ford 172 carb

tulsa zoo

Member
We have 2 trains that use the for 172 gas engine. one is a rebuilt train from Katrina. We have been running this train for 8 months with little problem. lately it has taken to fouling plugs. It is putting out more black smoke than normal. I have gone through distributor, coil, resistor and wires. I found the zenith e3jl carb does not have a main mixture adjustment. looks like mabe a set jet with a plug cap on it. Do you think I need to find adjustment needle or new carb? I'm not sure what else can be the problem of running rich.
 
If it has no mixture adjustment & a fixed jet only, then if now too rich & wasn't previously, then something must have changed to cause such, so find that cause rather than changing the jetting.
Float level change, bad/leaking float or needle valve/gasket, etc.
 
I thought it was the float needle. don't look like float is leaking...no gas in it. don't know how the level would change. didn't change anything on fuel pump or filters. good fuel pressure. I got a parts kit and change float needle and seat. but still putting out black smoke. I might let it run a couple hours see if it cokes up plugs.
 
If oil bath air cleaner, did you inspect/clean the down tube?

Not uncommon to find the down tube nearly closed off with oil soaked debris.

Dean
 
they were oil bath.. I changed them to an aftermarket filter for ease of cleaning. I run checks on them weekly.
thanx tho.
 

Well I take the air inlet tube off today and it has fuel in it. with new float needle I guess somehow the float is too high? it never puts enough pressure on needle to fully close?
 
Tulsa,You might want to remove the float and shake it ,it could have fuel in it after developing a leak.A float not floating properly and not shutting off the needle valve fully.That would cause the engine to run rich and blow black smoke also flood over. Check for leaks by dropping it in a pan of boiling water to check for bubbles if it leaking.
 

float is not leaking that I can tell. It is new viton tipped needle and seat that I checked for damage or debris. I adjusted the float about 1/16th inch lower and ran it, then left over night. it leaked into the intake tube again. should I lower float another 1/16th?
 
(quoted from post at 13:13:39 07/06/16)
float is not leaking that I can tell. It is new viton tipped needle and seat that I checked for damage or debris. I adjusted the float about 1/16th inch lower and ran it, then left over night. it leaked into the intake tube again. should I lower float another 1/16th?
eedle seat very tight & gasket good?
 

I put the seat in very tight but not slip the screwdriver. I have lowered the float twice. and today it still leaked overnight into the intake.
 
Since solution seems so elusive, you may want to try something like this & maybe you can see the problem?
 

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