Yamaha TRX850 Enthusiasts Forum

I read that a 4UN is a good upgrade, and if you can afford it, using the full injection system on a TDM900 and a power commander is excellent. (if you want to go along the injection path that is)

Im no expert at electronics at all. What is the difference other than rev limiting ? Does it provide extra tweaking for spark or anything ? and is there any other option for a replacement which would provide more benefit, such as a replacement coil, leads, plugs.. etc..

Thanx in advance.

I understand that the 4UN CDI box removes the top speed limter

Also, it can be further modded to fully advance the TPS and move the rev limiter to 10k rpm

As for FI - I personally don't see it as an advantage of FCRs. And if you use the TDM set up it will be expensive (the PCIII is prob the same price as FCRs)

phuk72 wrote:I understand that the 4UN CDI box removes the top speed limter

Also, it can be further modded to fully advance the TPS and move the rev limiter to 10k rpm .....

Can you tell us what are the advantages of such a mod ?are there any dangers ? how do you do the mod ,,thanks in advance

Normally unless you have some other engine mods (or carbs maybe) then the TRX peak power is well before 8000 revs anyway, so there's little to be gained from allowing the bike to rev further.

Forgive me if I am wrong but that's the way I see it.

That said, UK bikes (is that the 4UN CDI box?) will rev well beyond 8000 revs anyway, well mine does.

What Burty said is right

Stock, the rev limiter is 9.5k - without engine mods you will not see the benefits

Most TRXs make peak power at between 7,500 & 8,500

stop bragging, I'm getting an english box alright.

would be nice for the tacho to get to 7000

Dave E.

burty wrote:Normally unless you have some other engine mods (or carbs maybe) then the TRX peak power is well before 8000 revs anyway, so there's little to be gained from allowing the bike to rev further.

Forgive me if I am wrong but that's the way I see it.

That said, UK bikes (is that the 4UN CDI box?) will rev well beyond 8000 revs anyway, well mine does.

yes my bike is std but i do have the 4un cdi box and some t3 quill end cans ,,i guess if i want to go any faster i will buy a faster bike thanks for all your input though

what mods are needed to make magical power..

Say... carbie, airbox mod, balanced crank, cam and head work ? Oh, corillo rods or something of the like ?

From my experience (im no expert) but if i had the choice of having a bike that makes 100hp @ 7000rpm, or 100hp @ 9000rpm, wouldnt you want it at a LOWER rpm, coz its less work, and quicker to go from idle to 7k than idle to 9k ?

I know for a fact that NASCAR in america LIES about their rpm.. Each team has the tacho "faked".. Weather it be -10% of reading is the REAL rpm, or its 500rpm off thru the entire range.. Its how they hide their engine development.

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