Need some advice

[VaGent]

I have a 1986 70 HP Johnson outboard that I am told needs new rings do to low compression. I am also told that the carbs on my engine have fixed needle valves whereas the new engines (1995 & up) have adjustable needle valves thereby allowing for a much better setting. What I am interested in doing if it is even possible or makes any sense is to try & find the newer carbs & rebuild them & install them on my engine if I decide to have it rebuilt.

Does this make sense to do to an older motor or should I just leave the carbs like they are. If it "IS" possible & makes sense, where would I go to find "used" or "new" carbs that would work? Any help or advice would be greatly appreciated. I am using the Johnson 70 on a 24 ft pontoon boat I completely rebuilt last year but the engine doesn't want to idle below 1200 rpms unless it cuts off. The mechanic I went to said the compression was low (#1=123 #2=125 & #3=130) & that was way it would not idle lower. He is talking about rebuilding the power head to fix the problem. I was also told if I had the carbs that had the adjustable needle valves that would be a big help for the engine. Since I am not a marine mechanic I really don't know the answers.

And advice or information would be greatly appreciated.

 

[HighTrim]

Re: Need some advice

That motor is still a young gal compared to alot of the motors of the guys on here. That compression is not bad at all, a little decarb may even the numbers out a bit, worth a shot, but unlikely in my humble opinion that it is the cause of your low idle problem. Your carbs are fine, may need a simple cleaning and rebuild and sync, but hard to say without physically inspecting it. I definately would not let this guy rip my motor apart and do a powerhead rebuild.

 

[VaGent]

Re: Need some advice

That motor is still a young gal compared to alot of the motors of the guys on here. That compression is not bad at all, a little decarb may even the numbers out a bit, worth a shot, but unlikely in my humble opinion that it is the cause of your low idle problem. Your carbs are fine, may need a simple cleaning and rebuild, but hard to say without physically inspecting it. I definately would not let this guy rip my motor apart and do a powerhead rebuild.

Thanks for the reply. I had the carbs rebuilt with new plugs installed along with a new water pump & new prop installed as well just the past year & once I got it back from the shop it didn't want to idle. The mechaninc that did the rebuild job even came & tried to set the idle for me with no luck. The engine runs great above 1200 rpms but if I try to get below that when trying to load the boat on the trailer or even backing away from the dock, it just bogs down & quits. I've tried setting the idle "in gear" with the boat tied to the dock & once I get below that 1200 mark it just dies. I'm like you in that the compression isn't all that bad for the age of the engine & I'm hesitant to even think about a rebuild right now so I'm not too sure just what to do.

I ran it at 3800 rpms (cruise speed 24ft pontoon boat) with a 13.75X13 prop on it & was getting 17 mph GPS reading & it never missed a beat for over 20 miles on the water with 8 adults onbaord. That was a total of 40 miles up & back on the trip. But when it comes to the idleing issue it just refuses to idle below 1200. If I could find newer style carbs with the adjustable needle valves I would got with them "IF" they would work as that would be a lot cheaper then a rebuild job.

 

[daselbee]

Re: Need some advice

There is no way I would rebuild the powerhead with the compressions you posted. Something else is wrong.

Regarding carbs and adjustable needles....those carbs were designed the way they were, and ran great on thousands of engines. I would look for the true cause of the problem...it may be as simple as a Link and Sync....before shotgunning the carbs.

This mechanic is suspect.

 

[wilde1j]

Re: Need some advice

Most motors made in the last 40 years don't have adjustable jets, so I would forget that idea. Most people have no idea how to adjust them anyway.

 

[Silvertip]

Re: Need some advice

I agree that your engine is perfectly healthy with those compression numbers but your mechanic is not healthy (for your wallet). I think you need to have a look at the tachometer. 3800 rpm and 17 mph on a 24 foot pontoon with 8 people aboard does not compute. The reason your engine may not idle below 1200 is that the little calibration dial on the tach is set wrong and you may actually be trying to set the engine speed much lower than it is capable of running. It should be set on 6P (6 pulse). Turn turning the adjustment back and forth and then set it to 6P. Now see if the engine is still idling at 1200. If it still idles that fast, then there is still a carb idle passage or adjustment issue. Does the tach needle actually drop to zero with the key off. If not, the tach needle is sticking at 1200 RPM. If it drops to zero that's fine. The engine ran fine from the factory without adjustable idle mixture screws and it should still run fine that way. You need a different mechanic -- one who actually knows how to properly clean and rebuild a carb and then do a proper link & sync after the job is done.

 

[HighTrim]

Re: Need some advice

If you post your area members near you may be able to reccomend a reputable mechanic.

Follow Silvertips advice, if the tach checks out, you have 2 options. ..

A) Get yourself a factory OEM Manual and clean your carb properly with a sync after (members on here will be more than happy to help)

B) Find a different mechanic and have him clean/sync it for you.

 

[boobie]

Re: Need some advice

Have you or your "mechanic" done a really good de-carb job on this mtr. You can have good compression but can still have stuck rings which will give you poor idle. I use BRP/OMC engine tuner and follow the directions on the can. Sometimes you have to do it 2 or 3 times.

 

[SparkieBoat]

Re: Need some advice

I think Silver is on to something..either tach is not set properly or is bad..or could be the rectifier/regulator..3800 RPMs and 17 MPH with a 13 pitch prop on a pontoon boat does not compute. and do not use that mechanic ever again..

 

[Tim Frank]

Re: Need some advice

I 3800 rpm and 17 mph on a 24 foot pontoon with 8 people aboard does not compute. .

OP said that 3800 RPM is "cruise speed"...there's nothing wrong with that.

 

[levi_tsk]

Re: Need some advice

first thing id do is fire my mechanic ..... hes frigging clueless
second thing id do is check my fuel pump it may have a messed up diaphram
theoretically if the diaphram had a hole in the right place, if you revved the engine the pulse signal might overcome the pumps inability to provide fuel and because at lower rpm the engine's pulse signal is significantly less especially below say 1000 rpm and hence your problem

if that doesnt do it id get new carb kits and do it myself and i wouldnt let that dude work on yours or my motor ever again hes trying to take you man trust me 7 psi between cylinders is so minimal its isnt funny find another mech bro PLEASE!!

 

[VaGent]

Re: Need some advice

first thing id do is fire my mechanic ..... hes frigging clueless
second thing id do is check my fuel pump it may have a messed up diaphram
theoretically if the diaphram had a hole in the right place, if you revved the engine the pulse signal might overcome the pumps inability to provide fuel and because at lower rpm the engine's pulse signal is significantly less especially below say 1000 rpm and hence your problem



if that doesnt do it id get new carb kits and do it myself and i wouldnt let that dude work on yours or my motor ever again hes trying to take you man trust me 7 psi between cylinders is so minimal its isnt funny find another mech bro PLEASE!!

I talked to a "old school outboard mechanic" & explained everything I knew about the engine & exactly what it was doing. He asked me "who" had done the work on it & he just laughed & told me to bring it to him as he "believed" he could fix it. Sounded to him like it needed a "linK & sync" more then anything else. He also said the compression was bad but he felt like he might be able to inprove it some without having to put need rings in it. He also siad he trusted a "leak down" test more then a compression test. He said the "first thing" he would do is install the correct size "test prop" on it & run it in his testing tank & then go from there. He as referred to me by someone I trust & has been boating for years. I'm taking it to him the first week in Feburary before the bass fishing tournaments get to rolling as he will be very busy after that. Keeping my fingers crossed & will post the results in early Feburary. Thanks to everyone who gave me some good advice. He is also going to check out the tach settings too to make sure that is correct.

 

[wilde1j]

Re: Need some advice

(#1=123 #2=125 & #3=130) is great compression ... not bad. You may need to can 'mechanic' #2 also if he thinks those are "bad" numbers. They are only slightly uneven, but clearly w/in the generally acceptable +/- 10% criterion. You need someone who will trouble shoot in a logical fashion, then repair/correct as needed.