1978 Mercury Black Max V1500, Surging at high throttle.

[NateDJ]

Greetings, So I have a Mercury 150hp Black Max that starts great and Idol's great, but any thing over about 1/4 throttle and it starts surging and will not go over 3100 rpm, even in neutral.

So far I have replaced all electronics, Stater, trigger, switch boxes, all wires, Plugs, coils, Control Box And cables, Thermostats, Completely rebuilt all 3 carburetors, Rebuilt fuel pump and poppet valve.
Engine is running 125 PSI compression +/- 2 on each cylinder.
It doesn't seem to matter if the engine is under a load or sitting idle it still seems to do the same thing.
This is a "new to me" project So I am unsure where to even start.

When I picked it up I was told the engine had set for about 20 or 30 years If not longer Naturally everything on the outside of the engine was deteriorated very badly and had to be replaced.
Any help is greatly appreciated.

 

[NateDJ]

Here is the other side of the engine

 

[Texasmark]

I didn't notice a fuel filter included in your activities, nor replacement of fuel lines. Pull your fuel filter and cut it open. Tell us what you found and how much there was of it...picture.....

 

[NateDJ]

I didn't notice a fuel filter included in your activities, nor replacement of fuel lines. Pull your fuel filter and cut it open. Tell us what you found and how much there was of it...picture.....

Sorry, yes entire fure system was replaced except tank which was carefully cleaned.
I installed a new fuel water separator and filter and all new lines even new fuel tank filler neck.
Pre mixed to 50:1 with good fuel and oil.
All fuel lines on the engine were replaced as well.

 

[Chris1956]

Did you perform link and synch on that motor after replacing the ign components? If not you need to do so.

 

[Faztbullet]

Need to get rid of the automotive spark plug wires and get solid core back n there

 

[NateDJ]

Did you perform link and synch on that motor after replacing the ign components? If not you need to do so.

I have looked all over for instructions on how to do that and have asked around at several boat shops and have been told that that engine all you can do is make sure the carbs close 100% at end of the throttle and 100% open at full throttle, I have them all lined up and at closed throttle they are fully closed.
Any pointers on where to find instructions on this?

 

[NateDJ]

Need to get rid of the automotive spark plug wires and get solid core back n there

Interesting, didn't know there was a difference, see now I learned something new and am off to find some solid core wires.
Also after doing some testing last night I found that if I unplug the top 2 or the middle 2 sets of plugs the engine really doesn't run that much different, you can tell something has changed but all in all same symptoms. Unplug the bottom 2 and it will not even start. I find that ... interesting at the least, mean anything to anyone?
Running it at night I can not see any spark leakage from any of the coils or wires so I don't think it's that.
Will try solid core wires as well as rechecking all the connections to the trigger wires. I tested all the stator connectors yesterday as well as pathed out all the coil wires to make sure i put them on per the diagram, did not find anything that needed changed

 

[Chris1956]

Don't screw around, use Merc wires. You can get them aftermarket and save some $. Sierra likely makes them and they are likely avail in a lot of places.

You must do a link and synch. If boat shops tell you different, they are nuts.

You will want an OEM service manual. Succinctly, when the carbs are just ready to open the timing should be 0-9* ATDC. Max spark advance should be 21* BTDC. Throttle stop should be set to keep the throttle cable for forcing the carbs open. Idle stop should be set to allow idle at 800-900 in neutral, less if you can. Throttle cables may need to be adjusted to allow both throttle stop and idle stop adjustment.

 

[NateDJ]

Don't screw around, use Merc wires. You can get them aftermarket and save some $. Sierra likely makes them and they are likely avail in a lot of places.

You must do a link and synch. If boat shops tell you different, they are nuts.

You will want an OEM service manual. Succinctly, when the carbs are just ready to open the timing should be 0-9* ATDC. Max spark advance should be 21* BTDC. Throttle stop should be set to keep the throttle cable for forcing the carbs open. Idle stop should be set to allow idle at 800-900 in neutral, less if you can. Throttle cables may need to be adjusted to allow both throttle stop and idle stop adjustment.

Wires on order now, will try a few other places for the link and synch.
Will get back to you guys once that is done because it certainly sounds like a reasonable plan.
I greatly appreciate the advice!

 

[NateDJ]

Ok Link and sync done, wires, plugs and coils replaced.
Now to get a moment to drop it in the lake and test it out.
Any recommendation of where to get a good set of switchboxes for it?
The ones i have on it are new but from amazon and if this doesn't fix it I am thinking of replacing those, again.
Have already re-replaced the stator and trigger but sadly that didn't change anything.
Also re- rebuilt the carburetors. If anyone is interested in the files for a laser cutter to make the gaskets for these I would be happy to post them. I cut them using a cheep 3018 cnc laser cutter and some chipboard (single ply cardboard)
I also replaced the fuel pump with an electric one that provides 7PSI at 35GPH, basically several things went wrong and it became a cheaper option. I still have the old mech one if this doesn't work.

 

[Chris1956]

Gee, carb gaskets are cheap. Hopefully the gasket material is proper for the application.

CDIElectronics makes switchboxes and had ignition troubleshooting procedures.

The issue with electric fuel pumps is that if the motor stalls, and the fuel line breaks, fuel is continued to be pumped. That is a fire or environmental hazard. You really need some sort of relay driven off the stator so it will cut off if the engine stalls.

 

[NateDJ]

Gee, carb gaskets are cheap. Hopefully the gasket material is proper for the application.

CDIElectronics makes switchboxes and had ignition troubleshooting procedures.

The issue with electric fuel pumps is that if the motor stalls, and the fuel line breaks, fuel is continued to be pumped. That is a fire or environmental hazard. You really need some sort of relay driven off the stator so it will cut off if the engine stalls.

For reference:

https://www.cdielectronics.com/wp-admin/admin-ajax.php?action=cdi_spget&spurl=https://sharepoint.cdielectronics.com/Controlled%20Documents/Installation%20Sheets/IS-114-7778.pdf

Also, as to the gaskets, Yes I have used this material many times in many different applications with no trouble. Also I have the laser already and plenty of experience with Cad so it was actually easier than waiting on Amazon to deliver.
The fuel pump does come on and go off with a toggle switch so to cut the fuel all I need do is flip a toggle switch, the same risk occurs with the millions of electronic fuel pumps installed after the injection fuel systems were built and those operate at MUCH higher pressure so I'm not worried about the safety aspect, not that it is of no concern but that it is accounted for in the setup I have.
Also the fuel Toggle is not active until the ignition switch is in Run or Start which gives me a double out if there is ever trouble.

Thanks for pointing me in the right direction on the switch boxes, I was able to easily find the troubleshooting steps and part numbers etc with that! I attached the link for anyone else coming along needing this information as well.

Did a "Super Slo-Mo" 30 sec video using my phone of a spark tester inline on #1 cyl. I find that every 3rd fire is really bright then I get one really dim and one slightly brighter, changed to high idle (about 2kRPM on the mufs) and get the same thing.

Will update as I have more progress.

 

[NateDJ]

Here s the Slow Motion recording at about 2k rpm

 

[Faztbullet]

Get rid of the neon tester as does not show spark intensity, use a open air type like below...

Amazon.com: RGEEK Adjustable Spark Plug Tester Tool Automotive Ignition System Tester Flashover Gauge : Automotive

Buy RGEEK Adjustable Spark Plug Tester Tool Automotive Ignition System Tester Flashover Gauge: Spark Plug & Ignition Tools - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[NateDJ]

Get rid of the neon tester as does not show spark intensity, use a open air type like below...

Amazon.com: RGEEK Adjustable Spark Plug Tester Tool Automotive Ignition System Tester Flashover Gauge : Automotive

Buy RGEEK Adjustable Spark Plug Tester Tool Automotive Ignition System Tester Flashover Gauge: Spark Plug & Ignition Tools - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Hmm that makes sense I guess, so the Neon one basically sux then?
The adjustable one can help me determine the actual power of the spark generator by the distance it can jump, from my research. Sound right?
On order now.

 

[NateDJ]

Replaced the switch boxes now on the hose or in the water in neutral it sounds like one would think it should.

 

[NateDJ]

However in gear it doesn't have the power to push itself up on the traylor and in open water runs about 6 mph on the gps.
I have verified that the timing is correct and all carbs are working and in sync.
I removed the electronic fuel pump and reinstalled the rebuilt mechanical fuel pump with all new hoses, gaskets, check valves, filters, etc. Same situation.
Verified timing under load, 22* BTDC.

 

[Chris1956]

Does the engine rev up, or just run at just above idle? 6MPH is probably somewhere around 2000RPM, on most boats. Do your RPMs exceed 2000?

If so, the prop hub may be bad. if not, your motor is not making proper power for some unknown reason.

 

[Faztbullet]

How about vid when it acting up as motor can sound fine and rev up fine on 3 cylinders..