smokes at idle?

[jsandy]

ok so in the quest to make my sunsport perfect i'm gettin close to done. The only true worry i have with it, is that it smokes at idle. not horrible but its noticable especially if you are putting your board on and setting on swim deck. any ideas? running rich maybe? and how to adjust the carb to find out? 1991 351 btw

[OUI]

What color is the smoke?

[cadunkle]

Either running rich or burning oil. Easiest is if it's running rich. If that's the case you'll be able to tell easily from the smell. Does it smell rich? Like gas? Burn your eyes? If so go through your carb. With the air cleaner off watch the boosters while idling and after shutting off. Do you have fuel dripping from the boosters? If so, there's your problem. Adjust your float level and then reset your idle speed and mixture.

To adjust the float level pull the brass sight plug in the side of the float bowl. You want the float level to be right at the base of this so while idling no fuel drips out but if you rock the engine a little fuel will come out. Start with the primary side. Put a rag below the fuel bowl to soak up the fuel that leaks out. With the engine idling pull the plug. If fuel comes out your float level is too high, immediately put the plug back in, shut the engine off and wipe up any fuel. Loosen the flathead screw on top of the fuel bowl and turn the 5/8" nut in (tighter) 1 full turn. Start and let it idle a minute and pull the sight plug again. If fuel still comes out, adjust the 5/8" nut tighter another turn. Once you can remove the sight plug with no fuel coming out, you may have to turn the idle mixture screws out to richen the mixture and smooth the idle. Get it smooth so it idles at least somewhat well... With the engine idling and sight plug out, loosen the screw on top of the fuel bowl slightly, just enough to turn the 5/8" nut. Loosen this nut until fuel just comes out of the sight plug hole then tighten the nut a small amount until no fuel comes out the sight plug. Tighten the big flat head screw. Lean against hte motor and rock it, fuel should come out of the sight plug. When you have no fuel from the sight plug when idling and stationary but it comes out when you rock the motor you are done. Replace the sight plug and repeat the process on the secondary fuel bowl.

To set idle mixture use the screws on the side of the metering block. In is leaner, out is richer. You'll likely end up somewhere between 1 and 2 turns out from fully seated on each side. Start on one side, slowly turn the screw out until idle is smooth and turning it out does not increase RPM any more, Then turn it in until idle gets starts to drop or get rough and then back out 1/4 turn from there. Repeat for the other side then repeat again on each side. Check RPM and set the idle stop screw to achieve desired RPM (generally 650-750 in neutral). Then adjust the idle mixture screws as you initially did, then the idle stop screw again if reququired to get desired RPM, then idle mixture again. Repeat as necessary to get desired RPM at a smooth idle. Your last step of adjusting the idle should always be the mixture screws, not the throttle stop screw.

If the exhaust doesn't smell like gas it is probably burning oil. This will give a blue-ish smoke. Most likely cause is valve seals, followed by rings and then valve guides. If you're burning oil pull a valve cover and look at the valve seals. They are the rubber pieces inside of the valve springs. If they look cracked, damged, or missing they shoudl be replaced. It won't hurt anything if they are worn but it will burn some oil and might foul plugs if it's bad.

To replace these you'll need a valve spring compressor and a way to keep the valve from dropping into the cylinder. I only recommend replacing them if the engine is otherwise in good condition and a compression check shows the rings are fine. If not, run it until next winter and rebuild the engine then.

To keep the valve from dropping you can put the piston at BDC and put compressed air in the cylinder if you have a compressor. To do this I take an old spark plug, remove the porcelain so I'm left with only the threads, drill to appropriate size and tap it for 1/4" NPT for a regular air hose fitting. Hook to compressor and put about 100 PSI in there. Then use compress the spring, remove the locks and keeper, then the spring, pull the seal and replace with a new seal. To get the locks out you may have to hit the spring compressor with a hammer to break them loose. Be careful the locks don't go flying out or drop down the oil drains into the pan. I put a rag in each oil drain to prevent this. I also hit each valve stem and retainer with a hammer before compressing the spring as this usually breaks them loose.

[jsandy]

well thankyou cadunkle

[oldman]

well thankyou cadunkle

I also thank you cadunkle. Sharing that info and all your info from other posts has been very helpful! Thanks again Oldman

[jsandy]

suggestion! this should be a sticky for basic carb adjustment. especially since he mentions to tune boat in WATER and not on the trailer so the motor will be in its natural position.

[wotan2525]

Man! Awesome post!! I've never tuned my carb and have always though "if it ain't broke... don't fix it." Should I mess with it and follow these instructions? I always thought it was a bit of voodoo to get those things running correctly!

[jsandy]

it is voodoo but he broke it down pretty simple

[sybrmike]

Screw drivers, wrenches, & chicken bones - it's an iterative voodoo process for sure...

[cadunkle]

Glad this was helpful. Just looked over that again and noticed I left out the poor(er?) boys way to keep valves from dropping when replacing seals. Take a small diameter rope that will fit through the spark plug hole and thread a large amount of it into the cylinder. Then rotate the crank until you have it all jammed tight and can't compress the rope any more. This shouldn't take a huge feat of strength (we don't want to sever the rope in the cylinder!). Be sure to do this on the compression stroke so both valves are closed. Then replace the seals for that cylinder's intake and exhaust, move to next cyl.

Seals are cheap, on the order of $10-$20 for a set of 16. No reason to suffer oily smokey exhaust and high oil consumption in an otherwise healthy engine.

As for carb tuning, there's more to it than that to tune all around but I think I did an alright job explaining for to get a good smooth idle. If your carb is not stock or has ever been modified you may want to go through the process of rejetting, getting proper power valve, proper accelerator pump shot, etc. to get the best power and economy from your carb.

[skibumtx]

I've got the same thing on my 06 Launch 21V. Smoke burns my eyes when wake surfing, but does not smell like gas. Have fuel injection on this engine, so no adjustments. The throat is dirty, so I'll clean that up. Opened up a valve cover, but cannot see the seals. Here is a photo. How do I check the seal?

[rludtke]

cadunkle is right, but I do wish to color his carb float setting slightly. The Holley 4160 carb that cam standard on the older PCM's do not have the exterior float setting feature he describes. This is typical of a "Marine" carb, as it is a source for a fuel leak external to the carbuerator.

Fourtunatly setting the marine carburators floats is not much more difficult, but you have to take the bowls off.

This is the Holley replacement for the PCM 351http://holley.com/0-80319-1.asp
This is the float level setting procedure, but on Marine carbs, you can only use the "dry" setting procedure. http://www.holley.com/data/TechService/Technical/Adjusting%20Your%20Carburetor.pdf

[cadunkle]

The valve seals are inside the springs. Look through the coils and you'll see one of two types of seals. It may be a larger unbrella seal which slips over the valve stem or a smaller positive stop seal that fits tightly to the head. If they look cracked, broken, or otherwise degraded they are likely contributing to your smokey exhaust. Sometimes you'll see pieces of the seals in your oil or along where the oil runs to drain back to the pan, along the head.

[skibumtx]

I'll check that after dinner. Here is a photo of a plug, just replaced this weekend. Show lots of carbon already. Checked my distributor cap and the contacts are all corroded. Do you know the part number for the cap and rotor?

[cadunkle]

Not sure on the part number for the cap. I'd replace the cap, rotor, and plugs. If wires are older or have never been done it would be a good idea to do those too.

That plug looks either obscenely rich or like it's burning oil. Most likely some oil. When you check the seals have a look at your oil drainback holes in the heads. One at front and back low on the head. If they're plugged up with junk you'll get oil pooling in the valve covers particularly at higher RPM which will leak past the seals and burn even if the seals are in good condition.

That oil is obviously very dirty, change it. Good thing is the heads and rockers look clean so you're not all sludged up. Also clean the throttle body. Hold it wide open and spray it out with some throttle body cleaner, then wipe all around with a rag to remove the dirty residue. If enough is built up that junk can mess with your idle.