81gsl12a

iTrader: (1)

so i got a holley on my 12a and its not running right

stock port...i know the car is to big

car mods: Rb holley manifold,holley 650 vac 2nd, msd 6al, msd ss blaster coils, RB header 3in exhasut, high psi oil reg, NOS nitrous plate system(half inch plate). 1/2in spacer,

carb specs: holley 650 vac 2nd, 64 prim jet, 68 sec jet, power vavle block off plug, orange pump cam,

can any1 help me out and get me on the right track...how do i mod the air bleeds some ppl say smaller some say bigger, what jets should i have in it, what is a good place to start the ideal mix at? ive got it at 2 1/4 turns and it idles at 1300 till it warms up than goes down to 900

timing i have the leading on the yellow dot, trailing is about 2mm to the left of the red dot (retarded)

there is a flat/dead spot if i go WOT from an idle so bad that it will just die

anyinfo any1 can give me on the holleys wood be gr8 or im going ot have to just keep playing with if for a long time err would like to get it close and play with if for not as long thanks guys

13btnos

iTrader: (1)

Carb is way too big for stock ports you will never get it to run right! Either go with a smaller carb or go with a larger port like a bridgeport to use that 650cfm Holley. There is just no way a stock port 12A will run "correctly" with that large of a carb. Hell I use 600cfm Holleys on bridgeport 12A's and very large streetport 13B's. You'll have nothing but headaches and poor gass mileage along with poor response with that carb. Good luck to you...

81gsl12a

iTrader: (1)

any1 else what to add anything? like something helpful..... i know that the 650 is to big but i also know a lot of guys that run them..they just dont live around me and dont get online..... so is there any1 that might have something useful to say? I've git it idleing at 900. it revs up long as you give it gas slow but if you try to go from idel to half or WOT it dies out bad flat spot...

also i switched to the pink cam it helped

Alex-7

Carb is way to big. Nothing else to add. Nobody runs a 650 on a stock port 12a that I have ever seen or heared of. If you personaly know people that have great success running carbs nearly twice as big as they need for their motor you should make a stronger atempt to get ahold of them.

Sorry it's not useful info, but you have the wrong carb. Maybe try trading for a 465.

W/T v8 guys make this mistake all the time. running 750+cfm carbs on their 350's when all they have are headers and glass packs. lol. it just doesn't work like that.


good luck to you though.


--Alex

BlastinSideways12A

Can you change venturis on Holley carbs? If so, smaller venturis would help out. It is very true that it will be tough to get an engine to run well with that carb but you can get it to run decent, especially if performance is your main concern. A wideband always helps, so do EGT guages.

If you can trade the carb for a 465 that is prepped for a rotary, go for it.

Good luck with it.

mwatson184

650 vac secondaries? That doesn't sound right to me. Did you "convert" it to manual secondaries with the screw trick? Do you have a secondary metering block conversion kit on it? (otherwise i don't know how you would get jets in the secondary side, secondaries have metring plates w/ pre drilled oraphaces)

You are not getting a large enough acc pump shot when you stab the throttle. That is where the bog is coming from.

Put up a pic of your carb, I don't think you know exactly what it is.

81gsl12a

iTrader: (1)

ok i feel kinda dumb.. you are right the secondary side is go the blocking plate on it errr my friend was working on the carb up till a few days ago when i looked at it and i noticed i was wrong with what i said....

ive got it running but its still got a really bad flat spot like you said...ive got the 68 jets in there with a power vavle block off plug..pink cam on the 3rd hole, and im using a 31 squiter, and i have the airbleeds blocked off a lil bit with some small wire..its ideling at 900rpm now but still got that dead spot

ive also have a 1 inch spacer plate to give it an open plenum

is there anything else you need to know to help

mwatson184

My guess is it's a 600, not a 650

Are the vacuum secondaries opening by vacuum, or have they been wired to the primaries to open? If they are wired, then you will need a 50cc acc pump kit. When you wire-open secondaries on a normally vac secondaries carb, you have to make up for the secondary acc pump that is not there.

-Marques

81gsl12a

iTrader: (1)

they still open by vacuum.... should i i wire them to open? and change it? if i leave them vac what acc pump should i get? i am pretty sure its a 650 came off my pops 350 he bought it new...

thanks for all your help Marques

- patrick

mwatson184

Leave them vacuum operated, or buy a double pumper. I'm not a big fan of the bastard child of the two w/ bandaids to get them to work.

Before any tuning can be done, the floats MUST be set correctly. Pull out the sight plugs and raise the floats until fuel trickles of of the sight plug holes. Fuel pressure should be between 5 and 7 psi. Idle screws should each be around 1.5 (+/- half a turn) turns out. That acc pump should be fine, make sure it squirts a nice stream into both of the primary barrels. Make sure that your idle air bleeds are clean.

If you find yourself unscrewing the idle mixture screws more than two turns, you most likely have the primary throttle open past the progressive slots. Close up the primaries a bit, and open up the secondaries (small screw on bottom of throttle plate on secondary side). Jets sound like a decent starting point.

That's all I've got for now, I'll chime in again if I can think of anything else.

Josh LV

Im trying to figure out what you mean by prepped for rotary.
Im in a similar situation, ive got a 13b with stock ports and a Rb holley intake and i'm still trying to decide on a carb size. i was thinking 600 but it sounds like more problems than it's worth. I would like to do some future upgrades and i want enough carb for later on also. What do you recomend? 570? smaller?
thanks

Doc Holiday

iTrader: (2)

I have a 12a bridgeport with a RB mani and a holley 600 double pumper. I know bigger ports, and its a double pumper, but bridges have tons of overlap and that makes low speed drivability poor. I run 62's on the primary side, and I run a 7.5 inch power valve. The power valve performs some of the same functions the acc pump does when you open the throttle. It adds enrichment. You should only be removing the power valve if the engine pulls REALLY low vacuum (from a huge cam or port) or if its track only and you dont care or want to bother messing with the drivability. I run the factory 30cc pumps and the car drives VERY well. No bucking at part throttle, no weird bogs. With a vacuum sec carb, you should be able to floor it right off idle, if you cant, your tune isnt good enough yet. You just have to keep messing with it. BTW, I have a 1 inch open plenum too. I would never run a holley the way RB tells you too, it requires too much modding of the carb.

mwatson184

I had run an open plenum for a while, but they are pretty shitty for flow. I ended up taking a grinder to the RB manifold to make it an open plenum mani w/ smooth entries into the runners. Took about 8 hours of work.

81gsl12a

iTrader: (1)

up date...

car is idleing great 800 900 the dead spot is still there feels like it goes real lean just wants to die out if i dont keep the rpms up high about 3...and if i take off hard it spins takes off than falls on its face..i think its was caz the floats err didint have them set right... and my damn FPR is only at 5 it goes between 4 and 6 (damn holley FPR) some times its at 6 other times its not i seen it get as low as 3 err and its got the higher spring in it.. but i can fix that... jsut the transtion of going from idel to taking off is not there at alll

gravale

🚼🚼🚼🚼🚼 My 12A was running about the same for the last several years. I finally decided to do this myself. Opened the carb and found the the jets were drilled to about 80 (67 was the number) on both the same. Always ran reach. It had a mean sound but the running was not as easy. I down graded to a 67 and again to a 65 (both) As I looked at the needles noticed they had no length as others that I compared to. Found a new needle and realized that the one I had been modified (size 31)
The gas was not been shoot the the burn but it was dripping by the wall of the carb. Finally I got to the vacuum. The vacuum lines were all shot down. A few month before while looking for the problem I decided the install the vacuum lines to the ignition A few experts try to talk me out of it but since I had decided it my way. They check the timing and agreed the vacuum port to use. I noticed not much change but I went with it. When ask why no much change I was told that the vacuum on the ignition needed to be replace and was given a good price even for replacing them for me. I declined at the time. At this time a decided to change the vacuum port on the carb. That made my day. Never it has run this good. I am still making adjustments but it is running real good. The vacuum port using now is one directly under the primary jets bowl. My carb has only one there. Let's keep trying

che'srx-7

iTrader: (5)

chainreaction

700 HP Holley on a bridge-ported 12a: 628# sand rail, 300' sand dragsCurrent tune up: Running C10 race fuel with Amsoil Dominator 2 stroke oil mixed at 10 oz per 5 gallonsHave 4 coils mounted firing all at once. Timing is locked at 18 degrees. I turn the power on, retard 4 degrees to start, then retard an additional 4 degrees before running.Fuel pressure is at 6.5 psi. It pulls 12-14" of vaccum at idle (idle at 2400-2600 rpm's), it now has a 10.5 power valve in it. Primary side has .060 jets and a .028 squirter, black cam with a 25cc accelerator pump, the secondary side has .076 jets and a .025 squirter, red cam with a 50cc accelerator pump. Hitting the nitrous manually after the tach hits 6-7000 rpm's. turn's up to 11,800 rpm'sThis combination has gotten me the best throttle response. If I turn the idle up to about 4,000 rpm's there is no stumble. Running motor only, the plugs show just a tad rich. I have the nitrous tuned for a 100hp shot.
I ran a 650 Holley on a stock 12a for 11 years regularly turning it to 10,800 rpm's Made best power at 9,200 rpm's, I have a snowmobile clutch drive and it is tuned to seak and hold the rpm's at peak power.
This car holds the SSDRA National Record as the fastest naturally aspirated (4-cyl) dune buggy in the country.

73rx313b

iTrader: (40)

sounds very cool!! post pics!! vids?

chainreaction

Link to video clip:
www.facebook.com/darryltrafford/videos/cb.1363367266/10205300232969683/?type=3

www.facebook.com/darryl.trafford/videos/vb.1363367266/2040215689361/?type=3

This clip is the stock 12a with the 650 Holley DF DP
http://www.facebook.com/darryl.traff...620378/?type=3
www.facebook.com/darryl.trafford/videos/vb.1363367266/10206854299620378/?type=3
Full
BP 12a with 700 Hp Holley DF DP

chainreaction

If the link above does not work for you , you can copy an paste it into your address bar at the top of you screen to activate the link....

JOE68

smh.... I've seen this for years over cfm...sure you can make a 600cfm or 650 Holley work but for a street car just sucks..... on all my 12a s from stock ports BP to turbo... all I use are 390 hp double pumper ...trust me you will never look back....

Manny60602

RX71KING2, I am interested in learning more about your setup with the 390 HP double pumper. I am shopping for carbs at the moment and have been looking at that carb but I don't ever see any mention of it on this forum. It seems like it would work so well with its adjustable air bleeds but I worry about the low CFM rating. I have a 12 half bridge that I will be cracking open soon to go full bridge. Care to share your thoughts?

JOE68

I build cars to be street driven .. no 1/4 mile racing like the throttle response of a smaller cab..... if u want top end go with more cfm's. going with a full BP I think thats what you're looking for