Holley 390 float levels

[jefferybond]

Hi folks,

I'm having a bit of trouble getting my Holley 390 (vac secondary) to work well on my 3.5l RV8. On sudden throttle opening when cruising, I get a brief lean stumble before it takes off. I was wondering if it's anything to do with my float level setting, which may not be quite right.

Snapping the throttle open from idle is fine, so I think the pump shot is sufficient. I've played with the pump cam position and it makes little difference.

However, the carb sits at an angle, sloping forward, because the engine sits level and I have not used a leveling plate under the carb. To set the float levels, I removed the sight plugs and adjusted the levels by the book, but with the carb tilted forward as fitted.

The tilt would mean that the front bowl (primaries) would have a lower level than expected if the carb was levelled. Would this account for the temporary lean mixture?

Should I set the float levels with carb level? Would a low float level explain my symptoms?

Thanks,
Jeff

[kiwicar]

Hi Jeffery
on principle 4 barrel carbs should be level I am not saying this is the fault here, but I think it a reasonable assumption that it is not helping. .
I would surgest that you check that the carb is idleing on the idle circute and not on the bottom end of any transition/part throttle circute I would also check the part throttle arrangment is fully funtional and alowing the carb to go fully rich when the throttle is opened, the accelerator pump can mask faults in both these areas alowing you to only see a problem under specific conditions.
Best regrads
Mike

[sidecar]

Hi Jeffery
on principle 4 barrel carbs should be level I am not saying this is the fault here, but I think it a reasonable assumption that it is not helping.
Mike

I've spent ages messing about with my Eddy 500, I agree with Mike, they are sensitive to the angle that they are mounted at. My car would have a rich stumble when braking hard, a 5 degree cured this even though its hard to believe! I dunno about Holleys though! (Fit an Eddy!)

[jefferybond]

I dunno about Holleys though! (Fit an Eddy!)

I used to run a eddy 500, but that used to spew fuel out of the pump pushrod hole when cornering hard on the track! I will admit that the eddy 500 was easier to tune though.

Jeff

[mgbv8]

If you are just cruisng the float level should be pretty high and despite the angle of the carb it should not stumble if its set up right for the engine.

You say it picks up fine from idle to wide open throttle when stationary. Does it do the same from cruise rpm which I assume will be around 2500 rpm (when sationary) ?


The fuel comes from the jets which sit low down in the jet plate. Right at the bottom of the bowls. If you are cruising then the fuel in the bowls will be sitting level as its travelling at the same speed as the car. So hard acceleration would tend to make the fuel in the front bowl push against the jet plate and the fuel in the rear bowl well away from the jet plate. But it wont well far enough back from the rear jet plate to uncover the jets and lean it out. And your carb sits down at the front which makes it even less likely. You can get rear jet extensions so the pick up fuel from the rear of the bowl under hard acceleration. I dont have rear jet extensions on my holleys and my car pulls 0-60 mph in less than 3 seconds from a standstill.

What size squirter pump do you have fitted and what size squirter jets are fitted?

What size main jets are fitted to front and rear bowls?

Does it have power valves fitted in the jet plates. And if so what vacuum value are they?

The holley is a nice carb as is the Eddy. I use both in my cars from 500 cfm to 850 cfm. And they are both easy to set up and use once you have got your head around how they work.

Is this the first time you have used the carb on this engine or has it been running ok before?