'75 Merc 1500 performance issue

[mikevr007]

I have searched forums and have compiled a few answers. But, I need to ask a couple of questions regarding the answers I have found.

I took my 1500 out to the lake. All I had done was rebuild the carbs and made the basic static adjustments. I did NOT check or adjust the timing (stupid...I know.) Anyway, it started ok, but I had trouble getting it into gear without stalling. Once I successfully got it into gear I could SLOWLY get on plane and was able to get the boat up to about 45mph at about 4800, or somewhere there abouts. It wasn't running well and was very irratic.
After getting it home, I checked and adjusted the timing (its was WAY off, over 30 degrees advanced!) and readjusted the carbs and distributor linkage. It started much easier and idled better. Once out to the lake again, I still had trouble getting it into gear without stalling. Once I was able to get it into gear without stalling it accelerated just off idle but then quickly dropped off and would not go over 2000rpm. It would absolutely NOT go above that.
Now...the answers I have found to that particular problem are: the trigger or the high speed stator wires. Finally, my questions.
IF the problem is either one of those, why could I get on plane and have atleast some performance when the timing was so far off, the first time on the lake?
Also, is there are another name for the "trigger"? I can't find that part by that name. Of course it could be I haven't looked hard enough.
Thanks,
Mike

[Superdave]

Distributor motor or ADI? 30° advanced :eek: good thing it wouldn't run, you would have smoked # 3.
Dave

[Raceman]

Dave, he said 75 model, so it'd have to be distributor if he's right about the year.

I'm curious as to how you checked the timing. How bout detailing it so we can be sure it's right. Also, I'm wondering if there's a possibility you got the carb adjustment out of whack with all the adjusting where they're not getting full open now. I haven't seen the kind of problems with triggers that you're describing on any of my stuff, but I've read posts by people who think they have, so I'll leave that to somebody else. I WILL say that there was a Merc dealer about 25 miles from here that useta' throw a trigger at every inline that didn't run right, then the local dealer here usually ended up fixin' the engine later.

Jeff Grigg is excellent at trouble shooting these engines (although he disagrees with the way I set my timing:D ) Maybe he'll be around in a little bit with some ideas.

[crazy horse]

Mike, The trigger in that engine is built into the distributor housing assembly, part# was A-393-373A23. If it's firing it's most likely not the trigger. You should pull the cap and check to see if the distributor shaft has any slop at the rotor . The spark should be bright and as wide as the center electrode on the plug. I'd do what RM said, You should start over and retime it step by step and make sure that the carbs are opening up all the way with no binding and very little slop.

[mikevr007]

Raceman, I used your method to set the timing. I set the butterflies on the carbs (by "the book") when I re-installed them after putting kits in them. I know they are opening all the way. That's one thing I specifically looked at when at the lake. When I work them by hand they are very smooth. Everytime that I've started tuning at the lake, I set the mixture screws to 1-1/2 turns out so I know that I am starting from the same point each time.
Other details...
-New plugs
-New wiring harness
-Fuel pump kit
-New battery
-I did not replace the floats, but I may have to as the carbs drip fuel, especially the top one(even while running). Unless someone can give me some advice on adjusting them. I followed "the book" when I installed carb kits. The old floats weren't cracked.
-When I was checking/setting the timing, I thought the spark was pretty strong, but your description crazy horse leaves me wondering. The spark certainly wasn't as wide as the electrode.
-I did not check the spark at all the cylinders. It was obvious at the lake (and on the hose) that they are all atleast firing.
-After setting the timing to 20 deg. (after my first lake tuning experience), the motor would start at the bump of the key and idle very well on the hose.

And...the thing that really puzzles me, is why at 30+ deg. of timing, was I able to get the motor to actually run better at higher rpm than with the timing at 20 deg.????

crazy horse, I will check the distributor.

[crazy horse]

Mike, As long as you have a good spark all the time the trigger should be ok. What plugs are ya runnin? You should check the top carb if it's dripping after you changed the seat and needle, It might just be that the float is hung up on the post. I think I would get 3 new floats for it, set them so there perfect and be done wit em. It does sound like you have a timing problem to me. That might be why your stalling when you drop it in gear.

[transomstand]

You mentioned you have the carb needles 1 1/2 turns out. I have a 1984 90 horse inline on my Formula, it will not get on plane unless the needles are at least 2 1/2 turns out.

Pete

[Don's Marine]

It sounds very much like a switchbox gone bad. This is a good possibility, try another one you know is good if one is available.
Note: With the timing at 30 degrees advance, the engine should
really perform if everything else is O.K. (at least until detonation gets a piston)

[Mark75H]

Don do you really think that an inline switch box will cause an off idle/into gear stumble? I'd bet against it in this instance esp since we know that the carbs have been adjusted.

[Mark75H]

In the event that someone does need a new switch box Rapair is supposed to be shipping their latest batch of replacement switch boxes to their dealers this week.

[mikevr007]

Well, thanks everyone for the conversations. It really helps when you can read people thinking outloud.
What I am going to do now is:
-Double check/adjust timing
-Double check/adjust carb, throttle, and advance linkage.
-Check distributor and rotor.

I would think that;
-if the timing is right and the advance is working properly, then the carbs will only need to be reasonably close for the motor to run reasonably well until I can fine tune it.
-if any of the ignition or control components are bad, then I wouldn't have been able to get the boat up to 45mph at mid-4k rpms when the timing was at 30+ deg.

Which now that I think about it...
-a timing advance problem would be worse at 20 deg than at 30 deg. And that's why I had more problems with acceleration after I corrected the timing. However, the distributor is turning with the throttle linkage.

Which leads me to ask...
-What would cause a timing advance problem if the distributor is rotating during acceleration? (other than a bad distributor)
-Does the throttle and advance linkage have to be perfect for the motor to run reasonably well, or atleast well enough for me to fine tune it? I've made alot of static adjustments per the manual. I would think that even if I didn't get it exactly right the first time that it would be close enough to run better than it is.

Thanks!

[Raceman]

Mike, the adjustments on the 1500 are critical for it to run right, not so much so at substained speeds, but especially on initial acceleration. Since the timing advance is completely mechanical, and easily checked, I don't see how "bad distributor" could enter the equation. Erick B has a 1500XS on a repro Raveau and had a lot of trouble with it and it ended up being the upper pulley on the dist. was worn in the key area letting it move around on it's own. I've never heard of that condition anywhere else, but he had an awful time finding it. Most of the electrical problems I've had with inline 6's have been go/no go, rather than poor run characteristics, so I'm probably no help if it does turn out to be electrical.

Have you run a compression test? I'd probably do compression and leakdown before you go much farther. What about lookin' at the plugs for signs of water? The inlines are prone to leakin' around the exhaust plate and nothin' will make one run worse than water injestion. I'm wondering if someone previously cranked the timing trying to bandaid another problem.

If he doesn't see this thread shortly, why don't you E mail or PM JeffG? He's real sharp on diagnosin' inline problems.

[mikevr007]

Hey Raceman...yeah, I did a compression test. I don't have the numbers handy, but I do remember that 4 and 5 were about 10 points lower than the rest. I think the range was a low of 115 to a high of about 130.
A couple of the old plugs (either 4&5 or 5&6) had rust on them when I put new plugs in. The motor had been sitting for well over 2 years. I've pulled the new plugs since running at the lake and I don't see any evidence of water, but I realize it can be really hard to see if there isn't much.
The distributor doesn't seem to be sloppy at all. But when I work on it again I will check out the distributor more carefully.
Well...if anyone can think of anything else please add it. Meanwhile I'll be going over it again.
Thanks!

[Don's Marine]

There is one other thing that you may have overlooked if your engine has the single fuel pump mounted on the lower cowl. The round plastic cover for the fuel filter is bad about cracking from the tightening of the retaining screw. I have found two in this condition on engines of my own. The cracks are hard to see unless the plastic cover is removed so you can see the inside of it. It doesn't take much of a crack to bleed in a lot of air in the incoming fuel. The two engines I found these cracked covers on both had pistons ruined from detonation or a lean mixture. I now install the early style dual pumps and discard the single pump. The pump itself would be o.k. if Merc had made the filter cover out of metal instead of plastic.

[Raceman]

If it's a 74 or newer engine it would have the single pump on the pan. I asked my friend who worked at Merc for years, both in warranty and later as a service school instructor why Merc got away from the two pumps on the side of the powerhead. He said that in some cases they caused vapor lock problems, especially on the black engines. If you want to eliminate the pump and supply side of the fuel system, put an electric pump to it regulated to about 4 PSI, but based on your description so far, I'm kinda doubtful it's fuel unless somebody made big timing changes trying to fix another problem.

Mike, assumin' you've got a good guage and technique, I'd say the compression is bordering on gettin' low and the rust on the ones that show it are troublesome too. You might've even defined the problem with 2 cyls being low if the same are rusty. I still think you should E mail JeffG and see what he thinks. He's really good with inlines and does it for a living.

[Don's Marine]

To Mark 75H,
I agree that it may not be likely that the switchbox is causing the stumble off idle, usually it is the idle circuits too lean or dirty or insufficient timing advance before throttle pick-up. After reading about the rusty plugs, it now makes me suspicious of water leakage under the exhaust gasket or a crack allowing water in. It is hard to diagnose a problem by without hearing or seeing the engine run, hard enough when you can see it & hear it run. The problem could be something simple, like no ground wire from the block to the distributor. I mentioned the switchbox because They can cause all sorts of problems, not always the same from day to day.

[davidroland]

Hi Mike and others!
I also have a 1975 1500 sn#4123701 . mine at its worse sounds like yours after you got the timing set right.
I do know from my work with formula car engines with webers and o2 sensor for mixture info that you can run timing way high and hide a rich mix with out detonation ect and decent performance--not a good thing for lots a reasons--mileage and max hp mainly-probably carbon to.thats 4 stroke but might explain your situation.

i also had decent compression with only 10psi variation(or less)
and around 140psi

after setting and checking things lots of times(off and on for years!)we finaly decided the exaust must be carboned up--off with the cover--clean-very little carbon
while the cover was off i took a strip of popcicle stick and pushed on the rings through the exaust ports to check the rings tension--ha --the rings are stuck!(all but 2)rebuilt the engine--the bore was barely in re ring limits.

now it makes more power but has same problem.
compression is only about 10psi better with almost no variation.

kept hopeing it was rings not seated but after 80+gallons and lots of checking-rechecking the pump the carbs and timing and syncro and other stuff its only a little better.

the way i found out mine was rich was with a large pair of hemostats pinch off the fuel line one notch at a time and run it--it got better and almost perfect but would go lean at top end.be carefull if you do this--at the first hint of lean let loose of the fuel line imediatly!!

now if we can only figure out why its rich and fix it!!!

what jets and altitude do you operate at?

i have been posting under i6 float level

Raceman--where can i find you timing and syncro info?

i do have a spare power pack(switchbox?)that im going to try but after that all i can do is lean it down?what about the stator?have read somewhere it can cause problems--how to check?

[Don's Marine]

davidroland
you may have floats leaking though enough to cause the rich condition. If you have the original needles & seats in the carbs, the seats have very small o-rings that shrink & leak over time. The replacement parts I use have the Viton tips on the needles & solid seats which eliminates this problem. You may also just have too much fuel pressure if you are using an electric boost pump in the system.

[Mark75H]

The stator has nothing to do with the ignition on a Thunderbolt distributor I-6 ignition

(other than keeping the battery charged)

A bad stator can affect an ADI 6 coil I-6 because the trigger pulse comes from the stator.

[mikevr007]

Very interesting stuff, though I must say that I'm not getting very optimistic.

The fuel pump kit came with a replacement top, it is metal, and yes the old plastic one was cracked but not cracked through.

Someone asked what spark plugs I used. I used whatever the shop manual recommended.

Raceman, I have a brand new gauge and I removed all the plugs on a cold motor and turned the motor over about 4 or 5 revolutions for each cylinder. I did not do a leak down test.

I've read in a post here some tips on sealing the inside water jacket cover (or whatever you call it). It seems I remember that it was said that it can be a troublesome repair. Something about the surfaces not being square or true or flat or something. I bought a complete gasket kit in anticipation of doing this, I was just hoping I could get atleast one summer out of it before doing it. I've finally finished a two year rebuild of the boat and trailer and the only water they've seen is three unsuccessful tuning trips.
My main problem at this point is money AND time. I've put alot into the boat the trailer and the motor, way more than it's worth. Though on the other hand, I'm not about to pay thousands more for a new(er) motor. I'll buy a new boat first.
Anyway...I'll keep plugging along.
At this point would ya'll agree on these points before bothering to continue tuning?
-Repair possible exhaust/water jacket leak.
-Hone cylinders and re-ring pistons.
-Then base adjust everything and start tuning again.

It's obvious that this motor has been apart. NONE of the numbers match and the LU is from an older motor (according to someone that should know).

[mikevr007]

One more thing...
As far as the rich mixture is concerned, don't the mix screws and the float control that? I would think that if they are in good shape and adjusted correctly that it would be almost impossible to run rich.

[mikevr007]

Ignore my last post on mixture...
There's another thread that explains alot.
Thanks,

[Raceman]

Since the motor's been apart, you might check the main jets and see if somebody's been foolin' with them.

[Jeff_G]

Been away from S&F a few days and..... Norris your check is in the mail.

Start at the beginning. Do another compression test after the motor has run for about 5 minutes on the hose.

Check the spark on all 6. You can get a spark tester at any auto supply. Get an adjustable one, set it at 7 18"

Check the dist very closely. Double check the pully, belt locations as per the book. Check for roughness or loseness in the dist. If you have a dial indicator you can index the flywheel and check. You can also check the timing static.

Check the jet size for the main jet. Set the carb at around 2 turns out, you can adjust it later. If you adjust it for a real smooth idle, turn it out 1/2 turn it is too lean.

The syncro between the timing and carbs is not critical. The pick up timing lowers the idle. You could even set the timing at WOT all the time and the motor will run fine but would idle way too high. The timing should go to almost full advance before the carbs really open. What you don't want is the carbs opening before the timing advances.

Double check the plugs for water. Then do it again. If it is cyl 1-4 most probably side plate. If #6 the lower seals. The lower seals are quite common on older motors. If the inner plate is all carboned over and no sign of water leave it alone.

Just a few starting points, proceed in a logical orderly manner and you will fine the problem. They are great motors that can be made to run very reliabily. Since yours has been into your motor may have had a hack job. Check and double check. Run BUHW plugs or L76V. Run good gas and oil.

If all else fails call 843 844-8739

[mikevr007]

Thank you Jeff, for your reply.

-When I adjusted the timing I did set TDC with a dial indicator.
-I am using those plugs.
-I am pretty sure the rusted spark plugs came out of cyl's 4&5.
-I did not pay much attention to the distributor. I will next time.
-I did not check the spark at all plugs, I will.
-I did not check the compression on a warm motor, I will.

I'll get my manual out and start at the beginning. Knowing what's critical and not critical will help tremendously.

Thanks!

p.s. I'll update this post for future reference.

[mikevr007]

Hey Jeff...
When I put the carb kits in, I adjusted the float level per the directions. I am getting fuel dripping, mainly from the top two carbs. I've read on another post that the person adjusted the levers so they weren't exactly level so as to raise the float and lower the fuel in the bowl. Do you know how critical that adjustment is? I was going to take the bowls off and bend the lever up slightly to accomplish the same thing.
Thanks,

[davidroland]

Hi Mike
have done some more checking on my 150--check my latest post and see if yours is doing same thing?dont have a soulition yet--just another peice of info