1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

[davidkgt]

I just recently got the boat. Its a 16' bass boat with 1990 johnson 70 hp outboard. I am having problems. It starts okay, and idles a little low but okay when warmed up.

The main problem is the when I put it in gear It only goes like 10 mph when at full throttle. And it sounds like it running okay at that speed but the engine is not getting up to full potential. seems like around 2000 rpm.

When in neutral it runs fine, and when on water muffs even in gear it will wind up way more then in the water.

The prop is 13x19, which i though might be a little over prop but didnt think it would cause this much problems.

Changed plugs, adjusted needle valves per manual (which were close), fresh fuel, changed and filled lower unit gear oil, primer bulb gets hard when pumped before start, everything looks to be sync'd.

Please help, fuel filter? if so where is it. Possibly carbs, maybe only 2 cylinders working ( although it doesnt seem like it) .

Any help would b appreciated, thanks

 

[levi_tsk]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

try bumping the key while its doing that if the engine picks up youll need to rebuild the carbs
however if the engines been sitting for very long (over about 8 months) the carbs need rebuilding anyway so you might just wanna break down and buy three carb kits

 

[5150abf]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

Sounds like plugged high speed jets and you really want to stop running it till you ge this sorted out, no gas, no oil.

They are in the bottom of the float bowl and you need a really long skiny screw driver to get them out, you can buy them but easy to make, just grind down a screw driver till it just fits in the hole.

You need to remove and physically clean them with a stranded coper wire, just pull back strands till the wire just fits, scrub it in and out a couple times and you are good, cleaning the other jets won't hurt and blow out all the passages.

As a tip work on one carb at a time and keep the jets with the cover screw.

 

[emoney]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

It wouldn't hurt to do a compression test and spark test first. Just had another thread the other day with a somewhat similar issue. Once that poster was walked through the process, it was found out he was only working on 3 of 4 cylinders. Something easy to do and at leaste eliminate the option.

 

[davidkgt]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

levi_tsk, i have tried bumping the key when its goin as fast as it can but it does nothing. but it does work, because i have noticed it work when the is still warming up and wants to die.

Thanks for the tips, Im going to do the compression test and spark test next week. The guy i bought it from said that his mechanic told him something about low compression in 1 of the cylinders so i guess ill find out how bad it is if at all.

 

[davidkgt]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

and the guy that i got it from said that it was decarbed at the end of last year. (dont really know what that means) And he also said that he took it out on the water this spring and had it up to 40 mph. So i dont know.

Couldnt something have rattled loose on the 2 1/2 hours trip hauling the boat back home?

 

[Sixmark]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

try bumping the key while its doing that if the engine picks up youll need to rebuild the carbs
however if the engines been sitting for very long (over about 8 months) the carbs need rebuilding anyway so you might just wanna break down and buy three carb kits

You might want to clarify in the future to bump the push to choke feature, some people may mistake bumping the key as turning it , and you and I both know what that could lead to.

 

[emoney]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

David, anything can happen at anytime. That's why it's best to start at the top when there's any type issue, in my humble little opinion anyway, when you don't know any history of the motor personally. Not that PO is not sharing everything, but time lapses, memories grow weak, etc. etc. etc.

"De-Carbed" usually means taking a product and running it through the engine, a fuel additive, that's designed to remove some of the carbon build up. It's a good thing to do when done right, and wouldn't hurt to part of an annual "tune up" process.

 

[levi_tsk]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

You might want to clarify in the future to bump the push to choke feature, some people may mistake bumping the key as turning it , and you and I both know what that could lead to.

yeah true didnt think about that

ok then for clarification:

- if you push the key in to choke it when its running rough and if the engine picks up your carbs are dirty

if while its running rough you pump the primer ball and the engine picks up its the fuel pump

 

[emoney]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

While we're on the subject, you said it "sounds like its at 2000rpm". Does your tach work? Also, you mentioned revving it up on the muffs (I think). Don't push it too high on the muffs or for too long. May be a wive's tale (and these guys will confirm) but I've always heard that when the muffs are on, be gentle with throttle, and don't engage it into gear.

 

[levi_tsk]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

While we're on the subject, you said it "sounds like its at 2000rpm". Does your tach work? Also, you mentioned revving it up on the muffs (I think). Don't push it too high on the muffs or for too long. May be a wive's tale (and these guys will confirm) but I've always heard that when the muffs are on, be gentle with throttle, and don't engage it into gear.

what emoney speaks of is called a 'runaway" and its where the engine over revs and there no stopping it ones it starts all you can do is run away as the engine frags itself shutting off the key wont even stop it from blowing itself to bits so becareful and keep the revs under 2000 rpms on the hose and not under load

 

[flaxterra]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

For what its worth, I have a 92 60 hp evinrude. I am in the process of rebuilding it. If I were you, I would definitely do a compression test. There is a problem with these motors, including yours, where the number 2 cylinder overheats and causes cylinder damage. There are 3 or 4 service bulletins about it and corrections that need to be made. It may have nothing to do with yours but I would check the compression and then search for the bulletins to see if your motor has been updated. I am in the process of tracking down the bulletins myself. Hope this helps.

 

[davidkgt]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

*update.
Today I check the plugs that I just replaced and the top and the bottom cylinder plugs look good. little oil and look like right temperature. But the middle cyliner still look brand new, no oil, nothing burnt, everything still white.

Checked the spark on that plug checking 7/16" gap. I saw a spark but is was sunny out so I dont know if it was a bright blue spark but i did see it.

So I thought maybe the carb was clogged as previously discussed. So I took off that carb and took it apart. Everything was really clean. no passages seemed to be blocked, and all gaskets appear to be almost new. Float was adjusted correctly up and down.

I dont know what to check next?? seems to me that there is something wrong there. Think im going to get new plug wires and a new fuel filter, even if it doesnt help at least they will be new.

Any ideas???

 

[Monte1961]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

Before spending hard earned money at something your not sure is the problem, Check all the standard things first. 1. Is engine getting sufficient fuel? 2. Is engine getting a good hot spark? (Check with spark tester) should jump 3/8" and have a snap. 3. Is compression good in all cylinders and within 10% of each other? According to your post, the only difference is in the middle cylinder. You also stated that you took the carb apart. Were all core/welch plugs removed pryor to soaking for 24hrs.? were low/high speed jets removed pryor to soak? Did you rinse carb in fresh clean water? Was carb blown dry with clean compressed air? Was float, needle and seat replaced with new? Was float adjusted properly? I would go back and check these items again. Post back and let us know how you made out! Good luck.

 

[eavega]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

But the middle cyliner still look brand new, no oil, nothing burnt, everything still white.

If the plug looks spotlessly clean, you really need to do a compression test. You may be getting water in the cylinder? Check compression on the middle cylinder, and if it shows low you may have a bad head gasket allowing water into the cylinder.

-E

 

[Dave Brick]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

For what its worth, I have a 92 60 hp evinrude. I am in the process of rebuilding it. If I were you, I would definitely do a compression test. There is a problem with these motors, including yours, where the number 2 cylinder overheats and causes cylinder damage. There are 3 or 4 service bulletins about it and corrections that need to be made. It may have nothing to do with yours but I would check the compression and then search for the bulletins to see if your motor has been updated. I am in the process of tracking down the bulletins myself. Hope this helps.

Flaxterra, I have a 1992 60 HP ELEN. I bought it rebuilt from a highly reputable shop. I have never seen the service bulletins. If you find them, could you post them (or links to them)?

 

[davidkgt]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

monte1961, I did check the spark with a spark tester at 7/16 and 1/4 and neither time was I hearing a snap. I was barly seeing a wirery light blue line.

will hopefully do compression test time weekend weather permitting.

When I took the carb out, I didnt clean it or soak it. It all was clean already. previous owner may have had it done. I just check all air passages and all seemed clear. Float looked new, not absorbing gas, hung down 1.5" specs say 1 1/8 to 1 5/8 and when upside down sits level with carb body.

How do I check if it is getting sufficiant fuel? I unhooked the fuel line from the motor and squeezed the ball and it comes out fine there but I dont know how to go about checking it further.

 

[Monte1961]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

The thing of it is, You and I don't know what the PO did or did not do? And just because the carb looked clean, doesn't mean it is! The only way to make sure it's clean, Is to pull it and completely disassemble it. People just try and spray it with carb cleaner, and that's no BUNEO'. Remove any and all core/welch plugs and removable parts. Allow to soak for 24hrs in carb cleaner, rinse with fresh water and blowout any holes,ports including low/high speed jets with compressed air. Reassemble with OEM. overhaul kit. Note: when drilling core/welch plugs, do not drill in to carb, just enough to pull core/welch plugs out with a pick or? You might consider overhauling all carbs. Good luck and post back your results.

 

[AlTn]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

Spray bottle with fuel mix...boat in water, engine at rpm where problem is noticeable..spray mix in each carb throat individually... if motor bogs, it's got enough fuel, if motor picks up, that carb is lean...also...if you'll use an inductive timing light and clamp on each sparkplug lead....observe the strobe and you can detect a weak , intermittent, or non firing condition for each cylinder under load and running

 

[davidkgt]

Re: 1990 johnson 70 hp, starts, idles. but no power. Only goes like 10 mph, HELP!

Good point monte, will do. Alright ill try a few more things here and let you all know how it goes. Thanks