81 400 GS Mikuni

[Tim37]

Hi ,
     I have just got back my old 81 400 gs . I used to trail ride this bike about 15 years ago and it was good , fitted a ktm front end with a disc brake and Piggy back Ohlins .  I always had poor fuel fuel range and was using the std 40mm Bing . It drooled lots of fuel all over the cases but ran clean even if 40mm is in my mind too big for and enduro bike of that size.
I have an 82 490 Enduro and it has a 36mm Bing from the factory.

As I am going to make this a vinduro bike I am thinking I will fit a small Mikuni 34 bored to 35mm or a straight 36mm .
I have a shiny new GMC pipe and the top end is near new 1st o/size ..any one have some jetting specs ?
I am looking for smooth torquey power ,better consumption, less carb  wear ..set and forget ...

I swapped a 36 mm Bing from my Moto Villa 125 to a 32mm Mikuni with great success ...much wider poweband [less top end ] but much quicker in the real world of tress rocks & mud !

 Bings are good for Mx but do wear and drink fuel.

Thanks Tim.
 

[Mick D]

I reckon thats a great idea Tim. I am keen to hear how you go with it.

You have got me thinking now.

I have nearly finished my AW400GS. I have a new 36 Mik, but can use it else where. I will see how you with the 34.

If you go 36Mikuni and want to know what my jetting is? just say so Tim.

[sa63]

I have tried a 36 and 38 mik on my 81 400gs(reed barrel). the 36 give more down low , 38 was smooth all the way through. I chose the 36
Happy to give specs on the 36 if you pm me

[Tim37]

Thanks chaps , would love any specs ....
I think I will go with the 34 bored to 35.5 , the bottom end should be great but still flow enough as there are hardly any slide indentation after boring ...just need to get some ballpark jetting ..

[g465b]

hi,
have these specs written in an old book - relating to a 1980 GS400  I had ,

36mm mikuni     35pilot    Q5  #159 nj        6DH2 needle   320 main    3.5 slide

36mm mikuni      35           Q5  #159nj          6FJ6                 310            2.5


38mm mikuni       55          Q-O #166           6DH3               330            2.5                     cheers  g.

[Tim37]

Thank you so much ...great place to start !

[Mick D]

My piston port AW400 Radial; 36VM MIKUNI

pilot = 35

Needle jet tube = Q5

Main jet = 310

Slide cutaway = 3.5

Needle = 6DH2

FLOAT LEVEL SET AT 18mm

[firko]

A Mikuni on a Maico Mick? Normally you'd be thrown out of the Otto Society for that little indiscretion but I've managed to calm the chaps down.
Seriously....I've tried Mikuni's on Maicos of all shapes and sizes over a 40 year span and have always eventually gone back to Bings. I tried to like Mikunis on Maicos but the relationship was never meant to be.

[Mick D]

 

Well what can I say

I haven't tried it yet.

I have about twenty worn out Bings

They last a hell of a lot longer than Bings,
They are cheap,
Very easy to tune and jet.
They start second kick cold, first kick hot.

And I have some ideas, (shush)

I do intend to compare it against a Bing, but remember it is on a regoed adventure bushy and I want it to be able to start easily on a stalled hill.

And it is a 400 bushy, not really looking for extra zing at this stage

[firko]

Fair enough but I still reckon a well jetted and sorted Bing is the ticket. I enduro'd both the ex Laurie Aldo 6 day '79 400GS Magnum and '82 Maico 490GS with reed cylinder and they performed admirably with Bings. I was thinking about this subject in bed last night and recalled that I had a '73 250 back in the mid 90's that performed much better with the Mikuni that was on it when I got it than with the Bing I retro fitted. I remember trying every jet combination in the Bing catalogue and couldn't get it to run as sweetly as with that 34mm Mikuni. Strangely, the '74 250 that replaced it didn't work nearly as well with a Mikuni. Both bikes were stock except for aftermarket pipes.        http://www.bingcarburetor.com/

One thing I've gained from this post is that I will try the above Mikuni jet specs as base jetting to start the tuning process on my TM400 Suzuki and 360 Yamaha piston port bikes .

[Mick D]

yes, I am after smooth bottom end torque for the GS400. Hill climbing, low end throttle control, etc.

My still not finished CZ400 has a small Mikuni on it. Did a lot of trailing on it many many many  moons ago. It runs flat up top a little too early, didn't matter, the most enjoyable smooth short shifter of a tractor ever born.

[neil]

Hi, I am about to order a new Bing for a Maico 400 AW.
They have asked what slide, pilot etc to supply the carby with? can any one give me some help with this? Neil

[2 shocks]

Hope this helps you. My 77 AW 400 runs exceptionally well and makes very good power with these jetting specs. Standard equipment is a 36mm bing, Paul Stacker tells me that a 38 is the way to go, anyway my jetting is Pilot 55, Needle Jet 278, 220 Slide, Main 180, Needle 6L2 or 8G2 if you an get one, Needle clip position running in a rich setting. In my experience in Maico's, they love fuel, the richer you can get them to run the more power they make. Stacker gave me a tip years ago, keep up jetting til it blubbers and then back it off, just my opinion.

Ken Baker

[firko]

It took me ages to find my Bing jetting specs but I just found them written on the door of a cupboard in my shed . It's been a long time but this bike ran as crisp as Jatz cracker and ran consistent low 13's at the drags with my fat arse on board.

 79 Magnum 400 jetting for type 54 36mm Bing V54/II:
 Pilot - 65 to 75. Needle - 2H1 (clip in middle position),Needle Jet - 326,  Main Jet - 185 (210 for dirt track/drag racing), 210 slide.


 

[OverTheHill]

Quite like the old Bing Carbs. Have a 36mm carb on one my relics [DT1 gyt cylinder with wiseco liner] Was given to me years ago after one float fell off. I'm still using it minus that float & you'd never know as works perfect. Same guy loaned me a 38 for a year or so till he needed it back & had it on my RT1 ride to work bike--no air filter & went like hell with an RZ350 pipe [believe it or not], drank lots of petrol but hey--petrol was cheap back then.