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Discussion Starter · #1 ·
So after spending $100 on jets to try and jet the stock carb to my 146 with no avail I decided to ditch the stock carb and go with a real VM26. I bolted up the new carb and it runs better. Not extremely better, just better. After hours and hours of running the bike up a mile long hill with about a 4% grade with the throttle 1/8-1/4 open, then another run at 1/2 open then another run at full throttle in the tallest gear. After all of the runs I pulled the plug and adjusted jetting until my plug was a nice tan color. The jetting seems to be spot on with a 25 pilot and 190 main. Needle clip is one up from the middle. The problem is when I chop the throttle from a dead idle there is still a bog right at about the 1/4 turn then opens up and runs like a champ on the top end. I'm thinking that it's not the jetting but maybe the needle. The needle on the vm26 that comes from trailbikes looks pretty blunt. I'm also thinking that since this problem just exists on the x4r that the billet throttle might be snapping the needle up a little too quick. When I roll onto the throttle it runs great. Tomorrow I'm gonna try bolting up an old billet throttle I have sitting around. If that doesn't work I'm gonna either try and find a skinnier tapered needle or put the needle in my drill and taper it down with some 800 grit sand paper. What do you guys think?
 

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I say don't let good enough be the enemy of perfect, or do I have that backwards.



This isn't just a X4R problem, I haven't met a carb I couldn't bog yet with a quick snap at idle. But I haven't been snapping the throttle of many factory bikes either :)



Unless you are running an accelerator pump carb (big bike) this is just how it is IMO.
 

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I've had a bogless carb setup before... stock 70 carb on my 110cc build. It also choked me hard on top.



The bike is slightly overcarbed. Not enough flow at low speed to generate a clean signal. There are a few ways to get around it. 1, smaller carb. 2, raise the idle, never let the motor rev down to the point that it can't generate a clean signal at WOT. 3, stiffer throttle return spring so you can't whack the throttle that quickly. :p
 

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Listen, I Am Not The Carb Guru But I Know Alot About Carbs, I Was One Of The Only Guys To Figuire Out A 21mm Dellorto On A Pocketbike. The Pilot Is Too Lean, The Pipe On The X4 Flows Very Well, You Need More Fuel. John Is Running A 31.5 Pilot On His And I Rode It And It Runs Well. By The Way Kurly Your 70cc And 110cc Engines Dont Apply To What We Are Doing Unless You Have A 30mm Intake Valve In The Head. These Are Race Engines Not Back Yard Lawn Mowers.
 

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I know of ONE 70cc motor that put down more power than mine, so yeah, I think it does apply. I had it putting down similar power to new TB race head 88s, and that was with a stock import cam. I had just about eliminated all bog feeding it with a TM24 carb.



So yeah, I'm sorry I choose to play with smaller displacement setups due to class restrictions, but what goes on with these motors DOES in fact apply to larger motors. We're all overcarbbing the crap out of them, plain and simple. You don't choose the carb size by matching the intake valve size, you choose it by the flow/HP. Mikuni advises you don't go over 25mm at 15hp, and that a 20mm carb can flow enough to sustain 15hp by itself. The SUGGESTED size for that peak power mark is 22mm.
 

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Discussion Starter · #8 ·
YBS_Mike said:
I will say one thing, an out of the box 22mm works 10x better on the X4R then the 24-26mm did. I agree with the over-carbed theory.


True if you are using a stock engine. My engine is far from stock so a 26mm is definitely not over-carbed.
 

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twitchy said:
Are you making this stuff up?^^ There is no 31.5 pilot. In a previous post a couple mos. ago, you said jon was runing a 190 main. ????


you need to watch taking jetting advice from people on the 26mm. there are two different 26mm carbs out there and they take different jets that aren't interchangable. for example i'm running a 26 that has a 145 main and a 32.5 pilot. that's on my x4r 140/ported lifan head. no way would a 190 work, i didn't even have that on my drz 160 with ported se head. so just beware on jetting recomendations as it could really F you up if you are running the OTHER style carb.
 

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Twitchy I am running a 32.5 with 165 main I was running the 190 this winter with a smaller pilot the weather finally got nice enough for me to really dial it in I still do not like this carb as much as the OKO 26. I may not have told Dom the the right number Sorry for the confusion John
 

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Discussion Starter · #15 ·
Cool. THanks a lot Jon. Mikuni does have a 32.5 pilot. I am running the mikuni vm26-606 from Trailbikes. I wish I would have bought the oko 26. That carb ran really well on my x2r with 140. It almost felt faster than my 146 with race head.
 

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Discussion Starter · #16 ·
I'm gonna try a 30 pilot and a 165 main tomorrow and see what happens. My elevation is prob a little higher than yours so a 30 should work. John, is your carb the vm26-606?
 

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I put the 22mm on my x4r (stock) and it ran killer. I was clearing stuff a few feet further than when I had the 26mm on it. there are 2 reasons for that, 1. I'm not affraid of the motor cutting out have way up a jump and 2. the motor no longer lags due to the bog. Although I noticed I sacrificed some top end but its worth it.



I'll through a 26mm oko on it when I build my motor next month.
 

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yeah, i put a good ride into today on the x4r and this larger carb is a problem. I had the low end bog, which on a quick, bmx style track was not good. I had a nose dive when pulling on the gas on the last jump in a rhythm today and cannot get the bog out. You have to roll on the gas. I was going to order some jets but maybe the smaller carb will work as well.

what outlet is selling the jets here?

thanks.
 

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Discussion Starter · #20 ·
magiksc said:
I put the 22mm on my x4r (stock) and it ran killer. I was clearing stuff a few feet further than when I had the 26mm on it. there are 2 reasons for that, 1. I'm not affraid of the motor cutting out have way up a jump and 2. the motor no longer lags due to the bog. Although I noticed I sacrificed some top end but its worth it.



I'll through a 26mm oko on it when I build my motor next month.


Did you clear anything out there besides that table? You should be able to clear everything out there. You got the skills and the bike. It just takes ganas. :D
 
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