I am using 48 IDA Weber,not 51 on 13B 4 port, bridge ported.

The jetting size is:- main=225,air=140 and choke=42mm or main=180,air=140 and choke=39mm

which one is the best ? or any comment please.



Thanks

scot

It does not work just exactly like that. Not is "A" Better? or is "B" better?



For the best throttle response I would go with the 39MM venturies.



The main jets move the whole range to richer or leaner. Bigger number = richer.



The air corrector changes only the top of the range where most of the fuel is entering through the booster (or auxillery) venturi. Smaller number = richer



The emulsion tube adds air to the booster flow and is used to taylor upper and mid range.



I have F-7s, F-8s, and f-11s. I have only every used the F-7s.



A single number change in the main jets is about the same as a two number change in the air correctors.



There are only 4 people on earth that can dial in a Weber dead on for the whole range, and that tune only lasts a few minutes. But with a Weber, close is real damn good. (PS) I am not one of those 4 people.



Don't forget to drill out the land hole where you remove the plastic filter (under the brass cover nut).



Use a 350 Gross jet for the needle set, and run the float a little low with extra fuel pressure. We use 6 PSI with a Gross jet and never a problem. Normal for a Weber is 3 1/2 to 4 PSI

On a short straight you can empty the float bowl and go lean and miss a bit. Watch for that. Richer is better.

There are two accellerator pump tubes. Only one is used. Drill a hole, or use a 1/4" ball bit to cut a hole at the very bottom of the unused tube. Notch the top so that it cannot seal against the cover gasket.

There you go, More bowl volume.



That should have it running real well. Timing 22 to 24 BTDC. One ounce of 2 cycle oil per galon of 93 octane pump gas with no alcohol. Oil pressure 100 PSI.



Take movies of your EGT and tach at the same time.

Tune (richer/leaner) for about 1590-1600, that is about 13 to 1 A/F. Stay between 12:1 and 13:1 A/F and you won't hurt it. Allways tune at the same RPM. Like 7,500 or 8,000 RPM. Try to do it where you have not been side loaded for a second or so.



Just barrow jets to tune with. Then buy a set like the ones that run best. Buy jet numbers either side of those. Give the loaner jets back. Otherwise you end up with a 10 pound bag of jets nobody on earth can use.



It should last a good long time.





Lynn E. Hanover

Lynn,

Thanks for your comment

48 IDA's bowel and inlet land hole has been machined out, I am normal using 180 main,140 air,f7,39 choke and 3.0 brass inlet jet

But try change to as 42choke,225 main,140 air and f11.

The reason of change items is for "showmanship" which i am trying to produte the famous rotary rear exhaust flame that I never heard people making comment about it( not on the highway,but at race day).

I am going to buy a 3.50 gross jet from Mazdatrix.



Scot

Go way rich on the idle jets for the fireball. That and an air leak will give you a fireball and a report like a cannon. A real strong muffler of the round design will stand up to it. A flat style will not.



On a long spool-down from top speed the engine needs the richer jetting if you premix. No fuel at high RPM means no lubricant for the apex seals. The richer mix gives them a bit.



Lynn E. Hanover