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1970 Mercury 70HP carbs wont stop leaking?

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boatdock2

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Hey ya'll,
I have a 1970 Mercury outboard that I have put new needle and seat assemblies in, and a new fuel pump, and I can not get the carbs to stop leaking? Someone said it may possibly be the reed valves are weak? The motor runs great at wide open throttle but as soon as you throttle down it starts to run rough and then dies, with fuel leaking out of the carbs?
Any help would be appreciated, as this is driving me crazy!:confused::confused: THANKS
 
I run those as well, and they work well, so something is wrong here.


Here's how to stop them from leaking: Remove the carbs (again--ugh!) and rig up a way to attach the fuel hose directly to each carb (individually). Put one carb (at a time) in a vice to keep it level, then fill it with gas by pumping the bulb until it's hard. If (when) the carb leaks, drop the bowl and lower the float level about an 1/8 inch (ignoring what height they are supposed to be set at. That's theoretical only. Tis is real life.) Pump up test it again and, if the *^#~ still leaks, lower the float another 1/8 inch until it stops. Then do theother carb.

Jeff

PS: While the carbs are off, do yourself a favor and drill the butterflies to eliminate bogging problems. See the photo below. All three holes need to be 1/8 inch.

Note: Some of the later carbs have the center hole larger, but not the other two. Drill 'em, all!
 

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Unfortunatly the kits you get aren't always the right stuff.
Check the condition of the old parts.You might have to re-use them.
 
ignoring what height they are supposed to be set at. That's theoretical only. Tis is real life.)
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I TOTALLY disagree with this statement as the float level specifications are there to ensure bowl is full and carb/jet does not run lean. Lowering the float level can starve the high speed jet and cause possible damage engine. Replace the floats as they get heavy over the years and you can get these aftermarket thru sierra. You should not have to drill anything as these wont bogg if engine is set up correctly and I have not found a TSB from Mercury on this...
 
Wanna bet? The fuel level of a carb is too high if it floods with new parts. Lowering the float until it stops flooding simply adjusts the level to where it should be.

On the supposed danger of running with the float level lower than specified, your concern ise grossly exaggerated. Circle track racers (think Holley carbs on SB Chevies) routinely drop the float level an 1/8 inch and more to keep from flooding over bumps. I did the same thing with my autocrosser snd it worked perfectly.

On bogging of Merc triples, the factory added larger holes and a progressive carb opening ramp to reduce this COMMON problem. It was not enough. Others (like me) kept at it until I found a way to TOTALLY eliminate the bogging problem (by enlarging the existing holes).

Jeff (who lives in the Real World)
 
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circle track racers (think Holley carbs on SB Chevies) routinely drop the float level an 1/8 inch and more to keep from flooding over bumps.
Click to expand...
No...they use longer slosh tubes in carb..
On the supposed danger of running with the float level lower than specified, your concern ise grossly exaggerated
Click to expand...
Huh... Holley carbs say different...
"A carburetor's floats are designed to control the amount of fuel held in the bowls that is available to be pulled through the metering blocks. The carburetor jets should always be covered, but you don't want too much fuel in the bowls so that it sloshes out and into the vent tubes. If the floats are set too low, the fuel reserve in the bowls will be too small and increase the opportunity for the jets to become uncovered and the engine to run lean. If the floats are set too high, excessive fuel can slosh out of the bowls and into the vent tubes causing the engine to stumble.
On the classic Holley carburetor, the accepted method for setting the float level is to run the engine until everything is warm, and with the engine at idle, unscrew the plugs in the sight windows for the float bowls. Raise the float just until fuel begins to escape from the window, then lower the float back down a bit and lock everything in place.So if you are experiencing stumbles and power drops in the turns, you may want to take a look at your float levels. The problem is if you are having these issues it's impossible to watch the carb while the car is on the track to see if the source is too much fuel causing it to slosh out of the bowl or too little fuel causing the jets to become uncovered. Hill says the key to knowing which way to go is to communicate effectively with your driver to find out exactly what is going on. He says fuel sloshing into the vent tubes will cause the engine to stumble, but it will pick the power back up quickly and get going again. If the jets are getting uncovered, however, the engine will often feel like it's "falling on its face" " bog" and just die for power. Understanding what your car is doing is the quickest route to finding the cure.



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The height of the fuel in an average carb is at least an inch. Dropping that level an 1/8 of an inch makes no difference at all.

Jeff
 
The float level establishes a base line for carburetor calibration/adjustment. The low pressure signal in the carburetor venturi is the force that accomplishes the work of removing fuel from the bowl to the carburetor throat. The lower the fuel level, the higher it must be lifted. To move the same amount of fuel, the pressure must drop even lower. Engine operating symptoms of a carburetor with a float level too low can be hesitation and inability to handle load due to a mixture that is too lean. (which damages 2 stoke engines)
http://www.briggsandstratton.com/en...n_troubleshooting_detail_reference_guide.ashx
1/32 of a inch change will result in nearly a 1/8 inch internal level change so dropping it 1/8 inch twice will result in a fuel level 1/4 inch below specs, that why spec's are usually in +/- 64ths. The way I see it is like the fill line on a dip stick, it supposed to be at the fill line (specification) but if its 2 quarts low will it hurt anything? Maybe yes/no it but engineering came up with that level for a reason, same for float height and drop spec's they are there for a reason..
My final $.02...................
 
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