1996 Northstar blast mercury 120xr will not start

[Craig Guest]

Hi all

I have been doing lots of thread reading and see lots of issues with the sportjet xr but nothing seems to fit. I have a 1996 northstar blast with mercury sportjet 120xr engine. It has the cdm ignition system not cdi. I have replaced the reeds with boysen reeds, cleaned and rebuilt the carbs, replaced the trigger, rebuilt the fuel pump, and replaced the plugs gapped at .040. The stator puts out approx 12v ac when the engine cranks. There is spark at all 4 cylinders verified out of the engine and with a timing light. All 4 cylinders have between 150 and 155 compression. Basically the engine has spark compression and fuel, but no matter what I do it will not start. After reading a forum post about problems with the regulator, I bought 3 of the cheap mercury knockoff regulators the 5 wire kind 2 reds (jumped them together), two yellow and a gray. I replaced the regulator sprayed a little quick start in the carb and shockingly it started. I let it run for about 5 seconds it sounded pretty good and turned it off. I thought cool it's working. I tried to start it again and it fired right up. I went inside for about 15 mins to eat and when I went back outside, I could not get it to start again. Since the only thing different this time was to replace the regulator I tried to swap it out with the second. Still no start. I had a mobile boat mechanic come to my house to help diagnose it and have stumped him. With compression fuel and spark should it not start. He seems to think that it is the trigger but it was just replaced and had only been started once not even in the water before today. How fast should the engine be sparking at cranking speed. By the timing light it seems to be about 3 times a second. Does anybody have any idea what could be causing this problem. The battery reads 12.8 v at rest and drops to 11.77 at cranking. Please any insight that can be given would be really appreciated.

 

[Roger Ski Gapinski]

Hi, I have a 1996 Regal Rush with 120 sport jet for the past 17 years. It has always been very temperamental starting.
The things that have helped the most for me are:
1. Running the boat every 2-3 days
2. Using regular gas (no alcohol) with Stabil in it
3. Installed a water separator
4. Installed a primer bulb - pump till hard BEFORE trying to start. If bad fuel enrichner this will cause the carbs to flood however.
5. Check the fuel enrichner switch - when cold this helps provide fuel to carbs.
6. Not sure about gap on spark plugs - my shop manual says 030, but my mechanic set it to 040 I think.
I hope you have success in getting the boat running. Keep posting on your progress!
Good luck,
Ski

 

[RedBarron55]

The timing light should flash every rev. On each cylinder.
At idle the timing light should be at about 8 - 10 * btdc.
if you mark the flywheel 4 time 90 * the light should be on each cylinder as you go from top to bottom.
By the way the throttle plates need to be adjusted so that they are completely closed for the enrichment valve to work.
Check files I added to post above for the procedure for sync and link.
also google Force timing for information

 

[Craig Guest]

Hi all thank you for the suggestions it is very much appreciated. I think I may have found the issue the rev limiter. I disconnected the black/yellow wire to the rev limiter it fired right up twice in a row. Just in case it was the same issue as yesterday, I walked away for half an hour. When I went back it fired right up again. It's it still possible to get spark with a faulty rev limiter but not enough to actually fire the engine? How can you test the rev limiter. I already had another one ordered as well as another trigger and stator. I just might have some spare parts. Also I don't want to run it out of water without a water connection. I have the mercury flushing hose that connects to the top of the block. Is this the correct connection for running out of water or should I hook up a garden hose to the water intake or both? Again thank you for the insight

Craig

 

[RedBarron55]

Do not run the motor on the flush attachment that feeds the top of the block.
The dealer attachment goes in the line from the pump and the lower part of the exhaust manifold.
Google the Sport Jet cooling kit .
You can get the fitting at Lowes and adapt it to a hose connection.
Google some of my posts and other driveway cooling setups here and elsewhere.
The danger is that the filling of the manifold is not done from the top and the water does not flush the ride plate of fuel and sometimes the fuel that collects on the exhaust and ride plate ignites and blows the ride plate out.
Glad you found your problem.
The rev limiter cuts out the ignition randomly at speed and if it is doing that at starting speed it may not fire enough to keep running.
Replace the rev limiter and enjoy

 

[Craig Guest]

Hi again

Thank you I'll follow your advice. It looks like it is a standard flare fitting, do you know the size? On the ride plate, I decided to replace the ride plate gasket. When I was reassembling I could not get it flush with the hull on the port side at the front of the ride plate. It is flush on the starboard side and sticks up about a half an inch at the port side. I noticed the ride plate did look a little bent. Will it make a big difference in performance leaving it like this or should I remove it and attempt to straighten it. I have had this exactly a year and have not yet had it in the water. I have been doing all kinds of repairs and maintenance but I see the end is near. Thank you again and again

 

[RedBarron55]

The Lowe's fitting is the largest flare fitting that they have.
If the plate is not visibly bent then perhaps a large hammer and a block of wood?
If bent use the hammer and block of wood to straighten and flatten it.

 

[Craig Guest]

Just thought I'd give you all an update. Changed out the rev limiter yesterday and it fired right up with a water connection of course. Removed the ride plate and beat it pretty close to straight and reinstalled. It fit a lot better. One of the screws was stripped so I put it back in with jb weld. Hopefully this works our I'll be adding a heli coil later. Took the boat out on the water for the first time yesterday and it seems to be running really good. Going to go back out this evening for another test run. Fingers crossed. Thanks again for all your help

Craig

 

[Roger Ski Gapinski]

Great news! Hope it runs like a charm for a long time!