SX Viper TM33 Carbs - Rebuild Jetting Questions

[GasCans]

OK..sort of a newb to SX Vipers but can turn a wrench so no issues with that. I should add that I am learning as I go here. :-)

Just did carbs in my SRX 700 last month and noted the Mag side was the larger of the three main jets and everything worked great when I was finished. Now I'm doing my sons 2002 SX Viper and the main jets are all mangled from previous person being a hack artist. Cannot read the sizes so I was going to order some new jets and this is where I'm being thrown. I see some notes reference a Mikuni TM33 on a SX 700 and it simply states 156 Main Jet? (Does that mean all three carbs are the same size main jets in the SXV 700?)

Totallyamaha Sled Specs

Note: I also looked at the link above and see further reference showing staggered jets stating #1:145, and #2/3:143.8.

Which are correct for a 2002 SX Viper 700 Triple, and if it's the staggered sizes, which cylinder is #1 on this model. Is it the PTO, Middle or Mag as I read all kinds of info on some threads I have seen. Would love some acurracy before I order new main jets and pilot jets.

I ride at about western Alberta at 3000' above sea level, but may take the odd ride up a couple thousand feet into the rockies?
Here are a couple pics showing how someone mauled the jets. Almost impossible to read now.

 

[GasCans]

I should add...I found an 02 service manual and it shows the carb ID Mark as a Mikuni 8EK100 and I have verified that mark on the carb bodies. Assuming I'm headed down the correct rabbit hole. it notes the Main Jet as #156.3 with a #45 Pilot. Seeing the chart below, does that mean the SX Viper TM33 uses the same sized main jets across all three carbs/cylinders? (I was expecting them to be staggered sizes)

Obviously altitude also plays a role with jetting, but I recall reading some time ago that Yamaha specs the stock jets up until 4000' then requires a jetting change for elevations above mile high for mountain riding. Does this sound correct to anyone with carb jetting experience on these Mikuni's?

 

[littlejohn]

I should add...I found an 02 service manual and it shows the carb ID Mark as a Mikuni 8EK100 and I have verified that mark on the carb bodies. Assuming I'm headed down the correct rabbit hole. it notes the Main Jet as #156.3 with a #45 Pilot. Seeing the chart below, does that mean the SX Viper TM33 uses the same sized main jets across all three carbs/cylinders? (I was expecting them to be staggered sizes)

Obviously altitude also plays a role with jetting, but I recall reading some time ago that Yamaha specs the stock jets up until 4000' then requires a jetting change for elevations above mile high for mountain riding. Does this sound correct to anyone with carb jetting experience on these Mikuni's?

It's common to see a slightly larger main jet on the pto side . It's just fine to jet the same for all three cylinders if you choose to do so .

 

[littlejohn]

It's common to see a larger jet on PTO side carb from factory. You may run the same main jets of your choice straight across the board of you choose .

 

[74Nitro]

The Viper uses a larger CC combustion chamber on the PTO side. Yamaha did this from the factory so that jetting could be the same on all cylinders.
Your jets have a rough appearance because at some point these carbs were so dirty that the rotten fuel ate away at them.
You are right to want to install new jets.
From the 2002 Yamaha tech manual - 1700-3300ft will be 153.8
- 3300-5000ft will be 151.3
Those settings are good to minus 18 celcius.
I would go with 152.5, unless you are running in colder than -18
I'm assuming all else is stock on the machine.

 

[GasCans]

Thanks for that 74Nitro.

Yes machines are stock other than track extensions on a couple. Currently, I have a trio of low mile SX Vipers with one of them being a Deep Snow Special 144", and a pair of them having dealer installed 136" conversion kits. Neither of the conversions have rear tunnel exchangers, just a crossover pipe at the back of the tunnel extensions, and all engines are stock with stock head pipes on them. The one I am servicing now has an aftermarket MBRP can on it, but my son likes the noise so I have left it there for the time being.

We do sometimes ride in colder temps although I'm doubting we'll do much of that this year due to weather patterns (lol). We rode a couple of them in Manitoba last year at -22 to -24 with no issues. Carbs were cleaned last year by a freind of mine but I cannot recall the jetting in the other two. Right now I am doing the carbs on the 02 with the MBRP can. It currently has about 1800 miles (2800 Km) on it. I want to tune it and get the jetting spot on, and next I want to add rear exchangers on the conversion sleds and change out the chaincase oil on the trio.

In the off season, I would next like to learn to tune the clutches and get them all dialed in. The main goal is to ensure I have the alignment and deflection right while having them shift to perfection & launch well.Thinking I'll need a few pointers on this, and will likely need a few new tools as well. A bit for me to learn there I thinks. :-)

Here's the current trio of SX Viper's, and a couple others I have started to collect. Might have a few more 2 strokes coming early in this new year.

 

[littlejohn]

Thanks for that 74Nitro.

Yes machines are stock other than track extensions on a couple. Currently, I have a trio of low mile SX Vipers with one of them being a Deep Snow Special 144", and a pair of them having dealer installed 136" conversion kits. Neither of the conversions have rear tunnel exchangers, just a crossover pipe at the back of the tunnel extensions, and all engines are stock with stock head pipes on them. The one I am servicing now has an aftermarket MBRP can on it, but my son likes the noise so I have left it there for the time being.

We do sometimes ride in colder temps although I'm doubting we'll do much of that this year due to weather patterns (lol). We rode a couple of them in Manitoba last year at -22 to -24 with no issues. Carbs were cleaned last year by a freind of mine but I cannot recall the jetting in the other two. Right now I am doing the carbs on the 02 with the MBRP can. It currently has about 1800 miles (2800 Km) on it. I want to tune it and get the jetting spot on, and next I want to add rear exchangers on the conversion sleds and change out the chaincase oil on the trio.

In the off season, I would next like to learn to tune the clutches and get them all dialed in. The main goal is to ensure I have the alignment and deflection right while having them shift to perfection & launch well.Thinking I'll need a few pointers on this, and will likely need a few new tools as well. A bit for me to learn there I thinks. :-)

Here's the current trio of SX Viper's, and a couple others I have started to collect. Might have a few more 2 strokes coming early in this new year.

You may run your choice of jets across all three cylinders . If you won't to get spot on reading your plugs is going to tell you want needs what and where .

 

[GasCans]

Roger that. Was looking for a good baseline for jetting the carbs and to see if all three were to be the same size or not. Got that now and just about to order some jets this AM. Cheers

 

[littlejohn]

Your jetting chart is your best baseline ...it will never be spot on just ballpark . One jet size down for every few thousand ft above sea level and air temp is just important

 

[74Nitro]

Thanks for that 74Nitro.

Yes machines are stock other than track extensions on a couple. Currently, I have a trio of low mile SX Vipers with one of them being a Deep Snow Special 144", and a pair of them having dealer installed 136" conversion kits. Neither of the conversions have rear tunnel exchangers, just a crossover pipe at the back of the tunnel extensions, and all engines are stock with stock head pipes on them. The one I am servicing now has an aftermarket MBRP can on it, but my son likes the noise so I have left it there for the time being.

We do sometimes ride in colder temps although I'm doubting we'll do much of that this year due to weather patterns (lol). We rode a couple of them in Manitoba last year at -22 to -24 with no issues. Carbs were cleaned last year by a freind of mine but I cannot recall the jetting in the other two. Right now I am doing the carbs on the 02 with the MBRP can. It currently has about 1800 miles (2800 Km) on it. I want to tune it and get the jetting spot on, and next I want to add rear exchangers on the conversion sleds and change out the chaincase oil on the trio.

In the off season, I would next like to learn to tune the clutches and get them all dialed in. The main goal is to ensure I have the alignment and deflection right while having them shift to perfection & launch well.Thinking I'll need a few pointers on this, and will likely need a few new tools as well. A bit for me to learn there I thinks. :-)

Here's the current trio of SX Viper's, and a couple others I have started to collect. Might have a few more 2 strokes coming early in this new year.

That's a nice line up of sleds.

 

[littlejohn]

Nice sleds ....good looking dog

 

[littlejohn]

....yeah! Got a can for a old mtn max hidden in your dealership nitro ?

 

[littlejohn]

The Viper uses a larger CC combustion chamber on the PTO side. Yamaha did this from the factory so that jetting could be the same on all cylinders.
Your jets have a rough appearance because at some point these carbs were so dirty that the rotten fuel ate away at them.
You are right to want to install new jets.
From the 2002 Yamaha tech manual - 1700-3300ft will be 153.8
- 3300-5000ft will be 151.3
Those settings are good to minus 18 celcius.
I would go with 152.5, unless you are running in colder than -18
I'm assuming all else is stock on the machine.

74nitro I'm very interested in your comment about the PTO cylinder having a larger combustion chamber . Would you be willing to share that with me or point me in the right direction to find that info in the service manual ? I have heard many different assumptions why Polaris , skidoo, Yamaha and cat have done this over the yrs . Less cooling from one cylinder to the other , the way the pipes ,pipe flow also because that's where most of the load is ...this is the first I have heard this, I'm pretty new so a good explanation or clarity would be great . Yamaha actually took the time to find tune each combustion chamber ? Did they also do port work on that PTO cylinder ? Brand new ...so be easy on me

 

[Maim]

the srx sleds have all 3 head domes cut the same, so it needs the staggered jetting or that cyl will burn down as one needs more fuel.

the sx viper sleds have one cylinder dome cut more than the others so it has less compression so that they could run all the same main jets.

one thing to look at while you are in there is to see if the needles have been raised on the vipers. they came factory in 02-04 with a lean spot in the mid range that would blow the engine up when run at that range for extended periods. most guys did not have that issue but when their wives/girl freind would start riding them, they would ride in that range and blow the sleds up.

 

[74Nitro]

74nitro I'm very interested in your comment about the PTO cylinder having a larger combustion chamber . Would you be willing to share that with me or point me in the right direction to find that info in the service manual ? I have heard many different assumptions why Polaris , skidoo, Yamaha and cat have done this over the yrs . Less cooling from one cylinder to the other , the way the pipes ,pipe flow also because that's where most of the load is ...this is the first I have heard this, I'm pretty new so a good explanation or clarity would be great . Yamaha actually took the time to find tune each combustion chamber ? Did they also do port work on that PTO cylinder ? Brand new ...so be easy on me

I worked at a Yamaha dealer from 1997 through 2004. Went to the tech schools in Toronto every year.
Yamaha found over the years there was confusion about the staggered jetting and sometimes jets would get mixed up accidently.
Also of note was that the needle jet was different size. Making that chamber a little larger eliminated mistakes being made with jetting.
Porting was no different.

 

[littlejohn]

I worked at a Yamaha dealer from 1997 through 2004. Went to the tech schools in Toronto every year.
Yamaha found over the years there was confusion about the staggered jetting and sometimes jets would get mixed up accidently.
Also of note was that the needle jet was different size. Making that chamber a little larger eliminated mistakes being made with jetting.
Porting was no different.

May I have that information? Where in the service manual would I find this ?

 

[GasCans]

Maim said:
one thing to look at while you are in there is to see if the needles have been raised on the vipers. they came factory in 02-04 with a lean spot in the mid range that would blow the engine up when run at that range for extended periods. most guys did not have that issue but when their wives/girl freind would start riding them, they would ride in that range and blow the sleds up.

I remember reading that the needles should be factory set on position 3, but also recall someone saying to raise them to position 4 due to a lean spot?

Can you shed more light on that?

 

[GasCans]

I picked up an assortment of main jets, gaskets and fuel line hose yesterday. Planning to open up the tops and pull the slides this morning and finish up my benchwork before putting them back in with 153.8 jetting and adding some new new fuel lines.

Where should the needles be set at?

 

[74Nitro]

May I have that information? Where in the service manual would I find this ?

It's in the 2002 Technical update book from Yamaha.

 

[74Nitro]

I picked up an assortment of main jets, gaskets and fuel line hose yesterday. Planning to open up the tops and pull the slides this morning and finish up my benchwork before putting them back in with 153.8 jetting and adding some new new fuel lines.

Where should the needles be set at?

The book says them in #3 which is stock.
Have you ever seen my info about worn needle jets in other threads?