Air to Fuel Ratios By dimplepwr (Read 1,337 times)

[dimplepwr]

So, I bought a new scooter as a project bike. It’s a Chinese 157QMJ. I got rid of the stock air box and connected a 2 stage UNI filter directly to the carb. It ran like crap because it was getting too much air SOOOO I started rejetting.

I live at sea level, literally across the street from the ocean, and stock jets in the carb were a 124 main with 32 pilot. Since then I have put in a 136 main jet with a 40 pilot. The problem I am having is at the take off it acts likes it wants to die for a sec then takes off. It only happens when I idle for a couple minutes at a light. If I throttle real slow it doesn’t do it and it is fine at wide open throttle. I spent like 2 hours hitting different combinations of the pilot and main jet, 38-40-42 pilot, with 136-138 main jet but its still happening. Am I missing something? Isnt the pilot jet for the initial take off and the main jet is for over 15mph?

I think it might be too rich but wanted to get someone else’s opinion and hear about other’s carb set ups.

[Alleyoop]

Yes your WAY to rich dude and flooding it NO POWER. You see my Trike in my sig, I am running a #38 pilot and #122.5 main jet and my 157QMJ has a 62mm BBK and a 60mm Stroker Crank that is 30 more ccs I added to the motor. I have a K&N and Free Flow Supertrapp muffler. Your Main should be about 110-112 and a #35 Pilot.
Alleyoop

[dimplepwr]

Apr 19, 2012 19:46:45 GMT -6 Alleyoop said:

Yes your WAY to rich dude and flooding it NO POWER. You see my Trike in my sig, I am running a #38 pilot and #122.5 main jet and my 157QMJ has a 62mm BBK and a 60mm Stroker Crank that is 30 more ccs I added to the motor. I have a K&N and Free Flow Supertrapp muffler. Your Main should be about 110-112 and a #35 Pilot.
Alleyoop

Alleyoop, I have seen your posts on other threads and you have a lot of good info which I respect. This question comes from ignorance so bare with me...

The stock jets were a 124 (main) and 35 (pilot). When I moved to the pod filter and am getting more air, wouldnt I have to go up a bit... maybe like a 130 (main) and 38 (pilot)?

Thanks for putting up with my ignorance. Still learning about these little engines...

[ce]

That's a lot of fuel for a 24mm carb, I run a 40 pilot in my 250, and I'm at 5300 feet.

For a 150, a 35 pilot is plenty, and a 125 main is a lot, even at sea level, so start with that, then raise the needle in the diaphragm to richen if needed.

We run 110 and 35 in the 26mm, and 112 and 35 in the 24mm carbs, with needles set at highest adjustment.

[dimplepwr]

If the doc and Alleyoop say its true, im too lean... its gotta be true. Ill make the change and report back.

Also, my auto choke keeps coming on and turns off when I am at a stop light. Is that the autochoke or the carb getting ride of extra fuel?

[Alleyoop]

The 150s come witha 24mm Carb and the Main Jets are usually 105-107, so if it has a 124 it must be used and the owner put that in and sold it cause it ran like crap and could not get it to run right. I bet that sucker is a DOG no speed no power.

Now that is funny, about the choke on and off , what is happening is because of the HUGE JET it is dumping fuel in when your rpms are low or come to a stop. I am telling you, you are FLOODING the snit OUT OF IT.

The choke shuts off the EXTRA Fuel after 4 mintues after you start the motor. As long as the motor is running after 4 minutes the ENRICHER(AUTOCHOKE) is NOT I REPEAT NOT FEEDING EXTRA FUEL.

If you don't have or can get a #35 right away put in the #32 you can compensate a little by richen using the fuel ratio mixture. Heck even the #32 might work out you never know ALL motors run different.
Alleyoop

[ericrockstar]

Hey Lefty, I was a just reading in the tips and tricks at the Dawg Pound the other. I saw a chart that had all the different jet sizes and equivalent ones from the top three names. Well, maybe top 2 and then generic ebay el cheapo carb. Mikuni keihn and a third called dynajet. I think the third is Chinese standard. The number on the jets vary widely. Seemed like keihn was the only one with half sizes. But like 110 & 127.5 & 130 were like the same size just different brand carbs.

My eBay special doesn't even say what size jet is on there. Go figure.

I do agree with you though. He said its a Chinese so a 120 something is likely way too big.

[jct842]

You can always do like i did. I got a set of orifice drills then I soldered up the jet. Drill it out smaller. You can get drills from welding supply or a real hardware store. before you solder try the various sized drills to see what size just fits. When you drill do it with a pin vice by hand solder is real easy to drill. There are charts to compare drill size with orifice sizes. One day I will probably get a complete set of jets to play with but for now I won't be fixing what works. john

[dimplepwr]

So I called the manufacture and found out that the stick jet was 105. I was at 136. Dang, that was WAY too much fuel. I am back down to a 35 (pilot)with a 122 (main) and it runs a ton better. I think I might even go down to the like a 114-116. Just need to buy them.

[Alleyoop]

Yep, your going in the right direction, you will see a little better performing scoot.
Ride Safe
Alleyoop