Carburator won't prime

[The_Handier_Man1]

From: Coachmen1972 (Original Message)
Sent: 11/19/2006 10:19 AM

On "The Mission" this summer one of the floats stuck, and a half a tank disappeared down the drain in forty miles........

I did a roadside emergency repair (tapping the carb helped only for a few miles) and cleaned and adjusted the needles and float level in the "big barrel"......Unfortunately the "guru" on the phone forgot about two machine screws in the center of the lid, and I ended up cracking a corner on the plastic spacer.....duct tape to the rescue (fortunately it was not a bowl).

Did better after that and made it home.....

But it was clear that the carb was not healthy. So took it out and took it to my buddy. He rebuilt it, and returned it rebuilt with a brand new Edelbrock intake manifold, and then put it in for me.....All free! (I did take him sailing for a week on the Atlantic....).

All I can say is WOW!!!!! The thing runs like a million bucks.....no rough running during warm up.....shut down and let it sit for a few minutes, turn the key and it fires right up, instead of having to floor the pedal.......(as in flooded...) The sound out of the pipe is now crisp and clean......bet my mileage will be better too!!!!

One question. Just cranking the engine was unable to pull the gas all the way from the tank and prime the bowls....we had to fill them by hand a few times (I am NOT going to tell you how we almost torched the whole thing...) and finally the higher RPM running on the bowl fuel was able to get fuel to the engine through the pump.....

Has anyone else had a similar experience? Does it sound like the fuel pump might be under-performing?

 

From: Cooneytoones
Sent: 11/19/2006 11:11 AM

CM72....several things could be the cause...One of them, or a combination of them.....

First thing I'd check the fuel filter.....they can get pretty dirty after only a few miles if there is a lot of crap in your fuel tank. Use the clear universal installed just before the fuel pump.real easy place to change when you have to, and you can see if it is gunked up...

Second, any of the rubber fuel line connections....and there are several connections where this could happen.....the rubber comming from the top tubes of your tanks to the fuel tank selector valve, the rubber from the FT selector valve to the metal main line....or the rubber line comming from the fuel filter...or any where along the steel main line itself could get a pin hole in it from rust....connections (clamps) on any one of them,....if one is sucking just a little air or a little dry rot tear near one of the clamps or one pin hole...would cause the problem you are having...

Third.........a collaped or very dirty sock, inside the fuel tank on the pick-up tube.
One way to check that is to blow air back into your tank and listen for the bubbles...

Forth...the fuel pump... to check,  install a fuel pressure gauge...inline.....or use a vaccum gauge that can read fuel line pressure.
Pressure reading should be about 7 or 8 psi...I believe....

Good luck, let us know how you make out with the problem.

Timmy

 

From: Coachmen1972
Sent: 11/19/2006 5:02 PM

Have multiple fuel filters....one cheapy plastic in the line right outside the tank.....and a metal canister just before the pump. I like the blow back idea.....will have to give htat a shot. Thanks.

 

From: DanD2soon
Sent: 11/20/2006 9:05 AM

Oscar,

Carb vs Filter vs Fuel pump - I think Tim's list is pretty much in the right order - filters 1st - Dave Denison, who carries spare filter elements with him at all times, recently wrote that his can go for thousands of miles or may clog in a half hour - I think he uses one in line see-thru filter after his tank selector ahead of the pump.  I use two see-thru filters, one in each of the tank fuel lines ahead of the tank selector, and have the same results as far as clogging goes - only difference is that I can switch to the unclogged tank supply line until I can get someplace to check things.  Can't see any advantage to dual in line filters as you described yours - if either filter clogs, the other doesn't make any difference and the pump is pulling against a vacuum regardless of which one is the culprit - plus, you'd have to change both to make sure of a clear supply line.

Reading your thread, I get the impression that once the carb was replaced & you did get the pump primed, everything seemed to be O.K. and that you're just "planning ahead."  If that's the case,  I'd just check the lines & connections for breaks or pinholes as Tim suggests and replace the filter.  (Actually - replace 1, remove the other)  I'd be inclined to consider the priming problem a one-off situation if it hasn't happened again since then.  Don't think you'll do any damage if you use low air pressure to "back flush" the pick-up socks, but if your fuel pump was good enough to dump half a tank of gas in 40 miles, it should have plenty of Ummph to supply the new carb setup under normal conditions.

A final thought - If you still have the trouble with filter replaced, socks clear, and lines/connections checked, you may have knocked out the pump. The easiest way to destroy a pump is to operate it dry.  That was the mechanic's diagnosis three years ago when pulling MrsD's minivan through the hilly country around Cincinatti, I smoked the electric fuel pump that was on the coach when we bought it.  The filters were clogged and the pump, which the mechanic told us was neither high enough pressure or volume for our 413, was shot.  It was August and we were towed to Delightful Days R.V. Center in Florence, KY.  They replaced the filter elements ($6.65) Fuel Pump (BWD-EP4070 @ $154.20) and charged 2 hours labor for diagnosis & repair. ($120)  I winced at the retail cost of the pump but they had us by the b_ _ l s and could have charged WAY more so I felt pretty good about a total bill of $280.85 and everything's still working great!

Some Useful links:   Fuel pumps, Volume & Pressure ,  NAPA  fuel Pump  EP 4070 ,  Jegs link to Carter Competition Pumps   see Super Street 4070  &   2 Soon Setup

Later - DanD                                                     

 

From: Cooneytoones
Sent: 11/20/2006 7:27 PM

Oscar.....I agree with Dan.....Remove the inline cheezy filter and just go with one before the fuel pump...I had a problem using  two filters like this before the tank selector valve....and could not get it to prime correctly, and that was with an electric fuel pump....once I removed the filter closest to the tank it primed like it should. Just a little bit of air will cause an air lock....Air locks do funny things in closed lines when your trying to get liquid to move through pipes or lines without a bleeder valve.
So now I just use, the "Denison Special" ...the see through plastic one just before the fuel pump.....they are cheep enough, easy to change, and you can see when they need to be changed...I carry several spares with me also...

Timmy

[Steve1973]

Ok so my first post but you know what I had the same problem just many years later so hopefully it may prove to help someone else out. For me it was the check valve in the fuel pump. It failed and allowed the gas to flow back from the carb to the tank leaving the carb empty every time.

Replaced the pump and fixed the problem.

Maybe not your problem for this issue but it was mine !!

Ps a great group and has helped me a lot with repairs and keeping on the road

[brianhines919]

it could also be a pinhole in a line that doesn't leak fuel but will pull air as well as a loose hose clamp doing the same thing.