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

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.

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.

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.

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).

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"

Re: 2 bbl. Motorcraft & a dwell cam
 

If your spark plugs are dark, I'm guessing it idles best with the idle mixture screws all the way in?

Re: 2 bbl. Motorcraft & a dwell cam
 

First rule of any engine combo, find the restriction, build to the restriction. You've got way too much cylinder head and valve area, lots of valve lift and as I recall way too little compression so you can't be giving up cylinder pressure with a big cam. You've got a 350 CFM carb that's not going to make power at any kind of RPM so why spin it up there? It sounds to me like that big cam isn't making any vacuum.

Re: 2 bbl. Motorcraft & a dwell cam
 

You need to figure out how to generate more idle vacuum so you can close the throttle blades up. The t-slots need to be covered or you will have a tough time getting it to idle without closing the mixture screws all the way, and even then it won't be enough. More initial timing might help, if you run a distributor with a vacuum advance using the vacuum to add timing under no load can help. If you find that you have all the timing it will stand, I would look at advancing the cam.

As a last resort, make the idle feed restriction smaller, drop it to the point where it's tolerable at idle and doesn't cause a stumble coming up on the throttle. Being a race car you should be able to find the happy medium. You can try to solder the restriction after measuring it, it's the small tube in the middle of the larger one in the booster cluster. You might want to get a spare to play with to do this. The other place looking at what I can find is there may be an idle down channel restriction, making this smaller
will help as well. Again these are last resorts, making more idle vacuum to allow the blades to close is your best bet. Here is a picture to give you an idea on what is going on.

Re: 2 bbl. Motorcraft & a dwell cam
 

i see alot of good input on your thread

Re: 2 bbl. Motorcraft & a dwell cam
 

OK, lotsa input, thanks. Timing is @ 36 initial & 42 total. I bought a box full of these 2 barrel's off E-bay so I have some spare parts. I took all the jets to work & reamed them to between .064" & .070" but I don't know what that would convert to in a Motorcraft jet #.

G.A. - I'm curious what your 2G measures in the venturi & throttle blades.

Ed - Yes it idles best with the mixture screws closed, with the spare parts I've got I might go close up the transition slot too.

Billy - Without giving away secrets, what #'s roughly should the cam have? (or just tell the grinder 6K ?) Going smaller cam would be more palleteable than all the really stiff springs thick wall large dia. pushrod deal. But I'm almost committed to the higher RPM deal at least convertor-wise. I spent the money & got a nice one that will stall 5200 if I get my tune/gearing where it's supposed to be.

When I got the car to the track this year, the motor ran into a wall @ 5800. With what the cam company told me about the profile & the springs I have on it I figured that wall was valve float. Opinion's on if it was the carb ? It's a 1.21/1.68.

Re: 2 bbl. Motorcraft & a dwell cam
 

Be carefull with power valves in a restricted induction combo,It will pull manifold vacuum at wot and may effect power valve.The other issue with restricted combos is during overlap the high manifold vacuum will pull exhaust contamination back into combustion chamber,Valve seat and valve shape need to be designed to halt exhaust reversion contamination,also cam events are critical to control reversion.Bill C.

Re: 2 bbl. Motorcraft & a dwell cam
 

If it idles best with the adjustment screws all the way in, I would try drilling the idle air bleeds. Also, you may have in your box of carbs a pair of smaller idle fuel restrictions. Having all those parts you could try either (or both) approach(s).

When you get it leaned down it will likely idle up and allow you to close the throttle blades, and cover the transfer slots.

Re: 2 bbl. Motorcraft & a dwell cam
 

Just curious, but what CFM would the 2V carb be? I can't imagine a 2bbl Cleveland not pulling well past 6500.

Sean

Re: 2 bbl. Motorcraft & a dwell cam
 

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

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. :):)

Re: 2 bbl. Motorcraft & a dwell cam
 

1 3/8v either 1 11/16or 1 3/4 tb(can't remember sure) same size as a 500 Holley

Re: 2 bbl. Motorcraft & a dwell cam
 

Thanks G.A. for the input. Thats .165" bigger than my carb in the throat. Didn't think they made Rochester 2bbl's that big.

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

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.

Re: 2 bbl. Motorcraft & a dwell cam
 

i would say bingo,there be your high idle problem those carbs are very sensitive in that area, they also don't work well with power valves in race applications

Re: 2 bbl. Motorcraft & a dwell cam
 

Looks like I've got some more experimenting to do.

Re: 2 bbl. Motorcraft & a dwell cam
 

You mentioned the circle track guys turning 7000 rpm. I'm curious what duration cam they use......

Re: 2 bbl. Motorcraft & a dwell cam
 

Maybe they get to 7000 grand decelerating using the car's weight to push the motor!

Re: 2 bbl. Motorcraft & a dwell cam
 

When I was involved with that, the cams came straight from the catalogs & dwell cams were unheard of. #'s ? too long ago.

Re: 2 bbl. Motorcraft & a dwell cam
 

The local Cleveland guru we had around here in the 70s always used Schneider cams. It might be worth giving them a call and seeing what they have to say.

Re: 2 bbl. Motorcraft & a dwell cam
 

Just looking at their website they show this one good for 7000rpm. Not a lot of duration there.

Part Number: 0316
Grind Number: 290-0H
Intake Duration (gross): 290
Exhaust Duration (gross): 300
Intake Duration (.050”): 230
Exhaust Duration (.050”): 240
Intake Valve Lift*: .536"
Exhaust Valve Lift*: .536"
Lobe Separation: 110
Intake Valve Lash: .000"
Exhaust Valve Lash: .000"
RPM Range:
3000-7000

Re: 2 bbl. Motorcraft & a dwell cam
 

Well I futzed with it this weekend & got it to idle better. I tried throttle plates with an 1/8" hole, played with boosters, power valve block, air bleeds, float level & some other stuff. It now idles on the mixture screws w/adjustment, nothing coming out of the boosters. I can idle it down, some, without it dying. It's a lot snappier. But I am back with the 1/4" hole throttle plates. Just gotta get it back on the track & see what I've done to WOT jetting & if that 5800 thing is the springs or carb. Thanks for the input. Appreciate it. :cool:

Re: 2 bbl. Motorcraft & a dwell cam
 

David, I wouldn't worry too much about the converter situation. The stator can be changed ,which will lower the stall and change the characteristics of it.
That might end up being the way to go anyway.

Re: 2 bbl. Motorcraft & a dwell cam
 

Thanks Mark. If that wall is the carb, that's probably the route I'll go.