loss of power and hesitation when accelerating

[coop]

70 F250 Camper Spcl. 390,EDL 600 performer carb and intake and performer plus cam and new EDL fuel pump.

The weirdest thing has just happened. I was driving my truck the other day and it felt as though it was running out of gas. I have dual tanks so I switched over thinking I might have not flipped the toggle switch last time I switched tanks. It didn't change anything now the truck stumbles when you start from a start like it is going to die but then it takes off.

Last weekend I was coming home and there is a a good size hill on the highway and I had the truck floored and it would not go over 50mph! it has pulled 70 up the same hill before. I just took it out and romped on it and it accelerated to 40 mph and just sat there screaming it wouldn't shift or go any faster. And if you stomp on it from a dead stop it backfires occasionally.

I checked the fuel filter it is clean as a whistle cleaned the air filter and it is still doing it, it seems to be getting worse. The funny thing is the truck has been running great no problems. Last weekend I went to the desert with the camper on it and it ran like a champ. The truck seems a little harder to start, I usually give it one pump and away she goes. Now it will start and die then I pump it again and the same then it eventually starts "when cold". When hot it takes a little bit of cranking to light it off. There is no miss just a lack of power the engine seems like it is being held back a couple of times you could feel it take off then stumble back. It is like it is hauling ass but going nowhere?

I switched to the other tank and put fresh fuel in it, the same. I have the manual changeover valve " main - auxiliary - off and the dash switch for the gauge.

any suggestions?

[BobbyFord]

Have you checked the timing?

[1971ford]

Mine does the same exact thing... when it's cold. It's the choke, i need to adjust it. Maybe same problem with you? I'll take off from any stop, it will quickly bog way down (almost dying, or will die).

[coop]

I haven't checked the timing yet that was going to be next. It does seem like it might not be advancing? It still has the original dist and coil. I know the distributor hasn't moved it is still on it's mark maybe the vac advance? I will check it tomorrow.

I have checked the choke after it has acted up and it is wide open after it is warmed up. I will check it in the morning to see if it is shut.

[BobbyFord]

Also, Edelbrock carb is similar to AFB. If all other basics (timing, plugs, wires, vacuum lines, etc.) are good, pull the top of the carb off and remove the primary venturis and make sure that there is not a piece of dirt in the down tubes.

[coop]

Also, Edelbrock carb is similar to AFB. If all other basics (timing, plugs, wires, vacuum lines, etc.) are good, pull the top of the carb off and remove the primary venturis and make sure that there is not a piece of dirt in the down tubes.

I did look down in the carb on the secondaries and it looked a little wet. The other funny thing I heard was what sounded like a faint gurgling sound. My old carb the 2 bbl would bubble out fuel when you turned the engine off flooding the carb. I will give it a go tomorrow thanks.

[BobbyFord]

*EDIT*
Page 22: http://www.edelbrock.com/automotive_new ... manual.pdf
Remove the carb lid and remove both part #32's
Make sure that the skinniest tube pointing downward is clear, blast with compressed air, if available or use wire from wire brush as a pipe cleaner.
On page 21, you may have to loosen screw (#1) and pivot the (#2) piston cover plate aside to let the pistons and metering rods pop up in order to get the top of the carb back on (be careful, the piston/rod assemblies are lightly spring-loaded). After the carb lid is back on, while lightly pushing down on the piston/rod assemblies, move the metering rod around a little until the rods line up with the metering jet holes down in the carb body (you cannot see the jet holes; done by feel) then pivot the covers back and tighten the cover screws.

[coop]

Right on, thanks Bobby I will check it out.

[coop]

Ok here is what I found, I checked the timing and at idle it is at about 5 ATDC when I rev it it does advance. I did disconnect the vac hose when I checked it. If I remember it should be around 8 to 10 BTDC. It does seem like a timing problem. How could it be so far off? Does the stock dist also have weights in it along with the vacuum advance. Like i said the truck has been running fine up until now. I did put a new timing chain in it with the new cam?

Also when I started the truck and while it was warming up i had the filter off and blipped the throttle and it back fired through the carb no flame just a pop. and it did have that hesitation.

[george worley]

If your dist. has points the gap may have changed. That will change your timing. Your dist. may not be tight and moved on you.

[coop]

The points are fine and the distributor is still on the painted mark.

[ArizonaDan]

I notice no one has suggested checking your vacuum readings at EVERY vacuum hose connection. Manifold vacuum at sea level should be between 19" and 21". Subtract 1" for every 1,000' above sea level you are at.

Vacuum leaks can cause these types of performance losses. A loss of vacuum will cause the timing advance mechanism to be weaker than normal which leads directly to less timing advance under load.

I'm just sayin'.

Good luck

[BobbyFord]

Ok here is what I found, I checked the timing and at idle it is at about 5 ATDC when I rev it it does advance. I did disconnect the vac hose when I checked it. If I remember it should be around 8 to 10 BTDC. It does seem like a timing problem. How could it be so far off? Does the stock dist also have weights in it along with the vacuum advance. Like i said the truck has been running fine up until now. I did put a new timing chain in it with the new cam?

Also when I started the truck and while it was warming up i had the filter off and blipped the throttle and it back fired through the carb no flame just a pop. and it did have that hesitation.

Set the timing at 10* and take her for a spin.

[coop]

I will give it a shot as soon as it stops raining what could possibly make the timing change like that I know it couldn't of been that way since I had the heads fixed " long story" I have got about a 1000 miles since then and all has been well. I will let you know what happens. I will also throw the vac gauge on it too.

[iamthewreckingcrew]

"I just took it out and romped on it and it accelerated to 40 mph and just sat there screaming it wouldn't shift or go any faster. And if you stomp on it from a dead stop it backfires occasionally."

This part sounds like vacuum leak to me.