Rejet Question By bonbhead (Read 1,804 times)

[bonbhead]

I'm going to change the Jet size in my carb.  I have a GY6 150cc and the carb has a

102 jet

factory installed. I was looking at the link in the library Carb Rejetting I did read thru it. I noticed he had a stock 107 Jet and did change it to a

115

and I did notice he mentioned that should be the max jet for the

150cc

and go no bigger.

Assuming the scooter starts, take it for a spin. If the scooter runs better, you made a good choice for the new main jet. If it doesn't, then you picked the wrong size and you may need to try again. Most carbs on 150cc scooters have main jets from the factory of about 1.07 or 1.08mm (#107 or #108). If you fit a high flow air filer and performance exhaust you may need to go up as high as 1.3mm (#130). If you stick with the standard air filter and exhaust (like I did), maybe a #115 will give you better running, but #120 or #130 main jets would be likely to deliver a mixture that was too rich. I'm just about at sea level and winter is coming, so the air is cold (and denser). For me going from #107 to #115 made a significant difference, but for you it may not

I am going to run a stock air cleaner untill I get a high end air filter. I was thinking of taking it to a

120 jet

till I read his suggestions. Does anyone think the 120 would be too much.  I do live in a hilly, curvy part with a elevation of 1300 ft.

tks
Bonehead

[trashtruck12172]

if you're only going to change the filter a 120 may be too much. start small and work your way up.

[czmdiver]

Your Main will only affect throttle position from just about half way to Full Throttle.
Proper Jetting especially if ya ditch the factory air box and mount some better exhaust you will have to change the Pilot Jet and make a Jet Needle Clip position change along with the Main Jet
You really need to confirm what Jets are in Your Carb then purchase a half dozen sizes up from there. I Will Never recommend a Specific Jet size as Every Scoot is different along with variances in Altitude above Sea level, Fuel your using, Specific Intake and Exhaust. No two will be the same. What is ideal on one scooter will be less than ideal on another Scooter

[rks]

No "one size fits all" answer to this topic.
Jetting after mods, is always trial and error. Buy an assortment pack (5 or 6 jets). I'd almost bet that your stock scooter, with a 120 main, would struggle to make 25 or 30 mph. As soon as you opened the throttle half way.....it would bog.

I live at 1600 ft......operate at elevations between 500 to 2000 ft......I run a 115 main with a K&N cone, mounted as far from the carb as possible, and stock exhaust. A performance filter mounted directly to carb mouth, would flow differently, and need to be jetted accordingly. To many variables, for anything to be written in stone.

My air filter/carb jetting mods, were made at 366 odometer miles. Since then, my scoot has covered more than 11,000 miles without a single carb problem.....always starts, idles, and runs well. The image below is my scoot's original plug after running 11,500 miles. This is the way it came out of the head.....no cleaning needed.

[czmdiver]

May 3, 2017 6:03:05 GMT -6 rks said:

No "one size fits all" answer to this topic.
Jetting after mods, is always trial and error. Buy an assortment pack (5 or 6 jets). I'd almost bet that your stock scooter, with a 120 main, would struggle to make 25 or 30 mph. As soon as you opened the throttle half way.....it would bog.

I live at 1600 ft......operate at elevations between 500 to 2000 ft......I run a 115 main with a K&N cone, mounted as far from the carb as possible, and stock exhaust. A performance filter mounted directly to carb mouth, would flow differently, and need to be jetted accordingly. To many variables, for anything to be written in stone.

My air filter/carb jetting mods, were made at 366 odometer miles. Since then, my scoot has covered more than 11,000 miles without a single carb problem.....always starts, idles, and runs well. The image below is my scoot's original plug after running 11,500 miles. This is the way it came out of the head.....no cleaning needed.

What he said.
Good post, right on the money

[bonbhead]

I did take the advice and not go to big on the Jet. I Had a 102 so I moved to a 110 current. I was thinking of the 115 till i read the post on 20 to 30mph. It starts great and on the stand bogs just a tad on the beginning it may be too rich. I will attempt a 1/8 at a time on air mixture screw. Over all it was easy as pie.Only issue I have on mine is a crossmember in the frame need to be back a quarter inch and that would make it so much easier.

[rks]

This is how I solved the frame problem, (if that's what you were referring to)......I know...... it isn't pretty to look at, but it works well, and is durable, and none if it shows unless the seat bucket is removed anyway.

i1271.photobucket.com/albums/jj622/rks3526/IMG_0080.jpg

[bonbhead]

Is that a inch and a half radiator hose? I got a filter enroute for Saturday just like that. Of course I will be rained in till next wed. . I did take the scooter out for a ride after the rejet raising from 102 to 110 did make a difference. Tad better on top end and bit more to it when on a hill. No speed record but better. Probably when I get it broke in it will move pretty well. 4 yrs old with 430 miles. .

[rks]

Yes it is. Because of my filters location, it is subjected to some dust/dirt slung around by the rear tire. I wrapped a piece foam around mine, (cut to fit) from a lawn mower filter pre cleaner. At every oil change, I slip the foam off, clean, mist with oil, and slip it back on. If I was going to ride in bad weather, or be commuting every day, I'd make some kind of shield to protect it from water spray. But I'm just a fair weather rider, so don't need it.

[bonbhead]

Basically I have done the same thing since we posted on my

air filter

   

Works out well too after seeing your setup.

Now back to the

re-jet questions

Started out with the

stock jet size of 102

Moved up to a

110 jet

and changed the

air mixture a tad

and it ran Wonderful but gained nothing on a hill.

Now I currently have moved to a

115 jet

but now I do have a issue.

I have  pulled the plug to take a look at it which I will include a image



And I never had the black carbon build up as i see here  yet when I get to 3/4 throttle it will start to BoGG down.

Now for the advice I am asking on this for I was warned a

on the 115 jet may be way too much

Could a possible problem here be with the

Air Mixture

? My main goal is to get a little bit more speed on some of these hills I have here. 35 to 40 max. I can get around 52 mph on a straight stretch but but that is really pushing it on the "rpms"

If I have to I can go back to the

110

jet but I do like the way it does take off from a stop with the

115

installed.

So this is me

and I am too

rich

so I think I need to lean out a little. Which way on the air/mix screw should I go please?

My next step will be on considering on changing the Exhaust System from a Stock to a Performance Exhaust to relieve some of the Back Pressure but I imagine it will be alot louder. I just wish my

Boneheaded asz

would have went for the 250cc when I picked this up in 2012

[rks]

Let's see......110, scooter runs great......115, scooter bogs at or above 3/4 throttle, and is turning the entire combustion chamber black with carbon. This is not an idle mixture problem. You either, increase the air flow more and run the 115, or run the 110 with your current configuration.

But you had that figured out already.

An eight horsepower, 500+ pound GVWR scooter, will never be a rocket, but still fits the bill as a very basic, enjoyable, and economical form of transportation. Not fast enough?..... Save your money and get that 250cc......but a year later, you'll wish it were a 500. The only solution I've found to this conundrum, is having an assortment pack of rides.....but this can get rather expensive.

[bonbhead]

Well shut my mouth. I realize I am not going to get a

Rocket Ship

But I would like to keep it at 52 or 55 on a hill.

I

will Increase the air flow

and keep the 115.

I think I am going to consider the Exhaust Change and so some research on that to see if it will give me a little more.

As for a 250 that will have to wait. I had a

Valve Job done on my Heart in January

wife misses a month and a half work to take care of my sorry Asz and that is the rest of the story.

I believe we are only 7 hrs apart. Im in So Eastern Oh. Tks for the Help too

Bonehead