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Post by davedunsboro on Apr 30, 2008 6:25:34 GMT -5
I've finally worked out that the carby I got off a mate of mine is a HSR flatslider type (it certainly looks like the pictures of them anyway)On the site I was looking at they came in 42,45&48 versions . The one I've got measures 36mm internally on the engine side & about 40mm on the filter side. It was quite an easy fit as it went straight onto the standard manifold & it also took the dual throttle cables except for I had to transpose them . The K&N fit on with a bit of PVC pipe & a couple of hose clamps (plus help from a heat gun) Anyway I got it to run but no power , I drilled the jet to the same size as a standard carby more power but still not full, good off the mark to about 4k but won't pull over that on load in any gear hmm. I then cleaned up my standard carby & put that in to see the difference & it responded the same ! I've got a Harley type muffler on it , so there isn't any restriction ? I'm running 17t front 42t rear . Would I lift/lower the needle ,use a larger main jet ? It starts & idles well (if I could only get a couple of litres of super I could tell by the plug) Any comments /tips would be greatly appreciated cheers Dave.
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Post by aero on Apr 30, 2008 6:54:16 GMT -5
I'm not familiar with that carb, but even a 42 mm would be big for an SR.
If it won't rev above 4000 rpm I'd say it was over rich. If you drilled the jets did you mic the drill up and compare the size to the mikuni jet size chart that was floating about on here? Just banging a standard size drill through the jets is very hit and miss. The difference in hole size between the jets is tiny.
It may just be over carbed, A 38 is about the limit in most cases for a road bike.
Sorry if I'm suggesting an egg sucking session!
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Post by davedunsboro on Apr 30, 2008 8:30:13 GMT -5
OK that could be a good call as I did notice the bike not being very economical on the run I took it on( I put 5 litres in for about 60 ks) .Before I drilled the jet I was only getting around 3k before the power dropped off hmm the plug was black but unleaded fuel is so hard to be sure . Next question , how is a carby measured ? As I'm definately missing something here (It's obviously not the bore at the manifold end) cheers Dave.
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Post by fenz on May 1, 2008 16:08:45 GMT -5
Dave i put a 34mm flat slide on my bike (non pump) and tried jetting to similar specs as a round slide mikuni.
It would run but no power up top and it would back fire etc.
Thinking it was lean i went bigger but no good,out of frustration i went back the other way by a large amount and it runs great.
Current main is a 170 which you would think is way to small on that size carb but the bike runs fine.
I think that the flat slides seem to carburate more efficently therefore require smaller jets, i am no expert on the matter so may be some of the guys that have tuned on dynos with these carbs could give some input.
You are measuring correctly (internal diameter of the fuel side of the carb).
If you have plenty of jets try going around the 190 mark and see how it goes.
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Post by aero on May 2, 2008 3:54:24 GMT -5
Its quite common to find a bigger carb requiring smaller jets then the standard carb did.
If you want a copy of the Mikuni jet numbers to hole dia let me have your e-mail address, I finally got round to scanning it into my computer the other day.
Marcus
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Post by davedunsboro on May 2, 2008 5:08:11 GMT -5
Thanks for that good advice lads! I sort of worked it out to be that too (so what do I do solder up the hole & redrill it) I just thought I'd say that! Its off to the jet shop for a handful of jets I should think? The other thing this carby is good at ,if your looking into it & do the throttle thing as you watch the slider go up it skirts you right in the eye! I'm also going to put the carby out of my red SR into to see what it does ,just for a benchmark .I'll also note the needle clip & jet size as this one is set up perfect for the stock engine .I may as well do the homework now as winter is starting to get here ! My email is dunsrewinds@hotmail.com cheers Dave
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Post by caferacercarl on May 4, 2008 2:47:26 GMT -5
there is a huge difference in jet size between mikuni and keihin, keihin is in millimetres eg, 170 main jet is 1.7mm in a mikuni that would be close to a 400 main, will check up at the shop tomorrow.
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