I am going from the yamaha 33mm carbs to a set of 38mm Polaris carbs for my BB triple. I was wondering if there is a conversion for the carbs and needles to go from one style to the other? The Yamaha carbs have small round jets and the Polaris carbs hav the hex main jets. Thanks in advance.
Main Jet Size Converisons
- Thread starter lords88
- Start date
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spring snow hero
Well-known member
throw out the carbs and engine numbers.........
The carbs I am wanting to get rid of are stock 2000 Yamaha 700 mountain max, mikuni 33mm flat slide carbs. The carbs I am wanting to go to are stock poalris 700 xcr, mikuni 38mm round slide carbs. I just figured there would be an easy conversion chart for going from one type of main jet to another to get the same amount of flow.
G
gus bohne
Well-known member
start with the oem jetting for the polaris. Yes you have a smaller reed cage and a shorter stroke but it should get you going and allow needle tuning to get it crisp enough on the stand to determine your needs.
those are from the xcr with triples so the needle jet and needle will be close.
as far as mains go ,, each reacts to vacum differently so correlation is non existing.
gus
those are from the xcr with triples so the needle jet and needle will be close.
as far as mains go ,, each reacts to vacum differently so correlation is non existing.
gus
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NoSecondChances
Well-known member
Call Mikuni for the chart with the fuel in lbs/hr for the rounds and the hex's. This will give you an idea of what hex mains will flow about the same as the round 33's mains you had it in, but you're just going to have to tune it like Gus said anyway, but they might be able to help find a rough starting point (or at least confirm your thoughts).
NSC
NSC
I found a chart that roughly compares the two styles of jets flow. That should give me a rough estimate of where of where to start. Can the needle jets be swapped from one style to another or are they completely different also. This isn't actually for a 700, so the XCR tuning I don't believe will be very close. Its for my 944 mod, I thought it would benifit from a little more air flow and a little more tuner friendly carbs. I will also be adding power jets to the mix.
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NoSecondChances
Well-known member
Different needles since the carb throats are different diameters. The emulsion tubes (needle jets) may or may not swap, but I don't know for sure, never tried, but I would imagine they are different.
If you have the flow charts then at least you have a starting point. The power jets will give you a good tuning range as well.
NSC
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gus bohne
Well-known member
brass is not intercahngeable..
q-4 is a good start, 6dh2 needles is a good start also.
i do not remeber the xcr 700 having roundslides ?? thought they had oem mikuni flats like the 800 xcr,, all years..
for altitude you might end up with a q-0 nozzle but trial in field is best.
q-4 is a good start, 6dh2 needles is a good start also.
i do not remeber the xcr 700 having roundslides ?? thought they had oem mikuni flats like the 800 xcr,, all years..
for altitude you might end up with a q-0 nozzle but trial in field is best.
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theultrarider
Well-known member
I would go with the 40 mm flat slides. Much better carb imo. Plus the xlt 38's are tripple pull cables and the rack flat slides are single cable. The single cable would be much easier to setup and they pull WAY easier on your thumb!
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theultrarider
Well-known member
Like what was mentioned above by others what you want is a set of rack flat slides off of a xcr 700 or 800 of the 2000ish vintage. The needles are not really that hard to get at once you figure out how to do it. The are easier to tune as well and are not as picky as th eround slides either. Good luck with your mod and hope she rips.
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NoSecondChances
Well-known member
I would almost have to agree with theultrarider. The flat slides might be a little better, not to mention they will let the 944 breath a little better being that they are a little bigger, I don't think 40's would be "over-carbing" that motor, and once you get it dailed with them, you probably won't have to change the needles if you cut the dump tubes on your powerjets to the correct length. You might just have to keep an eye on the EGT's and not stay at 1/2 throttle for miles and miles and miles on the trail.
NSC
NSC
So I took the 40mm TM carbs apart today and this is what I found. The needle is a 6DP4 the needle jet is a Q-0, pilot is a 45 and the main is a 240. I know the main is too small but are is the needle and needle jet close to where I should be with the 944.
