wpgrexx

Hi all, first off I will give engine details.

old skool 13b 4 port
-Cermet B rotor housings clearanced for 10000rpm
-MFR stationary gear bearings and MFR hardened gears
-RB adjustable rear oil regulator, and shimmed front regulator.
-s4 na rotors and crank- new Mazda 2 piece 2mm apex seals, New Mazda 2mm corner seals(no plugs), FD corner springs, new Mazda side seals(clearanced to .003" and doubled springs on center plate side).
-all new viton seals and Mazda Water seals
-matchported oil pump land
-bridgeported just up to the water seal and small notch on the housing. Exhausts ported also
RB headers to 3 inch collected exhaust


Now I have a RB modded Holley 550cfm carb from a SP 13b 4 port. I am having issues with getting this carb to idle lower than 2500rpm. I cant really find any info on what RB does to modify carbs for bridgeports. I have been researching general Holley mods, and what I have found is that for v8 applications where a wild cam is used and there is overlap between intake and exhaust(like a bridgeport on a rotary) and where there is low idle vacuum, they recommend drilling some holes in the primary throttle plates. And if needed opening up the idle mixture bleeds.

Before I start drilling into a good carb, has anyone ever heard of this or done this. Or alternatively, does anyone know what RB does to their Holleys to make them run correctly on BP.

Also, I have a freshly rebuilt(MAzdatrix) Dellorto 48mm DHLA and manifolds. Will this potentially work "good" on my engine?

Jaime Enriquez

I think the 550cfm is way to small for a decent bridge...I'm pretty sure they run 650DP's on bridgeports. I ran a 600 on a streetport.

GLC13B

I myself have never seen a anything smaller than a 6oo Holley on a BP motor ! That carb my be to small for that type of setup.

mwatson184

There is a small screw on the secondary side that will open up the secondary throttles. Open them up a bit, and close up the primaries about an equal amount. Then you will be able to control your idle mixture a lot better with the mixture screws.

The problem you have is. You have uncovered the transition slots at idle, which completely takes away your ability to control idle mixture.

-Marques

wpgrexx

Well, no worries about that holley. I would agree with what you guys said though, the 550 is too small. I put the Dellorto on, just got it back from Mazdatrix yesterday. Started right up first try. I now have it idling at 1000rpm.

Any recommendations on total advance for ignition. running 2nd gen coils, Jacobs Rotary pro pak on the direct fire leading.Thanks for the input guys. So happy to hear this baby idle at a grand. Revs up super quick.