How lean can you run a carb?

[justin65]

1968/69 35hp Chrysler, #3551.


I am having a problem with alot of unburned fuel in the drum. Sitting at a low idle for only a few minutes I get what’s picture below.

I have cleaned and rebuilt the carb, set the timing, replaced the spark plugs, cleaned and reset the points, checked the fuel pump gasket for leaks.
Fresh fuel and TCW-3 oil mixed at 50:1. The jet size is .088 which the book says to use a .089 for sea level to 1250 above sea level. I'm at 106 feet above sea level.

Right now I’m ? turns out on the idle adjustment screw on the carb but the motor isn’t kicking like the books say it should to find the lean point.

Thanks...

 

[steelespike]

Re: How lean can you run a carb?

It's pretty normal to have oily water especially with these older motors.
Not unusual for a little motor to leave about the same sludge behind.
You can adjust the lowspeed a little leaner.Turn it in until it starts to die then out to the best idle in gear,then just slightly more toward rich not enough to effect the idle.For the health of your motor you are better off a little on the rich side.Jet size depends on the carb.I don't see 88 at sea level or 89 on any Chrysler from 69 up.I see .090,WB17A & WB17C lists .088 for 1250-3750. same carb is .090 for sea level to 1250.

 

[justin65]

Re: How lean can you run a carb?

It's pretty normal to have oily water especially with these older motors.
Not unusual for a little motor to leave about the same sludge behind.
You can adjust the lowspeed a little leaner.Turn it in until it starts to die then out to the best idle in gear,then just slightly more toward rich not enough to effect the idle.For the health of your motor you are better off a little on the rich side.Jet size depends on the carb.I don't see 88 at sea level or 89 on any Chrysler from 69 up.I see .090,WB17A & WB17C lists .088 for 1250-3750. same carb is .090 for sea level to 1250.

Thanks for the reply steelespike.
It doesn?t start to sputter until its about 1/4 turn out. The manual says not to run with 3/4 turns out or leaner as it would cause the motor to over heat.

I also forgot to say I checked and cleaned the puddle valves. It didn?t have screens, but reeds.

 

[Frank Acampora]

Re: How lean can you run a carb?

Less than 3/4, you run the risk of melting the top piston. In these engines, the top piston runs a little leaner than the bottom because of the arrangement of the venturi siphon tube and reeds.
The puddle drain gets rid of unburned oil and gas. In that particular engine, you have two reeds. They should be normally closed and set at .010 open by the stop plate. There are usually two screens covering the metered hole that the reeds close. won't hurt not to have them but without them, eventually, (after a lot of running) carbon will clog the metered holes and you will need to clean them to get a decent idle. You should also have one or two one way valves in the small black hoses that lead to the two to one block. This engine dumps the excess oil into the leg instead of recycling it into another cylinder to be burned. That's why you see so much oil in the water.

 

[justin65]

Re: How lean can you run a carb?

Less than 3/4, you run the risk of melting the top piston. In these engines, the top piston runs a little leaner than the bottom because of the arrangement of the venturi siphon tube and reeds.
The puddle drain gets rid of unburned oil and gas. In that particular engine, you have two reeds. They should be normally closed and set at .010 open by the stop plate. There are usually two screens covering the metered hole that the reeds close. won't hurt not to have them but without them, eventually, (after a lot of running) carbon will clog the metered holes and you will need to clean them to get a decent idle. You should also have one or two one way valves in the small black hoses that lead to the two to one block. This engine dumps the excess oil into the leg instead of recycling it into another cylinder to be burned. That's why you see so much oil in the water.

I'll recheck the puddle valve. (reed clearance)

Come to think of it I did see two lines running from the front (under the intake) to a "T" valve into a single line attaching to nipple on the bottom. That would also explain why the exhaust port doesn?t smell like fuel.

Would it be possibly to take the line off the nipple and make up a collection container to catch the fuel/oil? Modify something like a whiskey flask?

 

[Frank Acampora]

Re: How lean can you run a carb?

I don't see why not. The newer 3 cylinder engines recycle it to the cylinders through a small pipe in the bypass covers. I always thought about recycling mine into the carb bowl but never got around to it and testing it. There are a lot of things I need a "Round Tuit" for. It is a very useful tool. As soon as I get one, a lot more things will get done around here.

 

[eurolarva]

Re: How lean can you run a carb?

Pre 70s chryslers do not have recirulation systems. The condensed or unused fuel goes through the two hoses on the port side under the electrical strip and comes to a T type connector that is connected to the kingpin and is dumped into the motor leg and back into the water. That T connector is a valve not a check valve. When these motors were built they did not care about lake pollution. Decarb will help but not get rid of this. What I did was drilled a 3/8 inch hole into my lower cowling and disconnected the hose going to the kingpin and ran it out the hole in my cowling. I have a small plastic bottle attached to that to catch the unburned gas and oil and then dump it at the end of the day. It is not pretty but at least I am not leaving a trail on the lake.

 

[roscoe]

Re: How lean can you run a carb?

Yep, Its not pretty, but we thank you for saving our lakes.

 

[justin65]

Re: How lean can you run a carb?

I don't see why not. The newer 3 cylinder engines recycle it to the cylinders through a small pipe in the bypass covers. I always thought about recycling mine into the carb bowl but never got around to it and testing it. There are a lot of things I need a "Round Tuit" for. It is a very useful tool. As soon as I get one, a lot more things will get done around here.

LOL..You just gave my wife a new phrase...lol

I'm going to do some testing with it later on today. See what psi the line is producing if any and get a sample of the fuel.

I have a whiskey flask I can mount a nipple to. Might as will put it to good use since I quit drinking many years ago. Looking at making a slip in bracket to mount to the Leg Cover.

Hmm... If its not too dirty I wonder if you could just run a line back to the fuel tank?


Thanks..

 

[justin65]

Re: How lean can you run a carb?

Pre 70s chryslers do not have recirulation systems. The condensed or unused fuel goes through the two hoses on the port side under the electrical strip and comes to a T type connector that is connected to the kingpin and is dumped into the motor leg and back into the water. That T connector is a valve not a check valve. When these motors were built they did not care about lake pollution. Decarb will help but not get rid of this. What I did was drilled a 3/8 inch hole into my lower cowling and disconnected the hose going to the kingpin and ran it out the hole in my cowling. I have a small plastic bottle attached to that to catch the unburned gas and oil and then dump it at the end of the day. It is not pretty but at least I am not leaving a trail on the lake.

OOH RAH!
Cool beans.....Bud, pretty is not leaving an oil slick.
About how much unburned fuel to you collect in your bottle?

Ideas like yours need to be made into a "sticky" or a "Tips and tricks" at the front of each repair forum. Maybe with a pic or two.

 

[eurolarva]

Re: How lean can you run a carb?

After the decarb about 2 tablespoons. However I only run my outboard (1967 45hp Chrysler) about 10 to 15 minutes when I fish. Roscoe and I fished together in Wisconsin so that is how he can atest to how ugly it is. I go to my spot and use the trolling motor most of the day. The truth to this is not alot of pre 70 chryslers running anymore. The post 70 motors started using reciruilation systems to reburn the mix which still did not work worth a crap. I will post a couple of pics so you can see what I did and with some time and patience you can do a much better job. I am a hack and dont much care what others say about how it looks.

 

[justin65]

Re: How lean can you run a carb?

Ok I have my collector set up. I drilled a hole in the bottom near where the wiring cable comes into the motor housing. I used an old plastic oil container.
Works like a champ...

I used ?Sea Foam, Deep Creep? as described in the Engine Frequently Asked Questions (FAQ) form ?Decarbing Your Engine- The Process-HOW AND WHY?.
I was thinking about doing it again today on the lake so I could open it up full throttle.

I was wanting to ask you guys what brand of spark plug do you recommend?
I couldn?t find the Champ L4J as the book said. Right now it has what the sales clerk says is the same as the L4J, its NGK B7HS.


Thanks for all the great help and GREAT info!

 

[eurolarva]

Re: How lean can you run a carb?

L4J no longer exists. Champ L82C is the best cross reference. After running it pull the plugs and make sure they are slightly oily and not dry If dry turn the idle mixture out another 1/8 turn