Revival of the fittest - new buggy build

[ZeroAxe]

So.... with the closing-up of the air inlet for the fan, just where do you get fresh air from??? Or am I missing something obvious?

The air comes in around the alti. It's only closed in the back - but since this is an open buggy - I see no reason to pull air from the rear of the of the fan housing. Type 4 fan's direction is mos a bit different from the std beetle.

Ok, it seems like I am being lekker dof hier.... So you got a Type 4 fan fitted to the Type 1 Alt.? Hmmmmm, 'k

[AirPower]

Sorry - thought everyone knew that. Type 4 fan installed for as much airflow as possible. This meant I could reduce the fan speed - type 4 fan runs at engine rpm and does not need to run at 1.8:1 as the normal type 1 fan. Plan is run the motor upto 6000rpm.

This also meant I kept the beetle "look" to the motor - as you proofed.

Mario

[ZeroAxe]

*light goes on*

[Tony Z]

Correct me if I am wrong here.... the return fuel pipe runs right back to the inlet and not back into the tank.

I would like to suggest that you run the return thru a new hole, back into the fuel tank.
My reason for this, is that as you pump any fluid, you increase its temperature. So if you are sitting at idle for a long time on a hot road, your fuel temp will go up a lot and you might end up with detonation purely from the fact that your fuel is not warmer than usual and thus igniting earlier or you might ping because the flame front is moving too quickly...

Plus, the last thing you want in your fuel lines is a vapour lock...

Food for thought....

[Tony Z]

Rear brace is finally done. I'll tell you - in the end I had to put those adjusters in there - I found it impossible to get the pipes the right length - if you're going to try this go for something adjustable from the beginning. Only thing left to do is put some splitpins in to stop them adjusting themselves.

dont forget to put locknuts onto those adjusters

Please tell me you have put locknuts on your adjusters....

[AirPower]

"Correct me if I am wrong here.... the return fuel pipe runs right back to the inlet and not back into the tank.

I would like to suggest that you run the return thru a new hole, back into the fuel tank.
My reason for this, is that as you pump any fluid, you increase its temperature. So if you are sitting at idle for a long time on a hot road, your fuel temp will go up a lot and you might end up with detonation purely from the fact that your fuel is not warmer than usual and thus igniting earlier or you might ping because the flame front is moving too quickly...

Plus, the last thing you want in your fuel lines is a vapour lock...

Food for thought"

You know what - I think you've just solved some of the fuel supply problem I've been having. Not only the heat problem, but now that you mention it - if the small section leading back up into the tank is too restrictive, the returned fuel will pressure feed the pump, leading to a build-up of pressure ---- more pressure, more fuel returned, with more feed pressure which leads to even more pressure....

"slaps forehead" Look how stupid I can be sometimes.

Please tell me you have put locknuts on your adjusters....

Still adjusting them. With the Weber DCD's fitted, I tried another drag-start, but got an enormous amount of shudder. So much that the one rear shock came off the bottom rubber. Also the gearbox nose cone was hitting the body badly. So I'm thinking of slacking them a little. ALSO the DCD carbs have no where near the throttle response that I got from the IDF's, but I think the DCD's are too rich, so a jet change is on the cards.

This project is still FAR from finished, but being able to drive the car makes all the difference. Now the fun starts.

[Tony Z]

I understand your thinking here, but dont agree with it.

Fuel sits in the tank, runs down into the pipe. Goes to fuel pump, gets pressurised and goes to carbs, then returns back to the fuel pump inlet and the inlet to the tank.
There is less fuel returning than gets delivered to the pump (fuel consumption). Plus its under pressure. This pressure will be disspated to the fuel tank, plus fuel has to run from the tank into the fuel line to replace the used fuel and the tank has no pressure to do this.

2 options come to mind.

1) the fuel pipe is too small to flow the required quantity of fuel to the pump from the tank
OR
2) the velocity of the returning fuel creates so much turbulance around the inlet to/from the fuel tank that the fuel cant flow from the tank into the pump...


On another thought, if you are running carbs, why do you have a fuel return line?

[AirPower]

My problem is that I can't seem to get the fuel pressure low enough -----
http://www.aircooledvwsa.co.za/viewtopi ... 3&start=15

You can't "dead-head" a high pressure fuel pump, can you? That's the reason for the return line.

[ZeroAxe]

AirPower, if you are saying that your fuel pressure keeps on building up, are you sure that your fuel tank is "breathing" properly? I tend t oagree with Tony though. Your return fuel is less than what the f/pump is delivering to the carbs, as they use some of the fuel. If not( ) then maybe your fuel pump is too big? (assuming that it is an aftermarket electric pump used for the dual carbs)....

[AirPower]

The pumps were too big. The story went like this:

Bought the Golf 3 bar fuel pump and Malpassi regulator from CB performance, installed a new copper pipe from the front to rear.

Both the Weber 44 IDF's and the Weber DCD 7 carbs kept flooding (first tried the one set then the other set)

I then realized that I'm using a 1/8 pipe from the pump to the regulator, but only the std fuel pipe for the return (smaller ID). To fix this I installed another 1/8 copper pipe to use as a return line.

This didn't solve the problem - carbs still flooded.

So I went to the local Bosch dealer where a sales rep sold me a Bosch pump and a BMW fuel regulator/filter that was supposed to keep pressure to 3 bar only, which should allow the Malpassi regulator to drop the pressure enough for the carbs. So now I had a return line from the first regulator back to the tank plus another return from the Malpassi.

Still the carbs flooded. Checked the Malpassi regulator, but it was set to it's lowest setting. Then I changed it for another Bosch model which caused so much pressure the carb supply pipes came off.

That stage I said F!! THAT and ripped it all out, installed a Facet pump and Bob's my uncle. Could drive the car around a bit.

Problem is with the planned turbo conversion, the fuel pressure must be higher than the boost pressure to get fuel into the carbs, so the Facet pump will have to go at some time.

I still don't know what to replace it with.

[Tony Z]

The Webers want 4psi not 3 bar. HUGE difference.

[AirPower]

The Webers want 4psi not 3 bar. HUGE difference.

I think I've figured out what to do - all this discussion helps to see problems from a different angle. Tony the Webers never got 3 bar pressure - the regulator got fed 3 bar.

To solve it, I'm going to reduce the feed line to a smaller ID than the return. Reroute the return line to it's own opening in the tank. I'm 100% sure that will work.

The regulator reduces pressure by opening up the return line and allowing fuel to be pumped back to the tank. Same other way around - if pressure drops, the regulator closes down on the return line allowing pressure to increase. Now, like in my case, if the pressure and volume of fuel supplied is so much that even with the return line fully opened, the pressure is still too much, then there is nothing more the regulator can do to drop it further - hence the carbs flood.

To solve this - when the return line is fully opened, pressure must be and stay low. That's why the small supply and big return pipe should totally solve this.

[Tony Z]

dont downsize your return line.... it will reduce your max flow available when you need it.
Rather increase the return line to the same size as the supply or slightly larger

[johanb]

AirPower.. I had the same problem you had when I raced with my golf 1, (2.1 with sidedrafts), had flooding problems and got hold of an old Alfa fuel regulator, the one's they use on the GT Junior and Berlinas (Got a glass bowl at the bottom) Know I will be stoned for this, but resolved the problem as it will give the right presure to the carbs and the rest gets returned, , Don't try and use the regulator when you using a suck through turbo,, Don't have the desired effect

[AirPower]

Thanks for the advice Johan. Suck-through turbo setups are a bit easier to setup from what I learned, true, but they also have a few problems - icing up in the winter? closing the butterfly valve on a spinning turbo when you change gears? difficult to start cold?

I've decided to go with the blow-through simply because I recon I can solve the issues with that - lean under boost, leaking carbs etc.

Cheers
Mario