2 bbl. Motorcraft & a dwell cam

Dave Noll · 11-12-2013, 04:16 PM

On my 351C 240hp combo, the cam that the grinder sent me dwell's @ max lift for 60 degrees. The lowest the idle will go down to is about 1600 which isn't the issue. To get that idle with that cam I have the idle plate screw down about as far as it will go. which has the transition slots completely uncovered & I have a 1/4" hole drilled in each throttle plate. With so much air going thru there @ idle it's pulling fuel out of the boosters. I closed the needle valves, lowered the float level, & drilled out the fuel inlet (seat) to .125. The idle is cleaner now but the plugs are still dark.

Do I just live with that & jet for down track or am I just completely out in left field ?

Ed Wright · 11-12-2013, 05:13 PM

Don, you may also have to plug the power valve and use larger jets. You may be able to use a lower number (maybe a 35?) Holley power valve. If you plugged it right now you may be able to close the throttle blades enough to cover the transition slots. You likely don't have enough manifold vacuum to hold the power valve shut.
They look about the same, but as many years, and as many Holley & Ford carbs I have rebuilt I never tried a Holley valve in a Motorcraft 2bl. I would verify the Holley valve will work. I would probably just plug it myself. May have to tweak it some to clean it up on the return road.

Good luck.

Dave Noll · 11-12-2013, 05:29 PM

Forgot to mention that, It's already blocked (with a plug from a holley) & I have .066" jets in it.

Billy Nees · 11-12-2013, 06:52 PM

What is your duration @ .050? Lobe sep? Cam grinders tend to want you to put WAY too big a cam in 2V motors. No sense in putting a 7500 RPM cam in a 6000 RPM motor.

Dave Noll · 11-12-2013, 07:22 PM

Billy,
250 @ .050", 299@ .006", 105 lobe separation installed @ 103. Lift right now is .375" with the stock rockers but should be .407". They told me the cam wouldn't be the problem, the carb would. I protested a little cause it sounded big to me but they assured me this was a good one. (it's a Cleveland, run it like one).

G Anderson · 11-12-2013, 07:44 PM

Rochester 2G totally different but I would expose those trans slots play with the float level-need full timing at idle(On mine 39*) my cam is 260@.050 on the intake 107 c/l (installed to 106ic)runs good to about 71-7200 rpm ??? oh and would close these holes to about 5/32"

Bobby DiDomenico · 11-13-2013, 10:06 AM

Quote:

Originally Posted by Dave Noll

Forgot to mention that, It's already blocked (with a plug from a holley) & I have .066" jets in it.

Dave,
My Ford 2bbl stuff is away from here, is it possible the plug gasket is leaking some? Have 1/8" holes in blades, 1/4" seems plenty big to just about close the blades all the way. Did I read right it idles with the mixture screws turned all the way in? My current cam seems to require near full ign. timing, plan to change it to wider sep. Great info here

Dave Noll · 11-13-2013, 05:47 PM

Bobby, Yes you read it right. Idle mixture screws are shut. There's fuel coming out of the boosters @ idle , but with the 1/4" holes in the plates & the idle turned all the way up, that's a lot of air going thru there. I don't THINK I have a leak but I'll re-check.

Sean, This carb is 350 cfm. I know round track 2bbl. Clevelands regularly go over 7k, with a 4412 Holley. A while back I ran this combo on a simulation program & no matter what I tried, power fell above 6K but I figured we don't race computer's & blew it off.

Bill C., About all I can say on reversion control is the cam has 40 degrees overlap @ .050 & a 3 angle valve job.

JMark, I found an article that has the same illustration & saved the file, thanks. I may just weld the advance in the dist. & set it @ 40. Anybody have starting issue's there ?

Thanks for all the input guys.

goinbroke2 · 11-13-2013, 07:39 PM

[QUOTE=Dave Noll;408572]The lowest the idle will go down to is about 1600 which isn't the issue. To get that idle with that cam I have the idle plate screw down about as far as it will go. which has the transition slots completely uncovered & I have a 1/4" hole drilled in each throttle plate. With so much air going thru there @ idle it's pulling fuel out of the boosters. I closed the needle valves, lowered the float level, & drilled out the fuel inlet (seat) to .125. The idle is cleaner now but the plugs are still dark.QUOTE]

So, you have the idle screw turned in so far your bypassing the idle circuit and keeping it running by the fuel dribbling out of the booster. (poorly atomised fuel) To clean that up you lowered the fuel level and closed off the needles.
What happens if you lower the rpm, it starts stumbling/bucking because it's rich?

I would say open up the air bleeds to lean the idle mixture, right now if you open the mixture screws at all it sounds like unatomised fuel is dumping in causing the issues. Once it will idle down enough to cover the t-slots it will be more responsive to the screws.

Overall I think lack of vacuum is your main problem and opening the air bleeds will be a good band-aid. (also try reducing the idle feed restriction size if that doesn't do enough)

Oh, if you lock the dist at 40*, use a seperate toggle switches for ign/starter. Get it rolling over then flip the ign on, otherwise it will kick and break the starter nose off....don't ask, lol

goinbroke2 · 11-13-2013, 07:46 PM

Just thought of something else, you have 1/4" holes in the plates, I wonder if this is too big and effecting the t-slots. What I mean is, since so much air is going through the plate instead of having high speed air going by the t-slots, I wonder if this is why the fuel is coming out in blobs instead of atomised, which caused you to turn the idle up, which made it worse, so you turned it up more, etc, etc?

Try plates with 1/8" holes and see what happens, you might get some vacuum back and it might clean up the idle so you can use the screws/lower the blade angle closer to the t-slots.

11-12-2013, 04:16 PM	#1
Dave Noll Senior Member Join Date: Nov 2007 Location: Div. 6, Eastern, WA Posts: 709 Likes: 2,636 Liked 238 Times in 111 Posts	2 bbl. Motorcraft & a dwell cam On my 351C 240hp combo, the cam that the grinder sent me dwell's @ max lift for 60 degrees. The lowest the idle will go down to is about 1600 which isn't the issue. To get that idle with that cam I have the idle plate screw down about as far as it will go. which has the transition slots completely uncovered & I have a 1/4" hole drilled in each throttle plate. With so much air going thru there @ idle it's pulling fuel out of the boosters. I closed the needle valves, lowered the float level, & drilled out the fuel inlet (seat) to .125. The idle is cleaner now but the plugs are still dark. Do I just live with that & jet for down track or am I just completely out in left field ? __________________ Dave Noll, EF/S ,?/SA 6526

11-12-2013, 05:13 PM	#2
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: 2 bbl. Motorcraft & a dwell cam Don, you may also have to plug the power valve and use larger jets. You may be able to use a lower number (maybe a 35?) Holley power valve. If you plugged it right now you may be able to close the throttle blades enough to cover the transition slots. You likely don't have enough manifold vacuum to hold the power valve shut. They look about the same, but as many years, and as many Holley & Ford carbs I have rebuilt I never tried a Holley valve in a Motorcraft 2bl. I would verify the Holley valve will work. I would probably just plug it myself. May have to tweak it some to clean it up on the return road. Good luck. __________________ Ed Wright 4156 SS/JA

11-12-2013, 05:29 PM	#3
Dave Noll Senior Member Join Date: Nov 2007 Location: Div. 6, Eastern, WA Posts: 709 Likes: 2,636 Liked 238 Times in 111 Posts	Re: 2 bbl. Motorcraft & a dwell cam Forgot to mention that, It's already blocked (with a plug from a holley) & I have .066" jets in it. __________________ Dave Noll, EF/S ,?/SA 6526

11-12-2013, 06:52 PM	#4
Billy Nees VIP Member Join Date: Oct 2002 Location: On a hilltop in Pa. Posts: 4,479 Likes: 3,574 Liked 7,636 Times in 1,724 Posts	Re: 2 bbl. Motorcraft & a dwell cam What is your duration @ .050? Lobe sep? Cam grinders tend to want you to put WAY too big a cam in 2V motors. No sense in putting a 7500 RPM cam in a 6000 RPM motor. __________________ Billy Nees 1188 STK, SS I'm OK..........it's everybody else.

11-12-2013, 07:22 PM	#5
Dave Noll Senior Member Join Date: Nov 2007 Location: Div. 6, Eastern, WA Posts: 709 Likes: 2,636 Liked 238 Times in 111 Posts	Re: 2 bbl. Motorcraft & a dwell cam Billy, 250 @ .050", 299@ .006", 105 lobe separation installed @ 103. Lift right now is .375" with the stock rockers but should be .407". They told me the cam wouldn't be the problem, the carb would. I protested a little cause it sounded big to me but they assured me this was a good one. (it's a Cleveland, run it like one). __________________ Dave Noll, EF/S ,?/SA 6526

11-12-2013, 07:44 PM	#6
G Anderson Member Join Date: Dec 2009 Location: Iowa Posts: 105 Likes: 13 Liked 4 Times in 3 Posts	Re: 2 bbl. Motorcraft & a dwell cam Rochester 2G totally different but I would expose those trans slots play with the float level-need full timing at idle(On mine 39) my cam is 260@.050 on the intake 107 c/l (installed to 106ic)runs good to about 71-7200 rpm ??? oh and would close these holes to about 5/32" Last edited by G Anderson; 11-12-2013 at 07:46 PM.*

11-13-2013, 05:47 PM	#8
Dave Noll Senior Member Join Date: Nov 2007 Location: Div. 6, Eastern, WA Posts: 709 Likes: 2,636 Liked 238 Times in 111 Posts	Re: 2 bbl. Motorcraft & a dwell cam Bobby, Yes you read it right. Idle mixture screws are shut. There's fuel coming out of the boosters @ idle , but with the 1/4" holes in the plates & the idle turned all the way up, that's a lot of air going thru there. I don't THINK I have a leak but I'll re-check. Sean, This carb is 350 cfm. I know round track 2bbl. Clevelands regularly go over 7k, with a 4412 Holley. A while back I ran this combo on a simulation program & no matter what I tried, power fell above 6K but I figured we don't race computer's & blew it off. Bill C., About all I can say on reversion control is the cam has 40 degrees overlap @ .050 & a 3 angle valve job. JMark, I found an article that has the same illustration & saved the file, thanks. I may just weld the advance in the dist. & set it @ 40. Anybody have starting issue's there ? Thanks for all the input guys. __________________ Dave Noll, EF/S ,?/SA 6526

11-13-2013, 07:39 PM	#9
goinbroke2 Senior Member Join Date: Mar 2002 Location: NS CANADA Posts: 869 Likes: 1,462 Liked 355 Times in 140 Posts	Re: 2 bbl. Motorcraft & a dwell cam [QUOTE=Dave Noll;408572]The lowest the idle will go down to is about 1600 which isn't the issue. To get that idle with that cam I have the idle plate screw down about as far as it will go. which has the transition slots completely uncovered & I have a 1/4" hole drilled in each throttle plate. With so much air going thru there @ idle it's pulling fuel out of the boosters. I closed the needle valves, lowered the float level, & drilled out the fuel inlet (seat) to .125. The idle is cleaner now but the plugs are still dark.QUOTE] So, you have the idle screw turned in so far your bypassing the idle circuit and keeping it running by the fuel dribbling out of the booster. (poorly atomised fuel) To clean that up you lowered the fuel level and closed off the needles. What happens if you lower the rpm, it starts stumbling/bucking because it's rich? I would say open up the air bleeds to lean the idle mixture, right now if you open the mixture screws at all it sounds like unatomised fuel is dumping in causing the issues. Once it will idle down enough to cover the t-slots it will be more responsive to the screws. Overall I think lack of vacuum is your main problem and opening the air bleeds will be a good band-aid. (also try reducing the idle feed restriction size if that doesn't do enough) Oh, if you lock the dist at 40*, use a seperate toggle switches for ign/starter. Get it rolling over then flip the ign on, otherwise it will kick and break the starter nose off....don't ask, lol

11-13-2013, 07:46 PM	#10
goinbroke2 Senior Member Join Date: Mar 2002 Location: NS CANADA Posts: 869 Likes: 1,462 Liked 355 Times in 140 Posts	Re: 2 bbl. Motorcraft & a dwell cam Just thought of something else, you have 1/4" holes in the plates, I wonder if this is too big and effecting the t-slots. What I mean is, since so much air is going through the plate instead of having high speed air going by the t-slots, I wonder if this is why the fuel is coming out in blobs instead of atomised, which caused you to turn the idle up, which made it worse, so you turned it up more, etc, etc? Try plates with 1/8" holes and see what happens, you might get some vacuum back and it might clean up the idle so you can use the screws/lower the blade angle closer to the t-slots.