Gravity fed carb, fit a pump?
Discussion
The little Trabant gamely goes everywhere, but struggles up long or steep hills with less than a full tank of fuel.
The reason is the tank sits against the bulkhead under the bonnet and holds about 26 litres. It gravity feeds the carburettor, a drop of perhaps only 12 inches. You can see the tank here, and the arrow shows the carb position.
I'm wondering if fitting a cheap fuel pump would make things better or worse? A little in line one for about a tenner on the bay. But it's not needed all the time, just up steep or long hills of which there are plenty here in Devon! And only when there is perhaps half or less in the tank.
Any ideas for a cheap and easy fix?
The reason is the tank sits against the bulkhead under the bonnet and holds about 26 litres. It gravity feeds the carburettor, a drop of perhaps only 12 inches. You can see the tank here, and the arrow shows the carb position.
I'm wondering if fitting a cheap fuel pump would make things better or worse? A little in line one for about a tenner on the bay. But it's not needed all the time, just up steep or long hills of which there are plenty here in Devon! And only when there is perhaps half or less in the tank.
Any ideas for a cheap and easy fix?
Sounds like when I fill up at Tesco. Open the bonnet, dip the tank - no fuel gauge, fill with petrol, note number of litres, around to the boot, take out 5L can of two stroke oil, calculate approx 40:1 mix, top up fuel tank, put can away, head in to pay.
It's a mini service! And that's only if they haven't shut the pump off and yelled over the tannoy!
It's a mini service! And that's only if they haven't shut the pump off and yelled over the tannoy!
Yes, it's all brand new and flows fine. There just seems to be less flow up steep and or long hills. Helpfully Sachsenring fitted a flow meter for a bit of decadent Western gauge type stuff. The flow drops right away the long the car is going up hill. I've proven it's simply lack of pressure (I'm with you, I thought that was ample head of fuel) because as soon as you turn around, or it flattens out, things return to normal.
I was thinking that. Almost like having a bypass pipe in the supply to the carb, which goes via the pump?
Would splitting the line into two via a Y piece, half direct to carb (as now) and the other via a switchable pump, then back to another Y piece and into fuel line, work? That would permit excess pumped fuel back into the tank I think. Plus the pump wouldn't be required all the time.
I guess it depends how close the pump is to the carb will make all the difference with regards to how it works best?
For info, all fuel lines, fuel tap, filter and carb are all brand new. The drop isn't so huge when going up hill, there is probably no more than 18-20 inches laterally from fuel cock to carb inlet. Then remove half the fuel in the tank and the gravitational effect isn't going to be massive.
Would splitting the line into two via a Y piece, half direct to carb (as now) and the other via a switchable pump, then back to another Y piece and into fuel line, work? That would permit excess pumped fuel back into the tank I think. Plus the pump wouldn't be required all the time.
I guess it depends how close the pump is to the carb will make all the difference with regards to how it works best?
For info, all fuel lines, fuel tap, filter and carb are all brand new. The drop isn't so huge when going up hill, there is probably no more than 18-20 inches laterally from fuel cock to carb inlet. Then remove half the fuel in the tank and the gravitational effect isn't going to be massive.
I will check the cap, I imagine the breather will be integral with it. These are very simple cars and built as cheaply as possible.
Obviously Comrade, you have waited five years for your car, if you don't like it won't go up steep hills, give it back. We have many more worthy party members who would be delighted to own such a fine example of our glorious engineering prowess.
Obviously Comrade, you have waited five years for your car, if you don't like it won't go up steep hills, give it back. We have many more worthy party members who would be delighted to own such a fine example of our glorious engineering prowess.
Would this work with the aforementioned pump John?
https://www.ebay.co.uk/itm/Universal-Adjustable-Gu...
Or still too much pressure?
https://www.ebay.co.uk/itm/Universal-Adjustable-Gu...
Or still too much pressure?
oakdale said:
This type of gravity system worked well on motorbikes for years, I think under bonnet heat combined with poor flow is the problem here, extra heat when climbing hills (causing vapour bubbles) combined with extra fuel demand.
Two stroke mixture is quite viscous, so I'd ditch the funny little filter in the tank and use one of these where the return pipe is fitted to the carb supply pipe instead.
https://www.ebay.co.uk/itm/183113979336
I would also try to route the fuel lines away from heat as much as is possible.
ETA Not sure the separator includes a filter, so an inline filter may be required as well.
Can't easily ditch the in tank filter, it's integral with the fuel tap. There is an inline filter too that I put in. The return pipe is already teed off the carb supply.Two stroke mixture is quite viscous, so I'd ditch the funny little filter in the tank and use one of these where the return pipe is fitted to the carb supply pipe instead.
https://www.ebay.co.uk/itm/183113979336
I would also try to route the fuel lines away from heat as much as is possible.
ETA Not sure the separator includes a filter, so an inline filter may be required as well.
Edited by oakdale on Sunday 6th June 13:16
Good point Ambleton. The East German handbook states that it must ONLY be run on good quality petrol of MINIMUM 88ron premixed with MINERAL two stroke oil.
She must think she's died and gone to heaven running on Tesco 95ron and two stroke oil from a garden machinery place (still mineral, but low ash and easy mix).
She must think she's died and gone to heaven running on Tesco 95ron and two stroke oil from a garden machinery place (still mineral, but low ash and easy mix).
Very valid point. The carb is brand new (well complete refurb) and was apparently all set up ready to bolt in and go. Which I did and she was a pig to start and doing 15mpg. Turns out the air correction screw was all the way in!
There are only three moving parts, the float, the butterfly and the choke. It wouldn't surprise me if the float tab was a bit out and shutting off supply uphill. However, fuel line first, remove in line filter and go from there.
There are only three moving parts, the float, the butterfly and the choke. It wouldn't surprise me if the float tab was a bit out and shutting off supply uphill. However, fuel line first, remove in line filter and go from there.
Gassing Station | Home Mechanics | Top of Page | What's New | My Stuff