Yamaha TRX850 Enthusiasts Forum

Greetings to all,
Alcohol blend fuels are becoming a fact of life and sooner or later we are going to have to deal with it.
Viton is the best elastomer choice for ethanol blend fuels. If you want to know more about Viton(FKM) then read this excellent document produced by Oak Ridge National Laboratory
http://info.ornl.gov/sites/publications ... b27766.pdf The conclusion of that document is that Ethanol blend fuels are worse than pure Ethanol and that NBR, what your carb seals and o-rings are made from. is the worst material to use.

Now the richness problem with Mikuni BDST carbs, which I am sure many of you are aware of. Most carb seals are there to stop the fuel leaking out. However, the BDST carbs have seals that stop fuel leaking into the throat. They have to be in top condition or your bike will run rich and no amount of fiddling with float heights, mixture screws, main jets or needle clips is going to solve your problem. Please read this assembly guide http://www.litetek.co/Guide_MikuniBDST_ ... gAssy.html Also check the condition of the needles and emulsion tubes. There are several good guides on the internet that discuss wear of those two parts and Factory Pro http://www.factorypro.com/tech/needle_jet_wear.html is one of them.

Now where does all this come from? Well I own an FZR400 which uses the same carbs as the TRX850. I have been developing carb kits in Viton for various models and the TRX850 and Ducati Monster and SuperSport are coming on stream now.

I am aware that there is a no advertising policy on this forum, as there are in most, and I apologise if my post is seen that way but I prefer to see this as an infomercial. A member could stumble across my website and post a link to it here but I would prefer to introduce myself and let members know that I control the production of these parts so if you have a problem or a special request then it can be dealt with promptly.
Here is a direct link to the TRX850 page http://www.litetek.co/Carb_Kit_Yamaha_TRX850.html
cheers
Blair McIntosh

That's very interesting. Do you know if the kit is also suitable for the carbs on the 4NX (1995 Japanese market) version with accelerator pumps? Or are all these carbs basically the same?

I am sorry but I don't have a copy of the part numbers for that model. The Yamaha numbers are all on the web page, so if someone can point us to a source for the parts book that suits the 4NX then it will be simple enough to check. If there are any differences I should be able to put together a kit for that model without any difficulty. Lead time is about two months if I have to make complex seal shapes like float bowl seals.
cheers
Blair

Not sure what problems people have experienced with NBR seals as a result of ethanol in fuel?

Any elastomeric O-ring seal will swell to some extent when immersed in any fluid. The extent (but not the rate) of swell depends on the solubility parameter of the fluid and the elastomer combination.

Nitrile Butadiene Rubber (NBR) will swell in ethanol (but only to a low level; approx. 5-10 mass %) but it is worth remembering that O-ring seal function is dependent on many things and can be enhanced as a result of low level fluid swell. Swell only becomes a concern where it causes the seal to fill the groove volume completely at which poiint seal extrusion can potentially occur. This again does not necessarily mean that seal function will be lost.

At ambient temperature NBR will not age chemically at any appreciable rate. Much higher temperatures would be required.

The only thing I can think of that may be relevant is the possible leaching of processing components from the elastomer as a result of fluid absorption. This can cause an increase in seal modulus (stiffness) but the swell due to fluid uptake would probably offset this.

A more likely phenomenon is seal function being compromised as a result of compression set where extended seal compression changes the cross section diameter (CSD) hence reducing the seal contact force. Physical set can be removed by warming (with seal unconstrained) and then replacing the seal; chemical set (due to crosslinking) is permanent.

I agree that Viton would be preferable to NBR for sealing in hydrocarbon environments. It has a far higher temperature capability and chemical resistance is also excellent. There is of course a whole world of Viton materials (Type 1, 2, 3, 5) depending on compounding/application and each of them has specific material properties.

Better stop before I put myself to sleep!

maelstrom wrote:I am sorry but I don't have a copy of the part numbers for that model. The Yamaha numbers are all on the web page, so if someone can point us to a source for the parts book that suits the 4NX then it will be simple enough to check. If there are any differences I should be able to put together a kit for that model without any difficulty. Lead time is about two months if I have to make complex seal shapes like float bowl seals.
cheers
Blair

Unfortunately I've never seen a parts book or workshop manual for the 1995 model, but do some BDST38s come with accelerator pumps? And if not, where are the markings to identify the model of carb as I have looked all over and can't see a thing on them

Greetings maelstrom / Blair.
Send a personal message to Jak, she`ll set you straight with advertising policies etc of the site. I`ll let her know she can expect to hear from you.
Oh and misterdimwiddy, anorak wearer?
No seriously, great information lads, the ethanol issue is only going to get worse as the 10% by sold volume gets introduced, my Skorpion has an Ascerbis made plastic tank that`ll be feeling the ravages of it too.

Mincehead wrote:Greetings maelstrom / Blair.
Send a personal message to Jak, she`ll set you straight with advertising policies etc of the site. I`ll let her know she can expect to hear from you.
Oh and misterdimwiddy, anorak wearer?
No seriously, great information lads, the ethanol issue is only going to get worse as the 10% by sold volume gets introduced, my Skorpion has an Ascerbis made plastic tank that`ll be feeling the ravages of it too.

Mince

Apologies for my momentary outburst.

I work in the oil and gas industry doing elastomeric seal failure analysis and non-metallic materials research and development.

Someone's got to do it!

Will refrain from further comment.

Nooooo, your knowledge of such things is interesting and useful around the forum.

Quite a few members here went through fuel tap failures in the last couple of years. My thought was that was related to ethanol in fuel as well. Even buying the better quality fuels is no guarantee as shonky service stations are watering down the premium with ethanol and not just 10% either. I haven't had any problems with my Keihin FCR's yet but will there be a kit available for them i wonder?

misterdimwiddy wrote:

Mincehead wrote:Greetings maelstrom / Blair.
Send a personal message to Jak, she`ll set you straight with advertising policies etc of the site. I`ll let her know she can expect to hear from you.
Oh and misterdimwiddy, anorak wearer?
No seriously, great information lads, the ethanol issue is only going to get worse as the 10% by sold volume gets introduced, my Skorpion has an Ascerbis made plastic tank that`ll be feeling the ravages of it too.

Mince

Apologies for my momentary outburst.

I work in the oil and gas industry doing elastomeric seal failure analysis and non-metallic materials research and development.

Someone's got to do it!

Will refrain from further comment.

Please don't mister - I just thought you'd swallowed a dictionary and it erupted into keyboard fluidity....................a whirlpool of information - as I'm sure maelstrom will agree

I think every one of these replies is well worded and says a lot about the forum members. The TRX is a good design and probably attracts those that can appreciate the bike from an engineering point of view. As for the ethanol issue, obviously those that live in the US already know about the ethanol situation and the more information we can get the better. I have had owners of the V4 Hondas asking for complete 'ethanol' kits that include hoses etc but I think the owners can source these material locally easier than importing.
For Kevtrx, Yes we do plan to make Viton kits for the FCR carbs.
misterdimwiddy, judging from my experience with my Yamaha 400, the embrittlement and loss of material is the most significant downside to NBR. Please refer to Fig. 23 on page 32 of the document that I referred to. It is just not ethanol, but stale fuel also shortens the service life of NBR, and quite rapidly, caused by the crosslinking that you referred to. Reference page 13 of VitonExcellingInModernFuelSystems.pdf by DuPont.
cheers
Blair

Interesting information Maelstrom, thanks for posting.

I always avoid anything with Ethanol in the bike, but there will be a day when I can't, I guess.

I always avoid putting it the car because its a false economy!

Kevtrx849 wrote:Quite a few members here went through fuel tap failures in the last couple of years. My thought was that was related to ethanol in fuel as well. Even buying the better quality fuels is no guarantee as shonky service stations are watering down the premium with ethanol and not just 10% either. I haven't had any problems with my Keihin FCR's yet but will there be a kit available for them i wonder?

That's why I'm gonna fit the FCRs as soon as I can

Bob

Mincehead wrote:Nooooo, your knowledge of such things is interesting and useful around the forum.

I would be pleased to offer any help or information that I can re: elastomer compatibility or sealing issues

Do you make any condoms out of this stuff too... Had a few break down so maybe I might get a bit of extra Mileage from Vitoms