Slow DRR 70, why???

[hak231]

This winter I decided to do a freshening-up of my son's DRX70. I just wanted to do a top end rebuild with a little bit of port work. Turns out the bore of the sleeve was mis-aligned, and Hetrick couldn't do a bore on it. So I purchased a cast aluminum cyl and head, along with a piston kit. I also decided to do a little clutch updating. New belt, 4g rollers, and 2K RPM Torsion spring. I was excited for my son to be surprised about the new-found speed and power. To my surprise, the thing seems to have lost what little speed it had. The engine seems to rev fine with no dips or dives in the powerband. The plug looks slightly wet with a dark brown color through-out the RPM range and throttle position. I worked the belt and clutches to make sure they all worked smoothly. It has a stock pipe with a Uni filter on the stock intake pipe. It won't spin the tires coming out of the corners anymore. I clocked the machine at 22 MPH pre teardown, now it only goes 18 MPH. WTF??? Is there something I'm missing. Any Thoughts or "did you remember to..."s. Also there are two "outlets" on the new head where the old one had a bleeder valve. What do I do with these? It looked like they would just leak, so I connected the two together with some PVC tubing. Is that alright? Sorry for all the stupid questions, this thing just has me really frustrated.

[EthansDad]

its clearly simple - the gods hate you. you're going to need a chicken, some bones and a priest...:chinese:


it sounds like you've really gotten into this and know your way around tuning and setup and the value of having pre-post modification performance runs. very smart.

first things first - do you have a tach? you could really use one at this point to fine tune things and bench mark your jetting. it will become very important as you get into clutching.

second, on the head and bleeder valves, not sure what you mean and what type head it is. could be for a water temp sensor or something. if its not part of the intake system, but rather seals up the cooling system, I would not worry about it.


Jetting - sounds like you are good. would be good here to know peak rpms on the stand and peak rpms on the ground to know if your new top end is doing what you expect it to do. not knowing your hop ups, hard to say what you should be getting - but high 11k-high 12k would be a good guess.

to the problem - my money is on clutching. you have lower top speed and you've lost corner exit acceleration. tell us more about the clutching - what variator, belt, clutch type, etc.

going blind on data my guess is your torque spring tension is too high. I'd also bet you are getting some pre-shift or the variator is shifting out before you take off.

Here is what I might try - again this is a ball park, I don;t know your motor or full setup -

stock yamasida variator - put a 1mm shim in between the halves.
3.75 rollers
red malossi spring
782 belt
switch to an adjustable clutch - like stage 6
set stall up higher to 6500-7000 rpms

if you don't have a tach, a handy trick is to run it with the cover off, on the stand. can be a bit dangerous to you and the motor, but works. just don;t hold it wide open. better yet, I made a "peak-a-boo" case that has very big holes on top of both pulleys so I can see what is going on in there.

What to look for on the stand (if you could watch the CVT in action)
1. giving it a bit of gas and slowly going up, at what rpm do the wheels start to move? adj to 7k range
2. at engagement speed (stall, or when the wheels move) has the belt dived in ANY BIT into the rear pulley? if so, that is bad, you've lost 1st gear. shim the variator halves to delay shift
3. now rev it up a bit more say to 3/4 - how does it shift out? does it return (downshift) smoothly?
4. mark the variator face with a sharpie, put the cover back on and run it top speed for a couple of passes. take cover off, look at marks. how high did the belt go? getting it to 7/8 to the top is pretty good for mx. if its only going 1/2 to 3/4 up, need to come up in roller weights and make sure that did not screw up steps 1-3 again.

also, when you say "stock pipe" does it have the DRR 90cc pipe on it, or the 50/70? can tell the 90 pipe as it has an extra section with springs under the motor. your next $$ should go to a mid dollar pipe, or even the stock DRR 90 pipe. that will wake things up quite a bit more.

-EA

[hak231]

Thank you for your quick and detailed response. I guess I forgot to say that money is the secondary object here. I just dumped $400 into this and it is worse than with an engine that needs the top rebuilt. Sad....... That being said, the last thing I can do at this point is dump more dough into it. Might as well get a Raptor 125 if it will cost more money.


I was told by Hertick Racing that I was getting a Stage 6 cast alum. cyl and head,...don't know the series, but it was $220 with cyl, head, piston, rings, and gaskets. The kit came in a non-descript box, so I cant even verify the contents.

The pipe is the original 70cc pipe.

All clutching is stock except for the torsion spring and roller weights. I am not sure of the belt size, I let this up to Rich Hetrick to get me in the ballpark.

I did a pre and post mod run watching the belt and pulleys work (on the stand). I did not notice any variation from stock to mod, but I definately have an untrained eye. But it engages in the meat of the powerband now, whereas before it was too low in the RPMs.


No tach in this toolbox!

[EthansDad]

The stage 6 top end works well and does rip on the DRR 70ccs.

on the pipe - let's get detailed here. I know its what came with it. the DRR 70 came with an option of two different pipes. look under the motor, like 8 inches away from the header. is the pipe in two parts there held together with springs, or is the next section all the way at the silencer?

If you have the single section pipe, even on a budget you really need to find a dual section one. its the 90cc pipe from DRR that will wake that up and bet you can find one on here used cheap.

on the clutching, the on the budget recommendation would be to find a softer, 1500 rpm spring and try it. a 2k spring is quite firm for that motor and is likely not allowing your bike to shift out - that is why you are losing top speed. If all else fails, use an old spring to test the difference.

on getting the stall up, you can use the stock clutch (not stage 6) and change out the small clutch shoe springs to the koso 2k - those are also pretty cheap, but a pain in the arse job to install.

last, get yourself some 1mm shims to space between the variator to delay that shift some. you need to do that when you bring the stall or engagement speed up.

I'm sure this will get you in the ballpark and from there we can help you fine tune the clutch.

on the budget buy list:
DRR 90cc pipe - ~$80 (guess, should be able to get one used in this range)
1500 torque spring - $20
koso 2k clutch shoe springs $10
1mm shims - $5

[hak231]

Dude,you rock!!! Thanks so much for the info. I am totally new to this CVT stuff. I would almost rather split the cases on a King Quad 300, than deal with a CVT. But I guess I'm getting into it.

Pipe- It's a single piece with no seperations. I will look to buy a 90cc stocker in the near future.

I will try to put the stock torsion spring back in over the weekend to test for that shifting problem you speak of. I'm OK with the rollers for now, or should I get some 3.5g just in case, for fine tuning?

I've already had the clutch apart to clean it. Those springs weren't as bad as what I expected as far as removal. Do I need to roughen-up the bell with light sandpaper (150grit)? Also, the shim seperates the two halves of the variator right? Making the belt drop lower in the variator. 1 or 2 shimms?

Again, thanks for all your help.

[EthansDad]

yea, that 50/70 single piece pipe is really rated for 8-9k rpms. the stock 90 pipe will get things more in the mid 10k to maybe 11.5k depending on things. your stock ignition drops off at about 11.5k, so that is a good target for a mid-range setup. if you start scraping against that ignition barrier with the older style CDI, might look at getting a stock 2010 DRR CDI. can again find a take off on the cheap, and that will do 11.5k all day long. the older CDI gets grumpy at 10.5k or so. beyond that in mods, its time to break out the wallet.


on the rollers, its good to have like .5 grams in .25 increments around your target weight for tuning. on that 70cc, 4g is right about at the middle. on lower rpms, you will end up using more weight, and the higher you go on rpms, you use lower weights.

Its a balancing act on the weights. the more you go up, the more shift and top speed you get, however, when you go up, you also start to shift earlier (before the quad starts to move) losing first gear, thus the shims to counter act that effect. can try this trick - take one weight out (run 5 weights of what you have now). how does it run? my guess is it takes off in the first 15 feet like a rocket, then tops out at 10mph or so. what you want is both. you want the first 15feet to be a rocket, THEN shift out to get that top speed up to mid 30s.

and yes, the shims go in between the variator plates like take the front sheave off and put shim between that and the center pin. 1mm is good to start, 2mm might be better try it out. you will find at some point, your front half will not go on anymore correctly if you shim too much. also, keep in mind that 782 belt is .5mm thinner. its like getting an extra shim effect.

on the shoes, I use 600grit and just take the glaze off every once an a while.

[Coley'sdad#8]

I don't know what carb or throttle you have but take off your filter , open the throttle fully and make sure the slide is opening the whole bore of the carb.

[nastynotchback1]

If it will help you i have a used hetricks gen 2 pipe and a new 1500 torsion spring,3 new 2000 shoe springs and a new set of 3.75 rollers.you can get it all for 130.00 shipped.

[Ryki3r]

What is the squish? The stage 6 cylinder need to be checked.

[hak231]

Hey Nasty, I will check back with you in a week or so. Funds are pretty low right now. I just had to get the head gaskets replaced on the car.

[fomospede]

the stage6 sport pro cylinders are a single opening exhaust port

the prorace is dvided on the exhaust port

we have on of both they are excellent quality and make good power for the price point

[nastynotchback1]

Originally posted by hak231
Hey Nasty, I will check back with you in a week or so. Funds are pretty low right now. I just had to get the head gaskets replaced on the car.

Thats fine.It should still be here in a week.

[hak231]

I went through everything again to gain a better perspective of the problem. The cylinder is a Nitro kit, Hetrick told me that I was getting a Stage 6 ProSport. That's irritating, but it will have to do. The Nitro kit suggests to use a performance exaust and increase the main jet a size or two. I did notice some breakup when at 3/4 to full throttle. I will report back when I get the jetting cleared up.

The torsion spring is a white 1000RPM. When I took apart the CVT, I scuffed the sheaves and recleaned. That brought the speed up to 21 mph. I did notice that the belt would move up and down about an eighth of an inch on the variator sheaves while idling. I didn't know what to do to fix this. I would assume that the shim would help slightly.

Nasty, how would you like to handle this sale for the pipe and acc.? PM me when you get a chance.

[nastynotchback1]

Originally posted by hak231
I went through everything again to gain a better perspective of the problem. The cylinder is a Nitro kit, Hetrick told me that I was getting a Stage 6 ProSport. That's irritating, but it will have to do. The Nitro kit suggests to use a performance exaust and increase the main jet a size or two. I did notice some breakup when at 3/4 to full throttle. I will report back when I get the jetting cleared up.

The torsion spring is a white 1000RPM. When I took apart the CVT, I scuffed the sheaves and recleaned. That brought the speed up to 21 mph. I did notice that the belt would move up and down about an eighth of an inch on the variator sheaves while idling. I didn't know what to do to fix this. I would assume that the shim would help slightly.

Nasty, how would you like to handle this sale for the pipe and acc.? PM me when you get a chance.

You can paypal me and i will ship it to you.I don't know about you but if i paid for a stage6 kit then i would be packing the stuff you got back up and shippin it back to them in exchange for a stage 6 kit.

[hak231]

Allright! It's my fault. The jetting was the real culprit. Replaced the pilot with a #40, increased the main to #115, moved the clip on the needle up one slot, and now it is running great. Top speed of 25 MPH. I think the slowness was a combonation of jetting and lack of CVT knowledge by installer (me), kept it held back. I want to thank everyone for taking the time to help with my personal inexperience. I still swear the jetting sounded right, but results show different.