My rx has a large streetport 13b with a 51ida. Im just wondering what jetting everyone are using such as idle, air, main etc, as im trying to re-jet my carb due to a flatsport up to 3000 rpm. Otherwise, it haul *** with no problem

 

your flat spot is probably due to the 51ida having such big chockes and at low rpm there isnt enough air speed. many people call that the undrivable part of a weber as you said as it hits 3000 rpm's it takes off, that is the air speed building up. I havent heard of any one that uses a 51 ida on a street port. try going down a few sizes in the jets

 

Wacky,

What size venturis do you have in your carb? Is this a street car?

Chuck

 

The 51IDAs are usually reserved for bridge and peripherial port race motors.

For a 48IDA on a street port, Racing beat recommends
Venturi: 38mm
Fuel jet: No. 190
Air jet: No. 160
Emulsion tube: F-11
Needle valve: No. 250


Cody

 

this car is a daily driver with a 13b-4port monster streetport. its true that the 51 is set up for higher up portings but when i switched from a 48 to a 51, i noticed an improvement on top end. my prior 48 had 43 venturies with 240 main but not enough to give me goose bumps. At the moment, I’m using a 40 venturies and playing with different settings. I’ve also tried the racing beat’s recommend setting but I felt that its not sufficient for large ports since rb template is smaller.

 

Wacky,

If you're going to run larger chokes and try for more peak HP, you're probably going to have to live with that flat spot. Personally, for a daily driver, I would go with smaller chokes to give it more bottom end, but that's just my personal opinion.

My race car engine is a 12A with what would be considered a monster streetport and a 48IDA. The rules of our class limit us to 38mm chokes, so that's what I run. I have F-11 emulsion tubes, 185 air, 195 fuel jets (most of my races take place at about 1,000ft above sea level) and a 300 needle and seat. It makes great top end power, but it's a pig under 6,000RPM. At 8,400RPM, it produces 196 RWHP. At 5,400RPM, it makes a pathetic 107 RWHP.

One thing you might try if you don't want to go with smaller chokes, is larger idle jets.

 

thanks for the info everybody. i appreciate it.
btw chuck, what idle jet do you use.

 

Wacky,

I'll have to measure them to tell you. I had F65s in there, but we ended up drilling them out at the track one time to make them larger.

Chuck

 

i've got the same thing. drilled out f65 but dont even remember the size. basically, what i am getting into is that im planning to lower the idle jet just to see what if the performance will change.