Yamaha 200 loss of RPM at WOT

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bigshrimpin

Seaman
Joined
Jan 22, 2003
Messages
69
My yamaha is only turning 4600rpm at full throttle. I've scoured other message board for info, but I still haven't been able to figure out the problem.<br /><br />Engine: <br /><br />1988 200hp Yamaha.<br /><br />1. Compression is good<br />2. Brand new Fuel Pumps<br />3. Carbs are distributing fuel to all cylinders<br /> (plumes of fuel in the carbs appear to be equal at full trottle (nice fan shaped spray) and all plugs are golden brown)<br />4. Brand new NGK plugs gapped to .39 as recommend by the seloc manual.<br />5. Plug wires are all reading right around 2.50K ohms.<br />6. The prop is the same prop that the previous owner used to "achieve 5300rpm" (6 months ago). <br /><br />Any ideas??
 
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bigshrimpin

Seaman
Joined
Jan 22, 2003
Messages
69
Re: Yamaha 200 loss of RPM at WOT

yes, I remember on several occasions reaching 49mph on the boat(GPS). The RPM's bounced between 5300 and 5400 RPM. This was 2 years ago. I have only been the owner for 6 months.
 
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sharkcat

Petty Officer 1st Class
Joined
May 4, 2003
Messages
285
Re: Yamaha 200 loss of RPM at WOT

If you are correct & your motor is running on all cylinders.Do a Link & Synch it sounds like you arent getting enough advance at WOT.Also check that all the carb butterflies are fully open at WOT.A partilly opening throttle can cause probs like this.Good Luck :) I have just seen the results from your compression test.A Decarb might help as well :rolleyes:
 
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bigshrimpin

Seaman
Joined
Jan 22, 2003
Messages
69
Re: Yamaha 200 loss of RPM at WOT

Thanks Sharkcat!! I'll check both. <br /><br />I am actually please with the compression test. According to my manual and an old time yamaha mechanic the compression is right on for this engine. These yamaha's have a modified cylinder head design which varied the shape of the combustion chambers. So compression is measured in pairs. <br /><br />1 + 2 should have the same compression<br />3 + 4 should have the same compression<br />5 + 6 should have the same compression<br /><br />3 + 4 should be the highest<br />5 + 6 should be the lowest
 
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