1999 70 hp Johnson Runs great 10-20 minutes then...

[Gerald Barnes]

I just found your forum. Good questions, great advice!<br /><br /> I recently bought a boat with a 1999 70 hp Johnson (J70PLEEE) that appears to have had little use. Probably sat up for a good while. It ran great on the 20 minute demo through full engine range. But since then, I've taken it out 3 or 4 times and had a recurring problem. It runs like new for 10-20 minutes from idle to 5000 rpm and all in between. Then after I go to idle and stop, it idles good, but when I try to go into forward or reverse beyond 1000 rpm it dies. It will maintian only 1000 rpm and allow me to limp back in. However, more throttle will cause it to die. It always starts back up instantly and idles good.<br /><br /> Here's what I've worked on so far: new plugs, new fuel filter, new gas 50:1 mixture (disabled VRO), new fuel hose and squeeze bulb, new impeller, new starting battery.<br /><br /> The motor has good spark and compression (170, 168, 170 lbs.).<br /><br /> What puzzles me is that there is no sputtering, missing, popping, etc. Would that indicate electrical rather than something fuel related?<br /><br /> I appreciate you insights. This is the first outboard I've owned in over 30 years. There have been some changes in that time. I do have OMC manuals and basic mechanical knowledge. Thanks.

 

[DJ]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Elk River,<br /><br />What you describe is the number one issue, reported on these forums, regarding the three cylinder OMC loopers.<br /><br />Can you you "nurse" it through that mid range "bog"?<br /><br />Most of the posters here have fixed theirs by performing a complete carburetor overhaul service-all three.<br /><br />I went through tthe same issue with a 1995 model. The carb. work finally fixed it.

 

[Gerald Barnes]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

DJ, thanks for the post. To answer your question about nursing it through the mid range bog, I'd have to say there is no mid range. It won't ever get above 1000 rpm in forward. Dies at 800. If I'm careful and out of big wind it will crawl back to the boat ramp.<br /> <br /> I've been reading the manual about carb rebuilding. Wonder what carb kits go for? Any special advice, things to watch out for? Personal techniques? Special tools or materials not mentioned in manual? I may give it a shot in a few days. Appreciate any advice. Thanks.

 

[OBJ]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Elk....if it "sat" for a good long time, take DJ's advice and overhaul the carbs. Sounds like the bowls are varnished up. Kits will run about $16 for each carb. <br /><br />Don't hesitate to post any questions you may have.<br /><br />AND....if ya' don't have one, get a manual.

 

[Solittle]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Rebuilding these carbs is no big deal especially when you have the manual. The only tip I have is that after you disassemble it, soak it overnight and clean it take it somewhere where they have an air compressor if you don't have one and thoroughly blow it out. <br /><br />Normal work bench tools - nothing special.

 

[ob]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Elk,Have you tried repeatedly pushing in on the key primer before the engine starts to fall?If it responds ,it tells you one of two things.The low speed orifices in one or more of the carbs is restricted or the idle mix screws are set too lean.<br /><br />Another poissible cause of your symptom is the carbs are not synched properly with the ignition curves.<br /><br />That 3 cylinder looper is particularly critical of the mix screw settings and the carburetor synch.Otherwise ,once the adjustment sweet spot is found they're bulletproof.

 

[Gerald Barnes]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Great help, guys! <br /><br />OBJ, 3X16 sounds like a lot less than $80/hr in the shop. I've got the OMC manual and sure to have questions as work progresses.<br /><br />SoLittle, What would you use to soak carbs in? I've got a compressor. How much air pressure? Can any of those parts be damaged by too much air?<br /><br />ob, someone else mentioned the primer thing you did, but unfortunately I didn't know to try it the last time out. And I won't have that chance before they are rebuilt. Tired of walking home.<br />I am looking at the Sync adjustments in the manual. I don't have the OMC Piston Stop tool. May be able to use something else? Also, in checking Max Spark Advance, manual mentions test wheel which I don't have. Any ideas on that? Define "looper" please. Thanks.

 

[bubbakat]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Go to the parts store and get you some berryman carb cleaner,comes in a 1 gal bucket and has a strainer basket in it.<br /><br />you can make you a piston stop.

 

[Gerald Barnes]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Bubba, you're a genius! Makes me want to run right out in the garage and build one now. Thanks.

 

[ob]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Elk River ,Looper is just short for loop charged which refers to the design of the combustion chambers that are shaped to assist in the scavenging exhaust gas.<br /><br />When disassembling the carbs for cleaning ,before removing the idle mix screws ,lightly seat all three in the clockwise direction and note the exact turns that they are presently opened to.This will give you a reference at reassembly.Many times the factory settings are too lean and need to be opened a turn or so.There is no set in stone setting for these and the final one should be conducted after a water test.I'm guessing you'll end up at around three turns open.When cleaning carbs ,pay particular attention to the pickup tube in each carburetor bowl.They are prone to gummy restrictioins on engines that have set out of use with aging fuel mix.You can also perform a visual on the carb linkage before disassembly and note whether the carb linkage roller is exactly on center with the scribe line on the throttle cam and 'just touching' when the controls are in the neutral position.This is a predetermined factory setting that is a critical adjustment.Particularly in a throttle up in gear from idle scenario.Good luck

 

[DjPro]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Its not the carbs. Its in an alarm safety mode or something electrical. My 2 cents would be check the timing. I bet the timing won't advance beyond 5 degrees. Either that or you have a fuel line problem. Pinched hose or leaking hose.

 

[Gerald Barnes]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

Bubbakat. Forgot to ask you. How about a OMC Float Gauge, P/N 324891? Can I fabricate one of those too?

 

[DjPro]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

everyone is so quick to say "its the carbs, rebuild them" If it were the carbs, the engine would not run for 20 minutes and then shut down. There is a switch called the throttle sensor switch that could be out of wack. I had the same problem on a 200 hp suzuki last year.

 

[ob]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

DjPro,The engine didn't shut down after 20 minutes.The engine is having problems on throttle up.Reread his original post.Insuring all carb porting is clear on an engine that has set out of use is cheap insurance against a lean cylinder meltdown.

 

[Gerald Barnes]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

ob,I am printing off your advice and attaching it to the notes page of Section 2, Carburetor Servicing. When it comes time to do the work I will be referring to it. I appreciate your tips.

 

[bubbakat]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

elk river i'll have to see if I can locate that pix of the home made float gauge.

 

[Gerald Barnes]

Re: 1999 70 hp Johnson Runs great 10-20 minutes then...

DjPro, thanks for the reply. I was just looking in the OMC manual, Section 3, under "QuikStart Electronic Starting". Have not had a chance to digest it all, but it looks like it could be something like you are talking about. Here's a part of the manual, "Quikstart electronic starting also incorporates an RPM limit that cancels the ignition advance when engine speed exceeds approximately 1100 RPM." <br /><br /> In my original post I may have been unclear. Saying it another way: After running at various speeds a good while and coming to a natural (throttle back) stop, the engine idled good at 1200 rpm (a bit high, but running smoothly). Then, on going back into forward gear rpm dropped to about 1000. Upon accelerating beyond 1100, rpm would drop further and engine would quit at about 800 rpm. However, if I kept the rpm below 1100, around 1000 on the tach, it would run without spit or sputter forever. If I gave it a little more throttle, 1100 or so, it would die. Then, it would restart with a bump of the key no missing. So, on acceleration it isn't exactly bogging down, it just quits above 1000 to 1100 rpm.<br /><br /> So, now that I've thouroughly confused everybody, let me say. I think you may be on to something and I plan to pursue that line of troubleshooting. It would be great to resolve the problem with an inexpensive and easy to replace sensor.<br /><br /> In addition to considering the electrical solution I also plan to rebuild the carburetors since so many experienced boaters have mentioned the carb solution. I don't think I could go wrong degunking an engine that may have had varnish in it for a couple of years, thereby saving numerous future problems.<br /><br /> I certainly appreciate all the good advice coming from those who have been there.