76Merc1150 - fast idle speed only?

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gbillingsly

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Nov 2, 2002
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Well I got the new (old) boat on the water the other day and it starts and idles fine. Even the fast idle lever revs it up real high.<br /><br />When I put it in gear and advance the power lever, the boat increases speed up to the point where the fast idle lever would've taken it.<br /><br />When I go past that point slowly the boat keeps running, but at just fast idle speed. A couple times I stalled the motor by pushing the power lever all the way forward very fast.<br /><br />I really don't have a clue, but it seems as if the "fast jets?" are plugged up or something. I am hoping it is not something like a blown head gasket. Any advise on what I should check to diagnose and repair this? :confused:
 
rickdb1boat

rickdb1boat

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Re: 76Merc1150 - fast idle speed only?

Is the timing plate moving freely? Check throttle linkage and timing plate.Also, hit the choke button when it does this. does it speed up? And of course, compression! Also check for spark on all cylinders. Just a start!
 
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gbillingsly

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Re: 76Merc1150 - fast idle speed only?

Thanks Rick,<br /><br />I think the timing plate is moving freely although I'm not really sure what the timing plate is. The linkage and distributor cap seemed to be moving ok anyway.<br /><br />I think I did push the choke button while it was moving and didn't get any sputters or anything. I guess I'll have to take it out on the water again to try it.<br /><br />I was hoping not to have to spend the $$$ to have someone check the compression for me - but alas - maybe another trip to the boat shop is in order.<br /><br />I'll check for spark on all cylinders today and report back.
 
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Gold Bear

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Re: 76Merc1150 - fast idle speed only?

gbillingsly <br /><br />Check the color of the spark plugs. If all six are about the same color then plugged jets are probably not the problem. However if you find trash in the fuel system, don't count that problem out. One of the clear inline filters can help you "see" trash in the system.<br /><br />You should get a Merc Service Manual and perform the timing and synch procedure. That is adjustments to make sure the timing and opening of the carbs are adjusted properly.<br /><br />Is this engine new to you? Or has it just been worked on?<br /><br />Usually "bogging" as you describe is a sign of lean mixture / poor fuel delivery. Check / clean your fuel filter, and check the condition of the fuel pickup screen, fuel hose, primer bulb, etc. There are plenty of post here regarding fuel delivery problems. <br /><br />Since it idles fast, I would lean towards timing / synch. problems.<br /><br />Good luck, <br /><br />Gold Bear ;)
 
rickdb1boat

rickdb1boat

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Re: 76Merc1150 - fast idle speed only?

You can pick up a Compression tester for $20-30 at Autozone. Good to have anyway and very simple to use! I asked about the choke being activated because if it did'nt die down when you pushed it, you probably have a clogged jet in the Carb. Meaning, the fuel supply is good to the Carb., but the carb is not feeding the Engine. Which would mean at the least tearing them down and cleaning, and possibly a rebuild kit(Recommended). Don't forget to check the throttle linkage, to be sure the throttle plates are opening up fully. Have someone push the control lever forward while observing the throttle plates in the Carb.(Not running, of course) See if they open all the way. Post back!
 
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gbillingsly

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Re: 76Merc1150 - fast idle speed only?

Thanks guys. I took the boat out again yesterday, prior to reading your posts. By the way, the boat is new to me and may have been sitting in a barn for years.<br /><br />In the driveway, with water baffles on, I ran the boat and was able to go full throttle and it screamed. <br /><br />When I got on the water, the same result as before. It would start and idle fine, then when trying to go it would only go at a fast idle speed. It DID bog down when I pushed the lever past fast idle. I even tried to manually advance the carb linkage and that bogged it down also. <br /><br />Reverse seems to go wide open. <br /><br />Choking it while moving doesn't seem to do anything.<br /><br />Yesterday was a treat. Slow boat, put a scratch in the side of the boat at the dock, and lost my wallet. :eek:
 
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Gold Bear

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Re: 76Merc1150 - fast idle speed only?

gbillingsly <br /> <br /><br />Looks like it is time to rebuild the carbs.<br /><br />This is something that you can do yourself. Do one at a time. There are plenty of post regarding carb cleaning - so you can get some good tips.<br /><br />Running wide open with no load versus loaded indicates plugged jets. Also setting in a barn will result in clogged jets. (There is just something about barns! LOL).<br /><br />Do not run the engine wide open on the muffs. <br /><br />Good luck,<br /><br />Gold Bear ;)
 
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Rex

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Re: 76Merc1150 - fast idle speed only?

how many carb. 3?
 
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gbillingsly

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Re: 76Merc1150 - fast idle speed only?

Yep. 3 carbs, 6 cylinders.<br /><br />I'll surf the site for the best method to clean/rebuild the carbs one at a time.<br /><br />Thanks for the help!
 
M

mellowyellow

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Re: 76Merc1150 - fast idle speed only?

while you are at it, you might as well rebuild<br />the fuel pumps. it's cheap and a lot easier than<br />R/R the carbs. the diaphrams might be shot.<br />make sure you have a manual, you gotta tear<br />the engine apart to get those 3 carbs off.<br />good luck,<br />M.Y.
 
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gbillingsly

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Re: 76Merc1150 - fast idle speed only?

Thank You. It's nice to know help is just around the corner ...er keyboard.<br /><br />I'll let you know how it goes with the carb fix and fuel pump fix, although it may take some time. This looks a bit intimidating, although I'll probably go for it.
 
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brianmerc

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Nov 5, 2002
Messages
140
Re: 76Merc1150 - fast idle speed only?

Hey Hey! I have this same engine!!! I was having trouble with keeping the engine running once it fired up. It ended up being the fuel pump. I went and rebuilt it for about $7.00. To rebuild the fuel pump, you'll need a Diaphram kit. I also bought new check valves which were another $5.00. It is simple!! And this is my first boat, and I know almost nothing about engines! <br /><br />For 76 Merc 1150 parts, call [800] 255 - DSMI (3764) D i c k Sherrer Marine, Norwalk CA. They can mail you any parts you need for a very reasonable price. <br /><br />I did take apart the carbs, and rebuilt the fuel pump. It was easy once I had an understanding of the whole fuel system. To get to all 3 carbs, its easiest to take off the starter and the engine casing that keeps the starter in place. To get to the fuel pump is easy. You can't be scared, you just gotta get in there and do it. A 76 Merc 1150 isn't really that complex of a engine. You will learn as you go along. Thats what I did. I took my boat out today and had a fun day of wakeboarding!! Woo Hoo!
 
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gbillingsly

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Re: 76Merc1150 - fast idle speed only?

Thanks Brian, thats the kind of inspiration I needed to push past the fear of really fouling something up. I am surfing for a manual right now. Did you use a Clymer manual?<br /><br />I don't even know where the fuel pump is located.
 
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gbillingsly

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Nov 2, 2002
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Re: 76Merc1150 - fast idle speed only?

RESOLVED :) Thanks to everyone, like a real adventurer, I went ahead and got the kits to rebuild the carbs, and fuel pump then proceeded prior to my new Clymer manual arriving.<br /><br />The problem with the carbs turned out not to be sludge or worn needle valves, but rather, on two of the carbs - a previous owner/novice mechanic had the needle valve lift levers on backwards and bent so the needles would not drop. ((I dont think any troubleshooting manual in the world would anticipate that one))!<br /><br />Anyway, I got it back together and on the water and it's running great! Anybody need a new fuel pump kit?
 
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