84 merc 150 hp bogs down

First I want to thank previous replies to my problem!!! I am at my wits end after about a year so here we go. Problem started with cracked oil line that developed at WOT. Engine sucked air between tee(where oil and gas meet) and oil pump and died. Replaced line and checked compression in all six cylinders to be sure nothing terminal happened. Easy fix right? No way! Things just getting worse. Starts fine, idles OK, but when I Throttle up it justs bogs right down. As I said I checked Compression, Spark(jumps 3/4 in.) All check good with timing light so I thinking fuel problem.. Have fuel filter(new). New lines and pump ball. Took carbs apart after finding that three of six floats would saturate( foam type) after gas was in them for a while allowing needles to open all the time and allow to much gas. Replaced all floats with new(plastic). Cleaned carbs and all jets. I Replaced all needles and seats. Adjusted floats to specs. Link and Synced. Even did fuel pump diaprhram kit while at it. After all this I still bog at throttle up and can't get on plane. So i'm back to spark,air, or fuel issue. The only thing that I see is some fuel will shoot back thru carbs #1+#2 at idle and throttle up. Could reeds cause this as they look ok. This is a V-6 oil injected merc. I may need a great mechanic in Michigan!!

Re: 84 merc 150 hp bogs down

Jingy: See my 85 merc 75 hp post a few down from yours. You can borrow my Weatherby if you'd like.

Re: 84 merc 150 hp bogs down

If you opened the carbs up to check something and didn't replace gaskets, the little one around the emulsion tube will bite you by leaking gas from the bowl into the bore. It shouldn't be spitting fuel at you at idle.

Have you had the reed plate off for inspection? You can't tell much from the front side. A loose reed block or bad reed block gasket could have these symptoms, as well as a bad reeds.

Are you sure you are using the right linkage setup specs. Sometimes a bog can be caused by carb throttle plates opening prematurely.

Of course, jet sizes are important. On an old motor like this, it's hard to tell what's been tinkered with. I ran into one that had the idle ports drilled out to try to run E85. Had to junk the carbs and start over.

hope it helps
John

Re: 84 merc 150 hp bogs down

Thanks for reply John. All gaskets were replaced in carbs and mounts with gasket kit. The plates were linked and seem to be properly set up. I haven't removed the reed plate! These are Boysens which I installed a few years back. Wouldn't they have an effect on compression? Are you saying this would also cause the spitting? The jets have the right numbers on them for opening size. Would you disassemble all carbs again or concentrate on reed block?

Re: 84 merc 150 hp bogs down

Like John said, pull the reed block and hold them to the light to inspect sealing. a leaky reed may idle and immediately fail to hold the additional pressure as the throttle is opened.

Also, retest spark with the throttle cable disconnected and moving the throttle (timing lever) to WOT and back. A broken yet abutted trigger may fire fine at idle and fail as soon as the wires move, dropping a cyl or two.

Re: 84 merc 150 hp bogs down

A bad reed won't lower compression, but it will fuddle up idle and acceleration.

Re: 84 merc 150 hp bogs down

Thanks John and Charlie and all Repliers! I'm starting to tear it back down but after I do... to check the trigger should I be in the water or can I do it with the muffs on? I never gone WOT with muffs on. I'll let you know on the reeds. I hope I am like one of the many you guys have helped!!! Back to it. May take a day or two?

Re: 84 merc 150 hp bogs down

You can spark test/trigger test on the trailer without starting the motor.

Pull all the plugs, attach wires to gap tester and crank the motor. If testing one cyl at a time just ground all the other plug wires.

Re: 84 merc 150 hp bogs down

CharlieB said:

a leaky reed may idle and immediately fail to hold the additional pressure as the throttle is opened.

Click to expand...

Maybe I should have been more clear;
Fail to hold the additional 'crankcase' pressure as the throttle is opened and blow a 'cloud' of fuel back out the front of the carb much like the older two stroke dirt bikes did before they adopted reed valves.

Re: 84 merc 150 hp bogs down

Ok. Tested spark again thru plugs and also on spark gap tester. All would jump a good 3/4" or more. All carbs off. Looking at reeds from outside, is there any way to test pressure reeds should have on them? Is there a paticular sound a bad reed would have when gently tapped on? I know the block housing will have to come off but just wodering. It amazes me that a cracked oil line has led my engine to perform this bad!!!

Re: 84 merc 150 hp bogs down

The reed blocks need to come out so you can holld them up to the light, that makes it a lot easier to see the light between the reed and the block if the reed isn't sealing well. A gap much more than a sheet of paper will not seal well. No light should be seen on perfect reeds.

Aftermarket plastic/fiber reeds are more tolerant of very slight light leaks as they flex easier and seal with lower crankcase pressures such as at idle and low throttle.

Re: 84 merc 150 hp bogs down

You're only about 10 bolts and one gasket from having the entire reed plate assembly off the engine. Go for it.

Re: 84 merc 150 hp bogs down

Reed block tore down. Reeds on #2 Bad. One was ripped with whole corner gone! A few on other cylinders weren't closed all the way. I'm glad they were Boyesens! I'd like to show you an image but can't seem to get it to work. Should I replace with same or what do you guys suggest? Thanks

Re: 84 merc 150 hp bogs down

Chris Carson reeds are as good or better, and a lot cheaper. Any glass reed is going to succumb to poor tune and lean sneeze quicker than steel reeds, but are a lot more "digestable" if they do chip.

I would bet that if you lapped those reed blocks and throw in a set of new sport reeds, it'll be a whole different engine.

Re: 84 merc 150 hp bogs down

Thanks! Just orderd some from Carsons. Sport Reeds. Cheaper too!! When your lapping the blocks, what is the best method/materials. Pretty much the same as valves?

Re: 84 merc 150 hp bogs down

Here is the picture of #2 Reed

Re: 84 merc 150 hp bogs down

jingy said:

Here is the picture of #2 Reed

Click to expand...

Just e-mail Chris. His customer support is just shy of nagging. Basically, a sheet of wet or dry, a little WD-40, and a flat surface is what you need. A surface stone is best. piece of glass supported so it doesn't bow under a little pressure is almost as good.

Pits covered by the reed is not a problem. Just the "image" of the old reed.

That damage is typical of fiber reed damage from frequnt lean sneeze. Eventually the back fire burns the edge of the reed. On the plus side of that, good fiberglass reeds broaden the tune window at idle considerably. You really have to screw up to not get a decent idle.

Re: 84 merc 150 hp bogs down

While I'm waiting for parts. I took the reeds out and looked at the reed blocks. They looked really good. Still lapped them anyway with no apparent grooves or pits. When the new reeds come do I put loctite on the screws? They all seemed to have it on before. Loctite Blue?