Starved modified flathead

D

dschwartz

Senior Member
Help
I'm working on a modified 8BA flathead. The bore is 3-38 with stroke of 4 1/2. I' am trying to run four modified 97's that have the main jets 45 and the power is 65. When I start the motor it sounds like it is being starved I cannot keep the. motor running
Thank you
 
I do all initial start-ups, stock or modified, with a known good Holley 94 carburetor on a stock manifold. It makes life much easier.
 
That's a monster of an engine. compression must be off the charts. Yep one god 94 should start and run it just fine. I suspect the timing might be alittle off as well.
 
Ol' Ron said:
That's a monster of an engine. compression must be off the charts. Yep one god 94 should start and run it just fine. I suspect the timing might be alittle off as well.
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Agreed. When it's running, please post a video. I'd love to hear this beast. What does this come out to be, a 327 c.i.?
 
Ditto. You probably have synchronization problems with one or more carbs acting as a big vacuum leak. Get it running, idling and timed with a single carb manifold. Run each of the four carbs on the single manifold to be sure idle, accelerator pump, and power circuits are working well. Set the idle jets on each, but open them a little (quarter turn) from optimum idle.

To avoid rough idle and stalling with the quad manifold, you must have very sturdy "no slop" throttle linkage and working return springs on each carb, and precisely align the linkage so that all throttle plates return reliably to completely closed. All carb tops have to come off to do this alignment. Then carefully set each idle adjust screw (so that each throttle plate has just barely moved off of completely closed. With tight non-progressive linkage on a 4x2 any idle adjust should move all throttles, but there is inevitably a little slop. The idea is to get all idle adjustments set to give slight opening pressure, so that when the time comes to adjust idle speed, you can make the same adjustment on each carb and not have a bunch of tension along the linkage.

Be sure the linkage is working smoothly with no binding, and tighten the linkage arms. Then put the carb bodies back on the bases and fire it up. Raise the idle adjust screws, each the same amount, until it will idle at whatever RPM. After it has warmed up, try to get a higher idle rpm by adjusting the idle jets. Try closing each 1/4 turn. If you get the idle speed up, bring it down with the idle adjust screws and then try the idle jets again. Etc.

When this task proves to be impossible, get a 3x2 manifold with progressive linkage, so that all idle adjust is done on the center carb.
 
whoe up sounds like its drowning got to keep in mind you got 4 carbs opening at the same time thats got to kill air flow through the carb i would try rejetting down to 40s for mains and 70s for power valves as a starting point also whatever you do to one you must do to all float level and fuel pressure is critical and are often overlooked remember 97s are a low pressure carb 2psi@ and nearly always require a pressure reg me i always use a syncometer to balance air flow at idle with linkage disconnected but remember youve got 4 carbs so 1/2 a turn on each = 2turns on a single so gently does it when you get it set its only a matter of hooking up the links so everthing works together best way to check jetting is a good dyno but beware a cowboy operator can destroy an engine in less time than it takes to fart keep me posted on how you go sounds like it should crack hard when you get it rite
 
What is meant by a "modified 97"?? What is modified? My first guess would be too lean. If over rich you should easily see all the black exhaust smoke and notice the engine faltering as if the choke is being applied. I agree it is best to have carbs which have been certified. Does the description "can't keep it running" actually mean it won't idle or does it mean it won't run at any speed?
 
Thank you so much for your input. I adjusted the float level on each 97 and I re-assembled and the started the motor and I got black smoke. Do I need to adjust the air flow to 1/2 turn. I am having problems with posting pictures can you give me your email and I can send pictures and you can see modified top of the 97.
Thank you
Dan Schwartz dnlschwrt@aol.com
 
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If you are adjusting the needles on the carb, they control fuel, not air. Turn them in to decrease fuel flow.
 
when you say modified top im guessing someone removed the choke blades thats a BIG NONO on a 97 flow tests have shown no increase in airflow at WOT and at partial throttle the choke blade actually directs air flow over the discharge nozzle which enhances the carb response makes them a lot more drive-able remember with 4 of these you actually have 600 cfm plus sitting on top working as single unit (thats one big carb remember any 4 barrel of that size is progressive either vac or mechanical ) as a starting point i would set butterflys at 1+1/2 turns then bottom all fuel screws then out 1/2 turn should start and run then sync all throttles[ need a carb sync almost impossible to do by ear] dont get to worried about idle speed at this stage if its 1200rpm or under you can work your way through it [ again remember you got 4 carbs on top so what ever adjustments you where told to do by the supplier you need to cut buy 4 ie 1 turn in instructions will be 1/4 turn on each carb ] yeh its slow and painful but worth it in the end
 
Are you new to flatheads and this engine? What camshaft, what ignition, what initial spark advance and some history/details on the 'modified carbs'. Was the engine all together and had previously ran . . . or is it a newly built engine? All the details matter (to give us some background and context on the whole thing).

It could be anything from incorrectly setup carbs, to incorrectly setup throttle blades, to a big-*** vacuum leak, to incorrectly setup idle circuits (if it even has them), to a huge cam that won't idle unless it has a lot of fuel/air, etc.. We need a lot more to work from. :)
 
I don't think many people run 4 carb manifolds. There's probably a reason for that.

It would make sense to fully troubleshoot the motor on a single carb. then when all is well and everything is dialled in, take on the conversion to the 4-carb setup, so that is the only change on a known running unit. There will be a strong possibility of it being very rich. All that unburnt fuel washing down the bores can do nothing but harm. You don't want that scenario during the running in phase.
 
Last I heard Walt DuPont was running 4 x2s on his coupe and getting excellent fuel mileage. I don't remember exactly but maybe 20 mpg? Also, If I remember correctly, Uncle Max set them up. I hope my memory isn't too far off.
 
I just received an email from Dan with a picture of his engine. I'm sure we'll all agree it's a beauty. I'm sure that with all the knowledge on here, it will be running as good as it looks soon. He's a better man than I, trying the initial start with 4 carbs!
 

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dschwartz said:
Help
I'm working on a modified 8BA flathead. The bore is 3-38 with stroke of 4 1/2. I' am trying to run four modified 97's that have the main jets 45 and the power is 65. When I start the motor it sounds like it is being starved I cannot keep the. motor running
Thank you
Click to expand...

First off, that engine will absolutely run ok for initial checkout on gasoline with the jets you have. We will assume the throttle shafts are not worn excessively.
For final race tune main jets, you will probably end with .052 or .053 and 65 power valves. It doesn't matter what cam you have, the following procedure will get the engine running good enough so you can play with the various adjustments without it dying. This all assumes that everything else in the engine was done properly.

1- Remove all throttle linkage.
2- Make sure all of the butterflies will seat closed. Back the throttle stop screws all the way off to check this.
3- Doing one carb at a time, hold the throttle arm closed and turn the stop screw till it just touches the arm, Keeping pressure on the arm, turn the stop screw ONE turn in.
4- At this point, if you re not using rod end type linkage, you should be.
You need to be able to adjust the distance between each carb throttle arm individually. It is extremely important that the length of the rods between each carb be set with the throttle arm on the carb AGAINST the stop. When all linkage is attached, all of the throttle arms should be gently resting against the
preset stop screws.
5- Next, turn all of the idle screws on the carb bases ALL the way in (closed).
Back each one out 2 turns. This will get it running. At this point, loosen the distributor clamp screw SLIGHTLY so you can turn the dist. while the engine is running.

At this point, I set a large fan in front of the radiator to keep it cool while adjusting things.

If you need to bring the throttle up to keep it running, BE SURE to turn each throttle stop screw the SAME amount.
6- From here on it is just diddle with the idle MIXTURE screws and the ignition timing.
7- Advance the timing to where it runs best at idle. Note the RPM.
You will have to adjust the throttle stop screws and the timing for the RPM you want it to idle. Keep playing with the 3 adjustments till you get where you want it.
At this point, check where the timing is at idle which will probably be about 800 RPM for the street. 1000 to 1200 for circle track or Bonneville.

When you get it to where you can drive it, make a couple of full power runs and SHUT IT OFF CLEAN on the last one. Pull all of the plugs and read them. They should look clean and on the lean side. Richen the main jets as needed. Depending on engine use and driving style, you will likely end up with .050 to .052 main jets. With as much compression as you will have, you will have to run the highest octane gas you can get, on the street. You will have to set your final spark advance accordingly. You may not be able to go beyond 25 degrees with 92 gas.

This procedure has been used on 4 315 ci flatheads in the past and 2 321 ci flatheads recently, so it is a proven procedure, not something somebody has heard about on the internet.

As a side note, 97/48 carbs will absolutely make more peak hp with the chokes removed. It has to do with boundary layer flow, not maximum flow.
Think 4 hp on a 321 engine.
That engine will run better if you lose the metal wire looms.

I would be interested to know if you have a billet crank or an older welded one.
You can email me if you need any more info.
 
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That looks like a manifold that does not have an open plenum. More like an individual runner type. This will make it more difficult to tune/adjust.
My mistake. After enlarging the pic, it appears to be a real one-piece manifold.
Best advice from me would be to contact Walt Dupont
 
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Kahuna said:
That looks like a manifold that does not have an open plenum. More like an individual runner type. This will make it more difficult to tune/adjust
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Boy, I don't know. It looks like a "squarish" structure is connecting carbs 1 & 2 and 3 & 4. I can't really see what's between 2 &3 because the radiator hose is in the way.
 
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