Weber carb backfire= Gas Tank explosion
 

I installed a Weber on a M110 engine. The car has been sitting 4 months, with the Gas Tank completely drained of fuel.

So, Sunday I try to start the car.
I used a resevoir fuel source to the carb, and the engine kept dying.
So, then I feathered the accelator linkage manually. By this time, I had poured 18 oz of gas down the resevoir+hose. The gas must have been travelling back to the gas tank via the fuel retun line. No leaks.

THEN, a lot of feathering on the accelator linkage; Too much :eek:; backfire, and the carb shoots a flame 6" high.
Then, Ka-blam, from the rear of the car.
I assumed it was the exhaust backfire. Wrong!
The gas cap blew off, landed in the grass 10 feet away. :confused:
The tarp had a 2 foot diameter burn hole at the gas cap door.

Summation: The flame travelled back through the fuel return line to the gas vapors in the gas tank, causing the explosion (neighbor said it sounded like a rifle shot).
I talked with a Weber guy; he said to install a fuel filter on the return line.

I don't know if I have a problem here; I'm kinda spooked;
not sure a fuel filter on the return line is adequate.
ANY ADVICE?

At the least you need to take the fuel tank off and inspect it. Also please upload pictures of the tarp. This sounds wild.

I'm glad you came out OK.

have you got the fuel pump connected to the suction line and the return line hooked up correctly?
Theres No way on earth a flame can travel back down a fuel line if there is a fuel pump in the way.
It sounds like fumes in the return line exploded. Fuel by itself doesn't burn ,it needs to be atomised which goes a long way to explain why the tank exploded .Empty tanks = Fumes =explosive potential.
I'll bet the tank will be somewhat deformed now too so it will need replacing.

Take the tarp off the car in the future when trying to get it to run.

A similar thing happened to me once when I installed a distributor 180 degrees off on an old 7 liter caddy engine. Sputter, sputter, then a canon shot that echoed off distant hills. The exhaust pipe looked like when bugs bunny puts his finger in elmer fudd's gun.

Doesn't the fuel return go all the way back to the tank? I don't think it goes through the fuel pump at all. I guess it acted like a long fuse, how much time elapsed between the backfire flame and the boom?

Buy a diesel. Gasolene should be outlawed.

I had the muffler explode on my W108 280SEL. It was dumping so much fuel into the system that when I disconnected the trigger points so that I can crank it to burn off some of the fuel, the muffler exploded. I bound it back together and drove it with that muffler for about 3 years before I had enough of getting car sick and replaced the muffler for $60 at a muffler shop.

Glad you didn't get hurt! Makes me worry as I've been working on my carbs lately.

Nice visual Todd :)

I looked all over for one when I got my finnie and couldn't find one. It would be nice to avoid these worries.

You got one you want to sell? :-)

Diesel is for you rich folks . Gasolene is is cheaper.
http://www.ttnews.com/articles/basetemplate.aspx?storyid=19809

...and travel at glacial speeds behind a truly ancient Diesel engine design. Early Diesels are for enthusiasts who don't use the car much. You could always retro fit a 2.5 or 2.9 190 D or Sprinter engine to your finny to get modern performance( theres turbo versions too!) but the cost of Diesel as a fuel is ridiculous and not worth the effort.

Not sure how it is in OZ, but in the US diesel is roughly the same overall cost as gas, when you factor in the additional efficiency of the diesel engine. That changes from time to time- the "spread" right now is about 20% premium over RUG. IMO, diesels are more user friendly for the DIYer, particularly when you get away from carbs on the gassers. I have a K-jet VW Rabbit (not in my sig) that I am toying with now and I really detest all that highly pressurized explosive fluid coursing about.

Rick

Remember that the vast majority of cars this old are not going to make sense in the long run financially. Whether it's fuel or repairs or even basic maintenance items. I used to own a 240D in the ubiquitous w123 guise. Yeah, it made my 230S feel modern in comparison but for some reason I do miss it regardless. It was a bad example of a D though, had a big bash in the front L and pumped clouds of an embarrassing blue smoke/soot combination everywhere. I couldn't, in good conscience, drive it around the streets of Boston suffocating the pedestrians and bicyclists. It made sense as a winter beater though and was the most inexpensive car I've ever owned hands down.

Here in MA the diesel is more expensive than gas by quite a bit, although the prices are fluctuating lately. I think right now it's like 3.75 whereas regular gas (which my current car is perfectly content with) is about a dollar cheaper per gallon. Premium is closer but still cheaper than diesel.

Any mileage advantage comes out in the wash with these prices unless you have a big V8. The diesel's remaining advantages are less maintenance and very basic simplicity and durability, which to me is more important when cars get to be this old. In my current search for a winter ride, the diesels and the gas models are both equally interesting. Neither has a distinct advantage IMHO.

Hey, what's the story with that Citroen?

I'm actually a Diesel Engineer by training and I 've worked on Diesels ranging from 1 hp Petter single cylinder aircooled engines to Sulza 20,000 Hp marine installations so i have more than a bit of experience with the principles.
Here in OZ a 300 D W123 is far more expensive to run over a year than it's equivalent 2.3 liter gasolene brother.
Engine oil is twice the price ,injector replacements cost as much a $300 each and a pump rebuild is $1600 + .The fuel consumption is the same as a gasolene W123 regardless of the myths that others tell us.
A modern Diesel (one of which i just rebuilt and sold to finance a holiday..2.9 liter turbo) will require it's glow plugs replacing every 80-100,000 k's ( or miles) same as it's injectors. Pretty much the same as spark plugs so there's no saving there except you pay a lot more. Sure,the new ones will do 60mpg and 140 mph ,but how about particulate filter replacement?, or even the initial buy in cost?. The Modern diesel has a ECU which does the same job as a gasolene car so theres nothing simple there either . Forget the normal engine build quality associated with Diesel construction,thanks to Daimlers dalliance with Chrysler the heads and lower ends of Modern Mercedes Diesels are very light weight today.
When you really get down to brass tacks ,when you are filling up at the pump with fuel which used to be cheap as dirt and which now costs 1/3 to 1/2 times more than high octane why bother?

solution?
 

Would a charcoal canister, installed on the fuel return line, eliminate this from happening? (kinda like a spark arrestor)

Probably what made things go bad was that I holding the the linkage 'open', so plenty of air was available.