Need more RPM's

[L79corvette]

I need help on getting more rpm's. How ????
My setup is:
Predator 212cc
Billet Flywheel
Billet rod
Governor removed
14cc mild ported head
26 lb springs
DYNO cam .265 lift
stock carb with GX160 E-tube, #90 main jet
Mini bike with 16" rear tire
Maxi torque 10 teeth sprocket
Wheel spocket 41 teeth
I'm limited to 4950rpm. Why so low?

 

[Dragbikemini]

Stock head? Bigger carb. Stiffer springs? Lighter valve parts?

 

[L79corvette]

Stock head? Bigger carb. Stiffer springs? Lighter valve parts?

I have a 14cc aftermarket head with lite porting. Springs are 26 lbs.

I thinking my stock size carb is holding me back. WOULD a bigger carb like a GX390 give me more rpm's?????

 

[Camjamsdad]

I have a 14cc aftermarket head with lite porting. Springs are 26 lbs.

I thinking my stock size carb is holding me back. WOULD a bigger carb like a GX390 give me more rpm's?????

No.

With no govenor its your gear ratio that limits you.

 

[Camjamsdad]

I have a 14cc aftermarket head with lite porting. Springs are 26 lbs.

I thinking my stock size carb is holding me back. WOULD a bigger carb like a GX390 give me more rpm's?????

No.

With no govenor its your gear ratio that limits you. Or the throttle stop screw. Or valve float, but with your springs that's not the issue

 

[L79corvette]

No.

With no govenor its your gear ratio that limits you. Or the throttle stop screw. Or valve float, but with your springs that's not the issue

It must be the gearing. I have no throttle stop screw and 26 lbs springs. I just don't understand how a bike with the same setup but 43 teeth rear sprocket, stock cam, 18 lbs springs and running gas will out run mine.

 

[jprice]

too much spring pressure ?
I don't know much about that cam , but from what I seen it says 18 on the springs ,bored out carb , it sounds like the parts are fighting each other ....
is your flywheel advanced?
since you already have the cam, try going with 18 pounds springs ,advancing the timing 8 degrees ,see how it runs, if you need to bore the carb its pretty easy to do ,
your buddy will probably still pull out on you because the stock cam is more low end , but you should be able to run him down!
you can play with the rear sprocket to help with the bottom end also ,
.try them 18 pound springs it should solve the rpm issues , let us know how ya make out for sure !
love grudge racing Hahaha

 

[Camjamsdad]

I plugged your info in a ratio calculator. It gives a top speed of 55mph. How fast are you all running where your friend outruns a 55mph bike?

 

[L79corvette]

too much spring pressure ?
I don't know much about that cam , but from what I seen it says 18 on the springs ,bored out carb , it sounds like the parts are fighting each other ....
is your flywheel advanced?
since you already have the cam, try going with 18 pounds springs ,advancing the timing 8 degrees ,see how it runs, if you need to bore the carb its pretty easy to do ,
your buddy will probably still pull out on you because the stock cam is more low end , but you should be able to run him down!
you can play with the rear sprocket to help with the bottom end also ,
.try them 18 pound springs it should solve the rpm issues , let us know how ya make out for sure !
love grudge racing Hahaha

My timing is 33 degrees by degree wheel. I'll try 18 lbs springs this weekend. I wish I would have keeped the original cam. I made a trophy out of it for the race we had in memphis.

 

[L79corvette]

I plugged your info in a ratio calculator. It gives a top speed of 55mph. How fast are you all running where your friend outruns a 55mph bike?

My bike does 57mph by GPS. My buddies does 60.5mph. When I went to alcohol, I could pull him out the hole but he would fly by me about the 1/8 mile.

 

[davidlamb78]

I have a 196cc greyhound from HF with similar parts. I didn't do any porting to the head, but I am running the same head. I have the flywheel and a .20 over rod w/ a flattop piston. My carb is the "cheater carb" from Dover power sports. I wouldn't consider it to be a big carb. I'm getting around 7500 RPM when I open it up (according to my tach). I don't have it on my mini. I have it on a kart. I don't need that much on a mini. Maybe the lighter springs will do the trick? I will be buying the Black Mamba Jr. cam from Isky (along with all new valve train) next, and I'll probably call it done (at least, that's what I'm telling my wife).

 

[Dragbikemini]

No 18lbs springs! They will bind with your cam! Did you say 41 tooth rear? should do 80 when you get rpms up.. Air filter good quality? If your running air filter take it off. Some off the knock off K&N filters are garbage! 390 carb is good but throttle hookup is tough. Mikuni is good for easy throttle hook up just need to get right cable. Possible your not WOT? Something hanging up? Wait! Your running gas right?

 

[Dragbikemini]

Your running gas?

 

[Dragbikemini]

Dude your running alky? From what I see I'm no expert on alky. Your way too lean! Need big volume for alky. You want to run alky on a stock appearing carb try NRRacing for a blueprinted carb. Yup you said you changed over to alky in your post. Pretty important part of this puzzle! Your can't just pour in alky. Like I said I'm no expert but volume should increase by a least 25%. You need a blueprinted carb and high compression and big valves and and and... No try a blueprinted carb and see what happens. Or jet the crap out if your carb.

 

[trinik7597]

Your can't just pour in alky. Like I said I'm no expert but volume should increase by a least 25%.

found out recently when i changed my animal back gas that it takes 21/4 times the amount of meth on average :thumbsup:

 

[Camjamsdad]

I missed the alky part. I was hung up up on the 10t 41t. The ratio calculator says at his rpm he's doing 55 and his friend pulls away from him. How fast is too fast on these things?

 

[SnakePliscan]

26 lbs of revs and a side of mph

i would'nt pull the 26lbs springs, there stiff but not radical plus your gona need them when you finally get this thing to turn 7500 rpm like it's suppose to.

A 16" tire thats tall in the mini bike world. Do you race a 1/8 mile? and how far from the traps are the people who take home the trohpys when they hit there top speed. there gona be tached out from there to the finsh line and thats when you want to be turning 7500 rpm

Flat tappet cams need hi zinc concentrate oil to live, especially with high spring pressure and rpm. Lukus makes a hi zinc hot rod oil you can use.

 

[jprice]

your running alky with a stock clone carb ? and your jet is a 90? that doesn't sound right at all the main jet should be up in the 130 range or higher , I did it before but I forget what I ended up with,
dump the alky out and run gas your carb seems to be set up for that anyways ..
from what I seen on that cam they are saying 18 pound springs ,where did you get the cam?
try running it on gas before you do anything see if you get your rpm back

 

[L79corvette]

Dude your running alky? From what I see I'm no expert on alky. Your way too lean! Need big volume for alky. You want to run alky on a stock appearing carb try NRRacing for a blueprinted carb. Yup you said you changed over to alky in your post. Pretty important part of this puzzle! Your can't just pour in alky. Like I said I'm no expert but volume should increase by a least 25%. You need a blueprinted carb and high compression and big valves and and and... No try a blueprinted carb and see what happens. Or jet the crap out if your carb.

Yes for alky but I have 2 carbs. 1 for gas and 1 for alky. I convert back to gas to cruize. The alky is modified by drilling etube, main jet and pilot jet for alky. it runs great but it will not give me RPM's no higher than 4950-5000.. Air clean off has zero effect. Gas carb only 4800 rpm.

 

[L79corvette]

Dude your running alky? From what I see I'm no expert on alky. Your way too lean! Need big volume for alky. You want to run alky on a stock appearing carb try NRRacing for a blueprinted carb. Yup you said you changed over to alky in your post. Pretty important part of this puzzle! Your can't just pour in alky. Like I said I'm no expert but volume should increase by a least 25%. You need a blueprinted carb and high compression and big valves and and and... No try a blueprinted carb and see what happens. Or jet the crap out if your carb.

On my alky carb, I increased jet by 50%. Compression is 10.8:1.