what jets at 317 ft. above sea level?

jan bogert

jan bogert

Senior Member
i'm in eastern Pa. the sea level is 317 above. i'm running two large strombergs 97's. car running to rich, black what main jet should I be running? theres no way to lean it out anymore. screws now 3/4 out and still black and poping like to lean anyway back to the original question.
 
Is this "popping" within the intake or the exhaust? Usually intake pops are lean and exhaust pops are rich. The answer to your question is to start with stock(45) main jets. They will be close enough to avoid "popping" and will require only minor refinement changes.

Your engine must be viewed as a complete system and all aspects have to work together. Unless your carbs are working properly and your ignition system working properly and your mechanical basics are solid(meaning no leaking valves or damaged rings, etc) it will not be possible to tune up the dual carbs. Jets can be changed until the cows come home but that won't correct ignition problems or stuck valves. Did the engine perform correctly before the dual carb system was installed? Give some more info to receive better advice.
 
poping out intake. when I hit the throttle fast. the motor was a good running motor. dist., and coil, done by Skip Haney. I do know its the jetting. thanks i'm going to pull the carbs., and see which ones are in there. going to get 43+ 45's. good start.
 
I thought in another thread Uncle Max said he installed .043's and #69 PV,i could have read it wrong? But those #'s are in the ball park for a 2x2. 317' elevation is considered sea-level.That wouldn't even enter into it. Ive built many with that combo. I would try .045 if anything and or with a PV change to #67. OMO. UM is the gurue on these,we all look up to him. ken ct.
 
Popping in the intake upon rapid throttle opening is a sign the accel pumps are set in the wrong peg or are not functioning properly. or the float level is way too low or there is a serious vacuum leak. or the timing is off. That rapid throttle opening "popping" is a completely different subject line from the main jet sizing.
 
you probally right Kenct, I don't remember what size he put in them when he built them for me. but wouldn't 45's make it richer? the poping goes away when I open the screws, to about a little more than one turn out that's how I've been running it. car was running for a year now 600 miles but I don't like how much fuel its using. and the sooty black tail pipes, and plugs. that's why i'm asking these questions. i'm just saying its to rich, and uses to much fuel.
 
Jan,

Jets don't come into play during idle. Carbs are a three-stage system kind of like low, medium and high. Jets are for high.

I wouldn't distinguish between 317 feet and sea level. I would run stock jets and investigate what other problems may be causing your issues.
 
Carburetors generally can have the same jets up to around 6000 or 7000 feet above sea level. They will still run but it will run rich. Power valves are a little different in that respect since they work off engine vacuum. They can start to be affected around 4500 feet above sea level. Mike's 51 is correct about three stages for carburetors. As JWL mentioned, popping back up through the intake when you give quick throttle is definitely a lean condition due to accellerator pumps but generally only off idle. Too much fuel from accellerator pumps boggs the engine down. Flatheads were never known to have the best manifold pressures to make the power valves work correctly. Sometimes you need smaller ones to make it work. If you have a choke set up it can make things rich if it is even partially on. Air filters with too much restriction can act like a choke but you can run a little while without them to see if that's a problem. Internal leakage is the hardest thing to detect whether fuel or vacuum and can really make you pull hair until you find the problem.

I'm not familiar with what you are running there or what performance level it's at. If it is 8BA, I'd say ignition could be a problem especially if it is stock. If you are running 59 type or earlier engine then the vacuum brake can need adjustments too.
 
I am at about 550 ft above sea level in Northern Ohio. I run new .045 mains and new #71 (Stromberg model 81) PVs in two 97s on a Edelbrock Regular manifold, heat risers blocked with core plugs and about 5 gaskets between each carb and the manifold. I formerly ran .043 mains and #65 PVs - ran lean. Champion H10 gapped at .025 and timing 4 degs BTDC. Runs very well. .045 mains and #65 PVs - to rich.
 
That number 71 is a bit smaller than a 69. That's a lot of gaskets there. An insulator spacer with two gaskest a piece might be a better choice.

It seems like the power valve only comes open at higher throttle settings (near WOT) on the Strombergs. It shouldn't have as much effect at lower throttle settings. If it's rich there might be either a leak or an inlet obstruction.

Rumbleseats PDF- http://www.flatheadv8.org/rumblest/fuel.pdf
 
Put a vacuum gauge on the engine and adjust the idle mixture screws you may find about 2 turns out is better, smoother idle and higher vacuum, should result in smoother off idle transition. Max usually suggest .043 & 69. At this time I run .042 & 69, but I still have some tuning to do. The original single Carb. size is .045 & 65, so I would NOT go there
 
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