Rochester 2 jet tripower problems.

Hmmmn...well I do still need to check again for vacuum leaks, but having encountered that before on another motor, that was the first thing I checked...I think a friend may have a vacuum tester I can borrow to. The butterflies in the outer carbs were all very carefully adjusted in order to seal in the bores very well... They certainly do not seem to draw any air at all..the drilling of the holes already made a difference, but I'll go a drill size bigger...I do have spare butterflies if I go too big.
All being well I should have it up and running this weekend...I'll keep everyone posted as to what I find


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You can solder them up and re drill them.When I worked on Fiats we used to have some idle problems that were due to butterflies no being centered in the base plate.The cure was to loosen the screw and open the butterflies and let them snap closed a few times and then tighten them up. All good info here.I always make some block off plates and block off the front and rear carbs so I can figure out where the problem is.

 

Ok, so I yanked my middle carb and there is only one hole showing under the butterfly. So that means that I don't need to drill it right?
Thanks!
Jimmy


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I believe that is correct, but consider the source

 

this is a fantastic thread some great info and wise contributors
im planning on building a log manifold and running six carbs on my sbc
i have collected all of my materials,now ive just got to learn all about this stuff.
would like to here how the vacuum tuning works out
j

 

LoL! Thanks Clay. I hate to mess with it and make it worse, I mean I got probably 40k miles on it this way!! LoL!


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You CAN'T run 3 2G's with idle circuits together if you have any sort of cam at all. These little carburetors need a strong vacuum signal to draw fuel through the idle circuit. It's hard enough to get enough vacuum to make one carb idle------forget about 3. AS has been stated before you must make the effort to block the end carbs. Only then can you isolate the problems that are causing your motor to idle poorly.

 

Maybe I missed it, but I thought everyone in this thread was just using the center carb for the idle circuit?


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so after you drill the holes you can close the butterflies so only the idle hole shows is what i'm getting, also as i recall on engines with EGR valves the butterflies had holes from the factory right?

 

Lots of carbs had that hole from the factory.

The fact that one or two holes, or a transfer slot, or whatever is showing with the butterflies closed means little, in general.

What happens when the engine is running is that engine vacuum siphons fuel up hill from the bowl, and through the idle mix port. As any secondary ports or slots are uncovered, they come into action too.

The thing here is the word "uncovered", because we're talking about being exposed to sufficient vacuum, not about being exposed to just vision.

Whether you need to drill an air bleed in the butterfly (or elsewhere. It doesn't need to be in the butterfly to work) depends on whether the idle mix and speed can be adjusted normally (once every other part of the engine is in tune) or on whether you have a smooth or ragged transition from idle to cruise.

 

All 6 of mine have idle circuits. It runs great na and supercharged. You just have to mess with the air bleed size in the clusters.I had to reduce mine to get it rich enough to idle. I'm not saying anyone needs to run all 3 with idle circuits but it can be done and work well.


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Matt, Saw your truck yesterday but I missed you. However I was on bridge just before 4:00 and that truck runs damn good and looks awesome going down the road!!! Nice

 

In my 59 pontiac having trouble with too lean idle mix, i was drilling the idle emulsion/pick-up tubes slightly larger.That fixed my cars hesitation and rough idle problems.
I did ask from quadrajetparts.com what they would think that kind of solution before i did that and they agreed.

 

If you can reduce the air going into the emulsion tube the mix stays richer, longer. Adding air leans the mix more quickly as you accelerate. It leans it at idle to yet allows slight richening just off idle as vacuum drops, then leans more at cruise. This compliments the operation of the accelerator pump, which doesn't kick in 'til just a little later, and also the the economizer or power valve, which leans the mix at cruise.

The emulsion tube sucks air bubbles into the fuel stream in a way that increases atomization plus leans the mix as vacuum increases. It's like sucking coke through a straw with a hole in it. It's gonna burble.

This adds the air you'd be adding if you drill the butterflies, so I'd avoid doing both.

 

Thank you sir!


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To me the biggest mystery in carburation was why it becomes such a complicated mystery among our fellow gear heads. Good supply with the fewest fittings, solid condition of the related components and sealing systems, a short study of things as laid out in most rebuild kits or service books. Those 3 basics can get most anyone headed in the right direction. Cam changes and other mods (typically to make more power) will simply place more demands on how the motor is fed. You need .5lbs/HP/HOUR for gasoline. Every 90 degree fitting creates a momentary dead head as it flows to the carbs, which can also lead to aerated delivery if they're close enough. A gallon of gas weighs anywhere from 6 1/4 to 7lbs per gallon. Race fuel is typically 7, so how much fuel delivery is required to feed a 700HP big block race engine? How much to feed a typical "hopped up" small block making about 350HP?

Then you simply address driveability as was discussed here at length. I noticed it was called "hillbilly" to drill the holes, yet it works like a champ if the rest of the motor's design parameters call for it. Smart fuckin hillbillies IMO, especially considering it allows things to work without the original design parameters of the carb all mullered up to "fix" driveability. Truth be told, this shit can be as hard or as easy as anyone wishes it to be. I'll always give quarter to those who can't "see" these things well. Glad the OP is on his way now too.

 

HehHehHeh...

I didn't say they were stupid hillbillies.

My mom's folks are from the Kentucky hills, and Dad's from the edge of Appalachia, so I know better.

We're just not as fond of shoes as some folks.

(...and as I wrote above, many factory carbs came drilled too.)

 

Just to thank everyone again for all the words of wisdom...the motor is now running like a dream..I went up a couple of sizes on the drill bits testing each time. It really is like the hotrod fairies have come and worked some weird voodoo on the motor! I now have mixture screws that seem to do something and a motor that ticks over nicely at around 1000 rpm.
Thanks guys...I'm now going racing!


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That's great man. By the way I dig your truck. Have an A Pickup myself. Here's a pic. I hope you have someone take some pics of you racing on the beach. Would love to see it.

 

Yo brutha -6, you and that truck my be the death of my gennie! Just when I stop thinking, "...forget that sawzall...", you throw up another pic!

 

Hahahahaha I'd cut it! Did u see the pic of it made the Autorama coverage in the latest Ol Skool Rodz?

 

Thanks F6! Yeah our trucks have a very similar look! I'll be sure to get some pics when I'm out on the sand. It's going to be awesome!!!


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Can't wait to see them!

 

very informative thread...thanks to all

 

To block my end carbs, I used a couple 2 5/8 freeze plugs, and drilled a hole in the center and bolted them down on the top of each carburetor under the air cleaner and put a screw in each fuel line. I can open them up in a few minutes without having to pull the carburetors.

 

I used to leave mine blocked via foot pressure- because the linkage worked and secondary plates fit. I could drive on a 2 bbl and open them up from the drivers seat in a matter of a 1/2 second.

Nothing else like it

BuhaWHAAAAAAA !!!!!!!! Anytime you want

 

It's a little easier to iron out carburetor problems if you can temporarily block the ends and know that you are initially just dealing with the center carb.

 

There is alot of great information in this thread, thank you to all that have responded, helped me out very much.
What would be the best way to fit the butterflys in the end carbs to get a good seal? Sand the edges or use lapping compound? I can cover the ends with my hand and the motor starts to die so the seal is less than perfect. I have used some of the other info. to improve my off idle response it is much better and not near as rich, need a little more twiddeling.

 

I used lapping compound on mine. It worked well but it takes awhile.

When I put mine on top of my supercharger they were leaking and it wouldn't idle below 2000. After I lapped them in it idles around 1000-1200 now.


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Thanks for the input Mat, much appreciated.