Hello all I would like to start by saying thank you! These forums have been really helpful and the collective knowledge is impressive to say the least.
With some help from youtube and these forums I have recently built my first motorized bicycle. Although I am new to these 2 stroke motors I am no stranger to mechanics. I have been a backyard mechanic for over 15 years and studied automotive technologies at a 2 year vocational school. However my experience with carburators is limited as most of the vehicles I have owned or repaired have been fuel injected. But enough about me and on to the bike.
I have a 26" Huffy Lockland with a 100cc 2 stroke motor I bought from ebay. Both the intake and exhaust ports are 40mm. I keep forgetting to measure piston but according to the listing it should be 50mm. It has the NT speed carb, speed demon exhaust and a 3 prong spark plug. Im currently running the stock 44t sprocket with rag joint and both the stock 4-bolt tensioner as well as a spring tensioner. The sole purpose of adding spring tensioner was to stretch the chain with as little adjustment and work as possible. The bike is just shy of 200 miles and I have not had to remove any links since fitting the chain, and have had zero chain issues. So I'd say it worked quite well! I do have a clam shell adapter to replace the rag joint and plan on deleting the extra tensioner and refitting the chain. I have a 38t sprocket that came with clam shell that would be easiest to install but I'm not sure if it will give me enough torque. I believe it will but I have a throttle issue that keeps coming back I want to iron out before choosing which sprocket to go with.
So finally the reason for posting, THE ISSUES! The biggest issue im having is the bike will run fine while accelerating but if I decrease throttle at any rate the bike starts to jerk and shutter. If im below 20mph it even does this holding the throttle steady. 20mph to 24mph it takes a few seconds before it starts acting up but it will cruise smooth at 25mph to 27mph. The issue comes and goes. I thought it was tweaks I was making to the bike that was making it stop but now im not so sure. I first thought it was a symptom of my air leak at the intake. The threads for the intake port were damaged by leftover metal flakes from production. The intake manifold would snug up but would shake loose and eventually pulled out the remaining threads. I Installed helicoils and that fixed the intake leaks. The bike ran better but would act up again once at running temp. Found an air leak at the head. While torquing the head bolts one snapped. So I pulled the head and trued it, flipped the head gasket, and replaced all the hardware besides the what holds the case together as I didn't want to risk having to split the case. After I put it all back together it ran great. The motor stopped revving high when pulling the clutch and I could even let go of the throttle with no issues. I live in Hill country Texas and have next to no flat stretches road. So with my bike running good I added a couple of holes in the air filter housing and a 1/4 hole at the bottom of the stock exhaust which allowed me to get up the hills and around the block without being WOT. After about a week and a half it started shaking hard when decreasing throttle but no high revving this time and no air leaks. I then tried adjusting the throttle cable and idle screw and that seemed to fix it but it was right back to its old ways the next ride. So after some digging I thought maybe the 40:1 trufuel premix I was using might be to lean. I couldn't find any ethanol free but was able to get 93 octane with less than 10% and mixed at at 32:1 and had no real change in performance. After some time on the forums I read that it may be the intake gasket that came with the motor so I did as the guy advised and cut the gasket to the intake port as it comes cut for the manifold. Sealed it with a touch of rtv. The next ride was the smoothest I had gotten up to that point. I thought finally I have this thing figured out! But no the problem came back after a few rides. At a loss I replaced the intake gasket, upgraded the exhaust to a cheap expansion chamber, upgraded to the 3 prong spark plug, replaced the fuel lines and filter, and drilled a tiny hole the gas cap. After all that the bike ran the best it ever has. However it only lasted a few days. So I pulled the plug thinking it had to be an air fuel issue, it was darker than I'd like so I moved the c-clip from the middle to the second notch from the top. It then idled a little rough but overall performance improved but didn't fix my problem. So I went back to the 40:1 which smoothed out the idle and made it not shake as hard. However it still shakes but the intensity of jerks changes from ride to ride. It still hasn't ran as smooth as when I replaced the stock gaskets and exhaust but it has improved in torque and response.
If you are still with me you are saint and a scholar! And if you have any advice I am all ears. Im completely lost. I don't know if this is part of the break-in period? or If this because I botched the break-in by beating on it to hard or not using the right fuel or ratio? Seriously any input is welcome.
With some help from youtube and these forums I have recently built my first motorized bicycle. Although I am new to these 2 stroke motors I am no stranger to mechanics. I have been a backyard mechanic for over 15 years and studied automotive technologies at a 2 year vocational school. However my experience with carburators is limited as most of the vehicles I have owned or repaired have been fuel injected. But enough about me and on to the bike.
I have a 26" Huffy Lockland with a 100cc 2 stroke motor I bought from ebay. Both the intake and exhaust ports are 40mm. I keep forgetting to measure piston but according to the listing it should be 50mm. It has the NT speed carb, speed demon exhaust and a 3 prong spark plug. Im currently running the stock 44t sprocket with rag joint and both the stock 4-bolt tensioner as well as a spring tensioner. The sole purpose of adding spring tensioner was to stretch the chain with as little adjustment and work as possible. The bike is just shy of 200 miles and I have not had to remove any links since fitting the chain, and have had zero chain issues. So I'd say it worked quite well! I do have a clam shell adapter to replace the rag joint and plan on deleting the extra tensioner and refitting the chain. I have a 38t sprocket that came with clam shell that would be easiest to install but I'm not sure if it will give me enough torque. I believe it will but I have a throttle issue that keeps coming back I want to iron out before choosing which sprocket to go with.
So finally the reason for posting, THE ISSUES! The biggest issue im having is the bike will run fine while accelerating but if I decrease throttle at any rate the bike starts to jerk and shutter. If im below 20mph it even does this holding the throttle steady. 20mph to 24mph it takes a few seconds before it starts acting up but it will cruise smooth at 25mph to 27mph. The issue comes and goes. I thought it was tweaks I was making to the bike that was making it stop but now im not so sure. I first thought it was a symptom of my air leak at the intake. The threads for the intake port were damaged by leftover metal flakes from production. The intake manifold would snug up but would shake loose and eventually pulled out the remaining threads. I Installed helicoils and that fixed the intake leaks. The bike ran better but would act up again once at running temp. Found an air leak at the head. While torquing the head bolts one snapped. So I pulled the head and trued it, flipped the head gasket, and replaced all the hardware besides the what holds the case together as I didn't want to risk having to split the case. After I put it all back together it ran great. The motor stopped revving high when pulling the clutch and I could even let go of the throttle with no issues. I live in Hill country Texas and have next to no flat stretches road. So with my bike running good I added a couple of holes in the air filter housing and a 1/4 hole at the bottom of the stock exhaust which allowed me to get up the hills and around the block without being WOT. After about a week and a half it started shaking hard when decreasing throttle but no high revving this time and no air leaks. I then tried adjusting the throttle cable and idle screw and that seemed to fix it but it was right back to its old ways the next ride. So after some digging I thought maybe the 40:1 trufuel premix I was using might be to lean. I couldn't find any ethanol free but was able to get 93 octane with less than 10% and mixed at at 32:1 and had no real change in performance. After some time on the forums I read that it may be the intake gasket that came with the motor so I did as the guy advised and cut the gasket to the intake port as it comes cut for the manifold. Sealed it with a touch of rtv. The next ride was the smoothest I had gotten up to that point. I thought finally I have this thing figured out! But no the problem came back after a few rides. At a loss I replaced the intake gasket, upgraded the exhaust to a cheap expansion chamber, upgraded to the 3 prong spark plug, replaced the fuel lines and filter, and drilled a tiny hole the gas cap. After all that the bike ran the best it ever has. However it only lasted a few days. So I pulled the plug thinking it had to be an air fuel issue, it was darker than I'd like so I moved the c-clip from the middle to the second notch from the top. It then idled a little rough but overall performance improved but didn't fix my problem. So I went back to the 40:1 which smoothed out the idle and made it not shake as hard. However it still shakes but the intensity of jerks changes from ride to ride. It still hasn't ran as smooth as when I replaced the stock gaskets and exhaust but it has improved in torque and response.
If you are still with me you are saint and a scholar! And if you have any advice I am all ears. Im completely lost. I don't know if this is part of the break-in period? or If this because I botched the break-in by beating on it to hard or not using the right fuel or ratio? Seriously any input is welcome.
