Can you make a sport cylinder into a race cylinder?

[245luigi]

O-ring does seal can confirm.

I also can confirm almost all my times are faster after the decking but not fast enough. What I was seeing was about 4 sec 0-10 mph, 6 sec 0 - 20 mph, 9 sec 0 - 30 mph, 10 sec 0 - 35 mph, 12 sec 0 - 40 mph, and 17 sec 0 - 50 mph.

I do have some kind of bog when I whip the throttle open. I figured I would try tightening the clutch springs (Polini speed clutch) to see if that would get rid of it. I tightened them all a half turn, didnt seem to make much effect at all.

Then when fumbling with the clutch I turned some screws and totally messed up where my setting was (gah unwanted variable). So I just set them all to them same and proceeded. I also installed a Polini speed bell (I was running the stock clutch bell). I can tell it is lighter than stock, same size. I lost my footage so I missed some testing but I can tell the clutch is grabbing at a higher rpm. Still bogging though when whacking open throttle. Is this a consequence of the phbg carb? I can post a clip if needed.

With the unknown clutch setting and speedbell, something funky was going on. I was riding back from my test spot and it felt like the bike was losing power at WOT and revved out. Like giving it the beans but power was not being delivered. At first I was like holy crap soft sieze incoming but my temps were like 310f. Had a theory that it was the clutch bell slipping so I put the stock one back on. Symptom went away. So I was like ok its not trying to soft sieze. Testing my theory I put the speed bell back on and went WOT. Slipping feeling return but I kept it open. Nothing bad happened, temps stayed at 310f and RPMs stayed at 9800k. So I'm thinking now, maybe the CDI is restricted? We have always said the kymco CDI is not restricted but could that be my issue?

The unknown clutch setting and speedbell now also prevent me from even hitting 50 mph. The 9800k hits at about 47 mph and I cant go any faster. I do reach all 0 - 40 times the same as before. The bike just stops at 47 mph. I have clips of this as well. I think maybe the lighter bell is causing me to fly past the usual power band of 8-9.5k rpm and hit some kind of limiter. Thoughts?

As the race is 2 weeks away, I'm thinking go back to the stock clutch bell instead of redial the whole CVT for the new bell.

Is there some kind of universal unrestricted CDI? I count 8 pins in the CDI. I got the Naraku one for my bike back in the day but plugged it in and knew it immediately was a scam. I'll probably try it again before removing the bell.

[245luigi]

This past weekends testing was a wash. I went back to the stock bell and wanted to get the CVT tuned with the new cylinder. Heard what I thought was a sneeze from the engine after a first test. Engine temps were a little higher than usual and power was down. I thought if might have been the head gasket so took apart the engine. No signs of seizures. Head gasket deforms differently than a non-decked head but still seemed ok. Replaced it and still down on power and higher temps. Kept testing anyways thinking it was some variable I am messing with. Engine vibrations are up and the bike got louder, thought I blew my reeds. Nope, my buddy noticed my exhaust was hanging by literally one nut. Quickly ran to home depot and got loads of hardware (bolt for silencer, two bolts/nuts/washers to mount pipe back to bracket, and a nut for one exhaust stud LOL). Got it all together. It was 9pm at that point. Confirmed power and temps were back. No time for more testing and considered all tests that day invalid (4 different roller setups and test with the Naraku CDI).

So off to the races next weekend. Setup differs from last race 1) new cylinder 2) raised exhaust port 3) decked head 4) unknown clutch setting. Didnt get to adjust CVT. Thats for next year now.

[245luigi]

Races were rain delayed to September. I was able to do some more tuning. Tried to focus more on the CVT. As of right now I think I really can't get more out of the bike. The CVT really is a balance of top speed and acceleration. Based off my data, I am at the balance point where, lower weights raise 0-50 mph times, higher weights mess with acceleration. I was focused on Brent's 0-35 time at about 8 seconds. I actually could probably hit that with lower weights but then my 0 - 50 mph times would be bad. I threw some 5 gram rollers in and the bike really took off quick but had no good top speed That Elite I'm racing really is a beast because I know that its accel and 0-50 mph times beat mine and I really cant squeeze any more out of the CVT. I know at the end of the straight I was at about 47 mph so I really can't sacrifice the top speed. I may try a race with one set of rollers and see if lighter ones are better in the next race. Get the guys in corners then hope its enough for the straight!

I am running rollers, are sliders worth the swap? Curious if there is another way to get acceleration and some top speed without the CVT. Maybe decking the cylinder (head can't take anymore). Squish is at about 1.28 mm at the moment.

Also, something funky is happening with the bike. It seems like the exhaust constantly wants to shake itself off. The bike doesn't really have any bad vibrations, but I do have some kind of resonance that I hit at like 9 - 9.3k rpm. Its not bad though. I never had to use any Loctite on any of the exhaust components but after decking and raising the port, it seems like after almost any run, I've lost some exhaust bolt e.g. one that holds the silencer spring or the stud nuts have worked themselves loose. I have Loctited everything now, its just so strange though.

I also think I have some reed valve flutter at higher rpm. Best I can describe the sound is a bunch of vhs tape being slapped down hard on a table. Reeds are carbon fiber made by me. I inspected them today and they look fine.

Another thing I need to figure out is the bog off the line. Whacking the throttle open, the bike needs about a second to catch up. Seems to happen no matter what the clutch setting is. But it seemed to go away when I slapped some low weight (not usable) rollers in. Not sure about this one.

Sorry guys a bit all over the place. Tuning is fun!

[broyager]

Could be a rich bog or a lean bog unfortunately.

When I changed to the 21mm carb, which is overkill for the Malossi Sport, I had a lean bog after leaning up the carb pretty severly from stock.

The temp is what I watched to get it right, after some acceleration I could see temps spiking quite quickly when off the throttle, which said to me either pilot / idle or needle was too lean. I am at negative density altitude though... you may be too.

Sounds possibly too lean on the main in your case. Worth trying a few sizes higher anyway, to see if that works.

Might be detonation, at higher rpm, rather than reed flutter, which I think is only supposed to happen at much higher rpm. Could be way wrong there though, check plug for whiteness, and make sure your oil content is not so high that it's causing the whole thing to be lean.

Also the vibration could be anything else attached to the crankshaft, or that the crank itself is out of true / balance. Only way to fix this is replace the crank, or take the current crank out and true it. Never done this, but Alex has the best video explainantion of how to do this as far as I can see. It's expensive but might be worth throwing a new crank at it, especially if you are riding it pretty hard.

[245luigi]

Right, I have been having trouble in my mind trying to figure out what exactly in the carb needs to be adjusted for a whack to WOT. I have considered going back to the stock airbox with two holes drilled with stuffers (recommended by the Malossi carb kit, I went straight to pod filter from unmolested stock airbox). I get that pod filters are meant for race bikes but I'm not 100% sure I have a race bike just yet lol I believe its scooterstreet (some AU scooter shop that makes yt videos) said pod filters are good for race bikes but other than that, you can make em work, but can be a tuning nightmare.

I'll try going up 2-3 sizes on the main and see if anything changes. Thats an easy check. Ever since I have raised the port, temps have been lower since my unmolested kit. I assume thats because compression dropped. Temps came slightly up after I decked the head, but I still basically around the 320 F that was told to me earlier in the thread. Not hitting 380F like before anymore. I also removed my zip tie that held the oil pump open all the time so that should in theory richen the mixture. Off the throttle temps are going down for sure. They really only go up when WOT. Other throttle positions tend to bring it down.

I'm using some weird malossi recommended iridium plug so Idk how that affects tip reading. But I should be able to see detonation with a visual inspection no? I have opened up the cylinder head a couple times and all looks good. If I actually read the piston wash, I would say rich because its not even forming a pattern but perhaps that takes time.

If my vibration is crank itself, it came that way stock. I have had this resonance before, ever since actually getting a BBK 10 years ago or so, just happened to only happen downhill when I would actually reach the higher rpm. Now I can reach it comfortably on flats so hit it more often. I've considered new crank. Athena seems to be the only option but its OEM or OEM+

[broyager]

I've never seen detonation, but afaik it's white specs on the plug or top of the piston

Great idea re airbox, try that first before changing jets

Have you mentioned what jets you are running?

[245luigi]

No but I can go based off fuzzy memory. PHBG 19 carb, Technigas Triops Exhaust, Malossi Sponge filter, Malossi .35 mm reeds handmade

Carb should be set up as 52 Idle Jet, 40 (maybe 50) slide, W7 needle, AU 262 atomizer, 2T atomizer bushing, and 92 Main. Certain about needle and atomizer stuff, I'd have to double check everything else, but thats the ball park

[broyager]

Sounds about right, though 92 might be too small for open air filter, possibly just right for an airbox, maybe even higher.

Idle is probably going to be too big, but if it starts ok and doesn't foul plugs then maybe it's ok, for the pod filter. 

You will possibly need to go down around 40 if you put the airbox back on

I run the 36 idle on the 21mm PHBG, 50 slide, au262, W7, and 87 for a main, but those are with an airbox, snorkel in but opened up and non expansion pipe.

[245luigi]

Cool, I think I'll try some carb tuning next time I work on it. Lets see what happens

[245luigi]

Ok so races were this past weekend. Some updates.

I wasn't able to do any testing much of August and Sept because of hosting guests, weather, other projects, yadda yadda. So, Wednesday before the races, I went to where my bike was kept for some last minute testing. I wanted to try out the airbox and see about using a thinner but longer belt to cure my hole shot issues.

During the second test, with the longer belt and a higher contra spring, the ported Malossi cylinder decided it was ready to sacrifice itself to the gods of speed. After a nice, hilly push back to the shop, I opened up the engine. The piston crown at the area of the exhaust port was gone. Some piston ring bits were lodged into their groves, and both rings had broken into semi-circular shapes. I think I snagged a ring but not totally sure. When I get time I will post pics and you guys can give me your theories. The cylinder seems like it can be reused. No damage to the skimmed head. There were some metal flakes in the crankcase but I didn't see the missing piston crown bit nor bits of ring. The cylinder and head seemed to be covered in what seemed like aluminum anti-seize. Base gasket seemed like it may have been ripped as it looked wet and junky and 3/4 down the studs were wet.

Races in two days and my last day at the shop, it was time for a Hail Mary. I washed the crankcase out with carb cleaner and blew it out with compressed air. Did this three times. The shower of carb cleaner all over the bike didn't have any glittery bits in it so I called it good. Put in a Jasil small end bearing, my old unmodified Malossi cylinder and piston, and the skimmed head. Upjetted from 94 to 98 on the main since you guys told me I was too hot last races and now I was going back with the same engine plus a skimmed head. Confirmed it started and didn't test because if it was gonna blow up, I figured the track was the best place. Hoped the sacrifice was good enough!

Arrived at the track two days later. She starts just fine. Morning practice went well in that the engine did not blow up and temps were maxing out around 360 F. I could tell I lost something compared to the modified cylinder but the skimmed head gave me some power back. I learned auto scoots were going to be combined again due to turnout (you guys should come!!), so the races this round included me, a 70cc 2t Buddy, two 150cc 4t Chinese bikes (one being 303 from June), and a Suzuki 70cc 2t (I don't recall the model but its apparently the same as an Aprilia SR50 but with a carbureted Minarelli engine). The Honda didn't make it to these races.

As I was practicing, the Suzuki came out. I remember him being faster than me last races so I kept an eye on him. He was pulling away from me pretty good whenever the track went straight. Uh oh. I was running 6.25g rollers. During testing, I was getting times from 0 - 10, 0 - 20 etc up to 50 mph. Then selecting rollers that balanced acceleration and top speed. Well at the end of the straight, I'm at about 42 mph so 0 - 50 mph isn't so important. I actually noticed most of the track is run at 15 - 35 mph. Anyways, I rode over to my campsite and quickly swapped to a mix of 6.25g and 5g rollers, effectively 5.62g rollers. Got back out there and I was finally keeping up with him. He had more accel and top speed than me still, but the gap was closed enough that if he didn't run a perfect line and I was on my game, I could get him in the turns.

I entered the auto scoot race and the unlimited (basically a class of everyone who was at the races was eligible). For the auto scoot race, I lined up P5 (last ha) and kept the spot in the end lol. My hole shot really is horrible. The straight goes right into the hairpin and if you don't get that shot, it can make or break a race. The Buddy was P1, two Chinese scoots P2 and P3, and the Suzuki P4. The races looked like it was going to be the Buddy and 303 competing for P1, and me, Suzuki, and other Chinese scoot competing for P3. After quali, I swapped to 5g and 6g sliders, effectively 5.5 g. Another Hail Mary. Took them out for practice and immediately regretted the decision. I think they were acting like ~7g rollers. Lucky for me the Suzuki went down from 8g to 7g roller which he also said was a bad decision.

303 seriously improved. Last races he was my competition. Since then, all he had done was swap out his 13 in tires for 12 in tires since apparently 13 in tires are hard to get in the states. That got him off street tires onto KD1s. He said he was finally confident on those tires which resulted in his dramatic increase in performance. Good for him! The Buddy was running a Technigas Next-R, Malossi kit, 23mm carb, and open air filter. I'm not sure what specifically about his bike made him faster than me. He is a good rider and probably a good 60 lbs lighter too. They also have smaller tires.

1st race I take P2. The two Chinese bikes crashed in the hairpin taking DNFs and I was on a different line allowing me to avoid the mess and pass the Suzuki. I swapped my sliders for 5g and 6g rollers, effectively 5.5 g.

2nd race, I run the formation lap and as soon as I get to the starting line, the engine cuts off. I couldn't get it started again. Another push of shame for me. Long story short, the head gasket o-ring blew. I talked to a couple people and they recommended Ryan Crank as someone who could cut a deeper o-ring groove in my skimmed head. I'll have to reach out to him. Lesson learned readers, don't skim the head, deck the cylinder for reliability! I swapped the head for an unmodified Malossi head to ensure I wouldn't have to do another head gasket swap onsite, and put in a new O-ring.

3rd race - next day, the Suzuki had gone home. Despite my DNS in the second race, I was in the running for P3 podium still. This race was awesome. The Buddy got a bad hole shot and ended up behind the other Chinese scoot. 303 was leagues ahead and it was us 3 fighting for P2. The Chinese scoot is a boat and is so difficult to pass. Me and the Buddy swapped positions probably 5-6 times and one time I held P2. Finished the race in P3 ahead of the Buddy. The footage in my front cam got corrupt so all I have is the rear cam footage . Its up on my YT channel now, but I'll post a link when all videos are done. I did get a talking to for being too aggressive in my defense since these races are supposed to be for fun. Whoopsies. As far as going back to the unmodified Malossi head, mid range was rich and I lost some power. End of straight was like 39 mph unless I worked hard on chicane entry and kept speed up in the long left sweeper.

4th race, I was tied for P3. All I had to do was beat the other Chinese scoot. I don't really remember what happened in the race, I'll have to review the footage. But about halfway through, the engine starts running weird and I can't rev up. Darn chance for P3 gone. I baby it into the pits and start to diagnose...THE DAMN SPARK WIRE POPPED OFF!!! Aww man what a shame but it happens. The spark cap has never seated well because of the temp sensor. Looks like its time to cut a little groove into my cylinder plastics to make more room.

In the end, no podium for me. Buddy took P1 and the Chinese scoots P2, P3. These races had their ups and downs but I call it a success. I can take the current setup and get numbers as a baseline for more testing since its more correct for the track. Furthermore, my racing skills got a lot better. I started experimenting with riding position and have seen good results. I have found better racing lines. I'm getting better at passing.

I didn't recap the unlimited races because I'm middle of the pack in like a 14 person race. The mopeds and 200cc vintage vespas are the fastest there. In the 3rd race I did have my first crash. I was chasing the Buddy and this race was immediately after auto scoot race 3 above. I wanted to try to get him again. Instead I took the only right hander too fast and too tight, ran out of tire and away she goes! Here's the clip: www.youtube.com/watch?v=gic_eaO7y4A

Anyways future plans: 1) get numbers on current setup 2) see about getting deeper o-ring cut into skimmed head 3) hone modified cylinder and get new bits 4) improve hole shot. I'll be back with pics of cyl and edited race footage.

[245luigi]

Here are some pics of the damage to the modified cylinder after a wipe with brake cleaner:

Piston, the missing bit lines up with the exhaust port















Here is the cylinder. Only damage is near the exhaust port so only those pics are included. I can feel the grooves with a fingernail. More like pad of finger.









Bits of piston ring. I had one more semi-circular bit but I dropped it in the grass at the races.



Base gasket. Its still wet and very friable. I'm not sure why. I did apply grease to it for install. I think it may have blown, probably when the exhaust rattled itself off.

[aeroxbud]

Running too hot you think?

[245luigi]

Honestly, no idea. Right before it went, CHT was maybe 340F. I have run this thing for years at 390F, only since starting this thread have I been running it lower.

I think either the ring snagged on a combustion stroke or I had an air leak and it was running hot, weakening the exhaust side. I did find an aluminum anti-seize kind of paste in it after it happened. Maybe the top of the piston in that area was getting hot and melting(?) eventually giving up, releasing the ring, allowing destruction.

I have contacted Ryan. He will be able to cut a deeper o-ring and can deck heads. He no longer bores them out. I think I will send him my unmodified Malossi for decking .2mm as well as the skimmed head for o-ring cutting. Since I have an unmodified head, I can play with squish.

I found a site for a guy who overbores, decks, hones, and chamfers. www.billbune.com/ I think I will contact him and hopefully be able to overbore .4mm the modified cyl, deck it .2mm, and have him hone and chamfer it.

[245luigi]

All videos loaded up now: youtube.com/playlist?list=PLD4AfyDDotGkEpCbgqI2gQPCCD9OskMwD&si=83vNXUBNKZVEFoMH