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EFV-8 Club Forum / General Ford Discussion / 48 Merc surging

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Discussion Topic: 48 Merc surging

nelsonford

06-17-2017 @ 8:23 AM

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Have a 48 Mercury that runs pretty good until it gets well warmed up. Then it runs kind of rough and surges.I rebuilt the carburator prior and rebuilt another I have also tried but still.the same problem. The spark plugs get fouled with carbon quickly after cleaning. The carburetor must be running rich even though the idle mixture screws are turned in more than the specified amount. I had dual 94s on it before but had couldn't get the second carb to match the first and it didn't run well at all. Power valves are new and gasketed correctly I believe. I would appreciate any suggestions.
Thanks, Jeff

sarahcecelia

06-17-2017 @ 11:35 AM

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Leaning the idle mixture screws too much is not good, and idle mixture has nothing to do with surging, except it can make the motor "roll"at idle when they are not adjusted properly. Dual carbs have to be set so the both draw the same amount of air through the venturie. Without the gauge to set them you can set them by putting the same size object into an open butterfly of each carb to hold them open (such as a set of 1/4" drill bits,) and then adjust the linkage between them to fit with out moving the butterflies. Another way would be to block them full open and then adjust the linkage to fit them. Idle mix screws should be adjusted with the motor up to temp. Open them 'til the motor starts to roll. Then one at a time, turn the mixture screw in slowly as it picks up speed untl it starts to drop in RPM's. Then back it off about I/4- 1/3 of a turn past where the idle speed started to drop off.( IE richer) Then repeat the prcess and your done! The gauge to set multiple carbs is a "Unisyn" and can be had through speed houses and doesn't cost much. I had to have one when I worked for VW to set the dual carbs on them. If they are not in unisyn, the The cylinders they feed are fighting each other and performance suffers as you probably out! Call if you need help! Steve 352 666 9916 DST

Regards, Steve Lee

sarahcecelia

06-17-2017 @ 11:43 AM

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I just googled Unisyn carburator gauge and 3 places sell them for about $25.oo

Regards, Steve Lee

carcrazy

06-17-2017 @ 3:12 PM

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A crude i.e. cheap way to synchronize multiple carburetor setups is to use a length of fuel or vacuum hose approximately two feet long. Place one end of the hose at the entrance to the airhorn of one carburetor and the other end up to your ear. Listen to the sound of the air entering the carburetor. With the linkage between the two carbs disconnected, adjust the second carb until you get the same sound as you heard in the first one. Adjust the linkage so that it fits without disturbing the throttle adjusting screws, hookup both carbs, and recheck each to make sure the sound is the same.

TomO

06-17-2017 @ 4:21 PM

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When I rebuild a Ford carb, I assemble everything except the the base with the throttle bores and the top. I add gas to the bowl to cover the power valve and let it sit overnight on the bench. If the gas leaks out, I know the power valve is leaking past the gasket.

I use the power valve gasket with the triangular cutout and tighten it hand tight, then an additional 1/8 turn. If it leaks, I give it another 1/8 turn. The round gaskets in most kits seem to leak,no matter how you tighten them.

The surging is very likely caused excess fuel. If the power valve is set correctly, check your float level and needle valve.

With a stock cam, set your idle screws by turning them in to seat slightly and then back them out 3/4 turn. When the engine reaches operating temperature, set the idle speed to 450 rpm and turn both of the idle screws in 1/8 turn while observing the vacuum gauge or tach. If the vacuum increases or the engine speed increases, turn them in 1/8 turn at a time until the vacuum or engine speed drop, then back off 1/8 turn. If the speed decreases, turn the screws out in the same manner to reach the optimal adjustment. Then readjust the idle speed to 450 rpm.

Tom

nelsonford

06-18-2017 @ 4:55 PM

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Thanks for your info. I will try to make best use of it.

nelsonford

06-18-2017 @ 4:57 PM

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Thanks for responding to my message. I'm sure it will help.
Jeff

nelsonford

06-18-2017 @ 4:59 PM

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Thanks for getting back to me. I will check it out.
Jeff

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