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how critical is float level

S

ship wreck

Contributing Member
78 Johnson 140. Fresh powerhead but it's not running right. Running on the muffs it will act as though it is loading up at high idle and occasionally "skip" accompanied by a good puff of smoke then clear up for a bit and do it again. Under load it ran pretty well but would not come up to full RPM.

I pulled the carbs to ensure there was nothing in them and rechecked the float level. I do not have the float gauge but set them at the free end slightly higher than the seat end. Put it back together and it is running the same on the muffs.

Now I'm running 25:1 mix right now so I thought that might be having some affect but I'm unsure. Spark is good on all cylinders. I verified I'm fueling all cylinders as well. The front of the boat is tipped down right now so the motor is at a bit of a forward rake. Have not tried to level it out yet to see if that affects it but the motor should be able to be trimmed and still run fine so I have a hard time believing the float level is critical or the boat angle at the moment is causing issues but could it be?

Plan is to try and get out on the water on Saturday to see how it runs under load but this issue is perplexing. Thoughts?
 
Level is critical as it can cause lean out and cause piston damage. The "skip" sounds like a lean pop and these engine will do this if running on a hose as they have to have backpressure to idle correctly.
 
Run it in a tank to get proper backpressure for your testing/break in time.

Also, are you using L78V surface gap plugs? At 25:1 oil those can load up a little bit and cause poor spark. I don't remember if those motors can use an open gap plug but if it can that might be a good idea so you don't have fouling issues. This is especially true if you're doing extended idling.

KJ
 
Thanks Guys. Not concerned about leaning out due to float level as the levels are high is anything. High levels can cause mixture issue as the air bleeds that enable/assist the fuel pick can be covered or overwhelmed by high levels as well as fuel can be physically pushed out of the bowl. Now all of this is based on 4 stroke car engines that are designed differently from these carbs.

Yes I am using the surface gaps plugs. I pulled them last night after the latest muffs test run, and they are not fouled but the starboard bank was wet with fuel. That I"m sure could just be happenstance. as Pulling a plug wire on each cylinder while it is running causes the same change is speed, and sound on all cylinders. I guess it really does need a test wheel and tank to troubleshoot this properly.

My original thought on the last trip was some junk in the carbs high speed circuits but the tap of the choke trick would cause the motor to stumble not pick up so my thought was it is not running lean and made me think high float level. Inspection of the carbs revealed nothing but that is not really surprising. I have often fixed performance issues by cleaning a carb that looked clean.
 
Totally different operation...if the float is high when bowl is flipped over its too lean as the emulsion tubes has to be covered for proper carb operation, to high and bowl does not stay filled with fuel and runs lean..
 
Last edited:
faztbullet said:
Totally different operation...if the float is high when bowl is flipped over its too lean as the emulsion tubes has to be covered for proper carb operation, to high and bowl does not stay filled with fuel and runs lean..
Click to expand...

When I was saying high I was meaning fuel level not float level inverted. With the float is just slightly off level. Free end very slightly higher than the needle end.


Compression and spark are good.
 
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