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Mechanical fuel pump

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markberry

Jedi Trainee
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Hi All,
i've got a problem to throw out to all of you. The Bugeye has developed a problem since getting it back on the road last spring; after running it for an extended period of time (I.E, steady rpm of say 3000 or more for 20 or more minutes), when returning to idle the engine dies after a minute or two. Once dead, it takes about 45 min to start again. When it dies it's like a vapor lock or fuel supply death, not instant like an electrical circuit opened. I assumed it was vapor lock and re installed the missing portion of my heat shield that guards the fuel pump. That fuel pump guard had been missing since I bought the car fourteen years ago, so it was a bit of a stretch that this was the problem, since the problem I'm having is new. I bought one of the newer red rotors from Advanced Distributors thinking that might be the problem, as there is a write up out there describing a similar problem caused by the high carbon black plastic rotors with the rivited contact on it. I also went ahead and had Jeff rebuild a 25D distributor for me just in case the old DM2 was shorting out somehow (another stretch, I know). Now I'm leaning towards the fuel pump. I had replaced the original AC mechanical pump a few years ago when it started leaking around the diaphragm with a replacement pump from one of the catalog suppliers. When the most recent breakdown occurred, I cracked the output line from the pump loose and observed the fuel kinda trickling out. Then I took one of the flex lines off a carburetor and cranked it; no fuel came out.
The gas tank and fuel pipe were changed during the restoration and there's no restriction there. Gas cap vents fine also.
i guess my question here is: does anyone know much about these mechanical pumps? Like how much pressure/flow should I expect to see at a carburetor inlet? Does a trickle sound right? Has anyone had a problem with the current reproduction mechanical fuel pumps that are being sold by the big suppliers? I can't imagine there's more than one manufacturer for these and they're most likely from China.
thanks for the help and sorry for the long read:smile:
mark
 
Have you changed your fuel filter?
Don't know if that's your problem but I would investigate.
 
Trickle is not right. Spurt of some sort, visibly so.
You seem to have covered all the basics, fuel tank, pipes, checked gas cap..but, remember the first rule of automotive repair that states:
Just because it is a new part doesn't mean it's a good part.

When is the LAST time you checked the pipes and tank? When you put them in?
Solder slag across the inlet? Fuel cap vent accidentally blocked?
Improperly routed fuel line accidentally smashed flat by jack stands?

I have, in the past, removed mechanical pumps, clamped in a vise, run a hose to a canister of petrol, to the inlet side, outlet back to canister, clamped to the side, and with a flat bar, lever, leather glove covered palm, actuated said fuel pump to see if it really works.

I have seen (not in this instance) a spacer block from some other application, oh, 1/4" thick, installed between pump and block.

Once you check pump (and really, you can put another extension on fuel pipe from chassis to pump inlet, and try that to eliminate all issues), but runs for a while and quits sure sounds like tank vent.

Fully sealed crankcase and excessive crankcase pressure can hold the diaphragm out from the backside, but rare...common is 2-cylinder Onans...but worst case is a flat cam.
 
The fact that it runs fine at speed for so long then quits at idle tends to discount any restriction in the lines or lack of a tank vent but you can eliminate the latter by simply removing the cap. It sure sounds to me like a classic vapor lock. With lack of cooling air flow on an already hot engine the heat builds up so that's my guess at this point.
 
Absolutely not. One of the items I mentioned earlier was the piece of garbage floating around the tank. Maybe the spirited driving kept it away from the pickup tube, idling let it plug. Never know.
Now, as far as vapour lock. You saw his location, right? Just a bit north of me, in the classic convergence zone...colder that my place by a bit...and we have been in the 20's at night in the last couple of weeks, barely made highs of low 40's ....so, unless he has run his petrol delivery pipe full length clamped to the exhaust pipe...of he wrote this tome last July and just getting around to posting it....not sure vapour lock is in the cards.

The check valves in the pump body could be coming loose, and co-incidentally failing only when you come to idle. Return spring could be broken, and at high revs the cam may just be flicking the pump arm.

Which is why I recommended pulling the pump and manually operating it.
You will feel if the return spring isn't working. You can check pressure (observation) and flow, but ya know, it's always the coil.
 
An easy way to check if the engine is not getting fuel is to run the engine/car until it stalls. Then take the top of one of the float bowls off the carb. Look inside and check if there is fuel. I would check both float bowls at the same time.
cheers, Scott in CA
 
thanks for the replies All.
I've gone away from the idea of vapor lock now. the last time it quit I sprayed the fuel pump, lines, and even the ignition coil with carb cleaner to rapidly cool them, but the car still took 45 minutes to start up again. I also cracked the inlet line loose at the pump, blew into the filler neck and freely pushed fuel out of the line. I like the idea of checking the float bowls! I never thought of that. i'll take the pump off as TOC suggested and rig up a test to see how much flow I get. this has been going on for almost a year now and i've checked every fuel and ignition component multiple times. the weird thing is how it only happens after a period of extended steady operation. I can drive that thing around town all day and it runs fine (even better now that it has a new dizzy:smile:). the other wierd thing is how it takes 45 minutes to restart; that's why I spent so much time on the vapor lock/fuel cap vent theory.
anyway, thanks for all the ideas. I'm going to go forward with some fuel pump tests, but i'll probably just get the original pump rebuilt for good measure. if I find a smoking gun i'll let you know!
regards
mark
 
One other thing you can do to set a reference point..especially today, with 30 degrees and snow....is to pull the line off the carbs, stick it into a container, crank it for X number of seconds (write it down) and see how much petrol you have in the container (write it down). Then, after the next "spirited run" do it again and compare.

ALWAYS remember the first rule of automotive repair, which states:
"Just because it's a new part doesn't mean it's a good part".
 
Just out of curiousity, what colour are your plugs?
 
TOC said:
One other thing you can do to set a reference point..especially today, with 30 degrees and snow....is to pull the line off the carbs, stick it into a container, crank it for X number of seconds (write it down) and see how much petrol you have in the container (write it down). Then, after the next "spirited run" do it again and compare.

ALWAYS remember the first rule of automotive repair, which states:
"Just because it's a new part doesn't mean it's a good part".
Click to expand...

the problem with the extended spirited run is that it leaves me stranded no where near my home:(. but I agree, getting some data points would be helpful in narrowing things down. I could sit and spitball this thing all day but nothing beats real data.
 
JPSmit said:
Just out of curiousity, what colour are your plugs?
Click to expand...

plugs look really good(in the combustion area). there's some carbon dust on the outside that leads me to believe I need to get in there and look at those plug connections.
 
Just a wild guess.... could your coil be overheating?
I mean you say it runs fine all over town and then you can't restart it after shutting down. Have you tried a spare coil?
 
Gliderman8 said:
Just a wild guess.... could your coil be overheating?
I mean you say it runs fine all over town and then you can't restart it after shutting down. Have you tried a spare coil?
Click to expand...
Except for two things. He cooled the coil off, same issue, and the pump dribbles gas when hot.
My second (?) post:
You can check pressure (observation) and flow, but ya know, it's always the coil.
 
TOC said:
Except for two things. He cooled the coil off, same issue, and the pump dribbles gas when hot.
My second (?) post:
You can check pressure (observation) and flow, but ya know, it's always the coil.
Click to expand...

Can't disagree, I do think the "dribble when hot" is worth noting - sounds like something is heating up and needing 45 minutes to cool. A blockage should <should> be more random. We regularly see electric pumps overheat and trip a breaker - could mechanical overheat and lock up somehow?
 
JPSmit said:
Can't disagree, I do think the "dribble when hot" is worth noting - sounds like something is heating up and needing 45 minutes to cool. A blockage should <should> be more random. We regularly see electric pumps overheat and trip a breaker - could mechanical overheat and lock up somehow?
Click to expand...

that's why I need to take it off and rig up some kind of bench test. maybe the check valves are weakening after extended use, or maybe the diaphragm gets stretched out and less effective until it cools again.
I won't be able to re create the "3000 RPMs for 20 minutes" test point, but maybe i'll see something. I like the idea of pumping gas into a measuring container for a timed period and seeing if I can correlate the results to the pump specs in the workshop manual. I doubt it though. the easiest thing is to throw the $40 pump in the trash and pay to have the original gone through by someone that does this everyday and knows what He's looking for:smile:. At least I could write the pump off the list of suspects if it happens again.
thanks for the thoughts
mark
 
JPSmit said:
Might be worth getting the old rebuilt - I have certainly had issues with (not Fuel pumps) parts not having the same tolerances.

That said, I googled around and found this - flow rates among other things

https://www.svmgcc.org/tech_tips/SU_Fuel_Pumps_101.pdf
Click to expand...

thanks JP.
that was a good read. it brought up some good points about the diaphragm, check valves and diaphragm spring. maybe something is just out of tolerance.
Mark
 
Like I said in earlier posts...check valves and spring.
There is usually a whacking stiff spring in those...not sure your specific model...which is why when I recommended you remove the pump, clamp it up, use a leather glove to push the lever in.
Takes, generally, a lot of force.
If the spring has fractured (PRC?) it will do lots of odd things.
Once you have some idea of cold pressure and volume, if you cannot drive it to fail, pull the pump and check those out.
Some pumps (my mechanicals) have individual check valves, inserted in the proper direction on thin paper gaskets, held in the a almost hourglass shaped metal bridge and two screws.
Screws come loose, valves float around...you can lose one side which makes life interesting.
If PRC, might be staked in and no easy removal.

But.....check pressure and flow (my old vacuum gauges are dual vacuum/pressure for manifold and fuel) then take it off, check spring pressure, pull it apart and look...oh, and use a hacksaw blade or centre punch to mark the top and bottom so you get it "clocked" right when re-assembling.
 
Mark
Something that I haven't brought up is the question- how is your fuel line routed (from the tank to the pump in the area of the engine)?
This is important in that the exhaust will heat up the line (which is under suction) if it is not properly tucked into the frame away from the exhaust. It might be a good idea to look at the line to see if it is shielded (by the chassis) from the exhaust.
BillM
 
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