Built Predator 212 - WOT RPM expectations under load?

#1
Hi all, I just built a Predator 212 and am now trying to fine tune it. Idles great, very snappy off idle and mid range, but at WOT it gets to around 4,200 RPM pretty quickly but then hits a wall. When it's on the stand it will hit 6-7K.

My main question is around expectations...should I be able to reach 6K+ RPM under load?

Here's the specs:
- Predator 212 Hemi w/ governor & oil sensor removed (stock piston & rings)
- Billet connecting rod & flywheel
- Mod 2 cam
- 22lb springs
- Mikuni 22mm carb (Japan version)
- 140 main jet
- Needle is 1 notch off the lowest option
- Connected to a TAV2 / Comet torque convertor

I did a WOT run then shut it down to see what the plug looked like and she's still clean as a whistle. Probably too clean (although the whole setup has barely 30 mins on it).

I suspect I need to jet it up quite a bit but wanted to get some input from the more experienced folks before opening the wallet up further.
 

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#2
Hi all, I just built a Predator 212 and am now trying to fine tune it. Idles great, very snappy off idle and mid range, but at WOT it gets to around 4,200 RPM pretty quickly but then hits a wall. When it's on the stand it will hit 6-7K.

My main question is around expectations...should I be able to reach 6K+ RPM under load?

Here's the specs:
- Predator 212 Hemi w/ governor & oil sensor removed (stock piston & rings)
- Billet connecting rod & flywheel
- Mod 2 cam
- 22lb springs
- Mikuni 22mm carb (Japan version)
- 140 main jet
- Needle is 1 notch off the lowest option
- Connected to a TAV2 / Comet torque convertor

I did a WOT run then shut it down to see what the plug looked like and she's still clean as a whistle. Probably too clean (although the whole setup has barely 30 mins on it).

I suspect I need to jet it up quite a bit but wanted to get some input from the more experienced folks before opening the wallet up further.
Your problem lies completely with the TAV2. You need to change weights and garter springs in the torque convertor to "program" it to wait to shift until higher rpms. You'll need these:

https://www.OldMiniBikes.com/-2-genuine-comet-aluminum-weights.html

https://www.OldMiniBikes.com/-6a-garter-spring-set-of-2.html

For the garter springs, get the white ones. This will bring your engagement and shifting rpms up to match your MOD2 cam.
 
#6
I may have missed it but maybe the gear ratio could be optimized?
Haven't looked into that yet, in fact I'm not even sure how many teeth I'm running now that I think about it (other than stock, whatever that is).

I managed 47.8 mph on the GPS with it running as it is, and the low end is good but not so crazy that it's pulling the wheel up uncontrollably, so I definitely don't want to gear it down.
 
#7
Massacre has it right. Most do not understand tav 30 final drive ratio is an overdrive. You need to have at least a 6 to 1 ratio and if rear tire diameter is on the large side possibly more. Also 140 main seems large for a 22mm carb, is it possible you have a air leak. What are you using for a manifold?
 
#9
Massacre has it right. Most do not understand tav 30 final drive ratio is an overdrive. You need to have at least a 6 to 1 ratio and if rear tire diameter is on the large side possibly more. Also 140 main seems large for a 22mm carb, is it possible you have a air leak. What are you using for a manifold?
If you want to drive the TAV like a glorified clutch, then yes, gear down the final drive ratio.

I have two problems with that though.
1: When it gets into its highest overdrive ratio, the engine revs into its powerband and then you're stuck driving that speed just like if you ran a clutch anyway.
2: When it starts to rev above its normal shifting rpm when its in its highest ratio, the belt starts to eat your power anyway. This is because the driven pulley is open as far as it can, but the driver keeps adding more and more tension as the engine speeds up. Eventually, especially because of the shallow belt angle of the 30 series, the friction of the belt getting jammed in and out of the two pulleys eats power, heats up the drive, and glazes the belt.

The solution on any other CVT, such as a GY6, is to change weights, springs, etc... to tune the rpm the drive shifts at. This maintains the shifting aspect of the CVT that makes it worth anything in the first place. With a tuned CVT, you can run the rpms you want at 10mph AND at 40mph with the same exact setup (an exaggeration with a TAV2 but you get what I mean). With a clutch, or a geared-down stock TAV, you will only hit your target rpm at one specific speed.

Wouldn't you want to have your engine making its maximum HP at a wide range of speeds or just one? Why do cars have transmissions?
 
#10
For me just one they are all dragbikes, but for those I use either salsbury 330 or comet 340 but they still can cruse nicely around the neighborhood without running at 8000 rpm. This one is geared 8 to 1 I do understand what you are saying and agree but if you have been reading the very many posts on this you know it typically starts with “ I put a tav 30 on and now it’s slower” then someone will say put on a bigger front sprocket or smaller rear sprocket. That is wrong they are loading down the motor. By the way unless your rear tire is big like mine 6 to 1 front to rear sprocket is a good starting point without changing anything. With a mikuni that causes the engine to rev high with the enrichment on I will go to a stronger driver garter spring so the tav does not engage on startup.
 

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noseoil

Active Member
#13
At 2600' & down to 1600' I was running a 130 jet in the genuine Mikuni (VM22-133), with the new altitude of 6500' here in Raton, it's running the 110 main jet and seems to do ok. I still need to do a real high speed run, but for now it's pulling well & revs fast at WOT. Need to pull to 8000 rpm to see a plug test for heat (clutch, not TAV).
 

delray

Well-Known Member
#15
definitely need a 3000 stall springs and the gearing to make that engine wind-up.
I see you said you have a 140 jet? that seems way to big? when you get the gearing setup correct I would install a 120-121 jet and go from there.
also you have a 22 pound spring on a stock mod2 cam. you really don't need that much spring. the good thing is you might want to try some 1.3 ratio rockers. that will make the engine pull strong up to 7000 rpm's if everything is dial in right.
 
#16
I agree w/ everyone the jetting. In fact a buddy of mine built his 212 almost identical to mine (slightly diff cam), and ended up at 120 for a main jet as well, so looks like I need to pick one up.

As for springs, I did start with the 18# springs that came with the Mod 2 kit, but then my buddy gave me a set of 22# so I threw those on. I take it more isn't always better?
 
#17
Received and installed the 146.8 gram weights in the driven pulley today. Also picked up a set of white garter springs.

If the rain ever stops I'll try it first with the stock (blue) springs. That should set me at 3,300 RPM for engagement (stock was 2,200). I can jump to 4,000 RPM's with the white springs as a future test.
 

delray

Well-Known Member
#18
force, I ran a 196cc greyhound in the pass with a mod2 . engine only had 25/24 valves with just porting in the bowls into the runners little. ss narrow stem valves,different piston,milled head. cc out to 11.5 compression and that too only ran a 120 jet. it seem to pull good up to 7000+ with 1.3 ratio rockers,billet rod,flywheel. I only use it for one drag race and one short summer on a fox bike. I now have been playing around with ohh Tecumseh's and last year motor had a 22mm with 142.5 jet and turn 8200 rpm's....fun
well my little greyhound is coming out of retirement and going on a rupp for a small circle track race. also have to change the suspension and rear tire...etc make this little guy turn left.....:scooter:
it's no top fuel drag motor,but I aways like the way it ran. just a good strong motor....




 
#19
Anyone with a similar setup know where you ended up for a pilot jet size?

My Mikuni VM22/210 came with a 30 installed and 17.5 in a bag. With the 30 if I'm only 1 turn out, it picks up RPM's with 1/4 to 1/2 turn in, so IF I understand this right I could use a bigger jet, just not sure how far to jump.
 

delray

Well-Known Member
#20
I believe I am running a 12.5 or 15 pilot with a 120 jet. if that helps little? been couples years when I first put that motor together and today I didn't even touch the carb. just bolted it back on with a new intake and fired it up.
 
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