flow direction in slingshot manifold

[john in illinois]

In an Edelbrock slingshot does the rear carburetor feed the front cylinders.

John

[Bursonaw]

Yes, it does. Here is a picture of a slingshot manifold with the high rise removed. Both carbs feed in the center of the manifold.




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[john in illinois]

Thanks Tony. I am having trouble with lean mixture on front cyls and I wanted to
be sure which carb to check. I have put about 300 miles on the slingshot and really like it. Great throttle response.

John

[flatjack9]

With an open plenum, both carburetors feed both the front and the back cylinders.

[Talkwrench]

this help

[john in illinois]

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Thanks for the inside pics . I did not remember the inside design when I put it together.
The carbs do empty into a plenum ,but they do each flow to one end. I had clean plugs in the front and rich black plugs on rear. I have since adjusted float level and a leaking power valve and plugs are the same.

John

[itslow]

Originally Posted by john in illinois

The carbs do empty into a plenum ,but they do each flow to one end.

Both carbs will feed both the front and rear cylinders. The divider would need to extend down into the lower manifold in order to make it so that the carbs only flow to their respective ends of the engine.

[rotorwrench]

Vic Senior's sling shot was one of the first dual carb & dual plane (180*)manifolds marketed as speed equipment. He worked with Tommy Thickstun on the first of the PM manifolds but felt that his design with shorter runners would be better and Tommy sort of scoffed at his idea (Tommy was an engineer & Vic wasn't). Vic found the folks that would help him make his own design and that was the beginning of Edelbrock Speed Equipment.

The dual plane allows for about the same distance in the runners on each side and for a cross over to the other on each side. One side crosses over the top and the other on the bottom. It makes for a better balance of mixture flow and less tendency for fuel pooling in there.

[scicala]

The only way (without a flow bench) to see if one carb is running richer than the other is to block off the mounting flange for one of the two carbs, and run one carb at a time. It may just be the nature of the manifold distribution that make some spark plugs darker than others.
My opinion and experience says that if one carb is richer than the other, the mixture should basically equal out in the manifold after the carbs. Still could be caused by one carb being too rich.


Sal

[scicala]

Originally Posted by john in illinois

Thanks for the inside pics . I did not remember the inside design when I put it together.
The carbs do empty into a plenum ,but they do each flow to one end. I had clean plugs in the front and rich black plugs on rear. I have since adjusted float level and a leaking power valve and plugs are the same.

John

If you didn't already, you need to clean the plugs before you evaluate it being too rich, since once a plug gets black, it takes for ever for it to go away even when running the correct mixture.


Sal

[rotorwrench]

I don't think you could track it to one particular carb anyway. Two of the venturis (one on each carb front to rear) will reach to the front on one side but that pair doesn't feed both front cylinders. It feeds the front on one side and the next one back from the front on the other side. The other pair of venturis on the opposite plane feeds the opposite two of the front four cylinders.

When you check mixture using the spark plugs, you have to use a scientific procedure. I'd suggest running it at a particular rpm down the road for a while then shut the ignition off & coast to a stop. In other words, don't let it idle, just shut it off. Check your plugs then and you can see what it's doing for that power setting. If you let it idle down for any length of time, it will be affected by the idle circuit and change your plug readings. It can be a bear to sync the carbs at idle. It may be easier with an air fuel ratio tester.

[Andy]

A digital fuel air meter would be useful. 97 carbs can richer up with restrictive air filters. The fuel bowl is not vented to the air horn. Maybe the front filter is more restrictive or the carb has some internal difference. The fuel dump tubes can be easily crushed and that will change the mixture.

[john in illinois]

Thank you for all your replies and suggestions. Here is what I have done to date.
Discovered front carb had power valve leak.

Replaced valve and leak tested over white paper for 1 hour.

Looked into air horn while running. Reved up to very high idle, fuel was dribbling out front emulsion tubes.

Lowered free end of float 3/32” on both carbs. Drove it withclean plugs in 4 and 8. Seems to be even now. Very short 15 mi.test drive.

I do have an A/F meter and have used it to get approx best jetting.

Engine tilts 3* to rear snd I hope I that will work ok.
Car has always run excellent even when things are not quite right.


John

[rotorwrench]

I've seen folks make special wedge shaped carb spacers to get a more level positioning. Some just put taller tires on the back & smaller ones on the front. If it works OK then run it the way it is.

[john in illinois]

I think with the lower float levels it will work fine. If it ever stops raining I plan to drive with A/F meter hooked up and check it.

John

[Flatout]

I'm running my slingshot with progressive linkage on the carbs. It operates like a single 4-barrel carb. For reduced fuel consumption on a trip, I slide a shim under the secondary carb to block it. It works out well on my nearly stock 34 engine.