Dual Stromberg questions

rhphotord

rhphotord

Senior Member
Updating my AV8 flathead. Installed two rebuilt Stromberg 97's on an Edmunds intake and have tried synchronizing the carbs with no success. Seems the front carb is the only one responding to idle adjustments screws. I can put my hand over the rear one and the engine continues to run albeit poorly. The front carb stalls the engine immediately. What gives? Appreciate any input, Thank you
 
rhphotord said:
Updating my AV8 flathead. Installed two rebuilt Stromberg 97's on an Edmunds intake and have tried synchronizing the carbs with no success. Seems the front carb is the only one responding to idle adjustments screws. I can put my hand over the rear one and the engine continues to run albeit poorly. The front carb stalls the engine immediately. What gives? Appreciate any input, Thank you
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Perhaps swap the carbs around to see if any change of position makes a difference. Maybe then a carb to inspect .
Phil NZ
 
Hard to answer your question without some information.

BUT Is this how you went about setting both carbs?

When you run two deuces both need to work as one this means at idle both carbs should flow the same amount of air. To get the carbs each flowing the same amount of air a Unisyn gauge is used. To get both carbs flowing the same amount of air your adjusting the linkage connecting both carbs. The correct linkage to use needs to have a threaded rod that has a left hand thread on one end and right hand thread on the other end. Each end of the threaded rod has a rod end threaded on that connects to the arm that clamps onto the carb throttle shafts. Be sure both carb linkage connections are as close to each other visually including the arm angles as well.

Now with the engine running by placing the Unisyn on top of each carb you can see how much air each carb is flowing. To get each carb flowing the same of air you turn the rod and watch the reading of the Unisyn you move the gauge from carb to carb as your adjusting the rod to get a balanced reading.

To set the idle mixture screws a vacuum gauge is used. Connect the hose to the gauge to a vacuum location below the carb throttle plates. With this gauge connected you now adjust each of the four idle mixture screws so that the highest vacuum reading is seen on your gauge.

When both carbs are adjusted as I wrote you should be all set.
Ronnieroadster
 
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Both carbs have to be in top condition. No air leaks around throttle shaft and body, base to manifold. As Ronnie said, a Unisyn is the tool you need for this. I would suspect the carb that is not acting right probably needs a complete rebuild and surfaces all checked to be flat. I am running 2 97 on one car and 2 81s on another.
 
deuce_roadster said:
Both carbs have to be in top condition. No air leaks around throttle shaft and body, base to manifold. As Ronnie said, a Unisyn is the tool you need for this. I would suspect the carb that is not acting right probably needs a complete rebuild and surfaces all checked to be flat. I am running 2 97 on one car and 2 81s on another.
Click to expand...


X2 on this comment. Sounds like one carb isn't running right. Could be a lot of things or even something on the intake. All things considered, it's not the hardest thing to swap the carbs and isolate it to a single carb as someone else recommended.



Had the same problem. In my case replacing the throttle shafts with oversized units fixed the issue. But that's just one of many things it could be. These old carbs have to be rebuilt perfectly and all squared up, not just installing a rebuild kit.
 
Here's maybe a dumb question for this same setup (I too am using two stromberg 97s and an Edmunds intake). How the heck to you fit a screw driver in there (especially the front carb) to adjust the 4 idle screws? Just use a really small flathead? Space is tight with the generator!
 
It could be the power valve leaking in the carb that won't respond when you adjust the idle mixture screws. It happened to me on a brand new 97. You can test the power valve by putting it in your mouth. Gently suck and blow through it. If there is no difference in the flow in either direction, it is toast.
 
Idle Screw Adjusting Tool: I've had a 90 degree tool for carb idle screws that was made many years ago by I think Proto. I use it on every flathead multi-carb manifold . . . makes things so much easier.

I looked on Amazon and here is a "modern" incarnation. I highly recommend having one in your "tuning toolbox".

Note: I have NOT bought this particular tool - but it looks like it should work. If you don't like it, send it back!

https://www.amazon.com/Qiilu-Adjust...nowmobile/dp/B0BG9GP2MY/?tag=atomicindus08-20
 
The one idle RPM screw, on each Carb., is adjusted for sync. not the two brass idle mixture screws.

If the engine is running on just the front Carb. then slightly lower the front Carb. engine RPM and increase the rear Carb. RPM. Then repeat until both Carbs are sync together. Do this with the linkage between the two Carb.s disconnected.

The two brass idle mixture screws can usually be adjusted by hand so no tools are needed. You do need a screwdriver for the idle RPM adjustment.
 
The Edmunds intake has the front carb basically in the stock position, and the rear carb over the rear two cylinders. I have the same intake on my '47. You're never going to get the rear carb to pull the same vacuum as the front carb like they say you should with that style manifold. If you get the rear carb to sync with the front the idle speed will be ridiculously high. Set it so it runs good and leave the unisyn in the tool box on this one.
 
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The more I think about this issue the more I think its a function of the intake design as noted. The front carb does indeed sit directly over the center of the intake. Both carbs were completely rebuilt with new internals, surfaces checked at time of rebuild. No misfitted or worn throttle shafts found. All linkage was disconnected when adjusting idle. I have a unisyn and that is what I am using. Have three other rebuilt Strombergs so perhaps I'll swap one out for peace of mind if nothing else. Stay tuned
 
When you say rebuilt, were they done by a professional, like by Charlie from NY?
There's more to it then just installing a kit.
 
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