Idle Surging

[robeward]

got a 2010 5.7 vortec. edelbrock 1409 carb very recently been rebuilt by a very trusted mechanic.

i re installed carb and attempted to set idle mixture. i don't have much experience so i am sure it could have been done better.

it surges at idle. a little worse when it is cold but will still do it after warming up.

just trying to understand what are the possibilities so i can do some more learning before i can a chance to work on it again.

if i need to re-attempt setting idle mixture i can do that

 

[gbeltran]

Could be that the carb was not done properly. Why did you have the carburetor off to begin with? How did you se the idle mixture? Is this the factory carb?

 

[robeward]

believe me i understand the reason for your questions. trying to not go down the rabbit hole too far.

this is why carb was taken off and serviced.
http://forums.iboats.com/forum/gene...pics/661672-particles-in-fuel-water-seperator

i would say it isn't a factory carb as this engine/carb was installed by previous owner.

everything was fine before the fuel issue. at least i am pretty sure but only ran boat twice before it happened so never really got comfortable with it.

going with the most obvious, lets assume carb rebuild was done correctly could improper idle setup cause the surging?


my process.
bottomed idle mixture screws and backed out 1.5 turns.
warmed engine up.

then i think i turned mixture screws to increase idle until rpms would not react anymore.
then adjusted idle speed screw to drop rpms down to ~900

 

[gbeltran]

Which way did you turn the idle screws? Sounds like you used the right procedure for setting the idle. 900 however is too high. Shoudl be more like 600. It'll work at that rpm but you'll wear out the clutch in the drive sooner rather than later. I'm going with the carb in this case. Judging from the dirt you could have some of the smaller passages in the carb plugged up. Some of those passages are pretty small. Causing a lean surge. Perhaps the secondary butterflies aren't properly set depending on how far apart the mechanic took the carb to clean it.. You get a little extra air in the mix, rpms go up to the point where there's not enough fuel to sustain the higher rpm, so the rpm's drop down, and then the cycle repeats. There can be other fuel related issues, float not set right, but I'd suspect the carb. You have checked for vacuum leaks around the base?

 

[robeward]

I haven't checked for vacuum leaks. May just need to get a trained ear on it. A carb kit was put in it so I assume a pretty decent takedown was performed