TM 32 jetting

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mboddy
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Re: TM 32 jetting

#91 Post by mboddy » Tue Dec 31, 2013 6:56 pm

Badass wrote:They never used Power Jets on the Yamaha GP bikes, so if it was that good why is this? lol.
These look like power jets on the Roberts Yamaha YZR500 carbs:
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Badass
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Re: TM 32 jetting

#92 Post by Badass » Tue Dec 31, 2013 7:11 pm

Very cool, thanks for the pic. It makes sense that this is were it came from but I don't think they used them in modern gp 2t racers. Those are some funky looking carbs all connected together like.
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Re: TM 32 jetting

#93 Post by strutha » Tue Dec 31, 2013 7:36 pm

2002 yzr500 .
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Re: TM 32 jetting

#94 Post by mboddy » Tue Dec 31, 2013 7:45 pm

Mikuni TM and VM are old tech carbs.
A power jet is a low cost, easy to setup way to improve them.
The pic I posted shows them starting from half throttle.
Some more modern carbs have electronic power jets that start even lower.

For my road racers I normally have them starting about 2/3 to 3/4.
My initial tuning will be use power jet size 25% of main jet and reduce main jet by 25%.

For dirt bike I may start them from 1/2. Use power jet 20% of main and reduce main jet by 20%.

Do WFO plug chops to fine tune main jet like you would if you didn't have power jet.
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Re: TM 32 jetting

#95 Post by T.RexRacing » Tue Dec 31, 2013 8:51 pm

strutha wrote:2002 yzr500 .

Izzat yours????


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Re: TM 32 jetting

#96 Post by tankslap » Thu Jan 02, 2014 9:44 am

"Why do you think EFI is so accurate? "

Because fuel injection can put a 'bend' in the fuel delivery curve like a carb can never hope to achieve?

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Re: TM 32 jetting

#97 Post by tankslap » Thu Jan 02, 2014 9:57 am

"Liquids don't compress thus meter accuracy is easy at a given pressure."

Does an emulsified fuel air mix behave like a fluid or gas? Or sumfing in between?

If the needle/needle jet and sometimes the pilot circuit meter emulsified fuel on most carbs I have seen, why so?.....if it is such an inaccurate means of dishing out fuel?

I'm assuming of course that an air jet in a given circuit emulsifies the delivery some what.

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Re: TM 32 jetting

#98 Post by tankslap » Thu Jan 02, 2014 10:22 am

"It is difficult to meter precisely due to the ability to compress. The air jet is for fine tuning and is in the airstream to maximize accuracy. It is what feeds the needle jet air as well. Some set-ups do without it altogether,my YZ465 is one of those.

Why do you think EFI is so accurate? Liquids don't compress thus meter accuracy is easy at a given pressure. The air is metered by engine speed and throttle opening-both crude methods of metering."

These statements reminded me of two things.
The first is when I studied pneumatics and hydraulics during my trade cert.
Pneumatics and hydraulics are metered differently.(in a before/after sense).

The second is the media I remember reading when Mick Doohan tested fuel injection on his NSR 500 back in the day.
He reportedly chose to stick with the carbs even though Itoh if I recall correctly, used the injection probably to 'save face'

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Re: TM 32 jetting

#99 Post by T.RexRacing » Thu Jan 02, 2014 10:55 am

As far as EFI accuracy I base my opinion on 20+ years of writing maps. It's much easier to isolate a fueling issue (if indeed the problem is a fueling issue) and correct with the aid of a 5 gas analyzer and dyno.

In the needle/needle jet emulsification is actually used to determine when the main jet becomes dominant and is very effective. There is a point where pressure differential is sufficient in overcoming the weight to pull fuel straight up from the main using needle taper (or lack of) to meter thus bypassing the emulsified mix because the needle jet can't supply fast enough.

As far as Mick and Itoh go EFI has advanced considerably since then.
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Re: TM 32 jetting

#100 Post by tankslap » Thu Jan 02, 2014 11:32 am

Trex, your twenty years of dyno experience is exactly why I have to read your posts twice, three or more times to gather the meaning from them.
I'm being obtuse deliberately to push the envelope on the discussion.

When the pressure differential is sufficiently low to create a situation where the fuel flow is 'lazy', is this not a time when the light weight emulsions comes into play? Is this what the D/J excells at?

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Re: TM 32 jetting

#101 Post by T.RexRacing » Thu Jan 02, 2014 12:57 pm

And I'm being obtuse to wrangle a specific question from you. I don't feel like typing a treatise on EFI. I'm a one finger typist and it takes forever.

By D/J I assume you mean Dial-A-Jet? I've not one lick of experience with them so cannot comment.

When pressure differential is low the acoustic waves in the intake tract are clipped and become square at the peak/valley. You can hear it with a load cell dyno. This is part of what activates the Thunderjet and Powerjet (an assumption on my part) as pressure differential is insufficient itself to pull fuel.


The needle/needle jet circuit "adjustable/tunable" via air bleeds,so yes that's when emulsified fuel is a key player. In fact I did indeed refer to this in my prior post. Same thing with the early pilot circuit. I didn't say it was useless just inaccurate,tedious to tune and subject to changing conditions. Especially if you lack dyno time. Track time is best used for other pursuits.
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Re: TM 32 jetting

#102 Post by pushstartrearset » Thu Jan 02, 2014 11:28 pm

So.

Who is going to be the sacrificial dickhead for the dial-a-jet? :smt017

Someone already done it?

I'd really like to try it eventually on the ole RD (looks like you mounted a flux capacitor from the future up dair). Make up all kinds of shi* at the local starbucks. :smt045
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Re: TM 32 jetting

#103 Post by tankslap » Thu Jan 02, 2014 11:59 pm

I have fitted them to two bikes but I have no credibility on here.
I also don't have the track miles/ experience to quantify my seat of pants findings.

Little is written about the D/J (dial-a-jet) that I can find on my Google searches so I do tend to stir the pot when I can to stimulate some conversation about them.

Dicks Racing has a service where they fit the D/J's as well as venturi splitters etc.

The D/J's seem to get the attitude of 'it's snake oil' more often than not and usually from people who have never even had one in the hand!

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Re: TM 32 jetting

#104 Post by pushstartrearset » Fri Jan 03, 2014 12:22 am

tankslap wrote:I have fitted them to two bikes but I have no credibility on here.
I also don't have the track miles/ experience to quantify my seat of pants findings.
I'd be more interested in any midrange gains on the street. I think the dial-a-jet (works at basically all rpms and NOT a powerjet! according to Thunder) would be the much better option over the thunder powerjet (meant for larger carbs). Very pricey at 239.00 bucks though. And why I would like a solid eval. before i even think about dropping that much on an external piece.
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Re: TM 32 jetting

#105 Post by tankslap » Fri Jan 03, 2014 1:14 am

I think the price is probably the sticking point for most people. It's about the price of a new set of pistons isn't it?!!

But Iike i alluded to in another post I think, if it saves a melt down then it would probably pay for itself.

The Intelajet is the more evolved and robust product than the Dial-a-Jet in my opinion (I have fitted both BTW) and probably the better value.

Maybe someone like T-Rex could blag a sample product from Thunder Products and do some back to back dyno tests and publish some results on this forum.

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