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I recently did the RB head and carb mod and found my bike wouldn't run worth a darn. Ron and I determined that my OEM silencer was plugged up. I swapped with another OEM one and performance was restored. Very, very nice!

Being suspicious of the OEM silencer, I bought an FMF Q and tried it last evening.

Is it my imagination or have I lost a little bottom end?

It has certainly cleared up the last of the top end, this sucker screams (for a 220)

Is there any way I can get back the bottom end I think I may have lost? Maybe I should just pretend I've still got the OEM one on there?

Run a EG plug gapped a bit on the high side of the spec and see if that helps.

Normally the shorter silencers offer more bottom, it's only normal the long Q silencer may have less bottom. I run the Q also, but it was in place when I purchased the bike.

I'm running a BR8ES

I'll certainly try a BR8EG

I ran about an hour of single track last evening. It is not my imagination, a bit of bottom end is gone. Nice thing, though, is that the hit is a bit reduced and smoothed out. It was a bit much with the OEM silencer; right when the speed came up and the suspension started to "plane out", the motor would hit pretty hard. Distracting.

2001kdx wrote:Normally the shorter silencers offer more bottom, it's only normal the long Q silencer may have less bottom. I run the Q also, but it was in place when I purchased the bike.

I thought the LONGER Silencer assisted with low end, SHORTER would give a loss.

FMF TBC2 works well

Karl - What is your current jetting w/altitude and temp?

Reeds will get your bottom pulling like an electric motor,
but you sacrafice some topend....which will be your next post

Current jetting is, I think, 150 main, 38 pilot, CEK needle at position #3, sea level and 32 to 90 plus F degrees. Could be a 40 pilot-whatever Ron sends for initial start up on a 220
Boyeson Reeds

Don't get me wrong, bike runs great, I've no complaint. I can adapt style to motor.
I am a bit disappointed in the ~$200 silencer I bought. Sounds just like the OEM one. If I could have figured out a sure way to prevent or correct plugging of the OEM one, I probably would not have bought it. Maybe I'll put it on the CR/KDX hybrid

Green Hornet wrote:

2001kdx wrote:Normally the shorter silencers offer more bottom, it's only normal the long Q silencer may have less bottom. I run the Q also, but it was in place when I purchased the bike.

I thought the LONGER Silencer assisted with low end, SHORTER would give a loss.

FMF TBC2 works well

Yes I think you're right instead of me

When the silencer was plugging up it may have given you a touch more bottom end...

Apparently it had been plugging up for years. I put the throttle assembly off my KX on because it has a shorter twist to full throttle. What I was finding was that more and more I was needing full throttle, the KX assembly made that easier. I thought I was getting faster, when really the motor was loosing power. That's why I finally broke down and got the RB work done.
I think I'll put the OEM one back on to confirm the bottom end effect. I like it fine either way, SO much better than it was before the RB work.

It's a shame I don't know what it would run like WITHOUT the RB work but WITH a good silencer. Probably just like any other stock KDX out there.

I bet that new silencer finds it way on to the CR/KDX hybrid.

Here's an update on that:
I mocked up the whole bike, everything was together, all systems go.
I took it all aprt and have the lower half of the motor ready to go off for a crank rebuild.
While that is happening I'll replace the suspension bushings, work on the handlebar controls, install the wiring harness, etc.
Probably a month to run time.
So I'll have a slow motor in a fast frame!

I can't imagine a situation where anything commonly done modification-wise from RB-Designs would result in loss of bottom end.

I've not heard such a thing from other 220 riders..and it certainly wasn't so on my 200.

Anyone else with this point of view? Obviously I can neither gainsay or not what a 220 rider says....I don't have one.

You've tried a DEK and not liked it? I'd guess the CEK would fit better with a 152, the DEK with a 150. Comparatively speaking I mean. CEK/150 AND a 38 sounds to be on the lean side.

Boyesen-whats?

Buy a DF3 set.........

Although...it's humid in Alabama, ain't it?

I don't know that the -EG gapped wide works with an OEM lighting coil. I know it works with an Electrex coil...and there IS a difference.

Whoa, Nelly....

The RB work did NOT result in the loss of bottom end, the change fom OEM silencer to FMF Q did. Not much, but noticeable. Seemed to smooth out that hit a bit, too.

I can see where that impression might come from after reviewing the above posts. Communication can be difficult, accurate communication even more difficult.

To try to summarize:

1. My '02 220 is weak in the motor department and I got money to burn
2. Send my carb and head off to RB designs
3. Install Head and carb, starts first kick
4. Bike won't run worth a darn. In communication with Mr Black, we determine that my OEM silencer is plugged up.
5. Put on a different, not plugged, OEM silencer
6. Now it runs like a champ. In fact, never ran better.
7. Buy a FMF Q silencer because I'm suspicious of all OEM silencers
8. Loose a bit of bottom end
9. Miscommunicate this experience to the KDXRiders General Q&A Forum


Oh yeah, Boyeson 607's, CEK needle

I had the same problem. I had the exact same specs as you, the DEL needle did it for me.

As CC pointed out, I realized the CEL liked a 152 main, and I really didn't care for the C taper, so I run the D with a 150. Gave me a touch more bottom.

Nelly wrote:Got it! Thanks for clearing up my state of confusion!

Re: 'right when the speed came up and the suspension started to "plane out", the motor would hit pretty hard. Distracting.'

Classic 'C' taper response.

I could look it up I guess...but what is the 'Q' db rating? I wouldn't trust any piece whose primary benefit is to be quiet.

I've been running an OEM 'muffler' for a few months. It's little quieter than my PC S/A was..2-3db actually..but I like the downward/outward turned snout. The 'old style' bell tip of the PC made a mess of spatter with the airstriker carb. The OEM unit does a LOT less of that. It runs just fine! I'll probably pick up another aftermarket here pretty quick..but I'm not in any hurry.

It IS a good thing to know that the OEM unit can plug up. I wonder what a can of YCCC would do.........(Yammy combustion chamber cleaner).

Back to other things....see what an -EG gapped to a loose .028" does. And...DO you have an aftermarket lighting coil?

DO try a DEK..probably with the existing 150 and try a 152.

Off the FmF-Q. Run a can of YCCC through the OEM S/A. Plug it up and let it sit overnight maybe.

I'm assuming YCCC is liquid at one atmosphere pressure? I don't know that.

Heck...pour some of your Berryman's carb-cleaner gallon in it. Let IT sit!

I got money to burn...

Buy a DF3 reed block........

I think I can come up with enough cash for the DEK needle, need to have one around anyway.

I bet the YCCC would do something. A propane torch shoved up the inlet didn't seem to do much but generate a little smoke, and that was after an hour. I've heard there is no packing in the OEM muffler. I wonder, there is an awful lot of SOMETHINNG in there, it is very heavy. Maybe I'll cut one up to see.

I have stock ignition and lighting coils.

Off to tinker!

also karl depending on if you have enough cash the fmf fatty expansion chamber will give you a whole lot more top end with your aftermarket silencer however if it is bottom end power that you wish to increase then you would be very smart to go and buy an fmf gnarly expansion chamber and leave your silencer on there because the silencer will keep the top end up high but then the fmf gnarly expansion chamber will lower the top end down to even and bring up the bottom end power. if you wish you can try it because i have the same problem with my kdx 250 except i did it with a pro cicuit silencer as i already had it when i bought the bike and use the fmf gnarly expansion chamber. it cost me about $490 australian. it worked great for me.

RE: Temp from 32 to 90 plus . . . jetting needs would change from one end of that temp range to the other.

I've got a 220, I'm all RB'd, and at current temps running a CEK #3 / 148MJ / 38PJ. I witnessed a performance enhancement recently after dropping sizes on both jets from the 150/40 that Ron installed for the cooler weather (early spring). Jetting was a bit fat with the 150/40 as the summer came on.

Have you done a throttle chop?

I HAVEN'T fiddled with a DEK to provide a comparison. As described it sounds boring but I won't know that until I try it.

Oh, yeah: FMF rev, 607s, no airbox lid, and a Pro Circuit Type 296 S/A.

My 150/42 is getting a bit fat in the summer months, if I wanted to I could throw a 40 in I know it would help, but it's no big deal!

I'm not sure if I contributed anything to this thread but I needed to make everyone aware of my current jetting situation