Fuel hose/ hard throttle stumbling

[Phobos]

Hi!

2 times when ive been driving my 65 in warm weather, the engine has begun to stumble and misfire on hard throttle.

The engine is rebuilt this winter, and i did a ultra-sonic cleaning on the Edelbrock 1406 at the same time.

My theory is that i get too lean when the secondarys open, due to the rubber hose between the fuel line and the fuel pump gets squeezed when the carb wants more gas. The rubber hose propably gets softer in the heat.

Anyone has any similar experience? Does this sound plausible?

[jtschug]

I don't think the fuel hose is the problem. What would be squeezing it? The carburetor does not suck fuel through the hose, the pump pressurizes the fuel in the hose slightly, and then as the fuel bowl empties, a valve attached to a float opens to allow more fuel inside the carb, when the valve opens the pressure pushes fuel into the carb.

Does this only happen when the engine is warm? Are you absolutely sure?

Assuming this carburetor was working well on this engine and nothing has really changed except for a rebuild, I think you should start looking for a vacuum leak.

[Phobos]

Maybe it didnt get it right (english is not my native language…)- Its the hose connecting the fuelpump to the tank i talking about. :)

And yes- problem becomes evident when engine is hot and warm weather.

The car runs perfect until secondaries open.

I don't think the fuel hose is the problem. What would be squeezing it? The carburetor does not suck fuel through the hose, the pump pressurizes the fuel in the hose slightly, and then as the fuel bowl empties, a valve attached to a float opens to allow more fuel inside the carb, when the valve opens the pressure pushes fuel into the carb.

Does this only happen when the engine is warm? Are you absolutely sure?

Assuming this carburetor was working well on this engine and nothing has really changed except for a rebuild, I think you should start looking for a vacuum leak.

[David Langhorne]

Try advancing and retarding the timing in turn and see if that makes a difference. Doesn't sound fuel related to me.

[Phobos]

I replaced the fuelhose, thought i wouldnt hurt, the old one seemed a bit worn (didnt replace that one in the rebuild, all other is new…)

Drove for 30 minutes, and it worked fine- no stumbling what so ever at full throttle.

The outside temp is just 19C today, and the problem was evident in hotter conditions the other day though.

[jtschug]

Does your car have air conditioning? If so, see if using the A/C causes the stumble to return.

[Phobos]

Does your car have air conditioning? If so, see if using the A/C causes the stumble to return.

It doesnt have AC. :-/

[jtschug]

I agree with David, I would start with ignition. Look for loose wires. Did the spark plug wires get changed when the engine was rebuilt? Is it a points ignition or something else? Do you have another coil you could try? Coils start to go bad in the heat.

If ignition completely checks out, then I would start looking for vacuum problems before fuel.

Then with Fuel, start with the filter. Check float levels in the carb....

Tracking down this kind of a problem is not easy.

[64ZCODE]

Hi!

2 times when ive been driving my 65 in warm weather, the engine has begun to stumble and misfire on hard throttle.

The engine is rebuilt this winter, and i did a ultra-sonic cleaning on the Edelbrock 1406 at the same time.

My theory is that i get too lean when the secondarys open, due to the rubber hose between the fuel line and the fuel pump gets squeezed when the carb wants more gas. The rubber hose propably gets softer in the heat.

Anyone has any similar experience? Does this sound plausible?

It could be fuel delivery problem, like a bad fuel pump, collapsed fuel line, clogged fuel filter, stuck needle valve or float level adjustment. Could be weak spark.

[David Langhorne]

There's an old saying that all fuel problems are ignition related and that's what I've found on various cars. I would do the things jtschug suggests first.
If it were fuel line blockage it wouldn't happen straightaway as the fuel in the bowl would keep you going for a few hundred yards at least (or metres in your case!) until it ran out.
If the fault recurs it could be an ignition component which is breaking down under load and does not show when driving normally - just 1 faulty spark plug or lead, points, coil, condenser, crack in distributor cap, rotor arm - I have had all these - some on my tbird.

[Phobos]

Thnx for input guys!
Great to have access to all the knowledge here. :)