First build Rear Rack done Used 4 stroke 49cc won't start/run

UtiliD

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May 11, 2018
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Ok so, this is my 1st ground up build( Building rear Rack, using parts of a Kit...Motor/gear reduction/throttle kill switch, building mainly with some scraps/mechanisms I picked up for free, minimal hardware from Lowes)& I have very limited space but it's coming along nicely. Rack is done other than thread locker & notching the piece of 1/8th U aluminum 1-1/2 X 1 inch to mount the chain tensioner I made(pics later). The rack itself is some weird teflon coated 1/4" L shaped aluminum I cut in half then joined to make a U shaped rack. The U shaped brace legs are really ridged I got it from an old A/C ductwork square I broke down. Using this Fat tire bike & having a chain for 26in bike I'm taking the gear box & flipping it downward already checked my height after tensioner it's dead nuts where I wanted it.

My 49cc 4 stroke has been sitting for at least a year I'd say.
I got this motor/kit used on Craigslist for $80.
Changed the oil
I went through the carb to the point I could taste the carb cleaner it really wasn't that dirty to begin with. The air filter has good foam but the previous owner cut the air box I think to fit it on a mid frame mount.
Went to start it today & nothing...
Removed foam air filter(which has a light layer of oil) tried again & no go.
Pulled the spark plug & it had a lot of oil on it it's a torch plug gap was small went to .028 .032 nothing. Pulled the choke halfway same with the throttle & shot some carb cleaner up there & then pulled the cord & it turned over, ran for maybe 8 seconds, then died.
Couldn't get it to turn over again until I repeated the carb cleaner it turned over for 3 seconds & died. Fuel lines(gas supply line has inline filter) are good.

Questions
What is most likely wrong?
What can I do to clean/tweak/fix this to where it's next to new and dependable? I know it turning over is a good sign I want this to be a dependable daily rider
 

crassius

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Sep 30, 2012
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I'd guess you're not getting fuel - dry the plug and spin the motor, then see if plug is wet.
 

UtiliD

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Also I did mess with the screw on the carburetor that changes the gas air mix and it made no difference.
 

UtiliD

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I'd guess you're not getting fuel - dry the plug and spin the motor, then see if plug is wet.
I jumped the gun, you were right, I assumed I saw the spark plug wet then wiped it off with the same rag. It's not getting gas. I've got it to where it wants to turn over but will not at all. I think I'm getting good spark. Gas goes from the tank through the fuel filter to the carb & I guess is getting caught up in there somewhere. I sprayed every orifice with carb cleaner & with an air chuck. I pulled the jet under the idle screw(completely blocked now cleaned), took off the float bowl(float good bowl needed clean, main jet needed clean. I'm going to pull the carb apart one more time if it doesn't then look for a vaccum leak.
Your best way to find one on an engine that won't start?
 

crassius

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just as you're doing - clean and clear everything that should flow, clean and seal everything that should not leak
 
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UtiliD

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just as you're doing - clean and clear everything that should flow, clean and seal everything that should not leak
Have you ever seen any one run the transmission straight down instead of the normal straight back configuration. Do you think it can affect the performance. Since I'm running the chain in the same direction I wouldn't think so but I'm a pretty sharp noob that learns quickly.

What do you think about the tranny pointing down? What can I do to maintain the tranny?
 

crassius

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Sep 30, 2012
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sorry, 4-strokes aren't popular around here, so have not seen a enough of them to have opinion on diff types
 

UtiliD

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sorry, 4-strokes aren't popular around here, so have not seen a enough of them to have opinion on diff types
Well I finally got the time to get the engine started...


Iridium NGK plug

Cleaned carb 3 times

Cleaned gas tank

Cleaned & replaced o-ring in petcock(it attaches directly to the gas tank) what a process wish I started with a new tank petcock combo.

Set up gas/air mix screw

It runs like a beast now... sounds mean without the muffler on it(going to have to heat and bend it or cut it and add a flexible section in the middle so it will fit.

One thing I know I need to address is the thick carbon build up in the cylinder on top & bottom of the piston. My worry is that I know the previous Owner did not maintain this like he should of. The carbon build up it's so thick Ill bet it's filling some voids where the piston rings have probably been corroded and been eaten up & once clean open those voids & it will mess with my compression.
Am I being Paranoid?

What's the easiest was to clean out the cylinder & piston?

Thanks for any input guys!

By the way ...
Next motor I'm doing a build with 43cc 2 stroke with cent clutch from a poll going to start a post in 2 stroke thread to get input about the shaft not using a tranny going direct belt drive to a rim pulley. I'm attaching the rim pulley in a way I haven't see anyone do(no welding either) & I think is going to kick ass.
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UtiliD

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Well found the time to make progress and got to go for a ride. All that's left for me to be satisfied is I need a longer throttle cable, to bend my exhaust way down and over so I'm not getting smoke literally blown up my rear(ran with & without the exhaust), get a rear hub adapter and a seat with a back. All that wasn't going to stop me, I was going for a ride. It was a blast.

Anyone know where to find a "9 hole sprocket" compatible rear hub adapter specifically one that is for 1.25 inch hub?

Well here are some pics...
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UtiliD

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Wow I forgot about this... sold this bike awhile back

It was the carb as it almost always is. Just because you clean a Carb doesn't mean that the carb 'IS CLEAN'. Using strands of shift cable to clean out jets can help. Removing everything with an oring from the carb then dipping the carb in part cleaner or a sonic cleaner can help.

I think the best thing to do is start with a new carb and never let it get gummed up. I read a thread awhile back about using a small amount of gum out in every 4th gas tank. I've been doing that for awhile now and it seems to help.

Other things I learned from and since this build...

I can't stand Huffy

I'd never do another rack mount build again. While this bike rode fine and the rear weight wasn't that big of a deal(my friend was riding it & lost control 1 time when it was wet out plus the tires were not road tires)... frame mount is the way to go.

I'd only do builds on bikes with a head tube made for a fork with a 1 1/8th(or larger) steerer tube because it's almost impossible to find a good suspension fork with a 1 " steerer tube.

And on and on. I just ran across this thread and it brought back some memories.
 

Sidewinder Jerry

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Dec 19, 2011
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Wow I forgot about this... sold this bike awhile back

It was the carb as it almost always is. Just because you clean a Carb doesn't mean that the carb 'IS CLEAN'. Using strands of shift cable to clean out jets can help. Removing everything with an oring from the carb then dipping the carb in part cleaner or a sonic cleaner can help.

I think the best thing to do is start with a new carb and never let it get gummed up. I read a thread awhile back about using a small amount of gum out in every 4th gas tank. I've been doing that for awhile now and it seems to help.

Other things I learned from and since this build...

I can't stand Huffy

I'd never do another rack mount build again. While this bike rode fine and the rear weight wasn't that big of a deal(my friend was riding it & lost control 1 time when it was wet out plus the tires were not road tires)... frame mount is the way to go.

I'd only do builds on bikes with a head tube made for a fork with a 1 1/8th(or larger) steerer tube because it's almost impossible to find a good suspension fork with a 1 " steerer tube.

And on and on. I just ran across this thread and it brought back some memories.
I personally like adding Sea Foam to my gas and oil