Don Terrill’s Speed-Talk

Actually A friend of Gene Fulton, Patric Smith, tuned me up on that one.
The port was frightening to feel the pulses. Very strong and more severe going up than going in the head. All in the center. Real cold when wide open throttle. Nothing like a flow bench

Jon ... hadn`t thought about the diaphram resonating ..... I guess everything has a resonant frequency .
Since it`s raining here .... again , I have time to be anal . In your experience , which diaphram would vibrate the most down low and send the most fuel out the squirters , a 25 cc or a 50 cc . Since the 50 c diaphram is bigger than the 25 cc diaphram , it will have more material , so wouldn`t it be more prone to resonate pumping than the 25 c unit ? Carrying this further , I guess the same would apply to the check valve , but because its metal , it would have a different resonate frequency . So , two factors at play here ????

This might explain what I have been seeing on the IAB`s . Since I`m getting fuel pullover starting around 2000 rpm , and that`s where the engine starts to run rough and smooths out about 2600 rpm , it makes sense that the engine can`t use the extra fuel from the main circuit down low , but can above 2600 rpm . I found that if I went really big on the PIAB`s , 84 to 90 , it smoothed things down low out considerably and I could never figure out why , until maybe now . The "correct" IAB`s ( 70 ) made it run too rich . The larger IAB`s are delaying the main circuit from coming in enough so that the extra fuel from the squirters can be used from 2000 to 2600 rpm . Above that, the engine can use the fuel from both .... I think !
BTW , engine is an FE 482 with Ebrock dual plane intake , solid roller etc.

How far off base am I on that "theory" ?

JonKaase wrote: ↑Tue Oct 09, 2018 6:19 pm Most of the time what you are seeing is resonant pumping from the accelerator pump diaphram vibrating enough to pump fuel through the circuit. This really is bad with a sheet metal tunnel ram. and it will get worse or better with rpm, depending on the shake of the engine. You can throw a washer on top of the orange rubber check valve that will push it closed when the lever is all the way maxed out at WOT, but in our experience its better to have the fuel and tune around it. Its more vibration than air over the squirter!... Kaase

Have you watched this with a strobe light? - to see the flow as a pulsating flow rather than a steady flow.
Or better still replaced the diaphram with a flat/solid sheet to take the vibrating/pumping of the diaphram out of the equation?

Are you using bypass air at idle? Holes drilled in the throttle blades? This will create extra airflow through the t/bores & might be enough to pull fuel from the squirters.

63, now I understand your situation; completely different than the small carb syndrome. As Jon said there is probably a harmonic occurring in the diaphragm or the check valve (perhaps both). The 30cc diaphragm when installed is more flat than the 50cc; the more conical installed shape of the 50cc might help. FWIW: whether by design or chance there seems to be different "strengths" of pump springs (slight differences in wire diameter). I try to use the heaviest spring I have on the circle track alcohol carbs (larger squirters); with the camshafts currently used and rough track conditions it is possible for the driver to unconsciously "load up" the engine on caution laps even though he feels like his foot is not moving on the pedal. This usually results in a stumble on restart. If you can't find a heavier spring in your collection stretch one out a bit and see if it helps.

Ks ... you made me remember something from long ago . There are heavier diaphram springs available for that circuit . I was told many years ago to look for and use a green spring . Can`t find any reference to that on the Holley site .... and asking their tech is useless .
So , I`m going to look through my stash and see if I still have that spring and how it compares to others . Plan to mike wire dia. , check heights and number of coils etc . If need be , I`ll start stretching some and see if that makes any difference . I also plan to weigh some check valves and see what , if any , differences there are between the brass ans SS ones . Also have a set of the anti pullover squirters on the way .... will try one thing at a time . I`ll let you guys know what happens , probably next week as the TS/hurricane is supposed to pass over us starting tonight and tomorrow . I`m inland , but they`re now saying winds between 70 to 90 mph and lots of rain . Time to start moving stuff inside now .

Thanks for jogging my memory .

FOUND IT !!
The primary squirter wasn`t seating all the way on the back , so I had a leak when rpm went over idle and when accelerator pump was moved . Carb body is a BLP billet body and where they machined for the primary squirter to sit , it was a little shallow in the back . The O.D.of the squirter body would hit on the counterbore/spot face and the ears on the back of the squirter also had to be rounded off to clear the radius on the spot face . Five minutes work with a file and the squirter fits perfectly . Setting it on the carb without the screw , I looked down where the screw went and it mismatched the threaded hole in the body by about 1/32" . ... and thats when I the light bulb go off .
Retested this evening and no more flow down the carb throttle bores next to the back of the squirters . Problem was only on the primary .

This one was almost as frustrating as when I had an IAB problem and it turned out that Holley hadn`t drilled out one of the IAB`s ..... that one took a while to find .

FWIW , also found out the Holley anti pullover squirters won`t fit on the BLP billet 4150 body .

Thanks for the suggestions and help guys !

Good news!

BLP makes some stops to put in the springs to stop it at WOT, but I of the same thought as Jon just tune with it. I pull them out when I find them.

Some Webber carbs use the pullover for power enrichment.

https://www.forabodiesonly.com/mopar/th ... ks.143398/

Erland