Starboard Running Lean J90TLCUR

blimp

Petty Officer 1st Class
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Sep 30, 2009
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I have a 87 90hp that I just rebuilt and the starboard side is running lean. Plugs on the port side look perfect, chocolate, but the starboard side is lighter.

They look like 23 on this chart:
http://www.dansmc.com/spark_plugs/spark_plugs_catalog.html

which is "Hot or lean but OK(?)"

I noticed that my intake manifold is missing the extension on the starboard side, I have heard that if you run without the manifold cover these motors can run lean. I am wondering if the missing extension off the manifold could cause the same issue?

The part I am missing is:
0330939
EXTENSION, Starboard side

I just cleaned out the carbs, they were pretty clean to begin with, but I did not take off the welsh plugs. I did shoot carb cleaner through the idle circuit and it came out of the three tiny holes well.

Thanks in advance, this forum is awesome.
 
Joined
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2,598
Re: Starboard Running Lean J90TLCUR

Can't say for sure, but it's definitely a possibility that could cause a slightly lean condition. I've done a bit of work with airflow, and I've seen silly little changes make a difference. For the $20 or so that part costs I'd be getting one.
 

surrender

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Jan 25, 2009
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Re: Starboard Running Lean J90TLCUR

My 88 special seemed to be running lean on the bottom two cylinders so I swaped carbs to see if the problem moved to the top. Well now all four plugs are looking good and are almost exactly the same. I think just removing my carbs and having to do the link and sych again cleaned up how mine was running. Air flow must not have been the same between the lower and upper carbs. by having to re link and sych it looks like they are all the same now.
 

emdsapmgr

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Re: Starboard Running Lean J90TLCUR

My 79 has the plastic airbox extensions that you mention. Used up through the 86 model year. Looking through the parts list for an 88 model, I don't see them used on that engine. Is there any possibility that you have some mixed year parts on that engine? The factory jets the carbs to run with the factory airboxes (and extensions-if used on that model/year.) It is possible that you could have a slight lean condition on the side missing the extension. You could temporarily remove the other airbox extension and test run the engine then check the plug colors between both sides. I'd probably look elsewhere for an issue between the two sides: any possibility that you have a thermostat issue that is causing one head to run hotter than the other?
 

blimp

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Re: Starboard Running Lean J90TLCUR

Thanks for the replies. I have just replaced the thermostats and I have checked the heads while idling and after running, they are both around 145 with minor differences between starboard and port. I checked the 88 vs 87 and the 88 does not have the intake extensions, but the 87 does. No difference in carb jetting, so I am not convinced they are this issue. I am going to get the extension today from a boat salvage yard and I am going to tear down the carbs again to make sure. Seems strange that only the starboard side is affected, as they don't share a carb...
 

emdsapmgr

Supreme Mariner
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11,551
Re: Starboard Running Lean J90TLCUR

You are up on your maintenance. Yes, it is strange that it occurs on just one side-that's why I asked about the stat-for an overheating problem. Good that both heads are running that temp-very normal. Also a possibility that you could have a hot spot internally, that the stat can't compensate for. Have you pulled the head cover and checked the water passages inside! Also, how are the two rubber diverters internal to the block on that side?
Will be interesting to see what you find visually when you pull the high speed jets on the one side of both carbs.
 

blimp

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Re: Starboard Running Lean J90TLCUR

I had the heads off during recent rebuild, i did not take off the head covers. I didn't want to risk breaking any bolts. I blew through them with my mouth and with compressed air, they both had no restriction and air went through very easily. I'm not sure if that is a great test, but if the intake piece and the carbs/sync don't cure this, I will be tearing into that as well.
 

blimp

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Re: Starboard Running Lean J90TLCUR

Went through the carbs last night. I got over my fear of the welsh plugs, got em out, but it was very clean in there. Float heights were a little off, maybe that could be the issue. I picked up the intake part this morning, hopefully i'll be able to get out on the water tomorrow to test it out.
 

mamm7215

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Re: Starboard Running Lean J90TLCUR

Let us know how it goes...
 

blimp

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Re: Starboard Running Lean J90TLCUR

Got out for about an hour last night, running great. Still sneezes a bit on startup, but after warmed up it idles well and midrange and full throttle operation are great. I have the WOT timing retarded during breakin and was getting around 5200 rpms. Once i get the timing back to spec I am going to make sure its not lugging.

Plugs on starboard side still are leaner than port, but looking darker and a nice hue of brown on the ceramic portion of the plug. I'm gonna not worry about that anymore and just make sure its not lugging which i think was the root problem before my recent rebuild.

Is it normal to get a bit of sneezing before its warmed up? The #3 cyl is .030 oversize, could i bump up the midrange jet or idle jet a bit? not positive that is the one sneezing, but since its got a bit more volume it may be a tad lean.
 

emdsapmgr

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Re: Starboard Running Lean J90TLCUR

Most engines will normally sneeze till warmed up. It's not unusual to have to bump the key in a few times (choke it) to keep it idling during the first few minutes of a cold startup. You just don't want it to sneeze when it is warmed up. A .030 over piston does not need a carb rejet.
 

blimp

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Re: Starboard Running Lean J90TLCUR

cool, thanks. I'm going to call it good and enjoy the fun part, the boating!
 

blimp

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Re: Starboard Running Lean J90TLCUR

So that was a bit premature... Found an airleak where the crankcase halves meet, I'm tearing down again to reseal. Gettin to know this motor :)
 

Faztbullet

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Mar 2, 2008
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Re: Starboard Running Lean J90TLCUR

You are using "gelseal" and primer on the halves to seal it correct?
 

blimp

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Sep 30, 2009
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Re: Starboard Running Lean J90TLCUR

i had used "yamabond" like on all my scooters/motorcycles, but i will be picking up gelseal for this.
 

blimp

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Re: Starboard Running Lean J90TLCUR

Guys at the parts shop gave me a blank stare when i asked for primer. What kind of primer should i use and is it available at auto parts stores?

Thanks in advance.
 

daselbee

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Jan 20, 2009
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Re: Starboard Running Lean J90TLCUR

I just rub it down with acetone. Get all grease off.
 

Faztbullet

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Re: Starboard Running Lean J90TLCUR

The primer/cleaner activates the sealer, it will harden quicker and stronger with it, You need
Loctite 7649 primer n anaerobic activator and its in small spray can. If you use it be quick as it will set in about 30 minutes so dont walk away from it untill you get crankcase halves torqued....
 

emdsapmgr

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Dec 9, 2005
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11,551
Re: Starboard Running Lean J90TLCUR

Interesting that you found an air leak! Some good detective work..that would explain a lean condition. Once you get that fixed, you should be good to go.
 
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