[anzomcik]

Hi i am newbie to this forum. I am hoping every one can give me so advise.

1986 L6 90hp merc. i got it used but has sat for long time. i have put many new parts on it and now it finally runs, well almost

carbs were cleaned and rebuilt, new switch boxes, stator, fuel pump, fuel lines, plugs, timeing and carbs were syned.

my problem is she idles good, put it in gear idle is about 700ish give it throttle it will rev to 1000 any more she dies. i can hit the enricher and give it more fuel and revs to 1800 in gear, then takes off under power and runs awesome. i have a dead spot between 1000-1800. In neutral the idle is around 1300rpm is that noraml to have such a big drop from neutral to in foward?

i have tried the idle mixture from half turn out to 3 turns out, she likes it best around 2.25 out. but no major difference. i do notic at WO with mixture screws out past 2.25 i loose the sucking sound from the carbs. no diffence in rpm, just noise.

Any tuning tips or if any one has had this problem please help, i have so much time and money in it, i cant stop now. Thanks

[Laddies]

You might try removing the back drag jets from the float bowls and if that don't work check the primary pickup, some time if you retard it a little it will help a flat spot.

[anzomcik]

I have removed the back drag jets, but did not have a chance to run it. I am curious about what removing them will change, because i have never heard of this. Thanks for the quick reply.

[jetwhine]

The back drag system is for fuel economy. It leans the mixture out in the mid range, but the side effect in the long run is burned up pistons. Do what laddies suggests he knows his stuff.

[anzomcik]

Ok I had a chance to take her out last night. Not much had changed, there was a little improvement but it would still stall in the 1000-1800 range when in gear.

Would it be wise to do a leak down test to see if my cylinders are tapered? I know compression isnt the only way to gauge the heath of you motor. My compression is 135-145 all cylinders.

Would tapered cylinders cause the problem i am having, and what would be an acceptable leak rate? Thanks

[BM]

Your idle rpm up around the 1300 mark suggests to me that your engine quite likely has Merc disease. Your idle should be around 700rpm in forward gear and a healthy engine will jump up around 50-100rpm when shifted into nuetral.

When the older inline Mercs get old they suffer from a crankcase pressure bleed through the labyrinth seals. This is usually an uneconomical fix as it can require replacement of major parts (crank and block).

This problem is quite prevalent in the 4 cylinder 80 (blueband) and what it then became also (75hp brownband). The inline 6's suffered from it badly also.

Any time I encounter a Merc that has a high idle I start looking immediately for the other signs of Merc disease being primarily stalling when put into gear.

Of course, whoever performed the link and synch could have got it wrong. How they let the engine out of the workshop idling so high suggests they either didn't know what they were doing or they discovered it had issues but wanted it out of their hair, so you jack up the idle and hope it runs ok....

Cheers

[the big e]

I had similar problem with my 115, turned out to be a sticky needle in the carb, it was new too. I used some fine sandpaper to smooth it and fixed the problem.

[anzomcik]

Please excuse my inexperence but the labyrinth seals, where are those located? I have never heard of those.

Also i was wide open going across the lake, and i cut the throttle quick and went in to neutral and the motors revs shot up to 5k and for a few secounds before i shut it done for fear or blowing her up. Keep in mind i throttled her down so it should be at idle but it went to redline once i hit neutral. Any thoughts. Thanks again everyone is being real helpful