Rochester 2 jet tripower problems.

There ya go. Congrats man. Now if I could fix my own charging issues it would be a really great night.

 

Thanks guys, that was great advice! Well that's me one step closer to racing at Pendine


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I read this one with interest because I've got Rochester trips on my roadster and am always looking to learn. Really good info in every post, thanks from an onlooker.

 

Yes, this was a great thread. I learned something. Thanks for all the pics, gents.

 

Awesome!

Now I gotta yank my center one and poke some holes in it!! It's got a fairly decent cam in it and its pretty lazy off idle but pulls good after it gets going. Wonder if that'd help. It has to idle pretty high out of gear for it to idle in gear since it'll drop about 500 or more when you put it in gear.
Thanks for the tips guys!


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Yeah this is a pretty easy fix for a common problem. I first saw this when I worked at Kirks Carburetor. We always bought all of Holleys old stock that they didn't want. We had NOS carbs for cobras, thunder bolts, you name it. Stuff worth BIG money today. A lot of the real high horsepower carbs came from holley with the hole in the throttle plates. I asked the guy who was training me why and he was a great teacher. Explained it all in detail and taught me a zillion other things I still use to this day. Glad your on the way to getting the truck sorted out.

Nice truck by the way. Have an A pickup myself that I just started driving and sorting out.

 

Agreed, but they're just fuckin kool....

 

Hahahaha. That they are buddy. Hopefully this post took away some of the mystery of carburetion for some folks. I've had to do this on every car I ever put a cam in. Really improves the engines manners that's for sure. No more loading up at idle, saves gas, quits smelling rich and burning your eyes. We re-engineer countless things on the cars we build yet so many times little fixes like this are unheard of.

He could and may still have some sort of vacuum leak like others have suggested, I suppose it's possible. Had one on my truck recently that I couldn't find that was driving me nuts.

I suppose a modification like this, at first, may seem like an old wise tale. That's why I posted the pics to show what Ulu and I were talking about. Carburetion seems to be one of those grey areas. Once you learn how they operate you can get them under control.

I actually set my 3 Strombergs up like a GM/Rochester tripower. I run off the center carb at idle until about half throttle with progressive linkage. Then the end carbs come in. End carbs are closed completely at idle and have no idle circuit. Pontiac had a service fix for the end carbs where they put this stuff called Dag-213 on the end carb throttle plates to help seal them at idle. I found a guy online that sells small amounts of it. Got some and did mine that way. My tripower runs great.

 

Have you checked the power valve operation in all three carbs, it sounds like they may be hanging open.

 

Not really. You would be trying to fix one carb by adjusting another one. It's like trying to get your refridgerator to run colder by turning the heat down on your toaster. Two seperate devices. You would still basically have a small vacuum leak at the end carburetors regardless of the mixture setting on the center carb. The mixture distribution in the intake would still be wacky too with some cylinders running leaner than others.

 

this a great thread, thanks to Ulu and F6Garagerat for their input.

 

Pull your cluster trio and you will see 4 brass tubes. We are concerned with the 2 outside, those are the idle tubes. You need drill them out a least 2 sizes to start, and depending on the cam you may have to go farther but will notice an improvement after the first drilling. This is all providing you have NO vacuum leaks.

 

Hey buddy how ya been? If he is rich at idle because of the transfer circuit being exposed to manifold vacuum, isn't drilling the idle circuit bigger just going to make things worse?

I've drilled idle circuit restrictions to about .031 on a car with a lean idle condition before but not on one that was rich to start with. Or are you talking about drilling the idle air bleed? Which would lean it out but probably not give him his adjustment back at the mixture screws and leave him running strictly off the transfer circuit at idle.

Also, the OP drilled the plates and got rid of his rich idle/no adjustment problems already.

 

I knew all about carburetors. Until I went to BMW school in 1969...there was a myriad of information; air flow, vacuum coefficients, et al. The old wives' tales soon dispersed, and simple analysis replaced dark ages theory.

A simple carburetor 'tune up' included minute inspection of main jets. (on the 3.3 and 3.5 liter 6 cyl. cars with dual carbs) Main jets were wont to wear from fuel flow, at 30K+ miles; they were checked with wire gauges. 'Coke Bottle' taper was corrected by the installation of new jets, obviously; before installing these jets, (new or old) we polished their bores with cotton string. Oxydation ('barnacles') built up around and inside jet bores; I recently talked with a Hi-Po Pontiac builder/racer that was a 'jet polisher' as well...
Assembled carbs, got filled with non-petroleum based 'test fluid', thoroughly testing all circuits, and accelerator pump discharge quantity before installing carbs on the engine.

You had to be efficient in this operation. (time=$$$$) Pretty 'strict' steps, but when followed assured 'perfect' carb performance.
Fundamentals for 'future tools'...

 

I'm not doubting your setup runs good and maybe you can adjust for small amounts of end carb leakage. I'm just saying, for me, I chose to do everything I could to seal the end carbs as tight as possible. I can completely cover my end carbs with my hands and get no noticeable change in idle. It's just how I chose to attack it and it worked out great.

 

That being said, if you look at the

Wives tales or not, you can't run off the idle and transfer circuit at idle. No amount of jet polishing will fix that.

 

Thank you guys. I have the exact same problem. I am going to do this asap, I sure hope it cures my iss ues because i have tried everything else.

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Before you do, pull the center carb without touching any of the adjustments. Flip it over and see if it looks like the posted pics, both idle and transfer circuits exposed. If not, no sense in drilling holes where they don't need to be.

 

I have a question out of curiosity. Instead of drilling the throttle plates to allow more air into the engine, could you slightly crack open the secondary carburetors using the mechanical linkage? Kind of like on a Holley 4bbl - opening the secondaries to get some increased airflow so you can back the primaries out of the transfer slot? Or is this not a good idea since they are separate carburetors as mentioned a few posts above? I am getting close to firing my 3x2 SBC for the first time with a healthy cam, and I am just trying to prepare mentally for any tuning difficulties in advance (and hopefully avoid some frustration and mistakes). Thanks for all your help. Interesting thread.

 

Like I said before, the toaster won't fix the fridge.

 

Everyone always wants to start some kind of fight or point out some way that you kinda, sorta, maybe might be wrong. Is my setup the end all be all of tripower setups? No. Does it have some things that, with 2 months and thousands of dollars worth of diagnostic equipment could be improved upon some how? I'm sure it does. However, I don't have either of that. This is what worked for me, in my humble garage, with simple hand tools.

I'm glad it worked for the OP. I'm out.

 

Whether the analogy was perfect or not, he gets the point across. Each carb is independent and if you want to be able to tune the center carb you need to strive for no vacuum leaks on the secondaries, however you accomplish that. Makes perfect sense to me and I appreciate F6's contribution to this thread.

 

I agree. Thank you for your reply. It does make sense.

 

Trying to idle off all 3 carbs won't work well, because the whole system isn't stable and accurate enough to maintain a fine enough airflow adjustment at such low throttle openings. Your mix will fluctuate with temperature and pedal position, and you'll always be fiddling with the screws.

Also you don't want chokes on the end carbs to spoil the WOT airflow, and without choking all three carbs you can't idle off of them all either, unless you like squirting raw gas in the engine to cold start it.

 

It was expensive and required maintenance, plus didn't tolerate wear.

When a single carb wears a bit you can compensate with adjustments. When 3 carbs are worn just a little, there's no way to make it run right cause it leaks 3x as much air as a single carb..

 

Ulu, I understand what you're saying, but I think you were assuming I would leave idle circuits in all three carburetors. What I meant was fully functional center carburetor with true secondary carburetors, but instead of drilling primary throttle plates for extra airflow, opening secondary throttle plates slightly via mechanical linkage to let a small amount of air bleed past. I was just asking out of curiosity, I believe what's being said about the throttle plate drilling is a better option. I was just curious. Carry on.

 

I do understand that you're not running the outboard idle circuits.

You're just adding air by cracking the butterflies.

The thing is, that that's not a real accurate method, because he butterflies & linkage aren't that accurate or consistent in their operation. This is one reason why carbs went to having adjustable air bleeds. The bleed was a more accurate method than cracking the butterflies on multiple carbs. Even with just one big carb, the bleed is a better method.

Injected engines have a computer controlled air bleed to adjust idle air. They don't even try to regulate it by the butterfly.

 

Thank you for explaining. That makes sense. Maybe you can appreciate what I've done in anticipation of such issues:

 

You're quite welcome, Tim, but I can't really comment on your exact carb or mods. I'm only speaking in generalities here.

In truth, the drilling of butterflies is sort of a hillbilly method. Really the transfer ports should be blocked and re-drilled. But exactly where or how much is tough to determine without trial and error. Also the butterflies and bores should be perfect (especially on a multi-carb setup) but they never are, plus they all wear differently. That means continual tuning over the life of the carb, and that you eventually just drill the holes, once the carbs get worn enough they won't idle & transition well without them.

The differential wear and fussy adjustment was a big factor in the factory's avoidance of multi-carb setups.

 

New
Whether the analogy was perfect or not, he gets the point across. Each carb is independent and if you want to be able to tune the center carb you need to strive for no vacuum leaks on the secondaries, however you accomplish that. Makes perfect sense to me and I appreciate F6's contribution to this thread.
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I agree. Thanks for the info F6. I've learned alot from you guys the last couple days on these carb threads.
-Pat