490 bing/mikuni conversion

[huskibul]

 Sorry don't really care for dyno's and stopwatchs, i'am just after the carb that you can easily dial in, and keeps that beautiful wind-on maico torque ,but the main criteria is easy starting,not a lot of men can ride these things on the edge so i dont think 2 hp means jack .... to the average punter p.s baseline jetting spec's(sealevel)anyone?

[Mick D]

Again I think it is a matter of “horses for courses”. I fitted a 38mm Mikuni to my 250 reed mega2. It starts 2nd kick cold every time. 1st kick the rest of the time, all day long. I jetted it. It blows the performance of the standard Bing to the weeds in every single dept, including it’s journey to peak revs.
BUT, on a 490 Mega it is a much different story, I am yet to be convinced that anything works better than a fresh unworn Bing. If you want a Bing to start 2nd kick cold, I fit it with very soft overflow vent tubes. After you have held the tickler to the fuel flows, grasp your hand around the Bing so that you can pinch both overflow tubes shut, then use your other hand to depress the tickler again for another 6 seconds(as to prime the crap out of it). For MX, my recent experience tells me that the 490 is really suited Bing, for some reason. If it’s a drag race “on dirt” the 490 will win most of those as well.
The beauty about the 490 mega from the day it was born, has always been the way it delivers itself as an MX mount, and I really believe it has quite a bit to do with the Bing.  

[2 shocks]

Must agree with Roscoe, ie 414, tried the wizbang 38mm bored out mikuni from the states on my 81 490, went back to the bing carburetor, of course you have to make sure that the carby is in good condition. The bing carby would be the easiest to jet, you can even sit at the startline & take off the bowl with riding gloves on, its true, I had to do it one day, somehow I got water in the fuel & the thing was blubbering, I reached down, turned off the fuel, took the bowl off, held the floats up with 1 hand, tipped the water out of the bowl, put it back & holeshotted into last place   but the bike ran beautiful. There were guys on modern bikes watching me do this & could not believe it. In my opinion, the bing is the best carby for Maico's. I pushed my 490 into Keith Stackers workshop one day, Keith is the man when it comes to Maico's & all he said was, get that thing off, it wont work on a Maico, I guess he would know. 81 490 jet specs, running 278 needle jet, 185 Main, 55 pilot, 8 G2 needle or 6L2 needle, air screw 1 1/2 turns out, this is the jetting my son used in Tasmania in the Aussies to win Evo & Pre 85. Hope it might help you.

Ken Baker

[huskibul]

 Yeah thanks for that mick de and ken, sounds a lot clearer now and i have a baseline,do you think it's worth muckin with the carb resleeve or go for new? cheers huski

[firko]

I've tried 'em all on my Maicos, Mikuni, Amal, Dell'Orto and even a moment of madness when I tried a Lectron on my squarie and absolutely none of them work as well as a Bing on a piston port Maico.  I had some minor success with a 38mm Mikuni on my reed valve '84 Maico SC500 but the difference wasn't worth the hassle of buying a new air filter adapter.

Keith Stacker once told me a story about when Neil Hudson bought his '75/76 250 GP works Maico to Ausrtralia and left it at Stackers while he did the tourist sights of Melbourne. While Hudson was out they started his Maico and found it to be the usual blubbery, leaking mess so, seeing that Stacker had had some success using Mikunis on their own Maicos, decided to help Neil out by fitting his bike with one of their well jetted Mikunis. The bike started easier, was as crisp as a Jatz cracker and the bike felt like it was ooozing horsepower. Upon their return Hudson and his mechanics weren't very impressed by what happened but not wanting to insult their hosts decided to give them the benefit of the doubt and see how the bike performed during the upcoming practice session.
At the track the bike started first kick, sounded crisp and took off like a scalded cat. Neil put in some very fast lap times and it looked as if Stacker had done a good thing until Hudson came into the pits complaining that although the bike was crisper, it felt much slower. They quickly refitted the original Bing and the bike instantly picked up four seconds a lap. The Bing stayed on the bike and it wasn't long before Stackers Maicos went back to Bings as well. Lesson learned.

With big budgets and ample dyno and track testing at their disposal, don't you think that the works Maico, Husky and even the Montesa and Bultaco teams would have replaced their Bings with Mikunis if they had proved to be better?

[LWC82PE]

With big budgets and ample dyno and track testing at their disposal, don't you think that the works Maico, Husky and even the Montesa and Bultaco teams would have replaced their Bings with Mikunis if they had proved to be better? 

My thoughts are that they may have been stuck in their old ways and had brand loyalty towards the Bing. I could have never imagined they would of fitted a 'Japanese' Mikuni even if they were miles better than a Bing

[cappra]

Bings were cheaper in 76' 
$90 for a new slide is nut's.

[firko]

My thoughts are that they may have been stuck in their old ways and had brand loyalty towards the Bing. I could have never imagined they would of fitted a 'Japanese' Mikuni even if they were miles better than a Bing

You've gotta be kidding Leith. This is the works team where winning races is everything. Even the uuber trick Wheelsmith bikes in California had Bings. Trust me when I tell you that these blokes rooted around with everything imaginable to improve on the Maico and they left the Bing on unless the customer pecified a Mikuni. When I was researching my article on Wheelsmith for VMX I spoke at length with Wayne Meridjian who was the shop foreman and he told me flat out that fitting a Mikuni to a 490 Maico was a backward step.

I could understand the production department being locked into contractual and traditional reasons for sticking with Bings but the race teams had ample opportunity to experiment with carburetion and everything else in a bid to get an edge. Husqvarna did eventually go with Mikuni so not using a  Mikuni because it was Japanese doesn't hold water.

[LWC82PE]

I could understand the production department being locked into contractual and traditional reasons for sticking with Bings

yes this is what i was referring to/trying to explain. Guess i just didnt make it clear that is what i ment. I was indeed refering to the factory.

[GMC]

I have often heard over the years that Bings are the go for Maico’s, but I have always been intrigued as to what the difference is, as in a mechanical sense?
The carby just mixes fuel and air in the right proportions as it is sucked into the motor.
Theoretically any carby that is set up properly should be able to do this, but apparently not in practice.
So why is it that the fuel / air molecules can recognize when they are being sucked into a European cast barrel?
I have just heard a new urban myth about YZ 490’s being a copy of the Maico barrel. So would YZ 490 owners be better off fitting a Bing
The fuel / air molecules wouldn’t realize the deception until they are spat out the exhaust and they see Yamaha across the back of the seat.

So what is the actual working difference between the carbys?

[All Things 414]

So would YZ 490 owners be better off fitting a Bing

Probably. I'm gunna. 

[huskibul]

   Good point gmc i have the odd bing kicking around maybe i should try one on my 430 husky as well ,(someone said their not that much better on reed motors ?)come's to the point why did husky go to mikuni in the early 80's , maybe a  cost saving exercise ?

[maicoman]

My 1984 SC500 came with a  40mm (from memory) Keihin which was supplied by Tony Hatton. My wife grew up with his daughter and they live close by so jets and parts were easily obtained from him. After speaking to him it seems the prevous owner went from the Bing to Keihin because the bike seized up. It turns out that he was running it at 50:1. I'm not a fan of this but that's another can of worms altogether.
  There was issues with the carby boot not matching up. I fitted a set of Boysen reeds which are apparently listed the same as a 1981 CR450, and downsized the pilot jet and found the bike never gave any problems.
I have the original Bing and have never compared the two carbs, so I really can't comment from that perspective. as which had the best effect on the bike. I now have a FMF pipe on the bike but am yet to run it to see what it goes like now.

[NR555]

A dyno doesn't work for motocross. On a real motocross track you are only at full throttle for a small amount of time each lap.
The dyno only gives a full throttle reading..what about when you're coming out of a slick dry hardpack corner and only using 1/4 to 1/2 throttle on a 490.
Power delivery is more important than numbers and a properly jetted Bing gives good power delivery.

On a dyno, you pick the best gear and roll it on.  You don't just hold it wide open.  Rolling it on gives you the torque curve.  Peak HP is interesting, but not super important if the motor is ballpark.   If you can get good torque where you want it in the rev range, then you're headed in the right direction.  Pretty valuable on a motocross bike if you ask me.  Running a higher gear in corners, anyone?

[Lozza]

A dyno doesn't work for motocross. On a real motocross track you are only at full throttle for a small amount of time each lap.
The dyno only gives a full throttle reading..what about when you're coming out of a slick dry hardpack corner and only using 1/4 to 1/2 throttle on a 490.
Power delivery is more important than numbers and a properly jetted Bing gives good power delivery.

On a dyno, you pick the best gear and roll it on.  You don't just hold it wide open.  Rolling it on gives you the torque curve.  Peak HP is interesting, but not super important if the motor is ballpark.   If you can get good torque where you want it in the rev range, then you're headed in the right direction.  Pretty valuable on a motocross bike if you ask me.  Running a higher gear in corners, anyone?

EXACTLY a dyno is just a tool unless you have to know what your doing and looking at.Novices get caught up in peak numbers. Shape and area under the curve are the important things. More area under the curve the faster the bike is around the track, regardless of the peak number.
If the Bing can decrease laptimes in such a significant way the dyno will easily pick that up. 

As Geoff says what is the differnce between the carbs? I reckon there is a really simple answer........................