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Acceleration woes

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2Hacks
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Acceleration woes

#1

Post by 2Hacks » Mon Mar 28, 2011 1:23 pm

My '52 starts easily both cold and hot, but when I hit 3rd gear (3 speed w/reverse) it acts like it's starving unless I either give it full throttle or close the choke one notch. When I get it to cruising speed and maintain it, sometimes it will have the same symptoms unless I choke it or open the throttle all the way. I've adjusted the low speed and high speed needles and have run the high speed up and down a notch at a time and can't get the bad spot out of the acceleration. I have the Liberty float adjusted to exactly 1/4 inch all the way around the bowl. A friend told me that I should raise the float about 1/16 inch, but I'm afraid if I do that, it won't have enough clearance inside and will hang and not close the float valve.

Before I remove the carb and start tinkering, any suggestions will be appreciated.

Thanks, Roger



Cotten
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Re: Acceleration woes

#2

Post by Cotten » Mon Mar 28, 2011 2:09 pm

Roger!

Raising your float level would only mask a real problem elsewhere;
Please leave it at book spec.

'Opening the throttle' and 'closing' the choke are opposite operations.
Are you sure you do not have a manifold leak?

We can address the carb if your bubbletest is negative, including the pan cover screw over each intake port.

....Cotten

2Hacks
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Re: Acceleration woes

#3

Post by 2Hacks » Mon Mar 28, 2011 3:07 pm

I'll do the bubble test again when the weather warms because haven't done it since I removed the carb to put in the new float a couple of months ago.

Guess my 70 yo brain just don't work like it used to... I was thinking more throttle = more gas and more choke = more gas. That's why I thought it was starving.

Cotten, I know we discussed the float level before and that's why I didn't want to mess with it again.

Thanks...

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Re: Acceleration woes

#4

Post by Cotten » Mon Mar 28, 2011 3:51 pm

Roger!

The wider the throttle is opened, the less vacuum within the manifold. Maximum vacuum is when it is closed, or choked.

No two evil manifold leaks behave the same, except those that keep the motor from starting at all. Yours may be tiny, so please turn your regulator the full 15 psi, and check for casting porosities between the fins, as well as the rivets, pancover screws, etc.

If not even the tiniest blister of foam forms after a minute, then let us consider the carb. (But please do not forget to rinse off dishsoap thoroughly, as it is corrosive!)

The first thing to inspect is the carb to manifold flanges.
This interface cannot be pressuretested, so both the manifold and the carburetor's flanges should be arbitrarily ground flat on a stone, or an adhesive emery disc on thick glass.
They are nearly always distorted, with the area around the idle gallery plug, and its mating side of the manifold, to be the spot that "cleans up" to flat last.

....Cotten
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2Hacks
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Re: Acceleration woes

#5

Post by 2Hacks » Tue Mar 29, 2011 6:38 pm

Thanks, Cotten. I took the carb off and found no leaks in the manifold when I tested it. Just to be safe, I dressed the surfaces of both the manifold and carb, put in new gaskets and insulator block. Both the carb and manifold needed flattening... not a lot, but some. Put it all back together and it fired right up. Took it out on the road and still had a little hesitation, so I opened the low speed needle 5 clicks and it seems to be running fine now. When I set the low speed earlier, I ran it down one click at a time till it slowed, then backed it out 5 clicks. Guess that wasn't enough, so now it's backed off 10 clicks.

Thanks, Roger

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Re: Acceleration woes

#6

Post by Cotten » Tue Mar 29, 2011 9:51 pm

Roger!

Five turns on the LS is a lot.

Is your HS needle out more than a turn or so?

The LS circuit reverses at highway speeds, thus a "fat" setting on the LS needle actually leans the HS.
Please only re-adjust the LS at idle, not going down the road!

Please set your HS at 3/4 of a turn (this is an M74B with a fixed jet, right?), and adjust your LS at idle speed to find where it idles fastest, and reset the idle screw accordingly. (A lopeing-slow idle is not desireable.)

If all things are in order, this usually results in a setting of around three and a half turns.
The HS is typically insensitive with a fixed jet.
If your carb demands to be set radically differently, then something is amiss.

....Cotten

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Re: Acceleration woes

#7

Post by 2Hacks » Wed Mar 30, 2011 12:22 am

Cotten, I only adjusted the low speed at idle and it was 5 more clicks, not turns. The low speed setting is now set at a little over 3 turns and the high speed is between 3/4 and 1 turn. I also have the idle set fast.

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Re: Acceleration woes

#8

Post by Cotten » Wed Mar 30, 2011 2:21 am

Roger!

Oh.

Great!

....Cotten

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