30mm Carb upgrade
 

Got the new carb and intake for the atv. Its an ebay "Mikuni". Looks like a pretty decent carb and is noticeably bigger than the stock carb. Figured I couldnt go wrong for $25. The flange on the new intake tube is not exactly a perfect mate to the carb, but its a 30mm hole in it so I tried it out.
After adding a high performance cdi unit for the first mod, I didnt really notice any difference, except it ran a little smoother. Now after adding the intake and carb I noticed a HUGE difference in power. I didnt try the carb out on the stock intake tube because the tube was much smaller than the opening on the carb so I figured it probably wouldnt run too well like that. I highly reccomend a carb upgrade if you're looking for more power. Mine became a totally different bike after the carb upgrade. Gonna do the exhaust next, I'm expecting that I'll see another huge jump in power after I open up the exhaust now that there is a lot more air and fuel going into the engine. Just kinda wanting to see how 1 mod at a time affects the engine and see which mod is the most bang for the buck. I'll keep everyone posted on the next one.

Ron

Thanks for your writeup; I can totally appreciate doing one mod at a time to quantify results.

Please tell us more about the intake tube. Do you have a photo? If it would work on my Beast, I'd be all over it. Do you have a link that points to it?

Here's a link to the place I bought the intake tube from, it was an ebay special
http://cgi.ebay.com/ebaymotors/30MM-...Q5fAccessories

If the link doesnt work, just go to ebay and type in the search box "Mikuni 30mm Intake", many different styles of intake tubes will show up. The carb didnt mate up too well on mine at the flange, it seems the flange is a little too small for the carb to mount on to it. Part of the o-ring is exposed but it did seal. I couldnt believe the difference it made, its like someone stuck a bigger engine in there while I had my back turned.

if you can get your hands on a small peice of pyrex and a dremel.. you could very easly make a plate that will go between the intake tube and the carb for a better seal.. just put some high temp rtv (also known a gasket maker) on the pyrex adapter on the intake tube side to seal that up..

You did do the intake and carb at the same time you said? I wonder how much the tube matters more so than the carb?? Curious..

Yeah the intake tube on the link looks pretty darn close to the intake already on our beasts, but the 30mm GIO carb was a night and day difference on my beast.

I thought pyrex was glass, do you mean polycarbonate?
For a homemade carb spacer/adapter i use phenolic.

if you can put your carb close to the motor you will make more power

I did do the intake and the carb at the same time, I figured if I'm gonna put a 30mm carb on it, I might as well have a 30mm hole all the way to the intake port on the head. The carb seems to be sealed, its not acting like its got a vacuum leak. its a very small part of the o-ring thats exposed...probably will cause premature failure on the o-ring though. I couldnt stand to wait to get a new silencer for it so I went ahead and pulled the end cap off the muffler today and went to work with a dremel and a drill. Turned out there was 2 baffles inside that I persuaded to come out. Just pulled those out of there and put the end cap back on. Looks totally stock now, but no spark arrestor :( and loud :twisted: It didnt make as much of a difference as the carb/intake upgrade, but it did seem to add a bit more power. Gonna get the FMF pipe eventually and stick it on there. I think a little back pressure is probably gonna do it some good and probably will gain a little more power. Plus I wouldnt mind a few less decibels.

Ron

idle sound will get softer with the fmf and new packing.. trust me.. did it yesterday..

you need to rejet.. good rule of thumb and a good starting point.. go up 2 jet sizes for a new intake, and 2 jet sizes for a new silencer..

if you noticed or not idk.. but your intake filter should be hissing a little since opening up your muffler.

its like this with jetting, if you slap a intake and full exhaust on a car.. you will notice a little more power.. but if you slap a intake and full exhuast and then get it tuned.. you will notice a good amount more power.. jetting is tuning for carbs..

as for silencers i would suggest a powercore 4, tubine core.. also if you want a softer sound order the quite insert with the silencer.. also order a wash plug for the muffler, getting water inside to the packing will destroy it faster.. wash plugs are like 5 bucks a pop

Ya I was a little worried about running it too lean by opening up the exhaust. It runs really good but I'm sure its a little lean now. That'll be my next thing to do....I'll jump up a few jet sizes and see what the spark plug looks like. I pulled the jets out to look at em and didnt write down the numbers :x I think I remember the pilot jet having a 20 on it and I cant remember what the main jet was...ugh

Ron

Is there a "universal fit" type FMF pipe? or do I need to find one made for a Honda or whatever that has a somewhat similar exhaust system?

i think the stock mikuni main is 90 or maybe 100

its always a little safer to run a tad rich then it is lean.. but to rich can give problems too

do you have any back firing ?

ive noticed on mine at about 1/8 to 1/4 throttle, i have a fast rapid back firing that clears out once i hit full throttle.. at first i thought thats how the muffler sounded but after hearing it a few times its a super faster rapid backfire..

Not getting any backfiring. I believe the main jet was 100 now that you mention it.


Ron

Yeah, on my beast with the mikuni carb, CDI, UNI air filter and the performance exhaust with the monster muffler i had to go up 4 sizes on the main to 110, the pilot went up 2 sizes to a 25 and i have the jet needle on the 4th groove from the top.

just wrote that down, for when my mikuni gets here to use as a starting point.. altho i dont have a uni filter.. still using the barrel intake but i did remove one of the three layers of filter from it.. guess i will pick up a 105, 107.5 mian, and up the pilot one size and pick up a 25 pilot for future upgrades..

waynev, was it a must to raise the needle up a notch or was that done as a "safety net" type of thing incase it was running to lean in the mid

The clip was lowered 1 groove to the 4th from the top ( needle goes higher, richer ) because it just didn't sound right from 1/2 to 3/4 throttle, moving the clip smoothed it out, it must have been a touch lean.

i would assume that the carb i ordered is the same as your, same mods as you. the tuning should roughly be the same ?

prolly wont lower the clip to start off with but will run a 107.5 main, and a size lower pilot then you.. wont up the pilot untill i get a freer flowing intake..

Just to confuse you some.. :)

Your settings may not be the same because you may be higher or lower in altitude, and you may be hotter than where Waynev is.

It's a good starting point though. :)

I have an ATA-250 and did the same thing. As BangkokBlaster said, totally different bike. Engine use to run like crap and idle was impossible to set. My only problem is that I was shipped the wrong intake tube by the same vendor PCC 6 months ago, although he did refund me. Thank God you posted becasue I was going crazy just yesterday trying to find him again!