Engine cutsout in 4th gear

[DatDoug]

My friend RatTailDraggers 76 620 truck is cutting out when you get up into 4th gear. Stock L20 with ported manifold and weber 32/36 carb, electronic ignition. It was runnin great. It idles sweet and goes like hell thru first and second. Once you get high third and into fourth it falls on its face (BLUH-BLUH-BLUH) Any ideas?:blink:

[Cuts metal like mad]

Dual points? If so I blame the secondary set.

[datsunfish]

Gotta drop that gas tank and check all the lines and connections. Eliminate some of those stock multiple fuel lines. I am convinced it is a leak in the fuel line. Not necessarily leaking fuel but pulling air on a high demant from the pump. That or shite in the tank that doesnt hinder flow until the demand hits that sweet spot. I have seen that with rigs before. And so everyone knows,its not a problem with the carb. That has been verified.

I hope its not because of these mothballs I dropped in the tank...:fu:

[DatDoug]

Dual points? If so I blame the secondary set.

 

Cmon Zuum! Read the Post thorollee:fu: "E.I.":blink:

[datsunfish]

Be nice. Its late:D Why not pull the tank from the 79 shell at gregs shop and clean it out and put it in.

[Cuts metal like mad]

bah... maybe his truck is mad cause he's been away from the forum too much. :D

 

It's not like I read... I just look at the pictures and guess the words! :lol:

[DatDoug]

bah... maybe his truck is mad cause he's been away from the forum too much. :D

 

It's not like I read... I just look at the pictures and guess the words! :lol:

 

Yah I read the title and then kinda browse over it and decide weather or not my 2 cents is needed. Its got me baffled:blink: I guess we will do the tank and fuel lines like Benny said and then go from there. I was hoping this may have happend to someone else b4 and they could steer us in the rite dyerekshun

[Jason]

Is the wiring to the second set of points still there? If it is perhaps it is arcing in 4th?

[datzenmike]

No dual points on the '76 truck. Even so the second set could only work OR not and this would cause a 4 degree retard OR not... the advance set would always be there.

 

Sounds like a full carb runs dry after punching through the gears. A clogged filter or pinched line causes a lack of volume needed for sustained full throttle running.

 

Idle the car till the carb is full and shut off. remove the hose from the pump outlet and put a long hose on it and direct into a pail. Start the motor. The pump won't have the float and needle to restrict flow and will be pumping at maximum so watch out!!! Normally it should really squirt out. If there is a problem there will be less than that needed to run the motor a WOT or just a dribble. If there is lots of squirt then there is a blockage in the carb screen or needle/float set low.

 

For cryin' out loud be careful with gas. One cup of gas properly mixed with air contains the equivalent explosive power of 14 sticks of dynamite.

Edited February 10, 2009 by datzenmike

[banzai510(hainz)]

I would run it and stick your hand over the man barrel of the carb and try to use the secondary butter fly and see if car stays running(or stick finger to open secondary ..so there is enought vaccum to keep it sucking gas.

I wonder if 2nd main jet plugged

But if works in 1st and 2nd then I will assume it not that.If you floor it.

 

ck timming again. But I think you know this already.

[datsunfish]

This only happens when driving under load. Not able to make it happen when standing still. Maybe if we held it wide open for a couple minutes.

I have had this happen before,first time was a dirty filter the other time was a small pinhole in an old dryed out fuel line and started to pull air under a big load. I remember someone that had problems due to a rotted out emissions canister by the tank.

I have seen intermittent issues with generators on rvs due to sediment accumulating at the fuel pickup after a half hour of running.

[slodat]

I had a similar problem in my old 620 and my last 510. Both were solved with a new fuel pump. A quality Japanese unit, not a cheap aftermarket pump.

[DatDoug]

We changed the coil, carb, fuel pump and timed it. We think it is the manifold gasket. We will b replacing it soon. He had removed it and then used gasket sealer which u dont use on a mkanifold gasket:blink: So he is gettting a new one. Hopefully this will work:D

[datsunfish]

I seriously think he needs to get the fuel delivery in order. I know he does need a new gasket but it is not going to make the float bowl stay full. Its just so low now no one wants to drop a tank. I say remove the whole bed.:fu::D

[datzenmike]

Vacuum leak will affect idle but not above. You say it idles good and goes like hell through the gears then craps. This should indicate that everything it working fine!!! Top of third and into forth is when the engine has used up all the gas stored in the fuel bowl and needs more ... and isn't getting it. It's running out of gas...And craps out.

 

See if pump is delivering enough fuel!!! New pump is no guarantee it's good!!!

 

DO THIS

Idle the car till the carb is full and shut off. remove the hose from the pump outlet and put a long hose on it and direct into a pail. Start the motor. The pump won't have the float and needle to restrict flow and will be pumping at maximum so watch out!!! Normally it should really squirt out. If there is a problem there will be less than that needed to run the motor a WOT or just a dribble. If there is lots of squirt then there is a blockage in the carb screen or needle/float set low.

 

For cryin' out loud be careful with gas. One cup of gas properly mixed with air contains the equivalent explosive power of 14 sticks of dynamite.

 

If it's pumping lots of gas then the problem is forward of the pump.

 

Clogged filter, pinched line/hose??

 

Carb fuel inlet plugged? filter? Float set too low?

Edited February 11, 2009 by datzenmike

[haubstr]

Did this problem ever get fixed? My friend is having the exact same problem... New Weber 32/36, distributor, fuel filter, and changed the fuel pump. Still dying at high RPM's in the higher gears. If you keep the RPM's down it doesn't die... We haven't changed any fuel line yet... He is doing that today...

[az_rat210]

Some thoughts to try and help out.

 

Questions:

 

1) When it dies does it stutter or Flat Line?

2) Does it restart up immediately or in a few seconds?

3) Does it always cutout at the same speed range, say +/- 5 MPH?

 

If

1) = Flat Line

2) = Yes

3) = Yes

 

Then its possibly Vapor Lock. Could be as simple as the Fuel Line being too close to a heat source.

[kmc63]

So what happened? Did the vehicle get fixed? People can learn from these pages,if the problem is resolved it should be posted so we can all learn.C'mon common sense.