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 2008 Zuma 49cc dies at WOT 
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Newb
Newb

Joined: Mon Jan 14, 2019 4:38 pm
Posts: 3
Location: Kemah, TX 77565
scooters and mods: 2008 Zuma 50c, Carb Mod and Pirate Decals. Arrg!
Post 2008 Zuma 49cc dies at WOT
Hi, Newbie here... Just purchased a 2008 Zuma 50 with 975 original miles. I did a .5 mile test drive and scooter ran fine so I bought it. Took it home and immediately did the carb mod right away. Definitely improved the speed! I took it on about a 5 minute ride at about 3/4 throttle with bursts at WOT on some higher speed roads I had to cross. That's when the engine will abruptly stop. It actually skidded the tire for a second. I thought I broke the drive belt or something, but when I started it again on the side of the road, it did fire up and ran, but with low power. It did get me home-slowly. After resting it for awhile I can get on it and it runs perfect with no problem for about 5 minutes, and here we go again, same repeatable problem. I'm guessing it's starving for fuel and I saw in a post that the petcock may be a probable cause? Anyone have experience with this? I'm going to keep reading in the meantime, but thanks for any experience out there helping me get it running at WOT again! Patrick


Mon Jan 14, 2019 4:59 pm
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Scooter Addict

Joined: Fri Aug 31, 2018 5:18 pm
Posts: 190
Location: Fox Valley Wisconsin
scooters and mods: 2 2004 Vinos 2004 Zuma
Post Re: 2008 Zuma 49cc dies at WOT
The engine stopping like you describe sounds like a soft seize .
The piston is expanding because of over heating and sticking in the cylinder.

Lets check the Usual culprits first.
You may have a air leak causing you to run real lean or your main jet is undersized or plugged causing you to run lean
To check for a exhaust leak
Start the bike let it idle take a gloved hand with a rag and put your hand over the exhaust pipe opening and if the bike shuts off immediately the exhaust is good if it keeps running you need to reseal the exhaust gasket.
carb tuning
Do you have a stock airbox ?
Does it have any holes in it ?
Is carb stock ?
What jet is in it ?
Does the carb need to be cleaned ?
What does Current Spark Plug look like ? Post picture

You will need a box of plugs to do plug chops to dial in your carb.
I would do Plug chops at idle ,1/2 throttle and wide open .

_________________
2004 Vinos Derestricted exhaust and variator stock carb with mikuni 75 main jet needle down 1 clip 40 mph
2004 Zuma Malossi sport 70 cc breaking in with stock pipe then Technigas next r polini 107 mm clutch polini green springs high speed variator 84 main jet 46 pilot jet needle 1 clip rich
2005 eton beamer airsal sport 70cc 9200 peak rpm top speed 40 77.5 mikuni jet needle 1 clip rich

BBKs all around on the way


Mon Jan 14, 2019 5:33 pm
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Newb
Newb

Joined: Mon Jan 14, 2019 4:38 pm
Posts: 3
Location: Kemah, TX 77565
scooters and mods: 2008 Zuma 50c, Carb Mod and Pirate Decals. Arrg!
Post Re: 2008 Zuma 49cc dies at WOT
The people I purchased from were elderly and assured me that everything is stock. I was afraid of a soft seize and thought that was possibly the case, although there is some oil leaking out of the exhaust and the plug looks good with light oil residue, but wasn't fouled by any means. I took a photo for the plug number, but I'll go back and take another one for gap and color.

I will recheck the carb and see if oil is actually getting to it. I saw in the manual that there is a bleeding procedure and I can try that out as well. I would say that the carb is good otherwise because it idles perfect and has smooth power for the first 5 minutes of operation.

I probably should have used it more before I did the carb mod to make sure everything was running well first. Yesterday I drove it 3 miles at 30 MPH and it ran fine from what I could tell, but the throttle response is definitely worse as it warms up, which keeps bringing back to fuel delivery or soft seize.

I'm going to try out your suggestions and let you know what I find out. Thanks for your help!


Tue Jan 15, 2019 1:40 pm
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Scooter Addict

Joined: Fri Aug 31, 2018 5:18 pm
Posts: 190
Location: Fox Valley Wisconsin
scooters and mods: 2 2004 Vinos 2004 Zuma
Post Re: 2008 Zuma 49cc dies at WOT
Stock mainjet should be a 80
There was a carb recall that had everybody put in a 76 .
Check the main jet number # you want the 80 with the throttle mod.
If you change exhaust you would go to 82 or 84 .
By what you said about oily residue on plug and oil from exhaust lack of oil is not the problem.
3 miles at 30 you probably were not on the main jet but on the needle circuit in the carb.
If you did not have any problems on that run
The main jet or a exhaust air leak is where I would spend most of the time making sure are right.

_________________
2004 Vinos Derestricted exhaust and variator stock carb with mikuni 75 main jet needle down 1 clip 40 mph
2004 Zuma Malossi sport 70 cc breaking in with stock pipe then Technigas next r polini 107 mm clutch polini green springs high speed variator 84 main jet 46 pilot jet needle 1 clip rich
2005 eton beamer airsal sport 70cc 9200 peak rpm top speed 40 77.5 mikuni jet needle 1 clip rich

BBKs all around on the way


Tue Jan 15, 2019 6:47 pm
Profile
Newb
Newb

Joined: Mon Jan 14, 2019 4:38 pm
Posts: 3
Location: Kemah, TX 77565
scooters and mods: 2008 Zuma 50c, Carb Mod and Pirate Decals. Arrg!
Post Re: 2008 Zuma 49cc dies at WOT
So... I learned a lot about my scoot today. I broke everything down and looks like soft seize is the correct answer. The oil line was off of the carb, so it wasn't getting oil. Now I get to find out how durable the Yamaha motor is after running without oil. It still runs fine, but it's possible the cylinder is hosed now. I didn't remove the carb to do the mod, so I'm not sure if the line was already off or if I knocked it off? I did check the exhaust for leaks and it was good with no leaks. I also disassembled the air box and that other box connected to it by a hose. Both were internally very clean with no extra holes drilled or anything like that.

I also learned that I do not have a stock exhaust, which possibly means there are other mods like jets, etc. The exhaust is a LeoVince TT Handmade. I'm sure that the carb should be rejetted with that exhaust, so if you have a suggestion please let me know, but I will be looking it up too in the meantime. I ran out of daylight so I couldn't take the carb apart to see what jets are in there. I looked up the exhaust and I see that it comes with rollers and springs so I need to research that too. Lots of reading to do... Thanks again for your help and insight!


Tue Jan 15, 2019 8:16 pm
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Scooter Addict

Joined: Fri Aug 31, 2018 5:18 pm
Posts: 190
Location: Fox Valley Wisconsin
scooters and mods: 2 2004 Vinos 2004 Zuma
Post Re: 2008 Zuma 49cc dies at WOT
That is a good exhaust for a 50 or a 70 cc upgrade.
What was your top speed after throttle mod and now ?
Mid 40's is what range after throttle mod most see with that pipe is in a good tune .
If you are still breakin 40 that would be a good sign.
If you are still hitting similar top speeds to your first modifed throttle run would be great.
You will need to upjet for that pipe 84 main part #14T-14343-42-00 82 main part #14T-14343-41-00 are the yamaha parts to order from your local dealer about 5 bucks a piece.
You may need to change to the 05 adjustable needle zumarus has a fix it kit for that .

I would bet you knocked off the oil line when you did the throttle mod it is a common issue .
if the cylinder is way down on power going bbk is just a little more expensive and alot more fun than fixing the 50

_________________
2004 Vinos Derestricted exhaust and variator stock carb with mikuni 75 main jet needle down 1 clip 40 mph
2004 Zuma Malossi sport 70 cc breaking in with stock pipe then Technigas next r polini 107 mm clutch polini green springs high speed variator 84 main jet 46 pilot jet needle 1 clip rich
2005 eton beamer airsal sport 70cc 9200 peak rpm top speed 40 77.5 mikuni jet needle 1 clip rich

BBKs all around on the way


Tue Jan 15, 2019 9:21 pm
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