First thought is jets are not that expensive. Then you factor in two carburetors and the number of sizes and it adds up quickly. Looking at the Hot Rod Company's site shows them in 0.001 incements from 0.050 down to 0.041 then skipping a few numbers with 0.038, 0.035 and 0.033 rounding out the smaller sizes. This is for a more or less stock flathead with two 97's on an Edelbrock Super Dual. I haven't done any real work yet reading plugs or finding out what size jets are even in my carburetors, I just bolted them on and went. But it is evident that it is running pretty rich. How much difference does a thousandth make? Meaning once I pull the jets would it be smart to buy say, the three next smaller sets or maybe skip every other number? An example assuming they are 45's: do you thik it would be smarter to get 44, 43, and 42's? Or 43, 41 and 38's? Also saw the adjustable jet and was thinking it looked like trouble. But if anyone cares to weigh in on that or throw out suggestions on jet size for my setup I'm all ears.
Jet size realy stems from engine tuning demands as a base line. Its all very well to say our motor thats a 276 blown motor with max 1 cam and 5 speed in a moderately heavy 37 coupe uses 48 mains on 2 x 97s suits us but you need to go back to basics and do some seat of the pants tunning. You really need jets suited to your engine size and state of tune plus other variables to get you into the ball park initially.
I suggest using jet adjusters, simple and you can really fine tune the 97s. Duane. Vintage Speed has good ones..
Most guys over think the deal on tuning Stromberg's.The easiest way to get screwed up is to change a bunch of stuff at once.Suggest leaving the stock power valves and stepping down to 43 jets.Get the engine warm and take a cruise.Just drive it normal through all gears,click it in neutral,shut it off and take a plug reading ( don't let it idle very long before shutting down ) You want to wind up with a nice medium gray plug color.This is assuming the carbs are in good shape and you have a decent ignition ( and good compression! )
Kevin, my experience has been that with two carbs, the jetting has a bigger effect. I mean, with two carbs each two sizes rich is way more than just one carb. Does that make sense? My flatty ran well with one carb jetted at 48 and than I installed the other carb jetted the same and was way rich. I am running Holley carbs if that makes a difference. Sounds like flatheadjunk will get you on the right track.
First of all, I am a dick. (ask FHJ) I don't believe in adjustable jets. (where's the baseline?) I do believe in marrying the right jets with the right powervalves, remembering that a properly functioning powervalve starts to enrich the mixture at about 1/2 throttle - due to the "hydraulic" action of the accelerator pump, and becomes fully open at the end of the stroke. I also believe, for your flathead, assuming your're not planning to do much driving in the Andes or Himilayas, the best choice is .043 mains & number 69 powervalves. Set it and forget it.
Start with the original jets to see what you have. It should be pretty close because the original jets are sized based on the amount of air that the carb was designed to supply. Each carb is a separate system that adds the fuel based on the air that passes through that carb and it has no idea how many other carbs are on the engine.
Yeah. The venturis do the metering regardless, within the slightly higher range in which they actually function. The slight leaning that often produces the best reault is likely because there is less variation between the close and far cylinders with duals instead of single, so no need to run slightly fat to keep everyone happy. Need for big changes usually means you are covering a screwup elsewhere. Tune and test with no aircleaners. if things change then when you put the cleaners on, your aircleaners are actually chokes and you seriously don't want to tune carbs to compensate for tiny aircleaners! Adjustable jets are for industrial engines that can be tinkered at a specific speed and load that is not going to vary in use. Again, if the thing doesn't run right within a couple of minor change from stock something is wrong and you do not want to compensate for one problem by introducing another one.
Uncle Max knows of what he speaks. Use the numbers he gave you and I'd lay money he is spot on. He knows his Stromberg parts, rebuilding, and tuning (I personally run his work). And Bruce speaks of the philosophy of the Stromberg as eloquently as Max would, if he could.
I am running .043 jets in two Stromberg 97's on a Thickstun PM-7........seems perfect to me.......good power and reliability..... CB
I used these recommended jet and power valve sizes from Uncle Max. He's a great source for the parts too. They worked great on my 59 AB flathead with 2-97's on an Edmund's manifold. I'm still working through some timing issues but my plugs look great.
An old trick to find what jets you need......If they are, say, .050 and you want .043, find a piece of wire that's .007 and bend it up so it sits in both jets. Test drive it like that, if it seems right, then go find that size jets. Saves buying a whole shitload of jets that you don't need. I have actually driven thousands of miles with a carb "rejetted" like that.
also if using used jets if you find some that have been drilled by accident it can send you in a tail spin...
I would not quarrel with those who have setups, and have quoted numbers. However, if you have no input from those who have identical setups: First, make CERTAIN that the ignition is in good shape (poor voltage will act like an overrich carburetor). Build the carburetors STOCK, and then drive the vehicle. This gives you a baseline. On virtually any carburetor, one may TEST what different size jets will do by altering the fuel level. A fuel level 1/16 inch higher will approximate 1 size (.002 on Stromberg EE-1's) richer; while a fuel level of 1/16 inch lower will approximate 1 size lower. Obviously, from the above, making certain the float setting is spot on is critical. Fuel pressure is also critical. Too much fuel pressure will cause a higher fuel level even if the float is correctly adjusted. Do your testing BEFORE you buy the parts. You buy fewer parts this way. And NEVER, repeat NEVER believe what is stamped on a jet! Acquire a set of number drills and measure! Lots of folks drill jets oversize. Jon.
I think a good piece of sanity insurance, given the number of carb and ignition screwups any normal hotrodder can generate, is to spend a little extra time and run and drive both carbs individually on stock manifold...you should be able to swap a flathead manifold on a coffee break, and usually there's not even a real need to get a new gasket. If car runs well on singles, you have some assurance that they actually function as intended and that there is reason to believe your ignition works too. Then you floggem as duals, so now the possibilities of trouble are just the dual combination...you can believe the car and carbs are basically functiuonal. If you have trouble with a a vehicle that has new ignition, two fresh rebuilt carbs, AND a whole new manifold and linkage, you will have no idea where to look if it runs badly. Try to have only one thing at a time freshly screwed up; then you have a fighting chance!
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