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I am a racer, I don't need no stinking gauges, lol. I am old skool, I race by the seat of my pants, lol. Me and digital don't get get along very well,lol. Dude, your doing great keep listening to all us backyard mechanics and you will do well. Kind of like the wrist thing though. Them 5 spoke rims are much more balanced than the three, I tried both on a V block under the axle.
 

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Discussion Starter · #42 · (Edited)
So the video is pretty pointless to post because the audio is terrible and I didn’t get a clean shot of the best run. I’ll get it right next time. I guess the camera is only 720P as well, but it should be good for a safety DVR in case of any incidents. Can’t hurt. I may just get a body mounted GoPro, which I’ve always wanted anyway

Also, I never read this sticker but the bike is actually an MTA3. I can’t find much info on these.
Engine Family says 6ZSSX0.05TSM.

EDIT: According to THIS thread, it’s a 40mm piston or a 47cc, so my big bore 44mm kit is an upgrade. Awesome! The engine block number engraving starts with 40-6WQ, which probably means it’s a 40mm piston.
 

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Discussion Starter · #43 · (Edited)
I am a racer, I don't need no stinking gauges, lol. I am old skool, I race by the seat of my pants, lol. Me and digital don't get get along very well,lol. Dude, your doing great keep listening to all us backyard mechanics and you will do well. Kind of like the wrist thing though. Them 5 spoke rims are much more balanced than the three, I tried both on a V block under the axle.
I am only using it as a makeshift dyno to document the results of each mod I do. Like I want to see how many more MPH porting and polishing nets, if the powerband shifts in the RPM range, then the installing the carbon reed, head kit etc.

Yeah everyone keeps mentioning the wheels. I guess they are rare? This is actually an MTA3 which no one seems to specifically list parts for. Were they a short run model or something?

The form a gasket fix on the float bowl seems to have taken well. I’m letting it cure 36 hours and then I’ll install 1/4” fuel line and a new filter and check for leaks. Then it’s getting pulled for the port and polish and a dyno run.
 

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Very nice, I like the fact that you're going to get some data and then just make sure you write it down in a notebook and that way you'll have reference to go back to next time you build an engine.
No I don't know my MTA 3 chassis very well but I'm pretty sure all MTA2 stuff works on it. I think it was just something for emissions for the engine. But I'd be curious to find out what it really is
 

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Discussion Starter · #45 · (Edited)
So, to get ahead of the big bore install, what should I modify on the cylinder/piston/reed cage while it is apart? I just have the BB kit, rocket key, and CF reed right now. I am interested in attempting porting and polishing. I am reading this thread, but I am not sure I can do all of this competently, even though I am quite capable of working with internals on my Baja 28.5cc. I've never ported anything by hand.

Bookmarking this great port mapping video.: Port Mapping Free Porting Extrapolation Software
Question about measuring the port surface area- Would it be possible to use liquid volume to measure the port surface area? Like if you sealed off the port from the inside and filled it with water and measured the volume of water in a syringe. I assume this would wait until I have made in modification to match the port, considering it is for the purpose of making an exhaust pipe expansion chamber?

Also ordering a full circle crank.
Full Circle Crank $19.99*

EDIT: Holding off on the FCC after reading Mr.Kitty's posts about vibration and the flywheel being set for a stock crank. Sounds like the CAM2s turbo crank mod is the way to go? I'm going to research that now. Also looking for info on knife edging the conrod.

BTW-Damn these wheels are SICK.
 

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Is there a torque spec for the flywheel?

Another great modding video:
Issues with eBay Engines
I just use a little bit of loctite blue and about four or five clicks on the 12 volt Milwaukee I always replace the bolt with a high-grade steel bolt from the hardware store the same thing on the clutch side except if there is no woodrift key I just use a little bit of loctite red on the taper.


I feel bad for the guy in the video he does not know these engines...

So there is no side to side play in the connecting rod it has to stay in the center as well as the piston so the only thing that can move side to side is the bearing as long as the rollers of the bering stay on the rode end and don't move past you don't have to shim them...
( I have only had to shim one engine )

The Piston does not come all the way down that doesn't matter it's a brush cutter engine originally. We compensate for this by widening the exhaust port.

When he measures his squish the Piston should not rock around that means that his piston is too small or his cylinder is too big or both at this point you should try a different piston, cylinder or both.


Like I said all very common things with these engines what can you expect for 60$-120$
 

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Discussion Starter · #49 ·
Can anyone tell me what to check for this issue? Well, two issues. As you can see, I had a solid run and then it began bogging on the top end. If I lifted the rear off the ground and went full throttle it would run hard as it should then I’d get another good run. It sounds like flooding, I believe, and earlier the overflow tube was dripping u til I did a WOT woth the wheel off the ground

Second thing, after this video, I cut the petcock OFF and let it idle for a moment then got on and got several amazing 25 MPH runs out of it, (previous best was 23.1) with no bogging or hesitation at WOT before this issue came back.

Why is the engine still getting fuel with the petcock shut off? I’m assuming it’s broken in the on position or the previous owner modded it? Bearing in mind this is a new problem and that I did (a pretty clean) Form a gasket repair on the float bowl the other day, could this be related to something that happened in the repair? The overflow leaked previously as well.
 

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Dude, sounds pretty good to me. You need to a jet kit, the stock main jet is .64mm the kits come with .66, .68., .70, and .72mm, and even .75mm. I have hot rod engines that can't run a 75, to big. get the4 jet set, maybe $10. I would step up to a .68 and see how that works. Cold weather need bigger jets, hot weather smaller jets, cause the air is not as dense.
Pocket Bike Engines 101, lol, Chinese rubber sucks the gas here makes them expand and it damages them. , you drop the bowl and let it dry. This engines are backpack blower/ weed wackers, so some guy says lets put it in a pocket bike, lol.
They are design to run 6,000 rpms all day for a long time, in a pocket bike that all changes. You have a 200 lb dude on a 40 pound bike. that's a lot to ask for a small 39cc motor, there not 47cc. So, if you want to go faster, you need horsepower, many was to mod these engine cheap with hand tools.
 

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Can anyone tell me what to check for this issue? Well, two issues. As you can see, I had a solid run and then it began bogging on the top end. If I lifted the rear off the ground and went full throttle it would run hard as it should then I’d get another good run. It sounds like flooding, I believe, and earlier the overflow tube was dripping u til I did a WOT woth the wheel off the ground

Second thing, after this video, I cut the petcock OFF and let it idle for a moment then got on and got several amazing 25 MPH runs out of it, (previous best was 23.1) with no bogging or hesitation at WOT before this issue came back.

Why is the engine still getting fuel with the petcock shut off? I’m assuming it’s broken in the on position or the previous owner modded it? Bearing in mind this is a new problem and that I did (a pretty clean) Form a gasket repair on the float bowl the other day, could this be related to something that happened in the repair? The overflow leaked previously as well.
The float is stuck open and that's why it's overflowing and fuel is draining out. It's also probably why it's flooding out.

The petcock is a joke you should take it off and drill it out before it messes up and your bike goes lean and blows. Install a trusted inline one if you feel the need to shut your fuel off I personally drain my tank and the carburetor with the little screw on the bottom after every time I use it to prevent problems...
 

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The float is stuck open and that's why it's overflowing and fuel is draining out. It's also probably why it's flooding out.

The petcock is a joke you should take it off and drill it out before it messes up and your bike goes lean and blows. Install a trusted inline one if you feel the need to shut your fuel off I personally drain my tank and the carburetor with the little screw on the bottom after every time I use it to prevent problems...
Are you just posting to post??
The petcock I am pretty sure was already established. Thanks for the repeat.
He also already fixed the float bowl. That is for sure.
Thanks again!
Like the video, you can hear it start to rip. The low end needs a bit of power but it definitely sounds good and starts to pull around midrange. Definitely losing fuel at the top end, reason why it shut off.
Do that again, rip it until just before it would normally die and back off the throttle, I bet it keeps running. If so you need more jet like wannabe said. Check your plug for color. White is TOO lean.
 

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Is there a torque spec for the flywheel?

I am considering this pipe. I need to call them first to see if it will be a good fit with the mods I will have shortly. Anyone know where I can buy a stand?

Another great modding checklist video:
Issues with eBay Engines
I have an impact and I literally just full torque for a second. And I have never had any problems on many engines built, or technically just rebuilt.
And if you can find that pipe, great for you. As far as I know that company is long gone. But try to call them, I would love to know if they are still in business and actually have parts.
 

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Don't be afraid to do a little bit of blue printing on the case. Check out my last couple threads. The one isn't together and running yet but the first one is and it runs like a bat out of hell. I just need to take it to the parking lot to break it in more.
 

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Discussion Starter · #57 · (Edited)
Your right Francis, it like an echo here someone keeps repeating what we just said. Where is the You Tube Vid??
The video is posted above in my last comment. I know the petcock needs to be drilled out and it will be, but before I start modding, I want to get it into tip top stock condition to get the best pre-mod MPH number possible.

I’m trying to understand why the bike ran with the fuel petcock closed AND why it ran better. It was a night/day difference when I closed it, having hit 25 MPH vs the previous best of 23.1 MPH. I closed it hoping that would drain the float after noticing the overflow dripping.

There’s also no filter on the bike meaning it’s taking in more are than it would normally. Could that be it’s starving it for fuel at high RPM? As far as I know, everything else is stock, so the stock jet shouldn’t be an issue, outside of there being no filter.

Keep in mind, it didn’t start having this high RPM stuttering/stalling issue until I used the sealant on the float bowl. I’m wondering if a bit of sealant got inside and clogged the jet causing the starvation.
 

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That is definitely a possibility that some got into your jet. And those bowl gaskets are crazy expensive. Most of the time you can buy a brand new carburetor for the same price. I do like the fact that you want a baseline it. Out of all the pocket bikes I've ever had in my possession, only one did 23 mph but it was balls out off the line, I never counted the gears but I'm assuming it was geared more for torque. Then all the others were 26-28 every time. Never had one more or less. They were all stock and it didn't matter if they were 40 mm or 44 mm, but the only mods were better air filters and spark plug. Never did anything else until real recent with these two engines. And I'm only building off what I have read in these forums and the great people that posted them.
 

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Discussion Starter · #59 ·
I couldn’t even find the gasket by itself anywhere and yeah the whole stock 13mm carb is like $15 shipped, which is weird.

So the engine can run a minute or two with the fuel petcock shut off if the float bowl is flooded right? If that’s what happened when it was shut off and running like a beast for a few minutes, wouldn’t that be an indication that the sputtering/stalling was from a RICH condition rather than fuel starvation as someone else suggested?
 

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As you run out of gas it goes lean and the rpms go up, lean is fast if its too lean you burn up the engine. Most of mine the China rubber grows with the additives in gas, alcohol the worst. I take the bowl off and the rubber seal and let it sit till is goes back to its real size. You need a jet kid, China sends them here lean so they pass Smog. Every one of my 12 bikes has bigger than stock jets. Just buy a new carb, like ATV says and you will have parts, some day you will need them, lol. If you buy cans of chainsaw premix gas 94 octane 50:1 mix, no alcohol.
 
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