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Correct me if I’m wrong but the cap and the spring are not jetting changes. And the Rotax never came OEM with a small spring or the corisponding cap. But hey we all try and stretch the rules.
Doug,
Thanks for talking to Marty about that issue. Can we get it in official form?
20.3.10.3 Carburetors: OEM as supplied from the engine manufactureer. Jetting is open. You may install washers to the OEM needle jets for the purpose of tuning. The means that the throttle connect is non-tech, but you must use the OEM arm and shaft assembly.
So what does the little phrase, “The means that the throttle connects is non-tech” mean? To me that says, elbow, cap, spring, throttle cable are all non-tech. The carb rule expanded itself from the 2004 rules.
It really doesn’t matter one way or another for me. I do not see it as anything other than a time saving device. I never thought it had a tuning effect. If anything, it would be a detriment to change out the Rotax cap due to the large size of the Rotax black cap.
Can we get in writing via e-mail from a SKUSA official that the cap & spring are both tech items and must be OEM?
Just as Charles stated, I wish it would just say it plain and clear.
Tom
Marty did say that the Tag USA rules would be up shortly and they are clearifying some things. He has been watching this discusion and I’m sure will take that into consideration.
Angel,
It is widely accepted that all the parts you mentioned are jetting tools (ie. fuel metering devices). It seems pretty straight forward to me that any part that can be removed from the carb can be changed. No where does the TAGUSA rules with regards to the carb. direct you back to the Rotax rules. If I have missed where that is spelled out please show me. In fact the carb. rule is the same for all engine combinations. It is generic to encompass all the diferent carbs.
TAGUSA/SKUSA 2005
20.3.10.3 Carburetors: OEM as supplied from the engine manufactureer. Jetting is open. You may install washers to the OEM needle jets for the purpose of tuning. The means that the throttle connect is non-tech, but you must use the OEM arm and shaft assembly.
All this says is that a Rotax must use the Dellorto VSHB34 carb. Other than that all and any fuel metering components(ie. jetting)are alterable with out machining any permanent part of the carb itself
Heck, I still believe, inspite of what Doug Welch has said, that the cap and spring are interchangeable. Until it is in writing, open jetting means anything that can effect the fuel metering is fair game and legal to experiment with.
Just a side note, if Doug was the head tech official for the CSC and stated that the cap and spring or whatever else were off limits then I would put back on my Rotax cap and spring, but until the word comes down I will keep it the way I have it. I will always follow the rules, but I can not resist experimenting within the rules. It must have to do with my profession. 😀
Tom
Angel,
I will plead ignorance in the case of needle jets. Doesn’t the dellorto VSHB34 only have a needle not needle jets, as in plural? We have pilot jets, starter jet, main jet, atomizer, emulsion tube, slide, etc…I am assuming that the phrase changing of needle jets applies to other carbs than the OEM Rotax carb.
The other carbs have the ability to change out whatever they want without changing the OEM specified carb. The other OEM carbs have the ability to change on the fly. The Rotax is not competitive if run under the RMC rules. That is why “jetting is open”.From what I can tell or have discovered the other engine packages do not have a specific jetting package or internal parts only that the carb must be the OEM carb as supplied by the manufacturer. I have seen many different setups in the other carbs. There is not anything specific other than the carb is not polished or machined.
Therefore, it is my opinion, all carbs in the TAG series can and should experiment and change out whatever they want without polishing or machining there respective OEM carb. If anyone thinks this is not the case, they are just fooling themselves.
On last thing, have you noticed that there is no conversation about any of the other OEM carbs? Seems odd to me. It is not like the Dellorto is the only one. The only reason this becomes a discussion is because the Rotax has a set of original carb rules that only apply to the RMC. They should no way be applied to the TAG series. We have a Rotax series that I can run.
One other thing, if the Rotax engine weights are based on the dyno tests that were run by TAGUSA or SKUSA. I know for a fact that the Rotax was dyno’ed with a CIK air box two 22mm holes. If you try to run the CIK air box with only changing the main jet it will not work. Therefore, TAGUSA or SKUSA had to change out other parts in the carb and I am sure they did not do any polishing or machining. 😀
Tom
Angel,
Another thing, I count 11 different motor packages under the TAGUSA rules. How many different types of carbs are there? I believe the reason jetting is open is to decrease the difficulty for the tech director. All the tech guy has to do is look inside the carb and visually inspect. It takes more time to take the carb off than it does to inspect for machining or polishing.
When you wrote “My thoughts and interpretation: IF Rotax carbs can have their slide, needles and all orifices classified as jetting, then remember that all other carbs will also be allowed the same modifications……what then?”
It is my opinion that this is already the case.
Tom
If jetting is open the OEM tilly carbs owners should be able to drill the drill patterns of there carbs. Inspection of drill patterns would be difficult and not possible by veiwing down the throat. I haven’t seen the OEM drill pattern listed anywhere to even see if it could be compaired to other OEM carbs. In fact you would have to machine the carbs soft plug with at least a drill in order to inspect the drill parterns sizes.
If the cap of a slide crab is non-tech, what would stop someone like me from pulling a little more air threw the top? I can see the 2″ throttle sleeves with filters on them becoming quite popular.You made my point. Do what ever you want just no machining of permanent parts of the carb. Can you tell me if the “drill pattern” you are refering to has to be drilled on a non-removable part of the carb or can this item be removed from the carb and then machined?
I have never even seen a Tilly carb. So I obviously do not know what you are describing. But I do believe if you have to stick a maching type tool of any sort into the carb to change a drill pattern then that would be deemed illegal. Now on the other hand, if the drill pattern can be changed while outside the body of the carb then it sounds like fair game to me.
Remember, these are only my opinions.
Tom
Tom, All tillies metering holes are drilled threw the carbs body. Even the low and high side needle holes are drilled into the carbs body. The low side needle controlls the amount of fuel that enters under the low side soft plug, which is a plug that covers three different holes. The size and position of these three holes controll the amount of fuel that is available and mixed with changes in the air velocity seen flowing through the venturi. These holes can be seen looking down the carbs bore. Even removing the soft plug by an inexperianced person can result in a ruined carb with a wrong size hole in the wrong place of the carbs venturi.
Jet changeing of a tilly includes drilling of the carbs body in 7 possible areas for improvement or losses in controlling the fuel to air ratios through out a motors air velocity speeds. This is why with out any jet kits a tilly can be changed from the fuel requirements of gas to meth. That along with fine tuning of the high and low needle screws, makes the tilly quite appealing to on and off the track tuning. If all these holes were adjustable with out “machining” the carbs body, the tilly would cost more than a rotax slide carb, all it’s jetting kits, software and hardware.
If the loose term “jetting” is open in the rules, what would stop someone from elimating the fuel that has to go threw the venturi, replacing it with more air and introducing the fuel at the intake port? That would give me 7% more available air to flow through my resricted venturi size. I have a Tilly and intake that does this but it is set up for meth and drilling the drill pattern back to smaller sizes in the carbs body is quite tuff to do.I think I need to take a look at the tilly carb. That way I could understand what you are describing a little better. I barely understand the Dellorto, but I am learning and experimenting. I still stand by what my last post states. If it can be removed from the carb it is a tunable part. Seems pretty cut and dry to me for all the different carbs.
Tom
I think the new rules are pretty clear…….
If you start off with the TAG class “catchphrase” which is “if it does not say you can do it then you cannot……”, it’s pretty clear.
The dellorto can have any jet changed, (main jet, needle jet, pilot jet…)and also the slide, which is now included. For the butterfly carburettors you can add a washer to the stock “slow jet” and change the throttle linkage (to get over the tillitson weak point as fitted to leopards.)….and that’s it…….
Tom if you argue that other components should be changed then others will argue theat the tillotson shaft and butterfly mechanism can also be changed. Before you know it you are into big money carburettors, not to mention three different ones for different conditions and preferences.
The idea of the class is that a novice can buy an engine and have as much power as the guy who won the last race. By introducing special modifications and anything other than standard jetting I think the cost and difficulty to get to the front on driving skill alone rises, which is a bad thing.
I’d avoid any tinkering at anything other than the above as I think it goes away from the spirit of the rules and also runs a high risk of being illegal.@Angel Figueras wrote:
The slide assembly is included in jetting but must retain OEM replacement parts. Does that mean “as provided by Rotax” or “any Dellorto part made to fit this carb (they are the OEM, and not Rotax)
It means as provided by the OEM of the carb, which in this case is Dellorto. Rotax does not make or provide any carb parts. If the part has the Dellorto stamp on it, its a legal part.
So finally we agree. For the Dellorto carb you can change all jetting or fuel metering components in the carb.(main jet, needle jet, pilot jet,emulsion tube…)
What about one of the original questions of this thread? Is a different cap and spring legal to change , as long as it is an OEM Dellorto part? I think it is a non impact item as far as engine performance. It just makes the carb easier to take apart and work on.
Tom
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