The Stovebolt Site Forums The Shop Area Engine Shop Why does my carb seem to dry out over time?

Back when my '51 3100 was my daily driver, if I had this problem, it was only if the truck had sat a week or two without starting, otherwise I never had a problem with starting it up. I've rebuilt one carb, but bought a new one from classic parts when I still had a problem with it. I've been using my '05 Silverado for my daily driver for about 5 years now, and every time I attempt to start the '51, I have to pour a little gas down the carb to start it. I've had some trucks that would start after sitting for a year without having to prime the carb. What is going on here? Is the fuel dissipating? Is there a leak somewhere that I'm not seeing?

Once it's started and warmed up or driven, it will start like it should. For a while. But within a week, I have to pop the hood, unscrew the air filter and add fuel. I'd like to get this fixed, but I'm not sure where the problem lies. Any and all comments, ideas or solutions will be appreciated. Lee

Test your fuel pump. It should fill up the bowl while the starter is cranking the engine over before it starts.
Your fuel pump is working somewhat, otherwise it wouldn't run after you manually added fuel.
Once the engine fires up, a weak fuel pump will pump enough fuel to fill the bowl quicker than what the starter does before it starts.
Drive your truck more often too.

Your problem is most likely caused by the gasoline blends sold today. Modern fuel is much more volatile than real fuel from 60 years ago. It isn't even the same fuel that we had 20 years ago. Being more volatile, it evaporates much more rapidly and at lower temperatures than it did in the past.

My Toronado's Q-Jet evaporates most of the fuel in the bowl in an hour or so after parked hot. I've seen others on this site say that their AD truck fuel bowls will evaporate in 30 minutes after parking.

I drive my truck every day or every couple days. If it's 3 or more days I have to crank longer and pump to get it started. If it's a day later it's a little easier.

Carburetors are open to the atmosphere and will evaporate the fuel if not refreshed regularly.

Thanks, guys. Carl, i don't know where your reply went, but I'll do that. (I got an email that takes me right to it, but it's not showing up on my screen now). The fuel pump is not too old. I replaced the old one when I bought a dual action fuel/vacuum pump to help out with the windshield wipers. But I will check it.

Otto- I did a search and read that on this forum, but I thought I'd ask anyway, since it looks like it might be leaking from somewhere. I guess I should pull it and re-do the gaskets just to make sure. And since it's from classic parts, who knows where it was made or if there was any QC involved. Thanks guys!

If it's leaking, it can only go two places: Inside the throat and down to the intake runner, or outside the carburetor through the gaskets onto the manifold.

If it's leaking outside, you'd see and smell it.

After you park it after driving, take a look down the throat of the carburetor with the throttle open. See if there is any fuel pooled on the intake runner. Do that an hour, 4 hours, a day, whatever , and see what you find. I'm betting it's just evaporating.

I had this problem develop over the years as gasoline changed. Rather than fight the issue I installed an electric pump. Problem went away. Got a pump with 2-1/2 PSI rating at 30 GPM.

More likely 30 GPH

Yes, 30 GPH.

I've seen it leak from what looks like the bottom, and maybe on the sides, but when I'm pouring a little into the carb, it may have splashed over the side. I'll check it today. Otto, I would certainly consider an electric pump, if it weren't for my vac powered wipers. The dual action pump helps me out with that problem. (although my biggest problem with the wipers usually is keeping the rod from the switch to the motor from falling off at the worst possible moment, like when a sudden hard rain comes up) Thank you for the good advice, guys.

Keep the dual pump. The electric one will push fuel through it.

showme -- Is your carburetor a Rochester B or BC (auto choke)? Or even if it isn't ... If your "rebuild" was just taking the carb apart and replacing old parts with new parts from a FLAPS "rebuild" kit ... You may not have actually addressed your issues.

You might find it interesting (if not helpful, even ..) to read the Carburetor Issues/Rebuilding Tech Tips. Put together by our very own Jon G.

I've heard, but not experienced first hand, that the new carbs are built ... offshore ... and are lacking in quality.

If you choose to rebuild your carb again, also consider getting your kit from our fellow Stovebolter, Carbking (Jon H) at The Carburetor Shop.. He will send you a kit made for your specific carburetor, not a one-size-fits-all generic kit with a bunch of offshore parts you won't need.

Regards,
John M

68ironhead- Hmm! thanks for that tip IH, that makes a difference. But how would that be mounted? (since I know nothing about electric pumps for these, or how they're mounted on the engine.)

John- And thank you for that information, as well! Pretty sure it's a B, not BC, because mine is definitely not auto choke! It's a B. And I think I got one of those 3rd world crap carbs. If my memory serves me correctly, the rebuild job went south and I ended up ordering a carb from classic parts. As thankful as I am to have a places like classic parts to get unobtainable truck parts from, I'm well aware from previous experience with them that a lot, if not most, of their repro parts are sub par and built by companies who have zero quality control and even less in the personnel department. My first clue was when I ordered trim stainless for my inner door panels, and the quality was non-existent. That's when I first noticed "made in taiwan". I don't think I ever got anything from them that wasn't sketchy in the quality catagory, so this might just explain all the trouble I've had with this one. And thanks for the reference to Carbking's place. I'll be ordering from him shortly, it looks like. And, Hey!, he's in Missouri about 3 hours from me. Great!

I use mechanical pumps with no electric helpers on every vehicle I own. Even if they sit for long periods of time, it isn't difficult for the mechanical pump to get enough gas up to the carburetor.

The good thing about your 51 is the gas is all gravity fed to the pump so it doesn't even have to do any work to get the gas from the tank. It just flows out of the tank to the pump naturally. If the pump can't get enough gas up to the carburetor to start the truck, it probably needs to be rebuilt