Engine runs kinda "lurchy"

[Nomad]

Thanks to everyone for the replies to my questions on the other thread, I appreciate the input. I have been "shaking out" the motorbike and adjusting here and there, I believe I will have it secured and properly adjusted in a year or two

I have noticed that my engine feels like it's lurching at low speed almost as if it is only firing on every other revolution, it seems to smooth out if I open the throttle more, I did fix my chain with a solid link and some light work with a dremel, and a hammer and dolly bar behind the chain so I could "peen" the little studs over, works good.. I understand that this is still a "bicycle" so I don't want to fly around at wide open throttle, putt putt, is cool with me... I live in a retirement community and alot of the people stand there with their hands on their hips wondering what the "farg" just went by.... any help on this lurching issue?... ;thanks
Bob

 

[Large Filipino]

You may need to gear down a bit by getting a larger rear sprocket. This will bring up your RPM a bit higher eliminating that lurching. It seems to me you aren't running fast at all as it is. If you have a 44 tooth in back get a 48 tooth.
Is this a China 2 stroke?

 

[Bikeguy Joe]

How fast are you going when it's lurching?

Could it be "four cycling" and running rich so it IS only firing ever other stroke?

 

[Nomad]

Thanks Large Filipino, yes it is a China 2 stroke, I think I would rather eat crushed lightbulbs than to start changing the rear sprocket 2 days after I built it.... that sprocket was a real pita...
BikeGuy Joe, I am going really slow, just a little above idle, putt putting along, I'll say probably about 5 - 8 mph. I thought maybe my chain was to slack.. so I moved the tensioner, I still can't figure out how to bend that danged muffler pipe out of the way of my left pedal crank, I tried bending it in a vise ,even heated it with a propane torch... that sucker is hard to move at all..... any suggestions?

Thanks
Bob

 

[misteright1_99]

Thanks Large Filipino, yes it is a China 2 stroke, I think I would rather eat crushed lightbulbs than to start changing the rear sprocket 2 days after I built it.... that sprocket was a real pita...
BikeGuy Joe, I am going really slow, just a little above idle, putt putting along, I'll say probably about 5 - 8 mph. I thought maybe my chain was to slack.. so I moved the tensioner, I still can't figure out how to bend that danged muffler pipe out of the way of my left pedal crank, I tried bending it in a vise ,even heated it with a propane torch... that sucker is hard to move at all..... any suggestions?

Thanks
Bob

Mine was the same way. I dont want to go fast. I put on a 50t and I love it, top end is about 22mph, but I can ride at idle now. I bent my exhaust (when I had it) by bolting it to the workbench, heating it up at the bend (red hot) and pulling it to where I needed it....

 

[Nomad]

Well thanks gentlemen, that looks like a consensus to me. I will look into getting a bigger sprocket, but I gotta run it around for a week or three.

Thanks
Bob

 

[pedalpower]

porting the exhaust helped the lower speed/rpm smoothness a little. but going below 10 mph impedes the minimum rpm for 2 cycle operation because my idle is higher operation than what I'm asking it for. seems you are looking for the centrifugal clutch feeling found in those automatic moped thingys I see around. feather the clutch, or pulling it in and pedal-nothing about these little fireboxes want to go slow.

 

[Nomad]

porting the exhaust helped the lower speed/rpm smoothness a little. but going below 10 mph impedes the minimum rpm for 2 cycle operation because my idle is higher operation than what I'm asking it for. seems you are looking for the centrifugal clutch feeling found in those automatic moped thingys I see around. feather the clutch, or pulling it in and pedal-nothing about these little fireboxes want to go slow.

Hi and thanks Pedalpower, I will trim the exaust gasket before I put the muffler back on.... I like the last line, "nothing about these little fireboxes wants to go slow"

 

[Bikeguy Joe]

I would think 5-8 is a little slow for the stock sprocket!

Yes, order a 48-50T and you'll smile again.

 

[Large Filipino]

I know there's a consensus as far as using a boost bottle but it made my china engine run smooth down at the low end. Maybe you can give it a try.

Boost Bottle Industries

I got the 63 to 65cc to compensate for the tube.

 

[Andyinchville1]

HI,

Wow....5 to 8 MPH?.....You'll probably have to go pretty large to have the engine run without lurching at that speed.....The largest sprocket for a motorized bike I have made so far is 65T (we can go lager if needed) for a fellow that wanted to ride his bikes on trails in the woods....

Andrew

 

[Radmanfly]

Regarding your muffler crank interference issue...during the test fitting of my engine (while fabricating the front mount) I noticed that the muffler would hit if the engine was not perfectly aligned with the seat post (rear mount) and if the front was too high (i think), the muffler would interfere. I tried different heights along the seat post and made the front mount to accommodate the position that fit the best which turned out to be as low as possible but still straight with the seat post (parting halves of rear mount aligned to seat post) See pics!
Considering how many interference problems I have seen on here, maybe I just got lucky and the pipe I got happened to be bent right.

 

[deacon]

Ride the bike if it isn't too awfully bad and it will smooth out as it breaks in. I had that problem for the first hundred miles now I just don't notice it if it is still doing it. I think most of us are a little paranoid at first. We think the bike is going to explode any minute. Why wouldn't it after all we did the installation lol.

 

[Nomad]

Ride the bike if it isn't too awfully bad and it will smooth out as it breaks in. I had that problem for the first hundred miles now I just don't notice it if it is still doing it. I think most of us are a little paranoid at first. We think the bike is going to explode any minute. Why wouldn't it after all we did the installation lol.

Deacon, thanks for the reply, that's funny, but you're right, I do think it's gonna explode any moment. When I ride it there are times when going slow is appropriate, and I keep forgetting this is a "manual clutch driven" thing.. so feathering the clutch is a good tip from "Pedalpower".. thanks alot for the words of confidence..
regards
Bob

 

[Nomad]

Regarding your muffler crank interference issue...during the test fitting of my engine (while fabricating the front mount) I noticed that the muffler would hit if the engine was not perfectly aligned with the seat post (rear mount) and if the front was too high (i think), the muffler would interfere. I tried different heights along the seat post and made the front mount to accommodate the position that fit the best which turned out to be as low as possible but still straight with the seat post (parting halves of rear mount aligned to seat post) See pics!
Considering how many interference problems I have seen on here, maybe I just got lucky and the pipe I got happened to be bent right.

Thanks Radmanfly, I will pay particular attention to the fitment on the next one I build, OH yes I will build another one maybe more... your bike looks like the "Black Bart" of motorbikes, cool.....