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Post Info TOPIC: Belgian TTR carb setting issue


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Belgian TTR carb setting issue
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Did a first testride today on my secondhand 2006 TTR.

setup at purchase :
 
Stock airfilter with airbox snorkel
Stock exhaust with restrictor removed
50 pilot jet 
147 main jet
14 x 48 chainset
 
After carb clean replaced all o-rings + diaphragm + checked acceleration pump (ok)
 
Starts fine and revs out when not driving.
Once on the road the bike hesitates, splutters from 1/4 + midrange.
Impossible to lift the front, even in first!
After ride sparkplug inspection : black
All these symptoms made me conclude that bike was running too rich.
 
So i made some modifications:
- removed snorkel + installed twinair filter
- new 54 pilot jet
- new 150 main jet
- clips needle one position higher, leaner (second from bottom) 
 
Starts fine and revs out when not driving.
Once on the road the bike hesitates, splutters in midrange but bit less than before.
Still impossible to lift the front, even in first!
 
Because i thought the bike was still running too rich I decided to remove the side panel of the airbox.
Now the bike's response is much better but still not flawless.
No wheelies so far..
 
Can I conclude that my configuration is still (way) too rich?
Should I change clips position on needle or reinstall the original jets?
Are there other points to check, eliminate?
 


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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



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Hello Brian,

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

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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?

 

image.jpg



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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



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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)?

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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.

 



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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.


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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 :)



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