Carb jetting?, I got lots of top end, no bottom Options

[r_towle]

Slower velocity intake charge created a motor that lugged off the line, ran poorly under 3k rpms but scared the crap out of me (a big smile) from 3k -7k rpms...


EXACTLY what Zach's engine was doing on the ground with no load on it

In the old days a 48mm intake valve was the way to go...that is what FAT did...
Bigger was better. Bigger carbs, bigger valves.

Well, now we are here, today.
The smaller valves matched with the smaller venturi creates a faster speed, or higher velocity intake charge. 44-46mm intake valves are more the norm nowadays...44mm intake valves with the right cam are amazing if tuned right.
This introduces more air speed and a finer atomised mixture into the intake valve.

the larger carb venturis that Zach has do two things.
the air moves slower and so does the fuel...so the atomization is not good until you hit the VE of that venturi...so when you hit 3k rpm it takes off because NOW you have the velocity to actually do a decent job of atomising the fuel...

Big vents require big main and idle jets and a bigger qir correction jet.
All of the larger jets are just compensating for the slower intake charge.
The net result is the car will run, but not optimal.
It will get worse gas mileage.
It will run like a raped ape at WOT.
All of that is basically how you tune a race car/autox car that gets trailered to the event. These cars get 10 mpg.

For street you want smaller vents, more intake velocity and smaller main/idle/air correction jets.
Also think about the F7 emulsion tube that tends to produce a better transition circuit for street...again the F11 is great for a race car/autox car but sucks for the street...this is the classic 2800-3200 stumble that people speak about...

Rich

[Dr Evil]

(IMG:style_emoticons/default/popcorn[1].gif) learning a lot in this thread (IMG:style_emoticons/default/smile.gif)

[rhodyguy]

another thing to consider if you go chasing leaks. check the bases of the intake manifolds. used ones have been torqued countless times. overly so i think. if the bases are out of true the leak will be built in.

k

[r_towle]

another thing to consider if you go chasing leaks. check the bases of the intake manifolds. used ones have been torqued countless times. overly so i think. if the bases are out of true the leak will be built in.

k

(IMG:style_emoticons/default/agree.gif)

Standard setup is like this
head<>gasket<>spacer<>gasket<>intake manifold<>gasket<>optional spacer<>gasket<> carb

where you see the <> I use red, high temp rtv gasket material...a light coating so it does not ooze out..

Rich

[rhodyguy]

and...do not use steel cut washers under the intake stud nuts. this is where the (overly so) factor comes into play. what works real slick are the schnorr (sp?) washers used on the cv joint bolts. is does not take alot of pressure for them to do their job.

k

[904svo]

I also had a leak on my carbs which I chase for over 2 months. Found out that
the cooling tin which goes around intake on the heads was not recessing correctly
when the gasket and intake manifold were bolted on, the sheet medal was holding
the gasket and manifold up, although it look sealed. I lossen the sheet metal and
position so it was fitting right, below intake ports, added new gasket with rtv, No
more leaks!

[jmill]

[/quote]
My floats are both ~10 to 11 mm when closed. I have not measured the max open position, but the Weber tech book says that is not very important.

Zach
[/quote]


Max open is important. The lower the float goes the farther the valve opens. If you limit the opening you limit fuel volume when you need it the most. When the float bowl is almost empty.