lots of threads over the years of people trying to get more power from the ds90s. I recently looked at all the 90s and the ds90x was top on my list but the lack of power is why i went with the kymco 90. the kymco 90 has plenty of power for kids but just like any of the 90's its narrow and unstable. I'm in the process now of installing the dimond j + 6 widning kit, looks like a tough little kit. my first thought was just to add the ds 90x front end but after pricing it was to much $. how did you do you extended the front arms? and how much travel do the shox you bought have? interested how the rest of you build goes, so ill be following.

 

I have a KFX 90 for my daughter which is the same as the kymco 90, great machine.

To extend the a-arm I built a jig on my welding table. Do this at your own risk!!

-I flipped the a-arm upside down on the table so it sat on the shock mount and two bushings
-I used angle iron to build a jig for repositioning the bushings 3" away and stay parallel.
-I tack welded each side of the shock mount to the table.
-I tack welded a piece of flat bar from the table to the flat cross plate on the a-arm to hold its position.
-With the a-arm now held in position, I cut each bushing mount off cutting vertical leaving an angle in the tubing. Press the bushings out! Clean all ends from paint and make sure they are clean. I used sand paper to sand around the a-arm ends.
-I cut 3" of 1/2" black pipe from Lowes and chamfered the tips so the weld would be deep.
-I pulled the mounts back 3" to the new stoping point in my jig and inserted the 3" of black pipe in between the a-arm and bushing mounts.
-I will say you need a powerful enough gas mig welder that can penetrate all the way through for this job. Tack weld three points around the pipe.
-Once all the ends are tack welded, you can loosen the bushing mounts from the jig and free the a-arms from the table.
-Weld all the way around the joints making sure you are going all the way through
-Do not grind the welds down, it will make the joint weaker.
-Prime then paint.


I have beat on my set hard with my 180 lbs and no issues no far. My shock have more than enough travel for this setup and actually hit the bump stops just before the a-arms would make contact with the frame.

 

I bought this big bore kit and performance CDI and it should be here this week. I'll post any modification I have to do to make it fit. I also ordered the big gun mini full system because the stock exhaust will just chock it. I already tore the engine down ready for the new parts to arrive. It's amazing how simple these engines are.


EDIT!!!( The cylinder from this kit does not fit, I will be modifying it. you also need to buy the Honda 2 bolt cam gear.)

HONDA TRX90 TRX 90 1993-2006 114cc Big Bore Kit Race Head 26mm Mikuni Carb !! | eBay

Performance CDI BOX XR50/XR70 CRF70/CRF70 CRF 70 XR70 R NEW | eBay

 

The engine parts should be in this week so we'll have some fun assembling soon. The more research I do this DS90 motor is just a Honda clone motor. Because of the added power/heat we plan to have I also ordered this pit bike oil cooler kit to keep the engine happy. I plan to weld mounting tabs on the frame for the oil cooler rather than use the bracket the kit comes with to mount it off of the intake base.


Oil Cooler Radiator For Chinese Dirt Pit Bike Monkey Taotao 70 90 110 Motorcycle | eBay

 

I just wanted to post some information on widening the front end by extending your a-arms or using the Diamond J customs widening kit. You will need diamond j tie rod extenders to hook the steering back up. They normally have you put one ball joint on the bottom side of the hub so the tie rod will fit without hitting the a-arm. What I did was install the extender on the rod and flip the tie rod so the extender is on the inside mounting point. You want the ball joint with the longer mounting stud to go on the steering stem. Add a 10mm spacer on the steering stem ball joint and a 3mm spacer on the wheel hub side. This allows the tie rod to stay on the top side and not hit the a-arm.


Attached is a shot of the engine with the top end removed and ready for the new performance parts.

 

So the kit showed up yesterday and the cylinder looks to be unique to the Can-Am and Polaris Outlaws. The base that bolts to the engine case has two bolts while the Honda has one and is not as wide. The Honda also uses a chain wheel while the Can-Am uses guide rails. The heads, cam and everything else in the kit should work fine.


The plan is to modify the new cylinder by grafting the lower half of the old cylinder including chain tensioner to it. I attached some pictures showing how I milled the area out to start the process. I'll line everything up on the engine and then Tig weld it together. I'll also need to machine the slots for the chain rail to set in on the top.



The Outlaw 110 would probably be an upgrade but not a 54mm like this big bore kit. I'm waiting to hear back what the bore is on the Outlaw 110.

 

Not pretty but functional. It's hard to weld cast aluminum but it should not have issues holding oil from the chain tunnel. I just need to machine in the chain guide slots on the top and it should be good to go. Going from a flat top 48mm piston to a 54mm high compression piston should liven this thing up some!

 

If you plan to use a race E22 Honda head make sure you sand down all the sharp edges in the combustion chamber. Sharp edges and high compression don't do well together. Here is a shot of the head after some 150 grit sand paper.

 

Here you can see the stock carb vs the Mikuni 26mm. Big difference in size. I installed the stock cable on the carb and looks like it should work fine.

 

A few more things to add.... the cylinder was .020" or 0.5mm taller than the original one and the head gasket is thicker than the MLS factory one so the timing chain was too tight. I called T-Bolt to find out the compression of the piston for their kit and they said it was 10:1. I had the cylinder decked 0.030" and the timing came out great and i'm hoping i'm sitting around 11:1 to 11.5:1 compression. I'm adding the oil cooler to help deal with the extra heat so the engine should be fine. the engine is all back together and i'm in the middle of reinstalling it in the DS90.

 

is this a Honda replica engine then, or no? If so, all the pit bike engines would bolt right in. Thats why I bought Honda TRX90's, I slip Pirahna 140's in them and they absolutely fly!

 

It is and it isn't. It uses an E22 head but I have yet to find another engine other than the Polaris outlaw 90 that has the same cylinder. As for the engine mounts I can't say.

 

I did a cold compression test today and got ~183psi. With the engine warm that would be between 190 and 200psi, not bad!

I also put the wide band on to see if I could get the air fuel screw dialed in and it was WAY too rich, 9.5:1 AFR!!! I backed the screw out almost all the way and it went up to 10:1 AFR. I pulled the pilot jet out and it was a 22.5 so I ordered a 15, 17.5 and 20. There is a guy who has a TRX90 with this 114cc kit with VM26 carb on and he has a 15 pilot and 165 main jet so that's where I'm going to start.

Another note, I added the oil cooler and it definitely makes a major improvement. The inlet side if very warm/hot and the outlet is MUCH cooler to the point it's almost room temperature.

 

It really depends on what needle you are running in the carb. I have a VM-26 on my 140, and the factory needed was horrible so I put a different taper needle in it and it runs a million times better now. This needle requires a 27 needle (yes twenty seven), and then only a 150 main jet. It runs spot on and instant throttle response and no dead spots.
The nice things with the Pit Bike engines is they are dirt cheap, so if they puke, you just toss them and order a new one. lol The Piranha 140 really screams. Supposedly around 15-17hp and the stock Honda 90 was probably 3-5hp! lol

 

Oh I won't argue that point with you. I guess you can say these ATVs are my new hobby and I enjoy the challenge and tinkering more than anything. As for the needle, the mid range and engine response it's actually really good and the Wideband says it's responding well (mid 13's). But then again its pig rich and that could be covering up a lot of things.

On the tuning topic, what CDI did you use? How many degrees advanced above factory did you go for timing?

 

I just bought the hi performance pit bike CDI with the timing retard at start up, so it doesn't break my wrist pull starting it. I have no idea how much timing was added

If your wideband is showing 13 AFR, thats pretty darn close, I wouldn't touch it. Im sure you know, but check all throttle positions and see what the AFR's are at all the throttle positions and tune from there.

 

Update for all. If you want to use the lower cost AC CDI units off eBay, you have to remove pin 5 out of the harness connector because it's grounded the whole time for some reason. This is the kill switch pin on the CDI unit. I assume the harness is cutting the engine another way. I'll test it once my new pilot jets get here and I can start the engine. The kill switch also prevents you from cranking the engine over so I can just check for spark.

 

So final tuning of the carb came out great and I have a nice gold colored spark plug. For reference, I'm at sea level, Pilot jet is a 15, main jet is 165, and the needle was set one notch up from center. I want to try going with a 170 jet to richen it up just a bit more on the top end. I found a kit on ebay so I could convert the Mikuni choke to work with the factory choke cable.

For now I put the factory CDI back on and I do not plan to adjust the clutch until he gets use to the extra power because it's about three times what it had before as for acceleration. With the performance CDI you can feel the acceleration pick up even more once the engine RPM starts going past the CVT acceleration RPM. You can tell the cam kicks in at that point. I'm guessing about 500rpm more is the sweet spot for acceleration.

 

You guys are way out of my league by skill clearly, but I just bought a used 2009 DS 90 for my son. It sure seems to me that the clutch doesn’t engage until fairly high revs. I thought I read something about a fix for that but haven’t been able to find it. Any suggestions would be great. I’m brand new so if I missed it somewhere else, I’ll apologize ahead of time.

 

Hi, I picked up a 2019 ds90 as for some reason my son didn't like the X model and I'm looking at upgrading the suspension and putting in some rear spacers to give the same ride and stance as the X. Will the 280mm shocks from eBay still fit or does it require the A arm extension?

 

Did you end up getting the trx big bore to work?

 

Is the cdi dc or ac?
Earlier in this thread it appears ac. Another post says dc.

 

Bump