bluemerlin
New member
"Hi,
Happy Friday the 13t
"Hi,
Happy Friday the 13th!
My 5.7l with Rochester 4bbl carb is having trouble idling. We just rebuilt the carb and it did not help (made it slightly worse actually) chasing a high end issue. When trying to set the idle mix screws, we cannot get the engine to run at all below about 1000 RPM. It is super lean (covering the air intake with a hand to simulate choke clears up the roughness and the RPM jumps back to 1000-1200). With a little throttle to get the RPM at 1000, it purrs just fine. Any less, and it hesitates and stutters. Choking it helps, and adjusting the mix screws does not seem to have any effect. When it is running right at the threshold, looking down into the carb, it seems that one side is spraying more fuel than the other.
I think I can't adjust the idle screws until we get the RPMs down to the 600-800 range (with no extra throttle), so what should we check to get the engine to run that slow? Looking at the manual, I am guessing to check timing? I don't think there is a vacuum leak, since the vacuum break actuator sucks in just fine, and with just a bit of throttle, it runs great. I am going to get a vacuum gauge and timing light for the next trip to the boat. Maybe check compression? I don't suspect ignition, since it would probably be worse as the RPM goes up.
[The previous problem was that the engine would stumble and stutter when you tried to go above 3000 RPM. That just started to happen on the last two trips. I think that was a clogged carb fuel inlet filter, now replaced.] We have not tried it in the water yet - trying to set the idle mix now.
Thanks for any advice...
Chris."
Happy Friday the 13t
"Hi,
Happy Friday the 13th!
My 5.7l with Rochester 4bbl carb is having trouble idling. We just rebuilt the carb and it did not help (made it slightly worse actually) chasing a high end issue. When trying to set the idle mix screws, we cannot get the engine to run at all below about 1000 RPM. It is super lean (covering the air intake with a hand to simulate choke clears up the roughness and the RPM jumps back to 1000-1200). With a little throttle to get the RPM at 1000, it purrs just fine. Any less, and it hesitates and stutters. Choking it helps, and adjusting the mix screws does not seem to have any effect. When it is running right at the threshold, looking down into the carb, it seems that one side is spraying more fuel than the other.
I think I can't adjust the idle screws until we get the RPMs down to the 600-800 range (with no extra throttle), so what should we check to get the engine to run that slow? Looking at the manual, I am guessing to check timing? I don't think there is a vacuum leak, since the vacuum break actuator sucks in just fine, and with just a bit of throttle, it runs great. I am going to get a vacuum gauge and timing light for the next trip to the boat. Maybe check compression? I don't suspect ignition, since it would probably be worse as the RPM goes up.
[The previous problem was that the engine would stumble and stutter when you tried to go above 3000 RPM. That just started to happen on the last two trips. I think that was a clogged carb fuel inlet filter, now replaced.] We have not tried it in the water yet - trying to set the idle mix now.
Thanks for any advice...
Chris."