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350k idle fuel drip

68L71

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I have a 1981 super sport 170 with a 350k. The engine is all factory original. The carb was rebuilt because the needle and seat were bad. The carb was super clean and all idle circuits are clean and free of obstruction. I need to have the idle screws (fine threads) out 8-9 turns in order to stop fuel from dripping into the primary’s. Everything seems to run great, but after a long run it seems to get a little flooded yet and when I look in the primary’s at that time it has a very slight drip again. Any thoughts on what might be going on? I have verified the float level is good and the needle and seat are functioning.
 
that description suggests a Q-jet...and there's no good reason to have the idle mixture screws out that far...

What RPM are you adjusting the idle mixture screws at?

FWIW, if the dripping you are referring to is the primary nozzle drip, the idle mixture screws have no direct control over the drip...it is caused by physics...
 
that description suggests a Q-jet...and there's no good reason to have the idle mixture screws out that far...

What RPM are you adjusting the idle mixture screws at?

FWIW, if the dripping you are referring to is the primary nozzle drip, the idle mixture screws have no direct control over the drip...it is caused by physics...

Yes it is a QJet. I have 700-950 range for rpm. Do you think it’s possible I do not have the primaries open enough? When I close the idle circuit screws and open primaries a tad more it drips more. Maybe it all goes back to needing to lower the float setting some more?
 
no & no...

I believe your throttle plates are open 'too much' for the idle mixture screws to have any control at all...i would try that adjustment with the idle speed down around 600-650 max...nozzle drip is pretty rare on a small block in a standard production dress...

the float setting really doesn't have much bearing on the nozzle drip...that said, I prefer to set the float on the lower end of 'normal'...
 
Nozzle drip on Q Jet may be due clogged idle air tubes I had the nozzle drip on mine and really cleaned them & blasted with a air compressor. The typical base setting for your idle mix screws is 3-4 turns out. Your idle speed is too high it should be like 600-650 rpm.
 
Thank you! I though I had it idling as low as it would go and still run. I got it idling now just a hair above 600rpm and the idle screws set where they should be. Zero drip so far!
 
I took it for a long ride today and eventually it flooded again. Pulled the arrester and I had nozzle drip again. I set the air idle adjustment with a vacuum gauge, but it did end up about 5 turns out to get the best reading. If the idle mixture is too rich and it floods after a run of idle speeds, would that cause nozzle drip because the engine is choked up with fuel?
 
The nozzle drip is driven by the air mass flowing thru the carb....so think throttle plate opening ~ engine RPM...

did you change the float, needle, and seat or are they 'original'?

have you check the fuel pressure at the carb's inlet?
 
The float needle and seat are new. It doesn’t seem like the gas is going above the set level of the float. I have not measured the fuel pressure, but I have wondered if fuel pressure is an issue. The fuel pump is rebuilt because it was sending fuel into the carb via the vent. I checked the carb temp when it was doing this and it was 105 deg. I do have the float set below specification.

it ran great at 1/2 to full throttle for 1/2 hour. Then 20 minutes of 700-1000 rpm idling and then when trying to go back to 1/2 throttle it would not get up to the correct rpm. Full throttle would only get me 3,000 rpm vs 4200 where it should be. I presume, because it was flooded during the 20 minute period of slow speeds.

I observed nozzle drip when I pulled the arrester off when it was running crappy, trying to make it back to my lift. So if the throttle plate is open but the engine isn’t reaching the corresponding rpm, could that cause dripping? If yes it would just make the flooded state of the motor worse.
 
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getting back to basics, you have a 40 year old engine....when was the last time it received a tuneup? any idea when the last compression test was done? I thinking you may have other issues that are keeping you form getting the carb dialed in...a couple of fouled plugs or a cylinder with low compression can prevent you from getting the carb tuning correct.

once the throttle plate is opened past a given point, fuel will start to flow from the primary venturi...when it starts, it is usually referred to a 'drip' and when the throttle opens a bit more, the vacuum in the venturi increases and the drip usually turns to droplets and then a fine mist...

when the "flooding" occurs, can you smell the raw fuel in the exhaust?

Finally, have you checked the oil for fuel contamination? the sniff test after running is usually accurate enough to discern a concern.
 
I'll bring my compression gauge next time I am up at the lake and will do a check. Will look at all of the plugs then too. I pulled a few and they looked a bit sooty. I can't say I've smelled the exhaust when it does the flooding, but the exhaust does appear to a bit of mild steam like smoke when the flooding condition is happening. I do not smell raw fuel in the oil. The boat is new to me a few months ago. The engine looks to be all factory and has not been messed with very much. I bought it from the original owners son. It did have a new set of points installed just before I got it. The carb seemed very clean when I put in the new float, needle and seat. It ran great yesterday for the usual ~45 minutes.
 
I did a compression check and 7 cylinders were at 150psi and one at 60psi. I put a little oil in the cylinder and it went up to 90. So it seems the rings are bad. Bummer
 
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