A forum for owners of Yamaha TTR250 trail and enduro bikes!

Spietfriek · Member

Belgian TTR carb setting issue

TTRfan · Super Guru

Hi Nicolas

Sorry you have not had a reply but our TTR carb expert, Jarrah, has moved house and we haven't heard from him in a while cry

Before doing any more with the carb, have you checked the cam timing is correct? If not, it's worth doing as your symptoms point in that direction.

There are a few threads showing how the timing marks on the cam sprockets should line up with the head casting when the engine is at TDC but can't immediately find the thread I am looking for disbelief

Brian

Spietfriek · Member

Hello Brian,

I will do a quick inspection next week and come back on this afterwards...

Spietfriek · Member

Checked my cam timing today.

To my opinion not perfect, but not dramatical as well.

Should I change the timing chain right now or will it last for a couple of thousand km more?

TTRfan · Super Guru

Hi Nicolas - sorry not to have replied before. I thought I had but the reply got lost somehow confuse

The chain is not as worn as some I have seen and probably will carry on for a bit. The crucial thing is that the tensioner is taking up the slack so that the chain doesn't jump a tooth or two and end up bending valves. Is there plenty of resistance when you push down on the chain between the cam sprockets? If so, you are probably OK for a bit longer, especially if you aren't getting a "whooshing" noise from the chain.

I find it difficult giving this sort of advice because, if I get it wrong and your engine ends up damaged, we will both be very very unhappy so it has to be your judgement in the end.

It would be good to get some opinions from other knowledgeable members wink

Brian

brindabella · Senior Member

let me ask some dumb questions..

1. were the valve clearances ok, as that could effect performance too (independent of cam timing issues)?

2. if it appeared to be running rich, why did you install bigger numbered jets,
which could make it worse (assuming the jets are the same brand as the originals replaced)?

3. when you say the needle clip was moved to "second from the bottom",
is this "further away from the pointy end" (which would give an appropriately leaner mid-range)?

Spietfriek · Member

Hi Brindabella,

Sorry for the late answer, but I was on holiday.

- I did check the valve clearances and they were in spec (only outtake was limit), will be a winter job to resolve..

- I did install a larger jet because I thought that with the removed restricor it was needed.

- needle clip was set one step further away from the point edge

Meantime I did some more changes and here is my feedback :

First I went back to the original setup

Stock exhaust with restrictor removed

50 pilot jet

147 main jet

and did following additional changes

- 13 x 48 chainset

- made a large hole in the airbox

- needle clip one step further away from pointy edge ( now in centre)

- new iridium spark

CONCLUSION :

Bike is behaving much better but still a litlle dip just before midrange.

Revs out easier with the 13 tooth as well..

Perhaps I move the needle clip another step further away from pointy edge.

Wheelie in first only with a little help but I can live with that.

brindabella · Senior Member

that sounds good - maybe as good as it gets?

I'm no expert, but if you now have the clip in the standard position, you could afford to experiment going
one step leaner on the needle (especially if you ride at some reasonable altitude above sea level).

And then, if you had the time and were feeling like more experiments, you could try the
richer pilot (I have a suspicion that might be a better move than the rich main jet).

And finally for more fun, you could try temporarily taping over the hole in the airbox,
just to see if that alone can make it worse, justifying the hole (or not).

I guess by now any effects of changes will be very small, and may be even masked by such things
as the weather conditions, or fuel.

Let us know how you go.

PlumasDude · Senior Member

Sounds like its still rich, any pops/backfires on deceleration? Like Brindabella says probably the easiest thing to try would be to keep moving the clip to the lean and/or try smaller main jets (perhaps starting with 137).

Choke working properly?

I'm a terrible mechanic, but your situation sounds common -- you get the bike with a gummed up carb but it runs reasonably well, you clean the jets thereby letting more fuel through and it ends up too rich, so the first step might be to go leaner on the clip, and if that doesn't do it try a smaller main jet. That worked for me. But the carb cleaning should just take it back to stock condition -- why you would be so rich with the stock set up I don't understand. (My US model was rich at the stock settings even with a 137 main jet.)

I think the guys running oversize main jets are setting the clip very lean and using a less restrictive pipe; but they're all in Australia ... so maybe you need to turn the carb upside down :) Or, maybe in Belgium you need a special BELOW sea level set up :)