I just bought a brand new rb 465 for my 85 gsl 12A. Its an all stock engine with 75k miles and around 118 psi compression per each pulse of both rotors.

The carb was delivered with a 49 main jet and standard fare holley side hung bowls and the standard 8.5 hg power valve for smaller carbs.

After my install, done to RB standard using a sufficient fuel pump, dead head regulator and I switched to QFT dual feed cathedral bowls.

My first oddity: After my initial start up, the carb seemed to idle very poorly at the preset 1.5 turns out on the idle mixture. Experience told me to leave it alone until the engine and carb were fully warmed up. After leaving it run for 15-20 minutes I started the idle mixture adjustment. Virtually no combination of evenly adjusting the idle screws (as specified) yielded a smooth idle. To my surprise, turning the idle screw facing the front of the car in MUCH further than the opposite side sharpened the idle to a nearly perfect and smooth idle. Better than the stock nikki, in fact.

After this adjustment I set the fuel bowl levels to the mid point of the QFT bowls which is "right under the threads" on a typical holley bowl. This was the ONLY adjustment made to the carb that was typical and made sense.

After my intrepid defeat of the holley initial start-up boss, I set out for the first test drive. I was highly confused here. The damn thing wouldnt run AT ALL when the car was in gear and had load on it. It was far too lean and sputtering and dying unless I floored the accelerator and waited for what I presume was the power valve opening or the secondaries, which would allow it to run at wot, but virtually NO transition.

I parked the car for a few minutes trying desperately not to call RB foaming at the mouth, and started free revving the engine. With no load on it, it ran perfectly. Not too lean, not too rich. Maybe. I decided to check compression again, ignition, and fuel pressure, even whipping out a redundant gauge to ensure it wasnt lying about my fuel pressure. It was accurate, reading between 5.5-6.5 psi on either gauge. I hooked up a vacuum gauge to the intake manifold and it pulses evenly at idle between 15hg and 18hg. any slight blip of the throttle reduced it to around 5, or even 0 hg at large enough openings.

I called RB, who just told me the carb was fine and that the problem was my car.
I had to take the car on a 8 hour drive, so I temporarily jetted the carb up (12 ******* sizes) to a 62 main jet to make it run correctly and transition. I changed the power valve to a 6.5 to cause it to open later, which is what the much larger jet size ran better with (again, these are temporary changes until I can figure out how to make my car properly run this carb).

My theory is that the booster signal is very low, and is why it falls on its face and dies lean despite the massive jets at low rpms and off idle. Any Ideas what would cause this? Why does my carb only idle correctly when I turn one screw in further than the other? Why does it need jetted up 12-13 jet sizes on the primary for it to be drivable? I respect Jim at RB too much to just assume they made a mistake or did poor work when modifying the carb. I feel like the engines vacuum signal sucks, which I believe explains my symptoms, but why would it be so low with such good compression readings, and it being as physically as strong and fast as my very well sorted 84 GSLSE?


SORRY for the wall of text, but I feel like half explaining problems only gets you half correct answers.

I hope sterling or some other carb guru reads this. I need the help

 

it sounds like you might have a vacuum leak, or the float bowls didn't go on right, or something like that.

 

Great explanation of your problems wankel=awesome, I too am having the same problems, I have the same setup and would like to see the responses that are going to be given here, I installed my RB setup per RB instructions to the T and it idles smoothly but stumbles when I reach around 3k rpm, so I'm subscribed, and good luck bud

 

Well I called RB and Jim(T) asked me to check the timing on the dist... I will get this under way and see what happens, but im unsure how this could be affecting it in this way.

 

Did you test run the carb right out of the box as it came from RB? Or did you do a bunch of mods to it first and then test it for the first time?

 

Only change made to the carb prior to first run was switching to the cathedral (center hung) fuel bowls. Everything else was left exactly as delivered.

Im still feeling like this is a booster signal issue. I think my engine should be pulling more fuel through that 49 main jet than it is... Like, the booster is far too slow so the main jets would have to be HUGE to give the engine enough gas. As much gas as a fast booster with a small jet.

What im experiencing is common when the carb is far too large for the application on domestic engines. The common cures are to jet up, and reduce HS air bleed sizes. When this is done it typically will "run" the engine, but power output and efficiency are greatly negatively affected.

Which is damn near exactly what Ive done, aside from reducing the HS air bleed size to mend its low rpm performance.

For some reason the engine is not pulling a great enough signal to the carb, which is also why my idle screws are turned in so far. Thats another symptom of bad signal.


Im taking it to my buddys shop to hunt for possible vacuum leaks or other ***-clownery that could be causing this, and im going to verify the timing.

 

Ok. Good luck.

Before I go I'll just relay a quick story about an RB Holley 600. This seemed to run ok on a streetported 13B but it always had an accel pump issue. Like a stumble off idle. If you grab the accel linkage at idle and cause it to squirt it makes the idle stumble. But it also will stumble when you gun it too fast and no fuel pumps out of the nozzles. It has the same symptom whether lean or rich. So I had to learn to stab the pedal slowly enough to not cause the problem. I don't know how to solve it as I'm not a Holley expert.

It's like there is some sort of speed sensitive delay. I don't get it. It either doesn't squirt and stumbles or it does squirt and stumbles. But I think the main take-away is I left the float bowls alone. Never taken them off, never had any problems. So that is my experience with an RB modded Holley. You might want to bring your carb back to RB's specs and try again, eh? Not that I know anything about Holleys to be giving out advice like this...

 

i remember this one time i had an 83 LE, and the engine was fine, but it just wouldn't run under 2000rpm. my friend and i were playing with it, and he doesn't see any fuel going down the primaries.

so he made me rebuild the carb, no change. i went to my buddies house and got a low mile carb, and rebuilt that, no change. i rerebuilt the original, no change.

so i decided to block the ACV off, runs perfect.

pull the ACV apart, and its full of airpump shrapnel....

notice i condemned the carb THREE TIMES, and it was a big vacuum leak?

 

years ago, when i was tuning my brother's car (i think his was a 600 or 650 - i really don't remember), it would exhibit the same thing Jeff describes here. you had to sort of ease into the throttle for it to act right. i ended up playing around with the pressure a bit and it got better - maybe not Nikki-perfect - but better. if your search for a vacuum leak does not reveal anything, then maybe you can start fishing with pressures? do you have a regulator and gauge?

 

Timing is good, no vacuum leaks.

Im stumped.

The accelerator pump COULD be a factor because the new fuel bowls required swapping the pump housing from the old side hung bowls.

Fact is, accelerator pumps work or they dont. The cam actuates the pump arm which pushes down the pump diaphragm forcing gas through the discharge nozzle. Theres supposed to be some .015* gap between the pump lever and arm, which there is.

Im swapping the pump out next and switching back to the jets and power valve the carb came with.

 

Well it appears that the one idle screw being turned in further is indicative of one rotor wanting a different mixture than the other rotor.

wtf.

the compression is good on both, and I understand this problem having never been reported in 30 years to RB. See above "wtf"

Now im going to jet one rotor different than the other for ***** and giggles. Im excited.

 

So I put everything back exactly like RB sent it to me, and SURPRISE!!!!! It still runs like a little pos. Im going to do some research and see if I can swap my totaled SE's efi on this 12a. I spent something like 2k total on the RB carb swap and im thoroughly pissed this is the result for all the hard work.

As for changes made to the carb, I made them because thats what made the car run better, and thats not something unusual for a backyard tinkerer to do when you give them a scrap heap for a "tuned part". I know theres no way to get that 2k dollars back, but I sure wish the company would step in and throw me a bone. Its bad enough I spent 700$ on a holley 4bbl that one of the engineers at RB quoted "not a quality carb". If its not a quality carb, why was I charged 700$ for it?

 

An old carb tuner reminded me of something today. It has dawned on me.

He just noticed how rich the car was under accel, and said "You know if you remove that power valve itll run better for ya". I replied, "Yes, but removing that sucker equates to something like 10 jet sizes to get it right."


Do you not see what ive realized? That power valve, the one that came brand new in the RB holley.... Its not doing its job! This is why it wouldnt enrich with a 49 main jet, and is why I jetted it up just over 10 jet sizes. Im compensating for a power valve that ISNT doing anything. Im not sure why it isnt doing anything, but it almost certainly isnt. Now im interested. Ive swapped the power valves, but they dont seem to be faulty. It seems like theres some other issue here. like the metering plate is stopped up, or the power valve restrictions arent right.

Dear god... my carb is what it would be like with the power valve "plugged". The only thing about it is, with my massive main jet its so rich up top... like not tuned right. I dont know what to do about this... ive blown out the metering block and dicked with it until im blue in the face. im tired.... and im just ready to call it quits with this carb.

 

Wow! You've only spent a few days working with it and only one day on this site with a post up.
Patience and persistence will get you through this. Carbs are not digital like EFI. Sometimes it
takes lot of tinkering to find out what has gone wrong.

Do you really think RB can sell crap and still be in business after 30+ years in the rotary game?

 

Well if you search some of my older posts from years back, youll learn this isnt my first rb holley experience. My first and second one had defects as well. One of them was totally and radically changed to work on another car I had at the time and was ultimately a product of QFT/AED by the time the work was done. The only part of that carb that wasnt replaced was the main body. The other was one that during its modification at RB had 2 restrictions that not only werent pin vised to confirm their original holley casted size, but were also unchanged by RB when they reportedly were supposed to be 0.035 restrictions, they pinned at 0.028 and 0.017 because of an oval irregular shaped passage. I re drilled those with RB's graces and fixed it.

I also spend thousands a year at RB for one car or another, and I know they sell quality parts normally, but when it comes to these carbs.... im just not sure.

 

For those wondering if this was solved, it was.

I dont know why, or how this carb was fitted with a defective PVC, but thats what it was. bypassing the power valve and jetting up 10 sizes (as per holley recommendations),and the oddities were addressed. Including the oddball idle adjustment.

The carb now runs smooth and strong, almost making you forget its carb'd unless you are warming it up.

Final changes: Central hung bowls, power valve plug, 60 main jet.

RB feedback tells me the malfunctioning PVC in the carb is due to engine health. The engine as stated above has 75k miles and pumps 115-118 psi compression per pulse on both rotors. I believe the holley power valve itself is defective, and not opening as soon as what RB intended. Holley claims that there are regular situations like this with brand new power valves not performing to spec. I chose to bypass what is apparently bypassed on all other holley+rotary combinations.

 

Interesting. Maybe Holley changed something about the PVC spec that RB has not caught up with.

How did you measure the compression? Is it even on all faces?

So RB response is that its due to your engines health then? They won't replace the PVC?

I've seen wierd things with power valves on other carbs before. Specifically the ones on the
old Jeep Grand Wagoneers would get damaged if there was ever a backfire through the carb.
The only recourse was to pull it out and replace it.

 

haven't had the bowls off my 465 but the 600 definitely has a plug for power valve. i always assumed RB replaces all power valves with plugs.

 

I confirmed today that the RB 465 is built with a power valve if it is used on the stock port. But my engines vacuum simply doesnt drop fast enough to open their 8.5 hg power valve in time to enrich the main circuit.

Theoretically I could switch to a 10.5 to get the best result for enrichment. But, as for the casting of the unmodified 465, yes the new generation castings are used (the old hp casting design) and the 465 is even jetted differently now then it was 5 years ago, prior to being modified.

 

I was having issues with my holley 465 on my SP 12a after I moved from NM to Okla
it would pop after 4k and not rev up this issue illuded me that is until my dad metioned
to check the pvc and jets, much to my suprise it had a plug instead, tossed in a 6.5 and
she ran like a beast pulled all the way to 8k and still had more to give. If you have any
holley made after 1992 it is set up from the factory with a powervalve blow-out prevention
system and all older holley carbs can be set up with it, holley sells a kit to do it. In short unless
you drag with a holley put the pvc back in your holley will most likely run way better.

 

Well this particular carbs pvc (power valve circuit) is unresponsive, and when it finally does open its too late. I could switch to a 10.5 and possibly get it to do what I want, but it ran pretty super shitty with that 8.5 installed.

Tomorrow im trying another trick for making it a lil bit faster

 

Out of curiousity what main jets are you running, the only reason I ask is
for my sp I'm running #50 main jets so only a one size bigger than the
factory RB #49 jets.

 

So in reading this thread I assume my RB carbs power valve is plugged and I need to unplug it and install a powervalve in, which powervalve? How do I determine which Powervalve? By checking vaccuum at idle? Its a rb streetport carb by the way, last question is there a book or website I can read to learn all about Tuning this Carb

 

Most come standard with a 6.5 I belive (not 100% on that) and if I remember
correctly it goes by vaccum at idle.

 

Lets not misinform people here. All rb carbs EXCEPT for that carb for the stock port 12a have power valve plugs. If your carb has a plugged valve, its because that ported engines vacuum signal is not consistent, thus needs plugged to make way for a larger main jet. If you have a SP 12A i'd assume you'd need a larger jet than the 49-50 youre using, and is why the addition of a power valve fixed your lean problem. It comes out to about a 6-8 jet size up at a certain vacuum level.

If your carb has a plug in it, it was done intentionally, and likely curved around it. The emulsions circuits on the RB carbs are highly modified, and need to be for the proper curve. Adding a power valve without jetting one of those carbs down would cause an extreme rich condition and foul plugs anywhere beyond part throttle.

My engine wants a power valve that opens sooner, no idea why. I surmise that it is the circuit that references the vacuum within the carb, and is out of spec.

SO IF YOU DIDNT READ THAT-------------------> Dont add or remove a power valve from a RB carb unless the proper jetting to compensate has been achieved. Mine with no power valve is rich at cruise and idle, for obvious reasons. It was made for a 49 main jet curve at high vacuum, and my engines vacuum is actually higher than the norm--another thing i dont comprehend. I plugged it and jetted up so it is as if its open all the time, thus rich at low throttle situations and idle.


If you need any advice on tuning or modifying holley carbs, PM me and I can help you sort it. As you can see though, even those with experience are easily frustrated by bad tunes, especially when met with the cost of this product.