740 dft powe valve

[ih8boats]

Hi guys Im at the stage of my scc where I have built manifold, installed carb, tuned to a usable state. I bought various idle,main and air jets. swapped out and chased my own tail on test runs. now after reading and rereading joedrum's 740 carb review and studying the motorcraft740 manual I'd like to follow joe's advise and remove the power enrichment valve from the equation. so i guess my question would be is there a way to defeat the power valve with out using epoxy putty? Not that there is anything wrong with that method.

 

[ih8boats]

Was this detailed somewhere i over looked or is a silly question ? nobody wants to touch this?
I was planning on just cutting off the pin on the diaphragm that actuates the valve so regardless of spring or vacuum no excess fuel can be introduce at any time from power enrichment circuit.if this sound wrong to anyone please pipe up now before i screw up my chances of tuning irreparably.

 

[Dadster]

Wish I could help. Still running 4 carbs. I'm sure someone will chime in that's qualified to help.

 

[slabghost]

I think some have done it that way. Joedrum did extensive work on his. You can read on his efforts here.viewtopic.php?p=103999#p103999

 

[dan filipi]

Cutting off that pin is the easiest way to disable it

 

[ih8boats]

Thanks Dan I was wondering is that how you handled it and was it obvious before/after in tune-ability?

 

[dan filipi]

ih8boats » Today, 3:42 am[/url]":1071xu1y]
Thanks Dan I was wondering is that how you handled it and was it obvious before/after in tune-ability?

The power valve on mine was leaking so at the time I had no choice but to epoxy it closed.

 

[joedrum]

sorry i didnt post on this promptly...ive been gone for a week ...the dft carb on a oldwing has way to big idle circuit pathway ...power valve is a enriching device ..so it for sure in my opinion it is not needed ...some see it as ok ....my motor is way different in flow than stock motors most have and my dft carb is the biggest one made ...witch is biggere than 32-32 tom carb ...the power valve is not adjustable so it is hard to deal with it ...no matter how you jet ..when it kicks in jetting gets defeated...on my carb the power valve was never there to begin with ...it was factory blocked ...so its not like they have to have it ...good luck ...im sure you will see a difference in how it acts ...after doing this ...i did do much more to carb on mine as it was still way to rich at low rpm even without a power valve ....

 

[joedrum]

dan filipi » Mon Feb 29, 2016 9:20 pm[/url]":1ogg6g9y]
Cutting off that pin is the easiest way to disable it

hmmm i hate being not around all the parts i had ..cause my memory sucks ....i coiuld be wrong but i think if the pin is removed ..this actually makes the power valve flow gas ...seems if i remember right ..the power valve gas acyually flows on the inside of the diaphragm and the outside cap is where the vacumm pulls the pin away from its resting spot and gas flows ...so on the carbs i did was epoxy things as this blocks the flow completely ...on the carb on my bike ..witch is factory done block and came that way new ...there is a center brass like cap that seals the middle portion gas feed and no cap is use all in plain site ....

 

[dan filipi]

I just looked at the complete dft I have from Tom.
Cut the pin will defeat the power valve, or could just take the spring out.

 

[dan filipi]

The power valve is a ball-check which is pushed open by the center pin on the diaphragm. The spring pressure against the diaphragm is what pushes against the ball-check to open it.
Below-throttle vacuum pulls against this spring pressure to regulate the power valve action.....low manifold vacuum-valve opens (acceleration). Higher manifold vacuum-valve closes (idle or cruise).

 

[ih8boats]

wow thanks guys for the response i was hoping to jump in knee deep today but other obligations took priority.but i did look at diaphragm that i removes a couple days ago, after sitting on my bench a few days it was relay hard,dry and cracked. so- i believe im going to try replacing it with rubber gasket material (ie no pin, no spring.)tomorrow im pump and look forward to telling you all about my results.

 

[dan filipi]

I think that would work, could even work better than epoxy plugging the ports who knows, hasn't been yet that way I know of.

 

[ih8boats]

OK now were getting somewhere. blocked off power valve/enrichment circuit with flat rubber gasket material and removed spring, reassembled and test fired= wow complete about-face ! I had to reset all jets so i started back with what I think is recommended jets and settings/or not i dont know/cant remember but heres what I got.

idle=50
main/primary=105
air bleed/primary=200
idle/sec.=65
main/sec=95
air bleed/sec=160

cold start was not a struggle to get to stable idle but ill have to wait till tomorrow to see how it acts from here.
off idle OH MAN no more stumble just go!
cruise still a little squishy
wot is a kick in the @#$ relay feel it from 4500--6000 rpm.

I m choosing to be happy with my progress for today as i crack a beer and give the pavement a chance to cool.

 

[dan filipi]

Nice.

I really like blocking that thing since it makes much better control of jetting possible.

 

[joedrum]

good day ..time for reward ...those do sound like stock jets your using ... :beer:

 

[Denver]

Like that way to adapt things, you can always go back to stock, with no issues. :good: Nice work! :yes: