1988 Mercury 200 blackmax WOT low rpm

[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.

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

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

[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.