tuning or getting somone local to tune rochesters?

just picked up a new ride (new to me) and it has a crate 350 with 3 rochesters on an offenhauser intake and am having some problems finding someone to tune them up. id like to get them all timed up right since the idle on the car keeps fluctuating

anyway im in San Dimas California.

i will be out at pomona on sunday

here is my car

 

Nice looking sedan. Good luck on the tuning help.

 

If it were me - I'd do it myself - learning now is a valuable asset to have when owning any multi-carb setup - if you were closer I'd say come on over and I'll give a rundown, but since not....

Do all 3 carbs have idle circuits or does only the center carb have an idle circuit - important info to know when trying to get a smooth idle... Also be sure to check the basics (tune-up items, linkage binding, etc.) then if all 3 have idle circuts you'll need to get carb synchronizer (and ask for tuning tips), otherwise if only the center one has it - make sure the front and rear close 100% and don't let air bleed by the throttle plates (to provide a good signal to the working carb's idle circuit), and then set the idle mixture and idle speed just like a single carb... (do a web search there's a ton of information out there - or post back with the info on the carbs and we can go from there.

 

i might have to hit you up for tuning multiples on a stovebolt.

 

sorry for sounding stupid but what is a idle circuit?

the throttle cable hooks directly to the scond carbs throttle arm and on the opposite side (the side with the fuel inlets) there is a linkage and all 3 carbs are connected together there but the front a rear carb dont seem to be opening until i put my foot into it . they dont open along with the middle carb at low speeds

and the car just seems to run really inconsistant it will idle at 1500 sometimes and even slam the u joint when i put it in gear its so high and sometimes while im driving it will idle so low that i have to put it in nuetral at a light to keep it running

so i guess i need a good book on tuning these guys or find a local person to help me or even just pay to do it if i have to

but id love to learn myself im pretty car savy i just dont know much about tuning or setting up the inside of a motor

thanks everyone for your info in advance!!!

 

Hey Man - Nice sedan - Basically it is all about the vacuum. The piston moving down on the intake stroke creates a vacuum that sucks the air fuel mixture from and through the carb into the intake, into the head, and finally into the cylinder.

The general motor set ups came from the factory to operate progressivley. The car idles and runs on the center carb until you give it enough gas that the linakge opens up the outer two carbs.

The special outside carbs that had no idle circuit. The bases are different. Meaning the base of the carb has butterflies that seal off when the carbs are at idle and they don't have any idle air mixture. This eliminates the need to synch the carbs at idle - the motor runs off the center carb.

The center carb has the idle mixture screws and the buttlerflies never completely shut at idle. This allows idle gas/air to drip into intake for the motor to run on.

Here is where the problems with the outer carbs start - If your outer carb butterflies don't seal at idle - you'll suck in large amounts of air or you could call it losing vacuum and the motor won't run or run rough because there is way more iar than gas and your ar fuel ratio is off.

If you have idle circuits on all three carbs - then this won't apply and I have no experience getting those timed. Good Luck, PM me if you have any questions -

 

Oh - one thing I thought of - do you have a vacuum gauge? what kind of vacuum are you running (inches)? Does the engine have a big cam in it (lopey)

Everything that Tudor posted is correct, and it sounds like you've got the progressive setup. The only thing that I can add is that the center carb's throttle plates need to be nearly closed so that it only feeds fuel off of the idle circuit and not off the boosters (you'll be able to tell if you can't get the mixture screws to have a big impact on idle quality/speed.

Given the varying idle speeds I'd look at choke operation (center carb only if it's the progressive setup), linkage binding, and float levels (in all 3 carbs) as well as look for vacuum leaks

53sled - hit me up when you need help...

 

thanks for all the help guys

honestly im not expierienced/dont feel confortable enough to do that stuff myself. if i try the car probably wont run after at all! lol

too bad none of you are local.....

 

got the car tuned up but it seems everytime we get the car timed correct the idle adjustment screw on the middle carbs's throttle circuit does nothing to the idle when adjusted

the person that helped get the car all tuned thinks that we need to either rebuild the center carb or buy a new one.

so my question is do people usually rebuild them or is it cheaper and easier to buy a new one?

also question #2 is since only one of my carbs has the throttle circuit ( the middle one) is it better to have all three with the throttle circuit on them or should i say to you get more power on the low end with that setup

 

It sounds like one of the other carbs is still metering fuel and air and is overiding the center carb, much like a four barrel carb will do when the secondary or rear butterflys or plates stick partly open. Many street rodders in the old days used to shut the idle off completely on the front two barrels and idle off the rear butterflys and accelerate with the front. This kept the fuel passages on the rear full of fuel and dripping at idle and therefore when full throttle was applied there was no bog or gulp of only air then fuel to the rear barrels. On the single four barrel system the Front two barrels have the accelerator pump to rely on at low idle much like your front and rear carbs do. Don't try to idle off all three carbs. From my experience three identical carbs that are jeted the same will work fine on the 3x2 setup if you only idle and accelerate the Engine with the center carb up to say 3000 rpms or for streetablility and daily driving maybe 3/4 throttle and then the front and rear start kicking in. This is done by Progressive linkage that is adjustable. The front and rear carbs are linked together and the center has a slide that works with a fulcrum or lever that has a longer ratio than the front and rear do. Meaning the linkage swing of the center carb is longer than the other two. They stay completely closed until the center reaches approx 3/4 throttle and then it hits a stop attached to the linkage or rod that joins front and rear carbs together, only then do they open simultainiously in unison and with the help of their accelerator pumps do they start metering air/fuel. Take the linkage loose from all three carbs, Back off the front and rear carb idle screws until they no longer touch the idle stop, Seat the butterflys front and rear ( Driver's side view ) by using the handle of a screwdriver to tapp "lightly" on the carb shaft lever top, or counter clockwise towards the front of the engine, this will seat the butterflys to the carb base and should clear any corrosion in the base barrels, thus creating a vacum tight seal. Each carb has an accerator pump, idle jet system, pilot jet system and main jet system. the front and rear can work fine with the idle circuit shut off. to do this screw the two air mixture screws at the base of front and rear carbs clockwise till they are closed off, leave the idle screws backed off so the butterfly plates stay sealed at idle. Idle and accelerate only off the center carb and adjust the air mix screws for a smooth idle. The progressive linkage should be re-attached and adjusted to where the front and rear carbs do not even start to open until the center carb is nearing three quarters throttle and with full throttle the front and rear quickly prime and the accelerator pumps squirt as they achieve open bores, and if them Babies are working right, Hang on to your Arse! Even though all three have accelerator pumps to supply fuel, If all three open too soon the engine will fall flat on its face and die! Too much air/fuel at a low rpm is not really streetable, not to mention fuel milage. I would also suggest using three independent light accelerator springs, one on each carb, to make certain the front and rear return to a full seat and the center can return itself to an adjusted idle. Progressive type lingage has a lot of moving parts that can flex and fluctuate causing intermittant idle if the front and rear carbs stick even partly open. If it still won't idle correctly, the vacum power valve in the center carb is most likely stuck or you have a serious vacum leak somewhere, maybe the intake gaskets are leaking, or if those type of carbs have small air holes drilled in the butterfly plates in the base, the front and rear carbs may need theirs soldered up. I don't think they are large enough of a leak to cause any problems at idle. To find an external Vacum leak I use WD40 to spray around the carbs and intake while the engine is at idle, If it is sucking air the WD40 will make the engine idle or race higher when sprayed on the leaking area. I'm no expert on Nothin, But I hope all this helps ya.. Good Luck!