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Post by richied on Aug 26, 2007 7:46:05 GMT -5
HI to all,
Im looking for info on a flatslide carb for a sr motor. what is the magic # for a flat slide on a engine with a 540 piston megacycle cam and a cleaned up head?? I need to start looking for one for my project but I dont want to just get one and it be way to big or small.
Thanks in advance
Richie
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Post by wotavidone on Aug 26, 2007 19:40:45 GMT -5
Dunno what is best, but the rebuild article in VMX magazine seemed to suggest 40mm Mikuni.
That is a big step from the stock 34mm carb. You are in the right place to get the question answered, I reckon between them, CJ, SR, Lurch and others on this site have probably tried every combination going.
Mick
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lurch
Full Member
Posts: 217
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Post by lurch on Aug 27, 2007 2:08:33 GMT -5
I recon this may be a question for Stew Ross ,over 2 u Stew  LURCH |
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Post by colinjay on Aug 27, 2007 17:42:10 GMT -5
The 40mm Mikuni flat slide carbie as used / recommended by Carl in his articles in VMX Mag does seem to be the way to go now days.
On the racer that I am building, too comply with Period 5 historic race regulations, I have to use a carbie that was available during the period, so it is either the 38mm EI flat slide or a 38mm Mikuni round slide. I already have both carbies, but the EI is easier to tune (just adjust/change the the fuel rod) so it is what I am going to use.
CJ
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Post by StewRoss on Aug 31, 2007 7:17:54 GMT -5
Hi, Hmm, never used a flat slide Mikuni of any size. My brother run two 38s flat slides on his Darmah however, and they seem to go fine. Flat slides are supposed to 'carburate' better than a round slide...more efficient mixing. My take would be it depends on what you want to use it for. My experience has been to use no bigger than a 38. I have two 38 Mikuni's on different SR's and I have a 38 KeiHin CRS round slide ready to go onto my full-on engine in the new cafe racer. I have however heard of people using a 40 round slide Mic on SRs before and they seem to like them. The Japanese seem to use the 39 KeiHin flatslides on the road often as well. These are considered to be probably the best commercially available carby around...certainly one of the most expensive as well. As with the CRS they are true 'works of art'! A few notches above the Mikuni! My personal idea is that the really big carbs are only of any great use if you're at high revs often, such as in racing etc. I think that they'd work on the road but probably not well at low to mid range when compared to the smaller carbs. The larger the 'hole' the lower the airspeed through it... Sorry, I haven't really assisted you much I feel. In the end you'd have to weigh it all up...and probably buy it anyway...heh, heh... SR |
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Post by wotavidone on Sept 2, 2007 17:57:33 GMT -5
I see where you are coming from with this Stew.
I agree. If you want serious low to mid range grunt, a big bore carb is a contradiction. Low air speed, poor aspiration and mixing of fuel.
If you want a screamer, then you must have the top end air flow to feed it, so a big carb is the go.
It makes me think a couple of mm over standard is all you should do, unless you are making major changes elsewhere, e.g. porting, cam, exhaust, etc.
And then you need to be aiming for a big revving engine.
Mick
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Post by wotavidone on Sept 4, 2007 18:41:53 GMT -5
Down loaded a mikuni tuning manual from mikunioz. There is a graph in this manual which suggested a 32 mm carb is all that is needed for a 30 hp engine. Most people seem to think they get a worthwhile improvement by going up from 34 to 38.
I suppose it depends how you look at it. Is it a case of an engine which develops 30hp only needs 32mm, or is a case of if you have an engine which develops 30hp with a 32mm carb, then you get more by going up?
Mick
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Post by richied on Sept 7, 2007 20:52:53 GMT -5
I have the wiseco 540 piston 12:1, megacycle cam (not sure of the grind it is in a white bro's wraper and I havent gotten around to calling megacycle to find out what the #'s are for it yet)and 2mm ss bigger valves. the head is not done yet but I dont want anything radical it needs to work on the street. so with that in mind what do you all think?  |
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Post by fenz on Sept 7, 2007 23:48:06 GMT -5
Yeeehaaarrr is what i think
Should be a good package but you will need some good fuel to run 12:1
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Post by GraveSite on Sept 17, 2007 12:41:02 GMT -5
Anyone know why leaving the Vacumm tube to cock valve off? It runs better & idling eitherway engine surges on idle up & down.
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lurch
Full Member
Posts: 217
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Post by lurch on Sept 18, 2007 11:56:55 GMT -5
Hi Leaving the vac pipe off lets more air into the system giving a weaker mixture I suggest you check you carb for blocked jets & or float valve for leaking & correct hight ,also check the condition of your air cleaner Have you checked the color of the spark plug ?both with & without the vac pipe connected it should be a light tan color There could be a number of other things causing this like faulty ignition system . tight valve clearances or just simply a duff spark plug ? Don't want to state the obvious but have you turned the choke off ,up is OFF down is ON, you'd be amazed how many times I've seen this mistake made  Sounds like your bike just needs a good service LURCH |
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lancer
New Member
There is no substitute for PERFORMANCE
Posts: 10
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Post by lancer on Sept 19, 2007 0:43:18 GMT -5
HI to all, Im looking for info on a flatslide carb for a sr motor. what is the magic # for a flat slide on a engine with a 540 piston megacycle cam and a cleaned up head?? I need to start looking for one for my project but I dont want to just get one and it be way to big or small. Thanks in advance Richie As a rider of a Suzuki Savage 650 single which has been modified a bit with a midrange cam, shaved head and ported for better flow, hand built exhaust, silicone carbide cylinder with overbore and such, I use a 36mm Mikuni VM roundslide. The stock bike came with a 40mm CV which was a dog of a carb. The 36mm VM is way better in the performance area. It is capable of flowing more air/fuel mix than the engine can use, making max power available but still keeping the velocity of the air through the carb bore high enough to keep the low-midrange power and responsiveness very impressive. My engine was making up to 45 peak hp and 42 lb/ft torque while still at the stock 8.5:1 compression ratio. The current work wll bump the compression up to about 10:1 and open the exhaust ports a little more than before. I am looking for about 55hp when it is back together. I have tested at least 8-10 different types and sizes of carbs on my bike for about 5 years and have found the 36mm VM to be the best all around carb for great street riding. Going larger may enhance the very top end slightly but will hinder the low & midrange where we spend most of the time. I also sell carb kits (several hundred kits in the past 2-3 years) and this is the most used carb. I usually see a 34mm carb mentioned for the SR, but if you have done significant work with the head/valves, and have a really good free flowing exhaust, then you could move up to the 36mm. I am absolutely certain as well that by going to a 38 or 40mm carb bore you will hurt the overall performance of your engine for street riding If you are just racing and never get below 5000 rpm then the bigger bore may do you well. If you have not looked into it yet, I also suggest that you consider some parts from "Thunder Products" if using a roundslide VM Mikuni carb. The UFO (Ultimate Flow Optimizer) and the Dial-a-jet. The UFO handles primarily the low throttle range and the DAJ takes care of the mid and high throttle range. In a 500 cc engine you can realize a 5-7 hp increase with these installed in/on the carb. Low and midrange throttle response is dramatically increased. www.thunderproducts.comI don't spend much time on this forum, mostly on the suzuki savage forum, but if you wish to get into the carb stuff more deeply then you can contact me at power@savageperformance.com Have a good day Michael |
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Post by milkman on Sept 19, 2007 7:48:23 GMT -5
Dial-a-jet looks interesting.....for a "mess maker" like myself
Almost looks too good to be true.
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Post by GraveSite on Sept 24, 2007 21:44:38 GMT -5
Carb Vacuum tube on & off. The Air filter New. Carb doesnt leak at over tube. On starting i pump the carb 3 times & on kick start turn throttle like im accelerating which starts in 2 to 5 tries.
New, spark plug which is black fluff like soot running with the vac tube on or off but run better off.
Seems a good carb rebuild kit may fix the problem which where can one get a complete kit? This may also help the flame roll out sound going through exhaust when i turn it off.
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Post by GraveSite on Sept 28, 2007 17:48:16 GMT -5
Hello, After reviewing on carb choke. The choke lever down puts the choke in up & versa versa. which improved running status & no longer flame roll out like raw gas ignition in exhaust.
So, the lever down pulls the choke valve up. & up position pushes the choke lever down.. I found tried this and the Ol-girl wants to tear up the payment. Could it be that simple? I'll pull plug to read condition & let ya all know.
Other wise i would like to sell this thing for something that has a electric start...I can get get it running in 5 or less kicks. A neighbor complains it rattles his windows & false teeth.
Great forum Guys. I'll pass ya you along in the States Here.
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