Carb Adjustments

[punkassdave69]

Okay, I have a carb rebuild kit on the way. But I need help with the Idle mixture. I can adjust it all day long with the hose hooked up to it and I do not notice a difference. I put it in the water and I can barely run at idle speeds. Pull the plugs and they are black and wet. This is what I found in another thread:

Adjusting the idle mixture while on the garden hose you will end up almost 1/4 turn too lean once you are in the water.

Readjust idle mixture IN the water at idle IN gear.


How can I make the correct adjustment? Tell tale signs? I want to do it right the first time!!! Any help will be GREAT!!


Its a 1976 45HP Chrysler outboard. I think its a Type D carb?



Thanks Guys!!

 

[eurolarva]

Re: Carb Adjustments

If you are making adjustments and not seeing any difference then the idle circuits either have crud or are gummed up. If you take that mixture adjustment screw out you will see that it ends up where a welsh plug (looks like a dime but much smaller probably 1/4 inch diameter) that hides three tiny holes that come out near the throttle butterflies. Those holes need to be cleaned with WD40 or carb cleaner with a very small wire brush. When the screw is out spray carb cleaner with the straw and make sure that entire passage is cleaned.

As far as the adjustments go do it in the boat on the lake. Get motor warmed up and put it in its lowest idle speed and forward gear it will run on the lake and make the carb adjustments. Start around 1.5 turns from fully clockwise. When you find the exact spot where it should be turn it about 1/8 turn counter clockwise to make it slightly richer.

 

[punkassdave69]

Re: Carb Adjustments

eurolarva,

Thanks...my carb kit should be getting here tomorrow so I will take your advice when I pull it apart. My fingers are crossed!!!

 

[Frank Acampora]

Re: Carb Adjustments

Couple of hints:

Because they are only 2 cylinder engines, the idle speed must be set up near the top end of the 700-750 RPM range. This idle speed is in the water, in forward gear. Don't worry about the "clunk" when you snap it into gear. That's just the drive dogs engaging and is normal as long as it is not excessive. Yes! Snap it quickly into gear--do not ease it in.

If you do not have one, buy an inexpensive tachometer. It is invaluable for setting idle speed and experimenting with props and engine position. It is also good for fuel economy: when cruising at part throttle, set the control to use the least amount of RPM to maintain a given speed.

If the idle is too low, --even in the driveway, you will have trouble setting the mixture and, of course, in the water it will stall.

Buy a manual and be sure that the carb is synchronized to the timing.

Since these engines have two sets of reeds one above the other and fed from a common carb, the top cylinder ALWAYS runs a little leaner than the bottom. You can set the needle lean enough for a beautiful smooth idle but it will be too lean for running. So, err on the rich side to avoid piston damage. No matter what the manual says, and even if the idle is a little rough, do not set the needle leaner than 3/4 turn out from lightly seated--7/8 is better.

 

[punkassdave69]

Re: Carb Adjustments

So I got the carb rebuild kit yesterday and tore the carb apart and cleaned it out real good and got it all put together. The one question I have now is this; The welsh plug above the end of the mixture adjustment screw, do I have to remove this plug in order to clean those 3 holes? If so how do I do this? This is the last thing I need to do before I put it back on the engine. Thanks for all the input you guys have given already!!!

 

[JustJason]

Re: Carb Adjustments

DO NOT REMOVE THAT PLUG!!!!!!!!!!!!!!!! if you do the carb will be junk!!!!!!!!

the best way to clean carbs is with a high quality carb cleaner (the stuff they sell at motorcycle/dirtbike dealerships are the best) and compressed air.

 

[eurolarva]

Re: Carb Adjustments

The best way is to remove that plug and clean however if you do it wrong you can damage the carb as previously mentioned. Open the carb butterflies and you can see the tiny (probably three holes) right about where you see the welsh plug. Blast some WD40 or carb cleaner in those holes and use a thin piece of wire to clean those holes then blow the crud out from the carb with compressed air. I also like to set the carb float slightly less then the specs say. I have had more problems when I prime them using the specs that the needle valve will not seat under pressure and when I prime the bulb I get an overflow on the carb.

Note that WD40 and contact cleaner are better solvents to use on carbs then carb cleaner. There is a coating on the carbs from the manufacturer that will dissolve with stronger carb cleaners which will make the carb more prone to varnish.

 

[Frank Acampora]

Re: Carb Adjustments

Sorry to disagree Euro--but if you use wire to clean the (idle) metered orifices, (the three holes in the top of the carb) you run the risk of enlarging or damaging them and changing the calibration of the low speed circuit. They were drilled at the factory to specific sizes based on the engine and expected airflow. Better to just let the WD do the job and only if necessary, a stiff toothbrush poked in them.