Fuel Starvation on track.

[JS]

A common problem if your engine "hesitates" on the rpm when it makes the most newtons is to put in a larger fuel jet. Happened to me and it was the solution.

It you want to test the true delivery of your fuel system do as follows:
 - Remove your carbs.
 - Remove the bolt in the bottom of the float bowls.
 - Plug the hole with your(or friends) finger.
 - Start the fuel pump, let the bowls fill.
 - Remove finger and let the fuel pump freely into a bottle etc.
 - Put finger back in after 10sec.
 - Every 10th of a liter(quart) you have in the bowl should last for 120hp.

I learned this from JPM, will work for every kind of engine. 

[steve_pugh]

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

1 - a LOT  but obvously not enough.
2 - I know but I did a fair amount of reading up and some of the cheap "slosh about" sealers get some shoddy reviews.  So I put this off till I knew what to get.. Anyone used any thing they recommend?   some have scary stories of coming away from the side as if a giant poly bag!
3 - Fair point.   But I did run the car with no Cap on to test and there was no change.  so I've kinda discounted the breathing issue.
4 - No.. This was brand new hard line and brand new rubber hose.   I guess it's hard to tell if brand new hard line might have something in it, but there isn't a flexible hose much longer than 3 inches in the engine bay and only about 6" from the pump.   
5 - Good plan. But I think I've nailed it.  plus there wasn't really any time for me to get to a RWYB.   It's the finals next week so that'll have to be it.  :-)

At Shakey last month, it almost became undriveable.  So we lifted the tank and the filter was CAKED with crap... So we replaced that, and we took the carb tops off and cleaned everything and we drained the tank and gave it a poor mans clean (sloshed a gallon of fuel about in it and drained it...) and it didn't miss a beat all the way through the next run.

i have since also taken the carbs off the car and taken them apart and given them a proper clean out.  something I couldn't do at the track.   All the idle jets were blocked..  (Tho one it looked like sand..  We did have some shot blasting done in the Vent area under the rear window, but the filters would stop that..  But the fact the fuel filter was clogged up, My money is on it being INSIDE the tank that's the issue. )

i'm also gonna give the tank a better clean.  Rather than the sloshing method I think I'll put the tank on one end with an opening a the bottom.  Then put some cleaner in my spray gun and blast it in there to get into all the nooks and drain it through a filter so I can see the crap coming out.   When no more crap comes out, I'll assume it's clean...

if I can't get it clean, I have another tank I can use for the finals, but it should sort the issue.   
And I have a lead on a genuine early tank.

This kinda explains why it was ok before the works and crap after.   there must have still been grinding dust, and weld spatter inside the tank.   Not a breathing issue at all.

We will see how this runs now at the finals this weekend. 

[Neil Davies]

The sloshing method works great if you have something to agitate the liquid. I use a long length of chain, held at the filler neck. It knocks more of the crap and rubbish off than just liquid alone. Some people use a handful of stainless nuts and bolts but its easier to get chain out!

[Dead Dog]

It won't be the blasting - engine wasn't even in the building when that was done (& tank was out)
Sounds like you've got to the root of the problem.
I lobbed nuts & bolts in mine when it got the shakey shakey action 

[JamieL]

I've had this exact problem before - swapped out the tank for brand new one, welded in the mods before any fuel went in and happy days 

If your tank is shitty inside then bin it - not worth risking your motor for it...

[steve_pugh]

It won't be the blasting - engine wasn't even in the building when that was done (& tank was out)
Sounds like you've got to the root of the problem.
I lobbed nuts & bolts in mine when it got the shakey shakey action 

Only reason I was thinking the blasting, is every car I know that has had blasting, Inc Deans.. Sand just keeps coming out for yrs to come.   So it could be coming out of the vents and not getting properly filtered.   

I've had this exact problem before - swapped out the tank for brand new one, welded in the mods before any fuel went in and happy days 

If your tank is shitty inside then bin it - not worth risking your motor for it...

Well I think it's more or less sorted now.    My sloshing sorted the crap in the tank, but I have also bought a spare Proper EARLY tank, so will probably drop a chain in that and slosh it and then put a  sealer in it.    Still need to figure out the  best / most reliable sealer to get.
Plus this will look nicer as it's a genuine early tank.

I had some fueling issues still at the pod but it was more than a few hesitations.  I think that I had some air leak or seal issue on the carbs.  Have rebuilt them which has likely fixed that but now the mixture was all up the swanny.  So we fiddled for what seemed like hrs with the jets and idle mixture screws with various "Carb experts"  and we managed to beat our previous PB of 16.02 (soooo close to a 15) and SMASH that in to a 15.53!!!   

But the plugs are now all getting coked up at low revs it seems REALLY rich, but ok at high revs.  So if i let it idle too long, they coke up and then run like crap. so I had to keep blipping the throttle to keep it out of the idle zone and it ran like a dream, but on the way home, cruising at around 1500-2000rpm it's lumpy as hell.

So I need to get it back on the rollers and check these jets.  OR.. go to Fuel injection, then we could have just plugged in a laptop and sorted the Rich running with a few clicks.