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Hi
POsted this on the club cafe forum but with no luck


I think my Thruxton is running too lean since fitting new pipes.

Only mods on the bike are AI removal, 3 turns counter clockwise on the idle screws and fitted megaphone pipes from Speciality Spares. Also noticed that engine braking is not so strong, as expected with almost straight through pipes.
Bike appears to run well when warm, but when cold starting the choke runs ok for about 30 seconds then the engine nearly dies, even if I disengage the choke. Have to throttle to keep it going above 1000rpm. After a few minutes of warming up it idles ok at 1000rpm

Am I running lean and need to rejet? do I need to adjust the idle screws more?

cheers
healey100
 

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Sounds normal to me.
I dont see what the exhaust would have to do with engine braking, that is set by the idle speed.

Whe its cold (50F), my bike wont run without the choke, and wont idle without the choke till it warms up.

Before any mods, it did the same thing.

I dont like having the choke on, its bad for engine wear and MPG, so I use it to start the bike and turn it off after about 45 seconds, then maintain the idle speed manualy till the bike warms up and idles on its own.
That takes about 5 minutes.

Short of fuel injection, its hard or impoossable to have a carb work the same with a cold and hot engine.
Cold needs more fuel, hot needs less.

The mixture screws on the carbs are fuel screws, out is rich, counter clockwise is out, looking at the bottom of the carbs.
Mine are 3 turns out, and I might do better with bigger pilot jets as 4 turns out seems to be the same as 3 turns....

Brett
 

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Oh, I forgot, you can run on 1/2 choke, or anything between full on and off, after about 10 seconds, I usualy go 1/2 choke...

Brett
 

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Hey Healey,

I'm in Adelaide and ride a Thrux with same mods (Madaz not SS mufflers). My bike exhibits pretty much the same symptons except it runs a little longer on choke before cutting out. Try turning the idle screws out another half turn, especially if its popping on deceleration. Peter Stevens fitted my mufflers and played with the idle screws. They were adamant that Thruxs don't need rejetting with just a freer flowing muffler.
 

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Though the main jets may be right, you may wish to try shimming up your needles a washer or two. This will enrichen your midrange and smooth the transition between the idle circuit and the mains.
 
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