Weird? Scooter bogs at mid even with multiple main jet changes

[digginLA]

Wassup everyone!

This really has me confused! My scooter sat for too long and I had to replace the carb...easy. Then I decided to change the air filter and rejet but now the scooter is acting crazy.

The scooter starts fine, idles fine but is crappy after mid throttle. Original carb had a main jet of 107. I switched to 120, 125 and 130 and with each jet (including 107) it sounded exactly the same as the video (below). Spark plug is black so I think I'm running rich?? But why?? With the new air filter I thought I needed a larger jet??

Video



Hmmm any information would be awesome!

Thanks guys

2012 Motobravo Phantom 150cc, 8,000 miles

[carasdad]

Originally Posted by digginLA

Wassup everyone!

This really has me confused! My scooter sat for too long and I had to replace the carb...easy. Then I decided to change the air filter and rejet but now the scooter is acting crazy.

The scooter starts fine, idles fine but is crappy after mid throttle. Original carb had a main jet of 107. I switched to 120, 125 and 130 and with each jet (including 107) it sounded exactly the same as the video (below). Spark plug is black so I think I'm running rich?? But why?? With the new air filter I thought I needed a larger jet??

Video



Hmmm any information would be awesome!

Thanks guys

2012 Motobravo Phantom 150cc, 8,000 miles

Hmm..first of..just because it sat..why would you need to replace a carb? I have worked on Barn stored motorcycles and other gas powered items that sat for over 20 years and never had to replace a carb. Just soak and clean it is all. In fact in 30+ years of fixing small engines I have only replaced one carb..because it was dropped and cracked. With only 1 moving part in them..they simply and in reality would never wear out. So now..since you replaced the carb and none of the jets work properly with the new filter..have you installed the stock filter back onto the new carb and tried it? Hint when working on any engine..--> The first thing to cause you any problem..is always the last thing ya did. Simple logic is it not?.. It's very true as well. What size is the pilot jet in the new carb..and did you adjust the A/F mixture on the new carb? Ya see many will tell you the pilot jet ONLY affects the engine at idel to 1/8 throttle. HOWEVER..this is simply not true because the pilot jet is always on and open and giving small amounts of fuel to assist the main jet. Why?..because unlike the main jet which has a slide needle to adjust its flow..the pilot jet has nothing. It is just an open hole sucking fuel from the float bowl. What does all this mean? Well 2 things..try the stock airbox with the new carb and if it is the same..you will need to adjust your A/F screw..which needs to be done anyway with the new carb. A 107-110 jet should be fine with that engine btw. If you have an adjustable slide needle(cause some don't) you can try raising and lowering the clip on it 1 notch each way and try it. But the way the vid sounds..it is as if the A?F screw needs to be tweaked a bit. This MUST be done while then is warmed up and running.. Ponder all of that above..give the stuff a try..and keep us informed..
Glenn

[Rhompin45]

After I put a uni filter on I tried a 115 and a 125 both were bogging down like that. So I went to a 109 which was like a half size if I remember right. But once I modified the exhaust then I could go to a 115 jet. I am at 1200 feet.

[digginLA]

Originally Posted by carasdad

Hmm..first of..just because it sat..why would you need to replace a carb? I have worked on Barn stored motorcycles and other gas powered items that sat for over 20 years and never had to replace a carb. Just soak and clean it is all. In fact in 30+ years of fixing small engines I have only replaced one carb..because it was dropped and cracked. With only 1 moving part in them..they simply and in reality would never wear out. So now..since you replaced the carb and none of the jets work properly with the new filter..have you installed the stock filter back onto the new carb and tried it? Hint when working on any engine..--> The first thing to cause you any problem..is always the last thing ya did. Simple logic is it not?.. It's very true as well. What size is the pilot jet in the new carb..and did you adjust the A/F mixture on the new carb? Ya see many will tell you the pilot jet ONLY affects the engine at idel to 1/8 throttle. HOWEVER..this is simply not true because the pilot jet is always on and open and giving small amounts of fuel to assist the main jet. Why?..because unlike the main jet which has a slide needle to adjust its flow..the pilot jet has nothing. It is just an open hole sucking fuel from the float bowl. What does all this mean? Well 2 things..try the stock airbox with the new carb and if it is the same..you will need to adjust your A/F screw..which needs to be done anyway with the new carb. A 107-110 jet should be fine with that engine btw. If you have an adjustable slide needle(cause some don't) you can try raising and lowering the clip on it 1 notch each way and try it. But the way the vid sounds..it is as if the A?F screw needs to be tweaked a bit. This MUST be done while then is warmed up and running.. Ponder all of that above..give the stuff a try..and keep us informed..
Glenn

Hey Glenn, I only bought a new carb because after I took off the original I noticed that it was sealed and did not have screws to get into the tank to clean the jets. So I just bought a new one slapped it on and it worked before I put on the new air filter the next day.

Two things I discovered since my last post.
1. After adjusting the A/F screw I noticed the engine does not die when the screw is turned all the way (clockwise). In fact it has little effect whichever way i turned it. The pilot in the new carb is #35

2. I went to Sears and bought a screw and bolt remover to get into the old carb and I was able too! The main jet is only #103 and I have no idea how to determine the pilot jet size?? There isn't a number on it?!?

So I guess I am going to clean the old carb jets and try the pilot in the new carb. I hope to do this tomorrow but Los Angeles is finally getting much needed rain.

[carasdad]

Originally Posted by digginLA

Hey Glenn, I only bought a new carb because after I took off the original I noticed that it was sealed and did not have screws to get into the tank to clean the jets. So I just bought a new one slapped it on and it worked before I put on the new air filter the next day.

Two things I discovered since my last post.
1. After adjusting the A/F screw I noticed the engine does not die when the screw is turned all the way (clockwise). In fact it has little effect whichever way i turned it. The pilot in the new carb is #35

2. I went to Sears and bought a screw and bolt remover to get into the old carb and I was able too! The main jet is only #103 and I have no idea how to determine the pilot jet size?? There isn't a number on it?!?

So I guess I am going to clean the old carb jets and try the pilot in the new carb. I hope to do this tomorrow but Los Angeles is finally getting much needed rain.

Eww..those @#$^! sealed carbs..is that not annoying?? Yeah many just buy a new one in that instance..but as ya found out..you can get those useless shear screws out! As for the pilot jet..should be marked..but many are not. New jet is a #35? I usually find a #38 in 150 carbs. Turning the A/F screw all the way in all the way out..with zero results..means that by you trying to make it richer..you can't..because the pilot jet is apparently to lean already..so you can't make it richer even if all the way out. Soo Sir. I would put the pilot jet from your old carb in the new one..and bet you notice at least some difference AND adjust-ability.. Changing the filter to free flow types does affect even the pilot jet because..it runs on vacuum..and a free flow filter decreases that vacuum. Anyway....let's try this..use the 'old' pilot jet in the carb..tinker with A/F screw and we will see if it gets better. I have faith that it will..

[digginLA]

Originally Posted by carasdad

Eww..those @#$^! sealed carbs..is that not annoying?? Yeah many just buy a new one in that instance..but as ya found out..you can get those useless shear screws out! As for the pilot jet..should be marked..but many are not. New jet is a #35? I usually find a #38 in 150 carbs. Turning the A/F screw all the way in all the way out..with zero results..means that by you trying to make it richer..you can't..because the pilot jet is apparently to lean already..so you can't make it richer even if all the way out. Soo Sir. I would put the pilot jet from your old carb in the new one..and bet you notice at least some difference AND adjust-ability.. Changing the filter to free flow types does affect even the pilot jet because..it runs on vacuum..and a free flow filter decreases that vacuum. Anyway....let's try this..use the 'old' pilot jet in the carb..tinker with A/F screw and we will see if it gets better. I have faith that it will..

Finally the rain has stopped! So I put in the original pilot jet, tweaked the AF screw and the needle (not all at the same time) and I think it's getting better? Now my scooter stalls when the AF screw is closed so I guess that's a start in the right direction. I used instructions online on how to set the AF mixture and I'm confident it's okay but it still stumbles after mid throttle. I've used different jet sizes from 112-130 and still the same result?? Should I try higher than 130? Could my muffler have something to do with it? I think it came with a custom pipe?? I'm having fun with this and learning a lot so it's not too bad but I really would like to get this right! Hmmmm I don't want to but maybe I'll try to put all the original stuff back on to see how that works out.

[Rhompin45]

Do you have a stock intake?

[digginLA]

Originally Posted by Rhompin45

Do you have a stock intake?

I do have a stock intake manifold and I bought a extra one just because it was only a few bucks but both give the same results. The upgrades I bought for my scooter are below. I feel like its something simple I'm overlooking???

Carb
http://amzn.com/B005CWR5PO

Intake
http://amzn.com/B0072IDARI

Filter
http://amzn.com/B008OEQ6WU

[Rhompin45]

On mine when it was stock it had a big plastic box on the side with a filter in it. I removed the whole box and just stuck a uni filter on the carb but my stock main jet was a 107 even after I put the uni filter on I could not put a bigger jet than a 109 or it was bogging down past half throttle. It wasn't until I modified the exhaust that I could run a 115. If that stock air box is on there even if you have a better exhaust 120 is still probably to big. It also depends on you elevation. I am pretty low so I don't need as much fuel as if I were in the mountains.

[Rhompin45]

I just looked at your filter. So it is a open filter is it straight off your carb or is there a hose in between to kick it off to the side?

[digginLA]

Originally Posted by Rhompin45

I just looked at your filter. So it is a open filter is it straight off your carb or is there a hose in between to kick it off to the side?

Hey Rhompin45, I'm right in the heart of Los Angeles and I think the elevation is 290 feet. So does that mean I need a smaller jet? I tried a 107 and got the same results. I have a 103 which is what was on the original carb.

My air filter is off to the side. I got a tube at Lowes because when coming off the carb there is a bracket that was in the way and I had to extend it past it and to the side was the best option.

Is off the side bad?

[gitsum]

The higher the elevation the less fuel the engine needs because the air is less dense.

If you significantly open up the airbox and exhaust, you will have to retune the carb.

This means adjusting the air/fuel screw, raising the needle jet a notch or two (or using shims), and going to a larger main jet. There are plenty of tutorials online that will guide you through the process.

Be prepared for a lot of trial and error, it is the only way to make sure the carb it tuned optimally.

Since you got the old carb apart, it might be easier to clean it up and try using that first.

[Rhompin45]

Sorry i didnt soo you comment back.No it shouldn't be smaller than a 107... Weird and no it won't hurt it off to the side I was just courious. Mine is right off the carb but right in front of the rear tire. Even with a plastic shield over the tire it gets super dirty. Wells it's been a little while any luck?

[Rhompin45]

And as gitsum said its a lot of trial and error. But just do one thing at a time. Try a jet and play with air fuel ratio but keep track of what you did