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1998 Johnson 150 V6, idle issue

D

Davem02

Contributing Member
So I have a 98 Johnson 150 V6 Faststrike. I've rebuilt the carbs. The bowls were warped, replaced them twice now in less than two months. I've replaced the vapor separator cover & gasket (as it was warped and leaking). Now the motor uses way too much oil & smokes really bad. Repair shop wants $2200 to check manifold/throttle body gaskets, rebuild the carbs again & replace the fuel bracket. I also replaced the primer solenoid recently. The engine runs ok when first started, but when it comes up to running temp, starts to stall, run rough, and won't stay running. I can replace the aformentioned gaskets and fuel bracket for around $127.00. Repair shop said they put toothpicks in the air bleed holes, & the engine ran good. So they surmise an air leak. Any thoughts about where this air leak may be? Thought someone else may have had this issue before. Thanks Y'all. David
 
No need for you to replace carb bowls twice in two months. First off they are attached with Posi Drive screws. That requires a different screwdriver than a Phillips. With a Phillips you have to push down too hard to stay engaged. Check Ebay, they are as cheap as $5.99. It is important that the screws be tightened equally. If one side is tightened down first then you will have a leak.
Now for toothpicks and air leaks. Toothpicks are used to block the air bleed orifices in the front of the carbs. By doing this you would cause the carbs to go richer if not for an air leak somewhere else. The most common place is the side cover. It is held in place by 5 Posi drive screws. Take the starboard carb. cover off (don't have to even remove carb) and look at gasket. It should have an imprint of the raised rib on the side of the carb. Anywhere it is not imprinted or faint is a possible leak. I start with the screw in the middle and work around the outside tightening in even amounts. If you find problems the other side will have to be done.
The seal for the vapor separator does need to be replaced from time to time, but I have never replaced a top! If you are going to rebuild these carbs you need to use the OEM kits. They have Viton gaskets which resist the effects of ethanol fuel.
These are just some of the tips I have learned from dealing with these motors from before they ever went into production as an OMC service rep. Hope some of this helps you out.
 
Thank you for the tips. I just ordered the pozi drive screwdriver from ebay. When I replaced the carb bowls I was very careful not to tighten the screws down one at a time. I basically did an X patern, and tightened them the same amount each time. I did not tighten one down then the next. I'm not sure why the first set of bowls warped so easily. When I get the boat back I will check the side covers. Those are all brand new, but not OEM. I got them on ebay & they are after market. The separator cover was warped, and raw gas was seeping out between the cover and body. I replaced the cover and gasket with OEM parts. I'm going to order a new fuel bracket & hope this will make a difference in how it runs. I'm also going to look at getting new fuel lines and gaskets that go into the fuel bracket. The bowl gaskets are OEM, they all seem to be holding just fine. To say I'm frustrated with this motor would be an understatement. $2200 seemed rather high for what they said they were going to do. Any other suggestions or thoughts?
 
Compression check was done. There was one cylinder that was low. I think cylinder 6 is what he told me. It was at 110. The highest was at 125. That's right on the cusp of being unacceptable. They bore scoped it, and the walls were fine. He said maybe a stuck ring. Didn't seem too concerned about that. Nothing more has been done other than what I posted earlier. They wanted to pull all the carbs and check the throttle body gaskets, and see if anything else was warped. I didn't have them do that, as they wanted $2200. I just ordered the repair manuel from Marine Engine.

What started this whole ordeal was the motor wouldn't stay running while idling. I had to give it more throttle to keep it running, especially in the "No Wake Zones". When I went to load it on the trailer, it would stall. I finally started pushing the choke in with the ignition key, & the motor came back to life. I was then able to load it on the trailer. Eventually the issue got worse, as it was difficult to keep it running during idle. WOT, it runs great, no issues during WOT. The carbs were leaking really bad around the gaskets from the bowls to the carb body. I think that issue is taken care of now, with the new bowls and gaskets.
 
I don't think they did, no. At least he didn't say anything about that. Would that cause this issue I'm having though? Seems to be a fuel issue. The engine runs great WOT.
 
Your motor has staggered combustion chambers on #5 & #6 cylinders. A lower compression reading of as much as 10% is normal on these motors. This motor also has adjustable low speed needles. They are deep inside hole found in the front of the carb bodies. Just under the mid range jets. The needle is adjusted with a Torx screwdriver. A ball end type comes in handy on the bottom carbs. Your can turn the needles out (counter clockwise) 1 1/2 turns. The screws are 56 thread count so that is a small adjustment. Keep up with how much you move them so you can put them back if it doesn't help. Your motor is running lean. That's why it won't idle or load on the trailer. These engines came out of the factory lean, but not spitting lean at idle usually. Keep looking for air leaks. The adjustable needles could cover up the spits if someone has already adjusted them?
 
One other thing. Have you checked to see if the engine is up to temperature? It should be uncomfortable to keep your hand on top of the cylinder heads when warmed up to operating temperature. It is easy to take a 13/16" (spark plug size) wrench. Unscrew caps and pull thermostat. Check for debris on seat in block. Just something no one has mentioned. This motor will not run well cold!
 
I tried messing with the starboard idle adjustment on the upper most carb (not while running) just to see where it was at. It took 6 3/4 turns clockwise to seat it. I turned it back 6 3/4. The shop said they did adjust them while the engine was running & it didn't make any difference in the way it ran. They said it was fine when first started, but once up to temp that's when the problem showed up. Only thing that made it run good (no stalling, spitting or sneezing) was to plug the air bleed holes with the toothpicks.
 
Well I guess we are almost "Live". That is a sure sign of an air leak. You can find which cylinder it is on by unplugging one cylinder plug wire at a time. Ground the plug wire to the block (head bolt, etc.). When you find the cylinder that is lean the motor will stop spitting with that plug wire unplugged. Then you can concentrate all your efforts on just that carb body. It's messy but you can put a golb of grease around the cover on the side of the carb. Air can't get around the grease temporarily. It won't last but we are just trying to prove it is an air leak. Fixing the air leak is the easy part once we know where it is. Thick grease that will stay put.
 
Okay, so unplug each sparkplug wire one at a time, and ground it out? Seems simple enough. That won't cause it to arc out or anything? Of course if the leak is before the carbs (like in the fuel bracket) this won't help, correct?
 
If the leak is before the carbs it doesn't have anything to do with run ability issues. Ground the spark plug lead so,you don't have live energy to set a fire from any fuel. It also can be hard on the ignition system for a prolong period of time. Lost my computer battery!
 
I got the repair/service manual today. Great book. Shows you step by step, with pictures. Still waiting on new parts to come in. I even got the pizo drive screw drivers today. Huge difference with that, compared to a regular phillips head screwdriver. Now to find this damn air leak.
 
Also, i noticed according to the book that my idle needles are not where they should be. It took 6 3/4 turns to seat the needle. Book says for my engine model four turns. I'm gonna try setting them all at factory specs & go from there I guess.
 
Lean sneezing can be caused by two things....but both lead to a lean condition.

First....air leak. Sure, anywhere in the incoming air stream after the throat of the carb, if an air leak exists, it will lean out the mixture. Possible places are the metal side cover of the carb, the intake spaghetti gaskets, all associated gaskets in the intake to block assembly...etc.

Second. And here is where I think your problem is. Fuel restriction. If you have a fuel restriction internal to the carb idle circuits, the amount of fuel the idle circuits deliver to the engine is less than required. Therefore you end up with a lean mixture too.

I think you have blocked or otherwise restricted fuel bleed holes located in the throttle bodies. This is very common and very much overlooked.
Locate an easily accessible carb (the side of the carb) and locate the throttle body that the carb bolts to. There will be a metal plate bolted to the side. Behind that plate are tiny holes that are part of the metering of the idle fuel. The smallest hole could be as small as 0.010" . It is common for these holes to be restricted with fuel gum and resin. All six must be thoroughly clean.
 
I just replaced those small gaskets that you are talking about. I've pulled the carbs and throttle bodies. While the throttle bodies are off, I'll remove the small plates on both sets and clean the holes with carb cleaner. I'm also replacing the manifold to powerhead gaskets & the throttle body to manifold gaskets while I have everything removed. Buying the repair manual was the best thing I've done thus far. Hopefully after all this work, it'll run right.

I also noticed that the idle needles on the throttle bodies were not adjusted according to the manual. Manual states they should be turned 5 turns from seated position. Mine were at 6 3/4 turns. All six have been adjusted according to the manual. I went and bought a long arm Hex 9/64 tool to make the adjustments, as they are not slotted or phillips heads.
 
I would highly recommend doing an autopsy on those throttle bodies. In other words, examine those tiny holes before you shoot carb cleaner in, AND SEE IF THEY ARE CLOGGED.

I always look for the problem first, then correct it. I never just clean and hope I got the issue fixed.

Use a light to look thru all the holes. I have to use a welders tip cleaner set to run through those holes to get them clean. Carb cleaner doesn't always do it.
Do NOT ream out the holes to a bigger size. DO NOT!!!
 
I will take a look at those holes and see if they appear to be clogged with any debris. I didn't plan on sticking anything into the area, as I didn't want to damage anything as you mentioned. My manual unfortunately doesn't say much about these holes, other than to make sure they are clear.
 
I took the metal plates & gaskets off the idle "holes" on the side of the throttle bodies. I shined a light and all the holes appear to be clear. I didn't see any obstructions. I then sprayed a little carb cleaner in each.
 
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