Small Engine Start Issues - Thoughts?

[kingofqueenz]

Alright, so technically not a Hawk or TBR - mods happy to move this if more appropriate elsewhere, truth is I ONLY visit this part of the forum.

I bought one of those 49cc 4 stroke Chinese motorized bike motors that clamp to a mountain bike ( for fun ) last year.

Had it winterized, drained the carb, new oil change, tank filled with stabil etc.


Attempted the first start 2 days ago, a little squirt of engine start and she ran on the first pull, I let it run for close to 10 mins and she sputtered and spit while she ran... dang looked like a 2 stroke the way it was sputtering and spitting.

Shut it down never rode it, just wanted to de-winterize and ensure it ran.

Since then it has been all down hill, I cannot get it to start, confirmed I have compression and spark, after about 5 pulls the plug is very damp\moist with gas. I checked the oil which was replaced before putting away for winter and it was watery and stunk of gas, which typically points to the carb.

Carb is immaculate, pulled the jet, looks shiny new, blew through it, no obstructions.

Float seems operational and float slide pin glides easily, removed the slide pin, cleaned with a q tip down in the hole, again spotless, no dirt, grime, green slime.

I've taken the carb apart 5 times, everything looks perfect.

I even tried to spin the motor with power drill because I was getting blisters from the pull start.

I imagine I have flooded the engine and maybe need to let it dry for a few days.

Any thoughts?

[Megadan]

Gas flooded crankcase and over rich fueling screams of a float needle failing to seat properly or other such fuel leaking into the intake that otherwise should not be. Did you check the float needle operation after cleaning? Basically just invert the carb and try to blow through the fuel inlet. Nothing should pass.

[kingofqueenz]

Thanks Dan... makes perfect sense, and no I did not try that.

Just visually inspected to insure it would travel smoothly up\down etc.

Will do

[Megadan]

Thanks Dan... makes perfect sense, and no I did not try that.

Just visually inspected to insure it would travel smoothly up\down etc.

Will do

Hopefully it is something that simple. Carbs for those things are pretty cheap, so even in a worst case scenario it isn't that bad.

Early carbureted goldwings sometimes would have issues with flooded crankcases, or even hydrolocked left cylinders, because the float needles didn't seal, or the plenum seal would leak. Have one of those problems and leave the fuel petcock open... bad day.

[kingofqueenz]

DAN = THE BEST!!!

Outcome and lesson learned as follows

Pulled the carb for the 5th time and pulled the float - I initially checked the travel on the float needle, but I didn't check the function as you so astutely suggested.

Inverted the carb, blew through the fuel inlet and sure enough it wasn't a perfect seal. Visually the chamber was immaculate and the needle and black tip were an object of perfection, however upon very detailed inspection, the spring atop the float needle was the thinnest , cheapest material I have ever seen ( note: this is a small Chinese engine that cost $89 on ebay. The spring had warped a bit and was not applying enough pressure, I adjusted the spring, got it functional and the engine started but it was still a bit tough to start, had to spin it with a power drill.

Again, reviewing the 3 principles fuel, spark, compression.... I checked the spark again in pitch darkness (spinning the engine with a power drill so I can view the spark up close and it was weak as crap and I don't have a spare random tiny Chinese spark plug lying around ( and certainly not going out shopping for one in a zombie apocalypse ).

I broke out the sand paper, sanded the soot, and gapped the plug and tried again and had delicious spark.

Everything back together and she started up and ran perfect.

These tiny little junk carbs need alot of TLC, I then proceeded to tune the carb for almost an hour finding the right idle and air \ fuel mixture.

Tuning carbs is really like artwork, respect to you all that have become proficient at it.

This was a big win for me getting this thing running again, if I can't fix the simple stuff I have no business being a china rider.

Thanks again Dan :thanks:

[Megadan]

Glad to be of assistance.

Carbs are not art work. They are also not magical wizard shit, or other such things people tend to label it with.

Carbs are just another mechanical device, and like all mechanical devices, every part serves a purpose and works either in unison with other parts, or alone. Once you know and understand those parts and functions, then it is just a matter of keep it simple stupid and experience. Change enough jets and experience a few fouled plugs and you begin to learn how a rich mixture sounds, feels, and smells. Same with a lean one.

Guru's of carburetors are not mystical beings, just experienced ones.

The only benefit is that I can make some good side cash rebuilding carbs and balancing multiple carb setups for guys. I actually just made some bucks a couple of weeks ago doing an old Triumph T300 Speed Triple. Rebuild and balance, once the parts were in hand it took a day to do. Bike sat for 8 years, and the carbs were a nightmare.

[kingofqueenz]

Solid points.

Gotta feel great when you got that baby running after sitting for 8 years.

I think I am unfortunately a poster child for a potential problem with this hobby, we all want to get in this game, me being good with a wrench ( but not on motorcycles ) and being in my mid 40s, not much experience with carbs, we tend to consider them mythical devices.

We noobs buy a china bike, mod the carb ( because everyone says so, potentially without understanding ) , mod the airbox, after market exhaust, front sprockets etc. ..without taking a minute to learn something.

Truth is I changed the jetting of my carb immediately based on the forum, without fully understanding why.

The 2 days and last few hours I spent messing with this cheap little carb , I learned more than I ever have.

Thanks again

[Goob]

DAN = THE BEST!!!

Outcome and lesson learned as follows

Pulled the carb for the 5th time and pulled the float - I initially checked the travel on the float needle, but I didn't check the function as you so astutely suggested.

Inverted the carb, blew through the fuel inlet and sure enough it wasn't a perfect seal. Visually the chamber was immaculate and the needle and black tip were an object of perfection, however upon very detailed inspection, the spring atop the float needle was the thinnest , cheapest material I have ever seen ( note: this is a small Chinese engine that cost $89 on ebay. The spring had warped a bit and was not applying enough pressure, I adjusted the spring, got it functional and the engine started but it was still a bit tough to start, had to spin it with a power drill.

Again, reviewing the 3 principles fuel, spark, compression.... I checked the spark again in pitch darkness (spinning the engine with a power drill so I can view the spark up close and it was weak as crap and I don't have a spare random tiny Chinese spark plug lying around ( and certainly not going out shopping for one in a zombie apocalypse ).

I broke out the sand paper, sanded the soot, and gapped the plug and tried again and had delicious spark.

Everything back together and she started up and ran perfect.

These tiny little junk carbs need alot of TLC, I then proceeded to tune the carb for almost an hour finding the right idle and air \ fuel mixture.

Tuning carbs is really like artwork, respect to you all that have become proficient at it.

This was a big win for me getting this thing running again, if I can't fix the simple stuff I have no business being a china rider.

Thanks again Dan :thanks:

KOQ...OK...I'll ask the typical question...what's the top speed? I have always wanted to build one of those...shopped around all the kits, just never pulled the trigger. I even have a donor bicycle ready. If it could do 30, then I would ride it to work in the Summer for fun rather than my TT250.

[Megadan]

KOQ...OK...I'll ask the typical question...what's the top speed? I have always wanted to build one of those...shopped around all the kits, just never pulled the trigger. I even have a donor bicycle ready. If it could do 30, then I would ride it to work in the Summer for fun rather than my TT250.


Depends on a bunch of factors, but if you get a 2.5hp 49cc 4 stroke with the right gearing and tire diameter combination they can hit 30-35mph top speed usually without too much muss or fuss on flat ground.

[Its_not_a_honda]

If the float was open, drain the oil and put fresh in. 99.9% sure it contaminated the crankcase with gas. Also, even tho starting fluid makes engines start easier most times, it is the worst thing you can do to an engine. Don't use it unless it is a weed trimmer and your next step is to beat it on the ground. Then take a hammer and redesign the cooling fins. Only at this time should you use starting fluid.

[Megadan]

Solid points.

Gotta feel great when you got that baby running after sitting for 8 years.

I think I am unfortunately a poster child for a potential problem with this hobby, we all want to get in this game, me being good with a wrench ( but not on motorcycles ) and being in my mid 40s, not much experience with carbs, we tend to consider them mythical devices.

We noobs buy a china bike, mod the carb ( because everyone says so, potentially without understanding ) , mod the airbox, after market exhaust, front sprockets etc. ..without taking a minute to learn something.

Truth is I changed the jetting of my carb immediately based on the forum, without fully understanding why.

The 2 days and last few hours I spent messing with this cheap little carb , I learned more than I ever have.

Thanks again

That is the best way to learn. Diving in, hands on, screwing up, getting your nose stuck in and really looking at the parts. In truth, these carbs are probably the best ones to start learning on just because of how simple they are. Once you get into CV carburetors, or highly tunable carburetors like Webers DCOE progressives that have what seems like a million parts to deal with and endless numbers of different setups/adjustments. then the learning curve gets steeper.

Want a real challenge? Setup a carb for an engine going in completely blind. You will take that carburetor apart so many times you will wear out fasteners and seals lol.

[Goob]

Depends on a bunch of factors, but if you get a 2.5hp 49cc 4 stroke with the right gearing and tire diameter combination they can hit 30-35mph top speed usually without too much muss or fuss on flat ground.

So a Bike Berry 80cc should fly!

https://www.bikeberry.com/flying-horse-complete-79cc-pull-start-4-stroke-bicycle-engine-kit.html

[kingofqueenz]

Honda - I did change the oil again after realizing it was gasoline flooded.

Goob

The exact kit I bought from Amazon is this one:

https://www.amazon.com/Iglobalbuy-Powerful-4-Stroke-Compete-Motorized/dp/B06WRQRTH4?ref_=ast_bbp_dp

The price is more expensive now, I bought it for $129 last year.

Engine arrived perfect, nothing missing, nothing broken or scratched, easy to assemble following Youtube videos ( Project Farm has a good one).

Bike will do 34mph on flat level street ( per GPS phone app )

[JerryHawk250]

I did one of the 2 stroke kits a few years back. They are fun little projects. I have two donated bikes just sitting here begging to have a kit installed. :D That 4 stroke kit looks like a real nice kit.

[Megadan]

So a Bike Berry 80cc should fly!

https://www.bikeberry.com/flying-horse-complete-79cc-pull-start-4-stroke-bicycle-engine-kit.html

That motor only has about half a HP more than the 49cc, so "fly" would be a relative term. Maybe 40mph? You have to remember that kinetic energy depends on the square of the velocity. In simple terms that means to double the velocity of a given object the kinetic energy quadruples, or basically it takes 4 times the power to go twice as fast.

So, if a 2.5hp bike tops out at 35mph, then it would take 10hp for it to go 70mph (ignoring a bunch of other variables at least). If you do the math, an extra half a HP wouldn't add as much as you might think. What it would probably do is make the bike a bit more capable of hills and acceleration within the same speed limitations, and if you ask me that would be what I would aim for. The idea of going 40mph on most off the rack bicycles is a little scary to me. I ride big boy motorcycles for that reason.

[JerryHawk250]

I've never checked the top speed on the one i had but it went faster than i wanted to go on a bicycle. Great for just putting around the neighborhood.

[Megadan]

I've never checked the top speed on the one i had but it went faster than i wanted to go on a bicycle. Great for just putting around the neighborhood.

I always looked at a motorized bicycle as the scooter for people that wouldn't be caught dead on a scooter. Or as I like to view it, a Scooter that can still work when it runs out of gas lol.

[bogieboy]

That motor only has about half a HP more than the 49cc, so "fly" would be a relative term. Maybe 40mph? You have to remember that kinetic energy depends on the square of the velocity. In simple terms that means to double the velocity of a given object the kinetic energy quadruples, or basically it takes 4 times the power to go twice as fast.

So, if a 2.5hp bike tops out at 35mph, then it would take 10hp for it to go 70mph (ignoring a bunch of other variables at least). If you do the math, an extra half a HP wouldn't add as much as you might think. What it would probably do is make the bike a bit more capable of hills and acceleration within the same speed limitations, and if you ask me that would be what I would aim for. The idea of going 40mph on most off the rack bicycles is a little scary to me. I ride big boy motorcycles for that reason.

even on a purpose built road bike, if you dont have your speedo sensor exactly opposite the valve stem (i have since done away with it, using a garmin edge 200 (https://buy.garmin.com/en-US/US/p/90675) now) you can induce enough of an out of balance front wheel that will bounce itself right off the ground, not what you want when decending a long grade by any means...LOL thankfully that day i was able to get the speed down with the almost useless rear brakes to keep the front wheel on terra firma....

i find myself riding the pedal bikes much more these days than the motorcycle.... but that figures... met my wife on a cross country ride.... fun story about that here...LOL http://chinariders.net/showthread.php?t=12691

[kingofqueenz]

The idea of going 40mph on most off the rack bicycles is a little scary to me.

On this point let me just say, getting my standard HUFFY up to 30+ mph is a dicey scenario, the bike feels like its ready to rattle apart and I've gone through 2 sets of brake pads in 1 year, where you may not change brake pads on a mountain bike twice in 10 years ( under normal riding conditions ).

I built this for nothing but ridiculous, silly fun.... I mean why does an adult buy a Grom ?

Its pure backyard BBQ, block party, drunken buddies fun!

[bogieboy]

On this point let me just say, getting my standard HUFFY up to 30+ mph is a dicey scenario, the bike feels like its ready to rattle apart and I've gone through 2 sets of brake pads in 1 year, where you may not change brake pads on a mountain bike twice in 10 years ( under normal riding conditions ).

I built this for nothing but ridiculous, silly fun.... I mean why does an adult buy a Grom ?

Its pure backyard BBQ, block party, drunken buddies fun!

set of pads every year back when i ran rim brakes, now its every other for the discs....:hehe: im a big boy and i ride HARD though...