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How to adjust holley carb srew mixture |
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wakespirit 
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Joined: July-21-2012 Location: fr Status: Offline Points: 95 |
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 Topic: How to adjust holley carb srew mixturePosted: August-03-2014 at 9:13am |
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Dear all,
I decide to open a new thread on how to adjust the mixture screw of my carb holley because I see different post on internet but unclear for me. And as I am not get use to that prefer to have steps procedure. I have a holley carb for my correct craft of 1900 Ford PCM engine. I have place a post related to touble I get with heavy smoking engine and stuffing at idle and slow speed. Then been advise on checking mixture screw adjustemnet. First of all the carb is the original one but it is not new. Based on that I have seen some article where it is mention to do following step: - with engine off - screw in all mixture screw until it lock - screw out all mixture by 1 turn and half - Start then engine and adjust idle speed if needed I do not have vaccum gauge. What I would like to be sure is of the engine status during process (on or off) , can do that at shore first or do I need to drive the boat while an other person is doing adjustment... Thanks to validate or not the adjutment peocess, in clear steps to avoid confusion from different articles I jump too which makes me confused. Thanks for help Regards |
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SNobsessed
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Joined: October-21-2007 Location: IA Status: Offline Points: 7102 |
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Posted: August-03-2014 at 10:27am |
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Hey Wake, it would be best if you could stay with 1 thread on your project.
The best way is to have boat tied up at dock, or on trailer. Engine idling (lowest RPM) & put in gear (again lowest RPM). Having it in gear helps make the adjustment procedure more accurate. |
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“Beer is proof that God loves us and wants us to be happy.”
Ben Franklin |
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mamigacz
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Joined: June-08-2014 Location: Wisconsin Status: Offline Points: 96 |
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Posted: August-03-2014 at 10:29am |
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2 full turns from the seated position will allow the engine to start and run.
After its running at operating temperature you can fine tune it. Turn each screw in (clockwise) 1/4 turn at a time and montitor the engine rpm. After you hear the RPM drop, turn the screw counter clockwise a 1/4 turn. Clockwise will lean the idle mixture, counterclockwise will richen the mixture. The reason vacuum gauges are nice during this process is its easy to find that spot where the RPM drops (vacuum level drops). You might find out the 1-1/2 turns (total) is the sweet spot, but its a good idea to check. I liked that idea to tieing the boat to the dock, in gear while doing this. |
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wakespirit
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Joined: July-21-2012 Location: fr Status: Offline Points: 95 |
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Posted: August-03-2014 at 1:06pm |
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Hello,
You said " 2 full turn from seated position" What do you mean by that,screw in or out? first should I screw in fully all screw and then 2 full turn screw out ? Is this what you mean, or is is from actual scrw position ? please not that I have no idea if all screw are perfectly have all same turn. Thank to clarify Regards |
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wakespirit
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Posted: August-03-2014 at 1:08pm |
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Snobses, at which steps engine should be at gear idle spead ?
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Donald80SN
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Joined: January-12-2009 Location: Denver, NC Status: Offline Points: 3896 |
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Posted: August-03-2014 at 1:44pm |
Normally, I get flamed when I post under the engine repair forum, but I just went through this process with my boat and I feel that it is 95% dialed in. I am looking for that 5 more percent. My tach does not work all of the time and I am not sure how accurate it is when it does work. I believe a new tach is in order to get the additional 5% that I need. With the boat cold or on the trailer, turn the two air idle mixture screws in carefully until they gently bottom out. Be careful not to bottom them out too hard as to damage the needle tip and seat. Once they gently bottom out, back both of them OUT two or 2.5 turns. Start the boat or launch the boat into the water. Turn off the boat and remove the flame arrestor to see if gas is dripping into the secondary (rear) or primary (front) barrels / bowls. This dripping is what causes the black smoke. If your carb is dripping or pouring gas after shut down you may been a carb rebuild or the floats may need to be adjusted. If no dripping restart the boat and adjust the throttle idle so that the boat runs well at 700 RPMs. You need a reliable tach or shop tach to make this adjustment. Warm up the boat until the choke plate is fully open and the boat is up to running temperature. Tie the boat to a dock and get the engine to rev to 1500 or so RPMs. Then turn in the two idle air mixture screws 14/ turn until the boat stumbles and then turn the screw back out until it idles well. You will have to do both sides and may have to go back and forth several times to get it correct. I tried to adjust my carb on the trailer and did not have great success until I tied it to the dock. The engine has to be under a load. Also, you have to work with you main throttle idle adjustment screw. You may have to go back and forth multiple times with all three screws. I hope this helps, but please remember that I am just a hobbyist. Donald |
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Morfoot
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Joined: February-06-2004 Location: South Lanier Status: Offline Points: 5320 |
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Posted: August-03-2014 at 2:00pm |
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Granted, you only need to tie the boat up to a dock if you don't have someone who can drive the boat while you make the necessary adjustments. Kinda hard to steer and make adjustments by yourself.
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"Morfoot; He can ski. He can wakeboard.He can cook chicken.He can create his own self-named beverage, & can also apparently fly. A man of many talents."72 Mustang "Kermit",88 SN Miss Scarlett, 99 SN "Sherman"
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wakespirit
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Posted: August-03-2014 at 2:46pm |
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Hello,
Just come back from my boat to check. I notice 2 things : 1- I notice a fuel linkage at carburator fuel inlet 2- my screw actual position are 1 turn CCW. 3- if I screw in fully both screw, the engine still run. According to garry it should not when both screw are filly tight in. Any advise, after solving linkage of course Regards |
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cbr1000dude
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Joined: August-23-2011 Status: Offline Points: 330 |
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Posted: August-03-2014 at 6:02pm |
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If you close both idle screws and it still runs, your idle circuit is not working at all. It is plugged, or the idle screw seals (probably old rotten cork) are not sealing, or both. Your engine is running off the secondary circuit. The throttle stop is set too high. This will give you an erratic, surging idle. Or it is sucking air from the throttle plate pivot seal area, activating your secondary circuit.
Your carb needs rebuilding or replacing if you want it to run well. |
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wakespirit
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Posted: August-03-2014 at 6:22pm |
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What do you mean by rebuild ? Some part need to be change?
wich one exactly or is they a kind of repair kit? Does a rebuild is something easy to do as simple as changing joint for instance ? Where is the throtlle stop you are talking ? thanks |
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cbr1000dude
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Posted: August-04-2014 at 12:31pm |
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http://www.jegs.com/i/Holley/510/703-28/10002/-1?parentProductId=#moreDetails
Yes, there is a kit. Look for your list# on the carb body, something like 80262, this will tell you which kit to order. Frankly though, you may need some help if it's your first rebuild. Or you can just watch some youtube videos and learn the old fashion way like I did, trial and error. Google throttle stop screw. Go to Holly.com and download an exploded view of your carb. Read, read, read. Then take it apart, clean all surfaces, blow it out with compressed air,put it new parts, Tada! you've just rebuilt a carb. Might even run! 
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wakespirit wrote: