Real time diagnosis: losing power at 55 MPH

[ElHefe]

Got the 40 back on the road and inspected for the first time in about two decades. She runs like a charm around town now (thanks to Trollhole's carb replacement), but when I had her running at 55 for about four minutes, the old girl started losing power, backfiring and bucking back and forth.

I was keeping an eye on the temp gauge and everything was normal (around the first marking). So I pulled over, turned off the engine and let it rest for about two minutes. Turned it over and it ran like a charm around town back to my house.

Any ideas?

 

[zags]

Got the 40 back on the road and inspected for the first time in about two decades. She runs like a charm around town now (thanks to Trollhole's carb replacement), but when I had her running at 55 for about four minutes, the old girl started losing power, backfiring and bucking back and forth.

I was keeping an eye on the temp gauge and everything was normal (around the first marking). So I pulled over, turned off the engine and let it rest for about two minutes. Turned it over and it ran like a charm around town back to my house.

Any ideas?

I would remove the fuel filter and see how restricted it is. The fuel tank is is most likely rusty if you haven't cleaned it out, causing the filter to plug.

 

[ElHefe]

Checking that right now.

 

[ElHefe]

I think we have a winner.

 

[ElHefe]

Yep. Not supposed to look like this.

 

[ElHefe]

 

[pavieSD]

Early style gas tanks have a drain plug underneath the tank, you can pull that plug and let all the gas and gunk drain out. I took my auxilary tank to an old school radiator shop and he hot tanked it, and welded up a few pin holes for about 80 bucks. Well worth doing so that you know the tank is in good shape.

 

[ElHefe]

Pavie, I think that's what I might do. I just swapped out the filter and its starting to clog again. The previous gunked one had only been used for about ten miles...

 

[ElHefe]

Also, Pavie I have had a picture of your truck saved on my phone for as long as I have had mine. Good looking 40.

 

[ElHefe]

Early style gas tanks have a drain plug underneath the tank, you can pull that plug and let all the gas and gunk drain out. I took my auxilary tank to an old school radiator shop and he hot tanked it, and welded up a few pin holes for about 80 bucks. Well worth doing so that you know the tank is in good shape.

How long did it take to hot tank your tank? I'm going to need to do this since filter number two is near full of particles.

 

[1973Guppie]

or just purchase a new oem tank while they are still available.....

 

[DougAustinTx]

Be careful. Some (many) of the new tanks don't have the drain plug. With ethanol, if you leave the 40 parked for long periods, that drain plug could save you from the problems you are having now.

 

[ElHefe]

The past couple of weeks have been a mad dash to get the 40 street legal, inspected (passed today!) and road worthy to make a shake down run to Austin on Friday (the end of the week). I'm kind of pressed for time and I'm pinching pennies until the hard top and cash change hands.

I'm calling around tomorrow in the morning to see how much a hot tank treatment will be.

Now if only a 2F side cover gasket could just fall out of the sky, then I would be able to swap the ignition too...

 

[Eshu Elegua]

also,check-replace all rubber hoses, look for the fuel pump, carb bowl should be dirty already,jets cleaning are calling...it's a chain reaction

 

[ElHefe]

also,check-replace all rubber hoses, look for the fuel pump, carb bowl should be dirty already,jets cleaning are calling...it's a chain reaction

Will do.

I will say that once I cleaned the filter and reinstalled it, the motor ran like never before.

 

[Trollhole]

There is a prescreen on the carb. Right behind the fuel inlet pipe. Make sure it's clean.

 

[pavieSD]

How long did it take to hot tank your tank? I'm going to need to do this since filter number two is near full of particles.

My guy was super old school and a one man shop. It took him about 2 weeks between other jobs. The biggest issue was making sure that there was no gasoline or fumes in the tank before he did the braise welding on the pin holes. Assuming no pin holes, I'm guessing a shop would do it in less then a day. However it depends on work load etc. Thanks for the complement on the 40 and good luck with your tank.

 

[ElHefe]

Removed the tank, cleaned it a bit and decided to have it hot tanked and painted again for $55. Not too bad for some extra peace of mind.

 

[ElHefe]

I'm also replacing all of the soft lines and checking the fuel inlet filter on the carb.

 

[edwjmcgrath]

This is a walking ad for clear fuel filters. I don't know how many guys here have said, "I just replaced my filter a month ago. It can't be clogged." With a clear filter, you can see if it is!