Fuel Starvation Troubles

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Edwin Ek
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Fuel Starvation Troubles

#1 Post by Edwin Ek »

Complete rebuild of a stock 616/12 engine. Very experienced mechanic (working on these cars since new, factory-trained).

Rebuilt fuel pump. Fewer than 40 miles on new engine. Car runs fine on flats and downhill. Stumbles and dies going uphill, including slight grades.

The first time this happened, he checked pressure at rebuilt fuel pump. Reading was 1 or 1.5 pounds, which of course is too low. Removed gas line inlet to pump, and gas flowed freely. Installed another diaphragm (factory original diaphragm from nos 36-hp fuel pump). Checked pressure, and reading was 2 or 2.5. We took it for another test drive, and same problem- 1.5 pounds.

Cause?
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Steve Kram
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Re: Fuel Starvation Troubles

#2 Post by Steve Kram »

Is this an AB pump?
If it is, I have found that the black spacers between the pump and the engine can be different widths (you know how I know) and can cause low or high pressure under load. If you measure it I believe they should be around 8mm wide but please check a known good one.

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Re: Fuel Starvation Troubles

#3 Post by Steve Kram »

More about the issue:
viewtopic.php?f=1&t=46076

Edwin Ek
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Re: Fuel Starvation Troubles

#4 Post by Edwin Ek »

Steve, many thanks for the information!
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Mike Wilson
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Re: Fuel Starvation Troubles

#5 Post by Mike Wilson »

Ed: I'm assuming D.A. built the engine. Is the engine in your Roadster or another car? If in the Roadster, did D.A. install it and test drive it? If not, besides the fuel pump, I'd check the float levels, float needle valves and petcock.

Mike
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'63 B coupe

Edwin Ek
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Re: Fuel Starvation Troubles

#6 Post by Edwin Ek »

Mike, thanks for the answer. Yeah, it's my Roadster, and I did the test driving (lunch runs down and up the hill) with Dick in the passenger seat. Pretty exciting, because I hadn't driven it in 25 years. He has checked and restored everything mechanical, so it's like driving a new car: brakes, steering, suspension including shocks, instruments, horn, lights, wipers, engine, and transmission. Sure drives better than I remember!

He and I are reasonably confident that the fuel pump is the problem because the car drives fine on the flats and the pressure is not consistent. In the thread Steve linked to, two good suggestions were the spring and width of the black spacer.
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C J Murray
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Re: Fuel Starvation Troubles

#7 Post by C J Murray »

There are 2 factors to fuel delivery, pressure and volume. The low pressure doesn't bother me IF you have volume. There is probably a spec somewhere but it is a pain to measure. Usually I just see that the volume that I catch in a container looks like more than enough. Disconnect the power to the coil!

Poor fuel delivery can be caused by air leaks in the lines and hoses from the tank to the fuel pump. It is even possible that there will be no fuel leak where the air leak is.In other words, the pump can be pulling aggressively but little fuel moves because air is being pulled through a fault in a hose or steel line. Most of the time that means a fuel leak also, but not always.

When a car sits for a long time, like the one I am working on now sitting since 1973, odd things can happen. On that car the right Zenith fuel tubing had a clog. No fuel was getting to that carb. Using compressed air there was resistance then puff it was free and yet I never saw what blew out. Dried fuel? Insect nest? The line looked ti be in great shape but 1973 was a long time sitting.

Speaking of that, did you ever have a bit of the inner fuel line restrict flow. Maybe it tore when pushed over the tubing or when it was cut to length or it got a little old and is breaking up or collapsing?

If you have not replaced all of the hose and run compressed air through all the tubing I would do that. Oh, and don't forget about the gauze filter in the tank above the cock. Did you line your tank? When the coating is not applied correctly it comes off in sheets. 28 years ago I was driving my 100% restored Daimler SP250 home 30 miles on a highway when it progressively lost power and eventually would take nearly no throttle and putted home. The tank sealer was actually sucked into the fuel line.

Keep an open mind and best of luck.
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C J Murray
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Re: Fuel Starvation Troubles

#8 Post by C J Murray »

Remember the very short hose under the toe board!
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Re: Fuel Starvation Troubles

#9 Post by Edwin Ek »

CJ, thanks for the comprehensive response!
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Re: Fuel Starvation Troubles

#10 Post by Spike Jones »

I recently experienced a similar problem. Went through the fuel pump, pulled the carbs and went through them. Re- set the floats. Then pulled the line from the pump to the carbs to see if fuel was coming out of the pump...it was. After going through this same process several times, I finally pulled the toe boards to check the lines all the way from the tank and VIOLA!! A hose that I had run from the electric fuel pump , mounted in the footwell, to the hard line going through the tunnel had kinked. The fuel flow wasn't completely cut off, so the car would start & run but would not get enough fuel to run at higher RPM's. Fixed that & it runs great (268 miles yesterday).
So look at the last fuel system thing that was done to the car and know that there is probably something between the tank and the fuel pump that is the source of your problem, as C.J. has suggested.
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C J Murray
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Re: Fuel Starvation Troubles

#11 Post by C J Murray »

The basic flaws of the 356 fuel pump are conspiring against us. When the cars were new two things made the weaknesses much less important, the no ethanol fuel and daily usage of the cars.

Even then it was a bad idea to use a mechanical pump at the opposite end of the car from the fuel tank. It is far more efficient to push a fluid than it is to suck it through a small tube. Cavitation introduces air into the fuel and even the slightest loss of seal in the system causes failure. Contrast this to the supposedly inferior English who often placed an electric pump right next to the fuel tank. Problem solved, except for the stuck points in the pump, but a hammer usually fixed that, usually. :D

Heat is also a problem. The mechanical pump is attached to a hot engine just above the #4 exhaust header pipe. Ethanol fuel boils easily but even the old fuel would be better off kept cool and the carbs much prefer cool fuel. The early style pumps on my cars are prone to vapor lock if a hot car is parked for say 15 minutes and then restarted. The late style pumps are less prone to do that and the later pump seems to fill empty float bowls more quickly, better volume.

Porsche was a little slow on the uptake I think because even when the Weber equipped 911 came out with an electric pump the pump was in the engine compartment, a long way from the tank. At least the float bowls could be filled before starting and the pump was away from the extreme heat.

Last week, after 18 years, I installed an electric pump under the toe board of my 57 Speedster that is otherwise 100% stock. I simply got tired of abusing my starter every time I got in for a drive after non-use for awhile. I have succumbed. All cars that may sit at all should have an electric pump and there is no need to drill holes or cut wires to install one. I bought the pump and toggle switch at Summit Racing for less than $50.
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Re: Fuel Starvation Troubles

#12 Post by Gary Thies »

On this subject, I have found low float levels and on another occasion, the short curved fuel line that goes through the front bulkhead was clogged!
Gt

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Wes Bender
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Re: Fuel Starvation Troubles

#13 Post by Wes Bender »

Congratulations on coming over to the dark side, CJ. Now you can turn off the fuel a few blocks from home and the fuel won't boil over in the float bowls after you shut the engine off.

Re. your comment on the pump location and fuel "boiling", I did an experiment on my C once. I replaced the hose from the metal line under the left carb to the pump with a piece of clear plastic line. (Don't try this at home, kids. It isn't safe, but I did it only for the test and then put the regular hose back on.) With the engine warm and idling, minute bubbles were migrating back up the plastic line from the fuel pump and accumulating in the highest point of the plastic line. There wasn't any leakage within the pump. It was the ethanol boiling off from the heat that the pump was experiencing.
Some days it's just not worth chewing through the restraints.....

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Re: Fuel Starvation Troubles

#14 Post by Edwin Ek »

What are the merits of an electric fuel pump versus Ron LaDow's carb auto prime kit?
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Mike Wilson
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Re: Fuel Starvation Troubles

#15 Post by Mike Wilson »

Ed: from my perspective (and I have the electric fuel pump primer), not only can it be used as a primer but the electric pump could be used as a back up in the event the mechanical pump fails. I have seen Ron's primer and it is well-made and serves the purpose of priming the carbs.

Mike
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