Weber IDF Main jet help Options

[tornik550]

I am in the process of tuning my car after a rebuild. I have dual weber 40's. My engine is a 2.27L. Everything is going pretty well. I am slowly getting the jetting closer and closer. I was driving around at about 60mph yesterday. The head were hotter than I like (325 degrees). I checked the spark plugs and they were bone white. The main jets were at 160. I increased them to 170 (above 160 I only have increments of 10). With the increase to 170, the car is running very well and the temp at around 60mph cruising is around 275. I sped home, tuned off the car and took out the plugs- bone white. I was quite surprised.

The main jet size sounds high too me. Does it sound high to everyone else? Is it possible that I am needing a high main jet size because of the float level? I have my floats set at 10.5 with the gasket.

Any opinions would be greatly appreciated

[jmill]

Increasing the float height will not change the mixture unless you mess up and allow the bowl to overfill. The float work JUST like the one in your toilet tank.

When setting the float closed height (10mm or 11mm) make sure you don't compress the ball spring on the needle valve. You want the needle valve seated/closed, but not compressing the ball. If you do this wrong, your bowl will be too empty.

Fuel pressure will also not affect mixture, unless you set it too high and it blows the needle valve off it's seat. But there will be NO general mixture change between 2psi and 3psi.

Be careful. There is a LOT of misinformation about carbs out there.

You aren't kidding about misinformation.

As you increase or decrease float height you change the height of the fuel column inside the main fuel wells. The emulsion tube sits in that column of fuel. Air is sucked in through the AC jet and pulled through the center of the ET. This emulsifies the mixure which then enters the carb through the center of the venturi. The higher the column the richer the emulsified mixture.

As far as fuel pressure, the float has to fight the needle against fuel pressure to close it. The higher the pressure the harder it has to fight. With higher pressure what you actually end up with is a float that sinks a bit before it can shut of the flow. That gives you a higher float level. See above why that affects your mixture.