Upgrade Opinions and Pointers By nerdtastic (Read 2,163 times)

[nerdtastic]

So I have a new (well new to me) GY6 150 jmstar scooter with about 4K miles and I have a few questions that you guys might be able to help with. So here the deal it pulls great when I am at about 80% throttle but if I turn it all the way to WOT it seems to bog down and lose power when I am accelerating. I did some research and found that behavior described in one of the excellent tech notes posted in the "air, fuel and carb" library. The article said that most likely this was caused by a too small main jet. So I figured I would get three new main jets 115, 120, 130 and see if I can get the mix right. my thought is though if I am going to dig into the carb is it worth doing a few other things at the same time, such as high flow air cleaner and/or upgraded CDI? I am hoping to get a few more MPH out of this but I am not looking for a $500 full on mod. Also I see a lot of upgrade CVT parts out on the market is all of that really worth it or is that more of high performance modding for those trying to wring every last ounce of HP out of their ride? My budget is really small $100 or so at the most so I am trying to figure out were I will get the most improvement for the least amount of $. Any thoughts or pointers would be greatly appreciated .

[sprocket]

The only engine mods that will increase the mph is more displacement... BBK, 4 valve head etc

Aftermarket 'performance" stuff does nothing in my experience with perhaps the exception of
a free flow exhaust, but then you pay a lot to gain 3-4 mph...

CDIs do nothing... a good one from NCY may last longer and removes the rev limiter...

Air filters do nothing. If you go from a paper filter to foam you could go up 2 jets sizes. So 107 or 108 is stock, you go to a 109 or 110. You would never go to a 120 or 130 unless you are doing serious engine enlargement, and even then anything over a 120 is pretty rare...

If you are running lean, then raise the throttle needle .

The best bang for the buck is tuning the CVT, different rollers or sliders and up the rear end gear ratio...

You may squeeze another 5 -8 mph out of it...

[Bong]

I just have to say that is a very interesting scoot. I don't think I've ever seen one like that on the road.

If that has a typical GY6 engine there are many mods that can be done but, like Sprocket said the best thing to do is tune the CVT and add more displacement.

By the way, Welcome To The Best Forum Ever!!!!!!

[nerdtastic]

Thanks for the input Sprocket. I wanted to ask more about the needle adjustment I have seen several write ups on it and it looks pretty straightforward. What I don't understand are the pros and cons of upping the jet vs. adjusting the needle they both would allow more fuel but in slightly different ways. So in my case were it seems to be leaning out at between 80% to 100% throttle which would be a better choice? I kind of like the needle adjustment as it is a no cost option but if re-jetting makes more sense...

I am not interested in burning up this engine, this is a daily commuter for me and I need to make it last. So wile it might have been fun to run it up to redline, based on your comments and others I have been researching I think the "no rev limit" CDI is off the table. Tuning the CVT is on the list though along with a new drive belt. so what would you recommend for tunning the CVT I have seen a lot of kits and they all say things like "racing" and "High performance" but changing the gearing can be really tricky and I don't have the $ to buy 20 extra bits just so I can try them all out.

[nerdtastic]

May 18, 2011 14:00:34 GMT -6 Bong said:

I just have to say that is a very interesting scoot. I don't think I've ever seen one like that on the road.

If that has a typical GY6 engine there are many mods that can be done but, like Sprocket said the best thing to do is tune the CVT and add more displacement.

By the way, Welcome To The Best Forum Ever!!!!!!

Thanks for the enthusiastic welcome Bong, this has been the best place I have found and great bunch of folks who know there scooters.

I was in London (UK) a few years back and saw a few of them they were mostly BMW of course but still it was wild to see and businessmen running around in there suits on scooters with roofs. this one is built by JMStar and was sold under the Barron nameplate. They (JMstar) still sell it under the johnway namebadge as the BAS Pagoda in a 150 and 250. I have only seen 1 other one, in Seattle just a glimpse on one of the bridges in the pouring rain of course. It works really well you really do stay dry and living in western OR it rains a lot. The only downside is the extra weight and in a crosswind it can get a little squirrrely but you can take it down and it folds into the trunk. I'll take some action shots and post them to the pictures section.

[sprocket]

Well why do you need to up-jet? It is only done is response to changes in the engine intake or exhaust.

It is not a "my jet is bigger than your jet kinda thing"

It can also be a huge game of trial and error. These scooters all vary between manufacturers and things like exhaust system and air intakes. What is good for one scooter can be an utter disaster for another...

They also have their very own personalities .. but I won't go into that...

The throttle needle can be raise and it will often do the same as re-jetting. It enriches the mixture...if you are running lean, which most of these scooters are, right from the factory...

In racing we often change the profile of the throttle jet as well and that can have an effect on the gas flow and power curve, but again trial and error.. mostly error...

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[Cruiser]

A lot of good advice posted so far. Here's my take on your situation.

1. Stay away from aftermarket exhausts or even upgrading to a high performance air filter as this will only aggravate your WOT bog which is indicative of a lean condition. The gains from these mods are minimal and you will certainly blow your budget.

2. Raising the needle is a good idea to improve acceleration and mid range response, but it will do nothing for the WOT bog. Going with a larger main jet will help this situation and you might not have to adjust the needle. Adjusting the needle is a great way of fine tuning after the main jet is sorted out. Running a slightly larger main jet also helps the engine to run cooler which will help the reliability.

3. Since you are trying for more top speed and seem to be satisfied with the acceleration for the first 80%, I would go with slider weights of about the same weight as the originals. They will allow the same acceleration and will possibly give more top end because of their unique design. Going lighter with slider weights could give you more acceleration and will not hurt top end with the proper weights, but it looks like you are more interested in top end without hurting the acceleration.

These basic changes may satisfy your needs and you should have some $$$ leftover. ;D

[Bong]

Not sure if it helps But, That's a VERY Cool ride. Even if your jet is smaller than mine I am Jealous !!!

Can I ask if you have more pics? (we are a curious lot) Riding, Engine bay, Etc...

Also, everyting Sprocket and Crusier posted is great advice!!! These guys Know there scoots!!!!!

[89newbie]

i want one!!
More Pics Ill build one

[nerdtastic]

OK so I am posting a few more pics tonight in the pictures section. Thanks for everyones input so far it really helps to narrow things down a bit.

[nerdtastic]

May 18, 2011 19:32:19 GMT -6 Cruiser said:

A lot of good advice posted so far. Here's my take on your situation.

1. Stay away from aftermarket exhausts or even upgrading to a high performance air filter as this will only aggravate your WOT bog which is indicative of a lean condition. The gains from these mods are minimal and you will certainly blow your budget.

2. Raising the needle is a good idea to improve acceleration and mid range response, but it will do nothing for the WOT bog. Going with a larger main jet will help this situation and you might not have to adjust the needle. Adjusting the needle is a great way of fine tuning after the main jet is sorted out. Running a slightly larger main jet also helps the engine to run cooler which will help the reliability.

3. Since you are trying for more top speed and seem to be satisfied with the acceleration for the first 80%, I would go with slider weights of about the same weight as the originals. They will allow the same acceleration and will possibly give more top end because of their unique design. Going lighter with slider weights could give you more acceleration and will not hurt top end with the proper weights, but it looks like you are more interested in top end without hurting the acceleration.

These basic changes may satisfy your needs and you should have some $$$ leftover. ;D

Thanks for your clear explanations Cruiser that answers my question of which to do needle adjustment or jets. If I understand you correctly start with jet and then adjust the needle if it still needs it.
What is the difference between a slider weight and the standard roller weights?

[sprocket]

Generally for each gram in weight up or down...

Rollers will change your RPMS by 500-600

Slider will change your RPMS by 200-350

So, sliders allow you to zone in a bit finer than rollers...

[Cruiser]

This tutorial from the Scooter Doc library should help explain the differences between roller and slider weights:

scooterdoc.proboards.com/index.cgi?board=transmission&action=display&thread=158

[drjeff]

My scooter looks a whole lot like that one but in black.

[Alleyoop]

Nerdtastic,
If you are looking for more top end say around 8mph more top end. Then the cheapest way is to put in taller gears in the tranny. You will FIRST need to take out the Clutch and the 7 bolts holding the Clutch shaft. You pull that off and then Count the Teeth on the Short Shaft that the Big Gear meshs with. Then Count the Teeth on the Big Gear. Now to up it about 4-5mph you go UP 1 TOOTH COUNT on the Short Shaft and 1 DOWN ON THE BIG GEAR. I would not go more than 2 UP and 2 DOWN otherwise you will need more power from the motor.
Here are the gears I am talking about:
Alleyoop
www.partsforscooters.com/Gear_set_gy6