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4run4fun

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"I have a simple question to p

"I have a simple question to put to you guys. My 88 7.4L Merc's Quadrajet becomes completely saturated with black soot garbage after about half a day on the lake. Secondaries clog to the point that when they open, no additional fuel is added. I believe this to be just ambient air debris in the engine compartment, like belt dust, dirt and other stuff. The factory Merc flame arrestor is coast guard approved to kill backfires, I know, but it has no filter element at all. Does anyone out there use a automotive style breather can with an element to trap debris? I am curious if anyone has a homemade solution to Mercruiser's genius idea of a non-filtered air intake. Thanks."
 
Dialed.
Any type of filter ma

Dialed.
Any type of filter made with paper or other kind of material that can burn is not to be used on a boat engine.
There should not be that much stuff getting into the arrestor. It is best to find where all the dirt and stuff is getting into the engine compartment / arrestor.
My guess would be excessive blow by from the engine if it is black and oil soaked. Do a compression and leak down test.
A quick way to tell is by installing a pvc valve in one valve cover and connecting it to a vacuum port in the intake.
Then install a filter on the other valve cover for it to pull clean air into the crankcase.
Keep in mind that there is little or no vacuum when the throttle is wide open. So the engine can not vent as needed with the pvc installed. Do not run wide open for more than a minute or so.
If this helps keep the arrestor clean the engine may need to have the rings replaced.
Remove the pvc valve and return the system to the way it was after this test.
 
"If there's a lot of dust

"If there's a lot of dust in the bilge, clean it out. The air over a body of water tends to be pretty clean unless you're going through a dust cloud from a construction site. How clean is the flame arrestor? If the foam on the motor cover is disintegrating, replace it with a silver mylar insulation sheet.

Do a compression/cyclinder leakdown test. My guess is that you may have an intake valve or timing issue."
 
"Wow, thanks for the quick res

"Wow, thanks for the quick responses. I am relatively sure the internals of the engine are are good, only a small faint vapor escapes the valve covers on both sides, and it quickly disappears into thin air. A few years ago, I had a problem with rusty pulleys (which is why I hate v-belt systems) chewing through belts in a weekend. I finally removed, sanded and repainted them all to solve the problem. The debris in the carb resembles what it used to do when the belts were being destroyed; its fine black powder. The compartment still has some residue in there and some is still on the engine, becasue I cannot clean all the nooks and crannys. This is why I lean heavily towards general dirt and efeectively powdered rubber being the problem. I have seen multiple other marine setups that include a filter element of some sort, and I really believe that would solve this issue. The flame arrestor is covered in this crap, and not just where the PCV tubes connect; all over. I know its there for a specific reason, but somehow I think that flitering the incoming air carries almost as much importance as containing backfires. If I can, I'll take a photo of the butterflies on this carba nd post it, it looks as though the whole thing has been powdercoated black. The stuff comes off rather easy, but casues me major problems every weekend."
 
"Why not collect a bunch of th

"Why not collect a bunch of the black stuff on a piece of metal and burn it? If it smells like rubber, you'll know what it's from. If it smells like burning oil, you'll know it's from the PCV tubes. If there's a lot of rubber powder in the bilge area, I would think about getting the boat to a place that is away from the house and using compressed air to blow it out."
 
"Thanks Jim. I did exactly wh

"Thanks Jim. I did exactly what you suggested about a month ago, becasue I wanted to be sure it wasn't an exhaust leak or something else. I made the determination it was rubber and must just be residual from my previous belt problem. Sooner or later it will all be sucked out, probably by the engine, I'm just looking for a way to keep from having to clean the carb after every trip, and sometimes in mid trip."
 
Dialed.
Why not pressure wash

Dialed.
Why not pressure wash the engine compartment with the the drain plug out and remove all that crap.
Is this a dock sitter or is it on a trailer?
If you are still chewing belts you may have another problem like the pulley alignment or an accessory is not turning free.
As for the pcv just put it in the valve cover where the vent tubes are now.
There should be a vacuum port on the intake or at the base of the carb in the rear.
But it sounds as if you are sure it is belt dust.
 
"Its a trailered boat. I have

"Its a trailered boat. I have considered a good pressure wash, but I worry that I could wet something critical and cause more problems. Then again, it is a boat, and EVERYTHING in a boat gets wet from time to time. Looks like my choices are limited, so I'm pressure washing the engine bay and ordering a K&N arrestor. I still say that someone at Mercruiser got an award for making an arrestor with spare parts laying around."
 
"You don't need to pressur

"You don't need to pressure wash it. If you want, use a toilet brush to scrub everything and hose it off gently. That way, you can control where the water will go better. Again, compressed air will get rid of a lot of that stuff. Wear a mask and old clothes and have a big fan blowing it out of the way.

If you hose the motor off, use a blow gun to get rid of most of the water.

Actually, there probably isn't a PCV, it's just a crankcase vent. A PCV uses engine vacuum to draw combustable fumes from the crankcase to the intake and having the hose outside of the flame arrestor isn't going to open the PCV valve.

Most boats I have worked on had filthy bilges. This would be a good time to make yours an exception to the rule if it isn't already.

Mercruiser isn't the only company using this kind of arrestor. Yamaha, Volvo-Penta, OMC, Indmar, PCM, etc have all used it. Indmar has been using the K&N since the Mid '90s since they added MFI to their lineup but the TBI and carbed motors still use them or something similar."
 
"Yes, filthy bilge is my middl

"Yes, filthy bilge is my middle name. If your motor compartment looks like mine, you'd have to be a hobbit to get in there good. And forget reaching the underside of the engine, you'd need 3 elbows at least. That is why the bilge is filthy, cleaning it thoroughly is a near impossibility. Also, the tight quarters ensure that any dust or debris in there is well within reach of the carb's suction. I like the toilet brush idea, I think I'm gonna steal that and call it my own."
 
"Dialed.
That a boy. Just try

"Dialed.
That a boy. Just try not hitting the distributor and cover the carb. When you are done remove the cap and check for water in it.
As you say it's a boat. Spray the heck out of the area under the engine and the sides.
You'll need to keep checking the drain plug. They get blocked easy doing this. Once you get it clean you can get a better idea of what is going on.
Walmart has some ok engine degreaser.
House brand,super tech I think it's called at a buck a can.
It does the job and doesn't smell like diesel for the next 2 months like gunk does."
 
"" I like the toilet brush

"" I like the toilet brush idea, I think I'm gonna steal that and call it my own." I have an account on Paypal if you want to pay me. :-}

You could also use Simple Green for this."
 
"Ordered my K&N (coast

"Ordered my K&N (coast guard approved) flame arrestor with GENUINE filtering element, today. I'll install when it arrives and let you guys know how it fares. I can tell you that K&N thinks highly of their merchandise, but if it works, it will be worth it. Tonight's task is bilge cleaning to the best of my ability -- that's right, I'm breaking out the toilet brush."
 
I think you'll be happy wi

I think you'll be happy with the results. I would suggest wrapping the filter with something like cheese cloth un till you're sure the bildge compartment is clear of debris. It's alot cheaper that a new filter!
 
"Are your belts slipping? Hec

"Are your belts slipping? Heck, the stuff is coming from someplace, right? And it needs to be stopped before you breakdown.

Seems to me that you're putting a Band Aid on the problem instead of addressing the problem.

Jeff"
 
"Yes, I am a VERY LARGE Clemso

"Yes, I am a VERY LARGE Clemson Fan. 92-96 Tiger Band!

FastJeff,
The belts WERE slipping, until I sanded and repainted all the pulleys. I'll testify to the fact that a rusty pulley will eat a belt like sandpaper, in one weekend. They would grind so intensely, they used to produce a type of 'smoke' in the engine bay that would settle on everything and build up into layers of powdered rubber. All that has been rectified now, but the residual rubber debris is giving me carb fits. K&N filter should be here soon!"
 
"K&N setup arrived today;

"K&N setup arrived today; what a sweet piece of equipment! Gives me the feeling I have some kinda hotrod strapped to the transom. Just realized, though, that my old carb stud is waaaay too short to attach this thing. Oh well, I hope the auto parts store has one of those."
 
I installed a K&N filter a

I installed a K&N filter about 2 months ago. Had no problems installing it and it seems I got a little more UMPH out of the engine.
 
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