Mercury Sport jet 175 XR won't reach full speed

I recently purchased a 1998 Searayder F16 XR with the 175hp V6 and 139 hours. Here's the problem. The boat was running fine with a top speed about 50 mph, one day it just quit. Took to the marina. They diagnosed a bad inner switch box and replaced. The work order says "found inner switch box bad on kill circuit. Took it out, runs but not running well can't reach full speed only about 30 mph, took back to the shop they found there was no power from the outer power pack on green wire to #2 cylinder. It says "outer power pack R&R" but parts says switch box assembly. So far $1,800 spent and still not running right.

Took it to another shop They diagnosed both switch boxes are bad (defective)(from the work order) "The stator was totally dead on one side and erratic on the other Got different readings when the flywheel was moved back and forth. The voltage regulator was shorted from the stator on both yellow leads. It was shorted to the block"

They replaced both switch boxes, a trigger assembly, stator assembly, 2 ignition coils, and voltage regulator. Another bill for $1,187. The switch boxes were covered under a 1 year warranty from mercury.

Still can't get over 30 mph. $3,000 spent.

What else could it be? Anyone have any ideas?

Re: Mercury Sport jet 175 XR won't reach full speed

Nothing you posted on the services performed indicates a compression test which is the 1st thing that should checked on a SJ.

Re: Mercury Sport jet 175 XR won't reach full speed

I would have assumed that marine mechanics from 2 different dealers would have checked this. One a Searay dealer, the other a jet boat "specialist". In fact I suggested a problem like this and one said it couldn't be because the boat ran so well otherwise. I will check myself I guess. Before the initial problem the boat was running fine, topping out at 50 mph, then just died on the water.

Re: Mercury Sport jet 175 XR won't reach full speed

I sub-contract labor to several dealers and you would be surprised what other technicians will "assume".

Re: Mercury Sport jet 175 XR won't reach full speed

Like Fazt has said, the very first thing to check on ANY 2 stroke is compression, if any cyl fails to make correct pressure the motor cannot perform. Period

If compression passes then follow with a spark test. Any suspicion here we then pull out the DVA meter to find out exactly what component is at fault.

Your 'shops' have replaced the entire ignition system, at tremendous expense, and there is no way to tell now which, if any, of these parts may have been good/bad, unless you collected ALL of the old parts and someone takes the time to re-install them for proper testing.

After both compression and ignition are confirmed the fuel system is to be cleaned, inspected, tested to ensure full fuel flow as available. Carb linkage and ignition timing are adjusted to spec.

I highly recommend you invest in few tools
Compression tester
Spark tester
DVA meter

And most importantly, a factory service manual

Check these links to see if yours is available for download

http://1manual.com/Mercury manuals/Service_Manual_Index.html

http://forums.iboats.com/showthread.php?t=309079&p=2072211#post2072211

Re: Mercury Sport jet 175 XR won't reach full speed

I'm going to check compression today, what throws me is that the boat was running perfect at 50mph the day it died. I'll report back later today with what I find.

Thank you to all for the help



]Like Fazt has said, the very first thing to check on ANY 2 stroke is compression, if any cyl fails to make correct pressure the motor cannot perform. Period

If compression passes then follow with a spark test. Any suspicion here we then pull out the DVA meter to find out exactly what component is at fault.

Your 'shops' have replaced the entire ignition system, at tremendous expense, and there is no way to tell now which, if any, of these parts may have been good/bad, unless you collected ALL of the old parts and someone takes the time to re-install them for proper testing.

After both compression and ignition are confirmed the fuel system is to be cleaned, inspected, tested to ensure full fuel flow as available. Carb linkage and ignition timing are adjusted to spec.

I highly recommend you invest in few tools
Compression tester
Spark tester
DVA meter

And most importantly, a factory service manual

Check these links to see if yours is available for download

http://1manual.com/Mercury manuals/Service_Manual_Index.html

http://forums.iboats.com/showthread.php?t=309079&p=2072211#post2072211[/QUOTE]

Re: Mercury Sport jet 175 XR won't reach full speed

Hello;

Thanks for the suggestions so far. I did the compression test and all 6 cyls are 120 lbs. What would the spec be? If this is within spec any ideas on the what the problem could be?

Thanks

Re: Mercury Sport jet 175 XR won't reach full speed

Compression is fine.

Since the new ignition have you done a spark test to ensure a hot blue 7/16 arc to each cyl? Even a slight short/ground on the kill wire will impair the ignition and limit spark.

After you verify spark, move onto fuel. Disconnect the fuel hose to the carbs, pull the lanyard to kill the ignition, point the fuel hose into a suitable container and have a helper crank the motor while you watch the fuel flow. You should see a strong pulsed flow, any weakness will limit WOT power and RPM, and can cause upper carb to run lean to the point of melting pistons. Any weakness and you can suspect a weakening fuel pump, restricted hoses, or loose fitting allowing air to be sucked into the system.

Fuel pump rebuild kits are not expensive, just be sure to reassemble exactly as found, incorrect placement of valves will not work correctly.

Temporarily install a clear hose between the fuel pump and carbs, run the motor and watch for any air bubbles passing thru, showing air sucking into the line somewhere between the fuel pump and tank. Remember to remove the clear hose after repairs, it is not rated for marine use and is only for testing.

Re: Mercury Sport jet 175 XR won't reach full speed

Charlie, thank you for the help, I will pick up a spark tester and run the tests that you are recommending. I did find one odd thing that bothered me. When I went to pull the plugs for the compression test, 3 of the plugs were not very tight, with a wiggle and turn I could get loosen them with my fingers, no wrench needed. They were finger tight but obviously someone forgot to use a wrench.

You would think that if they were loose enough to cause a problem I would see fuel /oil residue on the cylinder or on the wall behind the engine?

Thanks

Mark

Re: Mercury Sport jet 175 XR won't reach full speed

Slightly loosened spark plugs will eventually leak and build oil around the spark plug, the more noticeable fault could be a poor ground contact affecting spark quality.

Tighten them properly and retest performance.

But check the fuel pump flow before hitting the water as a lean upper carb very easily could melt the upper pistons.

Re: Mercury Sport jet 175 XR won't reach full speed

Okay to further my tale of woe on my 1998 Searayder F16 with a 175hp Mercury Sportjet.

Put the boat in the water for the first time since having all these problems last year, visually checked the plugs and fuel pressure and both seemed good. Boat started easily and idled no problem. Got out on the water and WOT is only 4,200 rpm with a top speed about 32 mph.

What's next?

One thing, paid lots of money to have work done and one of the things was to replace the switch boxes. On the outside of the switch box on the starboard side of the engine there is a date 03 / 17/ 1997. If these were replaced should they not have a more recent date?

Re: Mercury Sport jet 175 XR won't reach full speed

Hard to tell about that date without seeing it, possible that it is a manufacturing date, but even that is stretching at.

ALWAYS ask for your old parts back, so you can see exactly what has been replaced.

Now, low WOT RPM can be caused by a few things,

1 Weak/low fuel flow/supply, weak fuel pump, restricted hose/fitting, dirty carb, test a coupoe things, while running at WOT squeeze the primer bulb, if the motor picks up any speed this shows still a lack of fuel supply to the motor. Next, just 'bump' the enrichener/choke, don't hold it, just a 'bump', if the motor picks up any at all this shows the carbs are not flowing fuel and still need attention.

2 Inadequate high speed stator/ignition voltage, unable to create a hot enough spark under full load/WOT. Test with a DVA meter using extra long leads so you can watch the high speed stator voltage at WOT. Repeat test on both stator lead to each switchbox as a low output to one switchbox will weaken spark to 3 cyls.

3 Excessive load on the motor. If this was a propped motor and some one replaced the prop with a different size/pitch, one a jet, this could still occur if someone has had the jet drive apart and reassembled with a new impeller and/or wear ring or changed the shimms that adjust the clearance between the impeller and wear ring.

I just re-read your original post, ran fine before it failed, so it is NOT a jet problem unless you have a bad bearing causing excessive drag. Just for giggles, remove the spark plugs, pull the lanyard so it will not spark, crank the motor. If cranking speed is normal then chances are the drive bearings are fine. Forget #3

Re: Mercury Sport jet 175 XR won't reach full speed

aikens said:

...............................visually checked the plugs and fuel pressure and both seemed good.............................................

Click to expand...

Fuel pressure alone cannot tell you if you have adequate fuel supply to the carbs UNLESS it is checked with the engine under full load at WOT when the carbs are flowing maximum fuel. Even a very restricted fuel hose/fitting can flow the minimum amount of fuel at an idle to create fuel pressure.

This is why FLOW is critical, disconnect the fuel hose to the motor and SEE if the fuel is a STRONG pulsed stream the diameter of the hose and at least spurts out an inch and a half or more, any less and that motor will starve, start to run lean and melt pistons in the upper cyls.

Re: Mercury Sport jet 175 XR won't reach full speed

Hello;

It's been a while but i finally got the boat in the water for some extended tests. Fuel flow is good but I noticed that one side of the engine is hot the other just warm. I read it may be switch box and to test you can switch the wiring and if the heat switches the problem is the switch box. How do I switch the wiring? which wires do I switch (colors). Are the switch boxes the ones on the lower left / port side of the engine below the silver box with the big plug in the middle? Frustrating considering the swirch boxes were already replaced.

Thanks

Re: Mercury Sport jet 175 XR won't reach full speed

Something I forgot to ask,

The switchboxes have a White wire connecteing the boxes on the Bias terminal, look to see if there is more than just the ONE White wire connecting the two boxes. If there is a second White wire that leads to a third smaller black box, remove that smaller black box, it is an Idle Stabilizer, and well know to cause many problems. So many that Merc discontinued use. Remove it and drop it in the trash.

A motor running cooler on one side than the other can either be a weakened spark on the cooler side or an Idle Stabilizer changing the ignition timing on only one switchbox.

The spark test to see if you have a hot blue arc across a 7/16 inch gap is a critical test. If either side fails, disconnect all Bias wires and retest.

Repost what you find.

Re: Mercury Sport jet 175 XR won't reach full speed

Hi,

I know this post is kind of old, but did you ever find out what was wrong with your 175 sportjet engine? I recently bought a boat that has this exact same engine and have similar issues. The thing runs like a champ...it is a 2000 bass tracker 185 pro team with the 175 Sportjet. The boat maxes out at 32 mph and from everything I have read, it should be a 50 mph boat. I am also only making 4200 rpm and have good spark, fuel, and everything. Otherwise it starts great, idles great, and runs fine wide open. I verified that I am only making 4200 rpm with a timing light/rpm gauge. Any info anyone has would be great.

Kirk

Re: Mercury Sport jet 175 XR won't reach full speed

Kirk,

it is bad form to tag onto someone else's thread, especially and old dead thread.

Start a new thread, copy what you have here and paste it into your new thread. Add any other info you have, things you have tried or done. We will do our best to help you get it figured out.

Re: Mercury Sport jet 175 XR won't reach full speed

Thanks for making me feel like an idiot Charlie B.....I was just trying to get help with a problem. Anyway ...if anyone is still reading this post, I figured out my issue and maybe this will help others with the same problem. My ignition advance was binding due to an improperly installed link rod. This kept my motor from revving past 4200 rpm. If you have had work done on your motor....especially on the stator or coils, it is possible that they didn't re-time your maximum ignition advance. This can cause a large loss of hp and rpm.
QUOTE=CharlieB;4241646]Kirk,

it is bad form to tag onto someone else's thread, especially and old dead thread.

Start a new thread, copy what you have here and paste it into your new thread. Add any other info you have, things you have tried or done. We will do our best to help you get it figured out.[/QUOTE]

Hello i had the exact same problem install clear gas line and see if you are sucking air. My problem was the line inside the gas tank