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Old 09-21-2021, 02:31 PM   #21
vincent
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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
Terry,OH
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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
Charlie ny
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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
Terry,OH
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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
Bill OH
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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
Bill OH
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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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