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Old     (jps120)      Join Date: Oct 2012       03-31-2014, 7:03 PM Reply   
ok sorry for the long story here but I want to give all the details.
Engine is indmar 5.7l carb with electronic distributor.
Last fall I had the head gasket replaced on the left side of the engine (I believe 1,3,5,7). Head gasket was blown between 3 and 5 cylinders. A mechanic friend of mine replaced the head gasket for me and we took the boat out and it ran perfect. we ran it for about 3 hours, running it wide open, cruising, idling and shutting it off a couple of times. On the way back to the boat ramp boat was running fine, and then I took the boat out of gear to slow down and I noticed that the engine was idling around 1100 rpm and there was some whitish blue smoke coming from the right exhaust. the following is what I have checked so far to
1. I adjusted the idle set screw all the way down and the rpms never fell. I could adjust it up but
not below 1100 rpms
2. I disconnected the throttle linkage to see if it was sticking open but it was all the way down
3. I replaced the pcv valve and conditions did not improve.
4. I checked the vacuum by using a vacuum gauge and was getting 20 lbs/in. I also checked for leaks around the vacuum hoses, base of the carb, and intake manifold by spraying starter fluid around those areas.
5. I checked timing and it was 6 BTDC.

As of now I am out of ideas and looking for so help
Old     (phathom)      Join Date: Jun 2013       04-01-2014, 8:52 AM Reply   
Bluish smoke indicates getting burned. After running for 3 hours I doubt there'd be any residual from the repair remaining in there.
High idle normally indicates it is getting extra air or fuel, not from the carb. This can indicate a vacuum leak. I see you checked for leaks already, but maybe there is something you could be missing. I had a similar problem on my car once, everything was exactly how it should have been, no leaks, damaged hoses, etc. But the cold idle screw had stripped out and was missing making a huge vacuum leak.
Is the vacuum it has now to spec of what it should have?

With a carb, you can always take a rag and cover the carb, if it doesn't die, there is definitely a leak somewhere.
Old     (cadunkle)      Join Date: Jul 2009       04-01-2014, 1:17 PM Reply   
High idle with throttle plates closing normally is typically unmetered air. Extra fuel will not cause a high idle as Surf Addict says.

Check the basics first, sounds like you've got a good start on that but not sure if you went all the way with it given teh detail you've provided.

When you adjusted idle set screw all the way loose did the butterflies completely close? They should be all the way closed, and if no vacuum leaks the engine will stall when idle stop screw backed all the way out. Did you verify the secondaries are not hanging open? Open them a bit and push closed, does high idle change? What type of carb is this? If plates aren't closing check for trash pinched against bore and butterfly right at the throttle shaft. If clean, you may have to loosen the throttle plates from the throttle shaft and realign them by closing the throttle fully and tightening the screws, then verifying it operates smoothly all the way to closed. You could also have a leak between the carb base plate and main body.

Check that your timing is advancing and returning to base smoothly as you raise RPM. If timing is not returning to base that will keep RPM higher at idle. Also not sure what your spec on base timing is for that engine but I usually run 10* initial. If it doesn't detonate it'll have a little more punch off idle and slightly less GPH at cruise. Also if you have 6* at 1100 RPM you may have less base timing depending on at what RPM that distributor starts advancing. Could indicate retarded initial timing, stuck advance, or just a slow curve (fine if that's how it was meant to be).

If you cannot find any external vacuum leaks and once the high idle started you are seeing bluish smoke I would suspect a vacuum leak under the intake. Try spraying around the edge of the intake where it meets each head, particularly the starboard head which you indicated that exhaust was smoking. If you don't get any indication on top, it may still be leaking below. Carefully remove intake and inspect gasket for leaks on the lower area of each port. Clean and replace, you can use a thin smear of RTV around each intake port, or a sealer such as gaskacinch. Also, thicker intake gaskets will help with sealing.

If idle is high with carb totally closed you have a vacuum leak somewhere, you just have to find it. For a leak under the manifold I'd expect it to still stall with throttle plates fully closed, or at least run quite rough with any intake especially a dual plane as I assume you have. For what it's worth I had a slight vacuum leak on my 454 under the intake. Causes intermittent high idle. Sometimes would return to normal idle and other times 100-200 RPM high. Adjust for when it's high and then eventually it'd seal and idle would be low and it would want to stall in gear at idle. I also had a 460 that was very hard to get the intake to seal. Thicker gaskets and coating the gasket around each port with sealant cured that. Both leaks were fairly small and caused slightly high or rough idle or couldn't get idle mixture dialed in just right, etc...
Old     (jps120)      Join Date: Oct 2012       04-05-2014, 2:15 PM Reply   
sorry for just now posting back. I have been busy this week and just had some time to look at it again today. I check compression on all cylinders and while they were low they werent showing any abnormally low cylinders. 150 on all cylinders starboard side and the port was as follows - 1- 150 / 3- 140 / 5- 135 / 7- 140. I checked again for vacuum leaks and found none. I spoke to the dealership and they think it is a carburetor issue and that it is running to rich. at this point I am tired of waisting my time when the weather is nice. I am going to take the boat in on Tuesday and be done with it.
Old     (cadunkle)      Join Date: Jul 2009       04-05-2014, 2:51 PM Reply   
Sounds like a questionable dealer. Rich condition cannot raise RPM. You can throw all the fuel you want at an engine and RPM won't increase unless it gets more air, rich enough and it'll misfire/bog/stall but not increase RPM. Could be a carb issue, but not rich. Could also be loose throttle shafts allowing unmetered air in. Base plates wear and if you can feel any play in the shafts the fix is either new base plate, bush the shafts, or new carb. Bottom line is it's getting air from somewhere, either primary or secondary not returning completely or a vacuum leak from somewhere.
Old     (jps120)      Join Date: Oct 2012       04-05-2014, 5:41 PM Reply   
thanks for your advice I will definitely mention it to the dealer. I have heard nothing but good stuff about these guys. (purchasing only not the service side). I sprayed the starting fluid little bits at a time all around the carb and base plate and the engine idle did not change. What will the exhaust look and smell like if the engine is running real rich? I am just confused at where this smoke is coming from. the engine never smoked before and we never even touched the starboard side and that is where the majority of the smoke is coming from. the intake manifold was taken off when we replaced the head gasket. If there was a leak at the intake gasket could that let oil in from the lifter valley into the fuel air mixture, which would explain the burning oil and high idle?
Old     (cadunkle)      Join Date: Jul 2009       04-06-2014, 5:04 AM Reply   
If it's running very rich you may see some smoke from the exhaust, it'll be grayish to a bit darker. Your nose will tell you if it's rich, smell the exhaust. It'll smell like gas and if it's very rich will burn your eyes. Hard to describe a smell, but it'll either smell a little rich or it'll smell a lot rich and sting your eyes/nose.

Blue colored smoke is oil. A leaking intake gasket from the bottom will pull both air and oil mist/vapor. It will burn a little oil, enough to get some smoke in the exhaust. Yes it can cause a high idle. From what you're describing my money is on that.
Old     (jps120)      Join Date: Oct 2012       04-07-2014, 8:20 PM Reply   
Cory I haven't been back out to mess with the boat but this just popped in my head. Saturday I was running the engine at idle and I removed the hose running from the flash arreator to the valve breather on the port side (not the pcv) and I put my hand over the hole and when I removed my hand I heard air clearly sucking in. I did this two more times to make sure it was sucking and not blowing out. There should not be any vacuum coming from the crankcase unless there was a leak somewhere drawing air out of the crankcase. Since I have been over the engine a few times looking for leaks this kind of narrows it down to the internal side of the intake manifold right?
Old     (cadunkle)      Join Date: Jul 2009       04-08-2014, 7:35 AM Reply   
Quite likely pulling that much volume from the valve cover breather is a vacuum leak. On a tight engine the PCV valve will pull air, a slight vacuum, from the opposite valve cover. Never seen one with enough suction to hear though, more like put your thumb over the hose and feel a slight suction. To test if it's the PCV you could just pull the PCV out of the valve cover, put your finger/hand over the hole and feel the opposite side breather. If it still pulls air then you've definitely got an internal vacuum leak and of course the only place it can be is the intake gasket.

Also put your finger over the PCV to block air that's pulling. I know you replaced it but you never know, could be bad or mispackaged and metering the wrong amount of air. If idle returns to normal or slightly lower with PCV blocked/capped it could be the problem and would also result in a lot of air being sucked through the opposite side breather.
Old     (jps120)      Join Date: Oct 2012       04-08-2014, 7:00 PM Reply   
Well I think I got it fixed. It was the secondary throttle plates. I checked them before but I was just visually checking them and trying to close them wih the linkage. Today I stuck a screwdriver down and pressed them shut it was only about 1/16 but the idle dropped about 300 rpm and the smoke stopped. After that I sprayed some carb cleaner on the plates and linkage and they worked just fine. I ran the engine back up to 1100 rpms and there was still no smoke. Going to take it out next week after work and test it out
Old     (cadunkle)      Join Date: Jul 2009       04-09-2014, 1:15 PM Reply   
Sounds like either just sticky or just preventing it from closing completely. Hopefully that was all it was.

Regarding the smoke, check while idling at temp and for a couple minutes after turning it off that you aren't getting fuel dripping from the boosters. That would cause a rich condition, potentially some smoke if rich enough, and indicate too high fuel level in the bowl for whichever side is leaking. This will also cause hard starting when hot after sitting for a few minutes with the engine off as it will flood. If so clean or replace the needle and seat and set float level.


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