427 dart block with 750 quick fuel, cold start trouble

[Gaz64]

We need to work out whether the fuel is leaking internally or evaporating (or both).

If you cold start the engine and run for a short period without putting a lot of heat into the engine, then let it sit for 2 days, do the float levels stay correct or drop down as stated?

If they do drop, I'd look at the power valve gaskets and/or the power valve diaphragms for leaks.

If they don't drop, then I'd be looking at adding a phenolic or wood carburettor spacer to help insulate the carb from the engine temperature at hot shutdown.

[Detroit Bill]

Originally Posted by Gaz64

We need to work out whether the fuel is leaking internally or evaporating (or both).

If you cold start the engine and run for a short period without putting a lot of heat into the engine, then let it sit for 2 days, do the float levels stay correct or drop down as stated?

If they do drop, I'd look at the power valve gaskets and/or the power valve diaphragms for leaks.

If they don't drop, then I'd be looking at adding a phenolic or wood carburettor spacer to help insulate the carb from the engine temperature at hot shutdown.

Wood spacer? I have not heard that before. Wood grows and shrinks with moisture content, that could be a vacuum leak waiting to happen.

[Gaz64]

Originally Posted by Detroit Bill

Wood spacer? I have not heard that before. Wood grows and shrinks with moisture content, that could be a vacuum leak waiting to happen.

Here's one:
Moroso Wood Carburettor Spacer 1 2" Single Holefits Standard Holley Carb MO65015 | eBay

[427BDR]

Originally Posted by Gaz64

We need to work out whether the fuel is leaking internally or evaporating (or both).

If you cold start the engine and run for a short period without putting a lot of heat into the engine, then let it sit for 2 days, do the float levels stay correct or drop down as stated?

If they do drop, I'd look at the power valve gaskets and/or the power valve diaphragms for leaks.

If they don't drop, then I'd be looking at adding a phenolic or wood carburettor spacer to help insulate the carb from the engine temperature at hot shutdown.

Good post thank you. So here's my experience based on the two scenarios you provided

1) hot shut down, engine oil temp 180-200F. Within 1 hr fuel levels in the bowl are no longer visible and if I take the air cleaner off I can see the vapor rising from carb. But at this 1 hr mark if I give it 1 pedal push it will crank for 1 second and start up with no stumble or smoke

2) cold shut down, ambient temp. With in 48 hrs the fuel in the bowls is no longer visible. It's at this point where the problem to start begins to occur.

But the question is why is it not flooding when it's hot but it floods on the 2nd and 3rd try when cold. I should also note that when I got the car in October I had none of these issues, but beginning in November we switch to winter grade blend in CA. Not sure it's the cause but that is when this cold start issue began.

[Gaz64]

I would say that your intake combo gets a little warmer than normal (acceptable) especially after engine shutdown, heat soak.

By the sound of it, you have both issues.

It has been compounded by the change to winter blend which has more low end vaporising composition. The fuel vaporises at a lower temperature.

The engine starts ok hot because most has evaporated. When cold it is more than likely flooded with liquid fuel, hence the flooded starting.

I would take the carb off, drain the bowls, take the bowls off carefully to inspect the back of the power valve AND the area within the main body where the manifold vacuum is presented to the back of the power valve from the base of the throttle body. Hope that makes sense.

There is a recommended torque figure for the power valves.

I fitted a QFT 750 to a mates car after I stripped it for inspection. Has never played up.

[427BDR]

Originally Posted by Gaz64

I would say that your intake combo gets a little warmer than normal (acceptable) especially after engine shutdown, heat soak.

By the sound of it, you have both issues.

It has been compounded by the change to winter blend which has more low end vaporising composition. The fuel vaporises at a lower temperature.

The engine starts ok hot because most has evaporated. When cold it is more than likely flooded with liquid fuel, hence the flooded starting.

I would take the carb off, drain the bowls, take the bowls off carefully to inspect the back of the power valve AND the area within the main body where the manifold vacuum is presented to the back of the power valve from the base of the throttle body. Hope that makes sense.

There is a recommended torque figure for the power valves.

I fitted a QFT 750 to a mates car after I stripped it for inspection. Has never played up.

Gary this is starting to make some sense. So when hot the fuel is vaporizing faster than it is potentially "leaking" hence not flooding. But on cold start when I crank and fill the bowls up, then the fuel potentially leaks and hence the cloud of smoke on cold start and no smoke on hot start.

Ok so when I take off the carb what exactly am I looking for? I'm handy but I don't have lots of carb experience. Am I looking for a gasket leak or tear somewhere?

thanks!