Power loss uphill?

[SnTnDan]

Hey all, I’ve read a million threads I feel like I’m beating my head sgainst the wall at this point. 
 

My ‘84 runs absolutely fantastic up until the point where I start driving uphill where it decides to have no power…. it won’t even make it and the moment I lift off the gas it idles perfectly.

 

I assumed vac leak but the only vac line I have left at this point is for the distributor which is fine. What else should I check for? Tainted fuel? 
 

thanks 

[datzenmike]

Classic dirty fuel filter. It still passes fuel but under high demand climbing a hill the engine uses it faster than it can be supplied. Fuel filter should be changed every 3 years. If you have never or don't know when the filter was last changed, now's the time. They're cheap so if it doesn't help no harm done. 

[powderfinger]

8 hours ago, datzenmike said:

Classic dirty fuel filter. It still passes fuel but under high demand climbing a hill the engine uses it faster than it can be supplied.

 

What he said :-) 

[SnTnDan]

9 hours ago, datzenmike said:

Classic dirty fuel filter. It still passes fuel but under high demand climbing a hill the engine uses it faster than it can be supplied. Fuel filter should be changed every 3 years. If you have never or don't know when the filter was last changed, now's the time. They're cheap so if it doesn't help no harm done. 

I thought so as well, I’ll try it out but I just replaced mine about 2 months ago.

truck has been sitting for awhile tho so anything’s possible. Thanks! 

[datzenmike]

Check that when you replaced the fuel filter that you did not kink any of the hoses.

 

There is a filter between tank and pump and the twist off bottom on the pump also has a replaceable filter. It's one possibility and cheap enough to try and eliminate.

 

If this does not help another possibility is the float level is too low and again the carburetor runs out of fuel faster than it can get in and replace that used. For now the filter is easier.

[Stoffregen Motorsports]

Reminds me of a story - I rebuilt a friend's Honda Accord motor because his wife blew it up. When he asked what happened, she said "it made that noise like when you're going up a hill..." Turns out she thought to go up a hill you would UP SHIFT, because when you up shift, your car goes faster. Wow!!! Logical, but not clear on the concept.

[bottomwatcher]

43 minutes ago, Stoffregen Motorsports said:

Reminds me of a story - I rebuilt a friend's Honda Accord motor because his wife blew it up. When he asked what happened, she said "it made that noise like when you're going up a hill..." Turns out she thought to go up a hill you would UP SHIFT, because when you up shift, your car goes faster. Wow!!! Logical, but not clear on the concept.

Yeah riding with the Wife in her manual subura outback I just marvel at the durability of the engine and trans. Try not to Mansplain things to her but the lugging engine pushes my buttons.

[DwayneOxford]

Secondary working?

[SnTnDan]

Welp, it would seem after exploring all my options I’m still in the same boat. Here’s what I’ve done so far: 

-new fuel filter

-new fuel pump 

-cleaned and gapped plugs 

-checked timing 

-eliminated vacuum system(vac advance directly connected to carb still) 

 

im a bit stumped at this point. Possibly need a new carb? 

[banzai510(hainz)]

fuel filter?  but was changed. Was the old one real dirty? If not then dont think its the proplem

 

timing set correctly?

 

2ndary on carb not opening or choke flap partial closed restricting air

 

did you change the pgus wires and since its a dial plug head you have them swapped? (Im really guessing on this one)

[SnTnDan]

1 hour ago, banzai510(hainz) said:

fuel filter?  but was changed. Was the old one real dirty? If not then dont think its the proplem

 

timing set correctly?

 

2ndary on carb not opening or choke flap partial closed restricting air

 

did you change the pgus wires and since its a dial plug head you have them swapped? (Im really guessing on this one)

Old filter was totally fine and relatively new but slchsnged it anyways.

 

timing is set correctly

 

not entirely sure on that respect, what’s the best way to test that? 
 

entire ignition system was done a few months ago( cap, rotor, wires, plugs) and truck has been totally fine up until a few weeks ago 

[datzenmike]

Still have this.  Float set too low.

 

 

On 3/10/2023 at 6:23 AM, datzenmike said:

Check that when you replaced the fuel filter that you did not kink any of the hoses.

 

 

 

If this does not help another possibility is the float level is too low and again the carburetor runs out of fuel faster than it can get in and replace that used. For now the filter is easier.

 

 

On the front of the carburetor is a small round glass window into the float chamber. Gas should show level in the middle. If low or not showing the float may be set wrong. If in the middle, take for drive up steep hill till problem presents and get clutch in and ignition OFF ASAP to kill the electric pump. Now look at fuel level in carburetor. If not showing the engine used the fuel faster than it could be replaced. So there is a fuel delivery problem.

[None_zero]

On 3/9/2023 at 11:12 PM, datzenmike said:

Classic dirty fuel filter. It still passes fuel but under high demand climbing a hill the engine uses it faster than it can be supplied. Fuel filter should be changed every 3 years. If you have never or don't know when the filter was last changed, now's the time. They're cheap so if it doesn't help no harm done. 

Damn I was gonna say this but you have beaten me to it. This was the very first problem I ever had from my 720 and it took me a week to figure it out

Lol

[None_zero]

On 3/10/2023 at 8:16 AM, SnTnDan said:

I thought so as well, I’ll try it out but I just replaced mine about 2 months ago.

truck has been sitting for awhile tho so anything’s possible. Thanks! 

I went through enough fuel filters when I first got my 720, that I quit buying them and started rinsing them out backwards and drying them before reinstalling eventually dropped the gas tank and added a chain and some cleaning agent and did a workout routine shaking that chain and Cleaner around in there. Rinsed check did it again. Maybe three times before I got enough of the rust and junk out of it that I was only having to clean my fuel filter once a month instead of once or twice a week. Eventually it cleared up and now I can't remember the last time I had that issue. Come to think of it I'm probably due 

Edited April 3, 2023 by None_zero