Performance Carburetor Options

[ibdennyak]

My stock answer: Anything over 50cc would violate the limitations placed on Motor Assisted Bicycles. Yes, it is a 4-stroke. It responds quickly when I squeeze the throttle. The digital speedo goes: 0....8....21....23....28.... about as quick as you read those numbers.

Ha ha.....good one Van. I was wondering how you were going to answer that.

 

[prism]

Carb actuation (sp?)

That helped - it seems carb sizing is nowhere near as critical as I thought it was. I went by A) what I had read, and B) the experience I had with my first bike back in the early eighties. I could never get that thing to idle steadily below three k rpm, even after replacing the 'kr**py Keihins' with 20 mm Mikunis.

Powerband: Below 3 grand: don't bother. 4 grand: has trouble getting out of its own way. 5 grand: passable, a bit sluggish. 5&1/2 grand: starts to wake up. 6 grand - decent. 7 - 10 grand - you'd best be putting weight on the bars and have it pointed in the right direction, and that while tap-dancing on the shifter.

Now you spoke of 'sqeezing' the throttle, rather than 'twisting' it. That seems to speak of a thumb throttle. Good, then - I have one of those planned. Now all I need is the time and energy to resume work.

 

[Alaskavan]

One change I did make. The spring in the Mikuni doesn't have near as much tension as the spring in the stock carb (it compresses easily and very smoothly), and I caught myself accelerating without noticing it. I put the spring from the stock carb into the Mikuni.

 

[geebt48cc]

For the money, the RT carb holds its own.

 

[Fabian]

The Walbro style diaphragm carburettor (with external jetting screws) is the best option i have tried and i have tried all of them.

Once you have gone down this route, you'll never go back to a float style carburettor.

 

[geebt48cc]

True, I'm sure Fabian..........

The only reason I back RT carb, is the performance/cost ratio. That's all.

 

[Deleted member 12676]

a Mikuni 18mm costs only $70 but needs idle and main jets for $9 more.

as to the previous question about oversized carbs- it is just an old wives tale that they ruin low speed performance. People that wrote that were tuning dorks. Once you get it jetted right there is no reduction in performance at any rpm. I have a Mikuni 18mm on my 55cc and it has never idled as strong as it does now. It runs clean and strong throughout the whole rpm range (1-8K).