Weird Holley 4bbl prob.

The early 70's Lazy Days in the slip next to me is equipped with 2 215hp Mercruisers [ Ford 302s I guess. Don't look wide enought to be 351's ]. He has been having trouble with the motors stalling and I volunteered to adj the float levels and the idle mixture screws. He went out to the pumpout and when he got back I went to adj the carbs while the motor was warm. <br /><br />The float levels were a little off but not really enough to significantly affect the running. The weird thing is that the idle mixture screws have NO effect on the running of the motors. You can screw them all the way in and there is no difference in the idle. Turn them 3 turns out and you get the same result. I set them at 1.5 turns and left it.<br /><br />What's up with these carbs? I have never seen a Holley equipped motor that wouldn't stall when you got the idle mixture screws way too far in or out.<br /><br />The other weird thing is that the bowl vents are straight, not bent over the carb throats ! The carbs are black and appear original.

Re: Weird Holley 4bbl prob.

You can screw them all the way in and there is no difference in the idle. Turn them 3 turns out and you get the same result. I set them at 1.5 turns and left it.<br />

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You obviously getting unmetered fuel from somewhere else in the carb.<br /><br />Are the throttle plates partially open?

Re: Weird Holley 4bbl prob.

Busted power valve(s)??? Unless theyve been retrofitted with the backfire protection for the power valves all it takes is one backfire to blow them. Look to see if the carb throats are wet during idle.

Re: Weird Holley 4bbl prob.

The thing is that the motors run and idle good. The stalling was mostly due to low idle speed and by running the the idle speed screw I was able to get the motors idling fast enough to not stall anymore. <br /><br />We took the flame arrestors off and the carb throats are pretty clean.

Re: Weird Holley 4bbl prob.

I was able to get the motors idling fast enough to not stall anymore. <br />

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That is DEFINETELY NOT good for the drives. Why wreck $2,500.00 drives over a $50.00 carb(s) rebuild?<br /><br />You/he still have a problem. I'm with Boomyal. The leaking powervalves can cause that. That also explains the stalling. (no power at idle). Fat mixture-unregulated.<br /><br />Rebuild the carbs and back the idle down.<br /><br />BE CAREFUL not to create any vacuum leaks. Replace ANY questionable vacuum hoses.

Re: Weird Holley 4bbl prob.

On a Holley non-resonponsive idle mixture screws usually means the throttle plates are open too far. uncovering what is known as the transfer slot, or low speed metering. The low speed metering takes care of mixture between idle and when the boosters (the round rings in the middle of the barrels) get enough signal to begin addling fuel to the air column. We now have to figure out why the throttle plates are open too far. Unmetered air is certainly the first place I'd look. Luckily, boats don't have many external vacuum lines, so you want to check the carb mounting flange and intake for sure. The mounting design of the Ford intake makes it prone to leaks into the valley. If you can work a little timing advance in without too much at full throttle, that will help out the idle. The problem I ran into on my Windsor was todays suspect fuel makes the total timing touchy. A compression test and vacuum gauge are in order also. Not knowing the history of the powerplants, they may just be too tired to idle well. Blown power valves pour a ton of fuel into the motor, the plugs should foul if this is the case. They are easy to check them by puckering up to the flat side and sucking on them, watchin' the plunger seat and unseat. I fought a long time to get a stable 525 rpm idle out of my 351 to help out my stringer, but it is worth it.

Re: Weird Holley 4bbl prob.

I bet the point gaps have closed up and the timing is retarded requiring the idle speed screw to be turned in to compensate. I had forgotten about the transfer slot deal. I only associate that issue with big cams that require a lot of throttle opening just to idle. The cure then is to drill a hole in the butterflies to allow them to be closed back to their proper position.<br /><br />They are not idling too fast just the idle has been getting progressively slower. I may take my dwell/tach meter to the slip next time and see what the dwell is.

Re: Weird Holley 4bbl prob.

Can you explain this?<br /><br />How does drilling a hole in the butterfly allow them to close back to their proper position?

Re: Weird Holley 4bbl prob.

Boomy,<br />It allows air to leak through the throttle valves so the idle stop screw can be readjusted to a more closed position. This allows the throttle valve to position correctly in the transfer slot creating the proper vacuum differential to allow the idle circuit to work. Its an old hot rodder trick to get a cammed up motor with low vacuum to idle better.<br />However this can cause problems too, if you drill too big a hole the boosters will dribble at idle and make it harder to get a good idle.<br /><br />Considering the setup looks original I would have to go with Boomy and the power valve on this one. Somethings letting fuel get in there when the idle screws are bottomed.