Tri power rochester end carbs once and for all

miraclepieco · Dec 23, 2011

Will JB Weld work as well as DAG?

spark · Dec 24, 2011

Haven’t tried JB, but if you loosen the screws on the throttle blades and give one side a slight tap, holding the lever in the closed position, it will centre the blade in the bore (often this gets it sealing or close to it).

“Lapping” the blade in using valve grinding past may be enough to get it to seal completely. It takes time but it is a permanent fix.

..
.

Sin7 · Jan 25, 2012

tommy said: ↑

This article by a GM engineer is what I go by. Manifold vacuum for vac adv.

When I built the carbs for the above system I stuck the nozzle of a can of gum cutter into the vac adv port on the carb to see here it went inside. It goes down through the body of the carb into the base plate and comes out under the butterflies....manifold vacuum. That's how GM does it and it's good enough for me. Unless you drill your own ports in the side of the carb, you can't run "ported vacuum" on a 60s era Rochester carb.
Click to expand...

I read the article you provided a link too as well as every page on this thread and it all makes sense to me now but now i think i discovered something about my own car...

I wanted to chime in on the last sentence of your post though. Everyone else has posted pictures of Rochesters with side vacuum ports that clearly run down to the base of the carb for manifold vacuum. However my 2 barrel is completely different and almost leads me to believe that someone may have actually drilled a port for "ported vacuum". My 283 sbc has always run off this port and until recently i thought it ran "okay". The last time i disconnected the vac advance hose from this nipple to adjust timing there was NO change in idle or TIMING marks for that matter. Regardless if it's connected or plugged, my idle stays the same and my timing marks don't move. It's always bugged me but i just kept putting off but recently i've been so intrigued to learn more about how all these things REALLY should work and how to properly tune your engine.

Could it be that i need to use the port on the back side of the carb base for my vacuum advance? Currently that base port is feeding my powerglide vacuum and brake booster. There is no other blank ports on the intake manifold either.

My carb. The brass nipples goes straight through and not down into the base

underside of the carb body.

cooger · Jan 25, 2012

You really need to go to the tech library and search out the ported vs. manifold vacuum article. It gives a full rundown on the difference.
I've got a set of 3x2, big base Pontiacs, and run manifold vac. for advance, the recommendation in the article.
Take a look.
cooger

Sin7 said: ↑

I read the article you provided a link too as well as every page on this thread and it all makes sense to me now but now i think i discovered something about my own car...

I wanted to chime in on the last sentence of your post though. Everyone else has posted pictures of Rochesters with side vacuum ports that clearly run down to the base of the carb for manifold vacuum. However my 2 barrel is completely different and almost leads me to believe that someone may have actually drilled a port for "ported vacuum". My 283 sbc has always run off this port and until recently i thought it ran "okay". The last time i disconnected the vac advance hose from this nipple to adjust timing there was NO change in idle or TIMING marks for that matter. Regardless if it's connected or plugged, my idle stays the same and my timing marks don't move. It's always bugged me but i just kept putting off but recently i've been so intrigued to learn more about how all these things REALLY should work and how to properly tune your engine.

Could it be that i need to use the port on the back side of the carb base for my vacuum advance? Currently that base port is feeding my powerglide vacuum and brake booster. There is no other blank ports on the intake manifold either.

My carb. The brass nipples goes straight through and not down into the base

underside of the carb body.

Click to expand...

dirt t · Jan 25, 2012

Thank's for posting guy's. I have learned alot today. I have never run a set up like these , but not affraid to now. Thanks again.

rjones35 · Jul 1, 2015

I know this is an old thread, but I just found it. Sounds like you guys know more about these things than I do! Ive got 3 of the small base 2gs on a 302. Just got it running the other day. These were carbs I bought from a guy as Tri power carbs, center has idle and mixture screws, the outers have the mixture screws removed and sealed up. The holes on the baseplate aren't filled in. The problem I'm having is one of the outers is really sucking air. Ive taken the baseplate off and centered the butterflies best I could. Holding a light behind it, you can see a tiny bit of light. I know its hard to say without seeing it, but is that enough? If I really push hard on the linkage I can get it to seal better. So I think it just needs to seal better? The other outer seems fine. I'm wondering if I can sand the edges of those plates and get a better seal, or get new ones and go from there. Is there anything else I should check/do? Thanks for all the info.

F&J · Jul 1, 2015

rjones35 said: ↑

These were carbs I bought from a guy as Tri power carbs, center has idle and mixture screws, the outers have the mixture screws removed and sealed up.
Click to expand...

Well, he lied. Real end carbs are not drilled for mix screws and not drilled for chokes, etc.

rjones35 said: ↑

Holding a light behind it, you can see a tiny bit of light. I know its hard to say without seeing it, but is that enough?
Click to expand...

Real end carbs have super thick butterfly plates to seal better and won't dig into the carb bore. Any daylight you see, is TOO much. A vac leak is a vac leak, which leads to idle speed problems, idle mix issues, etc.

You can try reworking/refitting. but I doubt it will be a stable fix. It may not seal right each time it closes, or at random times

rjones35 · Jul 1, 2015

Bummer. I have a buddy thats a machinist, might hit him up for some new plates.

chopolds · Jul 2, 2015

F & J is right, thicker throttle plates, and they are cut at an angle to seal better. Might be hard to modify the stock thinner ones to seal.

vtwhead · Jul 2, 2015

call Dickster. He can help. Back in the day GM had used a material that they would paint the bores and the plates with that sealed the bores after drying. I got some through the web and it worked out ok. Sold the car so I do not have much history on it after that. I believe Dickster has it in stock.

deathrowdave · Jul 2, 2015

There are no idle circuits in the correct end carbs . Taking out the screws does nothing but create a huge vac. leak . No choke plates on end carbs is correct also . You can purchase correct base plates . But still not the correct carb .

wheeldog57 · Jul 2, 2015

Some excellent info on here- and some crap. The outboard carbs do one thing- dump fuel at or near W.O.T. The butterflies have to be sealed (like many have said on here) when closed. Accelerator pumps are to be used and idle circuits need to be plugged. I used two part clay metal stuff cause I will not pay 400 for base plates. You will have to tinker with them once in awhile but they are not that difficult to tune. BAAAAWAAAAAHHHHHH!!!!!!!!!!! SO MUCH FUN!

rjones35 · Jul 3, 2015

wheeldog57 said: ↑

Some excellent info on here- and some crap. The outboard carbs do one thing- dump fuel at or near W.O.T. The butterflies have to be sealed (like many have said on here) when closed. Accelerator pumps are to be used and idle circuits need to be plugged. I used two part clay metal stuff cause I will not pay 400 for base plates. You will have to tinker with them once in awhile but they are not that difficult to tune. BAAAAWAAAAAHHHHHH!!!!!!!!!!! SO MUCH FUN!
Click to expand...

Definitely lots of info!! I understand the butterflies, I ordered some of the thicker ones. Hopefully they'll do the trick. I don't quite understand the idle circuit plugging. If the mixture screws are taken out and those holes plugged from the outside, the small holes in the top of the baseplate don't really go anywhere do they? Or do they still need to be filled in too? Thanks again for the help. The three duece setup is a lot more fun than a single 4!! For me, Thats what its all about.

Kan Kustom · Jul 3, 2015

Glad this thread came up. Working on one now and always like to hear other opinions.

wheeldog57 · Jul 4, 2015

I filled the inside holes too just in case but they are where the idle adjust screws go. There is no need for idle circuit- just full throttle- that's why its so fun

rjones35 · Jul 5, 2015

I got some of the thicker throttle plates. Took some Dremel tool work to get them to fit the shaft but they're in there. Got those aligned as good as I could and there was still light seaping around the edges. Thought I would bolt it back on to see. Its exactly the same. I guess I need to work on that some more. I didn't do anything with the little holes inside. I'm thinking that if the mixture screw holes are plugged up, those little holes don't affect anything?

rjones35 · Jul 16, 2015

The thicker plates didn't really do much of anything for me..I read that you could use a dry moly lube coating on the butterflies and throttle bores and that would seal them up. Tried that on one carb, along with sealing up the small holes in the baseplate while it was apart. It seemed to do something for that carb, so I'm doing the other one. I don't know if this coating will last or not. I don't think it will, seems like the gas would eat it off. We'll see I guess.

rjones35 · Jul 19, 2015

Ive got both carbs done. Definitely made a difference. They both suck less air and I'm able to adjust the center. BUT, its hard to keep idling now and doesn't run as smooth as it did before I "fixed" them. I'm going to make some plates to replace the end carbs and see if I can get the center running better. If not, it seems like I should just get some air flowing through the ends like they were, get it back to idling better and call it good.

F&J · Jul 19, 2015

..the new thicker butterfly plates; do the front and rear edges have an angle at the edge...not flat edges like a normal washer has?

and if they do have angle edges, does the angle seem to sit nice in the carb bore when closed?

You've got to have a leak free seal there, or it will never be right as far as a mint idle.

I am the cheapest guy here, and I only use GM genuine tri-power small base carbs. Damn, they are perfect. Got my first set on a 348 in a 55 chevy in the 60s, and I had zero tuning skills, and that thing was perfect.

rjones35 · Jul 19, 2015

F&J said: ↑

..the new thicker butterfly plates; do the front and rear edges have an angle at the edge...not flat edges like a normal washer has?

and if they do have angle edges, does the angle seem to sit nice in the carb bore when closed?

You've got to have a leak free seal there, or it will never be right as far as a mint idle.

I am the cheapest guy here, and I only use GM genuine tri-power small base carbs. Damn, they are perfect. Got my first set on a 348 in a 55 chevy in the 60s, and I had zero tuning skills, and that thing was perfect.
Click to expand...

Yep, the thick ones have angles edges and I made sure they were going the right direction.

Both end carbs are WAY more leak free than they were, still slight, not enough to kill it when cover them. Before I coated them and filled in the idle circuits the engine idled a lot smoother. Ive adjusted the center carbs mixture screws as good as I can, smells like it runs rich, but it seems to like it as far as rpm goes. Could it not be getting enough airflow through the one carb maybe? I'm hoping that by taking off the ends and covering them that I'll be able to really dial in the center by taking the ends out of the equation all together.

wheeldog57 · Jul 19, 2015

After reading this thread (and others) I pulled my outers apart again. The front is a factory end carb while the rear is not. I knew one was leaking by and it was the rear. BIG TIME. I put my hand over it and the car stalled. I took it off and yup, you could easily see light through the flutterbys. A wee bit of two-part putty and a bunch of adjustments, it is way better. Only problem now is I have to "test 'em out" all the time!

rjones35 · Jul 19, 2015

wheeldog57 said: ↑

After reading this thread (and others) I pulled my outers apart again. The front is a factory end carb while the rear is not. I knew one was leaking by and it was the rear. BIG TIME. I put my hand over it and the car stalled. I took it off and yup, you could easily see light through the flutterbys. A wee bit of two-part putty and a bunch of adjustments, it is way better. Only problem now is I have to "test 'em out" all the time!
Click to expand...

Nice!! Thats rough when you have to test them all time!! Have fun!

F&J · Jul 19, 2015

rjones35 said: ↑

I'm hoping that by taking off the ends and covering them that I'll be able to really dial in the center by taking the ends out of the equation all together.
Click to expand...

Besides the Olds tri-powers, we've also got a 340 Dart with a mechanical Holley secondary tri-power, and I made thick block off gaskets under the end carbs. As long as the linkage is unhooked so the butterflys don't cut a hole, the gaskets have held up fine while we do much other work to the car. It's over cammed, and it's easier right now, to only have to adjust one carb.

chopolds · Jul 20, 2015

Even if you use the thicker plates, I've found that they sometimes have rough edges that prevent them from closing all the way. I ran mine over a flat piece of steel with some 400 grit paper on it to polish them smooth. Then left them loosely installed, and kept tapping them around until they sealed well. I looked through the bores with a flashlight on the opposite end, first, then put a bit of water in there to see how fast it drained...it should be pretty slow if they are seated correctly. Final check is running on the car, use an air flow gauge to see how much air is going through the end carbs, should be almost nothing.

rjones35 · Jul 20, 2015

The water was a good idea, I should have tried that. Maybe I will when they come back off. I did sand the edges some to get a better seal, as well as leave them loose to get them centered as good as they could be.

rjones35 · Jul 22, 2015

So the dry moly lube coating doesn't work, it comes right off, like I thought it would, but had to try. Some plugs are fouled some are washed clean with gas. Running crappy. Running really rich. Took the end carbs off and covered the openings with plates. Fires right up, runs pretty smooth. What does that mean? The ends were sucking a little air, the idle circuits were plugged up. If it was sucking air it would be running lean, right? Not so rich it blackened plugs and burned my eyes. Unless it was creating a lot of vacuum and causing more fuel to be pulled through the center? Next step, buy new baseplates from vintage speed?

3banjos · Jul 22, 2015

The dreaded air leaking secondaries. With those upgrade kits, the outer carbs are altered ::
Totally remove all and anything to do with the choke. Plug all holes which you think may leak air.
Remove the power piston and valve. Plug that hole.
Replace jets to .055s
Remove the venturi cluster and remove idle mixture tubes. Replace cluster.
Remove your idle vent assembly and plug vent hole.
Add your new base and should be good to go.?????
I reiterate Should.
Center carb kit comes with the longer shaft for linkage, and a pair of over-sized idle pick-up tubes to replace smaller ones in the venturi cluster. Also change to .056 jets.

I see you reamed the thinner blade shafts to fit thicker butterflies yourself. That could be be giving you grief.
Precision tooling required there.
3 1/2 to 4 lb fuel pressure is all you want.
Notice on mine, if you drop the pedal after WOT, end carbs close good. But if I just ease off the pedal, they fail to close perfectly.
Good luck, you'll get there.

rjones35 · Jul 22, 2015

3banjos said: ↑

The dreaded air leaking secondaries. With those upgrade kits, the outer carbs are altered ::
Totally remove all and anything to do with the choke. Plug all holes which you think may leak air.
Remove the power piston and valve. Plug that hole.
Replace jets to .055s
Remove the venturi cluster and remove idle mixture tubes. Replace cluster.
Remove your idle vent assembly and plug vent hole.
Add your new base and should be good to go.?????
I reiterate Should.
Center carb kit comes with the longer shaft for linkage, and a pair of over-sized idle pick-up tubes to replace smaller ones in the venturi cluster. Also change to .056 jets.

I see you reamed the thinner blade shafts to fit thicker butterflies yourself. That could be be giving you grief.
Precision tooling required there.
3 1/2 to 4 lb fuel pressure is all you want.
Notice on mine, if you drop the pedal after WOT, end carbs close good. But if I just ease off the pedal, they fail to close perfectly.
Good luck, you'll get there.
Click to expand...

Thanks! Definitely some precision machining with my Dremel tool!! If the idle circuit holes are plugged or gone in the baseplate does anything have to be done with the venturi cluster still? Thanks again! Got the clutch working tonite, so thats a positive thing!!

3banjos · Jul 22, 2015

No, just ditch the 2 idle mixture tubes from the cluster. If your original secondary base plates have the adjustable sprung screws, discard and plug holes. I think it's a great idea to go the upgrade kit.

rjones35 · Jul 23, 2015

3banjos said: ↑

No, just ditch the 2 idle mixture tubes from the cluster. If your original secondary base plates have the adjustable sprung screws, discard and plug holes. I think it's a great idea to go the upgrade kit.
Click to expand...

Semi-unrelated, why does everybody run the linkage on the passenger side of the carbs??

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Tri power rochester end carbs once and for all

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