390 carb on 212 hemi predator seems to be working, or is it?

[Kartparter]

So I just put a 390 carb on my predator hemi 212 and I think I may actually have it set right somehow.
I think…
It idles perfectly with the choke off and does not sputter or cut out when you get on it or at any point. And the spark plug looks like the mixture is just right. It’s actually a beast on the low end, I really have to feather the throttle and keep my weight forward when taking off to keep the front wheel on the ground. It’s a little scary.

The thing is. I’m still only getting the same top speed and rpm as I got with the jetted stock carb and cam, about 4200 rpm and 45mph.

Here are the details on the engine and bike:

• CT200UEX (170# rider)
• 212 hemi predator
• 30 series TC, 10&50 sprockets (knockoff brand)
• PVL flywheel timed to 32* (top speed was about the same at 28*)
• Arc rod stock length
• CM cam (top speed was about the same with stock cam)
• 22lb springs
• Homemade carb adapter, no (obstructions and I’m fairly certain it doesn’t leak)
• “390” carb ($15 Amazon one)
• Main jet drilled out to about 100 size (.040”) Maybe a little bigger. (It did ok with stock jet)
• Stock Coleman air filter bolted straight to the carb inlet (it did not like running without a filter at all, would not idle and always had to keep the choke mostly closed)
• Pilot screw turned out 5 or 6 turns (that much to get it to idle and stop sputtering)
• Homemade exhaust, 3/4” pipe about 14” long, set up to be able to have two of the cheap 3/4” mufflers or just wide open (top speed has been about the same in both configurations
• Anything I haven’t listed is stock/unmodified

So, what could be stopping me from getting any more RPMs that just over 4000? Do I just need to lose weight? Lol

 

[BrownStainRacing]

So I just put a 390 carb on my hemi 212 and I think I may actually have it set right somehow.
I think…
It idles perfectly with the choke off and does not sputter or cut out when you get on it or at any point. And the spark plug looks like the mixture is just right. It’s actually a beast on the low end, I really have to feather the throttle and keep my weight forward when taking off to keep the front wheel on the ground. It’s a little scary.

The thing is. I’m still only getting the same top speed and rpm as I got with the jetted stock carb and cam, about 4200 rpm and 45mph.

Here are the details on the engine and bike:

• CT200UEX (170# rider)
• 212 hemi
• 30 series TC, 10&50 sprockets
• PVL flywheel timed to 32* (top speed was about the same at 28*)
• Arc rod stock length
• CM cam (top speed was about the same with stock cam)
• 22lb springs
• Homemade carb adapter, no (obstructions and I’m fairly certain it doesn’t leak)
• 390 jet drilled out to about 100 size (.040”) Maybe a little bigger
• Stock Coleman air filter bolted straight to the carb inlet (it did not like running without a filter at all, would not idle and always had to keep the choke mostly closed)
• Pilot screw turned out 5 or 6 turns (that much to get it to idle and stop sputtering)
• Homemade exhaust, 3/4” pipe about 14” long, set up to be able to have two of the cheap 3/4” mufflers or just wide open (top speed has been about the same in both configurations)

So, what could be stopping me from getting any more RPMs that just over 4000? Do I just need to lose weight? Lol

Suck up some helium before next ride, lol.
That cm cam loves compression rario, 10.3:1 minimum. My son's ducar 212 (non hemi head) with governor, .615" SA carb, stock airbox and filter has a cm in it, 10.1:1. It's a lil low, but he only weights 165#. It hits 5400rpm with me, at 200#, with 20" tire, 4.54:1 gear, 7" driven, aluminum flyweights, 3000 rpm springs in stock driver.
The cm cam closes the intake valve a lil too late for my liking, so to help it out, you need to up the compression ratio, and add more stall to the driver to get up on power, before it starts pulling weight. It really wakes up around 4500 with 10.5:1, and easily pulls passed 6500, if the rest of the build is up to snuff.
What's you weight??
Tire height??

 

[BrownStainRacing]

I see you weight now.

 

[Kartparter]

19” tire.
Everything I’ve listed are the things I’ve changed, everything else would be stock for the 212 or CT200UEX.

I’ll have to look into upping the compression. I didn’t do anything to the piston and head on this one, I’m not even sure how thick the head gasket is.
I am in no was shape or form an experienced engine builder, I’m mostly experimenting and learning. I just got the CM cam because it was cheap and from what I can remember reading seemed like a it would be a good one for what I was doing trying to do.

I do have a built non-hemi with flat top piston (-.020 or whatever, so still stock deck height), .010 gasket, and CS cam that I’m using for a totally different application right now. Do you think that cam/compression ratio combo would do better with this carb? I may have to stick it on the bike.

 

[BrownStainRacing]

The 6" driven has overdrive when it gets to the high end (belt drops all the way down on driven) its .9:1. So that leaves you with a final drive of 4.5:1 gearing. Even though you have 10/50 sprockets (5:1) that overdrive is killing power on the high side.
I don't care for the 6"drivens, myself, but helped others get em tuned to their set up.
1st thing is get 3000+ rpm springs in the driver.
Put a 9 tooth sprocket on the jackshaft, that'll get your 5:1 gear back, and make your power to weight ratio alot better on the high side.
I assume you have the stock red driven spring, in the middle hole????
If so, move it to the most resistant hole. If holes are at 12 o'clock, the most resistant hole is furthest on the left. This will let it hold a tad bit longer on the low side, allowing the engine to build rpm, before shifting starts happening. That cm cam pulls hard with 3000+ rpm stall in the driver. It can't make power until it's up on rpm.

 

[BrownStainRacing]

19” tire.
Everything I’ve listed are the things I’ve changed, everything else would be stock for the 212 or CT200UEX.

I’ll have to look into upping the compression. I didn’t do anything to the piston and head on this one, I’m not even sure how thick the head gasket is.
I am in no was shape or form an experienced engine builder, I’m mostly experimenting and learning. I just got the CM cam because it was cheap and from what I can remember reading seemed like a it would be a good one for what I was doing trying to do.

I do have a built non-hemi with flat top piston (-.020 or whatever, so still stock deck height), .010 gasket, and CS cam that I’m using for a totally different application right now. Do you think that cam/compression ratio combo would do better with this carb? I may have to stick it on the bike.

I like to pick cams that allow the DYNAMIC compression ratio to fall 7.8:1-8.1:1. I've found, any lower and the engine is a turd, and any more then I have to run 89+octane. It's a lil conservative, but I'd rather be safe then sorry. And I'm not pulling engines down to replace burnt up piston and rings. It jus works for me. I pick the lift of the cam to match to flow of the head. No sense in putting a .350" lift cam, when the head starts slowing down at .250".
Sounds like you need to pull the head off and measure compression ratio. There's plenty of good people here to help you out.
I'm not a hemi head guy, I swap em out for 18cc or 20cc non hemi heads.

 

[Kartparter]

The 6" driven has overdrive when it gets to the high end (belt drops all the way down on driven) its .9:1. So that leaves you with a final drive of 4.5:1 gearing. Even though you have 10/50 sprockets (5:1) that overdrive is killing power on the high side.
I don't care for the 6"drivens, myself, but helped others get em tuned to their set up.
1st thing is get 3000+ rpm springs in the driver.
Put a 9 tooth sprocket on the jackshaft, that'll get your 5:1 gear back, and make your power to weight ratio alot better on the high side.
I assume you have the stock red driven spring, in the middle hole????
If so, move it to the most resistant hole. If holes are at 12 o'clock, the most resistant hole is furthest on the left. This will let it hold a tad bit longer on the low side, allowing the engine to build rpm, before shifting starts happening. That cm cam pulls hard with 3000+ rpm stall in the driver. It can't make power until it's up on rpm.

I’ll have to see about getting different driver springs and a different sprocket.

I did not realize that the drivers could be adjusted. Are the knockoffs adjustable too? This is just a cheap one that I got from OldMiniBikes on Black Friday for $60 or so.

 

[Kartparter]

I like to pick cams that allow the DYNAMIC compression ratio to fall 7.8:1-8.1:1. I've found, any lower and the engine is a turd, and any more then I have to run 89+octane. It's a lil conservative, but I'd rather be safe then sorry. And I'm not pulling engines down to replace burnt up piston and rings. It jus works for me. I pick the lift of the cam to match to flow of the head. No sense in putting a .350" lift cam, when the head starts slowing down at .250".
Sounds like you need to pull the head off and measure compression ratio. There's plenty of good people here to help you out.
I'm not a hemi head guy, I swap em out for 18cc or 20cc non hemi heads.

I’ll be honest, unfortunately when looking at cam specs the numbers mean nothing to me. I just don’t know enough about everything yet, but I’ve been trying to learn. How the hell do people learn all of this stuff without being around it their whole lives?

 

[BrownStainRacing]

I’ll have to see about getting different driver springs and a different sprocket.

I did not realize that the drivers could be adjusted. Are the knockoffs adjustable too? This is just a cheap one that I got from OldMiniBikes on Black Friday for $60 or so.

Yea, that's all I use. The stock flyweights are heavy, but use em until you get some experience tuning on the tav.
As far as the cs and cm cams, I don't use dyno cams for my builds anymore. I'm not knocking em down, it's jus they have their place. They are designed for racing go carts, that hav a rolling start like 25+ mph and 4500+ rpm, and that's perfectly fine. I jus rather spend more $ for a custom cam with faster ramps that match what the engine is being built for.
The cs cam will close the intake valve sooner then the cm, but without knowing the CR, I'd have to say neither cam is gonna get you up on rpm.
Which hemi 212 are you working on??? the ducars/tillys has a dished piston, 20cc combustion chamber, and piston to deck around .010". The predator 212 hemi has a flat top piston, 22cc combustion chamber, and piston sits around .020" down in the hole. They all come out to around 8.3:1 CR, outta the box. A head gasket change will get em up to 9.0:1, but need to figure out which 1 you have 1st.
What engine has the non hemi head and flat top piston????
Might be able to swap some parts around to make em both stump pullers.

 

[BrownStainRacing]

I’ll be honest, unfortunately when looking at cam specs the numbers mean nothing to me. I just don’t know enough about everything yet, but I’ve been trying to learn. How the hell do people learn all of this stuff without being around it their whole lives?

Lol, being around it their whole lives.

 

[Kartparter]

Yea, that's all I use. The stock flyweights are heavy, but use em until you get some experience tuning on the tav.
As far as the cs and cm cams, I don't use dyno cams for my builds anymore. I'm not knocking em down, it's jus they have their place. They are designed for racing go carts, that hav a rolling start like 25+ mph and 4500+ rpm, and that's perfectly fine. I jus rather spend more $ for a custom cam with faster ramps that match what the engine is being built for.
The cs cam will close the intake valve sooner then the cm, but without knowing the CR, I'd have to say neither cam is gonna get you up on rpm.
Which hemi 212 are you working on??? the ducars/tillys has a dished piston, 20cc combustion chamber, and piston to deck around .010". The predator 212 hemi has a flat top piston, 22cc combustion chamber, and piston sits around .020" down in the hole. They all come out to around 8.3:1 CR, outta the box. A head gasket change will get em up to 9.0:1, but need to figure out which 1 you have 1st.
What engine has the non hemi head and flat top piston????
Might be able to swap some parts around to make em both stump pullers.

This is a predator engine. The non hemi with the cs cam is also predator. The flat top piston in it came from OldMiniBikes.
like I said in another post, I know nothing about cams. I got the CS on recommendation by Eric for what I was doing with the engine (sawmill). I’m trying to learn it all but there is a steep learning curve to get to you all’s level.

 

[BrownStainRacing]

This is a predator engine. The non hemi with the cs cam is also predator. The flat top piston in it came from OldMiniBikes.
like I said in another post, I know nothing about cams. I got the CS on recommendation by Eric for what I was doing with the engine (sawmill). I’m trying to learn it all but there is a steep learning curve to get to you all’s level.

OK, both are predators. The hemi head, I know is 22cc. I've measured a bunch of em. If it's the original predator non hemi head, it'll have automotive style keepers/locks and retainers, 5mm valve stems, outta the box. I think I have 1 in the shop, can't remember how many cc's it is. Maybe somebody will chime in and save me a trip, lol. But if it is smaller then 22cc, that's the head I would use to up the CR. Jus looking at the specs of the cs, I'd say it'll need a minimum of 9.8:1 CR to work good. it's hard to say, i don't know how lazy, slow the ramps are. Never used 1. I don't like dual pattern camshafts.

 

[BrownStainRacing]

This is a predator engine. The non hemi with the cs cam is also predator. The flat top piston in it came from OldMiniBikes.
like I said in another post, I know nothing about cams. I got the CS on recommendation by Eric for what I was doing with the engine (sawmill). I’m trying to learn it all but there is a steep learning curve to get to you all’s level.

Jus so you know, those cams will not interchange. The cam journals are different size. The cs is stuck to the non hemi block, and the cm is stuck to the hemi block.
The flywheels are different too. Taper is different and flywheels don't interchange. What kinda flywheel do you have on the non hemi????

 

[Kartparter]

Non hemi has the short fin arc flywheel.

My intention when I started playing with these engines was to be able try parts between each one and just experiment and see what works and what I could learn. Unfortunately I didn’t realize until later that cams weren’t interchangeable between them, so testing out all kinds of different cams became way more expensive lol
I do also have two hisun 196 clones to also play with though, as well as another hemi and another non hemi. (6 engines isn’t too many, is it? Lmao)

 

[Kartparter]

So as far as the carb, does it sound like it could actually be working? Or are all of these other things likely holding it back more and we won’t know until they’re corrected?

 

[BrownStainRacing]

Non hemi has the short fin arc flywheel.

My intention when I started playing with these engines was to be able try parts between each one and just experiment and see what works and what I could learn. Unfortunately I didn’t realize until later that cams weren’t interchangeable between them, so testing out all kinds of different cams became way more expensive lol
I do also have two hisun 196 clones to also play with though, as well as another hemi and another non hemi. (6 engines isn’t too many, is it? Lmao)

No way, thats not too many, lol. Keep at it, you'll learn more about these lil "turd motors". I like the clone 196's. I bet if you pull the heads off, at least 1 will have a 18cc 25/24 valves, cha ching......there's your big compression bump you need to run that cm with that hemi block. Use the clone lifters and push rods. Don't even think about those small valves, you won't even know it. My son's ducar 212 has a 14cc head, a lil port work, with 25/24 valves, it's a monster coming outta the hole, and it's a governed "turd motor", lol.
That 390 carb, I have no idea. I run a .670" bored SA carb on my 223cc, and it's more then plenty.

 

[Kartparter]

how did I not know that about the heads?! I swear I’ve spent hours upon hours reading and researching. I will say that one of the first things I learned was that there is waaay more to all of this that I ever imagined there could be, and I’m still getting my mind blown by how much there is to it all.

I’ve got the driven pulley apart now adjusting the spring. I have a 12t & 70t sprocket set that I may try out, the ratio will be just a little more than the 9-50 combo. They’re #35 chain though but I have plenty of chain.
I’m tempted to tear into one of these 196s and do a head swap tonight if I can find the time. I may play hookie from work tomorrow and play with engines haha

 

[BrownStainRacing]

how did I not know that about the heads?! I swear I’ve spent hours upon hours reading and researching. I will say that one of the first things I learned was that there is waaay more to all of this that I ever imagined there could be, and I’m still getting my mind blown by how much there is to it all.

I’ve got the driven pulley apart now adjusting the spring. I have a 12t & 70t sprocket set that I may try out, the ratio will be just a little more than the 9-50 combo. They’re #35 chain though but I have plenty of chain.
I’m tempted to tear into one of these 196s and do a head swap tonight if I can find the time. I may play hookie from work tomorrow and play with engines haha

Roflmao!!!!! You wouldn't be the 1st to lay outta work for this hobby. That's so funny

Yea, that's a better ratio, for your weight, imo.
Make sure you use the lifters and pushrods outta the clone, don't gett em mixed up. And lap the valves for a good tight seal.
I'm sure guys with more experience with 390 carbs will chime in. And Ole, should be around for more head info.

 

[BrownStainRacing]

how did I not know that about the heads?! I swear I’ve spent hours upon hours reading and researching. I will say that one of the first things I learned was that there is waaay more to all of this that I ever imagined there could be, and I’m still getting my mind blown by how much there is to it all.

I’ve got the driven pulley apart now adjusting the spring. I have a 12t & 70t sprocket set that I may try out, the ratio will be just a little more than the 9-50 combo. They’re #35 chain though but I have plenty of chain.
I’m tempted to tear into one of these 196s and do a head swap tonight if I can find the time. I may play hookie from work tomorrow and play with engines haha

Some 196's came with 20cc heads, some with 18cc heads. You would be better off with the 18cc head.

 

[BrownStainRacing]

https://www.omnicalculator.com/everyday-life/compression-ratio#faq
I use this cr calculator. Play with some numbers, you'll figure it out.