Gt 175 high speed "miss/bog"

[Jtreed99]

I have a 1989 GT 175 J175STLCEB that starts and runs great right up until top speed. At just over 5000 rpms it will begin to bump and hesitate. Carbs have been rebuilt and fuel pump changed. Plugs look good when I get them back to the house but I haven't had time to try a high speed shutdown to see how they look then. Stator, timer base, and pack are all relatively new. My best guess is a failing ignition coil or a spark jumping to ground through deteriorating wire insulation. Any suggestions on how to begin diagnosing this issue are appreciated.

[omcforever]

Take to the lake and when the problem starts, push in the primer/key button. If the issue goes away or gets better then you have a fuel delivery issue. If not the probably an electrical or ignition issue.

[Jtreed99]

Thank you. I should have added that I have pushed in the key during the issue and this just causes the motor to flood and begin to kill out so I definitely believe the problem to be ignition I just do not even know where to begin from a diagnostic standpoint. If someone would kindly point me to the correct service manual for my motor I would also appreciate that as I am having trouble identifying the correct manual.

[316jughead]

omcforever might have the manual he has downloaded several of the cross flow manuals for our members. If not look at the sticky at the top of the page. You will get the OEM manual not a junk one. Welcome to the forum, omcforever is our expert tech on your type of motor.

[Jtreed99]

Thank you for the help so far. I have inherited the boat from my father, he bought it new in 1989 but it didn't run for several years. I have got it back to being fishable but am worried that the top speed issue is a sign of something larger even though if I'm content to run 55-58 mph down the lake it does fine for the entire day.

[316jughead]

Spark plugs should be Champion QL77JC4 gap at .030. Is the power pack color blue?

[Jtreed99]

Spark plugs are as you stated. Pack is blue.

[316jughead]

Spark plugs are as you stated. Pack is blue.

That would be a CDI power pack, very well could be that the pack is cross firing, firing cylinders out of turn, that would cause the problem you describe. If I did have an enemy, I would not put a CDI pack on his motor.

[omcforever]

You have mail,,,Art

[Jtreed99]

Thank you Art I just saw that. I really appreciate it.

Jughead you recommend only the original OMC pack #0583865? Do you like the pack better than the coils or the connecting wires for this issue? I will dig into the manual this weekend now that I have it (thanks again omcforever) but if I had access to dva adapter do you know of a quick way I could I test it or will it only show anomalies during the issue?

I certainly trust the expertise here as I have none. My budget is not huge and I don't want to be just a part swapper as I like the learning part of the experience but if you are convinced even a 5 year old CDI pack with only around 30 hours is bad news I don't mind spending the money for an OMC pack as a preventative as I plan on keeping the boat for at least as long as my father is able to fish with me.

Thanks again.

[ChampioNman]

Check this adjustment on the throttle linkage.

[316jughead]

The problem you are having could be caused by a coil, the pack, the stator and possibly the timer base, and maybe the wires. It's going to be very hard to find out if it only does it at 5000 and over. I would follow the service manual and check everything, if your lucky something will show up, maybe you don't notice it until those rpm's. Follow the manual on how to index the flywheel and test for erratic spark. I feel birdy around that pack, but I'm not on point yet.

[Jtreed99]

Mine is not nearly as clean as the example you posted but I believe all is well with the linkage. Is there something else specific I am looking for ChampioNman?

[headhigh]

That would be a CDI power pack, very well could be that the pack is cross firing, firing cylinders out of turn, that would cause the problem you describe. If I did have an enemy, I would not put a CDI pack on his motor.

I'm pretty sure we agreed to not use the "C" word in this forum.

And for the record, if he was a true enemy, his whole fleet would get CDI packs!

[Jtreed99]

Thanks for the replies. Sounds like the pack may need to go regardless and the CDI pack relegated for future emergencies or diagnostics. I have access to a friend's blown gt 200 as a parts motor but I may only be able to use the coils and wires from that motor as I believe those are the sole shared ignition components.

ChampioNman am I looking for anything specific? As far as I can tell the linkages and positions of the components pictured are ok. I just had carb work and I believe a link/sync was done at this time but then again my experience with that particular mechanic are what led me to start doing the work myself, not so much to save money but because I would prefer somebody that cared about my property and my safety doing the work!

[omcforever]

If you can get it narrowed down to a power pack, I have a couple used OMC packs for that motor and I would probably let one go cheap.

[316jughead]

I'm pretty sure we agreed to not use the "C" word in this forum.

And for the record, if he was a true enemy, his whole fleet would get CDI packs!

and stators.

[316jughead]

Mine is not nearly as clean as the example you posted but I believe all is well with the linkage. Is there something else specific I am looking for ChampioNman?

Looks like the red lever on the primer is turned a little.

[headhigh]

Looks like the red lever on the primer is turned a little.

[ChampioNman]

Yeah what they said about the primer solenoid. Also inspect the red maintenance valve for cracks. The linkages look good but to make sure the plates are fully closed. Loosen the center throttle roller screw, move the roller away from the cam follower tighten it back up and give the roller a few blips to make sure the plates are closed. You can then move the roller back to the cam follower.