[Dean]

Hi again..i want 2 ask u all,im using p3 at the moment,i knw its a bit old compere it to p7,but if i change the carb to p5 or p6,will it be more power?i heard the carb it self is around $1000+ in kl rite,we have up coming event in brunei...on 17th&18th of august

[Mikko Nassi]

The carb shouldn't be any different - you mean like a Dellorto VHSB 34 QD versus a QS? I can't remember which is the "older" one, but the only difference in the actual carb is that the idle speed and airscrew adjusters are on the other side - there's no performance difference.

Of course there are the new floats and idle jet and the idle jet emulsion tubes which were updated. They are worth getting I feel it helps the throttle response a bit, especially good for tracks with lots of slow corners, for faster tracks the 5.2 might be better. They shouldn't cost too much either.

You need the 3.6g floats to replace your 5.2g floats and "60" idle jet and emulsion tube to replace your "30" idle jet and emulsion tubes. Remember that under Rotax rules you aren't allowed to use the "new" floats with the old jets.. if you use 3.6g floats you must use 60 idle jet+emulsion tube.

I still use a 3 or 4 year old carb in my kart, usually with the 3.6 floats and 60 idle jet+tube.

[Mikko Nassi]

Oh yeah and you might also want to check to see what Venturi you have! Generally a 8.5 is good for most tracks while 12 is good for really really fast tracks. To see what venturi you have look indside the carb where the slide goes and you should see either a "8.5" or "12" stamped on top of the venturi.

[James Leong]

To Dean, I would advise you of the following -

1. If at all possible change your P3 to the P7 which is now available at SHAP. If you are unable to due to cost etc, your P3 will still serve you well. Move to .99 piston if you are using a current .98 or if you are using .97 then move up to the next grade. Renew your circlips, piston pin and bearings. This will help you a bit.

2. For the carburettor, your present one will do. If someone ask you to change the whole carb, then it is more of a money milking thing. Your carb will work prefectly whether it is a new or old. Like Mikko has said, check the floats that you are using and buy the next grades that you are allowed to use. Change all the carb seals, especially the tube that is meant to collect all the dirt. Clean out your carb thoroughly and re-assemble. You should not have any problems after that. There is a service kit available from Rotax for gasket/seals replacement.

3. The code QD and QS meant left or right. This is for the idle screw. Newer version of carb comes in QS version. Older models is QD. The carb is the same.

James Leong
Rotax Distributor

[RocK]

Remember that under Rotax rules you aren't allowed to use the "new" floats with the old jets..

What happen if we use new floast with old jets. anyone tested?

[Mikko Nassi]

Might go a bit lean on the bottom-end... the 3.6floats will lean out the mixture over the entire rev-range a bit so that's probably why they have the 60 instead of 30 to keep the bottom end from going too lean.

[RocK]

Cool, good to know. Getting everything needed for the 3.6F from SHAP. be testing it soon..

[Dean]

owh ok,i starting to like this forum all the info u have given me is relly help full for someone like me with 0 experiance wth the rotex max ,btw some of my frinds told me that if i buy the new carb to compete wth the newer engin,before this no one told me to change the floter n all that they just say buy the new carb,i'll shold chek the manual again hehe...and change the things that u all told me,hope u can help me again soon...about the pistons i already change it and also new piston ring, if things get complecated and confusing i will ask u again.. heheh...btw the up coming event that i told u before,the track had a very long stright line and also small tight coners...

[RocK]

12 is good for really really fast tracks.

Which track for example.
also does rules allow 12mm? always tho its only 8.5mm

[Mikko Nassi]

Cool, good to know. Getting everything needed for the 3.6F from SHAP. be testing it soon..

Start testing with a main jet one size larger than you'd use with the 5.2.

Which track for example.
also does rules allow 12mm? always tho its only 8.5mm

Just realised it's actually 12.5(not 12) and 8.5.
btw might also not be mm but tenths of a millimeter or something like that, it's not the actual venturi choke size but a smaller hole that feeds fuel directly into the venturi.

From reports from others I've read the 12.5 is really only good for really big tracks like road-courses -not kart tracks. When I did a back-to-back test at the Sepang kart track I didn't notice a difference in the kart or on the laptimes, so I don't think it does a whole lot to be honest In theory it's supposed to improve initial response when you apply the throttle. Safest bet is to use the 8.5 because that's what rotax changed it to, originally all carbs came with 12.5.

Oh yeah regulations don't seem to mention it at all - so if Rotax don't think it's important enough to outline in the regs I doubt it can help much.

[RocK]

What was I thinking, 12mm & 8.5mm. tiny carb

Good points as always. Thanks for your tips Mikko Nasi

[Dean]

james im sory but wat is circlips?ill already change piston and piston ring,much better then before..but my carb everytime exiting corner the responce is very slow..like bbbbbrrrrrrrr........the bbbb taketime like 2 to 3 seconds.. hope you understand what im sayin sir ,one more thing,if my carb is still using QD so i need to change it to QS right?and the floter?resently i've already clean my carb the filter is clean... i just want to make sure wth you how to get the responce more to my carb...and what should i do wth the jeting?and wat is ideling jet for if i tune it up or tune it down?is that make my responce better or not?

[RocK]

3. The code QD and QS meant left or right. This is for the idle screw. Newer version of carb comes in QS version. Older models is QD. The carb is the same.

Dean, as James said QD and QS are basically the same carb. you dont have to change QS.

When you change piston, did you change the circlips, piston pin and bearings? ask you engine builder.

As for what jeting to use, I'll ask my Brunei fren to help you out on your coming race. Make sure you tell him the "bbbbbrrrrrrrr" part..

Good luck.

[James Leong]

For all you guys out there who runs Rotax Max engines, please note that we have a Rotax Service Centre located at USJ in SHAP's office. We have a crank balancer, honing machine etc to do all the necessary work on the rotax engines.

If you are from KL, you can come and pay us a visit. For outstation or overseas owners, you may want to send your engines back to us for re-builts or purchase the parts from us.

We will also be able to advise you on how, what, when to do engines repairs, carb setups etc. The advice is Free Of Charge.

For newcomers, you can download a Max Repair manual from the Rotax web site. If you have problems with it, contact me and I will email you a copy.

James Leong
Rotax Distributor

[Mikko Nassi]

For those that are interested in finding out exactly what goes on in the Rotax carburetor and how different floats, jets etc. might change performance download and read the pdf files on this website.