sound like i'm experiencing vapor lock sputter sputter

[dayton100]

after local road testing filled the tank i figured it was all good, boy was i wrong...

 

I took my car out for the first time on POTD 40 mile trip total that day.

72 510, L16, A87,EI Dizzy, header and SU's, stock mechanical fuel pump, vapor recovery tank totally removed (came ths way)and non venting gas cap. new plugs, cap, rotor.

 

First time to ever own an SU carbed 510 and ever experience these type of sputtering issues so bear with me.

 

half way through my trip i was on the highway doin about 65-70

i was happy as hell to be drivin a 510 that day then...

 

i knew i had gas cuz it was over 3/4 full. sputter,sputter no power like outta gas so i pull over in a couple of minutes power back, idling great, running fine so i take off, then maybe about 3 more times before i make it to buddys place i have the same intermittent experience.

 

figured i had a clogged fuel filter the one on there was old and dirty anyhow. had a new one, the see through type in trunk so we swapped it out. started up fuel filter filled up completely then emptied but not completely (first time with that style filter) kinda fishy but we figured thats how they work when pumping. or do they?

 

ran fine from federal way to the des moines marina so we figured it was cool.

 

so before leaving it started up normal and idled great, but icehouse and datdoug pointed out some fluid drippin from under the car. i popped the hood and we check it out it seemed i had some gas overflow from the front SU.

I hear this is normal to happen from time to time, obviously i have no overflow lines like many others running them.

 

 

after another guy runing su's said its just over flow.

i took off drove and drove away no problem, then about half way on my trip same shit on the opposite drection of the highway but this time it happend quite few more times then before so i limped it home. left it parked for a over a week.

 

after some research i figured ok maybe clogged fuel line so i blew it out from font to back with air compressor. and maybe water in line so i added some lucas total fuel system cleaner to tank. started and ran, drove fine ripped around the neighborhood for a little while then bam, stutter, stutter dead, left me stranded a 1/2 a mile from home. this time couldn't restart like it normally does after i shut it down for a few minutes. so my brother inlaw dragged me/it home with his chevy.

 

i question the pump and is probably screwed from all the starvation or its just bad, and will be testing the inlet and outlet sides when i get some time.

 

so i have a new fuel pump and some new rubber fuel line ready to slap in when i can.

 

does it sound like my fuel tank isn't venting?

 

sorry for the long post

thanks any positive input would be appreciated.

[DISLEXICDIME]

show me a under hood pic of how your fuel lines is ran to your su's and see how it runs with the gas cap off

[dayton100]

show me a under hood pic of how your fuel lines is ran to your su's and see how it runs with the gas cap off

 

 

I understand this pump is from an L20B

 

 

supposed to be full at all times? or do these empty somewhat and just bubble when pumping? i've used only stock filters in the past..

 

 

would a vented cap help?

 

and some 5/16 fuel line ready on standby

[datzenmike]

Run with gas cap loose, see if problem disappears.

 

You should install a return line. All L20B had them to prevent vapor loc from the heat. Fresh fuel from the pump goes to the carbs and then to a return tube that has a tiny hole to provide some restriction so the pressure will build. Without the small hole gas would just by pass the carbs and return to the tank. A small amount of gas passes the restriction and returns to the tank allowing fresh cool fuel to circulate past the carbs.

 

Generally the fuel filter can have gas and an air bubble, that's normal. They also normally stay at the same level and don't fluctuate.

[dayton100]

Run with gas cap loose, see if problem disappears.

 

You should install a return line. All L20B had them to prevent vapor loc from the heat. Fresh fuel from the pump goes to the carbs and then to a return tube that has a tiny hole to provide some restriction so the pressure will build. Without the small hole gas would just by pass the carbs and return to the tank. A small amount of gas passes the restriction and returns to the tank allowing fresh cool fuel to circulate past the carbs.

 

Generally the fuel filter can have gas and an air bubble, that's normal. They also normally stay at the same level and don't fluctuate.

 

"running without the cap loose and or off"

 

i'll try that later this week when i have some time to tinker. haven't tried to restart in a little over week since my tow home.

 

my car came with the factory return capped on the tank.

 

it was (the rubber plug)cracked and rotted and i was greeted with leaked fuel under rear the seat (a puddle) after one of my initial test drive trips so i did this with hose clamps and bolt.

 

[dayton100]

So i found one of these today to vent my tank, minus any hoses. am i supposed to use regular fuel line or is there a paticular type of hose? am i ok to vent it under the car below the trunk or should i just connect it to the hard vent line that exits up near the brake master like stock without the stock air cleaner into the engine compartment? as stated above i am running SU'S and was told this should solve my vapor lock type symtoms/issues.

according to a post from internet source my 72 should be running this with a vented cap also.Is this correct?

 

[banzai510(hainz)]

since you got a new pump swap it, or ck the old pump by pulling the output line and crank and see if gas come out. if yes I assume pump is good.

 

open vent the gas tank see what happens. Does your gas cap make a sucking sound when you take it off(vacuum?)

 

I personally dont think its vapor lock. I think SUs are always the main proplem.

 

As I run dual Mikkunis carbs, no return line and a STANT Brand gas cap(assume vented). had no issues

 

swap a weber DGV on a stock intake and youll know for sure.

[datzenmike]

The vent from the tank is purely an emissions thing and has nothing to do with vapor lock.

 

Vapor lock is when the gas in the fuel lines, the pump or the carb(s) gets hot enough from under hood temperatures, to boil to a vapor. As you can see the pump won't be pumping fuel and the carb can run dry.

 

This can be reduced by dropping the under hood temperature by venting the hot air behind the rad. (if possible) A header is a prime cause of under hood heat and can be wrapped with an insulator. Heat shields below or behind the carb(s) can reduce radiant heat from the exhaust manifold onto the carb body. Running the shortest possible length for fuel line will reduce thermal mass and heat absorption. Fuel lines can be insulated also. A cold air intake will help reduce carb temperatures. A return line that routes hot fuel from the motor back to the tank and recirculates fresh cool fuel from the tank is another good method.

[dayton100]

Hainz i think its probably something stupid like the pump on there now is toast.

 

is it possible they could act up intermittently then die or just die? i did have one just stop pumping back in my old 69 i used to own if i remember correctly.

 

dont recall a sucking sound when i open the fuel cap.

 

either way i will be checkin the pump, possibly swapping the pump, doing new rubber lines and adding the vented cap this weekend when i can touch the car.

 

first set of Su's look cool but we'll see how long they last.

 

wasn't it you car i saw a tank vent hose stickin down into the hole where your trunk plug would be? that was regular fuel line correct?

 

Datzen I am running a header and my carbs to have a heat shield hmmm..(venting)I thought all that was tied together somehow? at this point i'm anticipating to do what i can.

[datzenmike]

Rather that fuel vapors vented to the outside air (hydrocarbon emissions) they are routed to the engine where they are sucked into the intake manifold and burned. Later models had a charcoal canister that would store fumes from the gas tank and the carb fuel bowl vent when the motor wasn't running and burn them later. Both set ups had zero effect on the running of the car.

[dayton100]

so me and my old lady tested the fuel pump from the outlet side tonight and it pissed some fuel into the cup like a drug test

 

 

pull the choke and crank x4 for me to get started but she got to high idle open the choke some and idles real good, then no choke idling low smoother than ever. let it idle for about 10-15 minutes took it around a culdisac spilled a little fuel goin round. got to the driveway let it idle some more and shut it down..

 

although this is how it normally starts up it was done with the fuel cap off.

 

either way will have a vented cap tommorow its on order....

 

did notice something the hose fitting coming from the filler neck is open with nothing goin to it and the outlet from the tank is connected to the hose would normally go to the crankcase in the pic.

hmm suckin up air??

 

[banzai510(hainz)]

wasn't it you car i saw a tank vent hose stickin down into the hole where your trunk plug would be? that was regular fuel line correct?

 

 

I dont know what my gastank is doing never needed to ck it.

 

I had 2 fuel pumps go bad in my lifetime.

1 while in use the other I pulled off a motor as a spare then sat too long and I guess the diaphrame cracked.

 

 

I heard of pump that are intermittant by never seen it myself. I always figured they work or they dont.

 

I always figured SU would be more of the proplem as they are so old and you have a 50% chance more one is bad over the other.

[DISLEXICDIME]

Next time it does it pop the hood and feel the bottoms of the su,s fuel bowls if its how there is your problem

[dayton100]

Next time it does it pop the hood and feel the bottoms of the su,s fuel bowls if its how there is your problem

 

i'm assuming you mean hot?

[DISLEXICDIME]

Yah oops

[dayton100]

its the clogged fuel line/tank for sure

 

guess i gotta pull the tank to clean, clear the line and hook up the vapor recovery tank .....

 

sux

[dayton100]

its the clogged fuel line/tank for sure

 

guess i gotta pull the tank to clean, clear the line and hook up the vapor recovery tank .....

 

sux

 

got on it tonight

 

the hardline was clear. its the tank outlet that was clogged like a mofo, caked with rusty dirt mostly on the return pipe.

 

used a pipe cleaner on it worked great.

 

siphoned with a selfpriming kit from harbor fright cheap.

 

got out what i could and dumped the rest into a bucket.

 

look it wasn't too bad but bad enough that i'm glad i took it out!

 

i was really expecting it to be filthy but theres no crud on the bottom.

just some surface rust here and there on the baffles..

 

 

another issue was the fricken cracked tank outlet hose!!!!

 

 

so far i filled/flushed it with water sloshed it good about 3 times dumped it in a bucket and got sediment and rust (RUSTICLES) similar to the bucket shot above.

 

the two outlets on the bottom were flowing big time so i'm happy..

 

let it dry,install on sunday yeah!!

 

before washed

 

 

i'm gonna give it a light coat of paint too