Let's build a Stromberg 97 3x2

Thank you for posting all the good info! I think a lot of guys have been wanting good info that's clear and tested. I wanted to post this build so that we could all learn, like I said I'm all ears.

I ran the center carb for just a minute at idle. I didn't want to rev high as there wouldn't be enough cfm.

Once the center carb is at idle and the vacuum advance is unhooked it stumbles bad. Very smooth hooked up though.

The picture was of the plates closed all the way with the throttle stop screw out. I also was holding the throttle shaft closed tight. All three are this way. If I put the other two carbs on progressively won't this act as a vacuum leak?

Thanks again!

Tyler

 

Using all three idle circuits would negate the need for the butterflys to shut tightly.

 

Some very interesting info on here, Thank you very much! I am interested because of the planned future use of a 6x2 intake on a 301 inch chevy with streetable compression and a fairly mild solid lift cam.

 

Tyler, (I got your name, thanks.)
The throttle plates should shut pretty good. It's a production fit, so I'm not going to pretend that they are hand lapped like you might for a race car, but as I said, you'll probably run them a little open anyway. Here's the deal, for the engine to idle it needs to get some air and gas past the throttle plates. There are two sets of idle ports in a 97 base, lower and upper (transition), above and below the throttle plate. Technically this means you could get gas mixture through if the plate is closed, but usually that's not enough.

A vacuum leak is when the air is coming from outside the carb (typically through worn out throttle shafts) so it is not collecting its metered share of gas along the way. If the plate is open a little, we're talking air being drawn through the carb by the engine, and collecting the right gas to make the correct air/fuel A/F mixture for your idle.

Set all three carbs on the manifold with no linkage at idle. Get a vacuum gauge and balance all three carbs so each is set the same and contributing the same air/fuel mix to the overall engine. Aim for the maximum vacuum from all three carbs. You can adjust them using the throttle stop screws on the side of the carbs, and the idle mixture screws on the bases to keep it smooth and not lumpy. It's fiddly and you have to go around and around adjusting. There was a great post on the HAMB about carb balancing years ago if you can find it. But you should get a smooth idle at the rpm you want - using all three carbs.

Then you can fix the linkage making sure that it does not disturb the idle balance you have already. You can read how to set the linkage up on our tech center - http://www.stromberg-97.com/tech_center/pdfs/Stromberg-Linkage-Inst.pdf

Basically your outer carbs sit there (feeding a little in through the idle ports) until you hit about half throttle, at which point your centre carb will come onto the power valve and start enrichening the mixture just as the outer carbs start opening, adding more air and gas. The main jets start up literally the moment you open a 97, so they're good to go straight away as the signal is very accurate. It's that smooth progression that makes them work so well, (in my humble opinion!)

I would start them out of the box and then read the plugs or get the gas analysed. You won't be far off at 45 main jets and number 65 PVs (the 'out of the box' setting). And try it with the outer accel pump links disabled. Each application will differ slightly with local gas, elevation, cam etc.

Now, about the distributor vacuum. Is it connected to the manifold? I'm not sure why it is behaving like it is, but if it works, stick with it! My money is still on mechanical advance.

All the best, Clive at Stromberg

 

Unclee,

We have written a lot of tech information about the options for 6x2 on our Tech Center. Your chosen intake will also make a difference. Like most things, it all depends how fast you want to go, and how much gas you want to buy ;>)

Check it out....http://www.stromberg-97.com/tech_center/tech_center.html

 

That statement alone has me VERY concerned, on quality control. I have to question what else you might not be seeing that was fit with "eh, close enough"

 

This thread has really turned out well with good info. Clive thanks again for posting, means a lot. Hey I don't mind asking all the dumb questions so others don't have to!
So I have the other carbs back together and am going to get them bolted on in a bit. Need to go get a fuel rail so I'll be down for a couple days...may just make one so I can get going quick.

 

Hi everyone. Thought I might attach a couple of pictures of a random sample throttle body from today's 97 production to calm a few nerves. With nothing attached to the throttle shaft they close real tight. Thanks.

 

Just wanted to give an update on the 3x2 setup. I have the engine running and the coupe is on the road. I went ahead and ran the carbs as adirect linkage and the thing runs like a scalded ape! If my block was bigger i would run progressive, but with more carbs.The carbs perform great and i will be using them again. There is still some tuning to be done but they run great out of the box. I'll post a picture later and a short video. Thanks Clive for a great product.

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Very pleased to hear it Tyler. Thanks for your follow-up and kind feedback.

 

Excellent tech Clive, thanks very much. Jim M.

 

Any updates on the setup??? Pics? Video? I'm pondering a similar getup for a future 327 build. THANKS (killer thread)!


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Will be soon. I ordered a multi carb tuning gauge from EMPI, the old Holley style not the uni sync. I adjusted the carbs by ear and it runs great! But i know that it can be fine tuned.

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