Can anyone tell this 97cc runs good? I am planning to sell my Briggs 5hp Flatheads, don't need them anymore LOLs.
https://www.youtube.com/watch?v=J1mcegoPEQw
https://www.youtube.com/watch?v=J1mcegoPEQw
Thanks for replies, it's really running well, I am very happy with it. Will accelerate up hills, don't feel like I need 5hp Briggs anymore, will turn 5000 rpms quick, hit 30mph easy. Really fun to zip around neighborhood, not so fast to be dangerous IMO.
Mods: re-jet carb (hi/ low jets), drill out muffler, remove easy start bump on cam, cut head 2cc, pocket bike tires (equivalent to 77 tooth rear sprocket), black clutch spring, hydraulic brakes (which I need). Costs less than $100 additional.
:smile:
Mods: re-jet carb (hi/ low jets), drill out muffler, remove easy start bump on cam, cut head 2cc, pocket bike tires (equivalent to 77 tooth rear sprocket), black clutch spring, hydraulic brakes (which I need). Costs less than $100 additional.
:smile:
One of the 1st easy mods for DB30 is to buy the OldMiniBikes sprocket adapter and add a larger rear sprocket. With smaller pocket bike tires, you get the same effect without having to change to a larger rear sprocket. You have a 12 to 1 ratio because you are on a bicycle, I assume the effect is approx the same, approx 30mph at 5000rpms.
Perhaps I was confused. It seemed like you were saying those mods were necessary to achieve 5k. If that's not what you were implying, then I apologize. That is about right, 30mph at 5k, the point I was just trying to point out that I'm turning 5k without any mods other than the governor having been removed.
The point is lower gearing helps with acceleration.
For example: my neighbor has a Motovox with 79cc ohv engine. It runs maybe a little better than 97cc flathead but basically the equivalent. The Motovox comes with 11 x 75 gearing, unlike the DB30 that comes with 11 x 70.
Of course, he wanted to race, so I raced him with a stock 97cc DB30, but it was running excellent and had a black clutch spring. As expected, he took me off the line, but I soon passed him, because I had more top speed with my taller gearing. If I installed a 75 tooth sprocket, we would probably come off the line approx the same and have similar top speeds.
He doesn't want to race my modified engine. He can tell just by watching me zip around he wouldn't have a chance in a race, off the line or top speed.
I have tachs from my kart racing, so it is easy to put a tach on my minibike and see exactly what rpm the engine is doing. My experience with 97cc is it will free rev well over 5000, 6000 for that matter without floating the valves or other bad consequences. However, it takes HP to get to 5000rpms plus pushing a bicycle or minibike with rider down the road. That's what the mods do, make HP. The mods are not to allow the the engine rev over 5000rpms, it already does that.
Not knowing any better, I typically set the governor the limit rpms to approx 5000 to 5500rpms. I have never rev'd the engine just to see how many rpms it woud do, dangerous IMO, plus I don't want to damage my engine.
Cheers
For example: my neighbor has a Motovox with 79cc ohv engine. It runs maybe a little better than 97cc flathead but basically the equivalent. The Motovox comes with 11 x 75 gearing, unlike the DB30 that comes with 11 x 70.
Of course, he wanted to race, so I raced him with a stock 97cc DB30, but it was running excellent and had a black clutch spring. As expected, he took me off the line, but I soon passed him, because I had more top speed with my taller gearing. If I installed a 75 tooth sprocket, we would probably come off the line approx the same and have similar top speeds.
He doesn't want to race my modified engine. He can tell just by watching me zip around he wouldn't have a chance in a race, off the line or top speed.
I have tachs from my kart racing, so it is easy to put a tach on my minibike and see exactly what rpm the engine is doing. My experience with 97cc is it will free rev well over 5000, 6000 for that matter without floating the valves or other bad consequences. However, it takes HP to get to 5000rpms plus pushing a bicycle or minibike with rider down the road. That's what the mods do, make HP. The mods are not to allow the the engine rev over 5000rpms, it already does that.
Not knowing any better, I typically set the governor the limit rpms to approx 5000 to 5500rpms. I have never rev'd the engine just to see how many rpms it woud do, dangerous IMO, plus I don't want to damage my engine.
Cheers
Have you noticed any improvement in mpg after removing the comp release? I'm asking because since switching to the 19mm carb, it seems my mpg has decreased somewhat. So I'm hoping that removing my comp release will help. I'm doing it for other reasons too, but it seems that if the intake valve is being kept open through most of the compression stroke, then it might not compress the fuel enough to burn efficiently? Probably ok with the stock (16mm?) carb, but with a big bore carb, it's probably wasting a lot of fuel?
So, I gave it a try today. Cracked my case, pulled the camshaft, filed down the intake lobe a bit. Basically tried to get the intake and exhaust lobes the same height. Put it back together, and the darn s.o.b would not start. I tried my darndest to figure out why. What I ended up finding out is it will no longer start with the choke closed. It's also a little louder on the exhaust note and pulls a little quicker. Is this all normal?
Sorry, I don't think you removed the compression release. The compression release is not at the top of the cam lob.
To locate the compression release on the cam, I suggest you remove the head, rotate the crankshaft, and determine where the intake valve closes on the compression stroke. You do this by checking where intake valve closes against the seat on the compression stroke.
It's a fairly tedious process. Keep in mind, when the crankshaft is rotating counterclockwise, the cam is rotating clockwise. The compression release bump is very slight and almost not visible. It is located on the cam just after the intake lob.
To locate where the intake valve closes, install the side cover (with the bolts semi-tight), keep the head off, rotate the crankshaft, and keep your thumb on the intake valve. When the intake valve is open, you can twist it with your thumb, when it closes, you can't twist it. Then, remove the side cover to observe where the lifter is against the intake lob of the cam.
Then, remove the cam, and file the intake lob on the cam in that area. Do this over and over until the intake valve closes near BDC.
Before I filed off the compression release, the intake valve closed approx 1/3 from TDC. That means, the piston travels approx 2/3 of the compression stoke with the intake valve leaking. When you remove the compression release, you stop this leakage.
After the compression release is removed, the pull rope will definitely be a firmer pull.
One caveat, I think your 97cc engine is made by Lifan, mine is Hensim, so yours may be a little different.
Good luck, I hope the above is helpful.
To locate the compression release on the cam, I suggest you remove the head, rotate the crankshaft, and determine where the intake valve closes on the compression stroke. You do this by checking where intake valve closes against the seat on the compression stroke.
It's a fairly tedious process. Keep in mind, when the crankshaft is rotating counterclockwise, the cam is rotating clockwise. The compression release bump is very slight and almost not visible. It is located on the cam just after the intake lob.
To locate where the intake valve closes, install the side cover (with the bolts semi-tight), keep the head off, rotate the crankshaft, and keep your thumb on the intake valve. When the intake valve is open, you can twist it with your thumb, when it closes, you can't twist it. Then, remove the side cover to observe where the lifter is against the intake lob of the cam.
Then, remove the cam, and file the intake lob on the cam in that area. Do this over and over until the intake valve closes near BDC.
Before I filed off the compression release, the intake valve closed approx 1/3 from TDC. That means, the piston travels approx 2/3 of the compression stoke with the intake valve leaking. When you remove the compression release, you stop this leakage.
After the compression release is removed, the pull rope will definitely be a firmer pull.
One caveat, I think your 97cc engine is made by Lifan, mine is Hensim, so yours may be a little different.
Good luck, I hope the above is helpful.
If the compression release is not on the cam lobe, how does it open the intake valve? I didn't take my head off, but I did rotate the crankshaft and watch how far the valve lifters moved up and down. Before I filed down the intake lobe, the intake valve was lifting higher than the exhaust valve. Now they both lift the same. Did I mess up my engine?
I wish I could explain how to do it better, my bad. I don't think we are communicating very well on this one. The holes in the cam are for lubrication IMO, don't have anything to do with the compression release.
I don't think you can do it without removing the head. The compression release is maybe .002 to .004 high. You probably can't see it. When you filed off the top of the intake lob, you decreased the lift of the intake valve, not a disaster, but will decrease hp for sure.
Look around, you can probably get another 97cc cam cheap, and start over. Or, go with what you have, engine probably still runs well, about the same as before? :shrug:
I don't think you can do it without removing the head. The compression release is maybe .002 to .004 high. You probably can't see it. When you filed off the top of the intake lob, you decreased the lift of the intake valve, not a disaster, but will decrease hp for sure.
Look around, you can probably get another 97cc cam cheap, and start over. Or, go with what you have, engine probably still runs well, about the same as before? :shrug:
The head is easy to take off, I have never had to replace a head gasket.
Only issue I experienced, if the engine has a lot of time and never been disassembled, the head bolts near the exhaust may be seized. If so, they will be hard to get out, may come out with messed up threads. Be very careful not to break them off, or will be looking at a difficult fix or junk block.
I have had this issue on Tecumseh, Briggs, and now 97cc flatheads, so it is a common problem with old engines. When I reassemble, I put a little engine oil on the bolt threads to act as anti-seize, plus makes it easier to assemble and torque.
I am hoping you can get this mod figured out. I think you will be very pleased with the results. I know the engine runs a lot better, just don't know how much it will shorten it's life. Plus, after you get this one done, there is another mod to step it up a little more, if you are game. :thumbsup:
Only issue I experienced, if the engine has a lot of time and never been disassembled, the head bolts near the exhaust may be seized. If so, they will be hard to get out, may come out with messed up threads. Be very careful not to break them off, or will be looking at a difficult fix or junk block.
I have had this issue on Tecumseh, Briggs, and now 97cc flatheads, so it is a common problem with old engines. When I reassemble, I put a little engine oil on the bolt threads to act as anti-seize, plus makes it easier to assemble and torque.
I am hoping you can get this mod figured out. I think you will be very pleased with the results. I know the engine runs a lot better, just don't know how much it will shorten it's life. Plus, after you get this one done, there is another mod to step it up a little more, if you are game. :thumbsup:
Briggs
Love my 5 hp briggs on my doodle!
Starts right up, runs great,handles heavy riders, good speed , super easy to maintain and has a bazillion hours on it. I had to pull the cord 2 times to start it once ::: just once! Lol
Id keep the briggs on the shelf for later ,,,, or get another piston, rod and ring for under $20 ,,,, skuff the cylinder with some sand paper,,,,, like new!!!
Or put a performance rod on it and let her rip!!! So cheap to get stuff on a briggs and they are stupid easy to work on !
Ive run thru 2 clutches and 3 chains on my 5 hp briggs ! Just keeps singing
Love my 5 hp briggs on my doodle!
Starts right up, runs great,handles heavy riders, good speed , super easy to maintain and has a bazillion hours on it. I had to pull the cord 2 times to start it once ::: just once! Lol
Id keep the briggs on the shelf for later ,,,, or get another piston, rod and ring for under $20 ,,,, skuff the cylinder with some sand paper,,,,, like new!!!
Or put a performance rod on it and let her rip!!! So cheap to get stuff on a briggs and they are stupid easy to work on !
Ive run thru 2 clutches and 3 chains on my 5 hp briggs ! Just keeps singing