Project 90 (Stock 89cc And Beyond)

[90GTVert]

Project 90

"Project 90" is or is going to be the testing and modification of a 90cc engine. I will be trying to document the tuning and modifications from bone stock and beyond in an attempt to help others that have chosen to swap up to a 90cc Minarelli engine. While the information will hopefully be useful to the 90cc crowd, I hope it will at least be somewhat relevant for the little brother of that engine, the 49cc Minarelli/Jog/1E40QMB. I'm sure I'll forget to document some things I should, and there will be problems here and there as always.

I know I could just bolt on a big bore kit and throw in a stroker crank and get the wildest pipe and so on to take the "easy" route to max performance, but that's not what this is about. This project may never be anything that special in terms of performance, but if those reading this and I can learn from it, I feel it would be a success. Perhaps when I'm done with it, I can condense this thread into a smaller thread with just the facts and figures so to speak, that may prove useful for 2T scooter enthusiasts. We'll have to see how it goes. Those are my basic goals though. I must say, it feels strange to start a build with this sort of goal. I'm more accustomed to shooting for a performance figure.

Let me start the project off by showing you exactly what "Project 90" is starting out as. I picked up this engine cheap on eBay. It is a 49cc Minarelli that has been machined and fitted with a 52mm bore and a 42mm stroke, to make it 89cc just like most engines advertised and sold as 90s.



I went through the engine and discovered that the manner in which it was done would allow me to get it into stock trim. Only the necessary porting had been done, the crank is a stock style crank, and the cylinder is a stock setup. Anything that was not on par with a stock 90cc engine was swapped out for appropriate parts. Stock gaskets and clearances were used to the best of my abilities. The CVT was setup as commonly found stock on 90cc engines as well.








Specifications
(As The Project Begins)


Bore : 52mm




Stroke : 42mm

Note : This shows the travel from BDC to deck as the engine came to me, not the full stroke.




Displacement : 89.2cc


Cranking Compression : 150psi




Squish Clearance : 1.49mm

Note : The stock cylinder head is not a squish band design, as illustrated in the images below. The squish clearance stated is the minimum clearance from piston to head.






Exhaust Duration : 172°




Transfer/Boost Duration : 118°




Carburetor : Stock 49cc/90cc

Note : Most of the Minarelli engines from 49cc to 90cc or so use the same style of carburetors stock. There are some slight variations in styles, and jetting may vary from one scoot to another.




Main Jet : 78


Pilot Jet : Unknown size, stock.


Needle : Stock. Clip in center of 5 positions.


Air Filter : Stock airbox


Intake : Stock


Reed Block and Reeds : Stock


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


Exhaust : Stock 49cc.






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.


Ignition System : Stock CDI, stock stator/flywheel, Bando coil, NGK BR8HS spark plug. While the coil and plug are not stock, the plug is a stock replacement. The coil should have little to no effect on performance. The only time I've really seen much change with aftermarket coils or spark plugs is on much racier engines, and even then the difference tends to be small. The main benefit tends to be easier starting and more resistance to spark plug fouling.


CVT Belt : 788 17 28 Bando


Roller Weight : 6g


Contra Spring : Stock 90cc

The image below shows a 49cc contra spring (also called a torque spring or main spring) vs a 90cc contra spring. 49cc on the left, 90cc on the right.




Clutch Springs : Stock


Final Drive Ratio : Approximately 10.125:1

Note : I measured the final drive ratio by counting the revolutions of the clutch bell vs one revolution of the rear tire. It rotated roughly 10 1/8 times.



That should cover most of the specs. To sum it up, it's pretty much all stock. The exceptions being pre-mix instead of oil injection, a manual fuel petcock instead of a vacuum fuel petcock, an NGK spark plug, and a Bando ignition coil. I chose the stock carburetor setup from a typical 49cc Chinese scooter as well as the stock exhaust from a Chinese 49cc scooter, because I have had many people ask me if it's O.K. to use these components on a 90cc engine.



This engine has been installed in my stripped down Triton, that most of us here know as T2. The lack of fairings allows for much easier access for repair and adjustments, which is an incredible benefit for this particular project.








Other Info For Reference

Elevation : ~40ft Above Sea Level
Rider Weight : 260lbs
Fuel : 91-93 Octane (Premium)


I have more info to share, but I'm going to take a little break from typing and uploading. I may go out and gather more data? ;D

[shakerdriver]

How do you keep finding these deals on ebay Brent? I've searched and never seem to be able to find a 90 listed on there, but i'm also very much a newb to ebay so that may be why i never find anything.

[90GTVert]

Lots of time. When I decide I want an engine I will spend time on eBay every day, sometimes multiple times in a day, searching for all sorts of terms and going through every item even when the search term is 100s of results looking for that one deal. Eventually something will come along. No deals means no projects (not paying $400-500 for a motor), so I have a good incentive. lol It's like lots of other things, if you don't have a lot of money to spare, you probably need to invest a lot of time instead.

[2strokd]

Great project! So what kind of speeds did you see with a stock 90?

[90GTVert]

For the first try, I wanted to leave the carb just as I got it. I was definitely thinking the 78 main jet was too small, but it seemed like a good idea to see just how close it may be by doing nothing but transferring the 49cc carb and exhaust onto a 90cc engine. Again, thinking this may be useful for folks attempting a swap of their own. Besides, I knew I had someone to call with a truck for the worst case scenario.

As the video and pic will show, I got it up to 51MPH GPS. I believe it could have gone just slightly faster, maybe 1-2MPH, but it was too lean and would begin to drop off after WOT or close for much time. One cool thing is that I did get a soft seize on video for the folks that have never experienced this, or have but didn't know what it was. It was very mild and restarted easily. Sorry the camera gets kinda wild at times, I hang it from the zipper of my jacket so you can see the gauges a bit.





I should also note, I realize it's not the best idea to push it after even a very mild soft seize. As I said though, I knew there was someone with a truck if I needed it, and I never gave it much gas till I was very near my house. I also tried to keep it as brief as I could.

For those that don't know, you are likely to have at least some scarring of the piston, rings, and cylinder walls every time the engine seizes, even when it seems so minor like in the video. Heat is causing the aluminum piston to expand more than the iron cylinder, and with enough heat and expansion the friction is just too much and the engine will die out as you saw there. For comparison, a seize or hard seize is when the piston won't budge in the cylinder again, even after the engine completely cools. A hard seize will require engine disassembly and inspection. At very least, you will usually see rather severe scarring.

Max RPM on that ride was 8,160. I was pleasantly surprised that the CVT setup was reasonably well in tune for stock.

[190mech]

Not bad for a stock 90cc!Its been said the best money spent on speed increases is installation of a 90cc,I think thats very true!!

[90GTVert]

As we all know, I'm a huge fan and proponent of the 90cc engines. I think the results, even in bone stock trim, speak for themselves. If you were to pick up a new 90cc, rather than one that needed attention like mine, you should really only need to get it in a reasonable state of tune to see 50MPH. That's a great asset for folks that don't feel comfortable with engine modifications, such as a big bore kit. Not to mention, the torque of the 90cc engine will not be matched by 50-70cc setups. Also notice that with the stock carb, airbox, and exhaust you have a scooter capable of 50MPH that appears to be stock and has very mild street manners.




After the first ride, I decided to take a very simple approach to the initial tune. I looked at the plug and used my experience and feel on the first 5 mile ride to simply guess at a main jet size. After seeing so many people having trouble with 90cc swaps, I wanted to attempt to show that it really shouldn't be all that difficult to get into some sort of ridable state. Not likely to be a great tune, but something able to get you down the road. I decided to go with an 85 main jet and left everything else the same.

I went out for a 33 mile ride that night. Power output at WOT felt similar, possibly less. After all, engines do tend to run a little harder when they're lean. With the larger jet, anything much below WOT was noticeably rich. This was very obvious in town having to stop and start a lot and maintaining lower speeds. It took more throttle than I felt it should have to get the RPM up and get moving.

Riding on long stretches out of town was done at around 40MPH most of the time. In town I tried to go relatively easy on it as well. I stopped to fill up before I got home so I could calculate fuel economy. I used 0.741 gallons of gas in 30.41 miles, which comes out to 41.04MPG. That number was less than thrilling to me. I was really hoping it would be much more fuel efficient with the small carburetor, stock setup, and normal riding. I had hope though, knowing it was not quite in tune yet.

[190mech]

The final drive ratio is a bit higher than the stock 90cc Vento isnt it?That might alter your fuel mileage..

[90GTVert]

The Tritons were 11.125:1, this is 10.125:1. I do also believe that has a negative effect on fuel mileage, especially for a heavier rider such as myself. The scoots with deeper gears will get me moving with way less throttle when setup properly for lower RPM operation.

[90GTVert]

My project for the next day was to get the carburetor in a better state of tune, rather than just guessing at it. I started out by swapping over to a new spark plug. Here's how the previous plug looked after riding. Very oily. I noticed that the gas in my fuel filter was darker that normal, appearing to be more saturated with 2T oil than it should be. I assume some of the oil settled to the bottom after I mixed at the pump, not a problem I normally have with this oil. Just to be sure the mix ratio is correct, I drained the tank and then mixed that with a little over 3 gallons of pre-mixed fuel. Other than the little bit from the filter, the color of the rest of the fuel looked about right, so I believe it should be very close to normal.



After installing the new spark plug, I made a WOT pass up and down a stretch that's maybe 1/2 mile long and killed the ignition just before the driveway. Max speed was 48.49MPH and max RPM was 8,240RPM. Again, this is the 85 main jet. For these test runs, I am using the onbard Sigma speedometer, rather than GPS. It's very close to the GPS and easier to use for tuning runs. The TTO tach flashes the max RPM after the engine is shutdown, which is quite handy for this stuff. All runs were made sitting up.

Here's the plug from that run. Notice the mixture ring (the bottom of the porcelain insulator, where it meets the steel part of the plug) is a deep caramel color. I should also note for this and future photos, the flash of my camera tends to make spark plugs look lighter than they really are. Without the flash, you can't really see what you need to see.




I then moved up to a 90 main jet for a pass. Max speed over the same distance was 48.02MPH and max RPM was 8,020RPM. When looking at the spark plug from this pass, it appears to be lean at a quick glance. However, knowing the condition of the plug with the previous smaller jet, noting the pattern of coloring on the plug, and noting the excess fuel/oil on the end of the plug, I believe it to actually be rich but lighter due to excess fuel cleaning the plug.




Just to be sure, I stepped up to a 95 main jet. The first thing I noticed was very hard starting after the installation of the larger jet. Once it fired up, the sound of the engine was deep and "sputtery" for lack of a better term. In fact, it was so ric that I never even took it on the road. I had a hard time even getting it moving. I ran it WOT through the yard, and it felt like it took forever to hit it's max speed of 12.97MPH at about 5,000RPM. If the horrid performance wasn't enough, the amount of raw fuel on the plug makes it very apparent that the engine is running incredibly rich at this point.




I went back to the 85 main. I never tried below the 85. I know the 78 main that was originally in it was so lean that it soft seized after only a brief run. That, coupled with the 85's reading, made me feel safer sticking with the 85. Farther tuning could be done if looking for max performance with in-between jet sizes, such as 87-88, but I did not have those size to try. I feel that there would be a very minimal change in performance at best, if any.



I've got more tuning to share, but I have to go pick granny up. I'll try to finish up the rest of the info I have so far when I return.

[90GTVert]

After dialing in the main jet, I addressed part throttle and idle tuning. I knew the part throttle tune was way rich, but I did a plug chop from 1/2 throttle anyway. I did this on the center stand, while slightly applying the rear brake to provide some load. This would be best done riding under load however. This is quite obviously rich.




I moved the needle clip from the center position to the uppermost position, to move the needle down and make it leaner.

When I fired the engine up again, my idle had went from the previously set 2,000RPM to about 4,000RPM with the rear tire spinning quite fast. I knew it was rich before, but I didn't have enough adjustment in the mixture screw to get it right without swapping pilot jets. Leaning out the mix with the needle did the trick without needing a new pilot jet. I adjusted the idle RPM, then adjusted the mixture screw until the engine was running smoothly at the highest RPM achievable through adjustment. Then I turned the screw back in about 1/8 of a turn to leave it slightly on the rich side. With that set, I readjusted the idlle to right around 2,000RPM.

With all of that complete, I repeated the part throttle plug chop. Still looks rich, but again it's not under full load.



After one last check to make sure the throttle response was good and the engine ran smooth in different throttle positions, I was ready for another test ride.

I took a 31 mile ride last night. It was obvious that, even with the main jet the same, the part throttle and idle tuning had done a lot of good. I needed to use less throttle to get going, since the engine was not loaded up with fuel so much. It was easier to regulate speed with less throttle. Throttle response was much improved. Overall, the additional tuning made it a lot more enjoyable to ride. This made me eager to see what sort of gas mileage I would get. Riding basically the same way and with more wind (the previous night was calm, winds were about 15MPH last night) I got 45.09MPG. That's a 4.05MPG increase, just from getting in a better state of tune.

Since it was windy, I don't know that the speed is good for anything. I made sure to cruise easy when I happened to have a tailwind. I tucked down on a short straight that goes through some trees, so I was protected from a crosswind. The max speed shown by the GPS was 51MPH once again. No pic this time. I thought you'd get tired of seeing 51, 51, 51,....

[90GTVert]

I wanted to note, you probably won't see me giving all of those details every time I have to tune for a change. I just wanted to give some illustration of the process I use for tuning at least once during the project though. Again, I felt it may be helpful for someone.


I doubt that I'll get much done this weekend. Today we've got 25-35MPH winds, rain, and some "strong" thunderstorms coming in later. Tomorrow the winds are still supposed to be 25-35MPH. Not really great weather for testing or tuning anything.

[johnnyshere]

great thread. im picking up lotsa usable info here as im still very new to this type of engine design. getting my popcorn together

[drawkward]

Glad some one finally outlined their tuning process. Even after going at this for over a year, I'm still a bit weak when it comes to fine tuning my engines. This should help, once this rain clears up.

My 42mm stroke 54mm bore cylinder has the piston covering some of the exhaust port on BDC. I haven't measured anything, only quickly glanced. Still have yet to finish assembly. Just noticed in your pictures that it looks to be the same with your 42mm stroker.

[90GTVert]

Those pics were with no gasket. With a gasket it's a bit better. 2 gaskets would solve that issue for me and give better timings. I just didn't wanna go beyond stock to start.