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I have finally aquired all the bits I need to upgrade one of my Zuma vertical engined scooters.  I am after advice from anyone who has done similar about main jet size to use.  I have a set of jets up to 98 and plan to start with the 98 unless someone advises different.

The upgrades will be a DR 68cc cylinder, free flow manifold, 17.5 carburetor, (standard air cleaner), racing CDI (unrestricted standard curve), Leo Vince TT exhaust (with restrictor removed), heavier counter spring and weights set for about 8000RPM, torque driver (standard on later Zumas), heavier clutch spring and 30% upgear kit on the output gears.

Oil will be Shell semi-synthetic at 30:1 for the startup then 50:1 after run in.

Petrol should be 91 octane but I will use 95 octane for run in before checking for pinging on tuned engine.

This is not a racing setup, its about as mild as I can build while getting a well balanced package to commute in traffic on a 60km/hr road.  Gearing would take it to a 100km/hr scooter but it will never get over 75km/hr where I ride.  Using the standard aircleaner is deliberate and expected to be the governor on power for the engine.

When its sorted, my plan is to convert my second Zuma and have a pair of scooters for the family to use instead of various cars and larger motorbikes.

All up cost of parts including shipping has been just under $500 which might be overcapitalising the scooter but boys need toys.

So is a 98 main jet rich enough for start up or am I too small?

All went together brilliantly.  Carby came with a 90 jet which I used and it will be fine for running in.  Give it a couple of weeks back and forth to work then I will tune the transmission and chech the mixtures.  Pulls like a train after 55km/hr but I am limiting it to 60km/hr for run in.  Suspect I don't need the upgear for my use.  Will buy bits and do my partner's scooter when I have finished tuning.  Thanks to SIP scooters for the parts.  Ca't fit larger pump on vertical engine so using pump plus premix.

 Did the plug check and the mixture with a 90 main jet seems very lean, changed to a 98 main jet and its still lean.

Fuel consumption while I run it in is about the same as the standard 50cc engine.  The bigger engine is clearly running efficiently as long as I don't use the power.

I have ordered jets up to 125 to continue tuning the carby.

So I am running it in staying to about 55km/hr with my daily commute. 

I am not even starting to use the power, it runs at 55 to 60 km/hr on the speedo at about 30% throttle and accelerates up steep hills at 60km/hr to run the speedo off the clock in a bit over a house length.

Its got ample power for my daily commute in traffic, once I have the mixture sorted out its finished.  My guess is I will end up with the 120 jet to get it a bit rich and see how it goes.

My plan for the aircleaner to limit the power does not seem to work, the standard aircleaner is passing plenty of air for my needs.

Getting moving from 0-20km/hr is sedate, the standard clutch with heavier (2000RPM) spring does not get the engine to a reasonable torque and bogs down up hill.  I have ordered an adjustable racing clutch which should help with higher revs and more clutch slip when needed.

So far I have used about 3.5 gram roller with a +30% contra spring to get the engine on the bottom of the power band for comfortable acceleration (guess is its running at about 5000RPM) with the transmission running out at 50km/hr and the engine free reving over about 55km/hr.  I've had the belt slip once or twice under heavy acceleration but the transmission seems ok as is.

It feels like speeds over 80km/hr would be easily achieved but the chassis is not that good.  Once the engine is run in and tuned, I will find out its top speed with a GPS just so I know what it can do.

Sorted the mixture, the new manifold was leaking.  The rubber pulled away from the backing plate resulting in an air leak.  So the idle adjusted properly I put a 110 jet in which is a little bit rich and it has all the power I need for comfortable commuting.  The exhaust is noisy so we will increase the weight of the transmission weights to slow the engine a bit so there is less noise at the lower speeds.  I might have to check the packing of the muffler.  I will do my wife's scooter after I have done a few months on mine and am sure its reliable.  Working on the Yamaha vertical engine has been a pleasure with all the bits fitting easily and the tuning working the way its meant to go.  Power to 20km/hr is a lot better.

 The run-in is over, I've gone to a 98 jet which seems about right for cruising on 60km/hr.

Can't say what the top speed is, it winds off the clock easily but I am not interested how fast, my guess is over 80km/h true speed but the chassis is not up to those speeds.

Fuel consumption has settled at about 4 liters per 100km moving my heavy bum to and from work.  Flatout the fuel needle drops a lot faster than that but I don't ride hard very often.

I did put a better quality adjustable racing clutch in which makes moving off the line a bit easier and a lot noisier LOL.

Reading sites from overseas, this engine in this tune should last 20,000km on light work like my commute.

Would I do it again or buy a bigger bike or scooter, yes, the work was basic, the scooter does my commute well and the cost of registering and insuring a bigger bike or scooter is a pain in my deep pockets.

The smaller scooter is handy filtering through the cars stuck in traffic jams.  When I had bigger bikes and scooters I would get stuck when the distance between cars reduced.

I lost track of this post and did not upgrade the information for anyone concerned.

The bad news is that at about 5000km it had a major piston sieze that was not on the plan.

It took about an hour to put a new barrel and piston in and make the decision to increase the oil ratio.

On reassembly I noticed the aircleaner cover had a crack at a mounting hole which would have changed the inlet dynamics and probably caused the piston to overheat due to lean mixture.  A new cover was installed and the engine ran perfectly, not even a need to adjust the idle.

So 2000km on the new piston and cylinder and no issues.  I bought spares when I decided to do this engine, at $75 for the replacement cylinder I am not concerned about the money, just I wanted it to last 20,000km.

Time for an update, 10,000km and the piston siezed the day before Xmas holidays.

I've had a think and not done the piston and cylinder yet because I will put a thermocouple in the exhaust to see what temperatures I have before restarting the engine.

The plan is to run the egine in with the thermocouple to give me a base line temperature then tune the transmission to see if I can improve (lower) the exhaust temperature by running a higher engine RPM.

In the past I set the transmission speed at about 8000 RPM with the result that the engine worked at between 7500 RPM and 8500 RPM depending on things like headwinds.  The new transmission speed will be 9000 RPM as long as the exhaust gas temperature is not too much higher.

The recent engine failure was not at high engine speeds, it was below 8000 RPM labouring up a long hill.  My guess is the piston is not getting enough cooling at the slower speeds with load.

I've ordered a more agressive torque driver and  a bearing for the contra spring to try and get top revs under load more reliably and lower revs in low load conditions.  Again to avoid the labouring that might have killed the piston.

Parts won't be here for a couple of weeks.

http://www.ebay.com.au/itm/300855755557?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

http://www.ebay.com.au/itm/301009736872?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

http://www.ebay.com.au/itm/261328077370?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

I forgot to update this at the time I replaced the cylinder and piston.

I could not find a torque driver to suit so kept the standard one.

I sealed all air leaks on the cooling cowl which should improve cooling where the piston overheated.

And the big thing was I discovered a screw missing from the aircleaner which allowed an air leak that probably caused the piston failure.

Time for another update.

Last month I retired so that is the end of my 50 km commute.

So now the Zuma is used for local trips to the shops and the odd trip into Melbourne.

At my last trip to work, this cylinder and piston got close to 10,000 km with one soft seize a while ago that was probably caused by me riding very hard on a hot day. I have a new cylinder if this one expires but I'm not doing the distances or speed so it might go for ever.

One recent change was a new AGM battery which made electric starting cold reliable.

Now my justificationfor the scooter is reduced maintenance on the car.

I'm still happy with my mods but could not recommend a novice trying all these changes.

The Doppler variator has meant its done nearly 25,000 km without tuning or significant maintenance. Traditional roller variators are the work of the devil.