Technical Rotax Junior Max Advice

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Reid7774

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Hi
Myself and son have karts, a senior and a junior rotax, karts have Sat for nearly 5 years and it's time to get out on them again, my son would like his ( junior max) made into a senior if possible or made to go as fast as it can, what do i need to do to make it a senior if possible or just derestrict it to its max.
Also gona need a few new parts, so any advice on where cheapest for spare parts.
Any help much appreciated.
Thanks
 
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Adam

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Heey welcome to the forum!

Well before you start making things faster I would for sure give them both a good check over. After 5 years I would almost certainly recomend rebuilding the brakes and getting some new seals etc fitted and pads. I recently rebuilt my master and caliper complete with all news seals, springs, circlips, bleed nipples, pads etc at the cost of about ÂŖ100.00.

Dump any old fuel and make sure the carb is cleaned. Remove the float bowl, clean and inspect and replace gaskets etc if needed. You would more than likely need to rebuild the mikuni fuel pumps too. Gasket/diaphragm kit is about ÂŖ12.00.

Dump the gear oil and replace that too! Silkolene SRG75 is good stuff. 100ml for metal gears, 50ml for plastic gears if I remember.

However with all that being said, after 5 years the engines could very well need a rebuild or a check over at your local engine builder. It wouldn't be great to split a perished water pump seal or alike and cook the motor. Rotax recomend rebuild after 40-50 hours but most engines builder will recomend around the 15-20 hours mark or before.

You can find the full repair manual here:


Now onto turning a Junior into a Senior Max, it would need a new barrel to accomodate the power valve of the max at least. I don't have much knowledge at all on that tbh. But it could be most costly to upgrade a Junior than it would be to just buy another Senior Max. Again, better to ask a local engine builder.

Hope that gives you some kind of help?
 

Reid7774

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Heey welcome to the forum!

Well before you start making things faster I would for sure give them both a good check over. After 5 years I would almost certainly recomend rebuilding the brakes and getting some new seals etc fitted and pads. I recently rebuilt my master and caliper complete with all news seals, springs, circlips, bleed nipples, pads etc at the cost of about ÂŖ100.00.

Dump any old fuel and make sure the carb is cleaned. Remove the float bowl, clean and inspect and replace gaskets etc if needed. You would more than likely need to rebuild the mikuni fuel pumps too. Gasket/diaphragm kit is about ÂŖ12.00.

Dump the gear oil and replace that too! Silkolene SRG75 is good stuff. 100ml for metal gears, 50ml for plastic gears if I remember.

However with all that being said, after 5 years the engines could very well need a rebuild or a check over at your local engine builder. It wouldn't be great to split a perished water pump seal or alike and cook the motor. Rotax recomend rebuild after 40-50 hours but most engines builder will recomend around the 15-20 hours mark or before.

You can find the full repair manual here:


Now onto turning a Junior into a Senior Max, it would need a new barrel to accomodate the power valve of the max at least. I don't have much knowledge at all on that tbh. But it could be most costly to upgrade a Junior than it would be to just buy another Senior Max. Again, better to ask a local engine builder.

Hope that gives you some kind of help?
Thanks for the helpful reply, in the process of giving them a good going over but I didn't think on doing the master and seals, another job..lol
How do i no if i have metal gears or plastic, the junior engine had a full rebuild prior to storage and only done a couple hrs on track, karts only going to be used for fun so is replacing the water pump seals something I could do and any advice on how to do it.
Been reading alot and decided not to convert to senior, just want it upto it's max potential of a junior as think it was setup for minimax, have removed the exhaust restrictor, anything else I need to do, doesn't seem to be any restrictions in the carb, slider opens up fully, is there any need to replace jets.
Thankyou for any help, was complete novice before and still am, just picking up bits.
 
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Adam

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Essex - UK
Name
James 'Adam' Pell
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Senior Rotax 177
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Grice Racing Engines
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Tony Kart 401R
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J. A. Pell & Son Motorsport
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Thanks for the helpful reply, in the process of giving them a good going over but I didn't think on doing the master and seals, another job..lol
How do i no if i have metal gears or plastic, the junior engine had a full rebuild prior to storage and only done a couple hrs on track, karts only going to be used for fun so is replacing the water pump seals something I could do and any advice on how to do it.
Been reading alot and decided not to convert to senior, just want it upto it's max potential of a junior as think it was setup for minimax, have removed the exhaust restrictor, anything else I need to do, doesn't seem to be any restrictions in the carb, slider opens up fully, is there any need to replace jets.
Thankyou for any help, was complete novice before and still am, just picking up bits.
If it's Pre Evo I would assume you would have plastic gears. However you can always take the gear cover off to check. On the side of the gear casing it will state how much to fill the gear oil with though, saves any messing around. 100cc = 100ml and 50cc = 50ml.

From what I remember from years backs the Mini Max will have an exhaust and carb restrictor. Once you remove them both it converts it into a Junior Max. I do recall there being 2 different size pre evo carbs though? Jetting wise I'm not sure on at all tbh, best bet is ask around the track on the day. If it's an Evo engine you can always get the free Rotax app to help you!
 
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Reid7774

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Thanks again, much appreciated.
 
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