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Dusterbd13
Dusterbd13 MegaDork
11/14/17 5:28 p.m.

77 f150.

300 straight six 

Three on the tree

Fresh distributor 

Rebuiltcarb 

No traceale vacuum leaks

Damn thing wont stay running.  It will fire up and run like a top while cold. Will continue to run fine hot. Unless you try to drive it. Stalls every time you come to a stop sign. I replaced the distributor because the vacuum advance was dead. Ran much better, same problem. Rebuilt the carb. Same problem.  Adjusted the clutch. Made sure fuel lines were clear and filters clean.

Ive adjusted the idle to 2500 rpm, and it does it less, but still does it.

I give up. I berkeleying hate this truck and want it to burn to the ground, but its my brothers that he asked me to sell. I can't sell it running like this. 

What am i missing??????

Fueled by Caffeine
Fueled by Caffeine MegaDork
11/14/17 5:32 p.m.

How is the throttle stops on the carb for returning the butterfly to The ideal position?  Is it snapping or being sucked shut when you come to a stop. 

EastCoastMojo
EastCoastMojo Mod Squad
11/14/17 5:35 p.m.

My truck (mazda b2200) does this when there's trash in the carb. Pull the jets out, blow them out with the compressor and put em back in. I had put a new fuel filter on and replaced the rubber lines  but apparently that wasn't enough. Every now and again I have to pull the jets.

Dirtydog
Dirtydog Reader
11/14/17 5:35 p.m.

How much gas is in there?  Mechanical fuel pump,or electric ?  May not be drawing due to age or bad innards.   Float setting in the carb?  

Nick Comstock
Nick Comstock MegaDork
11/14/17 5:41 p.m.

My first thought is float setting.

Dusterbd13
Dusterbd13 MegaDork
11/14/17 5:47 p.m.

Float was set to spec in the rebuild kit. I cleaned the E36 M3 out of it when i rebuilt it two weeks ago (about 3 miles) with everything i could think of. Carb cleaner.  Dental picks. Brakeclean.  Compressed air.

1/2 tank of fuel. Put new rubber lines, sending unit, sock, and pickup in it a year or two ago.

Fuel pump is suspect. It still visually appears to be new, and the guy he bought it from 3 years and 20k ago said it was. I have a replacement in order anyway.

Throttle stops: had NOT thought to check those for wear or play. This carb has a reman sticker on it from the previous owner. 

 

Keep the ideas coming.  Im usually pretty good with diagnostics, but thus truck has been kicking my ass for a minth and i can't seem to see the issue clearly anymore. 

Dusterbd13
Dusterbd13 MegaDork
11/14/17 5:48 p.m.

If anyone can find me the factory float setting, i would be forever grateful. Im now doubting the specs in the rebuild kit. 

gjz30075
gjz30075 HalfDork
11/14/17 6:14 p.m.

Whatever the float level is now, just raise it a bit and see if the symptoms change.

Mad_Ratel
Mad_Ratel Dork
11/14/17 6:25 p.m.

I had similar issues with my 944, turned out unmetered air was getting in, so the car could not control itself.  It would idle fine, but hte moment the engine was under load it would die unless I hit the gas pedal, i got home by crawling down 485 at 35 mph hoping someone did not hit me from behind at 3 am. 

 

turned out when I'd leaned the last air fitler I'd bumped the air housing loose after the MAF.

 

Not a maf car I know, but chances are you are getting air in after the carb?  so it's not getting the right "command" for fuel when you ask for more gas.  Hence it cannot idle as the carb thinks airflow is x and it's really x+y.  spray carb cleaner around the intake/after teh carb while you've got it running.  if it starts to idle up, you;ve found your leak.

jstand
jstand Dork
11/14/17 6:38 p.m.

First thought:

Does it have power brakes? 

If it does, check the booster for leaks whe. You apply the brakes. 

Next idea:

If you get it rolling down the road and then put it in neutral and coast without touching the brakes will it idle, or does it stall?

Im wondering if there is an electrical issue that is causing the ignition voltage to drop or shorting it out when you hit the brakes. 

fasted58
fasted58 MegaDork
11/14/17 6:47 p.m.

The Carter 1-bbl carb body halves would get loose from vibration. It became a habit to have to tighten them frequently. That could give you a vacuum leak where you ain't looking for one.

Or, blue loctite the screws after setting the float.

Ignition control modules were suspect back then too when they got hot. That was many moon ago tho. 

Dashpot?

 

Appleseed
Appleseed MegaDork
11/14/17 6:51 p.m.

Can you check the carb to intake gasket? 

Nick Comstock
Nick Comstock MegaDork
11/14/17 7:07 p.m.

How did the float look? I'm not sure what they made those out of but I seem to remember having floats getting saturated and riding lower giving similar problems. With the disclaimer that I haven't messed with a carb in probably 20 years or so.

Fueled by Caffeine
Fueled by Caffeine MegaDork
11/14/17 7:10 p.m.

Floats another good one.  Clogged jets make it not want to start or idle.  

Donebrokeit
Donebrokeit SuperDork
11/14/17 7:11 p.m.

Does the truck use a heat riser for the carb? I have seen them cause issues like this on old Chrysler's.

alfadriver
alfadriver MegaDork
11/14/17 7:14 p.m.

Ignition?

Danny Shields
Danny Shields Reader
11/14/17 7:26 p.m.
jstand said:

First thought:

Does it have power brakes? 

If it does, check the booster for leaks whe. You apply the brakes. 

Next idea:

If you get it rolling down the road and then put it in neutral and coast without touching the brakes will it idle, or does it stall?

Im wondering if there is an electrical issue that is causing the ignition voltage to drop or shorting it out when you hit the brakes. 

Yeah, if it has power brakes, a bad brake booster could leak enough vacuum to stall the engine.  You could plug the booster hose to test it, very carefully.

Dirtydog
Dirtydog Reader
11/14/17 7:49 p.m.

Not too familiar with this carb, but does it have one of those stone filters on the inlet to the carb?  May be buggered.  I'm thinking float.  Years ago, a friend monkeyed with his floats on a dual carb set up for drag racing, and every time he went down hill, the car would shut down.  Agreed on spraying carb cleaner around to spot vacum leaks.

Dusterbd13
Dusterbd13 MegaDork
11/14/17 7:52 p.m.

Ive eliminated the booster from the system previously as a test, and no change in the driveway. Additionally, no change in idle speed when warmed up and idling and brakes pushed. So, booster checks out.

Theres a heat riser, i think. Its a 300 straight six.  The exhaust manifold physically contacts the intake manifold right underneath the carb. Im sure that there has to be something passing between the two, but never took it apart.

 

When i rebuilt the carb a couple of weeks ago, i inspected the float closely.  I found no evidence of fuel making it inside. No sketchy solder, no nouse when shaken. 

Ive searched for vacuum leaks.  Fixed all that ive found so far. I replaced baseplate gaskets between carb and factory spacer, and spacer and intake. I checked all for flatness, and dont recall finding anything

I just went back downstairs to check the idle screwlanding points. No wear or play that i can see.

However, i did see that the external of the carb body is wet with fuel, including the spacer and intake manifold. I had double checked all the carb hardware for tigness while i was replacing the distributor.  They were tight. It appears that fuel is seeping from the gasket abive the fliat bowl.  Tbis leads me to believe that the float is too high, or that fuel is boiling in the bowl. Hiwever, when it stalls, it seems to be a lean stall. Holding the throttle open doesn't restart it, but a shot of ether always does.

Electrical: wouldnt the issue present itself in the driveway before moving? Or be more prevalent with all accessories on?

Ignition: new distributor, cap, rotor, wires checked for resistance and that blue glow after dark. No issues. Have not checked plugs, but less than 5k in them. It has a ford electronic ignition box, but i have no idea how to test that for failure. 

Dirtydog
Dirtydog Reader
11/14/17 8:09 p.m.

If I remember correctly, there is a young man on here that had carb problems on a C4 Corvette build.  Danced a jig with carb changes, and rebuilding them.   Ended up getting a new carb.  I know, easy spending other peoples money.

SaltyDog
SaltyDog Reader
11/14/17 8:12 p.m.

IIRC, FOMOCO's of this era had an EGR plate under the carb that tended to rot and cause all sorts of vacuum related issues. couldn't see it without removing it and checking underneath.

Don't recall if the L6's had these plates or not.

 Good Luck!

 

Dusterbd13
Dusterbd13 MegaDork
11/14/17 8:34 p.m.

I can say a new carb, unless one can be sourced under a hundred bucks, ain't gonna happen.  Cheapest ive found is almost 3.

No egr on this that i know of, but i could be wrong. 

Dirtydog
Dirtydog Reader
11/14/17 8:40 p.m.

3 bills, Ouch!   Junk yard sourcing?  At least to check one out, can't be too much.

fasted58
fasted58 MegaDork
11/14/17 9:01 p.m.

Dry float level (fig. 1) for '77 F-150 300 is 3/8". Float drop as shown.

Per this kit as well as another Jiffy Kit:

 

 

Dusterbd13
Dusterbd13 MegaDork
11/14/17 9:16 p.m.

In reply to fasted58 :

That is most definitely a different spec than what i set it to. Mine was something/32

Im pulling the carb back out tomorrow to reset, and changing the fuel pump.  Will also double check flatness of things, as well as check manifold to head for vacuum leaks.  I dont remember if i checked that.

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