59AB with 2 x 97's get 5 MPG ??

[Robert Dip]

I have a ’39 Coupe that was built in the 50’s. 59 motor, Navarro heads and intake with 2 x 97’s, headers, etc. Did all of the ignition work, including new electronic distributor, plugs, wiring ( carbon wiring for electronic ) and rebuilt the 97’s completely..including removing the emulsion tubes. Engine basically runs OK ( not the best as it should ) and my problem is that it uses a ton of gas. I must be getting about 5 mpg. New plugs after an hour’s run are black & full of soot. Carbs are stock jets at .045, power valve also stock at 65. I am told to change the power valves to a higher # to decrease fuel flow. I cannot believe how this is sucking up so much gas with stock configuration carbs.. Comments / help would be appreciated…Thanks in advance.

[Bruce Lancaster]

Look into fuel level and fuel pressure...I don't think minor jetting changes are going to have anything to do with this problem!

Two sidelights...if the thing is actually that rich, it is also wearing out its rings at a VERY rapid pace.
New ignition...what is it?? Whatever, run it up against a timing light and see if you have functional advance. There are lots of ignition problems available for purchase nowadays, and lack of functional advance will mimic over-rich to some extent.

[Robert Dip]

Thanks Bruce, the new electronic distributor is a Mallory. Many different timing settings have been tried, with little recognized difference in fuel consumption. I will install a pressure regulator at 2 - 2.5 lbs, although I do not see any external fuel spills. The floats are set low, and it sure does not starve for gas. I run the engine at about 2,000 rpm ( stopped & no load ) and you can tell that it is not running as smoothly as it should. Valve train seems to be in great shape and compression checks out great on all cylinders.

[Charlie ny]

Robert,
I build the occasional multi carb setup and recommend checking
the power valves for integrity. Stromberg power valves , even brand new
ones can leak. The PV gasket face in the bowl is a semi frequent source
of leaks as well. Did you actually check the size of the jets with a wire
gage...all too often jets get drilled out....and of course they are never
restamped.
The jetting and PVs are not that far off to deliver only 5 mpg,
providing they are good.
Charlie ny
[email protected]

[flatjack9]

When you say different timing settings have been tried, does that mean you have an actual timing mark established? Also Mallory distributors are notorious for having an advance curve that is not suited to the flathead. Advance comes in way too late and at higher rpms is more than required.

[Robert Dip]

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Charlie ny, when re-building the carbs, I was given kits from Speedway. I did not use any of their parts....the supposedly .045 replacement jets miked at .047 - .048 Some other brass machined pieces would not engage the threads properly....originals worked just fine. The cheaper kits are not worth paper....and I do not want to damage good original 97 bodies. ( get the real Stromberg parts ) Present jets are actual .045 and I am waiting to go to .042. A local shop that recently did a similar duel set-up did mention that the plugs were rich also. They changed to power valve and this made the engine run smoother and the plugs went from black to a clean brown. They also mentioned that the sound of the engine changed…..to the better. So, could the power valves be the answer…..I have some on order…..Thks..Robert

[uncle max]

Magic combo for most rascally flathead 97 2x2 setups - in my opinion - is
.043 mains with # 69 powervalves. Keep in mind jets and pv's work together.

[Robert Dip]

uncle max, thanks....I was waiting for your input. .043 mains & # 69 powervalves sounds good. ( Magic Combo ! ) If this does not work....know of any tall bridges to jump from.....R

[Bruce Lancaster]

By timing I don't mean just the static timing, which is likely OK if around the stock 4 degrees. I mean the mechanical advance has to work...before studying that in detail, at least see if it starts maoving right off idle and advances considerably before 2,000 rpm. Also, late Mallorys can have numerous problems leading to misfire...there are a LOT of things that need to be checked and often changed right out of the box.
But...if you really are anywhere close to 5 MPG, you have a problem bigger than minor jeyying changes.

[40Coupe]

I have a very similar setup with 40 distributor. I have rejetted to .043x2 carbs as suggested in a similar thread. Checked relative size of jets with a tip cleaner..It runs rich as well...I have also moved from autolite 216 plugs to NGK B4L plugs which are reportedly one heat range hotter to deal with the sooty plugs. A similar setup runs well as posted over at the HAMB.

My Power valves are 65 but shouldn't come into play until further into the foot pedal (I realize 69s ideal). I filled each bowl with fuel and let set on bench covered with plastic wrap to prevent evaporation to test integrity of mounting shoulder/counterbore and valve. One of the carbs had an eroded shoulder which would allow a path for leakage so I used a spare body.

Car ran better with pressure regulator set at 3.5 psi than 2.5 psi..unfortunately the pressure overcame the checkvalves and I discovered why Dad beat the airhorns with a hammer prior to my work (I had a spare as well). I went back to 3psi...and will try that.

Haven't run the car since I rejetted due to vacation and the Monterey Historics but will report my findings when I start her up.

Lane

[uncle max]

Originally Posted by 40Coupe

I have a very similar setup with 40 distributor. I have rejetted to .043x2 carbs as suggested in a similar thread. Checked relative size of jets with a tip cleaner..It runs rich as well...I have also moved from autolite 216 plugs to NGK B4L plugs which are reportedly one heat range hotter to deal with the sooty plugs. A similar setup runs well as posted over at the HAMB.

My Power valves are 65 but shouldn't come into play until further into the foot pedal (I realize 69s ideal). I filled each bowl with fuel and let set on bench covered with plastic wrap to prevent evaporation to test integrity of mounting shoulder/counterbore and valve. One of the carbs had an eroded shoulder which would allow a path for leakage so I used a spare body.

Car ran better with pressure regulator set at 3.5 psi than 2.5 psi..unfortunately the pressure overcame the checkvalves and I discovered why Dad beat the airhorns with a hammer prior to my work (I had a spare as well). I went back to 3psi...and will try that.

Haven't run the car since I rejetted due to vacation and the Monterey Historics but will report my findings when I start her up.

Lane

It needs to be remembered that in a properly functioning Stromberg with new parts, the powervalve starts to function the moment you stab the gas - due to the hydraulic action of the leather pump - and becomes fully open at the bottom of the stroke. Important that jets & pv's are happy together.

[B-O-B]

Mine is a 36 LB & single 97. with elec fuel pump. All this one the car when I purchased it. Plugs & tailpipe black so put a holley pressure regulator on things have cleaned up & car runs & idles good. However with the 4:11 rear the mileage isn't something to write home about. A good pressure regulator helped in m case.

[40Coupe]

Originally Posted by uncle max

It needs to be remembered that in a properly functioning Stromberg with new parts, the powervalve starts to function the moment you stab the gas - due to the hydraulic action of the leather pump - and becomes fully open at the bottom of the stroke. Important that jets & pv's are happy together.

Ah ok...It was my understanding from another post (not yours) that the PV was activated with foot near floor..I assumed it was a mechanical event as the pin was depressed.
Does the PV discharge through the squirter circuit or are there two circuits? Is this hydraulic action an unintended consequence or the way the designers envisioned it?

I have good response to needle jet position when viewing vacuum gauge (Offy hi rise with "race cam").
Exhaust fumes seem unusually heavy at idle..any thoughts on leaning the idle circuit? Assuming rich situation on these 97 setups may be on idle circuit?...
One set of needles is new...I left an old set in w/o the slots as they appeared original. Both carbs seem to have about the same position in screws- about a turn out.

thanks U Max.......

Lane

[BUBBAS IGNITION]

Originally Posted by Robert Dip

I have a ’39 Coupe that was built in the 50’s. 59 motor, Navarro heads and intake with 2 x 97’s, headers, etc. Did all of the ignition work, including new electronic distributor, plugs, wiring ( carbon wiring for electronic ) and rebuilt the 97’s completely..including removing the emulsion tubes. Engine basically runs OK ( not the best as it should ) and my problem is that it uses a ton of gas. I must be getting about 5 mpg. New plugs after an hour’s run are black & full of soot. Carbs are stock jets at .045, power valve also stock at 65. I am told to change the power valves to a higher # to decrease fuel flow. I cannot believe how this is sucking up so much gas with stock configuration carbs.. Comments / help would be appreciated…Thanks in advance.

Send me that Mallory and I will get it right , they are terrible out of the box, way too much advance ( so much in some cases they misfire)' I will return the following day I get it.

[Ol' Ron]

Plus they have no vacuum component in the advance which will give poor mileage. I have a set of Uncle Max's 97 on 37 Don s 276/L-100 and it gets 17-20 and that's not Interstate driving. My friend George is going to 42 mains not sure what his PV is. He's running a converted 11A.

[Mart]

Not a 97 expert, but if everything was running right, but it was jetted badly, surely the fuel consumption wouldn't be 3 or 4 times as bad as it should be. The ignition being a bit out or having no advance would not make it that bad either.

I'd be looking for fuel flowing past the needle valves and flooding the carbs. Something like that would vastly overfuel the motor, not having jets or acc pumps that are a couple of numbers off what they should be.

Mart.

[artsflatheads]

You don't need another 2c here but I'll throw in mine anyhow. Put on a fuel pressure guage so you KNOW what pressure you have at the carbs. 3 lbs is TOO much for Strombergs and will cause rich running. Use adj pressure regulator at 2.5 or less. Also I have found dual 97s run better with 42 or 43 jets. Art

[John Kennedy]

Anytime you're looking at fuel mileage issues, take a moment to verify the brakes don't drag.

[Robert Dip]

Thanks all. I am installing the presure reg, waiting for the .043 jets and 69 power valve. I am anxious to do this to hopefully solve the problem....process of elimination. I shall report back when this is done. The next step is to also take care of the mallory distributor. ( thks Bubbas...will be in touch )