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ewirz

'98 Merc 75 hp question

12 posts in this topic

Hello all. I have the motor listed above. I just had it rebuilt - new rings etc. I just got done with the breakin period. The mechanic had retarded the timing on it I guess to keep from accelerating hard. During the breakin, it ran fine other than it ran rough and hesitated a little while accelerating, but once at WOT it was fine (mechanic said that would be normal). I re-timed it (5 deg at idle and 18 at WOT) and ran it last night. Still hesitating when acceleration. Whats the deal? Did I not time it right? Carb need adjusting?

Shop tach showed 800-900rpm idle, 5100rpm @ WOT with 13.24x17 prop on Alumacraft 175 tourny pro.

It's not the fuel line (brand new), also had the fuel pump rebuilt, no water in fuel...Thoughts?

Thanks for the help

ERW

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If you choke it during acceleration (when it hesitates) does it pickup or bog out?

How about long runs at idle? Does the motor load up? I'm wondering if the carb settings aren't quite right and the motor is loading up prior to take off or to lean and starving for gas at acceleration.

When was the last time you had your carbs gone through? Did you run gas stabilizer through the motor prior to startup?

marine_man

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I didn't try choking it but I will and report back.

I had it idling for a long run last night (trolling), and didn't seem to be loaded at all (too lean?)

I cleaned the carbs this spring top to bottom. They were pretty clean. I think the mechanic re-adjusted them while he had it and he's not known for doing a good job in that department. I always run stabilizer.

I'll try choking it and re-adjust the carbs and let you know. Thanks for the help MM.

ERW

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Well, ran the boat quite a bit this weekend.

This is what I observed. If the motor was realatively cold, it hesitated accelerating, choking and/or squeezing the bulb only made it worse. If the motor was warm (like I had been trolling or driving around) it did not hesitate.

Manual says 7/8-1 3/8 turn out on the idle screw. I started at 1 and tried at 1 1/4 (on all three cylinders of course), no difference.

Carb cleaning in order?

ERW

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Did you try 7/8?

When you say cold, can you elaborate? Like right after startup?

Having to warm a motor up prior to take off is not that un heard off, although not always the norm on a 2 stroke.

marine_man

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I didn't try 7/8 but next time out I can.

I guess I use cold a little loose. I always let it warm up for a good couple minutes at idle or just above before hammering it.

Before the rebuild, never had this issue. Cold or been running for a while, it always jumped right out of the water, just seems odd.

ERW

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Just another thought....

If its running too rich at 1 or 1 1/4 turns, would it still hesitate accelerating? Also would it idle a little rough and fast?

It just seems like if the gas was a little rich while accelerating wouldn't cause the hesitation but would cause a rough idle and loading up....

Thinking out loud I guess. Thanks again for the help. I'll giver' a shot at 7/8 and see what happends.

ERW

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I would think that it may load up, which you said it wasn't, but I'd like to exhaust that chance first...

Where did you get your timing spec from? Unfortunately I don't have it, but it might be worth double-checking it.

marine_man

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I got the timing specs from the Clymers repair manual. I also double checked the id plate on the cylinder head, both the same.

5 deg idle and 18 @ wot.

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I think MM is pointing you in the right direction. Lean out the idle to 7/8th.

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Just an update and another questions....

I triple checked the timing and I had it right. Although I forgot to set it at cranking speed, which helped (I think). I also found that the mechanic(if you could call him that) really screwed up on the throttle link and syc. I also found a few gas line clamps missing between the carbs that may have been leaking. After fixing all that, it runs like a top.

So the question....

Right now I'm running a 13.25x 17 aluminum prop on a '99 tournament pro 175. RPMs at WOT are about 5100 and getting ~33mph by my self, 1/2 tank and fishing gear. Hole shot ok but would like a little more speed if possible. I have a 19 pitch and get 34-35 but RPMs are around 4950. Can I move motor up a hole (on 2nd from top) or should I be happy with what I got?

Thanks again for all the help.

ERW

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