Hear a change in idle mixture screw setting?

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bergsofafeather

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Aug 2, 2003
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I've had a few different problems with my 85 hp 1975 Merc (you can read my other posts if you like), now I seem to almost have her fixed. Question now is, when you change the idle mixture screws from 1-1/2 turns out to 1, or to 2, should you be able to HEAR the motor loading up? I ran on the lake today, idle at the dock was almost dying, had to leave the cold start lever up a little bit, put her in gear, and then lower the lever. She ran kinda rough, but responded up to about6-7mph (sorry, don't have a tach), then as I increase the throttle slowly nothing happens, sounds almost like it's loading up (or if I do it too fast like she's gonna die), after 5-10 seconds she would start to accelerate and then take off. As I just ran a can of Deep Creep through her, and have sea foam in the gas tank, I ran the begeezers out of her for a good 10 minutes (34mph +/-). Then I slowed her down and started all over again. Same problem. I tried to just nail her like a hole shot for a skier, and she died. So I started her again (have to use the cold start a little bit most times), got moving about 4 mph and went to adjust the idle screws hoping it would help, I couldn't hear a change at all and I turned them both (dual carbs)at least 1/2 turn in each direction. I can slow her down from whatever to about 9mph, and then give her the throttle and she goes....any ideas? :confused:
 
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bergsofafeather

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Re: Hear a change in idle mixture screw setting?

At the suggestion of Corm (he should be a GOD), I checked both carbs looking for possible missing welch plugs on the port sides. What do you know, appears the top carb is missing it! All that is left now is some residue from a locking/sealing compound. However, I also found three little holes through the carb throat that are where the plug would normally be. They measure approximately 1/32, 1/64, and God only knows how small the last one is, I could only get one strand of braided 18 gauge wire through it. This being said, I also noticed a much more normal looking hole (we'll call it a port, apprx. 1/8) that is directed aft into the body of the carb. If it weren't for the three mentioned holes looking out of place, I would think they were a normal part of the fuel flow through the carb. I can't readily get to the bottom carb to see if it has the same holes or not. Is this also a problem, or part of the carb design? Incidentally, according to the book, they are Mercarb carburetors. Finally, does the welch plug come in a standard carb rebuild kit, or is it purchased separately, and what should I use to seal the plug in place so it doesn't fall out again?
 
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bergsofafeather

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Aug 2, 2003
Messages
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Re: Hear a change in idle mixture screw setting?

Yepblaze, thanks for the link. I am VERY happy to report it doesn't apply to me. Thank-God and knock on wood.<br /><br /> :) :) :) Just got back from the lake, can you tell I'm smiling?! Idle at dock in neutral: good. Low throttle through the no wake zone: good. Nail her to the floor: good. Slow down and back to neutral: good. Nail her, slow down, and nail her again: good. Real slow increase in speed from just in gear to about 6mph is just a little bit sluggish to me, but maybe since she's 28 years old that is to be expected. The only remaining issue seems to be that I tried to adjust the idle needles again on the lake and there is no difference with a 1/2 turn either way on either carb. I pulled the needles and looked at them, they look perfect. I'll take a stab in the dark and guess that the seats need replacing maybe, or the floats (or something) is a little sticky. Comments? Suggestions? I'm going to plan on pulling them both this winter and rebuild them. Maybe in the meantime I will run two bottles of Deep Creep through her and let her sit overnight before firing her back up. <br /><br />Will take your advice on the soldering of the wire and buy a solder kit soon and take care of that, maybe that is causing me some trouble yet?<br /><br />You're right in that I had to remove some stuff to get a straight shot at the welch plug. I elected to do it that way instead of removing the carb itself, I'm not sure if I'm ready for all that linkage stuff yet..... but I got her done, and it, along with the crankcase vacuum hose seems to have done a lot.<br /><br />As always, much appreciated,
 
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