So I am new to rctech and new to nitro. I bought the truggy back in september as a roller and have been slowly piecing it together as I got money for parts. So now I have it fully assembled to losi specs and reading here on the forum on how to set up certain parts, I decided to take it out on a day when it finally got above 50 degrees. I am using a used ninja mr 21 with a p3 plug and the stock losi clutch set up. I preheated the motor and started it on the bumpbox and it fired right up. While it sits on the bumpbox the wheels turn good and fast but when i get it on the ground it won't break 10 mph and sounds like its revving good but there is no speed. At first I thought it might have been a dif problem so i removed the motor and rolled it around and it rolled smooth with no sounds of grinding or whining. But when i put the motor back in its real jerky and makes a little bit of a whine. I set the gear mesh using the paper method, so I know its not too tight. My current clutch setup is 4 aluminum shoes with 2 silver springs and 2 gold springs. Any tips/help would greatly be appreciated. I live in lancaster and was planning on running at XRC a little this year if any local people were willing to show me some pointers at the track since I am new to the racing scene. Thanks.

I would run 2 green-2 gold springs in the clutch, the best set up ive found. I would look at your bearings in the clutch. Or locked up wheel bearings? Sounds like the ol-ninja doesent have enough a$$ to open them super tight silver clutch springs too me. Just a suggestion.

Are you sure the flywheel is tight on the motor?? Check the breaks make sure they are free.

yea i wrapped my channel locks with some cloth and really tightened down the flywheel. I am going to consider trying the green/silver spring clutch setup, but when i tore down the clutch i found some loctite got on my bearing thats on the outer part of the bell so im gonna get new bearings all around and try again.

Hi, donno if you sorted yourself out yet with the ninja but here is my story
I also bought an used MR21 in perfect condition a while ago for my eight t 2 and had the same as you're describing. Off the ground the engine would rev like crazy and immediately....but on the ground engine was starting out abnormally slowly and after a while picked speed and would rev high and move the truggy like hell....

What was the problem? Well after opening it up and after some research I found out the following.
1. the guy (ebay seller) has put inside an on road piston sleeve in a buggy engine.
2. The buggy engine (off road) is a simple or better stated, normal 5port racing engine while the on road has 8ports plus 3 exhaust (or 1 exhaust and 2 guide ports).
3. the on road piston is a bit larger than the off road.
4. consequently the on road sleeve thinner than the off road
5. and last the turbo button heads follow a same pattern...on road larger diameter, off road smaller. The buttons dont fit the different sleeves.
6. edit the piston pins dont fit either between the two.

My point is, that with the right combination you can be easily fooled as the manufacturer burned to the ground and parts are scarce or not available. So people just decide to put the on road stuff on that is easier to find available and sell.

Finally, let me tell you that I payed dearly for all this, to understand the problem first and then solve it; as I also probably have the last piece of sleeve and piston for the ninja MR21 B01 in the world! (still new by the way, unused and oiled in the plastic bag. Ninja box is an ashtray now) Nothing to do with engine tuning clutches or any of the standard solutions to acceleration and power.

Have a look at the piston sleeve you're wearing and please confirm that this is the case or not.

Hope this was helpful and if anybody would like pictures of the two let me know.

The MR .21 Ninja needs different collet on the Losi. The collet that comes with the ninja does not really fit the Losi flywheels.

losi flywheels have to use the losi collet or it will slip and not stay tight. you can use other clutch flywheel setups but u have to have losi's other motor mounts that u can flip around to move closer to the spur gear. king headz has the best on the market for this with the quick change and slotted for doing this better than losi does...

Please no stupid replys on this one. The guy is trying to get his truck running and possibly race. We need to start from the beginning.

First things First.
You said you have been peicing it together when you get money.
Is This the first time you have run the truck?
Did you break in the motor?
If it's broke in, Is it tuned correctly or close. Thats a big one and not a lot of people new to the hobby know how to do it correctly.
You said it sounds like its reving good so I would go to the clutch next.
Silver and gold is good and so is gold/green with all aluminum shoes. The traction level of the surface you run on wil dictate which shoes will be best.
If the clutch and flywheel are good and tight with the correct hardware, next is to check the diffs and drive shafts. A loose set screw on the u-joint could do some wierd stuff and the engine will rev fine but the truck wont go anywhere.
Have a friend hold the front wheels and you spin the rears. your center diff and clutch bell should spin but the front shaft wont. then check the front the same way. If the center shafts are spinning but the wheels are not ( or the wheels spin and the shaft doesnt), you have a loose set screw or uncoupled center drive shaft.
Let us know if you find out whats wrong and also answers to all the questions.

set-screws on the center shafts...?

You need to pull the engine and check the clutch, maybe shoes are on backwards...............

Its either the clutch or collet........

Hope this is NOT stupid............ I say just rebuild the whole thing. Its what I would do.

The set screws that secure the center shafts to the front/rear pinion. It's where the shaft ends at the diff cases. If the rubber boots are on, you may need to pull them back a bit to see. Make sure the screws are are seated on the flat part of the pinion shaft. it will keep them in place.. And dont forget a drop of blue threadlock to keep them from comming loose.

Any news on this?
Have you sorted yourself out?

I'm very curious on what was your problem in the end.

i was reading this forum and was going to suggest the same thing. i found out the hard way with this when i stripped my rear ring and pinion gears because i was running too much rear brake! and a similar problem as you are talking about happened over and over again, and it was the set screw on the rear cvd coupler coming loose and the hole thing was spinning on the pinion, therefore it was only front wheel drive and was revving like mad!...so check all that and make sure you dont run too much rear brake or you will tear the guts out of your rear diff! let us know how you go!