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Anybody know Mikuni VM44 set up; Rotax 604 carb set up
Topic Started: Dec 27 2012, 06:06 PM (2,158 Views)
stevenfuture
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Well here goesPosted Image lets see if this worksPosted Image-1_zps41168805.jpg[/IMG]
Testiculos habet ingens et bene sedeant
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stevenfuture
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stevenfuture
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stevenfuture
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Cuz
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Cheers Steven,somehow lost the ones you sent me when I replied to your email,good luck with the jetting. I'll stick a pic up of my 560 head in comparison to a standard 604,the 560 went like a rocket and I'm hoping to rebuild this year and stick in my other ccm604 frame,even though it originally came out of an.., eeermmm... ktm

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Edited by Cuz, Jan 11 2013, 01:06 PM.
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stevenfuture
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Took me a while to find a "yooth to learn me" but now I think I can do it, Just waiting for a bag of main jets from ABV Racing then its testing time with a plug spanner in my pocket, I like to do it the old way by feel & guessing, & finish off the "Mutant" on the back, they don't last very long but what a good tyre pity they are so expensive, I take it black one is the 560 head, the porting looks very tapered, is it smooth, or does it have ripples? but it looks wide open, should flow a lot of gas, exhaust side similar?
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Cuz
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The exhaust side looks standard.need to clean it up though to see if anythings been done in there. The intake looks like a similar finish to yours Steven. It needs new crank casings as the original magnesium ones have been welded but still leak. Could be tempted to get a set of porter brothers casings when I sell the other bike as I heard the standard ones are prone to cracking above 8'000 revs and when I had the 860 cam in the standard 604 engine it felt like it wanted to go above that,in fact it felt like it would have kept going till destruction lol
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stevenfuture
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Well here is the latest, on bodger Steve 'aving a go' it might be cold but that has given me heart to go smaller. so far I've now gone down to #25 pilot, (a big drop from the #45 that was in it) works quite well it ticks over well & stays there even when you stick the big stoppie on it, the pilot jet needle valve is now at a healthy 1.1/2 turns out (works good). (I've gone from #320 that was in it) #250 through all up to #300 on the mains & this is all done by feel & plug checks OK so no definitive results but haven't moved the needle from std (middle) position....yet I'm getting there. so what is the conclusion...ah more testing before the dyno gets me, dyno doesn't always give you the drive ability that I want so its the last thing I will do, & that's only to get the main jet right at full open throttle but I can say don't be afraid to go small on the pilot, anyway its ongoing.
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Cuz
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Was reading through some old info the other day that said high comp rotax's need to be run on super unleaded, thought I'd pass it on to you Steven,may help
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Monty
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Cuz
Feb 3 2013, 03:01 PM
Was reading through some old info the other day that said high comp rotax's need to be run on super unleaded, thought I'd pass it on to you Steven,may help
All rotaxs should run on super (97oct) acording to the manual. tho being tight mines run on std (95) set up accordingly.
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stevenfuture
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Cheers for the octane advise, I do use the expensive stuff as a matter of course, but had a go with a gallon of "LL 100" in other words avgas (light aircraft fuel) just for the crack. used it on my old Z1 Harris drag racer in the past made a difference then & this time oh did she like the 320 main jet then....but its a bit hard to just pop in to a aerodrome, but if you get the chance give a go its a laugh at the top end of the revs. but remember L.L. means 'low lead' (still got a lot in it) 100 is min octane rating & that bit is True!! anyway getting bored keep changing jets & thrashing the beast up & down the same road even 'plod' knows when I'm out & about now so might have to make friends with the chaps at the private airfield & get some time up & down the runway there well here's hoping I can find a TE lawrence fan...you never know?
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Cuz
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I remember Forteh saying it was essential on the high comp/no base gasket motors,I like you Monty am on as cheap as I can get :D

Don't forget Steven the crankcases have a habit of cracking over 8000 revs,thats when you get into the expensive porter brothers billet jobs

Try putting a Brough Superior sticker on the tank when you go down to the airfield
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stevenfuture
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I've got a got a base gasket on now, so lower compression for having that, revs is a bit of a problem as I've got no tacho but... how about this for a laugh they might let me tear up & down local airfield but after all flights finished, yep its dark &....... its grass!!.... need a few drinks to be getting that brave, so that's off the list, back to dodging the law again. anyway I'm on #280 mains, #25 pilot & still the air screw wants to be 3 to 3.1/2 turns out or more! just to tick over nicely, How small on pilot jet do you have to go to have a nice 1.1/2 turns out, I'd settle for 2.1/2, I'm not giving up just adding to my already large collection of jets now, so soon if new Southend matey gets some info for me to start with then yippee working benchmark. Been out today & it was just right the weather hint of cold, nice dense air, perfect for a high speed run....Hampshires finest out as well enjoying the weather, back to me having quick blasts then whipping the plug out, just like the old days with my two stroke Kwakers & Yams, thank God I've still got my Dutch licence, gives poor old Plod a head scratch not knowing what to do, anyway its a laugh pity the back tyre has had it, new one to go on real soon as this just slides coming outta corners now but I'm gonna kill it bald. & the chain is coming out in sympathy with it.
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RB636
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I did text you but unsure if you got it. My carb man reckons the following but I think I have a 310... Anyway.
300 Main
45 Pilot
Z-0 Needle Jet
7DH5 Needle
3.0 Slide
1.5 Air jet
3.5 Float valve
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stevenfuture
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What a star, seems like I've got to get my specs out to read whats on all the small jets & needle now, bugger this optically challenged stuff why can't I have eyes like I used to have or maybe find a magnifying glass there's an idea, I got you're e-mail but looks like my phone is missing again & cheers its a ace place to start even if the pilot seems rather large does you're air screw like 1.1/2 turns out mine just splutters & sends the plug all sooty & the tick over is all up the creek too when I had the 40 pilot in.
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RB636
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Potato Farmer
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My tickover has never been good from cold. In fact when cold it wont tick over without a bit of fettling of the throttle but is fine when warm. Once warm it's fine so there's no point (to me) messing with it trying to get it to run well cold. Start with choke until revs drop, choke off and away!

I found finding the best setting is like this. (kind of stolen from the vm44 handbook but in my own words) Turn the idle up to say 2000 using the idle screw. From all the way in, turn the air screw out until the revs are highest. If they are highest between say 1 turn and 2 turns out, 1 turn is where you should have it, the rich side of the highest rev you can find. Any more than 3 turns out you risk losing the screw when you ride as the spring wont be holding it in and it will be near the end of the thread.


I dont understand why you have half my size pilot but need more air via the air screw! Surging revs can mean too lean but if it runs better with an even smaller pilot then I don't know..
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stevenfuture
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Baffled that's me. it doesn't make any sense, I've started with #40 pilot' sooty plug, then came down to a sensible #35 pilot (std fitting) no bally difference....nuts it was cold (not much chance of over heating) so what the heck #25 pilot.... & its the same only happy at 3 turns out, it says NOT FOR AIRCRAFT USE on the carb pity because with that thin air up there it might work!!!! so here I am at #300 main. std needle position. #25 pilot. & a sooty spark plug, I've gone down to a #250 main & worked up to this what I have now & lots of combinations with needle down, trousers down!! even put my beer down, I fiddled more than "Jimmy Saville" it seems, shagged out the back tyre, now the chain & a few gallons of petrol, oh its going to be a laugh looking back on this when its good enough.
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RB636
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Almost want to take my carb off my bike and put it on yours to see what happens! (Almost, but not in this weather!)
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stevenfuture
King
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We have success, with this here problem, turns out the needle jet had been drilled out, & the air jet was not helping being to small, so now we have 1.5 air jet (pain in the arse to get out (std 0.5) , Z-0 needle jet (emulsifier) needle 7DH5, 2.5 slide (std, 3.0 maybe later?) & bingo tickover on 1.5 turns out on the airscrew still on 35 pilot jet (std),for now might go up to 40 or 45 if it needs it, mains on 320 that works. the begining is over, now the extra fine tuning begins........ :goodgrief:
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koban
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Hi Steven, glad your getting there I've got all that fun to come. The photos you put up were really helpful but still couldn't get an exact thickness for the intake adaptor plate that bolts onto the head. Because if its to long it won't fit and to short it will be hard to set up.would you or RB636 be able to get an exact measurement as myself and Cuz are going to have to make the plates and it would save us a lot of trial and error. Picked my head up from Bob Farnham today,he's taken quite a bit a out of both ports and said it was a lot of work. Nice fella I could talk to him all day and would recommend him.
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