Carb tuning info.

Displayman

Displayman

Senior Member
Just replaced fuel pump on our 47 Merc. 59A engine,
single down draft carb. Engine starts but is running really
rough. Adjusted 2 screws in back, one for richness, one for idle.
Still running crappy. Is there a rule, that you tighten screws, then back
off 1 1/2 turns or something like that? Appreciate any input.

Thanks,

Bob-Hampshire, Illinois
 
Bob, Crappy like a vacuum leak or crappy like too rich. Float level correct or to high? Give us some more clues. Walt
 
Was it running bad before you changed the fuel pump?
I agree with vtwhead check vacuum leak on the intake and also make sure it's not sucking air at the base of the carb. Then:
As a general rule set rpm at 350.
Adjust one idle screw at a time turning it out until the engine rolls then turn in until the highest vacuum reading is obtained. Repeat for the other screw then adjust throttle stop to desired idling speed.
If it still gives you problems write us back we will go to the next step.
 
Thanks for the replies.
Running crappy rich.
I might add carb ran great before fuel pump went out.
Neighbor didn't think it was fuel pump and messed with both screw
adjusments.

Bob -Hampshire, Illinois
 
Displayman said:
Just replaced fuel pump on our 47 Merc. 59A engine,
single down draft carb. Engine starts but is running really
rough. Adjusted 2 screws in back, one for richness, one for idle.
Still running crappy. Is there a rule, that you tighten screws, then back
off 1 1/2 turns or something like that? Appreciate any input.

Thanks,

Bob-Hampshire, Illinois
Click to expand...


I believe, if you will look closer, you have a two barrel carb and the two screws are both idle air correction jets. Each of these screws performs the same function, just on separate throats of the carb.
Just as 01A Ford detailed above, you adjust the idle speed at the throttle stop, then adjust each jet for optimum vacuum and then reset your idle speed with the throttle stop to the desired speed.
You may need to repeat the above steps a couple of times to achieve the best adjustment.
 
Displayman said:
Thanks for the replies.
Running crappy rich.
I might add carb ran great before fuel pump went out.
Neighbor didn't think it was fuel pump and messed with both screw
adjusments.

Bob -Hampshire, Illinois
Click to expand...
Just a thought, did you get a bunch of junk in the carb bowl when the fuel pump went south? Might be worth checking out if you can't adjust and are sure there isn't a vacuum leak. LouB
 
Bob, the other concern I would have is that the fuel pump is now putting out to much pressure for the carb seat to hold and allows fuel to dump into the engine giving you a rich motor. Just a thought. Walt
 
It does appear that gas is overflowing the top of the carb,
how do I adjust for the carb seat to hold?
Thanks,
Bob
 
As someone said both brass screws with the springs are idle mix screws,adjust both 1 turn out. the other screw on the throttle stop leaver i for idle speed. Possible crap in carb from old pump. ken ct.
 
You cant the spring in the pump is too strong causing excessive fuel pressure, A fault of these pumps made in China that are being sold.The big one under the diafram. ken ct.
 
Thanks for the info, and I will check if there is any crud in the carb
from the pump going out.

Thansk again,
Bob- Hampshire, Illinois
 
As others have said, I think that your new fuel pump is putting too much pressure at the carburetor and the float needle cannot stop the gas. The bowl gets too full and runs over into the engine resulting in a very rich misture, causing it to run "crappy".
 
All of us have given you our opinion about your problem, but no fix. Here goes my fix. Take the fuel pump spring out of the old pump and put it in the new pump and see if this does not correct the problem. JMHO
 
Good idea using old spring. Might try tomorrow.
I have taken apart top of carb, took float out,
took out float needle valve,sprayed carb cleaner
in all holes etc. Reassembled car is running smoother,
but now fuel pump is leaking a drop every once in a while around the diaphram.
I tightened all nuts. Stilkl leaking. Will take apart tomorrow
and reassemble.
Thanks for all the great suggestions.

Bob
 
jerry grayson said:
All of us have given you our opinion about your problem, but no fix. Here goes my fix. Take the fuel pump spring out of the old pump and put it in the new pump and see if this does not correct the problem. JMHO
Click to expand...

Good idea,

If some junk DID NOT get into the needle and seat (float valve) causing the float valve not to shut off when the carb bowl was full, it almost has to be too much fuel pressure. Try to find a buddy with a fuel pressure gauge and check it. If the fuel pressure if correct and no junk in the float valve, look at the float very carefully, it may be getting some fuel in it due to a pin hole. However I would think the problem is with the fuel pump as the car ran fine before you changed the pump.

I do NOT use the new pumps but rebuild the original ones. Mac's has kits for this that are not expensive.

If you take the fuel pump apart, to change the spring, befory you tighten the diaphragm screws, hold the push rod lever all the way up to "streatch" the diaphragm and tighten the screws while the lever is all the way up. This will cause the diaphragm to be relaxed when it is in the normal position. If you do not do this, you can wind up with a situation with the diaphragm streached when the fuel pump is actuated which can result in too high of fuel pressure.

I ran across this problem about a year ago and do not remember having this problem in over 50 years of working on cars. I about drove myself nuts with too high of fuel pump pressure until I finally found a notation about this in an old Motors Manual from the '30s.

Good luck and tell us what you find.

Chris.
 
Take the fuel pump off the stand, loosen of all the diaphragm screws, get something or someone to push the lever up as far as it will go and, while holding it in this position, tighten the diaphragm screws. This allows the diaphragm to move to its full extent freely without binding or restriction. This should stop any leaks from that area.
 
Thanks for all the replies.
I am going to take the fuel pump apart and reassemble
while a friend holds the lever up, while I tighten screws.

Have a great day!
Bob - Hampshire, Illinois
 
Took apart fuel pump. Reassembled while somebody
held lever as high as it would go. Tightened nuts slowly
and equally. Put on pump leaks a drop eveery 2 seconds.
Have carb adjusted using vacuum gauge while I adjusted idle
screws. Car idles awesome! Just need to find out how to stop pump leak.
I am calling Bob Drake, because that it is where I bought it.
I will update any info. Appreciated all the advice.
Greatest sight on the net. FORDBARN!!!!!!!!!
Bob-Hampshire, Illinois
 
Great news..........let us know how you make out with Drake. I'm looking at rebuilding my fuel pump as well. By the way, where did you pull the vacuum reading? Joe
 
Joe,
I totally reassembled pump again.
No leaks!!!!!!!!!!!!!!!!!!!!!!!
I pulled the vacuum off of a small pipe on bottom of carb(close to manifold.)
that had a black plastic cap on it.
I didn't get a chance to call Bob Drake, I just took my time
made sure the lever was in it's highest postion while I tightened
up the screws surronding diaphram.
Good Luck on yours,
Bob -Hampshire, Illinois
 
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