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Anybody know Mikuni VM44 set up; Rotax 604 carb set up
Topic Started: Dec 27 2012, 06:06 PM (2,155 Views)
stevenfuture
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Does anybody have a clue how to set up a Mikuni VM44 carb to run on a 604 Rotax motor, its fitted, its had the airbox taken off, its got a foam air filter on it, but its the low end I'm having trouble with the air screw, to much out & revs wont come down fast enough, to much in & yep the revs come down but its very rich, maybe there is someone with an idea, (I'm guessing 1.1/2 turns out is pretty much the norm) but otherwise its a lot of trial & effort not to mention fuel! seen a bit on here, but a bit more would be good, then again it does say "not for aircraft use" on it, but try as I can the old tractor just wont fly.
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Monty
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Charlie Big Banana's
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Hi and welcome to the forum!!!!!!!!!

Best way to set up the air screw is get a fast tick over

wind the screw in till engine starts hunting. count turns as you wind it out till it starts hunting again, set in the middle.

Not sure if there are any members on here with a 44 fitted, Cuz may have, some have the carb but not the inlet as it has to be made/modified (tho I may be wrong)

have a look here, may help with running probs

http://forum.ccmmad.co.uk/topic/785442/1/
Edited by Monty, Dec 28 2012, 06:17 PM.
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stevenfuture
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Cheers for the reply & the link (which I already have downloaded) But I have done everything you said, but I think I need a better idea of what pilot jet to use as the one I have seems to be far to rich, the manifold is a brand new right for the job oneI have now modified the air filter area of the inlet by putting an extension from the back of the carb to the air filter & yep it made a slight difference (sort of like a venturi stack that the old british bikes used to use), but it looks like I'm on my own here with the Monster carb, I will get there, might take trial & effort but I shall not let the bugger get to me, I done it before on other bikes so I'll keep on trying with plug checks & the like if "Plod" lets me do some runs. when I get some proper data on what I get done rest assured I will post it.
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Monty
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Find out what jets you have fitted, and let me know as I have a fair selection here for the mikuni's.

recon the main needs to be about 220ish

If I remember a member called motomanic may have a 44 and scorpion zorst, and runs a 200 main, hopefully he may resurface and add some pearls of wisdom, not sure what pilot tho.
Edited by Monty, Dec 28 2012, 06:40 PM.
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stevenfuture
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Cheers 'Monty' I'm gonna take a look when the weather allows, as I'm a bit of a lazy git when the rain sets in, But 220 main sounds about right I'll have to take the 'Mikuni' apart to check & see where the needle is set what mains are in it also most important the pilot, I also have the Dell'orto 40mm to fall back on but don't want to admit defeat with the 'Mikuni'. now I've got the Dunlop mutants on it & the Beringer front brake, sorted the suspension out, I need the power the Mikuni has to offer even without a accelerator pump in it, it has to work.
had a Husky 610e supermoto'ed before & that had a 'pumper' Dell'orto on it easy life!!, & this CCM Rotax is almost as good, & with a bit of effort I'm sure it will be better, ie not such a 'hanger queen' bloody Husky was a nightmare to keep going what with all the endless tinkering, oil changing, valve checking, not to mention Mad prices of every part if you could get them! also had a Husaberg that was the same pain in the arse keeping on top of it, so that is why I've gone the CCM route with the Rotax, because the Suzuki engined ones had the motor out of a 'Freewind' no where as easy to tune up as the 4 valve Rotax, I'm going for 60bhp out of the one I've got & with a bit of effort should be totally possible, after all they managed to get it out of the road racers with a seasons racing without taking the motor apart.
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Monty
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couple of lads managed 57rwhp with the rotax, lot of work done, head was main thing tho
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stevenfuture
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Aha Monty I've been around this site & guess what......have you heard of "firestarter1977" well I've got his old bike (white one No 6 on it) OK it has been through somebody else's hands (could that be the problem?) so I've e-mailed him through this site & with luck should get some more info, But what I have gleened so far is : head ported & flowed. 640 kit, slightly skimmed head, the mikuni VM44, & 57 bhp, um so close but yet so far to understanding what I need to know, don't want to take apart a good engine, just have a clue as to what I need to do to it to make it sort of more mine, if you know what I mean. & patience is not what I'm good at, kinda go at it full tilt & its my Christmas prezzy to myself, which means I've had it about a week, so with luck I might get an answer from the man who knows most about this bike. but you have been a lot of help so thanks, & have a Happy New years.
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Monty
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I know firey well, quick bike and was sorted. pics of it at the lakes meet in your other post in welcome
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Cuz
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I have a 44 off a rotax and will have a look at the jet sizes,not to say they're right but might be worth comparing. I think MM was on a Del Monty. When I went on runs with Firey the bike ran really well,I think the only prob he had was it developed a head leak at some point and he was on about dropping the comp by fitting the base gasket back on. I don't know if he used the orange loctite on the head o rings that I was recommended to use. Pretty sure he'd be glad to help you out if you can get hold of him

Just had a look and mine has 270 main 45 pilot needle 2nd from top (blunt end). As I say haven't tried it yet but it came off a Rotax and might give you some ideas. Is your spacer/adapter plate 8mm thick as I need one,cheers Cuz
Edited by Cuz, Dec 29 2012, 12:12 PM.
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koban
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Hi cuz on Allen's performance site they have adaptors for the mikuni 44mm. And they list the spacing as 8mm.I don't suppose your selling your scorpion exhaust as well .I can't get one anywhere.
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stevenfuture
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Cheers Cuz & Monty, I managed to get hold of Mark (firestarter1977) exchanged a e-mail or 3 with him, its been through 2 sets of peeps until I got it so he's a bit out of the loop, mind you he did have a queery from the chap I got it from ( who had it taken apart) & that fella sounds like a bit of a dick, but what the hey its in my paws now so I have to find out what has gone on since, but thanks for the jet sizes & needle position, its a starting point to be getting on with, I took it out today, full throttle shes great, its just the rest is all to pot & tick over is all over the shop the pulg is more sooty than sweeps finger, so rich aint the word!! but maybe the needle? dunno, so tomorrow gonna take the carb off check whats in there & have a fun time cleaning the insides, Would anybody know what the float height is off hand? I can look it up but every idea is a good idea until it fails so I'm open to all suggestions, cheers all & Happy New year to everybody
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Monty
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Float height is 17mm, I'm pretty sure, if not Cuz will tell you whats what. manual say 18mm, but I'm sure most have found 17mm works better

OOps setting is for the del not mik sorry
Edited by Monty, Dec 31 2012, 10:03 AM.
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Cuz
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The 17mm's for the del. Not sure what it is for the mik but they're a sight easier to set than the del. I had a very similar problem to what you describe on my del which was cured by replacing the float needle and its seat,could well be the problem on your mikuni. I'll have a look tomorrow at my mik and see what thats set at,may not be right but could be worth a try if your stuck. Just off to look at Allens and see what they've got in the adapter department,cheers for the heads up koban and sorry but the scorpions going on my 560
Edited by Cuz, Dec 31 2012, 11:27 AM.
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Cuz
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Looked on Allens koban but I think your on about the rubber manifold adapter which I've got,can't see anything else.Its a round plate that goes on the head to replace the original manifold that the rubber fits onto that I need the thickness of so I can get one made up. Think its 8mm but not 100% sure. I know if I get it wrong the carb wont fit in,its mega tight in there. Can you see what firey did to the headsteady brackets steven 'cause I know they get in the way as well. I remember something about the lugs being bent out of the way,was going to cut mine off and re weld a bit further forward but would be nice to know if theres an easier way.

edit: just measured the float height and its bang on 17mm, Monty's always right :D the manual for the 44 says between 17-19 I think, so theres a good chance this carb was set up right for a racing Rotax
Edited by Cuz, Dec 31 2012, 12:00 PM.
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stevenfuture
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Cheers chaps, I looked up the specs & 17 to 19 mm float height seems to be the way to go....for the starting point, as sold std the mikuni VM44 comes 310 mains 35 pilot & that's the way "Husky's have it in the US, now because the weather is "pooh" & its a drinking day I've put off looking at the old girl untill next year!! so when I'm a bit more sober & without a thumping hangover the sun shines I shall take a photo or 2 & see if I can upload them, but don't hold you're breath as I'm not very good at this computer stuff, might have to get a "youth" to help......
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koban
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Sorry Cuz I thought the plate adaptor was what I needed.I,all have to look at Stevens pic,s to see what goes where.Looks like I'm gonna have to get an exhaust made probably from Gibsons unless anyone's got any suggestions.
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Cuz
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It's my dodgy terminology koban.The plate manifold on the allens site needs to bolt onto a piece of alloy as a replacement for the Rotax intake flange. This is what I've been calling an adapter plate (soz for the confusion) It needs 3 countersunk holes for the screws that go into the Rotax head and another 2 tapped holes for the manifold plate. I don't think theres any other method out there that'll squeeze the 44 in. What we need to know is how thick to make this new part 'cos I know its a real tight fit in there and its crucial. I have 8mm in my head but not sure. Want to get it right first time as I have to get someone to make it for me. I've tried to work it out by fitting the carb into the frame I'm using but its impossible for me to tell accurately. Glad someone else is having a go,more heads the merrier lol
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stevenfuture
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cuz & koban, I've been out taken the VM44 mikuni off today took some photos, wanna see em? well I don't know how to put photos up, call me a 'luddite' but if you tell me how I shall do it, anyway I had to loosen the subframe at the front top, swing it back to get the carb out, also the choke lever is a very tight fit against one of the head steadys after all that , I've got 320 mains - 45pilot, & the needle is in the middle, float height is 19mm, what this means is the pilot airscrew will work sort of 3 &1/2 turns out THATS to much might fall out , the spring WILL NOT hold it at that range. So this what I'm going to do. Pilot jet down to 35, needle 2nd from top ( or a drop of one notch) leave the mains as is. an extension on back of carb (to mount airfilter as before it was hitting the frame shock mounting.) yet again you can laugh but outside diameter of back of carb is 70mm, so a visit to the guttering on the shed & i came away with a sleeve almost 70mm inside diameter & air filter fits nice on smaller bit, its a bodge but as it works I'll on it improve later
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Monty
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open a photobucket account,

upload your photos

once uploaded, hover your curser over the photo you want to put on here, a drop down box will appear.
put curser over "image code" and left click, should say copied in code box.

Open thread on this site and right click then paste.
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stevenfuture
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Well the latest up date on this Mikuni is 320 mains seems just far to big, changed the pilot for a 35, easier to start, better very low speed running, so down came the needle 2nd from top, not much of a change, so dropped it all the way down, aha... just a little better, but I have petrol swilling around the top of the slide, now thats rich!! so I'm gonna bite the bullet & go smaller on the mains, & put the needle back to the middle just what size to try?. 250 all the way through to 310, then I shall have a good selection to go for a whoopah with. easy to change the main due to the nice people at Mikuni. knackered the back tyre so far doing this had to buy a new one anyone tried a heidenau super rain? got it for £42 so more to spend on fuel testing!!!
more to follow as I progress.
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