First Generation Ascots > Tech Section
Mikuni Carburetor Information Links
J6G1Z:
Carb specs:
36 mm VM Mikuni
#25 pilot jet
#2.5 slide
#210 main jet
#P5 needle jet
#6DH3 needle--dropped down as far as it will go.
Specs provided by OldGuzziGuy on the Yahoo Ascot Owners Group. These specs seem to impact fuel economy.
J6G1Z:
....I can wholeheartedly recommend a Mikuni 38mm roundslide carb. I had one of these on my XR500 I vintage raced, and besides giving a little bit of boost in power, it is a very easy carb to live with. Starts well, idles smooth, takes sudden/quick throttle openings well (you do have to sorta roll the throttle on smoothly & quickly), & is overall easy to tune. I have some jetting specs, if anyone is interested......
Carb: Mikuni 38mm VM Round Slide
Slide Cutaway: 2.5
Needle: 6DP1, clip in the middle notch
Pilot Jet: #35
Needle Jet: Q-0
Main Jet: #220
Air Jet: #2.0
Hope this helps some!!!
Added in Edit: This was the first VM Roundslide carb I've ever had to change that "Air Jet" mentioned on the last line of the jetting specs. It's the little brass one that takes a smallish regular/slotted blade screwdriver to remove from the "belled-out", or air intake, end of the carb. Sits at approximately 6 'oclock or so in that part of the carb, and mostly controls idle/low throttle openings, if I recall......
Found on the Thumper Forum
J6G1Z:
Copied from the Yahoo FT Ascot owners Group.
Just wanted to say THANKS to everyone on the list that had a suggestion for my mileage issues after changing from the stock 35 mm Kehin carb to a 36 mm Mikuni carb on my 83 FT500.
I have to report that after some more research and picking a few more brains that I have my mileage back to what I consider an acceptable range. Had the bike out this afternoon and when I filled up after the ride my mileage was back up to 52 mpg! Not quite the 60 mpg I had before, but I'm able to live with the 52 mpg and the extra performance and tractability from the Mikuni.
Final set up is a:
#25 pilot jet,
a P4 needle jet,
a 6DH3 needle set in the middle notch (could drop it a notch, but doubt if I will),
and a #200 main jet.
The bike starts and idles well, runs strong, accelerates well, no surging at steady speeds, plug is a nice light tan color, and it hits the 6800 rpm rev limiter on the Ricks CDI box that I installed.
In hindsight I think that the mileage issues arose mostly from my use of the stock FT500 air box. The carb was probably jetted for use with a clamp on pod filter, and was just jetted way to rich for use with the stock air box.
I'm a happy camper again!!!!!!!!!!!!!!!!!!!!!!!!!
Neil
scottly:
I checked out a 36mm Mikuni that came off my buddy's '82 XR500. Before fitting the new carb, he had already installed a higher compression piston, a White Bros exhaust with a Supertrap, and a White Bros cam, and was a bit disappointed with the power increase. After fitting the new carb, the bike came alive!!! All the new parts seemed to be working in harmony. I believe the jetting is the same as supplied by White Bros.
#35 pilot
#220 main
6DH3 needle; clip in highest groove
1.5 slide
J6G1Z:
--- Quote from: scottly on May 24, 2014, 10:46:23 pm --- ...and was a bit disappointed with the power increase. After fitting the new carb, the bike came alive!!! All the new parts seemed to be working in harmony....
--- End quote ---
Excellent post! When modifying an engine for more power, the whole package needs to be addressed either in one shot, or in steps as budget allows. All the performance parts should "complement" each other & work together as a system to flow more fuel & air through the engine.
So the loss of the accelerator pump when swapping to a Mikuni carb does not seem to be much of a loss at all I take it?
Thanks
J.
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