Yamaha TRX850 Enthusiasts Forum

I have just bought a TRX and love it, however I have a problem. My bike has Beowulf stainless pipes with the baffles in situ, a k&n filter and a dynojet kit fitted that was set up on a dyno. At about 5000 revs if I wind the power on there is a pronounced step in the power delivery, the bike will momentarily hesitate and then pick up. If I gently wind the power on there is no problem, If I open the throttle quickly there is no problem anything in between displays what must be just like turbo lag. I am not overly experienced with the TRX so is this maybe normal behaviour, although I will be surprised if it is.

Stock gearing, 17 front 39 rear?
At 5000 rpm a TRX should be very responsive, you say `wind on` so I`m guessing rolling the throttle open in top gear gives this effect?
Can you get the same thing at 5000 rpm in other gears?
Not all dyno set-up`s are good ones, there could be a weak mixture `spot`, or indeed a rich one too.

what throttle position are you in when the "step up" happens? ie 1/4, 1/3, 1/2 etc

About 1/3 throttle opening.

stock carbies?

my first step would be to check the fuel levels are right and the carbs are balanced, then (assuming they are) at 1/3 throttle you are right in the needle jet.

Have a look at your plugs, and see if they are reading lean or rich. (both plugs should look the same)

If lean I would move the clip on the jet needle down a notch and see how that goes. If rich move the clip up a notch.

the page at the link below is pretty helpful

http://www.iwt.com.au/mikunicarb.htm

I do have stock carbs with the addition of the DJ kit as mentioned. All advice greatly appreciated...thanks.

Here`s a thought..............................

A Dynojet kit richens the mixture to accomodate different air cleaner elements and / or exhaust modifications but if it`s added to carbs with already worn emulsion tubes you`re going to perhaps have some intermittant and slight plug fouling issues whan you begin to roll the throttle open, then she clears her throat and picks up again. It`s a bit of an odd one for sure. Does she belch black smoke out of the cans at the point when this happens, maybe just on one side?
Before ripping the carbs off, I would try a pair of new plugs first and see how you go on .

Nice link Con Rod.

I will try new plugs...by the way I think Dave said the imulsion tubes had been replaced. What I might do is put it back to standard and see what happens, thanks again David.

Bean speaking to a chap in the local bike shop and he also says check the plugs and see if it is running lean or rich. One thing I have noticed is the header pipes are very Blue.

Kenvis Repesco wrote:Bean speaking to a chap in the local bike shop and he also says check the plugs and see if it is running lean or rich.

Yes you should do that (as previously suggested).

Con Rod wrote:my first step would be to check the fuel levels are right and the carbs are balanced, then (assuming they are) at 1/3 throttle you are right in the needle jet.

Have a look at your plugs, and see if they are reading lean or rich. (both plugs should look the same)

If lean I would move the clip on the jet needle down a notch and see how that goes. If rich move the clip up a notch.

the page at the link below is pretty helpful

http://www.iwt.com.au/mikunicarb.htm

Kenvis Repesco wrote:One thing I have noticed is the header pipes are very Blue.

The blue on the pipes is normal, but in anycase, it is not going to tell you anything useful for setting your carbs.

This page mostly the same stuff as in the previous page I posted, but also has some extra information for tuning at the bottom

http://home.everestkc.net/malsin/Motorc ... ry_101.htm

First of all I must appologise for my incorrect description of the carburation problem I seem to have. What is actually happening is, at speed and higher revs 4000 revs up if I close the throttle and open it up again there is a hesitation quite a big stumble for an instant and then it revs normaly. If I open the throttle quickly after shutting of its fine. If I open the throttle slowly after shutting down it ok. Its just when I open the throttle somewhere in between. I will whip the plugs out and check those this week as suggested, and if necessary try moving the circlip either up or down depending on the colour of the plugs. Its not a massive problem...it just bugs me a bit if you know what I mean. Thanks again David.

Whent out with my brother today did about 200 smiles. The bike is running like a bike thats running badly. My brother said he could smell fuel sometimes from my bike, the problem also got proressively worse the hotter the motor got, to rich methinks. Got home tank of, carbs out with a view to raising circlip a notch. On inspection of the needle they look really worn, the ends are really rough and uneven so the main jets are probably the same. The needles etc are dynojet items. I was under the impression the kit had been fitted recently(ish) but they are so badly worn I think they have been in there a while. I was given the standard needles jets etc when I got the bike, and they dont seem to be in bad nick so unless the problem is sorted by dropping the needles I may put them back in and see how I go. Am I right in thinking my problem could be down to the worn needle jet. Should I get a replacement DJ kit or new Yamaha needles and jets any advice greatly appreciated.

I had a set of worn dynojet needles in a bike I bought. I contacted Dynojet to see if I could just buy the needles rather than a kit. They asked me to return the needles and sent me a new pair FOC. Brilliant customer service.