Rough Idle When Pointed Uphill

[kippmw]

Hi all. I'm scratching my head a little with this one. I have a good Zenith 2 on my car that runs great down the road with good response and power. The idle get's a little odd under certain circumstances. It idles great when the car is on a flat surface or if the car is pointed downhill, but it idles rough when the car is pointed uphill (i.e. on my driveway with the front of the car point uphill). I'm a little confused by this one. Thoughts??

Thanks in advance!
Matt

 

[J Franklin]

Must be the float setting.

 

[kippmw]

Must be the float setting.

That would make sense, except the gas would slosh to the back of the bowl where the jets/passages are, right? Not starving the carb of fuel?

 

[bruceincam]

Not enough fuel flowing from the tank to the carb when you ask it to over come gravity by pointing the flow path up hill.

 

[J Franklin]

There would be plenty of gravity in a model A, but too little or too much gas can cause rough idling.

 

[nkaminar]

Suggest you point it down hill or keep it on the flats.

 

[Rob Doe]

How steep? And did you tighten the GAV a bit?

 

[CT Jack]

I tend to agree with bruceincam regarding fuel flow from the tank. Have you tried testing in uphill position with a full tank? If it improves the smoothness at idle then you might have a restriction in your fuel tank. A change in head pressure might affect fuel flow when in the uphill position with a low level of fuel.

 

[kippmw]

You'd think it wouldn't run well down the road if there was a fuel flow issue, but it runs great down the road with good power.

Not enough fuel flowing from the tank to the carb when you ask it to over come gravity by pointing the flow path up hill.

 

[kippmw]

Typical driveway steepness of maybe 4-5% grade, so not that steep.

How steep? And did you tighten the GAV a bit?

 

[kippmw]

It has 3/4 of a tank right now. It runs great down the road with good power, which you wouldn't expect if there was a fuel flow issue.

I tend to agree with bruceincam regarding fuel flow from the tank. Have you tried testing in uphill position with a full tank? If it improves the smoothness at idle then you might have a restriction in your fuel tank. A change in head pressure might affect fuel flow when in the uphill position with a low level of fuel.

 

[Brentwood Bob]

Might change the float. A worn spot above the float valve??

 

[kippmw]

That's a thought. I've got a bunch of floats, so I'll try that. Thanks!

Might change the float. A worn spot above the float valve??