When driving across the plains my gas tank would have a lot of pressure built up and woosh out when I open the cap to refuel. Is this normal? I am now having problems. I lose power going down the road. Seems to do this after driving fir an hour or so. Engine doesn't die, just bogs down for lack of a better word. Seems like since my problems started I don't have that pressure in tank when refueling. What do you think?

I'm going to go out on a limb here and ask a few questions.

Do you have or use any of these devices on your motorhome?

MPG FUEL CAPS, ram-air intake, low-rolling-resistance tires, front airdam, Mini Supercharger....a carb base spacer with a free-wheeling propellor and an air bleed, Magnets that attach around the fuel line, Gadgets sold at fairs that purported to allow your engine to run on water, Fuel pressure regulators, K&N air filters, Chevron F310 gasoline, Auburn triple electrode spark plugs, Splitfire plugs, The Fish carburetor, Vapor injectors, Magic metal in the fuel line, Tornado, Iskenderian mile a mor cam, Edelbrock SP2P manifold, Turbonator, and Slick 50.

You see, these are fuel saving devices and each report to increase the fuel mileage between 5% & 30%. If you have too many of these things installed your fuel would runneth over as the combined savings would be in the range of around 180% and you might need to register with OPEC as an oil producer.

Anyway...

1) I'm guessing the real culprit is probably your dual switching valves for the 2 fuel tanks. 1 is running over and the other might be sucking in air.

Try plumbing 1 tank as your supply and return and see what happens. Try the other one too. Remember which one is for your generator so you have extra fuel in there for that.

2) Or, perhaps your vented cap isn't vented after all. Check both caps and make sure they're vented at the cap. If your fuel is trying to suck up in a tank that isn't vented, you're actually creating a vacuum in the one tank and all the fuel goes to the other tank.

No add ons, just one tank.

maybe run a bottle of "Seafoam" additive thru the tank (available at Walmart) and change the fuel filter. ??

Fuel filter is new, gonna try seafoam. Hard to get in the tank.

quote:

Originally posted by Charlie and Angi:
When driving across the plains my gas tank would have a lot of pressure built up and woosh out when I open the cap to refuel.... I lose power going down the road. Seems to do this after driving fir an hour or so.

What do you think?

Still sticking with #2... Perhaps it's still the same thing with the fuel cap.

The woosh is a massive influx of air going back into the suction of the tank. No air is being allowed into the tank so now the tank is under a vacuum.

Now you're loosing fuel psi/power because you're not getting the fuel pump to overcome the vacuum created in the tank.

If your fuel is wooshing out, it might be coming up the vent tube and splashing back because of the vacuum.

Try driving for a few hours without the fuel cap on. You'll probably have an increase in power.

Is the tank vented or the cap? Maybe you have the wrong cap or perhaps the vent on the tank is kinked or plugged up.

quote:

Originally posted by Charlie and Angi:
...gas tank ...pressure built up ...now having problems... after driving fir an hour or so. Engine ... bogs down ... don't have that pressure in tank when refueling. What do you think?

I think you have some problems with the tank venting. Could be wrong gas cap, could be plugged recovery line, charcoal canister. Driving across the plains, could this have been during the 100+ weather? That might keep the tank pressurized even with the fuel drawdown. Loss of power after and an hour, perhaps 60 miles or 6 or 7 gallons? That is a fairly large percentage of the tank volume. If the cap/tank is not vented it will be pulling a bit of a vacuum and reducing the capacity of the fuel pump. Lean fuel with high loads burns pistons quickly. Don't screw the cap on tightly and see what happens or get a new cap that is appropriate to the unit, check the lines to the pump and recovery can (if there is one).
Fuel pressure gauge and manifold vac gauge could tell a lot, both are relatively cheap and easy to install, if you get by St.Charles I will give you one.

quote:

Originally posted by ccctimtation:

Fuel pressure gauge and manifold vac gauge could tell a lot, both are relatively cheap and easy to install.

I have felt stupid a few times when a fuel pressure gauge woulda showed me where to go.

How close is the exhaust system to the gas tank? Does the exhaust leak?

I had an exhaust leak heat the gas tank to the point that it could be heard boiling when the car was stopped. Galumph, galumph. Removing the cap allowed a big outrush of air.

Susan and I each had a beer and wired the cans over the leak and continued with no more difficulty.

Beer cans and baling wire will fix anything duct tape can't.

Hi Charlie,

With me not being particularly mechanical and still being new to Barth foibles, I'm perfectly willing and capable of asking dumb questions.

Are you still rambling around the high mountains? Estes Park is over 7000 feet elevation and the road over the Continental Divide is over 12,000. Do these older Barth gassers have any issues in the high country, vapor lock or anything related to vehicular altitude sickness?

Great photos and wonderful adventure.

Thanks,
Wally

quote:

Originally posted by Charlie and Angi:
When driving across the plains my gas tank would have a lot of pressure built up and woosh out when I open the cap to refuel. Is this normal? I am now having problems. I lose power going down the road. Seems to do this after driving fir an hour or so. Engine doesn't die, just bogs down for lack of a better word. Seems like since my problems started I don't have that pressure in tank when refueling.

We have had experienced this to the point that while driving, gas was spewing out of pass side cap, we havent been on the road in years and now planning for nov. 1...I am having the carb rebuilt as we speak, buying vented fuel caps, trying to determine the cause, always releasing pressure even while camping, especially if sun is on one side, frustrating, will let you know this week what works, i am not going in any other coach, had this since 94, thanks for sharing, KATE PS: NOW REGRET CARB WORK, THINK IDLE IS HIGH DUE TO PRESSURE IN GAS TANKS. katebob4@yahoo.com

The idle in our 78 barth was runnign so high our guy that works on our cars said the carb had to be rebuilt, now I regret it, It is all due to pressure in tanks, buying vented fuel caps today, will then try all suggestions I have read until I fix problem, mechanic now tells us we need a gas regulator @ $200. , I think we will try your ideas, any suggestions welcome, Back in 02, went to onan gen. in syracuse, worked on gen all day, charged 1000.to switch tanks so right tank feeds gen, did not fix gen, but realized after heading south, gen is fixed now, but that is when fuel problems started, spewing gas while driving, etc, all suggestions welcome, need to fix for winter trip in nov., thank you: KATE

Kate, follow the fuel lines, all of them front to back, trace them on paper and see what is happening at the junction of the y-valve. Refer to Bill N.Y.'s post on the 19th where he mentions the dual switching valves. It almost sounds like a transfer pump doing its own thing.
Look at the billing from Onan see what all they replaced, added and claimed they touched.

Thank you, will start with that, really appreciate your input, will update, thank you: Kate

Its been awhile since I had connectivity. Replaced gas cap. Don't know if it did anything, but rolling on, made it through the mountains, Colorado, Utah, Wyoming. No problems like before. Thanks for suggestions, will check on things when I get home. May still have venting issue.