Doing a little on the road tuning on my heap. V8-60, slightly warmed over with single 97. 50 mains, 65 power valve. Seems too rich, plugs sooty and missed at high rpm. Stock V8-60 uses 35 mains and 71 (which is leaner than a 65) PV in the Stromberg 81. That would be too lean for a 97 I'm thinking. How does the fuel from the power valve get into the venturis? Not through the mains right? If I disconnect the accelerator pump will that disable the power valve and give me a leaner open throttle for testing? I'm trying to figure out if I should go leaner on the jets or the power valve, or likely both. I have none of this stuff so I have to buy it all, or find someone with a jetting stash. It's not a vacuum operated power valve btw.
The accelerator pump pushes fuel through the power valve and discharges through the curved nozzles in the venturis. Stock 97 mains are #45s, and is what I would start with.
http://www.flatheadv8.org/stromberg.htm About half way down the page it the pictures of the main and power valve circuits. It looks like the power valve adds fuel after the main metering jets. Here is a good stromberg article on how to tune the main and power circuits. http://www.stromberg-97.com/tech_center/pdfs/stromberg-what-jet-size.pdf
Go back to stock 97 for starters...any tuning needed will end up at least close to that. .050 jets have you off the map, you probably have no power andyour rings will wear out in a few hundred miles. Jet sizes relate to the whole design, especially venturi size...hence the much smaller jets in the 81. You cannot correct the effects of totally wrong jets by messing with other parts! Over-rich jets might come out about right if you kill power valve, but will still be drowningly bad at part throttle.
Thanks guys, I'll start with 45 mains. Yes, I can see in the diagram how the power valve sends the fuel out the pump nozzles.
OK, a friend lent me some 45 mains and it runs better but still won't rev up without cutting out. In a moment of self perceived brilliance I soldered up my 50s and drilled them to .035". Now when you stab it it just dies, unless you give it the choke to get it going then it revs up better than with the 45s. So I don't know what's going on. Accelerator pump is working. If I disconnect it and push it all the way down with engine running I should see fuel coming out of the pump discharge nozzles if the PV is working, right? Any other way to test it? Oh, also, I'm running 12V, a smallish 4 ohm coil with stock pancake distributor and no ballast resistor, stock pancake points and condenser. The coil might be off a motorcycle. Also resistor wires. It fires right up and idles great but I suppose it could be too weak at higher rpms.
Your jet needs are going to be somewhere close to .045, and I doubt that 045 would be far enough off to cause much of a problem. .035 is too lean to run and you have gotten it somewhere close to usable by choking... Put the 045's in, get a standard pv, pump set on leaner setting. Check float level, if good mebbe even lower it a 32nd... Check pressure delivery...even many "stock"pumps are too high, shoot for 2 PSI Air bleeds if clogged will richen the mixture...remove jets, pull out the brass tubes (I've posted on doing this with tooling available at home depo), clean everything, see that the tiny sideways holes are open and round, clean the matching hole in casting where tubes go into carb throat Clean idle bleed, a hole in main body between idle jet and carb throats With engine idling, slowly turn idle mix screws in as far as you can without killing engine...idle and off idle circuit feed some gas up into road speeds Jets are close enough to function and are not your problem, 045 should at least operate the thing
PS!! Do all testing and tuning with no aircleaner...stock ones or small paper hotrod ones can be fertile sources of trouble. Once everything is beaten into submission, THEN put the cleaner back on...and if anything changes, you need a different air cleaner! Many people have gone mad trying to tune a carb with endless jet changes when the actual problem was the little chrome aircleaner with its lawnmower size element.
Thanks Bruce. No air cleaner yet. I did remove the emulsion tubes when I rebuilt the carb (not easy but they came out without damage), I could check them again. Also cleaned every passage. The power valve is a 65, stock for a 97 I believe. I set the float level yesterday at 15/32, it was too low and dying off idle. I'll try 1/2" When I put the pump on the leaner setting the rod hits the butterfly lever and it won't got back to low idle. It idles great, pilot screws adjusting mixture in proper range.
Fuel level or float level? That's right for fuel level, there isn't an actual factory spec for float level but it is very small...I'm sure you are talking fuel level because float probably can't go that low with a hammer in play! Next get holf of a pressure gauge. If pressure is high, it overrides everything else.
Fuel level, sorry. I'll check the fuel pressure. I just have the stock mechanical pump on the intake manifold. And I guess I can bend something to make the leaner setting on the pump work.
Stromberg intended for the FUEL level to be set with the air horn removed from the carburetor. With 3 pounds pressure on a gauge between the fuel line and the fuel valve, the fuel level was to be 15/32 inch. Stromberg suggested this setting would be obtained when the toe of the float (the end opposite the hinge) is flush with the top of the bowl casting; so the suggested FLOAT level is ZERO. Perhaps the zero is why float levels for this carburetor are not often seen. This setting is with the 0.098 inch fuel valve seat. If the optional 0.130 seat (for alcohol) were used, the FLOAT setting was 3/16, which still maintained a FUEL setting of 15/32. Jon.
Fuel pressure is 4.5. Can I adjust the stock mechanical pump somehow or is it manageable at 4.5? Regulator? I set fuel level with a T gauge, air horn and gasket off, idling, until it just touches the fuel. I turned the accelerator pump lever around on the air horn so the ball faces forward instead of backwards, now the rod clears the butterfly lever at the bottom on the lean setting. Probably not right.. Edit: well, looking at some pictures it appears I had that lever on backwards.
Well, 4.5 is fairly high...BUT if you have had it idling with lid off you have kind of checked it out. If the pressure were overwhelming the inlet, you would have had a very unstable or even overflowing bowl while you tried to set it. You may be OK there unless it gets worse at higher than idle speeds... Ford bulletins called for fuel level to be set on the bench with the actual pump from the car running on a special little machine, and neither Ford nor Stromberg published a float level...all instructions were based on fuel level just like you handled it. Ford did put a level gauge in their later rebuild kits for the 97...I guess there was no longer anyone left who even understood the concepts, and they had to be given a float gauge or their heads would explode.
Yes, float level is stable with top off, maybe my gauge is off. I just disconnected the accelerator pump. Started it up and peered down the carb. When I push the pump down all the way I get the initial squirt out the nozzles but shouldn't pushing the pump down all the way open the power valve and send fuel out the nozzles? I'm not getting anything past the initial squirt by the pump.
Pump fuel is sent out by the pump under pressure and so functions at any speed. Once pump is down and PV is open, fuel is AVAILABLE but cannot flow through the nozzles until there is enough airflow through venturis to pull it. Different holes, but same as main jets...fuel has to be pulled by venturis.
Required reading: Go here http://www.norgv8club.org/norg/inde...rs-and-tech-tips/category/9-service-bulletins Read the carburetor bulletin noting Stromberg operation...you need to scroll past the Ford carb section. That will help guide your thinking. Rebuild info is in the other bulletins there, again stromberg and Ford under same click.
Ah, gotcha. Well I took the power valve out anyway, and it'f fine. But I can't find any markings on it for size whatsoever. Going to put it back together with the 45s back in it and try it again with the pump on the lean setting now that I have the lever on right.
Back together, same thing. Starts right up, idles great, drives great under 1,500 rpm or so. Goose it hard and it dies. Pedal it slower and it gets up to about 2,000 and misfires. Pull the choke and it takes off, then goes rich and craps out. Push the choke back in and it goes pretty well once it's up in the rpms. It's as if the power circuit isn't working somehow. Bruce, as you said above, if I rev it high enough in neutral, at some point it should reach enough velocity through the venturi to pull fuel out the pump nozzles from the power circuit shouldn't it?
like Bruce said air flow is important to the flathead and the 97 carb. I had the little cheap round air filters on my engine and it ran way too rich no matter how I set the carb up, runs great with out a filter..........anyone think running no filter at all is bad? all I have been doing is putting around with one of those bug screens over the top of the carb. engine runs great this way.
I strobed it yesterday, using a zip tie head as a piston stop to find tdc, which I think Bruce mentioned somewhere else. Worked brilliantly. I don't have a tach but it seemed to be all in pretty quick. I have the vacuum brake screw backed out all the way and total set at 24 degrees.
Ah, progress. To cut to the chase, referencing the photo below, I now have the pump rod on the summer, or lean ball at bottom. When I put it on the winter or rich ball ahead, the rod has to drop down, which pulls the pump up higher in the carb such that I don't get any squirt for the first part of throttle opening. Why this is I don't understand, it's like it's raising the pump up into the slot, I don't know. But on the setting where it is now I can accelerate well. Still fat on top I think, going to try 40 jets next. Thanks again all for the input.
The markings on the original power valve referenced drill size; which is why a "65" is larger than a "71". If you have access to a set of orifice drills, you can measure the opening in the side of the power valve. My guess would be the 45 jets might be OK, but the power valve may be too large. Going to 40's on the main jet is a SIGNIFICANT change. Jon.
It does appear to be a Rochester valve (or possibly a Holley), and the plunger is longer than the plunger on a Stromberg valve; plus the 4 holes are all about the same size as the one on the Stromberg. Jon.
So I'm thinking: A) The Rochester meters that circuit with something other than the valve, since it has no size markings, and B) I'd better get a Stromberg valve before I do anything else. Funny that it fits right in.
So I have a Stromberg 65 power valve in place, started with 35 mains and have worked all the way back to the 50s for best performance, otherwise I need to choke it on acceleration. I disconnected the accelerator pump at the top and it runs the same except for having to feather it to get it moving. This leads me to believe the power valve isn't kicking in. Trying to diagnose, I have a strong stream from the accelerator pump, and the power valve is opening when I blow through it while holding the pin down. I don't know what else I can do to test that circuit.
I know this is super old but did you ever figure out your issue? I’m going through a similar situation with my flatty and dual 97’s
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