Fuel Starvation on track.

[steve_pugh]

Ok, so I've been messing and we welded up the fuel filler flap and also modified the late fuel tank blocking off the stock filler location and welding the filler neck onto the corner of the tank.
I've just done bug jam and I was getting massive fuel starvation when passing 4-5000 rpm.   juttering and spluttering.   
All the plugs and leads are ok.  and driving normally it's fine.   
Ideas were, that I was emptying the float bowls in the burnout box and they didnt' have time to fill before the run.
Tested this by NOT doing a burnout and it helped as 1st and 2nd gear was 'ok' then in third, it was spluttering again..
So I swapped the facet cube pump out for a borrowed Silver-top and still the same issue.   (Was wondering if it was not flowing enough fuel...)

Another idea is that the tank is not breathing enough now we have cut off the stock filler neck.    That it's creating a vacuum in the tank.   
It was very very annoying as I just know that the power is being sapped out of somewhere.

Contemplating back to back runs down a long straight, one with the cap on and one with it off to let it breath and see what happens..   

[stretch]

Steve, the tank in my oval is breathed through the filler cap.  What time of filler cap did you use on the modified tank?

[steve_pugh]

Steve, the tank in my oval is breathed through the filler cap.  What time of filler cap did you use on the modified tank?

It's basically the stock filler neck and cap that would have been under the wing mounted filler flap.   



Blanked off area on the right where there is clearly a large hole and a smaller breather.. 
Welded the filler neck and cap on the little flat section on the top left of this photo.

Only breathing i can see is the little tiny tube dead centre on the left.   

Standard beetle cap from 1972 1200.  Bayonet fitting..

Kinda wish we used an early filler neck / cap..

[steve_pugh]

You can kinda see on this photo in my car.

[stretch]

That could well be the problem Steve.

Can you fashion some kind of breather from the fuel sender location?

[steve_pugh]

That could well be the problem Steve.

Can you fashion some kind of breather from the fuel sender location?

I need to be sure I guess that it's the problem.  There is a nice straight bit of road by me where I can floor it just like on the track.   One with and one without the filler cap on.   If it solves it then I will have to look at fashioning some kind of breather...  Or cutting this filler neck off and fitting an early one with a breathable cap.   or junking it and buying a fuel cell...     

Life wasn't this complicated before racing.  :-)
But it also wasn't as fun. 

[richie]

An early tank bolts straight in, get one and have a -8 fitting tigged into the filler neck, then use that as the vent and fit a roll over valve to it at the same time, that way you know you have enough vent for whatever you upgrade to in the future   You know you will upgrade

cheers Richie

PS make sure the outlet from the tank it big enough as well and not restricted at all, those pumps really aren't up to it and the slightest restriction and they just don't work well enough

[Rick Meredith]

Yeah if you don't have a breather it will starve.

[steve_pugh]

An early tank bolts straight in, get one and have a -8 fitting tigged into the filler neck, then use that as the vent and fit a roll over valve to it at the same time, that way you know you have enough vent for whatever you upgrade to in the future   You know you will upgrade

cheers Richie

PS make sure the outlet from the tank it big enough as well and not restricted at all, those pumps really aren't up to it and the slightest restriction and they just don't work well enough

Is the early tank Already vented off the neck?     I can bolt in my sender too can't i as the early tank is mechanical and mine electric.

you are correct tho'.   I know i will upgrade!  It's inevitable.  :-)

[Rocket Ron]

Yes an early tank is vented on the neck and you can bolt in your sender

I found an early Australian tank that had the filler neck on the drivers side of a RHD car that i wanted to use. It had no cut out for the sender but had the depression for one, it was just a case of cutting a hole for the sender and taping some holes to screw it down    
 
99%The venting is your is your problem, I had twin 40's on an engine I ran and the vacuum that built up in the tank when gunning it on a long straight was enough to cause the all the symptoms you describe. I put in a larger vent and that is enough to run twin 48's

pic of early tank neck below

[steve_pugh]

Yes an early tank is vented on the neck and you can bolt in your sender

I found an early Australian tank that had the filler neck on the drivers side of a RHD car that i wanted to use. It had no cut out for the sender but had the depression for one, it was just a case of cutting a hole for the sender and taping some holes to screw it down    
 
99%The venting is your is your problem, I had twin 40's on an engine I ran and the vacuum that built up in the tank when gunning it on a long straight was enough to cause the all the symptoms you describe. I put in a larger vent and that is enough to run twin 48's

pic of early tank neck below

That doesn't look like enough Venting either.   
In a way it's comforting to hear that you had a similar issue.    I guess I have gone to the trouble of modifying the tank already, I  could just drill a 1/2 hole and mount a breather in the same way that early tank has..   
Could I just mount a bolt on breather similar to the outlets you put on Rocker covers?


It shoudl seal ok as it's only a breather.  The sender is only bolted on with a rubber o-ring, and the cap is only loosely fitted with a seal.   Just trying to avoid any more welding.   :-)  It's Open Sports Nationals in a few weeks.

[Rocket Ron]

Steve

I'd just take riches advice and get an early tank and fit a larger breather with a roll over valve

If you're racing at shakey they will always pull you up if you haven't got a roll over valve fitted

You're a brave man welding a petrol tank anyway, I've been there when a well cleaned out tank goes off its not a pleasant experience

Regards Ron

Ps you're right the breather in the picture is too small the picture was for your info of what an early tank neck looks like

[leec]

I'd echo what Ron said, no one should weld a used tank. When my dad did his apprentiship that was one golden rule, don't weld a petrol tank

[Andy Sykes]

Nothing wrong with welding a tank done it times and still got all my hair   Remember you still have the stock breather small I know but worked before and you had a fooked fuel cap gasket so I don't think it's the tank vacuuming

[steve_pugh]

Nothing wrong with welding a tank done it times and still got all my hair   Remember you still have the stock breather small I know but worked before and you had a fooked fuel cap gasket so I don't think it's the tank vacuuming

The stock breather was on the other side where the filler fed to.  You have welded that up :-) so it may have worked before but it's probably on your workshop floor!  :-)
See bottom right in this photo..


And I replaced the cap with the dodgy seal like a good boy.   I could run the cap with broken seal to add the venting back... But I'm pretty sure it should vent to the outside...

[Andy Sykes]

That's not the breather for the tank that aids filling up without the burps

[steve_pugh]

That's not the breather for the tank that aids filling up without the burps

Ahhhh...  (Hangs head in shame).  So that piddly 2mm pipe on the left of the pic is the breather?! 
I must have been getting the extra breathing from my cap then.   

I need to MOT it so I can test this..    One run cap on.  One cap off...

If it's NOT tank vacuuming.  Any ideas Andy?! 

[Andy Sykes]

A few ideas

Have you checked your fuel pump flow rate ?
Have you checked your filter?
Any kinks in the fuel line as you have just rebuilt the car?
Electric or mechanical pump ?

[steve_pugh]

A few ideas

Have you checked your fuel pump flow rate ?
Have you checked your filter?
Any kinks in the fuel line as you have just rebuilt the car?
Electric or mechanical pump ?

Electric pump.  Simple cheap facet cube. 
Swapped it for a silver top at bug jam as Russ was out so we stole it!
Ran a fresh 8mm hard line all the way. (Had a 6mm running down the inside next to the tunnel)
So shouldn't have any kinks and it's much bigger.
I did wonder if my pump couldn't flow as much. But the silvertop should have been better. 
How does one measure the flow?
Filter seems ok. But I'll be removing it as the silver/red top has one.   

[Fiatdude]

When I first read your post, My first thought was the screen on the pickup in the tank, then a restriction in your fuel line, then a pin hole in any of your fuel lines, especially the rubber ones OR if the fabric covered rubber lines are old they will colapse / clog at high flow -- -- Your engine with a stockish fuel pump won't put a vacuum on the tank in 15 seconds

[steve_pugh]

When I first read your post, My first thought was the screen on the pickup in the tank, then a restriction in your fuel line, then a pin hole in any of your fuel lines, especially the rubber ones OR if the fabric covered rubber lines are old they will colapse / clog at high flow -- -- Your engine with a stockish fuel pump won't put a vacuum on the tank in 15 seconds

These are good points.   I have pretty much replaced everything.   New 8MM hard line down the side of the car goes right up into the engine next to the left carb.
Then all the horrid fabric covered lines chucked away and a hard line put between the carbs (8mm again) and brand new short sections of rubber to the unions.
After the issues in the first 2 rounds, I wondered if my Facet Cube wasn't flowing enough, so I borrowed a higher flow Silver top Pump, and a holley Reg and fitted that with the braided hose.  (Basically lifted it off the ghia engine and mounted it to mine. )  So there should be no issues with pin holes in lines, or collapsed hoses or fuel flow rate (And I just bought a Red top off here so I can give the other one back.  I should be ok for flow now...
the one I had was which is for low fuel requirements / street use.  Not blatting it flat out through a burnout and down the strip)  

However.. I have replaced the fuel elbow under the tank for an 8mm one.   But... I haven't had the screen out..  (Schoolboy I know.. )  I have a glass filter just before the pump which looks clear and clean but when revving slightly it wouldn't fill up but fuel would slosh about in it.  should it be full up?

I'm gonna take the tank out again, and check the tank exit screen/mesh.  Then remove the glass filter as it's not needed (And it's 2 less joins.. I hate too many joins), AND Andy, I'll probably be over at some point asking if you can fit a bung to my filler neck so that I can fit a ROV.

I do hear your point tho'.  I'm surprised that my 100HP engine and an electric fuel pump could vacuum the tank that quick but something is wrong..  And it's preventing that last 2 tenths to get me into the next second bracket..   #frustrating

[dragvw2180]

Why not put your vent hose on the gas cap ? When you run do you have enough fuel in the tank to keep your pickup point covered in fuel ( sloshing away) ? Mike McCarthy

[steve_pugh]

Why not put your vent hose on the gas cap ? When you run do you have enough fuel in the tank to keep your pickup point covered in fuel ( sloshing away) ? Mike McCarthy

This is not a bad idea.   saves any more welding near the tank.  :-) 
I put about a galon in the tank.    I would have thought that a gallon would slosh back on launch, but settle on the run. But that's entirely possible that it's an issue...  I guess I'm always reluctant to put too much fuel in at just under a kilo per litre...

someone hinted that Points would be an issue at high revs, but others said that a pertronix is more hassle than it's worth too and that points rule...
The fuel is missing around 4-5000rpm on each gear change.

[stretch]

Did you have any problems before you altered the tank layout?

[Taylor]

From experience, if it does it at the same rpm every time it's not a fuel delivery issue.

[steve_pugh]

From experience, if it does it at the same rpm every time it's not a fuel delivery issue.

Just had an interesting conversation with James at Stateside, who might tend to agree..
My stock points could be having an Epi at the high revs and bouncing.   So he has suggested that I upgrade to a 6AL in the long run, but for time, and cost, the other option is the upgraded Bosch points that have a better spring to eliminate the bounce.   
He also seemed to think that running 3psi is WAY too high for webers and that 2psi should be a maximum.   That my issue could be the OPPOSITE of fuel starvation but that the higher pressure could be pushing the fuel past the jets and effectively extinguishing the flame.  My ignition isn't up to burning it so that could be my flutter.
He's recomended lowering it to 2psi which is all that is needed to fill the floats and the carb will squirt the correct amount as is required.

He did however agree that my cheapo facet cube might not have the flow rate to keep up, so the new pump with a higher flow rate will be a good thing.   

So I have lots to play with at OSN.   I can add a bigger breather to the tank.  I can change the points, and I can mess with the fuel pressure to attempt to get rid of this annoying gremlin.   

[richie]

Points are cheap and easy so would be top of my list[you can remove the spring section from an old set and double them up as an even cheaper option], then vent the tank better, I don't see to much fuel pressure being the problem, it would more likely show up at idle as then the bowls are full, at wide open throttle it will be using the fuel way quicker so never likely overflow.
Personally I find webers like 3-3.5 psi with stock needle and seats, and then slightly less if using aftermarket 3.00 needle and seats

cheers Richie

[steve_pugh]

Points are cheap and easy so would be top of my list[you can remove the spring section from an old set and double them up as an even cheaper option], then vent the tank better, I don't see to much fuel pressure being the problem, it would more likely show up at idle as then the bowls are full, at wide open throttle it will be using the fuel way quicker so never likely overflow.
Personally I find webers like 3-3.5 psi with stock needle and seats, and then slightly less if using aftermarket 3.00 needle and seats

cheers Richie

I ordered the points as they were pretty cheap.  Well not as cheap as normal points but at a Tenner, it's hardly breaking the bank.   Never heard of the double spring option, but that's a good idea I guess.  I'll try saving some old points and have a modified double spring set as a spare.   

I see what you are saying about the pressure.   It won't hurt to do a few different runs with different pressure to mess about.   But If it turns out to just be venting and points bounce then I'll be super stoked!   

Once I get to the bottom of the 'flutter' then I can look at more interesting things.   A proper ignition and some Nitrous..   *Giggle*  It's gonna be a fun winter.   

[markvo]

The glass fuel filter is the problem if you haven't fixed it yet!

[Dead Dog]

1 - I don't know how well you cleaned the tank out after it was welded? I know when I had mine done what came out after the first wash was mingin! so I washed it out LOADS.
2 - you didn't seal it after as Andy recommended, that would help with the fuel going in from then on in.
3 - just increase the breather hole/ improve the breathing! - it can't hurt!!
4 - did you clean out the new lines, made sure there was no swarf/blockage, same with the new hoses?
5 - get your ass to a rwyb and do some testing there, rather than an event you've paid to race at, will only have 3-4 runs a day only to find you still have a problem. rwyb you can really test your modifications and get your car sorted