15mm Bing on stock E50 head

So.... I put a 15mm Bing with a 15mm intake on my stock E50 Magnum head.

It runs....but not as good as the old 12mm that was on there originally.

Now...I haven't plug chopped yet or changed jets (as I know I should)....but my main question is this:

Since the port is only 12mm....should I bore it to fit the new 15mm intake? The new intake is CONSIDERABLY larger than the port....and a different shape too.

Will it perform better if I bore the port to match that intake shape and dimension? Does the cylinder displace enough to handle the significant new amount of gas/air coming in?

Or should I say 'fuck it' and just suck it up and slap a Metra or Polini on there.

Oh....and I run with an Estoril, which screamed with the stock carb. Now....the bike is just normal again.


Re: 15mm Bing on stock E50 head

Стев Браун /

To answer your questions, yes and yes.

You have a 15mm opening mated to a 12mm port, obviously that's not optimal.

I'd be willing to bet your bike was running lean when you had the 12mm in combination with the Estoril. Leaner is faster, until you blow up anyway.

You'll probably need to downjet the 15. It sounds like you already know what's going on, you're just looking for reassurance. So, I'm here to tell you you're right.

As far as the kit, you have to decide if you want that extra power and the "possible" reliablity issues that goe along with it. I'm sure you'll make the right decision.

Re: 15mm Bing on stock E50 head

u need to make sure your bike is jetted properly before you can talk about it not giving u a performance increase. you can slap a polini on, not jet it right and it will do 22mph when it has the potential to do 50+

yes port the shit out of that intake. match it exactly to the shape of the 15mm intake. also make sure you use gasket sealant where the carb meets the intake and where the intake meets the carb. they never fit right and always leak.

Re: 15mm Bing on stock E50 head

just get a metra kit. and beat the crap out of it. 65 cc metrakit from a puch will fit, either that or get the tomos metra kit if they have that one in stock at your local ped dealer. it's not too expensive, and won't kill your reliability. as long as you break it in, after installing properly...switch to a 40:1 oil mix to run a little more oily, run the bike for around 20 mins, but don't go all out, just play with the throttle and don't stay at the same speed the whole time, after that it'll be straight

Re: 15mm Bing on stock E50 head

Right -

Yeah...makes sense about the kit. I figure I'm within two or 3 jet sizes.

I'm going to get the jetting down right, and then think a little more about it. It had an old 12mm on there and it runs about the same speed. My buddy Randy said the same thing that Steve mentioned: was probably running a little lean with the Estoril and now a little rich with the new carb.

Plug chop....get it right and then see where I'm at.

Cool.....thanks everyone.

Re: 15mm Bing on stock E50 head

so i just got a 15mm bing and have a 14 mm intake. am new to the game and am wondering......what is this port that has to be matched up.

i have a plethora of jets i can use to match up with it so is this that drastic ie am i going to have to fuck with this???

Re: 15mm Bing on stock E50 head

Well....as far as I can see, the port I have is significantly SMALLER than the 15mm intake.

You have the 2HP head and a 14mm port. The difference isn't going to be that large, actually. In fact......well, you'll see when you take the intake off, that the port on top of the head is going to match the 14mm intake orifice.

I haven't seen what it looks like, but I saw it from the outside (on my buddy's Maxisport) and it looks close to the 15mm intake. You won't have to dremel a thing.

BUT, you will have to re-jet a little. Not nearly as much as I will because you're going from a 14mm to a 15mm. I was going from a 12mm to a 15mm....which is significant. I am running a little rich...it's obvious not only in performance, but sound, and plug color.

Drop the 15 carb in. You might even be able to keep the 14m intake.

15mm Bing on stock E50 head

cool. im not worried about jetting, i have a bunch of them. question on here was just confusing me and was wondering if it was just one more thing i was gonna have to tinker with.

Re: 15mm Bing on stock E50 head


Nah. You're good. Should run like a champ.

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