Project 49 : Horizontal Minarelli Performance

[90GTVert]

"Project 49" is a 49cc two-stroke scooter performance project, based on the Minarelli / Jog / 1E40QMB engine. It is the most common 2T that I have seen in Chinese scooters. My intention with Project 49 is to show performance of the engine from stock and beyond and to provide useful information to help the reader achieve their performance goals. I have already done a "Project 90", similar to this Project, but starting out with the 90cc version of the Minarelli horizontal two-stroke. You can see that HERE.


I picked up a 49cc long case motor from a Vento Triton, missing a few bits and pieces some time ago. The major missing parts were the cylinder and piston.




I pulled the 49cc engine off the shelf this afternoon to start tearing it down a bit to be cleaned up. Here's some stuff that won't be going back on. I will pre-mix my fuel 50:1 with AMSOil Sabre Professional 100:1 2T oil. I only use 50:1 because it is an oil intended for lean mix ratios. Even with synthetics, you generally don't want to go beyond 40:1 if you pre-mix.






I checked the crank and bearings and such over to be sure the bottom end was sound and that all looks good. One thing I noticed while looking the engine over was the poorly aligned and matched transfer and boost port areas. You can see in the pic below that the gasket/cylinder wasn't matching the case well at all (notice the brownish areas).




I dug out a stock 49cc gasket that I got from Vento years ago and used it to verify that this case is mismatched with a typical 49cc cylinder.




I suppose for a true stock test I should leave the case alone. However, looking at this just annoyed me and I'm sure some scoots come with cases machined properly. None of mine have, but there have to be some out there. lol I used a carbide burr and files to match the cases to the gasket.




Once that was finished, I cleaned up the cases and CVT cover.




Next, I started trying to figure out what I wanted to do for the top end. I bought this stock replacement cylinder kit from Scrappy Dog Scooters shortly after I bought the engine, with the intention of it being used for Project 49.




I noticed the boost port seemed really small on the cylinder though. After some searching, I found the cylinder that came stock on my Keeway Venus and compared the two. As you can see, the stock Keeway cylinder has a much larger boost port. It matches up to a 49cc gasket and case well.




I started looking over the two cylinders a bit more and found other variances. In the photo below you can see the Scrappy cylinder has a very small circular exhaust port and a small flange. The stock cylinder has a half circle port, but it appears to be similar in size to the small full circle. The stock cylinder has a larger flange. You may also notice the stock cylinder is a little taller.




Inside the cylinders, the Scrappy kit has smaller ports than the stocker. You should be able to tell by their conditions, but the top is stock and the second pic is the Scrappy cylinder.






After looking at both cylinders, I decided to make a top end out of new and leftover parts. I'll be using the Keeway stock 49cc cylinder, the Scrappy Dog piston kit, a stock head, and of course stock gaskets.




I cleaned the stock head and then drilled and tapped it to accept a cylinder head temperature gauge sending unit. I'll be using a CHT to help speed tuning and to look for any major swings in temp when modding.






The stock cylinder had very low mileage so it's main problem was rust from sitting around so long.




I cleaned, painted, and honed the cylinder and it was ready for use.






I installed the cylinder using 1 stock base gasket.




Even though the deck is pretty good, looking at the head and gasket it's obvious this engine's gonna have a lot of room between the piston crown and head.




Sure enough, a check showed a minimum clearance of 1.85mm.




I installed the stock reeds and intake and then proceeded to do a pressure test. The intake/reeds are leaking at the gaskets. I'm not sure why I ever bother to try just gaskets for the reeds? Every time it leaks unless I use RTV.






I sealed up the intake and reeds and did another pressure test. Still leaking. This time it was the stator side crank seal.




I replaced the seal and then everything seemed fine.




Then I moved on to cleaning all of the CVT and starter clutch components.




Even the "restrictor" was included with this motor. From the looks of the variator, it was working.




On closer inspection, I'm not sure if this will prove to be really restrictive or not. The worst restrictors are larger than the diameter of the drive boss, so they'll prevent the variator from closing all the way. This one is the same diameter, so it's more of a spacer. It could limit speed by making it harder for the halves to close, but it shouldn't be as severe as the ones that absolutely will not let the variator halves close.




The stock 4 gram rollers were mildly flat spotted, so I replaced them with another set of stock 4g rollers I had around.




There's a slightly worn area in the torque driver that indicates either slow cruising speeds or the inability to max out the CVT. Either or matches up to the poor markings on the variator.




I'm starting out with the "restrictor" in place so we can see what difference it really makes in or out of the transmission.




Below are looks at the rear pulley (easier to see the difference there than in the front) with and without the spacer/restrictor. The top pic shows without the spacer. The lower pic shows with it. Even if it does limit top speed, the initial "gearing" should be better with the restrictor/spacer in place. That means it should have a stronger launch.






All together.




I did a bit of simple CVT cooling mods to the cover before installing it. Just a series of holes to let some heat out around the clutch mostly. The clutch seems to be the single largest heat source in the CVT. Once again I'm deviating from stock I suppose, but this is a mod that I feel every scooter should have. It won't affect performance when the scooter is first started and ran, but it helps to eliminate the decline in performance as the CVT heats up and springs stop working like they should as well as keeping the belt cooler to perhaps increase it's life.






With the CVT and kick start stuff installed, I could finally do a compression test. Turns out the electric starter and a good battery cranked the 49cc to max compression without needing to kick it. I suggest that you always kick the engine over to look for an increase vs the electric starter though. I got way more compression than I expected after seeing the wide squish clearance. Just over 180psi. On the 90cc builds I've been more accustomed to, 175-180 is about where I need to stop if I want to run on pump gas. I'm thinking that won't apply here and the cranking compression max target may be higher for a 49cc. Time will tell.




I pulled the 103cc out of T2 and got the center stand, brake shoes, rear wheel, and fan shroud off of it to use on Project 49. The fan shroud is the one from this 49cc, I just had to use it on the other engine for a bit.




While I was transferring stuff, I remembered that I had not checked the durations of the cylinder setup like stock. I stripped some parts back off of it and got out the degree wheel to see what we've got.



Exhaust Duration : 171°
Transfer Duration : 125°

Very mild. Suitable for peak somewhere between 7,000-8,500RPM I'd guess.


After hooking up the bare necessities, I fired the engine up long enough to get some heat in it so I could re-torque the cylinder nuts. The vid below is actually the second start. First start required two hands. Since there's no airbox and no enricher hooked up yet, I had to manually choke it. I didn't have a stock airbox at that point. You will notice there are no shrouds. NEVER run your engine without the shrouds. I only do this on the first start and let it run long enough to warm up. If you ride like this it will overheat quickly. If you run it on the stand long it will overheat. Use your shrouds!




The carb being used is a "Leader", pretty common on Chinese Minarellis.




I'm using the cap from another stock carb that had already been modified to work with my aftermarket throttle.




I checked the jetting, but the only change I made was to the idle speed. The main jet is a 70. The pilot is a 22.5. The needle clip is set in the center position.




The enricher will be powered by an on/off switch attached to the battery instead of being wired into the scooter's charging system. This scooter's wiring harness (custom made) has no provision for the enricher.




I'll be using a completely stock airbox and filter.




When everything was together and all the loose ends were tied up, I went for a ride. No tuning or checking anything. I wanted to ride just as if the scooter was fresh out of a crate. It ended up, appropriately, being a 49 mile ride.


Acceleration is certainly sluggish. I didn't mind it terribly though, aside from the times I forgot how slow I was and pulled out in front of cars. I did put a foot down for a push start leaving one light in hopes of keeping with traffic. The initial launch is quite slow with the stock clutch engaging around 2,900RPM. The engine doesn't seem to start picking up a lot of steam until closer to 6,500RPM, so it has to work it's way through a few thousand RPM to really get moving.

Once RPM got to 6,500 it pulled pretty well for a stock motor, up to a max of 7,600RPM. Wide open throttle cruising, sitting up, kept speeds most often in the 37-40MPH range at 6,900-7,200RPM. Max cruising speed was 44MPH, but I was sitting up, going down a decline, and had a tailwind for that. My max speed tucked was only 43MPH. It seems I generated more power by sitting up and acting as a sail than I did by tucking down and trying to let 49cc horsepower work.




I got 59.29MPG. The problem is I ride wide open most of the time. I have to in order to keep up with traffic in town or to cruise 40MPH on open roads. The CHT gauge was showing 340° or so peak at WOT.


Here's a video of the 0-35MPH acceleration in stock form. Just shy of 18 seconds. I need to note here that you will see some inconsistencies in early 0-35MPH runs in this project. I started out using a couple of different locations that seemed to be flat, but times varied between them slightly. I also found some issues with the transmission's torque driver later that changed things a bit.





Project 49 : Baseline Specifications

Bore : 40mm
Stroke : 39.2mm
Displacement : 49.26cc
Cylinder : Stock
Exhaust Duration : 171°
Boost/Transfer Duration : 125°
Cranking Compression : 182psi
Squish Clearance : 1.85mm
Cases : Stock

Carburetor : Stock "Leader" 16-16.5mm
Main Jet : 70
Pilot Jet : 22.5
Needle : Stock. Clip set in center position.
Air Filter : Stock Airbox

Fuel System : Stock tank, 1/4" hose, 1/4" fuel filter, manual petcock.

Oil Delivery : Pre-mix. I removed the stock oil injection system in favor of pre-mix in order to provide consistent oiling with any modification. I am using AMSOil Sabre Professional 100:1 Premix, mixed at 50:1.

Intake : Stock
Reed Block & Reeds : Stock

Exhaust : Stock

Ignition System : Stock CDI, stock stator/flywheel, Bando coil, NGK BR8HS spark plug.

CVT Belt : 788 17 28 Bando
Variator : Stock
Roller Weights : 4g
Clutch & Bell : Stock
Contra Spring : Stock
Clutch Springs : Stock

Final Drive Ratio : Approximately 10.125:1


Max Speed : 43MPH
Cruise Speed : 37-40MPH
Fuel Economy : 59.29MPG


Other Info For Reference

Elevation : ~40ft Above Sea Level
Rider Weight : 300lbs
Fuel : 91-93 Octane (Premium)


The engine is in the scooter I call T2. It's a 2004 Vento Triton that I have stripped down and modified. It allows for easier access to do the work necessary for a project like this.

[90GTVert]

Now that we've got a baseline of the performance in stock trim, I want to take some time to dial in the carburetor and CVT. Even though it did better than I expected stock, it's important to verify that the carburetor is in a safe state of tune first and foremost. A lean condition can overheat and damage an engine.

I pulled the spark plug after the first ride to have a look. With 340 degree temps, I expected it to look worse (more lean) than this.




The plug really didn't look bad, and it should have been fine to continue riding jetted as the carb came stock in this case. That said, I wanted to see if it could be better. I switched to a 75 main first, from 70. CHT dropped a bit and performance seemed to improve slightly. I tried an 80 as well and temp dropped another 5-10 degrees, but performance seemed to degrade, so I went back to the 75.

Next I adjusted the needle clip one notch higher to the next to leanest position, because it sounded and felt a little fat part throttle.

I finished up the carburetor tune by adjusting the idle mixture and speed. The mixture screw is now 1 1/4 turns out, from 2 turns out previously.

With the carburetor tuned up, I went for a ride. The jetting had made very little difference. Takeoff seemed very similar and cruising speeds were about the same. It did seem as if the scooter was more likely to stay at the upper end of it's previously stated cruise MPH (37-40), but it didn't pick up enough that it ran above 40 often. At best I'd say the proper jetting may have been good for a .5MPH on average. Not a lot of change, but it all adds up.

From my house, running WOT, I hit peak temp about 8 miles away. That's after letting it warm up on the stand a bit before leaving. Max CHT was about 325°F, about 15 degrees cooler than with the smaller main jet. Dropping temps is worth the effort in my opinion. Could mean more headroom for hot days or future modifications or just to help prolong engine life.


I planned to try running with and without the spacer / washer / restrictor in the variator to see what it did, so before I took the afore mentioned ride I pulled the CVT apart a bit for some preparation. Here you can see the variator with a black ring showing the extent of the belt travel I've seen so far. I've seen as much as 46MPH with a heavy tailwind at this point, and there is just under 6mm of travel left on the variator's face.




I used a permanent marker to make a thick line across half of the variator. This method makes multiple checks easier than trying to tell where the belt has been every time by wear or a thin line like above if you're lucky.




I found a small hill and topped out at 45MPH tucked at 8,000RPM. Where I live is pretty flat, and I suspect some of you living in hills or near mountains may not even call what we have around here a hill. I had to get a long run up to it to about top out tucked, which I think was 42MPH entering the hill. Not completely sure. Once I got back, I took the variator apart and measured the remaining black mark on the outer edge. Just a little more left than when I measured the black line from the belt at 46MPH left. Both are roughly 6mm of potential remaining belt travel.




I filled the mark on the variator back in with marker and re-installed the variator, this time without the spacer/restrictor in place. Be sure the splines of the crank don't come out past the kick start washer or you could damage the splines or worse. It's best to put the spacer in place either behind or ahead of (as shown) the variator. This also keeps the kick starter working properly.




I went for another ride and the change without the spacer was easy to feel. There was a definite difference in acceleration, especially from the initial launch. The spacer had allowed a deeper "gear ratio" (or maybe pulley ratio is more appropriate?) for acceleration from a stop. Without the best take off "gear", the 49cc struggled more to get moving. Here are pics from earlier in the thread to refresh your memory. The top pic is with the spacer, the bottom is without. The farther the belt rides outward on the rear pulley and inward on the front, the deeper the "gearing".






Once the scooter got moving, RPM was lower than with the spacer. That degraded performance a bit. Cruise speeds seemed to be a little lower, generally staying between 37-39MPH, pushing to 40MPH less often. RPM while cruising was 6600-6900. With the spacer in place cruise RPM was 200-300RPM higher. Lighter rollers or a stiffer contra spring could get the RPM back up, but if the RPM was equal I don't think you'd really see a benefit vs the spacer in place, and you'd still have the weaker launch.

I went to the same hill as before and topped out at 46MPH at around 7,500 or 7,600 RPM. I don't know 100% because I was looking at a Crown Vic, trying to figure out if it was a cop.

I'm not sure if the extra 1MPH has anything to do with the spacer removal, or just circumstances. At any rate, close enough for a good comparison of belt travel. You can see in the image below that there was roughly 1mm more belt travel without the spacer.

The additional belt travel might be nice with more tuning or more power or a lighter rider. On the stock engine with my weight, I prefer the spacer in place. Similar, but slightly worse, cruise speeds and slower acceleration... that's not a restrictor by my definition. Again, I understand that the average person weighs half of what I do so you may get a difference result. I still don't think it's going to be a big restriction even with a 150lb rider when dealing with stock 49cc power. At any rate, I'd suggest trying it both ways before you toss out a spacer or restrictor.

Here's a video of 0-35 acceleration both with and without the spacer. With the spacer was more than 3 seconds slower for me. Pay close attention and you can hear that most of the extra time is the engine struggling to increase RPM off the line.

You may notice that the time now with the spacer and the tuned carb is slower than stock. Stock showed 17.78 seconds 0-35MPH, while this time with the carb tuned and the spacer in place, just as it was stock, the time is 18.58 seconds. From other results, I believe that the very first stock time is faster than it should be. Likely from a tailwind. I have made notes of other good times from different test sessions ranging from 18.50 - 19.00 seconds. For that reason, I would say the above video, with spacer in place, is a better baseline than the one in the first post.

Sorry for the inaccuracy. I'm doing the best I can with what I have. Even if the times don't come across dead on or with complete accuracy, I believe you will be able to hear and see the difference just watching the videos as the project progresses.


Next, I worked with clutch springs, which control the initial launch. I tried stock, +1,000RPM, +1,500RPM, and +2,000RPM springs. Here's a table showing clutch engagement RPM with each set of springs. These are observed with me riding, not free revving.

Clutch Springs	Engagement
Stock	4,200RPM
+1,000	4,700RPM
+1,500	5,300RPM
+2,000	5,800RPM

The stock engagement RPM is a bit odd. I normally observe around 3,000RPM engagement. Today it shows 4,200RPM. I did all tests with no CVT cover installed and the clutch stayed very cool. I had no trouble working on it immediately after a run, and normally the CVT would be extremely hot then. I'm thinking perhaps the stock springs just fade quickly with heat, so I got higher engagement sans cover.

The video below shows each clutch spring set in action.




It seems the best launches come from the 1,500 or 2,000RPM clutch springs. The 2,000RPM springs do a better job of getting the revs up, closer to the powerband, but the CVT is changing gears before the clutch ever engages. The 1,500RPM springs offer a nice improvement in RPM and the belt isn't on the move, or at least not much, when the clutch engages. I ultimately went with the 1,500RPM springs. If you tune the clutch springs prior to tuning the roller weight and/or contra spring, I suggest checking their operation again once everything is in tune. With lighter weights or a stiffer contra/torque spring the belt may not start moving as soon, so you may be able to use stiffer clutch springs and still retain the best "gearing" for takeoff.

There is a definite improvement with the stiffer springs. The lag to really get moving is still there, but it's not as bad. That slow takeoff was probably the worst part of riding the stock 49cc, especially when surrounded by traffic, so I strongly suggest spending the time to tune the clutch.


After feeling how cool the CVT was riding with no cover on the clutch tests, I decided to open up my cover a bit more. Riding without the cover isn't an option, because the rear pulley and drive shaft need support from the bearing in the CVT cover.






It's definitely cooler and easier to work with after a ride. The clutch bell stays reasonably cool. Still can't handle the pulleys without care, but they aren't as hot as they had been.


Next, I moved on to roller weight and contra spring tuning. I'm a fan of slider weights and wanted to use them for this project, instead of standard roller weights. I've already discussed the differences in roller and sliders in the Project 90 thread, so you can CLICK HERE to read more as well as see more pics and video comparisons from that project. There are also numerous discussions about rollers vs sliders that can be found by searching the forum. The stock rollers are shown on the left in the image below, with Dr Pulley sliders on the right.




The stock rollers are 4g and the lowest weight sliders I have are 4g. I tried just swapping to the 4g sliders first. It seemed like acceleration was a bit improved, but cruise RPM was pretty similar to what the rollers were doing and I wanted to try getting the revs up a bit.

Since I couldn't increase RPM with just sliders, I opted to use a stiffer contra/torque spring to help get the revs up. I have a selection of sliders from 4 to 9 grams, so I could probably use any contra spring that I'd like. I went with a 1,000RPM contra, the softest aftermarket spring (at least that's commonly available). I don't think a stiffer contra and heavier weights will do anything more than make it more difficult to work on the CVT. When you install a very stiff spring, it makes the rear pulley harder to open. That makes almost every job you'll do under the CVT cover a little tougher. The 1,000RPM spring is still easy to compress, but should be stiff enough to allow me to use the sliders I have to achieve the RPM I want. Below you can see the stock contra spring (left) beside the 1,000RPM spring (right).




4g sliders were too light with the 1,000RPM contra spring. I saw above 8,100RPM around 37-38MPH. It was pretty easy to tell the engine didn't like revving that high. After swapping weights back and forth, I ended up with 5g sliders. They kept RPM right around 7,500 while cruising. From the testing I've done so far, it seems pretty apparent that this engine's peak output is right at 7,500RPM. I believe it may have accelerated a little faster with 4.5g sliders, but then it revved higher cruising. I think if I can keep my cruising at peak power, it should make cruising speeds more steady. That may not be quite as important in some cases. I don't especially enjoy having to cruise much below 40MPH, so I tune that way. If you spend a lot of time around town or at lower speeds or if acceleration is most important for you, you may prefer a weight that gets the revs up faster even if it sacrifices a little max cruise speed. If you like seeing the highest MPH you can get tucked down or on a hill or whatever the case may be, then you may wish to go a little heavier with the weights so peak power would be above typical cruise speeds. One CVT setup isn't right for everyone.

The CVT setup that I chose ended up being 5g sliders, a 1,000RPM contra spring, and 1,500RPM clutch springs, with the original spacer/"restrictor" still in place.


I rode about 40 miles with the new carb and CVT tune. Cruise speeds have improved just slightly. Previously, cruising was mostly done from 37-40MPH. Now it's 38-41MPH most of the time with the RPM at 7,300-7,600 usually. Not a big difference there, but it helps a little. Gas mileage was lower at 55.44MPG, versus the baseline of 59.29MPG. I was WOT pretty much all of the time. I even rode faster in town than normal. Gas mileage should be slightly decreased with a larger main jet when I'm WOT so much and revving higher. I would expect the difference to be much less under the same riding conditions however.

I did some 0-35MPH passes on the ride, so here's a vid of one.




As you can see in the video, there's a definite improvement having it tuned up with just simple swaps. Carburetor tuning in this case accomplished very little as far as performance. Jetting seems to vary quite a bit though. If you end up with a scooter that comes with one of the 50 something main jets, it may be essential for you to rejet just to avoid engine damage. Some that have came with larger jets may be too rich for best performance, though at least that's safer than lean. Altitude, temperature, humidty, and other factors will all affect jetting, so what worked for me may or may not work for you.

The real gains came from getting the CVT better dialed in. The biggest change being the initial takeoff. While it's still not going anywhere fast, I enjoy riding around traffic much better with less lag to get moving, and then once I do get moving I can cruise at a slightly better speed more regularly. Looking at 0-35MPH, proper CVT setup was good for roughly 1.5 seconds faster times. More if you consider how bad it took off without the spacer in place. I know that doesn't sound like a lot, but I assure you it feels much better.

In my opinion, you should always go over the tune on every new scooter or new engine setup. The effort and small amount of money required is worth the chance and increasing performance and possibly reliability, and it's an opportunity to learn more about your scooter. Do it!


Once more I want to make it clear that not all scooters are the same, even with the same engine. Some will come with different jetting, different weights, and different gearing. Add that with variations in climate and altitude, rider weight, and rider preference, and there is just no one setup that will work for everyone. Here's a small list of difference with certain variables just in case they are helpful to anyone...


Temperature : Higher temperatures make for less dense air, so jetting would need to be more lean. Lower temperatures cause air to be more dense and jetting would need to be more rich.

Humidity : The more humidity is present, the more oxygen is displaced from the air your engine is breathing. High humidity calls for leaner jetting. Low humidity requires richer jetting.

Altitude : Air density decreases as altitude increases. So if you ride at sea level you will need richer jetting than if you ride thousands of feet above sea level.

Gearing : Scooters that come with numerically lower gearing and larger tires more suited for higher speeds tend to need lighter rollers. Otherwise they struggle to pull the load of the scooter. Those that come with numerically higher gearing and smaller tires for better takeoff usually need heavier rollers so they don't sort of overpower the CVT. As an example, I find that I need roughly 1g heavier rollers for my scooter with a numerically higher gear ratio than in my scooters with a numerically lower gear ratio.

Rider Weight : Heavier riders will cause the engine to struggle more than lighter riders. For that reason it will take longer to get to the powerband with a heavier rider and the same weight as a lighter rider. You can use lighter rollers to help alleviate this, but you must be careful not to use weights so light that top speed is lowered, unless you don't mind that sacrifice. Heavy riders may find it much more important to have the CVT operating at peak power where they feel it's most needed (acceleration, cruise speed, max speed).



Resources

Here are some other articles/info that you may find useful for topics mentioned in this post :

Carburetor Setting And Adjustment How-To Videos

Jet Drilling Information

Two Stroke Spark Plug Reading Information

Clutch Spring Installation Videos

Full Service CVT Video

CVT Basics