Question on a 96' 70 hp Evinrude

[ob]

Last outing had noticeable increase of exhaust smoke exiting relief ports on upper midsection.Since then ,to rule out any cooling issues that may or may not have existed,I installed a new waterpump assy. and T/stat assy. and a fresh set of Champion QL78YC plugs.Just restarted engine on hose in driveway and still have an abnormally high flow of exhaust exiting relief ports.When in water running at 4500 or so there is spritzes of water present out the reliefs but still seems to smoke visibly.This engine has had the vro bypassed for several seasons and is running on premix at 50:1.Only noticeable performance change that is evident along with this excessive exhaust relief issue is a loss of 200 or so WOT rpms.<br /><br />Question:does anyone have an idea of what may be causing this symptom?I was thinking leaky inner exhaust housing gasket or possible failed exhaust cover gasket but not sure.There is no external leak coming from the exhaust cover . Any help is much appreciated.

 

[Solittle]

Re: Question on a 96' 70 hp Evinrude

Any cooling issues after you replaced the t-stats & wp? - - I'm thinking possible partial blockage in a water passage somewhere.

 

[rodbolt]

Re: Question on a 96' 70 hp Evinrude

sounds about normal. the holes are open to the exhaust to allow the engine to breathe at low speeds. with the motor submerged you will see water exit when the relief valve or t-stat opereates.at a steady 50 to 1 expect more smoke.<br /> good luck and keep posting

 

[Walker]

Re: Question on a 96' 70 hp Evinrude

ob, have you done a compression test. How about maybe some bad gas. Not unheard of. Did you by any chance add oil to the gas twice.

 

[ob]

Re: Question on a 96' 70 hp Evinrude

None at all SoLittle.Even temp sticked it in several locations and engine is not overheating.This excessive exhaust relief flow is present immediately after starting engine cold.<br /><br />Would a partial water passage blockage cause excessive exhaust relief?<br /><br />Weird thing is ,is that when starting cold ,it doesn't seem to need as much key priming to get engine to settle out,if that makes any sense.I usually have to bump the key primer at least a couple of times when starting cold.I was thinking possible leakby of solenoid primer causing a fuel rich issue but couldn't rationalize the increase in exhaust flow from the reliefs.Plugs also looked normal.<br /><br />Thanks for your input.

 

[ob]

Re: Question on a 96' 70 hp Evinrude

Walker,Compression is from top hole to bottom..135,135,& 138.Dumped and changed the fuel and changed brand of TCW3 oil with no change.Definately didn't double oil the fuel.Thanks for your reply.

 

[ob]

Re: Question on a 96' 70 hp Evinrude

rodbolt,Thing is ,is that I've operated this engine reguarly since new and never had the present volume or visible smoke exiting the reliefs like now,even at the 50:1 premixing for the last few years.Thanks for your input.Something seems amiss.I just don't know what.

 

[Walker]

Re: Question on a 96' 70 hp Evinrude

ob, I just went outside and looked at a 70hp. midsection I have. Man, I don't see how there could be an obstruction in the exhaust unless its in the foot. The only thing I can think of is maybe your base gasket is blown out into the water passage at the rear.

 

[ob]

Re: Question on a 96' 70 hp Evinrude

Thanks for your insight Walker.I'll probably just drop the lower unit sometime this week and have a look at the upper exhaust seals.Just came back from a watertest and reliefs didn't seem to smoke as much.Go figure.Even caught a few decent specks.Maybe I did get a slug of some bad fuel and it's taking a while to run through.Also the tach face has some moisture trapped in it that may be causing it to read bad.Any rpm setting over 5500 makes the needle dive back and forth periodically.My setup usually raps out to 6000 with a light load and by ear and feel it seems to be.Reg/rec is only about a year old ,and the charging system is working good ,putting out 13.5 volts at 3/4 throttle.I'll post back after I've checked the exhaust seals.Think I'll install a new tach this week as well.Thanks again to everyones input.

 

[ANDREW SMITH]

Re: Question on a 96' 70 hp Evinrude

OB, the forward motion of the boat in the water creates a suction pressure behind the prop that very powerfully draws out exhaust and t-stat water. At idle in the water, the exhaust and t-stat water will flow thru the two relief ports, because the prop is blocked. Certainly if you have relief in forward gear at 4500rpm you have a blockage in the inner exhaust tube or the lower leg. Remove the lower leg and inspect. Shine a light down the exhaust passage and look for it from the prop side. Look at the condition of the rubber gasket at the base of the lower leg. Is it mangled, missing, poorly fitting? Black crud can build up on the inner wall of the exhaust tube. OMC Engine tuner will clean it easily. Hope this helps, and good luck.

 

[ob]

Re: Question on a 96' 70 hp Evinrude

Thanks for your input RebelRipper.I usually replace the lower rubber seal of the inner exhaust tube but not on the upper portion where it exits the powerhead.I plan to get into it this weekend and have a look.I know for certain that the lower seal is new and seated as I recently replaced it along with a new pump.I'll repost my findings.

 

[R.Johnson]

Re: Question on a 96' 70 hp Evinrude

With what I have read here, if you don't have a leak-down tester, I would pull the cylinder head. That drop in WOT does'nt sound good.