'99 Prebug Zuma Build

[billwill]

So, did some thinking and am having second thoughts about if I cut deep enough into the case to create clearance for the over range. There is limited info out there around what is deep enough.

I was purposely approaching the grinding conservatively in order to avoid any case cracking down the road but based on some vids I saw of some guys in France and Italy who has done it to boosters, I feel that I can safely remove more material in hopes that it’s currently rubbing a bit and hence my issue with top speed.

Here is how she looks today. Whatever the case (no pun intended lol) there’s an opportunity to smooth things out and remove some ragged and rough edges.

[billwill]

Picked up a cheap half inch belt sander from harbor freight and did some further removal of the cvt side of the case. There were definitely a few spots that the belt was slapping on maybe not under load but during deceleration or idle. All in all, didn’t gain any top speed and still seeing 64mph on flat.

Been thinking more and more about this top speed issue and now I’m wondering if I am geared too high for these taller than stock wheels and tires. They are not taller by much but equate to a diameter of about 1.5 inches greater than stock. The chalk markings in the one pic below compare the two. With 15/50s and what I’m guessing is at least a 16hp motor I feel like it would be enough to pull them. Maybe I’ll just throw the stock Prebug rear wheel and tire on to see. I’ll have to run no rear brake and hang the caliper somewhere though since I’ve committed to disc. 

[Zino]

Reference pigs build he was running more extreme gearing than you on one of his pre-bug builds he was going to go to 9 to 1 gearing from 11 to 1 which is where you are at right now with gears
49ccscoot.proboards.com/thread/17391/pigs-65mph-2002-70cc-prebug

Your higher rolling resistance over stock tires over stock is probably holds you back a few mph along with the wall of wind you are fighting through as you increase speed

Per the speed list and my experience on the now defunct Zuma forums on these 2 stroke 70cc a ton of verified 50 mph builds with just a few over 65 mph and hardly any breaking the 70 mph .

Those last few mph are so hard to get but they sure are fun to chase if you have the budget and time .

[billwill]

May 6, 2024 7:00:17 GMT -5 Zino said:

Reference pigs build he was running more extreme gearing than you on one of his pre-bug builds he was going to go to 9 to 1 gearing from 11 to 1 which is where you are at right now with gears
49ccscoot.proboards.com/thread/17391/pigs-65mph-2002-70cc-prebug

Your higher rolling resistance over stock tires over stock is probably holds you back a few mph along with the wall of wind you are fighting through as you increase speed

Per the speed list and my experience on the now defunct Zuma forums on these 2 stroke 70cc a ton of verified 50 mph builds with just a few over 65 mph and hardly any breaking the 70 mph .

Those last few mph are so hard to get but they sure are fun to chase if you have the budget and time .

Yes dude! Man, if I had a nickel for every time I pulled up PIG's build thread, I would be a rich man right now!

Wealth of information in there and I've referenced a TON of what he has done. We are at the same gearing right now at 11:1 final drive.

I really do think it is the wheels holding me back right now. He also lightened the stock flywheel and I've done nothing with the ignition. 

Pig, if you see this, I'm curious what your overall transmission setup was. I gather you were running something like 3.5g rollers but could never find anything on torque spring. 

[billwill]

Think I can chock this up to the big wheels. Been chatting and following a buddy's build on one of the Facebook groups and we have similar setups. He was hitting 70/71mph with a particular setup and 10" wheels and just moved up to 12" wheels and a larger tire. He just went out for some top speed runs and got the following result.




He is also running 15/50 gearing like I am. Here is our tires side by side:



I am going to try going all the way back down to stock gearing and see what happens. So is he. Exciting times. Between this and the ignition, I'll be she has 70 in her.

[billwill]

So for those of you following me and this build (probably tired of hearing from me by now) - I'm back with an update.

Could not get this bike tuned for the life of me. Tried jetting all over the place, different wheel and tire combos, pipes, etc.

I even leak tested when I put the kit back together after fine-tuning the squish to stop pinging on pump 93 and it held but not great. Decided to grip it and rip it and go thinking the leak down test was subpar, but ok. It dropped from 6psi to about 5psi after 30 min or so.

I finally did another leak down test and found it dropping from 6psi to 5psi after 15 minutes. And after about 90 minutes, completely down to 0psi.

I was able to check the crank seals tonight thinking it was there or even worse at the case halves.

Neither… I found a leak (or maybe even two) in the most bizarre place.

Gonna slap some JB weld on it and test tomorrow. I swear this motor is built of aluminum that’s like lava rock lol.

[billwill]

So in order to fit the over range, I had removed the steel ring for the starter clutch that sits around the case flange where the crank bearing is. These two pinhole leaks appeared beneath this. In chatting with some people in a Facebook group last night, I found out that you don't even have to remove the steel ring on Prebugs, only Bugeye Zumas. I remember doing it based off a video I saw online where someone else did it and thinking that it didn't seem necessary. Oh well, hindsight is 20/20, live and learn. I'm just laughing to myself wondering if these leaks have been there the entire time, or if I exposed or exacerbated them by removing the steel ring. 

Anywho, the toddler decided to not sleep and get up early today, so up with her I was and once getting her back down, couldn't wait to do a quick pump up and leak down test to see if the JB weld fixed the leaks. 

I pressurized things to 6psi and stepped away. When I stepped back to check on the gauge - CRAP. It was reading just below 6psi. I gave it a good 15-20 minutes and came back and it was under 5psi now. Oh no. I went on to check the spot I patched yesterday with JB weld, both crank seals, the cases, and just about every other possible area on the engine.

I figured it must be my homemade leak down tester. Checked all of the joints and found a super small leak at one of the brass fittings going into the gauge and tightened it up. Still had a slow leak somewhere. Finally I popped the pump ball off the end of the system and sprayed some soapy water in the end of it. Voila! One big bubble, slowly growing.

Now onto how to seal this. I found some rubber caps and pressurized the system again to just over 6psi and popped the ball pump off and threw a rubber cap on. She's been sitting at the same reading now for just over 20 minutes and I couldn't be happier. Calling this a win for now and hoping this allows for proper tuning... finally.

There are a few other things I need to take care of while the transmission is apart and the bike is down. I noticed the rear wheel had some play in it and I think the rear wheel bearing is shot so going to replace that and then hopefully we're in good shape.

Update: 45 minutes and holding strong.

[billwill]

After figuring out the high rpm stutter and miss, this thing is running real strong now. Idles good, sounds good.



It's still quite hot and I suspect that I may have to re-adjust the squish again to lower compression, and/or it's just running on the lean side right now. It could also be that the stock ignition and CDI timing curve is not ideal for this setup. I swapped out the stock CDI for the Malossi CDI yesterday and it didn't seem to make that much of a difference.

On WOT runs, she gets hot real quick. After about a 20-30 second pull, it will get close to 400º very quickly. This is on a 50/50 mix of pump 93 and VP c12 too. Oof.

Right now its got the 30mm Polini PWK with a 42 pilot, 144 main and JJN needed set to the middle clip. I'm going to try upping the main. I suspect it will probably want a 146 or 148, but part of me just wants to throw on a 150 and hope it takes and cools things down.

It could also be that the JJN needle is just too lean. It has a visibly (to the naked eye) thicker profile than what came with the PWK, but when I've run the PWK needle it feels very rich and bogs sometimes. Now that there isn't a spark issue, who knows though.

Plug looks pretty good... this is a fresh plug after about 5 miles of mixed riding.






It pulls pretty good too and while I have yet to break 70 on flat ground, I'm certain I'll be able to tune for it. This video is slightly downhill so the numbers are a bit skewed. There is probably some opportunity to add some weight to the variator. In this video I'm running 4g rollers and a malossi yellow spring. After this I switched to a stage6 pink spring and I didn't notice much of a difference. People seem to prefer the stage6 springs over others though, and this one is built for overrange unlike the yellow malossi so I'm going to stick with it.

[billwill]

Went ahead and took my time installing the MVT digital direct ignition over the weekend. I had been waiting to get the bike tuned and running right before slapping it on but with recent changes in upping to a 148 main and moving the needle up a clip to the 2nd richest spot, the bike was keeping its cool finally.

Holy cow. I wasn't expecting this much of a change with the ignition but the thing feels like a completely different beast now. Before I had a little bit of a bog off the line that I had been having trouble tuning around but it wasn't significant enough to worry about. Now, the bike lurches off the line and is hard to keep down for the first 60 feet or so. The overall change is wild.  I set it to .4 btdc as MVT suggests.

Here is the first startup with the MVT.



The bike actually seems to run cooler with the MVT as well. At idle, with stock ignition it would sit around 190º and with the MVT, it goes up to about 165º. Which is strange, because I thought it had crazy advance at idle. Cruising temps seem a little bit cooler too and it will come down from the upper 200's much quicker now.

I started using one step colder of a plug, so the b10hs, per MXS's recommendation with an aftermarket iggy. I didn't gap this one down like I did for the others, hoping the MVT would have enough juice to cover the gap. Thankfully, it does, and no high RPM sputtering anymore with a .024" gap. I may gap this down to .022".

Some pics of the fresh plug with the above settings after about 5 miles of mixed riding. Would be happy to hear thoughts.



Once I got things in order and figured it was setup OK, I took it for a spin and a dragy run. When I went to put my phone in the holder, I realized the locking clip had broken off, DOH. I wanted so bad to get a good camera angle, but the seat cam had to suffice. New phone holder should be here today from Amazon.

Performance is good and I was able to break into the 11's on the 1/8th. Still only saw 65mph max, but I suspect I can tune the CVT for this. I know the Aerox wheels aren't doing me any favors here with all of the rolling mass. I did switch out to Michelin Pilots and this saved me a total of 4.5lbs vs. the old heavier tires.

Still REALLY want to break 70mph since that was my original goal. I think I can up the roller weight and that should help. I'm running 3.75g right now and with the way this MVT let's it spin, I think moving back to 4g or even 4.25g is the move. 

[billwill]

Upped the rollers quite a bit this evening to 4.4g and it seemed to be a little too much for its liking. Threw the 4g rollers back in and went up to a 154 main jet. Surprisingly, it took this main jet just fine. No signs of stuttering or being too rich.

Did a top speed run and dragy couldn’t find satellites so I didn’t have access to a dragy recording but did track 66 top speed on flat ground. I really think these bigger wheels are hurting me at this point.

As I was a mile or two from home the bike started to run a bit louder and vibrate more than usual so I stopped, hopped off and took a look, sure enough, cracked pipe header.

Oof.

This is now the second pipe I’ve done this to.



Not sure what’s causing this but I’m suspecting either mounting it off a bit to the side to fit the aerox wheel and 140 wide tire has the pipe sitting at an odd angle or I’m still just running too tight of a squish or still lean and the EGTs are going crazy.

Pretty bummed.

I could also possibly be running too high of gearing still. It’s only at 11:1 now though. Maybe I’ll switch back to stock gearing to do some testing with. 

[billwill]

Pulled the plug just to see what was going on there and am relieved to finally have what I believe to be a richer reading. It seems like the bike finally met its match with a 154 main. Going to step it back to a 150 I think.

Almost as frustrating as cracking a pipe, it’s odd to see the temps still so high even when it seems to be running so rich. After a WOT run of about 30 seconds, temps would spike up to 380 under load and then shoot up to 395/400 when coming off the throttle.

I really didn’t want to have to pull the cylinder and readjust the squish but may have to. Right now I’m at .68/.69mm and thinking maybe somewhere around .8mm would be better to try. 

It could also be the gearing paired with these larger wheels/tires so going to try moving back to stock primary gearing as well. 

[billwill]

Found a great spot about 15 minutes away from me that said they could weld both the ST and SCR exhausts. I'm not sure what the going rate is for welding and pipe repair but they quoted me at 1-2 hours worth of work, so around $100-200 to fix two exhausts. This sure beats the cost of two new pipes so I gladly had them get me on schedule.

With the bike out of commission at the moment, I've been thinking I may need to turn back the advance on the timing with the new MVT setup. Temps were still getting way hot even with the rich 154 main. Before I get the repaired pipe mounted I'm probably going to retard the timing a smidge and drop back down to a 148 main.

Hopefully that cools things down. If it doesn't I may be going back to stock gearing and/or having to adjust the squish. Right now I'm at .68/.69mm and thinking I might need to be more around .75/.8mm.

[myers]

I think with mvt you lost top speed becouse off lighter spinning mass on flywheel. Back when i had minarelli vertical engine in my bws with mxs racing cylinder i was testing stock ignition vs malossi selettra. With malossi ignition scoot was more aggressive on throttle but not faster in 1/8m loosing trap speed about 3km/h. With stock ignition and stock short mina vert gearing 1/8M it did in 11.25s @ 85km/h

[billwill]

Jun 6, 2024 5:43:02 GMT -5 myers said:

I think with mvt you lost top speed becouse off lighter spinning mass on flywheel. Back when i had minarelli vertical engine in my bws with mxs racing cylinder i was testing stock ignition vs malossi selettra. With malossi ignition scoot was more aggressive on throttle but not faster in 1/8m loosing trap speed about 3km/h. With stock ignition and stock short mina vert gearing 1/8M it did in 11.25s @ 85km/h

Well, I didn't really gain or lose any speed, if anything I picked up 1-2mph on flats. I think the gearing along with larger rear tire and wheel than stock is what's causing a lot of my headaches and temps. I may have to adjust the squish to be greater too. 

I got both pipes back the other day and they looked good. Popped the SCR back on and while I was at it checked timing. I suspected it had either changed a bit or that I had it set to be too advanced. When I had been kick starting the bike, it had been kicking back like it wanted to start in reverse. 

Sure enough, timing was a smidge advanced and set to about .45mm. Nothing wild but more than is called for. I set it to .35mm and we'll see how she does with this setting. 

Again, I suspect between the additional rotating mass of the wheels I am using and the larger circumference tire AND the tight squish, that the bike runs hot. I'm not sure which plays the larger role but I have some testing to do. 

I started the bike up and it runs well and gave no reverse starting kick back like before. It doesn't feel as snappy but that might be placebo and totally in my head. I haven't gotten a chance to ride it and observe temps under load and WOT throttle but if its still hot, I probably have to take the jug off and reset squish to something like .75-.8mm. I did check it today when i had the spark plug out and its still at .68mm.

[billwill]

Getting things slowly dialed in with the help of the Dragy! Bike had been running hot (and still does if I keep it WOT for more than 30 seconds or so) but retarding the timing of the MVT dd seemed to help a lot. For now she’s in a good enough spot where I don’t have to worry about meltdown but I still feel like I will need to adjust squish from .69mm where it’s at now, to something like .8mm so that I can reliably run on pump 93. Still only seeing a personal best of 69mph but with some more tuning and possible gearing switch up, I know 70 is there. What I’m really happy with is the 1/8th time right now.