'98 Johnson 25hp misses at high RPMs

[renelson]

I need some expert advise. <br />I have a 1998 25hp Johnson two stroke electric start. It runs just fine at all RPM's except when it's wide open. At WOT, the engine sounds like it's missing about once every second. If I let off the throttle just a hair, it runs smooth, and when I go back to wide open, it starts missing again. I thought it might be bad gas or something (even though I run it often), but this morning I filled up with gas (and oil) and the problem was still present. <br /><br />Any suggestions?? <br />Thanks

 

[mikeyzx2]

Re: '98 Johnson 25hp misses at high RPMs

Welcome to iboats! Have the plugs been changed in a while? If not give it a shot and see if it helps any. Make sure they're gapped correctly too.

 

[steelespike]

Re: '98 Johnson 25hp misses at high RPMs

Check the plug wires to be sure they haven't rubbed a weak spot in the insulation.

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

Thanks a bunch for the tips. I'll try both of those suggestions. I haven't changed the plugs since I got the boat a year ago (used), before that I am not sure when they were changed. <br /><br />The other day I had a parts guy at the Johnson dealership tell me, "if it were the plugs or wires, the motor would be missing at all RPMs not just at WOT." Is he blowin' smoke?? <br /><br />Thanks

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

Oh yeah, does anyone know a where I can get a manual for this engine online? Also, since I don't have a manual, can you tell me what kind of plugs to get and the gap distance? <br />Engine Model: J25TELECB<br />Thanks,<br />WW

 

[MCM]

Re: '98 Johnson 25hp misses at high RPMs

Found this on Ebay web page, its the only one I found. You could also try Marineengine.com or KenCook.com

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

That Johnson parts guy (the one I talked about in the above post) told me that it was probably the power pack. I have no clue. Any ideas? Thanks.

 

[MCM]

Re: '98 Johnson 25hp misses at high RPMs

WW, <br /><br />Start with a fresh set of correctly gapped plugs as has been suggested. Plugs should be QL77JC4 gapped at .030 for sustained high speed opperation or .040 for a better idle.<br /><br />Since power packs have a higher markup than plugs it wouldn't be above some parts suppliers to suggest the pack over the plugs if you catch my drift.<br /><br />Start with the plugs since you don't know their history, then troubleshoot the problem from there.

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

Well, I changed the plugs. The engine still misses at WOT. I also bought a service manual from Johnson. It said that the problem might be a linkage adjustment problem. So, I adjusted all the linkages and will let ya'll know what happens when I get it on the water.<br />Thanks.

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

I ran the motor today. The engine still seems to be missing at WOT. Like I said, I adjusted the throttle linkages and I changed the plugs (gapped at .030). Anyone got any other ideas before I pay a fortune to get it checked out?? Thanks.

 

[Walker]

Re: '98 Johnson 25hp misses at high RPMs

Yes, tear the carb down and give it a good soaking in a suitable carb cleaner. Rinse it off with (I like to use aerosol carb cleaner) and blow it out with compressed air making sure to get each and every orifice and passageway clean. Re-assemble with an OMC carb kit.

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

Thanks Walker. Now, correct me if I am wrong, but just by looking into the air intake on the carb, it seems very very clean. Should I still put a carb kit on it?

 

[DHPMARINE]

Re: '98 Johnson 25hp misses at high RPMs

Filling the gas and oil tanks does not eliminate a water problem.Draining,cleaning and refilling does.And only after rebuilding the carbs.I'd have someone pump the primer bulb when you have the problem.It could be a fuel supply problem.<br /><br />Also pull off each plug wire at the plug and the coil.Using pliers,squeeze the terminals until they are slightly oval,and reinstal.I have seen this to be a problem on twins before,and only show up at high RPMs,on the water.<br />Good Luck,and keep posting.<br /><br />DHP

 

[Locked Up]

Re: '98 Johnson 25hp misses at high RPMs

Dude, all good advice. Especially starting cheep and working your way up. Just a tip, sounds like your like me and run the boat in the cold duck hunting. Make sure there isn't any crap in your fuel tank that might be obstructing the flow. Also I had a buddy that had some what a simular problem. One thing they looked at was the temp. sensor. It's somewhere on the block by the plugs. If your water flow is restricted from mud or something you could be overheating a little.

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

LU, thanks for the help. Would it be safe to temporarily remove the temp sensor and see if the engine still misses? To do this, can I just unplug the sensor? Also, my manual doesn't show a very good picture of the sensor. Just to make sure I am looking at the right thing, is it on the top left (port) section of the back of the engine (the cylinder head)? I think I am looking at it - it looks like a small guage wire going directly into the engine block back by the plugs ('98 johnson 25hp)...thanks!

 

[Solittle]

Re: '98 Johnson 25hp misses at high RPMs

Removing or disconnection the temp sensor will have zero effect on your problem. Follow Walker's advice & rebuild the carb (it is an easy job). And no you can't tell the condition of the carb by lookin at it.

 

[Scaleman]

Re: '98 Johnson 25hp misses at high RPMs

I am not hear to offer any assistance as many before me are on top of this problem. I am amazed at the knowledge on this site. I was just riding home and telling my buddy about the site.<br /><br />WWM, as I sit hear having dinner with my wife I cracked up at your screen name. I love it! Primarily while i replied to this post.<br /><br />We are done up hear in NJ. Good season but too warm.<br /><br />Back to troubleshhoting, apologies.

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

Solittle, <br />Thanks for the advice. I plan to hit the carb job asap. May have to wait, I'm a student at the Air Force Institute of Technolgy, and right now, number one priority is getting a thesis done so I can graduate. <br /><br />Scaleman,<br />Yeah, I wish I could take credit for the name. I got it off a hunting comedy video - "Outdoors with TK and Mike" By the way, my post says that I'm in Jacksonville, AR. Well, that will be true in about a month. I'm getting based at Little Rock AFB (which is located at Jacksonville, AR), close to family for a change. I've been at Wright-Patterson AFB in Dayton, OH. Terrible duck hunting. Last season I had one good duck hunt - when I went home to Arkansas over Christmas!<br /><br />Thanks for the tips & God Bless.

 

[renelson]

Re: '98 Johnson 25hp misses at high RPMs

I took off the carburetor and cleaned it up good. Today i am going to go get a carb kit for it. I have one question. When I removed that carb and took off the float chamber and saw that the emulsion pickup tube (the tube that helps to rid the bowl of any water that might be floating in the bottom of it) was off center. <br /><br />You can see in the picture below what I am talking about. See how the little tube is off center from the larger tube that it's in? Is this okay? Or should I try to bend it back to center? I really don't see how it would hurt anything if it is in this position.<br /><br />Thanks...<br /> http://i4.photobucket.com/albums/y131/amynelly/Presentation1.jpg

 

[jim_in_day]

Re: '98 Johnson 25hp misses at high RPMs

Don't bend the little tube, it is supposed to be that way, I can't remember exactly why, just leave it alone, it's fine