WOT power loss question

[2cycle]

Hello, I have a '75 Merc 1500 that is propped to make 5500 RPMs with a 17 P. A little history: I changed the fuel pump diaphragm last year and have both a built in and portable tank that I can use/alternate. My problem is that when the motor gets to about 52-5300 RPMs, it suddenly loses power back to about 4800 and won't respond/maintain that last little bit of throttle. It runs flawlessly otherwise. The power loss happens on both tanks. Assuming this is not a fuel delivery issue, what would be some general things to possibly pinpoint if it's an electrical problem? The timing is set at Max 21 degrees at cranking speed. My main worry was that could this be a symptom of detonation? Any and all replies appreciated, thanks!

 

[Texasmark]

Re: WOT power loss question

For a quick SWAG, look at your carb's butterflies at WOT. Are they parallel to the air flow or are they at some angle. If an angle you have the answer to your question. Tweak your linkage to get them flat.<br /><br />Otherwise you have some sort of fuel restriction limiting your fuel delivery at WOT.<br /><br />Mark

 

[timmathis]

Re: WOT power loss question

I have a 1975 150 h.p. 1500 also. <br />First have you ran a compression check? <br />last year I had a wot problem too. That did about like yours. My local shop had replaced my trigger. After a few hrs of run time it started. In my case the trigger bolts worked loose and made the timing to be off at wot.<br />Probably not so in your case But I would check the timing at about 3500-4500 rpm's just to make sure it is no more than 21 degrees max. You can do it at the lake Just hook timing light up and pull throttle arm off and rev it by hand. <br />Good luck , Tim