Malossi MHR Replica Porting-Help Pls

[adas]

Aloha, I have a MHR Replica, 21mm carb, Yasuni R on my Minarelli engine and just cleaned up the ports. For those who have ported and know this cylinder, can you advise me?
Here is what I did and the results:

1: I matched the exhaust outlet to the Yas pipe

2: The case outlet openings were 2.5mm wider than the inlets to the cylinder, so I matched them as well as the base gasket.

3: All the ports (exhaust and transfer) had a 1mm "lip" (on the top or head side) as they went into the combustion chamber. I removed 1.5 mm from the exhaust and smoothed out the whole port, while not changing the shape. I did flaten out the port a bit on top and made it about 1mm wider on each side. Since I flatened the exhaust port, I also put a very slight chamfer so I would not snag a ring.

4: I also removed the lip from the transfers, thereby raising them by 1mm. And I checked their heigth to be sure they opened at the same time, so the right ones I think I raised 1.5 mm and the left only 1mm. The rear I left alone.
I did not change the direction of the front transfers that cause the gases to hook to the back of the cylinder instead of toward the exhaust.

5: I cleaned up the transfer ports by the base by smoothing and knife edging the divider in the port.

The results?
Before: Cylinder head temp (yes it is water cooled engine) was running 325 F at 3/4 throttle cruising speed. 90kph
Before: bottom end and midrange seemed more snappy

After: Cylinder head temp now runs at 215 F. WHY? Maybe since I removed the lip on the tranfers, the direction of gases now seem a little more up toward the head-spark plug and less toward the piston, thus more cool head. ?????

After: Feels like it is running lumpy and a bit rich at low speed and mid.

After: Top end now has no quams hitting-overrevving down a slight incline at 120kph and 12500 rpm. Runs 9500 and 85kph easily 3/4 throttle up the hill.

My conclusions: Drop about 1 gram off 3 weights, lean out the pilot a bit. maybe drop a point or two off the main jet, OR drop the needle one clip.

What do you all think. I would especially like to hear from those of you that have ported the MHR replica.

thanks Frank

[Modular Overrev]

if it's blubbering or running rich at low to mid rpms try turning the idle mixture screw or drop the needle 1 notch leaner, did you knife edged the bridge between the side transfers at the base of the cylinder? i usually do the opposite & make them round at the leading edge much like an airplane wing.

you should have also kept the roof angle of the transfer ports flat so the charge doesn't short circuit out of the exhaust port, if you have done this (rised the roof angle) don't raise the exhaust port.

when tuning the rollers drop or add weights one roller at a time, not all three at the same time, it makes your engine run closer to it's true settings & don't worry about it being unbalanced b'coz i have been doing it for several years now with no ill effects.

[adas]

Aloha. I dropped 1 gram on three rollers and that did the trick. As you mentioned, it was running a bit rich, (that is why it was cool). Now it runs 300 degrees F like before. The Yasuni R sure has a wide power band from 8000rpm to 12500 @ 110kph and more on the flat and really works well with the MHR replica. I cannot use WOT as the pipe is like the energizer bunny, and I don't think the stock crank will sustain 12.5 or 13k. Another advantage to the Malossi LC conversion, is that the engine is much, much quieter than an AC, and you do not notice the higher RPM associated noise. Anyways it is like a rocket now.

hmmm....on the rounding vs knife edging the transfer webbing. Have you proven this to yourself??

I did not change the transfer port angles except to remove the 1mm lip on the tops of each port. Seems almost like the nikasil coating slopped into the ports a bit and formed a small bead. (you can see this ledge a bit in the photo)

Modular.... what is the rev range of the Malossi MHR Replica. Malossi on their website says max hp at 8500, but another tuning site says max power at 10700 to 11700 rpm.

frank

[Modular Overrev]

rounding off the edge on the transfer tunnel bridges i got that from a technical article written no less by Keith Wilson who is noted to be the best intake manifold tuner (porting) in US autoracing, airflow is less disturbed with a rounder (blunt) edge & keeps the fuel atomized & suspended in the airstream, it also keeps the airflow laminar b'coz a knife-edged bridge produces eddy currents that make the airflow turbulent reducing airflow velocity & volume.

i have done this to my 70cc MHR Team racing cilinders & it's probably the fastest/most powerful 70cc in the country (if we still had a 70cc class), since we no longer have a 70cc class we moved up the ladder & raced in the 90cc class where we have won several times against scooters with much bigger engines.

i think you have already seen my test & race videos in this forum i'll let the actual performance speak for itself, we even managed to place 3rd in the 125cc class at one time by beating several 125's dragscooters, we won the first race of the season this year when the yasuni c21 was first used, incredible performance gain over the lousy MHR Team pipe.

i think my scooter makes 21+hp & revs past 15000rpm judging by how fast the scooter runs against the fastest 90cc dragscooters in the country, i have done my homework with this set-up & now i'm prepared to take it to the next level with a 2F4R 80cc kit for the minarelli engine.

so you just chamfered the port edges ok that would be no effect on roof angles, rev range will vary depending on what exhaust pipe & carb is used, 8500 rpm is usally where peak hp/torque is produced but rev ceiling will certainly 1500 to 2000rpm higher, a heavier race crank (more inertia) will allow the engine to rev a little higher as evidenced by the MHR Team 2000 crank which is the heaviest race crank for the Minarelli & Piaggio engines.

[ime]

id love to find out more about this stuff. howto round ports, tune the engine all together. Can u lot give me some links or some sort of guidane toward this. Maybe thers a book for this type of stuff?

[Modular Overrev]

i recently tuned an MHR Replica kit for a Yamaha Jog here are the specs i gave it;

185 main exhaust port
180 aux exhaust ports
128 main transfer
124 secondary transfer
boost port untouched

squish clearance is set to 1mm, we used an MHR copy pipe, 24mm carb, runs 120+kmh on the flats

i staggered the port timings & angled the roof of the transfers a bit upwards so the transfer doesn't interfere with each other like it was with a flat roof angle.