I don't think this will work

[MJL]

Like many others on this forum I have been the victim of the dreaded vapour lock syndrome. So yesterday I decided to go the route of installing an electric fuel pump, bypassing the mechanical pump. I used a Carter P60504 pump with a fuel filer in-line between tank and pump and output from the pump direct to the carb (Zenith).

It started up and ran well but after a subsequent hot start it only ran for a couple of minutes before dying and I had to let it sit for about 15 minutes (bonnet up) before it would restart. I noticed that there seemed to be a fuel leak from the carb itself (not input line) as though it was getting too much gas. Once it restarted it seemed to run fine. That was its last run of the day.

I thought about installing a filter with a return line to the tank as has been suggested in other threads, but therein lies my problem and what I'm not sure about.

The fuel system (1972 Series III) is fitted with an emission control system for evaporative loss. This uses the connection on the top of the tank that I want to use the return line to. I thought about installing a T-piece so that I could connect both lines (existing one leading to the expansion tank and the new one from the filter return) to the tank.

If I do this would I need to put some kind of restrictor into the expansion tank line to prevent fuel from just being pumped into the expansion tank?

Also, would doing this prevent the main tank from venting properly? The fuel cap on the vehicle is not vented and the system relies on the expansion tank and charcoal filter for proper breathing?

See the attachment below for more details on the emission control setup.



Any thoughts? Has anyone already solved this problem when installing a fuel filter with a return line?

Thanks in advance for any feedback.

[chuckstp]

I haven't gotten so far as to try and solve the problem yet, but at least with my vehicle, this is what I noticed. I have a clear fuel filter in line, and when I have the vapor lock issue, I can see there is no gas in the filter. When I take the fuel line off the carb, I get a quick shot of gas from the line which implies the float valve is shut and the fuel pump has pressurized the line locking it shut so it cannot pump more fuel into the carb. When I have released the pressure and activated the fuel pump, up comes the fuel, and the car starts. I've only done it a few times.

If it is a simple matter of alleviating the pressure, and the condition for the issue are fairly obvious, it seems you could make the return line work with one minor addition. If you were to place a shutoff valve inline with the return line which is accessible within the cab, you would have the problem licked. Simply open the valve, start the car, and shut off the valve again. Ideally, you could find a spring loaded valve so it is normally closed, but I don't know how hard it is to find such a thing.

In my case, I do not have the emission control issue, and I just got a new gas tank. It has two fuel ports, so I could easily put a return line and have it dump back that way.

[bsims88]

I drive a 1974 Series III. I purchased it new that year.

I took all that vapor evaporation stuff off years ago, pulled out all the tubing and tossed it, with the charcoal filter, into the dustbin. I cut off the line at the tubing fitting on the fuel tank, bent the end over to seal it, plugged the other fittings where the tubing attached around the engine bay, and, I have been happy ever since.

Can't help with the vapor lock problem, never had it. Based on the previous reply, I'd tear down the carburetor and figure out why it pressures up.

[MJL]

Thanks for the feedback guys. Sorry for delay in responding but more important things like my wife and I driving from NH to MD to visit our week old granddaughter (first grandchild)!!!

Will be heading back to NH on Tuesday and will pick up the problem then.

I'd like to see if I can keep the evaporation system and get it to work properly as it is performing a useful function. I plan on installing a see through filter on the line from the top of the tank to the expansion tank. I will install it so that the preferred flow of fuel is from the expansion tank back to the main tank and it should act as mild flow restrictor so that fuel/vapour from the return line on the main filter close to the carb is being returned to the main tank and not the expansion tank.

I also intend overhauling the charcoal canister as I'm sure the carbon is completely saturated after 42 years and that could also be causing venting problems. Should know later in the week how or if it all works. If it does I'll take pictures and post what it all looks like.

Cheers
Mike

[wgnwheel]

I was downtown admiring this guys 49' convertible, forget right now exactly what make, when he popped the hood to his inline 6.
I looked at the fuel pump and how eerily it looked like the ones in our Rovers. I told him so and he said that sometimes he gets a vapor lock issue and is still trying to run it down. Until then, he said he puts an old school wooden-split clothespin on the line and it helped.

I am not saying to do this, but has anyone ever heard of this before?

[LaneRover]

I have heard of it. I forget if you are supposed to put it on wet or at least damp. Either way if gives the heat a place to go and potentially dissipate.

I have also heard of cutting a raw potato in half and putting it on the line.

[o2batsea]

I question your assumption that you have a vapor lock issue.

[MJL]

Why? What would you suggest the problem might be? It has happened regularly during hot weather for the last 3 years. I have just avoided using it when the weather gets hot.

[o2batsea]

You need to do more eliminatinging. Your assumptions engender replacing a bunch of stuff you may not need to. Try using a separate fuel supply to eliminate the possibility that your carb is messed up. The dribbling carb leads me to think your needle valve is stuck, which will give very similar symptoms (flooding)
Also, vapor lock can be cured by simply rerouting the fuel supply line. Have you tried that?

[ignotus]

Hi,

I question the vapor lock issue also. Seems to me, and I'm no petrol head, that the use of a electric fuel pump is the(a) cure for vapor lock. I also don't think the vapor recovery system is part of the issue unless you are creating a vacuum in the tank which over powers the pumps suction.
My thought is you need to find the source of the carb leak and fix that first. Then go after the possible fuel starvation issue (how's the coil, condenser, points?). Fuel and electrical problems can often give similar symptoms. How many #'s of fuel pressure does your carb need and how many is the pump putting out?

.02

[Jdnewberry]

My SIII has the same pressure issue with the carb. All I do is treat it like its flooded. I hold down the accelerator while I turn the key. After the engine turns a few times, it fires right up.

The stopping part may be a separate issue. That sounds just like a coil to me. 20 years ago, I had a Chevrolet that did exactly the same thing. When it was hot, it would just die. After it cooled off for a few minutes, I was back in business. It took me forever to figure out. If you have access to a spare coil, you might give that a try.

[chuckstp]

Mine sounds very similar. After being hot, stopping for 5 minutes, it starts up, but then only runs for a bit, and dies. With the idea of rerouting the fuel line, I simply took the line off the carb, and activated the fuel pump while pumping into a metal can. Sometimes that helps, but I notices bubbles coming into the glass bowl when I pumped the gas. I tightened the clamps at both ends of fuel line (which were lose), but didn't stop the problem.

There are two causes I can come up with for this. One is a hole in the diaphram of the pump which leaks air when hot. The other is the gasoline effectively boils due to the drop in pressure as the pump attempts to draw gas. Since the fuel is much hotter after sitting idle, it is closer to the boiling point. Once it begins to run, new fuel is cooler and less likely to boil. This would also suggest that cooling it off with a potato, or possibly beer might help out.

Either that, or drink the beer and wait for things to cool down.

[bugeye88]

I also think this crap ethanol fuel is greatly to blame as it lowers the boiling point of the fuel (among other bad things ) insulating the fuel lines, filters, electric pumps in the engine bay may help.Tends to happen when truck is left sitting say for 30 min when hot. Longer cooling off eliminates the problem. Cold start is good.

Cheers,
Rob
Bugeye88

[slowmo]

Dang it. I didn't have this problem until I read this thread. Lately mine will start when hot, run a few seconds until the fuel in the carb is exhausted, and then it dies. Disconnect line at the carb and pump the lever on the fuel pump, and nothing for a bit. Eventually, after furious pumping I get fuel, reconnect at carb, pump a few more times, start it up and drive away as if nothing happened. It only does this when hot. In the morning it starts right up.

I have a new replacement mechanical fuel pump and will report the results.

[siii8873]

the next time it will not run remove your gas cap and listen for a vaccum in the tank. Maybe your evaporative system is plugged and not allowing air into the tank. The gas caps are sealed on this arrangement. It the tank cannot let air in it will not pump fuel out.

[slowmo]

Good idea. I'll report back.

[chuckstp]

Just one thought for those who put in an electrical fuel pump. I don't know how they mount, but if it were possible to mount it farther aft closer to the fuel tank, that may alleviate your problem. I heard one person talk about installing a heat shield, but he never included an update. I'm going to see what the feasibility is for installing one on mine.

I had already gone through the gas cap trick, and the first time I tried it, it seemed to work. I think it was just the additional time and movement of gasoline because it hasn't prevented it since then.

[slowmo]

Checked the fuel cap and I did not detect a vacuum. The next day I replaced the fuel pump and problem solved. The old one was apparently...old. I also got the water temperature gauge to function AND the horn now honks. Three, count them THREE issues solved without a single scraped knuckle. The list is getting shorter.

[MJL]

I haven't had much time to investigate my initial issue but I did get an opportunity to do some stuff yesterday. I recreated the cutting out shortly after a hot start. I checked for spark and all looked good - so back to the fuel delivery.

O2batsea suggested I may have a sticking needle valve so I carefully poured some water over the top part of the carb close to the fuel entry hose. This cooled the carb down and the car immediately restarted.

This morning I removed the top part of the carb to check the valve (which of course showed no sign of sticking when cold !). The needle valve is one with the rubber tip but I have a new all brass one from a rebuild kit I've had lying round for a while so I thought I'd give that a try. Unfortunately the gasket between the 2 halves of the carb broke when I took it off and I didn't have a new one of those. I do however have a spare (old) zenith carb which didn't work properly last time I checked (years ago) so I removed the gasket from it.

Herein lies my question - when the emulsion block was removed from both carbs to get the gaskets off I noticed that on the carb just removed from the car that there was no ventilation screw installed, but there was one on the old carb. Should there be one? Should I just install the one from the old carb?

There is a discussion of the purpose of this screw in the zenith carb service manual. Is states that by variation to the ventilation screw it is possible to alter the mixture ratio between low and high speeds at part and full throttle.

Is it possible that the ventilation screw is not used in zenith carbs when used in LR's? I've been using this carb for years without it with seemingly no detrimental effects. I bought the carb as a rebuild replacement from our hosts - so that is the way it was delivered!

So what is the recommendation? Rebuild the carb with the ventilation screw from the old zenith (not necessarily a carb from a LR) or leave it out?

Mike

[MJL]

Here's want I ended up doing. The green bible clearly references the ventilation screw so I decided to use it. I rebuilt the top end of the carb using the emulsion block, gasket and top cover, I installed a new idle mixture screw and economy diaphragm (just because I had one) - I transferred the jets and float from the original carb put it altogether and installed it. I was amazed - it started right up and when warm just needed a minor tweaking of the idle speed screw.

However when I let it sit for a while and started it up it behaved exactly as before, it would start and run roughly for a few minutes, popping through the exhaust and finally cut out and wouldn't restart. I had a new coil so I thought what the heck - let's try it. Put it in repeated the sequence and it still behaves exactly as before.

As soon as I cool down the carb by pouring water over it, it will start right up and seems to run smoothly.

Any thoughts? Could it be the float, I did reuse that. Could it be the rubber ring around the throat in the base of the carb? I looked OK but is the only component in the base I could think might be the problem.

Very frustrating

[chuckstp]

In my case, after being hot and sitting idle for some time, the car starts right up. It is after driving it a few dozen yards, it sputters and dies. I did come up with one solution which seems to have worked so far although I haven't tried it enough to call it conclusive. Keeping with the KISS principle, this takes no additional parts or basic modifications of the vehicle.

The technique is slightly different whether the vehicle is a left hand drive or right hand drive. For the left hand drive, lift the hood and leave it up during the idle period. If you happen to have a right hand drive, you would want to leave the bonnet up instead.

The hope or thought is, some of the excess heat is allowed to dissipate allowing the carburetor and fuel pump to stay a few degrees cooler. Like I said, I haven't done enough times to make a solid claim, but it can't hurt.