Flat spots on very low throttle.

[dandywarhol]

Glad you've got it sorted ☺

[goose202]

Ok, so a longer ride has shown this is not fixed. As I mentioned, I hadn't changed any settings in the carbies, simply put the new seals from the Keyster kit through it so this is doing my head in a little. Posting this as much for a record of what I've done as anything else.

Pilot screw at 3.5 turns out made it better but there's still a big flat spot.
The (unknown) aftermarket needle clips were on second from top groove, so I raised the needles one clip, and set the pilot screw back to 2.5 turns. Probably should have only changed one thing at a time, but anyway. Flat spot is still there. Even cruising at 110km/h (4000rpm) you can feel it surging. Pulling the choke on seems to fix it.
So now I've set the pilot screw back out to 3.5 turns out, haven't ridden it again to test.

Needing to go one needle clip and another full pilot screw turn after simply replacing seals doesn't seem right to me. Perhaps the float levels were way off before or something. Perhaps I broke something. But idle and big throttle seems good.
Next step if this doesn't fix it I think is to chuck the needles, emulsion tubes and jets from the Keyster kit in, carefully inspecting everything as I go, and see what that does.

[dandywarhol]

Pulling the choke on throttle shouldn't affect it as the choke circuit is bypassed after idle.
Did you change the choke/enrichener seals?
Mine were very brittle and perished when I replaced them with Litetek Viton seals. The carbs can draw air past those perished seals at light throttle.

[goose202]

No, I didn't touch the chokes. But that's another place to look, perhaps they have started leaking.

[dandywarhol]

No, I didn't touch the chokes. But that's another place to look, perhaps they have started leaking.

Here is the enrichener seal that came out mine. I used a Litetek kit http://www.litetek.co/Carb_Kit_Yamaha_TRX850.html , cracking value and ethanol "friendly"

[cobbadiggabuddyblooo]

Check the air cut off valve cover ... It's the plastic white disc on the side of the carby.. They deteriorate over time and seems a common issue popping up now with the TRX aging gracefully..

http://www.kedopartsaustralia.com/searc ... uery=28211

Internal Rubber Valve kits are also available.

[goose202]

Continuing on the "log" of my saga.

Last ride showed that the problem is still there, although I think reduced a bit.
Choke plungers are good. No cracked air cut off covers.

So I've put the stock needles, tubes and jets from the Keyster kit in. I'll see how that goes. Haven't got past checking that it still starts.

[cobbadiggabuddyblooo]

Ta da problem solved .. Yes ???

[goose202]

I'll let you know after I ride it next, cobba!

Family and work means I tend to get plenty of opportunities to get stuff done in the shed but not so much to actually go for a test ride...

[goose202]

Just got back from a ride.

Still not good. It feels just the same. So I'm running out of ideas.
Idles fine. Bigger throttle openings (say >35%) fine. It feels exactly like I'm about to need to switch to reserve, but as I wind on the throttle it clears and goes.
Trying to cruise 80-100km/h doesn't work too well, it's just lightly surging the whole time. Pulling the choke on does seem to help.

So given that pilot screw settings didn't fix it, different pilot jets, main jets, needles and emulsion tubes didn't fix it... what now? Remembering that it was all running well until I put new seals in.
When changing over the jets and needles, I confirmed all the seals looked fine (ie I hadn't pinched one or something like that).

What I haven't tried is putting the old float valves or pilot screws back in.
I think that's where I'm at - put everything back - seals and all, and see what happens.

It does feel like this is a problem with tuning on both cylinders, although I couldn't be sure it's not just one that's the problem. It had crossed my mind that perhaps there's some muck blocking a passage in one carby somewhere.

[Bostel]

Could it be the rubber that sits between the carb and manifold?
Maybe the rubber was already a bit worn through age, then you took the carbs off and put them back on again and damaged it a little more by fiddling with it?
Just thinking with you.

[cobbadiggabuddyblooo]

I think if they haven't been replaced previously by this time they would be a recipe for disaster as will be the air cut off valve plastic cover. If they haven't gone by now, they wouldn't be far off and will only frustrate you once again not far down the track.

[goose202]

Bostel, that's certainly a good suggestion and I have checked them out. They are not in brilliant shape but they certainly don't look bad enough to me that they'd be leaking.
Although that does make me wonder about the fuel tap and pump. I wonder if they are able to leak enough to still function fine but cause tuning problems.

Cobba, what's the symptoms of the air cut off covers? Doesn't that normally cause popping and backfiring as a first symptom? I'm not seeing any of that. Not to suggest that this can't be the problem with mine (although they do inspect fine, I haven't pulled them off to inspect closer though).

[cobbadiggabuddyblooo]

Rod had similar issues as you described, he even tried covering the plastic cover to seal any possible leaks.
He bit the bullet and spent $20 and bought a new plastic cover and problem solved.

[goose202]

Ok, interesting, thanks.
They appear out of stock at the moment though in the link you previously provided.