them sync'd in time I'll put the Mikunis back on.

Thanks and I'll update this thread as I discover more.

Kontoboy

FCR's make noise Konto!! They just do. It's not always too flattering either. Mine have a marked volkswagen type rattle below 4000 rpm, I can easily tell it's the carbs though - and not the engine, so if your noises are different, then disregard this.
The noise is the vaccum release plates (in the carbs) responding to intake vaccum signals when the cam overlap is anywhere below "full suck" in the rpm range.
Grab a handfull 'O throttle anywhere over 4k to hear the sweet song they can make.........
I wonder if the cam chain tensioner on yours is playing by it's own rules?
I built a sync guage set from individual guages, I'll get a pic up here shortly.

Here's the guage set - 2 1/2 inch common gauges, the ones I found are German made, seem to be good enough quality, and were pretty affordable at less than $20 appiece. It cost more for the brass fittings and tube than the guages, at least I could afford the box they all got stuffed into. Be sure to find some tube restrictors for the hose ends, I stole some from my merc tube set...........an adjustable needle valve would work just as well though, but your on your own for that - I spent enough on brass with this set-up.



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I have had good success setting the throttle plates with the engine running, and yes it can be done with a drill bit - I think it depends on how much time and patience your willing to part with.........
I have found the vaccum signal to be significantly more sensative on the FCR's than with C/V carbs. you will need to account for air filter restriction to get them to balance properly.

I seem to remember that some racing spec carbs (keihins??) may have had needle or some sort of roller bearings for the slides to give best response/minimal stiction....the downside being a rattle at low rpm's due to induction/engine harmonics...racers didn't care because they were all high rpm's.

And yes to this statement from student FZR - that backs up my own experiance exactly....

I seem to remember that some racing spec carbs (keihins??) may have had needle or some sort of roller bearings for the slides to give best response/minimal stiction....the downside being a rattle at low rpm's due to induction/engine harmonics...racers didn't care because they were all high rpm's.

Now...this is from the depths of my memory and as such I may be swimming up the wrong creek but...something else to consider??

Dave

Yes the FCR's have bearings that are adjustable...
Another thing to think about is the hyvo chaqin to the starter clutch....
Them can be some noisy cuss's

That also confirms what I read on another forum--FCRs just chatter at low RPMS. And the pattern of disappearing at 4K is consistent with my bike. So I'm sticking with the carb sync and chatter theory which fits the symptoms. When I fire it up tonight I'll try to confirm.

On eBAy I can get a Motion Pro Deluxe for $117 shipped, or a MP basic for $55 shipped, but I still need those 7mm adaptors for the Yamaha. And I wouldn't get them in time. I think that goes for building my own set too--just wouldn't get it done it time--I'm working all week.

You said if I sync I need to account fo the filters--does that just apply to the drill bit method? If I Mercury sync the carbs with the filters on I presume I'm OK.

With the reassurance that I didn't drop a nut down the inlet I'm going to run it around the block a couple times tonight and see how it goes, but at this point I think the safest and least stressful thing to do is just put the Mikuni's back on for the weekend and sync and sort the carbs when I have more time over the winter. That was my original plan anyway.

Kontoboy

Ok - on sync'ing - the reason I have the vaccum guage set is because I didn't trust that I would be able to manage RPM well enough to keep the mercury in the tubes, and I didn't feel like entertaining the consequences.............my bike will sometimes go imediately to 4k on start up (with no warning), and untill the stuck vaccum release plate un-sticks, it will stay there.........could suck in a bit of mercury doing that.
The drill bit method is for static setting only, I wouldn't tempt a running engine with a metal object of that shape close to an intake port......and neither should you.....
I think (hazy recollection here) that I was able to do the slide adjustment/sync proceedure with the air filters in place - I'm also running pods - But I do remember that I had better adjustment access with them off, and that the engine would not be balanced as soon as they were re-installed. The only successful method was to do the balance with the filters in place, Or somehow compensate while syncing with them off.
I went through a bit of song and dance to figure that out, but once again - the vaccum signal at idle is very low........so any adjustment will have an effect - including mixture to some degree.
They aren't all that bad to do - just wierd and finicky in there own way. The more time you can spend sorting them out, the more comfortable you'll be with them. (not to be redundant, but it's way more true of a statement on these)
I made up adapter tubes from 6mm hex head bolts that were long enough to have a straight shank section under the bolt head, (that's important for a place to hook up the tubes) drill through them with a small drill bit free hand, then cut the heads off. A little de-buring and your ready to go. It was quicker than ordering them in my case, and cost effective as well.
Just use a copper washer beneath the jamb-nut and they'll work fine.
Whew, sorry to run like that, but it takes what it takes.......... , good luck then......
~B~

OK, definitely the carbs chattering. I fired it up last night and listened closely, put a little finder pressure on a couple carb plates and could hear the difference. It's the sliders rattling. What a relief.

I warmed it up and tooled around the block a couple times, kind of. When cold it responds very poorly to throttle coming off idle with no load. When warmed up it responds fine, but still without load. Under load warm coming off idle there is no power at all--it's like I was trying to start out in 3rd gear. I kept stalling out pulling away from the stop signs.

By 3000 RPM it seemed was fine, but I didn't get much above that or out of 2nd--residential neighborhood.

From the volume of fuel I saw squirting from the acclerator pump I would say it was way rich. But I'm no expert and have no experience with FCRs, so who knows. With no time to sort it out, I pulled the FCRs off. I'm debating just taking it to an experienced shop with a dyno over the winter and let them sort it out. Anyone know any good places with FCR experience in the MD/DC/VA area?

So I Mikuni's back on. Now I just finished rejetting these with a Dynojet kit (Stage 1 settings w 122 mains, third notch, 2-1/2 turns out, new FP emulsion tubes). I fired it up (no rattle--thank you) and it idled rough but wasn't really warmed up. Unfortunately I didn't get a chance to drive it around the block--too late to wake the neighbors. I'll run it tonight and see if the Dynojet gives me any problems. If they do I won't hesitate to swap the stock needles and jets back in.

EFI is looking better and better.

Kontoboy

EFI is looking better and better.

I agree, It would be nice to just plug in a laptop, look up a live data stream, and adjust a few rheostats.......
I went through some low end jetting woes on mine also - it's working best with 55 or 60 low speed fuel jets and 100 low speed air (one turn out if they're spring loaded adjustable).
Don't give up on sorting them out yourself though - at some point it will be really usefull info to have.

Hahaha, well you worked it out so excuse my little chuckle, I thought a similar thing with my SP which has FCRs std. & yeah, just take the box off & put your fingers on the slides, sinc’d or otherwise -they rattle.

The accel pump squirts neat fuel into the tracts, not sure you can adjust it much, but don’t despair, this is a good thing. Sure helps throttle response.

Of course you have to get the rest of the jetting right & unless they have a TPS setup they will be prone to chugging at low revs if you whap the throttle on with reckless abandon.

this is all great info for me to try and remember. i have a set of flatslides i will be running with a full ram-air box.

konto, we should hook up some time when my bike is running and fool with carbs!