Help! ...No Idle - 1989 Mercury Inline 6 115hp

[mmccurry]

Over the past few weeks my Inline Six "Tower of Power" has started stalling more frequently at idle speed when I try to shift it into gear. It also been more difficult to start when cold.

Today the only way I could keep it running was to push the throttle half way up in neutral @ 2000 rpm....anything less and it stalls. The throttle idle position is set at 800 rpm so when I shift it into gear it stalls.

Since it has gradually gotten worst my thought is to change the aftermarket water separator and the inline fuel filter...perhaps these are getting clogged? I have no problems at WOT under load....just idle

Any thoughts?

 

[dlplost]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

"I have no problems at WOT under load....just idle"
Well, it isn't your filter. clogged filter would cause loss of WOT.
sounds like idle jets in carbs getting plugged.
I'd look there...

 

[NJCinMN]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

Sounds right. After rebuilding my carbs I had idle screws out 1 1/2 turns. It did the same thing. I ended up turning them out another half turn to 2. Try turning idle screws out 1/8 turn at a time starting with top carb. If that doesn't help and you get much past 2 turns out I think you might have to rebuild or do a thorough cleaning of your carbs. Best of luck.

 

[jeff_smith_0423]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

Carbs could very well be the problem, but since you're in there, take a proper compression test first. You may have a cylinder down and be throwing cash at parts you may never well use if you require a powerhead rebuild.

 

[mmccurry]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

Thanks everyone! I'll try the carbs and compression on Sat morning.

Earlier today I checked the spark plugs and found that the wire connector on the bottom spark plug was BADLY corroded and probably not firing. I got a new cable "end" at NAPA and fixed that problem. Now the engine has a "smoother" idle @1000 rpm but only when throttle is half way down (where it should be running 2000-3000 rpm). If I pull the throttle back to neutral it stalls.....

I also replaced the fuel water separation filter and inline fuel filter with no improvement.

I changed the idle position lever to make it stay running @1000rpm in neutral position but when I took it on the lake @ 4000rpm it had very noticable power loss. It also "flutters" up and down while underway and almost sounds as if it is running out of gas...engine catches and runs strong for a few seconds and then fades.

I'll disassemble and clean carbs Sat morning along with compression test and link/sync Let me know if you have other ideas

Thanks

 

[NJCinMN]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

Sounds like you're on the right track. If the fixes you say you are going to do don't produce any results it might be worth checking your fuel pumps. While running if/when engine starts to die pump the primer bulb, if engine picks up then you likely have an issue with the fuel pump. The rebuild kits are readily available and the rebuild is pretty easy. There is also a volume test outlined in the repair manuals. You take the fuel line off the top carb and crank engine. A sufficient amount of fuel to keep the motor running should pump out.

 

[mmccurry]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

Just to update this thread.....

I checked compression and results appear good - 110,114,111,109,110,103 are the readings I got on a cold engine in order from cylinder 1 thru 6.

I completely disassembled the carbs and found a sticking float valve in middle carb and also found the middle carb float was half filled with gasoline. I've now rebuilt all three carbs with new kits and floats and will put the carbs back on the engine on Tuesday.

Looks like the root cause of these problems mentioned above was dirty carbs and corrosion on the #6 spark plug wire causing a no-fire condition.

Thanks for everyone's help.....hopefully it will run well once re-assembled.

 

[emckelvy]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

The compression is a bit over the map, and it could be due to a little extra carbon buildup from the 'leaky' carbs.

A de-carb using Seafoam, Yamaha Ring-Free, OMC Carbon Guard, Chevron Techron etc would clean up the innards real good and ensure the rings aren't sticking from carbon issues.

Here's a good article from the FAQ section:

http://forums.iboats.com/showthread.php?t=158076


Cheers.........ed

 

[mmccurry]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

Here's an Update--

• Rebuilding the carbs didn't resolve the problem -- the motor will idle at 900 RPM but only at a higher throttle position than previously....I should be a 2000 RPM with the same throttle position as is currently required to run 800 RPM
  
• Squeezing the bulb does not change idle speed so I don't think it's the fuel pump.
  
• My next thought is the spark plugs / wires. The original issue I found was corrosion (rust) on the end of the #6 bottom spark plug wire -- and the plug looked brand new...no oil or anything...probably hasn't been firing for some time.

Question: If a cylinder has not been getting spark what would you expect the spark plug to look like....oil fouled or clean?

 

[Chris1956]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

If the plugs look new, with no oil on them, you may have water intrusion. If it is just #6 cylinder, new seals in the lower end cap may fix it.

Double check those plug wires. You can get new ones aftermarket, and they are not too expensive.

 

[mmccurry]

Re: Help! ...No Idle - 1988 Mercury Inline 6 115hp

Re: Help! ...No Idle - 1988 Mercury Inline 6 115hp

Okay...Here's an update...very frustrating...

• All sparkplugs have been replaced
  
• Carbs have been rebuilt
  
• Found no spark on cylinder #2. Swapped switchboxes and the problem moved to no spark on cylinder #5. Purchased new mercury switchbox and installed with no improvement.
  
• Swapped spark plug wire between cylinder #4 and #5 and suddenly all cylinders started firing in the spark plug tester at cranking speed.
  
• Started motor expecting significant improvement but not better...still will not idle much below 1000 PRM as it did a few weeks ago....formerly I could do 650.
  
• Noticed that engine would not stumble upon turning idle screw on top carb to lightly seated per the Clams link and sync procedure....idle screw on all other carbs would cause the engine to stumble.....not sure why since carb was carefully rebuild using new kit
  
• Noticed that pumping the bulb VERY HARD causes slight fuel overflow from the throat of the bottom carb......assume this is normal for rebuilt carbs
  
• Removed fuel pump and am in process of rebuilding .... diaphram is not torn but perhaps stretched out a little....will re-assemble soon.
  
• I've not adjusted timing since replacing the carbs but assume that is not necessary since removal of carbs did not require touching the timing adjuster. Timing was checked and set perfectly last October.
  
• I rechecked cylinder #6 for possible water intrusion and the spark plug had oil on it and looked just like the others after idling for 20-30 minutes....I didn't see any water and don't think that's my issue at least at idle speed. Perhaps the old plug was just "cleaner" because the rusted spark plug end had been keeping it from firing. Once I get this thing running on the lake I'll check again to confirm

My next steps are to finish rebuilding the fuel pump and check the timing....any other suggestions?

 

[Chris1956]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

Carefully adjust the idle mixture screws to be set as lean as possible, but still give good acceleration. This will give the smootest idle.

 

[raray1221]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

Chris 1965, i have been fallowing this thread and learning myself, please explain the above instructions and how to do it. thank you for your time, i am new at this and this is great help

 

[bullbat]

Re: Help! ...No Idle - 1989 Mercury Inline 6 115hp

i had the same prob the other week on my 77 1150 merc it had jumped one notch retarded on the timing would idle to save my life but new timing belt and and reset the timing and she purrin like a kittin