Yamaha trx 850 loss of power

[al2244]

I have a yamaha trx 850 super sports it had been sitting for two years old fuel been drains carbies have been cleaned new plugs new battery idles ok rides at very low reves open the throtle and put a bit of load on it dies crackles and pops until it gets back to Low reves any ideas what it is

[jaffa90]

Did you clean all the jets out and check the function of the diaphragms ?

[al2244]

Hi jaffa90
Thanks for the reply the carbies where stripped cleand by an expert apparently a lot of black goo in them hopefully he knew what he was doing and would have replaced anything that needed to be

[jaffa90]

What about the black goo in the tank / tap/ pipes ?
Can you see the carb slides lifting (c.v.carbs) when opening the throttle?

[al2244]

Every thing has been cleaned and double checked their mikinni carbs it's driving me crazy just about to check the coils I don't know what else it could be

[al2244]

Took bike for ride gently throttle on may get up to 3000rpm open the throttle more it dies in the arse pops and farts flat out getting up a small hill in first

[jaffa90]

The pilot systems work mostly up to 3,000rpm, so you need to find out if them vacuum slides are lifting to release more fuel into the engine.
Mikuni BDST38 carb)???????????????

[Snod Blatter]

[al2244]

Ok carbs coming apart today

[jaffa90]

Use google for checking / servicing your carb, i suggest you fit if possible an inline fuel filter in between the fuel tap and carbs.
Talking about a fuel tap is yours a vacuum operated fuel tap and pump as well??????????

[al2244]

There is a spring loaded diafram thing on the fuel tap and a fuel pump between that and the carbies

[Snod Blatter]

The vacuum fuel tap is a load of crap and never works properly but this just means it supplies fuel all the time, it never stops supplying fuel so I doubt it's part of your problem here.

The pump never seems to give any trouble, it barely ever gets mentioned on the TRX forum. I'd be very surprised if it is that.
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[andys675]

my FZR1000 suffered from the slides sticking when left as they're not horizontal check they're opening, bit of wd40 sorted it
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Some people feel the rain, others just get wet.

[Robby]

If the carbs were full of shit, then the fuel system upstream was also full of shit. A rusty tank is likely.

Petrol is an extremely effective cleaner, but the stuff it cleans out has to go somewhere. This means that all of the shit tends to end up in the carbs. Fit an inline fuel filter and be prepared to clean/change it fairly soon. If the filter keeps clogging up, then the tank needs a proper clean out and probably a de-rusting. I won't go into de-rusting in detail now, come back in a month and ask if that needs doing.

Get the carbs out for another clean, and check the settings against the workshop manual while you have them on the bench. My preferred carb cleaning method is the easiest one, buy a couple of cans of carb cleaner, remove everything you can from the carbs, and squirty cleaner through every hole using the nozzle. Make sure you remove the mixture screws and clean out the circuit, it has very small holes so it likes to get clogged. Wear eye protection, carb cleaner will try to squirt you in the eye and it hurts.

This bike may also be vulnerable to emulsion tube wear, it was a common problem on the old TDM850s, tended to become an issue around 30k miles and cause poor running in the midrange. The fix is new emulsion tubes, and you might as well fit new jets and needles while you have it apart. Turns into quite an expensive job for some very small bits of brass.

[Snod Blatter]

They do suffer with emulsion tube wear but it tends to manifest itself as difficult starting and a surging sensation on light throttle. It is recommended to replace the tubes and needles as a pair but I noticed no difference after replacing the needles as well, I wouldn't bother again.

As an aside, if you find you need new seals after all this messing then I can absolutely recommend the kit from Litetek. Even though they're not original they really do fit, and they're cheap and they don't take long to arrive. I was hugely impressed.
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[al2244]

Happy new year
Took carbies of again totally stripped them attacked it all with carbie cleaner then whent over every part with a magnify glass all perfect was a bit of black flake behind one diafram pulled fuel tap and filter apart drowned it all in carbie cleaner checked with magnify glass all good pulled apart fuel pump same thing all good blasted carbie cleaner and air through every hose all clean while carbies where of I blasted wd40 onto valves checked wires to the coils one conecter very lose from cleaning earlier replaced it put back together started lots of blue smoke wd40 idles perfect take for ride heaps mor torqu revs to about 4000 open full throttle dies in the arse pops farts like usual back of and it surges back to about 4000 stil idles fine think I might change all the clips on the fuel lines next

[jaffa90]

Have you found a way of checking my first/second posts?
Them slides have to lift upwards to release more fuel into the engine.

[al2244]

Thanks for the advise after stipping the carbies down for a fourth time poking wire in every hole the bike is flying now the folk seals have poped probably new folks the crome is very pitted

[Robby]

Depends how bad the pitting is. In the first instance I would recommend stripping down the forks and giving the pitted area a good rubbing down with a finishing pad. A finishing pad is like very fine sandpaper, it will attack the fairly soft rust but not affect the hard chrome still remaining.

A fork seal can continue to function for several years on quite a bad surface. The correct fix for pitted forks is replacement (where the chrome often isn't that good) or rechroming (which is nearly always going to cost £200 - a significant proportion of the value of the bike).

Always use genuine Yamaha seals. This goes for any manufacturer. Aftermarket/pattern seals are always crap. I've done many sets of fork seals over the years, back in my younger days I used to try to save a tenner with pattern seals, and I'd be doing the job again in a couple of month. Genuine seals are worth the money.

[Snod Blatter]

You want NOK seals in the size 41x53x8/9.5. If you wish to guarantee this by handing over a wedge to Yamaha then go ahead. Do not buy Nikone, Athena, those weird triple lipped pink things that All Balls were trying to shift or anything else, stick to NOK.

If you find the original forks are absolutely dire in their action (most do) you could look into replacing them with Thundercat right way up cartridge forks. I haven't done it (I went with cartridge emulators instead) but I believe it's a simple swap.
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL