1988 Mercury 200 blackmax WOT low rpm

[speedman79]

Hey everyone -I posted about this in October but didn't get to many replies on the topic and I still chasing the issue...

I'm trying to find some good advice on diagnosing a problem with my 1988 200 mercury black max. I'm not getting full RPM at WOT - I know this motor should be capable of 5800-6000 rpm on my 21' Seebold eagle - I bought it without a water test - wow stupid I know. It starts an idles perfectly but will not go over 4400 rpm without trimming out the motor - still only gets 5000 trimmed high. I have a very common chopper prop for this size boat 14X24" with correct height and low water pickup. Others agree it should not be over propped - besides I'm off by way more than 200-400 rpm. I have completely gone thru the fuel system:

New poly tank
New fuel line all clamped with no air leaks
New water separater and inline filter under the cowl
Fuel pressure tested at idle 4.5 psi
Carbs cleaned/inspected found no issues/float height 1/16th below the gasket surface when inverted as per the Seloc manual
Checked compression - 125psi even all 6 cylinders
BU8H plugs

Nothing has helped the issue and I'm now wondering if its a high speed miss or timing issue? I talked to some local mechanics and to be honest they sounded like they knew less than I did so I refuse to pay for their hourly wage when I can swap electronics myself. I checked basic connections on the switch boxes/rectifier/coils - I cleaned them but they seemed ok. I tested coil resistance they were in spec @850-875 k ohms. My plugs looked new but I replaced anyway - never any fouling or water than I can see. The motor is not running thermostats which I don't think would cause this issue...I've also read that this motor uses an advance module that only gives more timing above 5600 rpm which I cannot achieve. Supposedly this can be removed and you can set the timing statically to max WOT timing.
I guess I'm looking for a magical diagnoses from someone who really knows Mercury 2.4's since I can't find any around me! I would hate to buy a stator and switchboxes to find a coil defective...I need a good place to start ruling out the fuel system - I never pulled the intake but the reeds all looked fine when I pulled the carbs.
Any advice is extremely appreciated.

-Tom

[davemvegas]

i am new at outbord repair but in last couple months i have been learning how they work by having my 200 in pieces looking for speed. but i would try running in water at wide open throttle if it wont go past 4400 rpms i would try pushing key in to activate choke if it is wanting more fuel it should breifly increase rpms if it does i would ckeck fuel pump.but all fuel problems i have had run great and just nose over and quit same as tank going empty. a dead cly sometimes is hard to hear other than a little shutter under load.the best way to check is to pull all spark plugs and get a spark checker from any parts store. adjust gap on tester to about 1/2 inch hook plug wire on one end and the other end to a clean ground have someone turn key and when motor is cranking over look for strong purple spark.check all 6 clys one at a time if one has no spark or weaker orange spark you will have a clue where to start.also while plugs are still out put spark tester on number 1 cly open throttle all the way hook timing light to #1 plug wire spin motor and check timing it should be about 20 degrees btdc.

[johnboy 88 vegas]

Step 1 is to remove the timing box and set timing to about 23* @ WOT and check the compression to make sure you dont have a bad cylinder. Step2 do what dave just said but also get a dva meter and check the stator for peak voltage. Really sounds like its dropping a cylinder or either its way lean or way rich so check the size of the main jets in the carb if everything else checks out.

[speedman79]

Carbs have stock jetting for wh46's -.056/.080/.082 and im at sealevel. Trying to find Eva adapter- still not entirely clear what the DVA does-freezes the peak voltage reading? How can I see if the stator drops voltage using a device that ...

[davemvegas]

my carbs are marked wmh on 1991 merc 200hp. idle air jets in front are .034 and main jets in bowl are.066 it would turn 28 chopper 6600 rpms on 20ft vegas and as far as i know it was a unmodified motor. so what i am wondering is what is the difference between wh46 and wmh carbs that would cause such a big change in jet size on same size and hp motor.

[speedman79]

I was wondering why the wh46's seem to be so far off from most other V6 carbs too. Per the seloc manual carb specs it's stock though.. I just reread most post and realized that I left out some troubleshooting I already did... I did verify spark on all six cylinders but only on land not at wide open throttle - I really can't see myself running the boat on li sound hanging off the back with a timing light- maybe on a calm lake but thats not where I'm running... Way to heavy a chop for that! Can anyone explain in a little more detail how/what the DVA does diffently than the multimeter? Also my voltage at the battery is high- 15.5volts! Jay from jsre said thats way to high - others have said mercs run high like that normally... I think it's high but not sure if that means the rectifier or voltage regulator of do I change both?

[transomstand]

Static tests with a multimeter will only show short, open, ground, or high resistance. DVA readings are more "real world", and show actual voltage being produced. DVA can also be tested on high and low side, so no reason to risk life and limb running wide open hanging over the back of the boat.

The charging issue may, or may not be related, but 15.5 does not give me any great concern.

If oil injection is already removed, trash those idiot timing modules, they're nothing but a problem, and have ruined many good engines. Run timing and synchronization procedure, set max timing to 22 degrees. My bet is that will solve it.

[speedman79]

Thanks for DVA explanation. Yes the oil injection has been previously removed by an old owner -supposedly the the motor was rebuilt within the last 10 years so maybe it was done then. Many things have been modified on this engine which makes it harder for me to know what the stock setup should look like... The original airbox is removed and there are velocity stacks mounted instead - from what I have seen the advance module/ idle stabilizer is usually mounted on the air box. I found drawings in seloc manual of different modules and it seems to be on the port side of block behind the flywheel. My problem is that ive seen voltage regulators on eBay that look exactly like it so can't identify which module it is-'it may already be removed... My rectifier is on the side of the motor as normal- then there is a small square box with only two wires attached to lugs (red/white) dead center on top of the block behind the flywheel. Then the mystery module is next to it- about the size of an iPhone- lol. It also never had a flywheel cover so I bought one but I need to calibrate it and need to get a dial caliper to find true tdc. Could the timing hold it back by 1000 rpm? I guess if it was really off.... Thanks again for the reply- if anyone has pictures what this motor should look like or the actual rectifier/voltage regulator/idle stabilizer please share!

[transomstand]

Shoot some pics of that thing so we can see what's there.

Yes, low timing could cost 1000 rpm.

[speedman79]

Will do this week - I'm not home today. Is timing the motor without it running acceptable and accurate ? I wonder the advance module was removed and never properly timed.... That would be nice!

[transomstand]

Is timing the motor without it running acceptable and accurate ?

Yep..

[XstreamVking]

Just had the same issue with my 2.5 efi. Lost some r's at the top. Pulled all the black boxes off and now it runs great. Connect the white w/black stripe wires from the switchboxes together. Check out thttp://www.biggerhammer.net/mercury/ the timing process is detailed here by jay smith. Good info on lots of things mercury...

[speedman79]

Ok, I identified the advance module (93772a 2 -high speed control assembly) on top of my port side of the block. Should I check timing with it connected first then compare with it disconnected to check for malfunction? I am waiting on a DVA and borrowing a dial indicator for the pointer alignment to TDC. Any tips on finding true TDC I've never done it on a 2 stroke outboard - on my old Bronco I was able to ballpark TDC on cyl 1 and just dropped in the distributor, this needs more accuracy since the flywheel cover/pointer is not stock to this motor. Also what is the .462 mark for if .150 is 25 degrees?
XstreamVking can you elaborate on your post "Pulled all the black boxes off and now it runs great. Connect the white w/black stripe wires from the switchboxes together." I wasn't sure what needs to be done if I remove the module beside retiming...

[blowitup]

This might help you you.
http://www.screamandfly.com/showthread.php?244423-2.5-Timing-done-properly!!

[speedman79]

Thank you - I have seen Jays method and will definitely use it once I'm clear on how to properly disconnect the black box module. I have a feeling my motor may have had a separate idle stabilizer that was removed - all I have is a high speed module. Anyone aware of any mods that are needed when removing the blackboxes besides re timing. Any jumpers needed?

[speedman79]

Not sure where everyone lives - but I'm in NY and with Christmas and snow around the corner I needed to throw in the towel for this season and close it up till March... I did check ohm readings on my stator high side 60ohms, low side 8000 ohms... The low side seems to be out of spec. Stock stator calls for 6000 and CDI units 2250 ohms. I plan to change it along with the trigger and rectifier since the insulation on the wires is "mushy" (wires inside seemed ok though).

One thing I could use some input on is jetting. The only mods that I know of are drilled exhaust (uses a bob's exhaust add-on to relieve exhaust above the plate) and bob's velocity stacks on the carbs. Should jetting up be necessary for these add-ons? I'm thinking I could be running slightly lean. I have quickly "choked" the motor at WOT and it bogs rather than speeding up but maybe it's just too much fuel that way.... Currently my WH46's are running stock jets at sea level .056's and .080/.082's.

Thanks - I want to put a checklist of troubleshooting together for the spring.

So far:
-Remove advance module and retime to 22 degrees WOT
-Replace stator/trigger/rectifier
-Adding thermostats
-Possibly jetting up if issue not found
-Prop down to 22 pitch till I find the issue

[johnboy 88 vegas]

You need to check the stator with a DVA meter which is the only reliable source cause an ohm reading can lie to ya sometimes. On the jetting you need to run it down the river wide open and shut it off and check the sparckplugs to see if they are charcoal brown. White means lean and wet/ black is rich or not being burnt.

[speedman79]

I've been busy with work and winterized the motor so DVA test will need to be done in March when I unwrap it again... My plugs always look "clean" not brown, white, wet... This is after idling all the way back to the ramp and flushing in my driveway though. If anything they have a slight wet fouling. Your talking about running flat out and then immediately shutting down to read plugs right?
How high should my motor be for this boat -it's similar to 21 superboat or challenger. I thought it was right but I'm starting to think it's low for a chopper prop. The cavitation plate is above the pad but only by about an inch. No jackplate. I've read that streams usually run the propshaft at pad level... I doubt I could go that high and be able to plane off with out crazy cavitation.

[200VEGAS]

wow, thats a gift. thanks mr xstream.
www.biggerhammer.net/mercury
and thanks to the authors. i love this place

[speedman79]

Good link - second time that was posted in this thread! LOL
Any input on engine height?

[speedman79]

I posted this in another thread too so your not crazy if your reading it twice!
Finally got the boat unwrapped and ready to start trying to diagnose this ignition issue. It's been a while - so my issue is a high speed miss ( I believe). I will take off the high speed timing module and try testing the stator and trigger with a DVA. Still not 100% on how to do this when I can't operate the motor at WOT in my driveway on the hose... I figure up to about 3000 rpm for a short period of time should be ok to get a reading. Anyone want to throw their 2 cents in here...?

[Allaaan]

How did it all end up, did you get that last 1000rpm finally, and if you did, what was the problem? Was it timing? Im having the same problems as you once had, so if you see this, please take your time to reply and let other people with similiar problems know how you fixed it :)

// Allaaan

[speedman79]

How did it all end up, did you get that last 1000rpm finally, and if you did, what was the problem? Was it timing? Im having the same problems as you once had, so if you see this, please take your time to reply and let other people with similiar problems know how you fixed it :)

// Allaaan
allan it's been sitting on the side of my house for the last two years... Had my first child and had no time for boating last year. I'm picking up where I left off now. I'm leaning toward a stator but I'll keep you posted. Your post is pretty old at this point - if you had a similar issue and resolved it since please share your fix as we'll!

[j_martin]

allan it's been sitting on the side of my house for the last two years... Had my first child and had no time for boating last year. I'm picking up where I left off now. I'm leaning toward a stator but I'll keep you posted. Your post is pretty old at this point - if you had a similar issue and resolved it since please share your fix as we'll!

Just read this thread. Here's my thoughts.
1. It's summertime. You need a camp fire. That Seloc manual would be a good fire starter. Get the factory manual.

2. The ignition currents in these things are fast rise, radio frequency stuff. The only things that can display the information in a way that's useful for diagnostics is an oscilloscope, or a peak reading meter (DVA). The DVA is by far the easiest and least expensive way. Scopes are for us burned out EE's with nothing better to do, but it is fun to see things as they really are.

3. Fuel is critical. If you have 2 year old gasohol in that thing, drain it out. Use it to help start the above said fire. Most of us run "unoxygenated", ie alcohol free gas in these things. It doesn't separate and has decent octane, making top end timing less critical. It's more expensive, but much cheaper than parts.

4. Check the simple things. The fuel bayonet, for instance, should either be bypassed, or be the mercury metal one. The Atwood aftermarket replacement fuel bayonets won't pass enough fuel to run your engine at WOT. (Verified personally with pressure testing.) Get a DVA and verify that the stator is indeed in spec. Ditch the add on timing modules. They seldom work right, and sometimes will go full zero bias and grenade the engine in a heartbeat at WOT. You may be lucky and have an advance module that's going full bias at 5 grand. It's common, and the symptoms would be just what you're seeing. Don't forget to give the high voltage parts (6 short spark plug wires on this engine) a good inspection. They get pretty stressed out at high speeds and performance.

5. It's been over a year since it's floated. Throw a kit in the fuel pump. It's much less expensive than a perforated piston. Likewise, it would be good to put an impeller in the water pump, and check the rest of it, replacing warped housings, scored base plates, etc.

6. Running cold can make these engines seize up. The only engines that should run without t-stats would be all out competition engines that only have one running speed, ie flat out. Then they need precisely sized washers and the cooling verified. Cooling is critical. Your engine will go from stone cold to operating temperature in 20 seconds at idle. BTW, you should wait for that, verified by the tell-tale stream before you can the throttle.

7. If you verify decent compression, get good gas in it, get good fuel delivery, get the Link-N-Sync right, and it still balks at WOT, you may be dealing with what some of us have seen in used engines. Sometimes an ace (usually spelled with a double S) will decide that the Mercury factory doesn't know anything about carburetors and drill out idle ports or some other foolishness. Sometimes they do it to try to run E85. It might be worth trying a different set of carbs.

BTW the answer to your jetting question (last year) is that although the WH carbs all take the same gaskets and valve parts, they vary widely in internal porting. Always start with the jetting setup for the carburetors you are working with, then go from there. Some engines, yours is probably among them, will need a slightly different set of jets on one or two cylinders. That's pretty easy to figure out using a bit of common sense and the original specs for your engine.

Keep at it. The folks on this board are among the sharpest Mercury troubleshooters on the planet. I bought an XR4 that ran rather lousy, and with these guys help shot out about a dozen faults that a "certified" Mercury mechanic had installed maintaining it. I had to go buy a steeper prop because the engine then would over-rev. That 27 year old engine still turns heads when it's screaming.

hope it helps

[speedman79]

Firestarter LMAO.

I agree Seloc is not good... and covers too many motors to really give any details about my specific motor. I do trust that its data is correct for stock jetting for my carbs, etc. The jets don't appear to be tampered with but who knows...

I did follow normal maintenance before throwing it in the water:

Head gaskets - just because I wanted to...
Water pump
Fresh 93 Octane /Quicksilver Oil - I did not run old gas
I directly connect fuel hose to the carbs - no bayonet
New BU8H's
I do run t-stats-143 degree
I currently disconnected the high speed advance module so timing will be low around 18-19 degrees.

I didn't think to do a fuel pump kit but it WAS pushing a solid 4.5 lbs when I stored it. When I DVA tested the stator on the high and low side it was within spec but I will be testing it again and recording my results so I don't forget the numbers... I will be testing for spark strength with a gap tester as soon as I get some time this weekend.
My one question is about the lync and sync - I see this come up over and over - I did the basic lync and synch (followed the Merc manual instructions Dave Strong posted I believe) but never was able accurately check timing - the motor had no timing mark / flywheel cover. I bought one but I have to go through the dial caliper to find TDC process.

Thanks for your input : I know I will have a beast of a 26 yr old motor when its all sorted out!

[j_martin]

Here's a mathematical truth (boolean algebra) that most folks don't realize. Boolean algebra is mathematical binary logic, ie true/false.

With any formula, if one of your inputs (assumptions) is wrong, the answer MUST be wrong. It cannot be right. Another way to say it is if you have perfect logic and a wrong input (assumption), the result must be wrong.

In diagnosis, if you guess an answer and it's wrong, all the following tests and procedures assuming that it's right are invalid.

In other words, till you set a timing pointer and check your timing, you have no idea what you have.

That said, not having a flywheel cover shouldn't slow you down unless you can't find a piece of coat hanger with which to fashion a pointer. I don't know where my flywheel cover is. A 40 amp cover won't fit under my clam shell cowl. The coat hanger pointer is a permanent fixture. I use a cheap digital caliper (depth gauge) for the pointer setting.

Time it my friend, then mess with mixture and throttle linkage. With 93 octane gas and normal compression, you can go at least 23 degrees WOT.

[transomstand]

In other words, till you set a timing pointer and check your timing, you have no idea what you have.


:iagree:

Also true in 2nd grade rithmitic, don't even need algerbra:D

With the advance module disconnected you could easily be 6-10° retarded at WOT, and would pretty much account for the rpm loss.


And speaking of retarded, don't eliminate the simple step of making sure the throttle plates are completely open, this happened to someone I know recently who lost about 1500 rpm:rolleyes:

[speedman79]

I'll definitely do that this weekend. I was afraid to up the timing because if it is running with a misfire or lean it would be lugging the motor even more...I was afraid of detonation.I'm going to test with a gap tester, dva the stator, and time it on Saturday. A friend of mine is going to come for a ride and give a quick shot of something in each carb throat to see if a cylinder is lean.

[speedman79]

Had a little time tonight for stator dva test and spark testing. DVA voltage was 130v on high side and 240v on the low side. I used the gap tester inline with the plug still in the motor and opened the gap about 3/8". With the motor idling - the starboard bank all had a very consistent bright purple spark. On the port side cylinders 2and 4 seemed to have a weaker spark not as bright... Also started seeing some arcing from the coil to the block until I closed the gap slightly and repositioned the tester. I started to get excited that the issue was a bad switch box but then cylinder 6 looked perfect.... Then I ran thru all the cylinders again and now even the starboard side cylinder 1 was completely erratic... I'm wondering now if things are failing once the motor heats up... How much of a gap should I be able jump without seeing a degraded spark? Those issues cleared up with lowering to a 1/4" gap (plus the plug still had to jump). I have to set the pointer and check timing in the morning. Here's what bothers me about the static timing: I recently sold my viper back to the guy that sold it to me and that merc 2.0 150 ran 18 degrees total timing at WOT with no module and it could easily spin over 6200 - I just cannot believe that my timing would be so far off that I'd be down 30% power. I'll check it cause I'm not retarded :) but my gut is telling me it's not the issue. If it is ...I'll be the first to tell you I was wrong and that you were right.... No one else thinks statically timing will help grenade this motor if it's running on three cylinders and already lugging? I've heard you don't want run 3-4k rpm range with the static timing route? My plan is to be very conservative like 18-20 if it's lower than that to start with. Going out tomorrow with a friend and a can of carb spray to rule out a lean cylinder to satisfy that question. I'll keep you posted.

[davemvegas]

you cannot do a spark check and get a real result if you have to gaps. pull wire off spark plug and connect to tester. connect other end of tester to ground.

[speedman79]

you cannot do a spark check and get a real result if you have to gaps. pull wire off spark plug and connect to tester. connect other end of tester to ground.

I thought that may be an issue. Then spark seems fine at least on the hose in the driveway...
I was not able to lync and synch the motor for the Saturday test run - since a buddy of mine was adamant it was fuel related I headed off with a can of carb cleaner and put my smaller prop on to ease the load on it. Same old story, spraying a shot of gumout into each throat during fast trolling 1500 rpm or 4000 rpm had no effect - if anything it just bogged it down more. I'm not sure if this just started but cylinder 6 was flooding pretty badly. I'm ordering gaskets and needles and seats.
On Sunday I did the full lync and synch and checked the pickup and max timing and it was pretty much right where it should be. 10 ADTC primary and 18 max. I moved it up to 20 max for now since I disconnected the advance module. I have a bad feeling I will go thru these carbs yet again and nothing will change but I need to do my due diligence... I'll go thru these carbs one last time before I unbolt this thing in the middle of the LI Sound lol. Then I'll get into the packs and stator...

[speedman79]

I timed the motor and it was stock settings 18 degrees total... Same issue so I'm going thru the carbs again. cylinder 6 was flooding at idle but this is new issue. I have another stator I'll be trying hopefully this weekend.

[dnelson964]

change the stator is my first quess

[speedman79]

I had an epiphany as I was rebuilding my carbs the other night (since one was flooding out cyl 6 at idle) and it was bothering me that these carbs look perfect, and if anything my motor seems rich not starving. Plugs are always clean or have some wet fuel mixture on them. I opened a separate post to look up my serial number which I have done countless times to determine the year but I could never get a definitive answer on the hp. The serial range is the same for all v6's for 1987/88. I had looked up the carbs in the past and they are 200 carbs so it all fit. This motor has no plate on the mid just a freeze plug stamping B279359. Well a couple of guys with the actual Brunswick lookup just told me it's a 2.0 1987 150..... Someone put wh46's on it and it's completely over carbed. Luckily I had a parts motor with Wh29's and stock jets so fingers crossed I'll be testing it this weekend with those. At this point it is what it is but I thought I'd share the story of a craigslist seller that either had no clue himself or completely f'd me over with a water logged boat and a misrepresented motor. If this is the fix I will be extremely - happy even if it isn't a 200.

[speedman79]

The saga ends, putting appropriate carbs and jetting and now it runs like it should. I will need to retime it to get full advance but it was turning about 5400 even with the timing low. Screams up on plane instead of a gargling struggle. It's ridiculous how long it took to figure this out but it's over. Thanks for all the input guys.