1970 25hp deceleration after run at WOT

[davidmbv]

Rebuilt the carb today and cleaned out all fuel lines. Forecast calls for rain tomorrow but will take it out on the next clear day and try pumping the bulb and test using timing light.

 

[oldboat1]

Loosen the cap on the fuel tank.

 

[clemsonfor]

Loosen the cap on the fuel tank.

Yes do this!!! My brother in law bought a brand new Plastic tank and he was asking me why it was leaking. We test ran his motor that had been out up for years. I looked at the tank to make sure the vent was open, it was. I said it looks like it's leaking around the vent. As we were sitting there it was swelling up. I loosened the cap it vented then. Put it back on made sure the cap was vented, started to swell again from the sun heating it up. Again I cracked the cap I said your brand new tank has a bad cap. Just leave it cracked to keep pressure off it. He swapped to the older tank cap and no problem with the vent. Stuffs not good quality anymore and so many QC issues on stuff.

 

[kbait]

That’s how they make the caps now.. safety for no fumes in bilge. Cap vent screw only lets air in to replace fuel used.. annoying.

 

[davidmbv]

The new gas caps do suck. I ended up buying the old style cap with simple vent screw on top on eBay last year. They are harder and harder to find. The vent on the cap was open. Hopefully I can get the boat out in the next few days. Weather has put a delay on taking it out....it’s been raining

 

[davidmbv]

 

[clemsonfor]

That’s how they make the caps now.. safety for no fumes in bilge. Cap vent screw only lets air in to replace fuel used.. annoying.

I don't see how that's any safer...can't vent so it swells up so much it starts puking gas out of the top from the pressure!!! Makes sense! Haha

 

[clemsonfor]

View attachment 358883

That's the type cap that wouldn't vent.

 

[davidmbv]

It’s the old style cap.
Simple screw with hole and o ring . It vents when you unscrew the top screw like the cap on my old Johnson metal tank-manual vent.
I have a plastic tank that I put this cap on. Vents like old style metal tanks (not pressurized).
Check online reviews for the cap I attached a pic of. It’s the fix for newer “eco-friendly” tanks .

 

[clemsonfor]

Yea, that's the cap that wouldn't work for a brand new tank. Looked just like that, it's supposed to vent when the center is unscrewed. It didn't work allowed pressure to build up and tank to swell. He got it off Amazon, said lots of people had problems with the cap not venting after I told him that cap isn't venting. Only way I could get his tank to vent was to unscrew the whole big cap to let pressure out

 

[davidmbv]

I’ll check the cap next time I’m out on the lake. Good idea , thanks

 

[Crosbyman]

a common bolt say 1/4 inch with a section of threads filed flat would allow allow air to seep in when unscrewed & adding a oring will allow the bolt head to seal when screwed back in

 

[clemsonfor]

a common bolt say 1/4 inch with a section of threads filed flat would allow allow air to seep in when unscrewed & adding a oring will allow the bolt head to seal when screwed back in

Your correct. My point was that this was a brand new gas tank and cap! Haha

 

[davidmbv]

Took out the boat today. After thoroughly cleaning the carb, clearing out fuel lines and connectors with compressed air, and replacing the fuel pump gasket it runs like a top. Ran great at WOT and seems to be running better.
Thanks for all the suggestions. My guess is some junk clogged up the high speed orifice/jet and was causing it to lose gas/power at WOT. It Idles great and lots of power now at WOT!