WOT RPM troubles

[houdini1966]

I have an 90hp 1985 evinrude with a 13 3/4 15 prop carbs rebuilt last season about 20hrs on them on a 1984 170 tourney grady white hull everything runs fine wot rpm runs about 4500 to 4800 at about 23 to 26 mph BUT every so often it will jump up to 5000 to 5400 rpm and the boat speed jumps as well ( to the point of pulling me back falling down if not siting or holding on to some thing) also if i come off of wot at all the boat comes off plane and slows to 14 to 16 mph..... would a different prop help here of is it something else any ideas.... oh ya i forgot .. i do seem to have good fuel flow as well curent prop is 3 blade alum lookin at a 4 blade composit adjustible pitch ( 13 16"-21") propulse by brand

 

[ob]

Re: WOT RPM troubles

From your description above ,I'd say you may be have one or more cylinders misfiring.My recommendation is to perform a spark test on all four and insure that the plug leads will jump a 7/16"-1/2" gap to ground at cranking speed.

 

[houdini1966]

Re: WOT RPM troubles

and if it won't then...replace the power pacs??? also will i need supply water to the pump for this test???

 

[ob]

Re: WOT RPM troubles

Originally posted by houdini:<br /> and if it won't then...replace the power pacs??? also will i need supply water to the pump for this test???

#1 question: Not necessarily.If you find you have a spark issue after test,it could be several items.Each would have to be tested and eliminated as likely culprit.Stator,trigger,powerpack,coils,wiring,etc.<br /><br />#2 question: Yes,it's probably a good idea to at least have some low pressure city water cut in to the intake to lubricate the waterpump impeller during the cranking process.

 

[houdini1966]

Re: WOT RPM troubles

ok thanks i will try replaceing the power pac too as i was able to pick one up for 50 bucks today ( yes it is new dont ask why so cheep mispriced i think unless it is clearance) i called around and they were going for aroung the 120s called a shop i know of that is switching over to yamaha and merc from evinrude and got lucky... i fugure it cant hurt to have a spair around anyway i will let you know how it works out thanks for the info . btw any other tests i should do other then the ones in the shop manual? i can probley do all the ones that are in the book that dont requier special testers

 

[KYHunter2]

Re: WOT RPM troubles

I wouldn't install a new anything until after the tests . <br /> Its possible , not likely, but possible.<br /><br /> Something could cause damage to a powerpack.<br /><br /> I'd trouble shoot , then change/repair whats needed.<br /><br /> If something did damage old pack, it could do the same to new one.<br /><br /> Then you'll have two bad packs, and a problem unidentified.. <br /><br /> Good-Luck,<br /> <br /> KYHunter

 

[houdini1966]

Re: WOT RPM troubles

true, i'll test first but i'll bet i know the main cause... time ... it sat for a while at least 2 years that i know of for sure maybe more before grandpa passed but for 50 bucks i dont think it will hurt to have one around

 

[KYHunter2]

Re: WOT RPM troubles

Heck no , for the price you bought it.<br /><br /> I have a spare around as well.<br /><br /> Just saying , find out problem before installing new pack.<br /> KYHunter

 

[houdini1966]

Re: WOT RPM troubles

well i ran the tests after the ground wire fell off the old power pac..... everything tested ok but the stator coil... intill i looked at my tester and saw that the low battey warning was on...replaced the bat pulled the old power pac off and saw where the person that installed it had crushed wires under it and the insulatition was broke so i said the heck with it and put the new one on took it to the lake and i think someone stole my boat........ runs great thanks for the help guys happy boating