Mikuni Carbs Installed on 450 - Page 3 - Honda Rebel Forum
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post #21 of 32 Old 07-22-2015, 09:36 AM
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I share your frustrations guys that is why I am going to convert my 450 to fuel injection .Seems the best thing to get my fuel system fixed for good .Am sick of my carbs changing their mixture from day to day lol



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post #22 of 32 Old 07-22-2015, 03:00 PM
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Did you buy the carbs used or new? How much for the pair?
I have a couple of 450's and am also tired of them not staying the same and not idling.

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post #23 of 32 Old 07-22-2015, 05:13 PM Thread Starter
 
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Did you buy the carbs used or new? How much for the pair?
I have a couple of 450's and am also tired of them not staying the same and not idling.
The carbs are new form Sudco.com for $149.95 each plus shipping. They are true Mikuni, not the Chinese look-a-likes, were suppose to be pre jetted, I was in hopes they would at least be in the ball park, they were not! Sudco did not bother to tell me they had no experience with 30mm carbs on any 400 or 450cc engine until after I had them mounted but that did not stop Sudco from selling me almost $400 worth of needles, needle jets, main jets, idle jets, and slides. I am all but finished with the jetting, waiting for hopefully the last needle jets that I will need. I knew the 30mm carbs would hurt the 450 Rebel some on top end because the engine came with 32mm carbs and it did top speed is around 90MPH and the slow to mid range is as crisp as can be expected. As I have said before I will be going with a pair of VM32mm carbs to try and get back the top end.

1986 Honda Rebel 450 28,000 miles
1987 Honda Rebel 450 5,000 miles (sold)
2009 Honda Rebel 250 8,000 miles
1983 Honda CX 650 twisted twin 6,000 miles
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post #24 of 32 Old 07-22-2015, 09:49 PM
 
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When you say didn't take to much work, could you elaborate( diffrent jets,linkage,etc)
For starters I bought a universal cable for the VM series carb, a 42mm china cone, the carb I bought was a flanged carb, and I made a adapter but you can buy a 26mm VM with a spigot mount, This is a VM made for a 4 stroke engine on a china quad or pit bike, not a two stroke variant.
I used a AEM wide band to tune the thing, got the main jet almost 100% correct at wide open throttle using a 110 large mikuni jet, the stock pilot jet worked ok with the pilot screw out 2 1/4 turns, and it took several 1mm changes to the float height to get the thing to run clean at idle and just off idle, I fixed a lean spot at around 1/4 throttle lifting the needle a ring or two. you can also use shims to get a half of a groove change. that's about it most of the work was done in one afternoon with a late start and from time to time I pick at it to make it a little cleaner in a attempt to get better mileage. best mileage so far was 74mpg city and highway combined,

'00 SV650, '00 GSX1300r, 91 EX500, '85 CMX250C, '75 XS650.
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post #25 of 32 Old 07-23-2015, 08:04 PM Thread Starter
 
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Gixxer1300, would you please correct the type-0 of a 42mm china clone carburetor on the 250 Rebel. For I do believe you meant to say 26mm and this stuff in complicated enough with out confusing me.

1986 Honda Rebel 450 28,000 miles
1987 Honda Rebel 450 5,000 miles (sold)
2009 Honda Rebel 250 8,000 miles
1983 Honda CX 650 twisted twin 6,000 miles
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post #26 of 32 Old 07-24-2015, 10:09 AM
 
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You must be real confused the carb is a China Mikuni VM 26mm, it has a 42mm inlet so a used a 42mm CONE FILTER on the 26mm VM. I've been building and racing bikes for years I guess when I explain something I'm used to talking to other mechanics, and racers so I don't use much detail. Sorry

'00 SV650, '00 GSX1300r, 91 EX500, '85 CMX250C, '75 XS650.
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post #27 of 32 Old 07-24-2015, 10:22 AM
 
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As far as spending $400.00 more for 32mm VMs I would get rid of the stock airbox and use a set of K&N pods at 100.00 for the set. The bike will breath a lot better, have better than stock low and mid rpm throttle response, with a better top end. Also you said you had the fuel right and it was lazy in the middle. Where were you setting the fuel 14.7 to1? Fuel number don't have to be at stoich (14.7 to 1) idle yes, cruise close, but high RPM street bike stuff at full throttle 13.7 to 13.9 will make it pull better without killing mpg, high compression high load stuff on the dyno I have seen good power at 12.9 to 13.7 depending on the bike and engine type. Your street bike shouldn't be throwing coal, but a little richer makes good power, end even though your using a wide band use clean plugs often and read them they are your best indicator. I've never spent $400.00 to tune a set of two carbs and have built bigger twins close to 100hp. inline 4s nearing 200hp

'00 SV650, '00 GSX1300r, 91 EX500, '85 CMX250C, '75 XS650.
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post #28 of 32 Old 07-24-2015, 10:57 AM Thread Starter
 
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Thank you for the clarification. This is what I said about the middle the slow to mid range is as crisp as can be expected. I am shooting for a ratio of 13.0 to 1. at mid range and full throttle. Just a little rich I know but I want this bike to have a long and happy life and not run hot.

1986 Honda Rebel 450 28,000 miles
1987 Honda Rebel 450 5,000 miles (sold)
2009 Honda Rebel 250 8,000 miles
1983 Honda CX 650 twisted twin 6,000 miles
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post #29 of 32 Old 07-26-2015, 09:27 AM
 
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Fuel demands at cruise and acceleration differ, try leaning the mid a little closer to 14.to 1 to 14.5 to 1 at cruise. If you have the right needle and pilot jet it will go in the 13.2 to 13.7 when you wack the throttle. Most two valve engines like to cruise lean, and like a little more fuel when you accelerate. Again I'd consider playing with a cheap set of Uni- filter cones. Uni is about 1/2 the price of K&N, you can wash then in your shop sink, and use any filter oil on them you find at the auto parts store. A set can be had for about $40.00 at Dennis Kerk or other online cycle parts shop.

'00 SV650, '00 GSX1300r, 91 EX500, '85 CMX250C, '75 XS650.
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post #30 of 32 Old 07-26-2015, 09:50 AM
 
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Originally Posted by Gixxer1300r View Post
For starters I bought a universal cable for the VM series carb, a 42mm china cone, the carb I bought was a flanged carb, and I made a adapter but you can buy a 26mm VM with a spigot mount, This is a VM made for a 4 stroke engine on a china quad or pit bike, not a two stroke variant.
I used a AEM wide band to tune the thing, got the main jet almost 100% correct at wide open throttle using a 110 large mikuni jet, the stock pilot jet worked ok with the pilot screw out 2 1/4 turns, and it took several 1mm changes to the float height to get the thing to run clean at idle and just off idle, I fixed a lean spot at around 1/4 throttle lifting the needle a ring or two. you can also use shims to get a half of a groove change. that's about it most of the work was done in one afternoon with a late start and from time to time I pick at it to make it a little cleaner in a attempt to get better mileage. best mileage so far was 74mpg city and highway combined,

For anyone doing this pilot jet was a 15. Its a VM28/486 style some carbs come with a 17.5. Main jets I used are large head Mikunis, they can all be bought cheap at JetsRus.com they sell Mikuni and their brand. I'm contemplating a jet change to a 105 main, and maybe a needle change to get rid of a tiny lean spot just at 1/3 throttle in a attempt to get the milage to stay at a constant 75ish. The lean spot is nothing you can feel really just seeing it on the wideband drives me crazy. Oh with cruise AFRs fluctuating from 13.8 to 14.7 or so I can still put my bare hand on the cylinder at 60 or so mph and count to three or four fast before I have to remove it.The bike is not over heating, and the plug color is a nice medium to light tan color.

'00 SV650, '00 GSX1300r, 91 EX500, '85 CMX250C, '75 XS650.
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