Greetings everyone,

I imported a used Racing Beat Holley 465 intake system for my stock-port 1983 RX7 which has the stock 12A and automatic. The system starts and accelerates well but I've never been happy with the part-throttle acceleration (say between 40-60km/hr or 60-80km/hr) always feels like is lean misfire/surging.

Certianly if I give the accelerator a decent jab the large accel pump squirt helps get things going, but part throttle at low speeds, eased on, stumbles and misfires and basically doesn't run anywhere near as well as RB seems to imply it will in their literature over the years.

So I've decided to tear the carb down and rebuild it, and have ordered the required original Holley trick kit.

The carb is a proper RB modified one, but I see the previous owner has blocked the top breather on the primary float bowl (what's that there for, anyway?) and so I'm wondering if the carb is running lousy because maybe they've changed the main jets or power valve?

Can someone tell me what the orignal main jet and power valve sizes should be, as supplied by RB? (If they have been changed I want to return them to original RB spec.)

I figure RB spent a lot of time getting these running right over a lot of generations of early rotaries so since my engine is stock, then the carb as supplied by them should be smooth and drivable.

Other details: fuel pump is a Holley red with a regulator down to 5PSI, and the carb is a #16634

Any help is greatly appreciated.

Ian in Melbourne.

 

Anyone?

I just need the main jet sizes and power valve number?

Ian.

 

if the carb is in deed a rb carb, it has no power valve. the accelerator pump cam may be worn to the point that it's not providing enough of a squirt when slowly moving the throttle. throttle plate where the throttle shaft goes thru may also be worn causing the shaft to wiggle a little and may irritate this problem as well.

 

Thanks, I'll confirm that when I disassemble the carb on the weekend. I'll also report back what size jets I find in there.

When you say there's no PV, does that mean there's a plug or something in there?

I think I read somewhere when you remove the PV then the main jets need significant richening, like 6 or 8 sizes minimum.. does that sound right?

Ian.

 

4 to 6 sizes would be closer but it depends a lot on altitude etc. . There is a small ball under a flat spring in the acc pump assembly there could also be a bit of **** in there preventing it from working when just getting tickled but working fine with a more rapid acceleration ,.. There should be a healthy squirt of fuel even when only stepping a bit on the gas. The acc pump linkage should start to travel even before the throttle plates move ( accomplished with the spring incorporated in the linkage assembly on some models ) . for good performance there needs to be a shot of fuel at the throttle plates when they start to open to fill the void under the plates and begin the rev cycle no matter what RPM the engine is at . vacuum leaks also contribute to lazy acceleration check everything well before spending a ton of money . If the air horn is plugged off there very well could be a hole drilled between the carb sections to prevent the engine from building vacuum in the float bowl and flooding. I doubt that changing jet sizes will fix your problem , maybe when driving aggressive but not when you are going at it fairly easy . JMO Gerald m

 

yes they use a plug in place of the power valve.

 

Haven't had time to remove the carb to rebuild, but richening up the idle screws half a turn seemed to help smooth the cruise mode a bit.

Will keep you all posted.

Ian.