hello i have a vm34 (round slide) mikuni on my stroked blaster. i finally got it to idle i had to put the 35 pilot jet in it and i ended up puttin a 260main jet in it and the needle is on the 4th clip down(1 up from bottom clip).it will rev fine wen its not under a load but once u try to take off with it it will bogg and die unless u keep it revved up pretty good. any suggestions?
vm34 carb on my blaster boggs and dies on take off?????
- Thread starter jreds4mill
- Start date
most larger carbs from other bikes have way too rich needles in them for a blaster, no matter what clip position you use.
a call to Carburetor Parts Warehouse set me free from months of chasing my tail with the wrong needle.
dude knows his shiz and will recommend/sale you the correct needle for your mods/engine
carb tuning in this order.......
is it spotless clean ?
http://www.blasterforum.com/carburetor-138/how-clean-your-carbureutor-254/
check/set the float height ?
http://www.blasterforum.com/carburetor-138/float-heights-how-adjust-them-50565/
set airscrew/pilot:
http://www.blasterforum.com/carburetor-138/adjusting-your-airscrew-pilot-jet-51060/
adjust needle from carb parts warehouse up(clip down) until it rich bogs,
then back up 1 clip position
then you can plug chop for main jetting
http://www.blasterforum.com/carburetor-138/how-plug-chop-53237/
a call to Carburetor Parts Warehouse set me free from months of chasing my tail with the wrong needle.
dude knows his shiz and will recommend/sale you the correct needle for your mods/engine
carb tuning in this order.......
is it spotless clean ?
http://www.blasterforum.com/carburetor-138/how-clean-your-carbureutor-254/
check/set the float height ?
http://www.blasterforum.com/carburetor-138/float-heights-how-adjust-them-50565/
set airscrew/pilot:
http://www.blasterforum.com/carburetor-138/adjusting-your-airscrew-pilot-jet-51060/
adjust needle from carb parts warehouse up(clip down) until it rich bogs,
then back up 1 clip position
then you can plug chop for main jetting
http://www.blasterforum.com/carburetor-138/how-plug-chop-53237/
ya i got it from a guy online he rebuilds them and cleans them and sells them, this one came off of a inline 4 motorcycle and it came with a 200 main 22.5 pilot and the same needle but in the 4th position just like i have it in. it wouldnt idle with the 22.5 pilot in it and barley idled with the 30 in it so i put the 35 in it and it idles fine now
An inline 4 motorcycle sounds like a 4 stroke. Correct me if I'm wrong, but I don't think 4 poke carbs will work right on 2 smoke motors.
it came off of a kz1000 drag bike if it wont work i guess ill stick my stock bored carb back on and call it a day and sell it to my buddy to put on his 4 poke 
everything seems fine once ur moving its fine and wen its idling it fine its just on take off u have to rev it high so it wont bogg
everything seems fine once ur moving its fine and wen its idling it fine its just on take off u have to rev it high so it wont bogg
It all depends on the carb. A CV-type carb won't work properly on a 2-stroke engine, but being that this is a regular VM-series round slide carb, its simply a larger 34mm version of the carb which came stock on all Blasters. Many older (pre-1980's) street bikes had traditional round-slide carbs installed right from the factory.
On the tuning problems, I used to run a Mikuni TM series carb on my Blaster. I could never quite get it tuned correctly for my engine, but if it helps any, I had it running acceptably (read: ridable and safely rich) on a 35 pilot, 320 main, P-8 needle jet (non-bleed type), and a 5fp17 needle. Since the TM and VM carbs are similar, you can probably use these specs to get you close. Then its just a matter of finding the proper needle for your bike and doing some plug chops. The needle selection is where I got stuck....Mikuni does not like sharing/publishing needle specs (I wonder if that's out of fear of Asian copycatting...look what happened to Keihin), and nobody would take the time to help me over the phone, so I gave up and bought a Keihin PWK 33. Hopefully your luck is better with your carb.
that guy was on here for a while, zedeco or sumthin like that.
i saw thats what he was doing, taking 4 carbs off a streetbike and adding the parts needed to run them single.
where is the airscrew on this carb ?
near the back is an airscrew for a 2 stroke, near the intake side is a fuel screw for a 4 poker.
i saw thats what he was doing, taking 4 carbs off a streetbike and adding the parts needed to run them single.
where is the airscrew on this carb ?
near the back is an airscrew for a 2 stroke, near the intake side is a fuel screw for a 4 poker.
ok and thats wut i thought also thank u very much! i appreciate it and do u think my needle is too rich or too lean right now? and obviously my main is way to small haha but i have main jet sizes 230-320 and its a 260 in it now and if the main is way to small id have problems once i tried takin off and givin it gas anyways right? so there is a possibility that the needle thats in there is usable until i get a different one? im suppose to go riding this sunday haha
well the screw is on the opposite side of the reeds just like the stock blaster carb its just on the right hand side if u were sitting on the quad instead of the left like the stock blaster carb
I didn't notice it was a VM series carb. Should be fine. I'm a keihin guy and won't be of much help.
you think it may be lean ?
i'd skip riding it at all until you get it correct, unless of course you take a tow rope and have a secret stash of pistons.
the main jet only comes on after 3/4 throttle.
i told you above how to get the right needle.
its ok thx neways i appreciate any and all info! and AWK08 and Braaaptor thank u keep the help coming plz haha
Needles vary greatly from one to another, and even two which look similar may perform totally different. Needles are categorized by length, taper, and in some cases distance between two or more tapers. First off, in your case, you'll probably want to put in at least a 290 main jet. What mods have you done to your engine (pipe, porting, intake, etc)? The more wildly-built your engine has become, generally, the richer you'll need to jet it.
After putting in a bigger main jet, its time to look at the needle. A bog between 1/4 and 3/4 throttle is usually caused by an incorrect needle or needle jet. The main jet does not directly deliver fuel into the venturi until after 3/4 throttle, and the only way a main jet can cause you problems down low is if the orifice in the jet is so small that the needle jet also starves for fuel upon acceleration. Also, too small of a needle jet can have the same effect, although I seriously doubt this is the problem in your case.
I'd be willing to bet that you have too rich (small in diameter) of a needle currently in the carb. One cylinder of a 1000cc bike is still 250cc, and in full drag form it will need to be jetted and needled much richer than what a Blaster engine could ever need. It sounds like your engine is flooding out as you get on the throttle, and only cleans out after a period of running only on the main jet (full throttle). Take Awk's advice and make a couple phone calls. You should be able to find somebody who can tell you what needle(s) will get you tuned in close. VM carbs have been made for years and put on everything you can imagine, so you're not alone in struggling to tune one correctly.
On another note, you may also need to drop your needle jet down a couple sizes, per the advice of a tuner of course. I'd ask while I had him or her on the line.
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ok i will put my 290 back in set the needle in the middle and just see wut happens im sure the needle is wrong haha but my motor is a +4 stroker, fmf fatty with a shortened fmf silencer, carbon 2 stage reeds, .040 over timing advanced 4deg, reed spacer, k&n filter, jugg is mildly ported, 14t front sprocket i run a br9eya plug
Why are you running that plug? Put in a b8es and a bigger main. Then start tuning from there. No need to run a cooler plug on your setup.
ok ill put a b8es plug in it it just made me feel safer in the summmer wen it was really hot out and a splash of race gas help keep it cool cuz we ride from dusk till dawn in the spring/summer
Ok, a 290 main will be in the ballpark for your mods, although you could still be lean. Be sure to do plug chops to confirm the main jet is correct as soon as you can. Otherwise you risk damaging your engine.
Having been in your shoes before, I can be pretty sure that your needle (and possibly the needle jet as well) is the culprit. To help you figure out for sure if you're lean or rich, install a fresh spark plug in your warm engine and go for a test ride at or around half throttle. Keep the throttle in the position where the engine bogs the worst (as much as you can anyways) for several seconds on end. Then shut down the Blaster, pull the plug, and have a good look at it. You may need to cut off the threads to analyze the "smoke ring" at the base of the insulator. Lots of black deposits or a thick black ring? You're rich. Light brown or almost no deposits? You're lean. Plug analysis can be done at all throttle angles, not just WOT.
the heat range of a plug only determines what heat range the insulator of the plug runs at to fend off fouling, not the engine temps
ok and will do ill slap a b8es in there and put my 290 in it i also have a 300 310 and 320 main jet so im good on that there r 3 shops near me that i can call and talk to them also ill pull my needle and see wut the number is and see if they have anything leaner in stock or richer after i check the plug around 1/2 throttle
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