5200RPM to 4600RPM

[ricksrster]

I took my boat out today. The engine ran 5200 RPM at WOT at the beginning. Then it died dowm to 4600 RPM, Speedometer dropped in speed. Every once in a while it would go back to 5200 RPM and the boat would fly. Would moisture in the gas cause this, or I am I looking for somr other problem. The motor is a 1977 850.

 

[andy6374]

Re: 5200RPM to 4600RPM

Could be a fuel problem (ie. bad fuel pump, primer bulb, dirty carbs), but sounds like you might be loosing spark on one cylinder intermiantly. If so my guess it's the switch box. Let's see with others think.<br /><br />-andy

 

[ricksrster]

Re: 5200RPM to 4600RPM

How do I check the switch box?

 

[andy6374]

Re: 5200RPM to 4600RPM

IF you have consistently had no spark one cylinder you could perform a series of tests to tell whether or not it is your switch box. But if you are intermiantly losing spark it is very hard to test. Because you can't test it if it's working. <br /><br />Maybe try running it and when it cuts back, connect an inline spark tester on each cylinder to see if you have lost spark.<br /><br />Don't really know what to tell you. I have heard of this problem before and it turned out to be be a poor switchbox. However, that's alot of money if it doesn't fix the problem. Considering that they recommend placing both switchboxes at a time at $168 a pop.<br /><br />As a check make sure you have good ground connections to all your ignition coils, as well as all other connections (tight and non corroded.)<br /><br />-andy

 

[andy6374]

Re: 5200RPM to 4600RPM

Question: When it dropped in RPM, did it do it suddenly (ie. 5200==>4600 within seconds) or did it do it gradually. If it was imediately then you definitely lost a cylinder.

 

[ricksrster]

Re: 5200RPM to 4600RPM

it would take about 45 sec to a min. to die down. About the same when it decided to go back up.

 

[KCLOST]

Re: 5200RPM to 4600RPM

I'm not sure you even have a switchbox on that engine... And if you do, probably only one...<br /><br />45 seconds, doesn't sound like a spark problem...

 

[ricksrster]

Re: 5200RPM to 4600RPM

I have a switch box. It is a type V ignition system with 4 coils. I was looking in the Seloc book. I think I should start by checking all the wire connections and grounds. A loose or bad connection might maybe possibly be the problem. I will check the simple first and let you know how I make out. Thank you for your help. I really hope it is something easy and not expensive.