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jays22b

07 yz450fw and new high comp piston 13.5:1 carb setting

4 posts in this topic

Hi guys been awhile, Anyway yamaha shop talked me into a 13.5:1 piston even thou i dont race. It's in and running ok but it's running way to lean. I think the bike was a little lean when stock but ran well for me. Now the exhuast is glowing on warm up and on warm days it's starting without choke and starting to pop a fair bit.. ( i have not road tested bike with new piston yet , bit scared to ).

 

So I need to richen the mixture abit now and never played with the carb and asking for advice on which way to proceed.

 

Shop said to change clip position but I'm reading drop a bigger main jet in. Becuase of how hot it's getting within the warm up's in the shed I'm not sure if it's worth playing with the needle and just go straight for main jet. I can get the whole header pipe glowing red hot inside of 1minute on 1/3 throttle or less even to the point of going passed red to white , and thats were i shut it down before i destory it.

 

anyway this pic is what i call normal

135to1normal.jpg

 

 

and this pic about the same test conditions is now inside of 1 minute again. Very warm day.

Screenshot_2014-11-30-16-35-11.png

 

 

 

So i ride in winter normally but there's no way Im leaving it set like this and have the next 3-4 months to sort it out before our Australian winter comes back..

 

So what do u guys think ?

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The header glowing is simply letting it run with no airflow over the engine.  The point bump in compression shouldn't make a bunch of difference in the jetting.  At most it probably needs a fuel screw adjustment or up a size on the pilot.

 

I ran 13.5 pistons in my 07 with pump gas with no issues with the same jetting as stock compression pistons.

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Ask yourself: if it starts without the choke (a device that makes the mixture richer for cold starts), how is that an indication that it's lean?

 

The main jet and needle height have zero effect on idle, BTW.  You probably have your idle turned up too high combined with a pilot jet circuit with too big a jet or the fuel screw backed out too far. 

 

Either way, Mike's right, let it idle at a standstill and the header will glow.  It's .040" thick (or thinner) titanium.  Red heat visible in low light is about 800 degrees.  Normal exhaust temps are 1300-1500.  What do you think is going to happen?

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Ask yourself: if it starts without the choke (a device that makes the mixture richer for cold starts), how is that an indication that it's lean?

 

The main jet and needle height have zero effect on idle, BTW.  You probably have your idle turned up too high combined with a pilot jet circuit with too big a jet or the fuel screw backed out too far. 

 

Either way, Mike's right, let it idle at a standstill and the header will glow.  It's .040" thick (or thinner) titanium.  Red heat visible in low light is about 800 degrees.  Normal exhaust temps are 1300-1500.  What do you think is going to happen?

Yeah sweet, thanks for the info. The tail pipe is clean without excessive carbon build up so i assumed it was not rich also. alway been that way from new. And when writting post I knew it sounded funny saying without choke but unsure of my self and wanted to give correct info for dianostics .

 

I make billet steel and know what liquidess of low med and high carbon steels , but not titainium etc. Your correct that u see low light red at 800 degrees C i just thought this was excessive the amount of heat been produced from the upgrade piston.

 

Some more info on steel liquidess for u for reference

 

Low carbon steel 1520-1530 deg C .. carbon range 4-13       small rod for concert

med carbon steel 1510-1520 deg C .. carbon range 14-30    Large angle for construstion

high carbon steel 1510- 1450 deg C .. carbon range 30-75   jack hammer bit    (in the cooling process we can split a  150x150mm billet in half if not carful)

 

The alloy component has is big factor on these too but for the general publics info there basic temps . The liquidness is were it goes from liquid to solidifaction process.

Enough of that anyway, 

 

Thanks once againg Mike and Grayracer , Im of to learn about pilot jet circuit with too big a jet or the fuel screw .

Edited by jays22b

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