Technical Starving problems

[riprowan]

I've read several of the threads here regarding fuel starvation. I hope it isn't a problem like topolino2000 had where he had to replace the rigid fuel line!

Here are my symptoms:

- Car won't idle with the choke in, even if engine is warm. Needs to fast idle in order to keep running
- Occasional cutting out at high speed (90-95 km/hr)
- Hesitation when accelerating - give it gas and at first it stalls, then kicks in

Here is what I have done:

- Replaced fuel filter
- Cleaned carb with carb cleaner

Would this be a fuel pump problem? It's clearly pumping fuel... but maybe not enough?

TIA

 

[oopsadaisy]

Did this happen suddenly or is it something that started happening and got gradually worse?

 

[doc18015]

Hello and welcome, not sure what carb is on the car, but it sounds like the jets /internals are blocked w/residue. Cleaning carb w/carb cleaner and while running does not get to all the passages as required. I would take thew carb off, remove the jets, chokes and soak/clean and reassemble w/initial settings. Please advise what carb you have....may be able to help more. I would also make sure the timing, points, etc are in good working order.

 

[Bambino]

Rip,

I start with a disclaimer - I'm no expert and it's always difficult to diagnose problems from so far away.

So having said that, here's my 2c worth.

1) The fuel pumps do fail, are cheap to buy and easy to replace. Because of the relative positions of the engine and tank, gravity feed will ensure some flow with the car on the flat. As you accelerate, the engine my starve and stall though the car should idle normally. If the fuel pump is pumping, it's probably not at fault.

2) Yep, the carby may be dirty. It is easy to remove, easy to clean and easy to setup again. Gasket kits are readily available. If in doubt, do as Doc suggests. Soak everything in a good quality cleaning solution and blow dry with air. Please do not probe fine channels (eg: jets) with wire etc. - all you will do is destroy them. If there is a lot of crud, you may have to go through the soaking/blowing cycle a few times. Once clean these little IMB carbies will perform adequately. They are not great, but they should be reliable.

3) Oops & Doc have a good point - slow onset implies things like wearing points, dirty plugs, fouled carby etc.

4) 95kph out of a 500. I'm impressed. Mine takes half a day just to get to a top speed of 90kph

Regards,
Chris
500 Enthusiast

 

[riprowan]

Hi All - sorry, I didn't see all the replies sooner.

So, I think there is possibly a fuel system problem. I replaced the filter and pump, and did a light cleaning on the carb. When the car is running, the fuel filter runs dry - there are air bubbles coming into it from the pump. Both pumps (old and new) do this so I assume it isn't the pump. So I am guessing perhaps the (old, rusty) rigid fuel line is spongy. It doesn't seem to show a leak - it's dry - but if it's spongy the vacuum might be sucking in a little air. Maybe.

Can I temporarily replace that line with a flex hose to see if it fixes the problem? Or is that too dangerous? And if I want to replace that line myself, can I use 1/4" copper tubing? Or what kind of tubing must be used?

 

[maddogmorg]

Have you tried disconnecting fuel hose near carb and placing into a jar to work out how much fuel is put out in a given amount of time, and if that figure is suitable for the cars needs?

not personally convinced that fuel is the issue here but then i can't tell from certain from here! Also a clear fuel filter appearing to run dry when car is pumping although strange is apparently no indication that pump is not pumping.

have you checked for air leaks around where the carb mounts to the engine?

 

[riprowan]

Have you tried disconnecting fuel hose near carb and placing into a jar to work out how much fuel is put out in a given amount of time, and if that figure is suitable for the cars needs?

So, how is that possible? If I disconnect the carb, the engine (and pump) will stop. What am I missing?

not personally convinced that fuel is the issue here but then i can't tell from certain from here! Also a clear fuel filter appearing to run dry when car is pumping although strange is apparently no indication that pump is not pumping.

The pump is pumping. It's pumping air. I see quite a few bubbles filling the fuel filter until it's pretty much dry, just a tiny bit of fuel in the very bottom of the filter.

Thanks for your help!!!

 

[maddogmorg]

So, how is that possible? If I disconnect the carb, the engine (and pump) will stop. What am I missing?



The pump is pumping. It's pumping air. I see quite a few bubbles filling the fuel filter until it's pretty much dry, just a tiny bit of fuel in the very bottom of the filter.

Thanks for your help!!!

sorry was thinking of an electric pump! forgot these have a mechanical pump?! will go sit in the corner with my dunces hat on!

 

[Bambino]

On my little car from the tank to the engine it goes -

Fuel tank, flexible hose, rigid pipe, flexible hose, fuel filter, flexible hose, fuel pump, flexible hose, carburettor.

If you disconnect the fuel line before it connects to the fuel filter, you should get a nice gravity fed flow of clean petrol, or gas as you guys call it If you don't, there is a block somewhere .....

When I rebuilt my car, I replaced all of the flexible fuel line as well as the rigid pipe. The old pipe was full of crud and split at one of the bends. I can't remember the gauge I used, but it is good quality copper pipe bent to follow the underbody contours. I guess you could use flexible hose throughout and this would be a good temporary fix, but the rigid pipe stands up better to the under-car environment. It wasn't expensive and one of the local pipe people actually drove out to my place and bent, brazed and terminated it for me in the back of his well equipped van.

I don't know where the filters are supposed to go in these cars, but as a matter of habit I always have them upstream of the pump and orientated correctly. I guess as a matter of safety you then have fewer connections between the pump and carby and your pump always gets nice filtered fuel.

Finally, some filters seem to flow better one way than the other and if this is the case, they are usually marked with a directional arrow.

I've attached a couple of photos that I took during my restoration. The final photo is a bit blurred because the engine is running

Hope this helps,
Chris