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Old 09-12-2021, 02:31 PM   #1
kingskid
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Default Stromberg 97 adjust

I have two Stromberg 97 carbs on my 59ab. Trying to adjust the idle mixture screws. Is there a special screwdriver needed? Do I have to take the carburetors off to accomplish this? Looking for a 90° flexible screwdriver to do this. Any advice or ideas is appreciated. Thanks in advance King's kid.
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Old 09-12-2021, 03:46 PM   #2
Henry Hopper
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Default Re: Stromberg 97 adjust

They should be able to turn by finger pressure... if tight you can use a washer to fit in the slot to turn them.

Last edited by Henry Hopper; 09-12-2021 at 04:16 PM.
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Old 09-12-2021, 03:53 PM   #3
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Default Re: Stromberg 97 adjust

Offset driver
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Old 09-12-2021, 05:05 PM   #4
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Default Re: Stromberg 97 adjust

I've got a special screwdriver designed just for this purpose somewhere. It has a cylinder shaped piece over the slotted part that holds it on the adjusting screw so it doesn't slip off. It is on the end of a flexible shaft (kinda like a speedometer cable) with a nob on the other end. I'll try to find it an post pictures. A "Google" search may yield the same thing quicker.

EDIT : Try this : https://www.amazon.com/OEMTOOLS-2506...1484361&sr=8-5.
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Old 09-12-2021, 09:46 PM   #5
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Default Re: Stromberg 97 adjust

Maybe he has some originals with no slots?
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Old 09-12-2021, 11:41 PM   #6
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Default Re: Stromberg 97 adjust

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A little trick I learned on here with twin 97's, is to find some rubber hose that slips snugly over the heads of those mixture screws, cut to suitable length to be able to access.
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Old 09-13-2021, 10:13 AM   #7
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Default Re: Stromberg 97 adjust

The original screws have a slot almost half way across the head.
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Old 09-13-2021, 04:31 PM   #8
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Default Re: Stromberg 97 adjust

Years ago I bought some that had knurled heads you can grab with your fingers instead of slotted for a screwdriver. I could swear they came from Uncle Max. If he doesn't still have them he would sure know where to get them.
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Old 09-13-2021, 04:52 PM   #9
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Default Re: Stromberg 97 adjust

Quote:
Originally Posted by alchemy View Post
Years ago I bought some that had knurled heads you can grab with your fingers instead of slotted for a screwdriver. I could swear they came from Uncle Max. If he doesn't still have them he would sure know where to get them.
Just got a new run. 600 available. Fat Finger Friendly.
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Old 09-19-2021, 10:06 PM   #10
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Default Re: Stromberg 97 adjust

Thanks for the replies. I was able to use clear plastic tubing over the screws.
Two duce set up too close to get hand in there. What is the correct setting on these? Many different suggestions. From 1/2 - 1 1/2?
As you can tell I'm new to this. Was checking the carbs off the car- one has throttle plates in the base, the other one doesn't. What's up with that? I just got the car 47 Bus. coupe. Running real rich. Offy. heads and intake, 2- 97's,
Isky #77 cam, Fenton cast iron headers. suggestions? Thanks, kingskid.
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Old 09-20-2021, 06:06 AM   #11
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Default Re: Stromberg 97 adjust

Max's design is just enough longer so your thumb and fore finger are the only tools required.
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Old 09-20-2021, 06:22 AM   #12
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Default Re: Stromberg 97 adjust

Both MUST have throttle plates!!! With two 97's the adjustment is about 1 1/2 turn out. Are you running the Carbs with linkage synced or progressive? Typically synced is good. You may need a Uni-Syn or similar gauge to monitor the air through the two Carbs at idle to adjust each so they work together equally. The idle vacuum will be lower with two Carbs about 15"
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Old 09-20-2021, 11:51 AM   #13
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Default Re: Stromberg 97 adjust

Quote:
Originally Posted by kingskid View Post
Was checking the carbs off the car- one has throttle plates in the base, the other one doesn't. What's up with that?
You're kidding right? How does it even run with no throttle plates in one carb? WAY TOO MUCH air getting in with not enough gas. You must mean choke plate I assume.
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Old 09-20-2021, 11:54 AM   #14
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Default Re: Stromberg 97 adjust

Quote:
Originally Posted by Brian View Post
A little trick I learned on here with twin 97's, is to find some rubber hose that slips snugly over the heads of those mixture screws, cut to suitable length to be able to access.
Ditto
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Old 09-20-2021, 12:42 PM   #15
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Default Re: Stromberg 97 adjust

No, not kidding. I thought to myself "how does it even run"? I used some rubber hose and got the mixture set. Pulling 16" of vacuum at idle. I thought that was in limits considering the cam. Still baffled about the throttle plates. There is throttle plates in the carb, but not the base. That is the front carb which should be the secondary right? I'm using synced linkage. Hard to start when warmed up. Cooled down starts right up 1-2 Rev's.
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Old 09-21-2021, 08:05 AM   #16
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Default Re: Stromberg 97 adjust

The synced Carbs are both operated at the same time by the linkage with both operating together at idle. Neither is considered secondary and both Carbs should be identical. For example tri-power that is set up progressive, the front and rear Carbs are secondary since they no not operate at idle

Your front carb is a dummy, it is there for appearance and to block the holes in the manifold. The throttle plates in the cast iron base were removed so a plate could be installed to block any air from going through the Car. You should also find no fuel going to the front Carb. When your car is running you should be able to place your hand over the front Carb and nothing will happen, the engine will continue to idle. On the front carb, take both idle adjustment screws and screw then in all the way and adjust the idle mixture with just the rear carb.

Just the rear Carb is working and it may not be set up properly resulting in improper idle adjustment and poor operation being rich. I would think the idle mixture screws should be out about 1 turn or slightly less not 1/4 turn. Your vacuum should be closer to 20" For a 97 I believe you want .045 mains and #65 power valve. If you want both Carb to operate there is a lot more to be done.
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Old 09-21-2021, 11:27 AM   #17
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Default Re: Stromberg 97 adjust

What manifold do you have on the engine? Most 2-carb manifolds should have two fully functional carbs - no dummy in either location. If you only run one carb, you can get really uneven fuel distribution to the cylinders that are furthest away.
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Old 09-21-2021, 11:43 AM   #18
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Default Re: Stromberg 97 adjust

If you have one of this type dual manifolds, you can probably get away with running one carb blocked off (the rear carb), as the front carb is in just about the position as a stock manifold. It's better to get two running correctly, though
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Old 09-21-2021, 12:20 PM   #19
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Default Re: Stromberg 97 adjust

Forgive me for entering your thread but I have a couple questions that if answered might help you as well to get your carbs sorted.
What mainjets would you run in a twin (GB) Stromberg 97 carb set-up? The reason I ask is that I am not getting info anywhere. No response from the makers in GB so far. The engine is running rich and smells badly.
What I did until now:
lowered pressure to 2,5 psi
lowered fuellevel 1/8" below the recommended 1/2" level
fitted smaller mainjets (around 0,040")
adjusted the idle with the mixture screws, have nice and even tick-over and good response to the pedal.

Are the mainjets really responsible over almost the whole rev range? I want to lean the carbs out a bit more and will make a couple smaller jets on my lathe to try.
Thanks for any wisdom you could share with me
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Old 09-21-2021, 01:05 PM   #20
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Default Re: Stromberg 97 adjust

Vincent, I wish I knew enough to answer your questions. I am not very familiar with the 97's. I had Holley's on my fifty. I think Terry,OH answered my situation. The car runs fine under acceleration. I just wondered why no butter fly's in the one base. Never seen that before. Thanks for your reply.
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Old 09-21-2021, 02:31 PM   #21
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Default Re: Stromberg 97 adjust

I have investigated a bit more: the homemade jets with 0.034" have no influence on idle - thats what I thought anyway. The car will not accelerate without a lot of hesitation/burps until it reaches about 2000 revs, from then on its fine but a bit gutless. Pulling the choke a bit helps a lot so now I will open the jets to about 0.037" and try again. At least now we know that the mains are responsible over the whole range.
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Old 09-22-2021, 04:50 AM   #22
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Default Re: Stromberg 97 adjust

0.037 did almost work but even after warming up the engine enough it was slightly hesitating when slowly pushing the throttle in. However when pushing throttle quickly the accelerator pump squirts enough to overcome this area. At higher revs the thing is flying so now I need to find a way to richen up the area when just moving the butterfly away from its stop. I found that the mainjets are perfect now but the pick-up is a little bit too lean. I need an expert to tell me what to do next. Meanwhile I fit the 0.040" jets as they are rich enough to cover the low throttle area as well.
Anyone out there knowing what to modify/change for my problem?
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Old 09-22-2021, 06:50 AM   #23
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Default Re: Stromberg 97 adjust

In what location is the accelerator link in the throttle W or S? If W go to S and open the mains up a couple of thousands more. You should see the pump squirting with small movements of the throttle, if not look for anything loose or missing springs on the accelerator pump in the Carb.
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Old 09-22-2021, 04:57 PM   #24
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Default Re: Stromberg 97 adjust

Terry, I tried the 0.037 first with the summer setting but it was still too lean on the transition from idle to butterfly lift. So I put the links onto the Winter setting which helped a bit but not enough. The problem is the slow acceleration off idle and keeping the engine there with the butterfly barely lifted. There is no squirt as there is no movement in the pump and clearly this area is too lean compared to the rest.I can run the car on 0.040" and cover this area good enough but it is a little bit too rich in the upper revs - hence the question what to do to richen up just the transition area between idle and the first movement of butterflies... It is not doable with the mains or the idle circuit so I need a tip what to change on the carbs. On a motorcycle I would change the slide for a smaller cut-out but I donŽt know enough of these carbs until now so I need to investigate.
Idle is perfect at about 700 revs, ignition is at 4 degr, full advance around 24 degr at 2000 revs, plugs are a nice brownish color on the isolator.
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Old 09-23-2021, 06:33 AM   #25
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Default Re: Stromberg 97 adjust

Are you able to idle at about 500 RPM? If so adjust idle mixture screws there. Check vacuum, adjust mixture for the highest vacuum. Even at 500 the throttle plates will be open slightly. When the throttle is moved off idle the accelerator pump has to move or you will have the problem you are experancing. The S setting is supposed to be leaner than the W. As mentioned previously the main jet size of an original single 97 on a flathead is .045" and the power valve #65=.035" I see no reason why your engine, if 85-90HP, should run better with smaller mains. Have you checked the power valve size? The float level and the fuel pump pressure 2 to 2.5

Last edited by Terry,OH; 09-23-2021 at 06:40 AM.
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Old 09-23-2021, 08:32 AM   #26
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Default Re: Stromberg 97 adjust

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Terry, I got a reply from Stromberg GB and will check the points that Clive mentioned. I will do the tests that you suggested as well and see where this leads. We will eventually find the problem / solution. IŽll write my findings as they come.
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Old 09-23-2021, 10:06 AM   #27
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Default Re: Stromberg 97 adjust

The Stromberg 97 is an extremely simple carb - it doesn't have a bunch of circuits to deal with - really has about 4 things you can tune:

1) Idle - using a combination of the throttle plate screw to set the air flow and associated RPM and the mixture screws to adjust the rich/lean at idle. Like most carbs, you turn them in until the engine starts to stumble a bit, then back them out about 1/4 to 1/2 turn.

2) The main jets control just about everything off-idle (except for the enrichment circuits). Typically you'll find that the higher-speed RPMs might be a tad richer than you'd like, but you'll need the larger jets to overcome a too lean condition off idle.

3) The power valve does just what the name implies . . . a bit similar to the Holley vacuum operated valves, but strictly mechanical.

4) The accelerator pump has two slight adjustments - the 'W' for Winter and 'S' for summer (supposedly). On my larger cube, big cammed engines, I tend to always use the largest stroke I can get - which is the 'W' setting. On Stromberg 48's you only have a single setting - though you can swap 97 bases onto 48's and get the two position adjustments.

When using an O2 meter to measure my AFR, I find that in order to make it run the best under all conditions, I have to live with a richer AFR at higher RPMs than I'd like - closer to 12 - 1 (284 cubic inch engine, ported, big valves, big roller cam, etc) . . . though there are no viable means to adjust both the higher RPM AFRs and not impact the lower RPM AFRs. These carbs are simple - which means not too many adjustments! LOL
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Old 09-23-2021, 12:03 PM   #28
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Default Re: Stromberg 97 adjust

B&S - thanks for writing your findings, they confirm my thoughts.
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Old 09-23-2021, 03:20 PM   #29
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Default Re: Stromberg 97 adjust

Did you get it figured
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Old 09-24-2021, 04:07 AM   #30
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Default Re: Stromberg 97 adjust


Larger picture of Twin Carbs supplied by alchemy
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Old 09-24-2021, 07:28 AM   #31
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Default Re: Stromberg 97 adjust

To 'time' the squirt with the throttle it is often req'd to bend the bell crank arm slightly,
it makes a difference. Do not over look he possibility that the model 40 or 48 acc pump

link is mistakenly being used....it is SHORTER that the 97/81 link and makes a difference
in timing the squirt in relation to the throttle position.

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Old 09-24-2021, 10:36 AM   #32
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Default Re: Stromberg 97 adjust

Here are a couple pics so you see what is under my hood. After receiving Clives advice I reduced the pump pressure further down to a little under 2 psi - seems to help. The floats or the power valves did not leak when I tested them on the pump at 2,5 psi. So now the pump delivers less which will lower my float level a bit more but still the car drives nice and with crisp response, no stumbling when warm but needs a bit of choke for the first mile - just what I expected. If I cannot stop the smell I need to find a way to keep it out of the car. My exhaust pipes run straight under the car and end about 3" after the rear bumper. I took great care to make sure the headers and the tubing going rearwards is gas-tight. No leaks under the car. I ducktaped all openings on the floor or firewall but I can still smell a little bit when running with open windows and slower than 40mph. At 65 and above the car is probably too fast for exhaust fumes to enter or it runs lean and clean at those speeds. The plugs are a nice brownish color so its not on the edge..
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Old 09-24-2021, 10:58 AM   #33
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Default Re: Stromberg 97 adjust

From your photo I notice your using just the front carb choke. If the front carb is blocked shouldn't you be using just the rear carb choke?
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Old 09-24-2021, 01:28 PM   #34
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Default Re: Stromberg 97 adjust

Terry, I use both chokes, have made a little contraption to go over the rear choke lever and thus both chokes move. Both carbs are fully working as the butterflys are linked.
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Old 09-24-2021, 08:49 PM   #35
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Default Re: Stromberg 97 adjust

I took the carb off and checked the base. It does have throttle plates. the throttle connector on the drivers side just spins on the shaft. that is why I thought it did'nt have any. My bad sorry for misleading ya"ll. I should have pulled it off first, before posting. I got the mixture adjusted and it runs fine. Thanks for all the comments.
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Old 09-25-2021, 10:19 AM   #36
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Default Re: Stromberg 97 adjust

On the advice of another person, I installed 43 mains and 65 PVs in a pair of 97s. Hesitated off the line unless PVs were open - ie WOT. I went to 45 mains with 65 PVs and the engine would bog when the PVs were opened. I kept the 45 mains and installed 71PVs, which is half of the 65 PV. Engine runs fine and is very responsive with the idle mixture screws turned out one turn. I am using a stock mechanical pump, no regulator, an no chokes. I am in Northern Ohio at an elevation of about 600ft. Hope this helps.
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Old 09-25-2021, 10:29 AM   #37
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Default Re: Stromberg 97 adjust

On the advice of another person, I installed 43 mains and 65 PVs in a pair of 97s. Hesitated off the line unless PVs were open - ie WOT. I went to 45 mains with 65 PVs and the engine would bog when the PVs were opened. I kept the 45 mains and installed 71PVs, which is half of the 65 PV. Engine runs fine and is very responsive with the idle mixture screws turned out one turn. I am using a stock mechanical pump, no regulator, an no chokes. I am in Northern Ohio at an elevation of about 600ft. Hope this helps.
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