Rich idle, bog, no hole shot. Reeds? Coils?

[DHag]

Sorry for the long post, but I wanted to be sure to have ALL the information.

1978 "V1500" Mercury 150 HP V6
1979 "16-8" Champion bass boat

Symptoms:

• 
  [*]When trimmed down for idle and no-wake operation, seems to "load up" with fuel. Burns very rich. No-wake operation is difficult at best. Will stall if throttle is applied too quickly in gear.
  [*]Hole shot? What hole shot? Throttle must be applied gradually, or it will just bog or stall. Can be helped by trimming up, but then the boat's attitude is all wrong for coming up.
• Long crank time on cold start. Pump the bulb up hard. Engage choke (key in). Open throttle slightly. Total crank time over a minute (in proper short bursts). Hold key in for a moment after start. (No "fast idle lever" on this motor.)
• After running, will start almost instantly all day long.
• At speed, no problems.

Work done. All work and adjustments done according to the official Mercury manual for this motor:

• New head gaskets. Compression balanced 110-120 per cylinder.
• New thermostats.
• Fuel pump rebuilt.
• Carbs totally rebuilt. All jets, ports, passages are clean and clear. Jets are correct sizes and not worn out. Float levels set "by the book."
• Carbs synchronized "by the book."
• Both ignition boxes are new.
• Replaced OEM-type "surface gap" spark plugs with extended-reach conventional gap plugs of correct heat range. (Made a MAJOR improvement in running, but didn't help this issue. Yes, there's plenty of clearance to the piston tops.)
• New plug wires.
• Ignition timing set "by the book."

Other points:

• The carbs have NO idle mixture adjustments. The only way to affect idle mixture is to adjust the float levels (for only a slight change), or replace the jets.
• I have not replaced the coils. They are the originals. They seem to be firing just fine, and pass all diagnostics "by the book." This does not appear to be a spark issue.
• I have two props, a 3-blade stainless Hoss, and a 4-blade composite Piranha. Both are properly sized for the boat and motor, 5500 rpm at WOT.

I've searched and read a lot of stuff (here and elsewhere) on my issue, and I came to the conclusion that it must be the reeds. So last night I pulled the reed block. I was planning to make a new set of carbon fiber reeds for it. But....

According to the book, the reeds are "perfect." They are clean and flat. They are all fully closed. Shining a light through from the back, no light can be seen under the reeds. They all open freely. The block surfaces under them are smooth and not indented. The limiting plates are all at the specified 0.200" gap.

So, should I go ahead and replace the reeds with new carbon fiber reeds?
Should I replace the coils just because they're old and they're the last remaining parts of the ignitions system?
Would it help to advance the timing a bit at low speed?
Should I replace the low-speed jets?
Should I just get a new fuel-injected motor? (Just kidding on that. Can't afford it.)

 

[Chris1956]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

You might stick with the surface gap plugs. It is unknown the effect of another spark plug. Did you synch the spark to the carbs? I presume you synched the carbs to open/close at the same time.

I doubt it is your reed valves.What color are the spark plugs, after running?

 

[Laddies]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

Most V/6 engines with factory jetting will run rich tucked under and a little lean when trimmed out it's the nature of the beast. fill a glass with water and tip it back and forth, that's what the fuel in the carb bowl does. Are you certain the float levels are right? Never saw a control without cold start either a small lever or a center button or the whole handle pulls out the release the shift

 

[DHag]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

You might stick with the surface gap plugs. It is unknown the effect of another spark plug. Did you synch the spark to the carbs? I presume you synched the carbs to open/close at the same time.

I doubt it is your reed valves.What color are the spark plugs, after running?

It took a lot of research to come up with a correct heat range for the plugs of a different design, and I called on my 30+ years experience with motorcycles. Believe it or not, I hit it first try. Should have bought a lottery ticket that day.

It's impossible to test heat range with the original type surface gaps. But to test the extended tips, I did the same test as with a bike. Get it fully warmed up. Run a couple miles at WOT, then cut the motor. Pull the plugs right there. The insulators are a light tan color. Perfect.

With a new set of OER surface-gaps, I was having misfires at speed and noticeable rough idle. I measured the piston/head gap very carefully to check for clearance. Of course, I got plugs with the same thread length. With the extended-reach plugs, the spark is actually right in the center of the combustion chamber. The misfire at speed is gone, and the idle is smooth. That is, until it loads up being over-rich.

The principle is sound. Move the spark up into an area where it gets maximum contact with the mixture. A surface gap spark is heavily shielded from the mixture, being at the surface of the head. Back in the 70's when this motor was built, surface gaps were designed primarily to prevent fouling, and they work very well for that. But with modern oils, it's not an issue. I use only full-synthetic TC-W3, pre-mixed in the fuel, which burns very clean.

Works with performance cars, motorcycles, and my ATV. By golly, it definitely works with the boat, too. :joyous:

 

[DHag]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

Most V/6 engines with factory jetting will run rich tucked under and a little lean when trimmed out it's the nature of the beast. fill a glass with water and tip it back and forth, that's what the fuel in the carb bowl does. Are you certain the float levels are right?

Oh, yeah. I'm certain the floats are spot on the factory spec. I double- and triple-checked. Even took them off after running a while, and checked them again.

It makes sense that it would get richer when trimmed down. But this is a LOT richer!

I have not taken a wire gauge to the idle jets. I only inspected them for size markings, plus they "looked" undamaged. Perhaps I should get a gauge and check them?

I forgot to mention.... Now that you bring it up.... A previous owner had drilled six holes through the lower cover and into the exhaust tube. I presume it was a misguided attempt to increase power by reducing back pressure, as I have seen done on some 4-strokes. But on a 2-stroke it just messes up the tuning. And made it loud. I worked out a way to plug them again by tapping the holes and running full-thread stainless bolts in from the cover into the tube. Quieted it down and made another big improvement in how it ran. Plus now it looks kinda cool with those six stainless bolt heads.

Picture's kinda fuzzy, but you can see my bolts in the back.

But when somebody screws with a 2-stroke exhaust, it's common to mess with the jets. Maybe that guy drilled out the low speed jets, too. :facepalm:

Yeah... I'll have to check those. It'll be easy, since the whole intake is sitting on my bench right now.

Never saw a control without cold start either a small lever or a center button or the whole handle pulls out the release the shift

I had to replace my controller not long after I got the boat, as the handle snapped off. It was really stiff, anyway. I got an aftermarket controller with same controls as the factory unit. All it had, and has now, is a center button to release the lever from the gear shift, so you can throttle up while not in gear. It has a lock button in the handle. The only other cold start control is the electric choke actuator, operated by pushing in on the key.

What I had read about cold-start was a lever on the motor itself. I read so much, though, it could have been for a small motor, and I just missed that part.

 

[Chris1956]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

Sounds like you have it under control.

 

[Dukedog]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

If that motor won't run with BU8H or BUHW'S ya got a problem with it somewhere else. If its running that fat at idle its either gonna be in tha carbs, timing and/or trigger. Maybe even tha switch boxes. Some motors for whatever reason will not run on "by tha book" idle timing. Ya gotta put in tha water, in gear, under a load and set it wherever its happiest..............

Whats tha dia. and pitch on those things?
These things are similar to tha bikes but yet completly different...............

One other thing. If that is an unmolested motor those carbs have tha type floats that "can get fuel soaked" over time..............

 

[quicktach]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

Sounds like a sync problem...like you're not advancing fast enough. Check the mechanical linkage that moves the trigger coil. Are all parts under the flywheel clean and firmly mounted ? And wires snagging anywhere that could affect motion ?

 

[DHag]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

I'll take into account the suggestions on timing advance. The ignition boxes are new, because the old ones were definitely bad.

I just dug in and did some real checking on the carb jets. I had inspected them before, and they are mechanically fine. However, since a previous owner had jacked with the exhaust (as I noted above), I wondered if I needed to inspect the jets more closely.

Here's what I found:

Specified by the Mercury Service Manual:
Main fuel jet: .052
Idle Air Bleed jet: .064
Bowl Vent jet: .098

Installed:
Main fuel jet: .056
Idle Air Bleed jet: .060
Bowl Vent jet: .098

So it looks like when the guy drilled out the exhaust, he also rejetted the carbs. Drilling out the exhaust tube would lower the overall chamber pressure, causing a lean mixture from excess blow-through in the cylinders. So he may have installed larger main jets and smaller idle air bleed jets in an attempt to compensate.

Bad, bad, bad all around.

Basically, this means a richer mixture across the board. Question is, is it enough to be the cause of my running issues? Those numbers don't look that much off of stock, but doing the math means the main jets are 16% larger than stock, and the idle bleeds are 12% smaller. Those are significant numbers.

Opinions?

 

[Dukedog]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

That plus a small idle timing issue "could" possibly be a problem. As for tha exhaust. On tha Merc its not that big a deal. Its totaly different from tha motorcycle world. About tha only thing tha exhaust is "tuned" for in "production" motors is tha bottom end. Its done with tuner lenght mostly. 150's usually have a very long tuner. You can change it to tha short 200 tuner and see absolutly no change in anything except a small bottom end loss. It will idle a little different but its because tha shorter tuner is not buried in water. A jetting change is not necessary on any exhaust change on a "production" motor. Very seldom needs a change even on tha stem winder hot rod either. I've seen cases where a motor has ran for a coupla years without a tuner at all. It had broken off and was laying at tha bottom of tha can. It was found when a water pump change came............These things are like tha motorcycle motors in a way. There are lotsa ways to improve their performance that are "not" in tha book. Some are even said to be definite no no's but.............Especially tha "production" motor.

Prop size?

Also keep in mind that tha idle circuit is just that . Once off idle just tha slightest amount it goes away.

 

[DHag]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

As for tha exhaust. On tha Merc its not that big a deal. Its totaly different from tha motorcycle world. About tha only thing tha exhaust is "tuned" for in "production" motors is tha bottom end. Its done with tuner lenght mostly. 150's usually have a very long tuner. You can change it to tha short 200 tuner and see absolutly no change in anything except a small bottom end loss. It will idle a little different but its because tha shorter tuner is not buried in water. A jetting change is not necessary on any exhaust change on a "production" motor.

But you're nailing exactly what has happened here. The guy drilled 6 3/4" holes through the outer cover and into the exhaust tuner, above the water line. That's the equivalent of a 1-1/2" open pipe, which on a 2-liter 2-stroke basically means he removed ALL tuning affect from the stock exhaust.

If, as you say, the exhaust is "tuned" for the bottom end, that pretty much destroys all bottom-end tuning. Thus the jet changes, rather than admit he screwed up with the exhaust. I just figured out an easy and inexpensive way to close it back up.

Very seldom needs a change even on tha stem winder hot rod either. I've seen cases where a motor has ran for a coupla years without a tuner at all.

But the primary outlet would still have been under water, right? Under water = back pressure. At least at idle, the can should be acting as a larger-sized chamber.

Prop size?

My Hoss 3-blade is 14" X 21". When last I ran it, the engine revved to 5300 rpm and the boat ran 51 mph. That was with the extra weight of rotted, water-logged stringers; a big, uneven, rough, badly-finished patch on the port side of the pad; bad ignition boxes; weak shrouded spark; and a bent prop shaft....

My Piranha 4-blade is 14" X 19". I got it after I had the prop shaft straightened, and saw some damage on the Hoss (still to be repaired). The engine would rev to 5500 with it, but top speed only got to 46 mph. The motor was running stronger after a lot of tuning, but the boat was heavier after more leaking.

The book specifies WOT range as 5000-5500. But a guy intimately familiar with my setup says Champion found that both motor and boat were much happier at 5800-6000. (His father and grandfather both worked for Champion before it was bought out by other companies. His grandfather had the exact same boat and motor I have. Same year, same model, same color. But I digress.... ) I'm bettin' when I finish the boat rebuild, and it's a hundred pounds lighter than stock, smooth hull, and properly-tuned, the Hoss prop will be perfect, and the Piranha will need blades another couple inches steeper.

Also keep in mind tha tha idle circuit is just that . Once off idle just tha slightest amount it goes away.

That's good to know.

My main issue is that at idle it gets all loaded up with excess fuel, or I should say, extremely rich mixture. It's so flooded out that it won't come out of the hole without opening the throttle gradually. So I need to address the idle circuit, AND play with that bottom-end timing.

 

[Dukedog]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

My main issue is that at idle it gets all loaded up with excess fuel, or I should say, extremely rich mixture. It's so flooded out that it won't come out of the hole without opening the throttle gradually. So I need to address the idle circuit, AND play with that bottom-end timing.

Think your on ta something there.............but like said before. These things do not like idling trimed on tha way in even when perfectly tuned. Level or a tad positive is always better......Ya just gotta remember where its at when ya hammer it!

Loud always brings on tha false impression of faster to most folks with these things. Put tha exhaust ta bed and don't worry about it. Tha motor will be a lot happier at 6 grand but ya gotta take all things in. Weight, offset, propshaft depth, type prop (over hub/thru hub), gearing are all determining factors. Its a little vertical reed 2.0 motor that doesn't make a lotta torque.............

 

[DHag]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

Level or a tad positive is always better.

One day I was out with it and it would barely get up on plane. Found out it was the timing had slipped somehow. So I went through the process. Again. I've been setting the ignition timing "by the book." But it's a strange process. You probably already know that you have to turn the crank so #1 piston is set a particular fraction of an inch down before top dead center (I put a depth micrometer in there best I can.), then set the timing marker on a particular degree on the flywheel. Downright goofy.:facepalm: I'm gonna try to translate that to a way to start at "top dead center" using a piston stop, then make a permanent timing marker. Much more precise.

So, are you saying that stock timing, or a little advanced, is best for these? How many degrees before it's too much?
About 5? (Just asking for starting points.)

Ya just gotta remember where its at when ya hammer it! .... Tha motor will be a lot happier at 6 grand but ya gotta take all things in. Weight, offset, propshaft depth, type prop (over hub/thru hub), gearing are all determining factors.

The boat is 1050 lbs empty, stock. When I'm done rebuilding using foam instead of wood for the stringer cores, some math says it'll be about 950 lbs. The motor is about 375, so total weight with motor, half-tank of fuel, and me will make the whole package about 1650. Not very heavy for 150 horses. That's just 11/1 weight/power.
The boat came with a riser plate on the transom that my classic Champion friends have told me puts the prop right in the sweet spot. The transom/stern already has built-in set-back that they tell me is spot on for best performance. Of course, it's thru-hub exhaust. Gearing is 1.7.
I realize it won't launch like a car with the same weight/power ratio. But it should still come out of the hole with some gusto.

Loud always brings on tha false impression of faster to most folks with these things. Put tha exhaust ta bed and don't worry about it. Its a little vertical reed 2.0 motor that doesn't make a lotta torque.............

Yeah, like Harley owners. Even with 4-strokes, these guys don't realize that louder is actually hurting their performance and cutting gas mileage. But it "feels" stronger 'cuz it's loud.
Oh, I know I fixed the exhaust when I put those bolts in it to plug the holes a couple years ago. MAN, that thing was loud before that! Anyway, I'm not touching the exhaust. It's stock. Just trying to figure out what a previous owner had in mind, and what he did.

 

[ENSIGN]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

Check the output voltage of the stator windings.A weak high speed winding will cause it to bog and stall.

 

[Dukedog]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

Do tha timing just as tha book says. Your flywheel should have tha .462 mark which is where ya end up. Are you using a dial indicator ta get tdc and your .462 mark? There is another way but its not necessary for your motor. Set idle just like it says. Then put it in tha water, in gear, adjust idle timing screw until its happy. You will see what I mean when ya do this. Unless someone has changed tha gearcase it should be a 2 ta 1. Its standard for ALL 2.0 motors. Thats what tha little motor needs. If its not that will be contributor ta tha poor hole shot. Other than tha 3 liter all production V6's came with 2 ta 1, 1.87 and a coupla 2.3 something ta one for high altitude. Only type of case for these V6's that would be 1.78's are tha XR4 and XR6 (early model). They are easy ta spot because of the size hub. Its a small 4 1/4" and only 4 intake holes on each side. You're gonna find out about "set up". Things that work on similar boats might get ya in tha ball park but may not be what "yours" needs. These things are worse tha women. There are no two gonna be tha same........

 

[Chris1956]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

Just so you know, the .462" mark and procedure are designed to set the timing on the leading edge of TDC. TDC represents a few degrees of flywheel movement as the piston stops on the way up and sits for a bit, and then starts on the way down. Using the .462 procedure eliminates the slack in the timing.

BTW If your idlejets are larger than stock, that will cause the motor to load up at idle. They only used non-adjustable idle jets on a few year's motors. Maybe there was a reason.

 

[Dukedog]

Re: Rich idle, bog, no hole shot. Reeds? Coils?

BTW If your idlejets are larger than stock, that will cause the motor to load up at idle. They only used non-adjustable idle jets on a few year's motors. Maybe there was a reason.

Gotta disagree with this Chris. Tha fuel amount at idle never changes. Tha idle jets are strictly "air". Increase tha air and ya go leaner also increases idle speed. Smaller makes it "fatter" and sloppy. All V6 merc/mariner carbs have this same system but tha wmh and wmv's in later years did add a "screw" that can be tweaked on a little...........

 

[christianfreiss]

Whatever happened to your motor? Did you get it running right?

 

[GA_Boater]

Whatever happened to your motor? Did you get it running right?

He disappeared.

Closed.