carb problem?
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Freshman User
Joined: Sep 2005
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carb problem?
I have a 69 F-100 that I just rebuilt a 390 for (less than 1000 miles), it is mainly stock with a carter 625 carb on it and all is good except for two things. The first is when I try to accelerate to quickly it wants to sputter and then it takes off, I have to feather the gas a little to avoid it. I rebuilt the crab so it isn't full of junk, but it might not be adjusted correctly either. Some one told me the accelerator pump isn't pumping in enough fuel initially and that is why it sputters. The second problem only started lately, when I first got the truck running and adjusted the choke and air fuel screws it would start by bumping the key even in the dead of winter. Now if it sits over night I have to crank it over pump the gas and then crank some more then it starts and idles almost imediately. If the truck sits for only a couple hours I can bump the key and it starts great. Is the fuel possibly bleeding out of the line back into the tank behind the seat? Any ideas?
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Just a short note,
Sounds like all you have to do is readjust the choke so it closes when cold and your Air/fuel screws = more gas less air. or you have an intake leak= bad rubber lines, carb bolts lose, dist. advance, WITH great care you can spray starting fluid at carb base, side of intake mating areas vacu-lines Not the dist. area You don't want a FIRE. only do this out in the open air away from a building if you have never don't this before. Have a water hose handy.
Not to scare you, but if you don't somethings right the first time bad things can happen.. Also when engine is running air-filter off put you hand over the carb air intake just enough so it runs. If engine rpm goes up it's running too lean. If it starts loping it's running rich. Only do this when the engine has warmed up..Old school stuff Hope this has helped you in some way..
orich
Sounds like all you have to do is readjust the choke so it closes when cold and your Air/fuel screws = more gas less air. or you have an intake leak= bad rubber lines, carb bolts lose, dist. advance, WITH great care you can spray starting fluid at carb base, side of intake mating areas vacu-lines Not the dist. area You don't want a FIRE. only do this out in the open air away from a building if you have never don't this before. Have a water hose handy.
Not to scare you, but if you don't somethings right the first time bad things can happen.. Also when engine is running air-filter off put you hand over the carb air intake just enough so it runs. If engine rpm goes up it's running too lean. If it starts loping it's running rich. Only do this when the engine has warmed up..Old school stuff Hope this has helped you in some way..
orich
Fleet Mechanic
Joined: Jul 2002
Posts: 1,297
Likes: 34
From: S/W Virginia
You should have to choke it to get it started, especially in the winter. If it's got an automatic choke, you would have to tap the gas to get the choke to close. The hesitation is probably it not pumpimg enough fuel from the accelerator pump, or even too much. It sounds like the truck is too rich to me, but i'm not expert carburator tuner. Could the floats be out of adjustment?
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It was pretty cold out when I set the auto choke, maybe since it is warmer out now it is hanging open a little. I will also put my hand on the carb to see if its rich or lean, I'm thinking lean, the air fuel screws are only out well less than one turn. I might also retard the timing some, the initial is set around 6, I think this is what the chilton's said, I try around 8 or 10 and see if anything changes. I wanted to avoid this since I would need to redrop the distributor to retard it any more, I should have done that to begin with. I don't think there is a vacume anywhere and the floats are within and 1/16th inch, so I doubt its this either.
Freshman User
Joined: Feb 2005
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I suspect something is not correct with the accelerator pump. On some carbs you can adjust the point that they start to shoot fuel. Remove the air filter and look down the carb and open the throttle, you should see it shoot fuel as you open the throttle. Also before you do that look to see if the choke is going shut when the engine is cold. As stated above you have to hit the throttle to set the choke to the closed position with a cold engine. If the choke is going shut maybe then the fuel leaks out the bowl after sitting overnight. If you think this is the case remove the carb and set it on a newspaper over night and see if the bowl is leaking, no way could the fuel leak back to the tank. Also not good to have the fuel leaking into the engine and mixing with the crankcase oil.
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Freshman User
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I can adjust the accelerator pump, if I can should i make it start to spray just as I start to throtle it? Also if the choke is closing and the carb is leaking fuel, where could it be leaking from, I agree I do not want it draining into the engine.
Freshman User
Joined: Feb 2005
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Adjust the pump and make it shoot sooner and see if that fixes your problem. If not go the other way with the adjustment. If the bowl is leaking take the carb apart and see how it could leak, I do know that can be a problem. Also ADVANCE your timing to 10 degrees and see if that helps, if it pings on a hard pull back off to 8 degrees. (disconnect and plug the vaccum to the distributor while adjusting the timing) Also remember the fuel/air adjust screws only work at an idle.
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Fleet Mechanic
Joined: Nov 2004
Posts: 1,857
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From: Northern CA
Your note that your dizzy would need to be re-seated tells me that you might have it in wrong. Check to ensure that it is indeed installed properly first. You should have no trouble going from TDC to 30 deg BTDC just by rotating the distributor.
gw
[QUOTE=69monster] I wanted to avoid this since I would need to redrop the distributor to retard it any more, I should have done that to begin with. QUOTE]
gw
[QUOTE=69monster] I wanted to avoid this since I would need to redrop the distributor to retard it any more, I should have done that to begin with. QUOTE]
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