Jet Suggestions

I have been jetting around for the last week or so trying to find the best fit. I have been doing plug chops but I am having trouble determining the best jet.

Here is my setup.

Stock puch magnum xk head (no modifications)

15 mm bing carb

hi flow intake

estoril techno pipe

I have been jetted from 68 - 82, all with mixed results. Either I have nice low-end and no speed or some speed (30ish) that bogs at WOT.

What are some recommendations? Are there other carb adjustments I should be making (pin height, throttle cable length)?

Re: Jet Suggestions

Luke “Funkenet” Hosfield /

The main jet only controls the upper throttle range. You need to adjust the needle setting to get better lowend. I would guess on the lower end of those jets you got.

Re: Jet Suggestions

Shane, I would say upgrade from the bing.

I know, I know it's been with your since your moped birth, but its like training wheels.

I bet your problem is with the air fuel mix during different operation RPMs.

If your choke works, I would run some test runs.

Take your choke out and grind away the little seat pin that makes the choke open at WOT.

Now you can adjust your air to meet your nessesary fuel consumption, like I said, you will have to be playing with this during the RPM range.

What you will notice is that your engine likes to run better under different conditions.

I noticed on my yamaha qt50, there is a fuel air mix screw which helps tuning so much, bings don't have this capability.

if by "pin" you mean needle, you poor thing.

the needle will allow fuel to be sucked in at certain times.

By raising the needle, the fuel comes in sooner (Lower RPMS)

Raising too high, boggish and the powerband may lose significant power

By Lowering the needle, the fuel comes in later (higher RPMS)

By Lowering too low, the engine may not have enough fuel and can run TOO LEAN.... LEAN IS BAD..... BAD BAD BAD..... (yes lean can be faast, but awful hot)

Run it Richie Rich for your bikes longevity.

My Idea for you is throw in a 72 and adjust your needle to the correct setting. If you find that the bike runs better with the choke a little on, upjet and re-needle.

Good Luck.

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