Holley 750 carb problems...boat won't idle in gear
07-02-2014, 06:59 AM
#1
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Location: Millstadt, IL LOTO 17MM
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Holley 750 carb problems...boat won't idle in gear
I am having Holley Carb problems on my Cafe Racer. I am running Holley 750 double pumpers on my 502's. I took carbs off last winter and had local machine shop rebuild them. Boat ran fine first 2 times out this season. Third time out I couldn't get the port motor to stay running. I pulled off float bowl and front float was half full of fuel. I replaced the plastic float with a brass float. Reset float level on bowls. Set idle to 900 rpm. Air/idle screw 1 1/2 turns out. Port motor will not idle under 1000 rpm when cold. It will idle when warm in nuetral. As soon as I shift into gear it dies. Is this a carb issue or vacuum leak?
07-02-2014, 09:34 AM
#4
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You could try looking at the secondaries. They should be adjusted open approximately 30 thousandths up the slot. However to do this the carb does need to come off as the adjusting screw is on the bottom facing up.
07-02-2014, 09:35 PM
#7
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Blow out the idle air bleeds too, using carb clean and the little red straw thingy.
When you back out mixture screws, you are enriching the idle, but also adding more fuel/air overall, since its already emulsified when it is entering the engine from the idle discharge ports.
When you back out mixture screws, you are enriching the idle, but also adding more fuel/air overall, since its already emulsified when it is entering the engine from the idle discharge ports.
07-03-2014, 05:01 AM
#8
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The idle air screws don't richen or lean the idle mixture.
They supply the idle circuit with more or less of the mixture dictated by the idle air bleeds.
The size of the idle air bleeds determines how rich/lean the idle mixture is.
I'd check the timing first and then look at fuel delivery.
Ps. A quick way to see if you are too lean at idle is to put your finger/fingers over the idle air bleeds and see if it improves. If it idles in gear with the air bleeds restricted, you have a lean idle mixture.
They supply the idle circuit with more or less of the mixture dictated by the idle air bleeds.
The size of the idle air bleeds determines how rich/lean the idle mixture is.
I'd check the timing first and then look at fuel delivery.
Ps. A quick way to see if you are too lean at idle is to put your finger/fingers over the idle air bleeds and see if it improves. If it idles in gear with the air bleeds restricted, you have a lean idle mixture.
07-03-2014, 05:14 AM
#9
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iTrader: (3)
The idle air screws don't richen or lean the idle mixture.
They supply the idle circuit with more or less of the mixture dictated by the idle air bleeds.
The size of the idle air bleeds determines how rich the idle mixture is.
I'd check the timing first and then look at fuel delivery.
Ps. A quick way to see if you are too lean at idle is to put your finger/fingers over the idle air bypass ports and see if it improves. If it idles in gear with the air bleeds restricted, you have a lean idle mixture.
They supply the idle circuit with more or less of the mixture dictated by the idle air bleeds.
The size of the idle air bleeds determines how rich the idle mixture is.
I'd check the timing first and then look at fuel delivery.
Ps. A quick way to see if you are too lean at idle is to put your finger/fingers over the idle air bypass ports and see if it improves. If it idles in gear with the air bleeds restricted, you have a lean idle mixture.
Alot of guys can be confused a bit by this. Being that the mixture is already emulsified, turning the screws is allowing more air and fuel, not just fuel alone. But, the engine is gonna also be getting air past the throttle blades already.
This area can be a problem when car guys set up boat carbs. Race car guys are used to dealing with manual trannies, high stall converters, etc. They can really lean the idle down and get it nice and crisp. Problem is in boats, when we shift them into gear, the load between nuetral and in gear, is quite a change. Usually you need a richer mixture, to keep it from stalling out. This is pretty much why you hear the boat guys with big old roots blowers surging around the docks. Alot of times, with bigger cams, high pitch props, etc, if you tune the 'surge' out, you may have trouble with it stalling when shifting.
