ValvTec DeCarb ???

[LI Grady]

I've read others mention de-carbing their motors. What exactly does this do? Is it purely preventative in nature?

One of my '90 250 Yamaha's is sounding a bit like a cement mixer. I've got great compression and the motor starts great and runs fine with just a little gas and/or oil slick out the back. The mechanic (who I don't trust and am replaceing) is kind of non-commital. His opinon is a possible ring let loose. Does this sound right?

Thanks

 

[Grog]

You should run ring-free or like to keep the carbon from building up. Also a once a year spray-n-soak with seafoam or a heavy dose of ring-free.

If a ring let go, the compression would be off in that cyl. It could be bearings or junked up carbs (hard to tell without hearing it) but give it a good de-carbon and see how it runs.

 

[LI Grady]

Thanks Grog

I'll give it a shot this weekend. I know I'm being optomistic but if the compression is good I'd like to think its nothing major. I just want to get a good year out of these motors before repowering.

 

[Grog]

If you pop off the air horn, you can spray (I think it's called deep creep or something, basically a spray form of seafoam) right into the carbs when it's running. Let it sit for a while, then start it up. It will SMOKE and STINK for a while just so you know and not piss anyone off.

I looked at the valve tech stuff at West Marine and it actually costs more to use than ring-free.

 

[LI Grady]

Ok...so I should try the "deepcreep" instead of the ValvTec decarb? Where can I buy it?

Also just to pick your brain a bit on start up the "good" motor smokes until it warms up a bit (standard 2 stroke outboard stuff) but the "problem" motor has very little to no smoke....strange huh?

 

[choogenboom]

blue smoke or white steam on that "good" motor?

Are the 1990 engines oil injected? The fact the "bad" motor does not smoke on startup is of concern - I am pretty sure that the startup smoke is caused by oil injection and if you are not seeing it I would be concerned your oil flow is impaired.

 

[LI Grady]

The smoke on the "good" motor is white....it has a petroleum smell to it but I'll double check it.

They are oil injected motors. Both of the auxillary oil tanks (not the one on the motor) seem to been at equal levels. Same for the tanks on the motor, but again I'll double check.

If there was an problem with the oil feed wouldn't the motors have cut back the RPMs and gone into limp mode (or just shut down) to avoid damage?

Thanks again I really appreciate all the advice and help.

 

[choogenboom]

The exploded parts view of your engines oil injection pump system is here.

http://www.boats.net/parts/search/Yamah ... parts.html

Note that its an entirely mechanical system with NO safety sensors. No pressure sensors, no flow sensors, nothing to prevent an oil delivery system failure from resulting in a seized powerhead. In other words the oil pump could fail and you would not know it until your engine seized. Or one or more of the 6 oil feed lines could be obstructed and again, you would not know it. Or the oil hose from the under the hood resevoir to the pump could be obstructed. You get the picture.

Pretty sure from looking at this diagram that the only "limp home protection" is if the oil level in the tanks (either external or under the hood) is low the engine cuts back to limp home mode.

Bottom line here is there is enough evidence warranting an inspection of your oil delivery system. If you want to DIY let me know and I will post a how to.

 

[LI Grady]

Thanks and I do get the picture. The previous owner did have the boat in storage for a few years and I'm not 100% sure but I think he used Penzoil oil, which I understand from other threads here has a tendency to jell up.

Thus I blocked oil line or lines is a very real possibility. Any advice on how to check it out would be appreciated of course.

 

[Grog]

The only real safety is oil level. Get a manual, it describes how to purge the oil lines. Basically you hook up an external pre-mixed gas tank to run the engine while the oil injection is purged. If you're not getting smoke out of a 1990 motor when starting, something is wrong! While you're at it remove the remote tanks and check the oil in them and change the filter on the bottom and check the tank on the motors.

 

[seasick]

I am not sure that you should be running the motor if you suspect that there is insufficient oil flow but if you do, here is a sugestion. Remove the connector to the oil pump on the main storage tank. Check that both engine oil tanks are the same level (cowels removed). Start both engines. The oil will be drawn out of the engine tanks and should drain at about the same rate. Note that at some level, an alarm will be generated. The down side other than the issuse of runnig without oil, is that it may take some time for the level to drop enough to compare between the two motors.

 

[LI Grady]

Thanks guys I will give that a shot.

To be clear, the possibility of there being any oil delivery issue only came to my attention as a possibility in the last hour or two. Since splashing the boat the motors have about 5-10 hours on them. The engine noise has existed since we splashed/recomissioned the boat but has seemed to get a bit worse.

I know there is really no way to answer this but how much should the motor smoke? There is smoke just not nearly as much as the other motor and since that motor doesn't make any noises its not supose to I assume (dangerous word) its the standard I should compare it to.

 

[choogenboom]

With still air, when I started my 1994 250 there was enough blue smoke that I worried it would bother my neighbors. A cloud of blue smoke about the size of a small motor home would hang in the air.

IF the problem is oil delivery the likely scenario (consistent with your lack of blue smoke) is oil delivery to the injection pump is obstructed. The oil pump itself is a high pressure gear pump so very hard to envision any blockages downstream from the pump.

1) If your oil tank under the hood has oil in it (which I assume it does otherwise you would have received a low oil warning horn) then it’s safe to assume that the oil delivery from the external tank to the internal tank is working.
2) My guess is either the strainer in the tank is blocked OR there is air in the oil line that delivers oil from the tank to the gear pump. The Clymer manual (linked to below) mentions that the oil line should be bled after long periods of storage, and the injection pump has a bleed screw on it which its safe to assume is there for a good reason.
3) To check the strainer remove the oil level sender on the top of the under the hood oil tank. http://www.boats.net/parts/search/Yamah ... parts.html shows you the exploded view and where the filter is.
4) Handily the Clymer repair manual is viewable online here http://books.google.com/books?id=wkEZPF ... #PPA413,M1 and details how to bleed your oil pump as well as measure the rate of flow.

 

[BobP]

Never seen white smoke out of a 2 stroke, blue smoke is oil, blacker smoke is unburned gas. I had both with my old carb'd Johnies, enough to make your eyes water when the twins idled up for a while.

You have to make sure the oil injection system is pumping oil into the motor while it is running, and not water or something else, or nothing at all.

You will get no alarm if the oil pump dies, for instance. There may be a temperature alarm but probably too late to avoid permanent damage.

I did the Dunk decarb Seafoam method a few weeks ago on one of my motors, and got a little bit of white smoke out, a puff, on restart, even the next day, just a little puff. Didn't bother doing the other one with those results. Never any other time seen white smoke.

In cars, white smoke is associated with burning coolant.

 

[LI Grady]

Thanks for all the great info. I'm going to bleed the oil pump (looks pretty easy) and have the incoming mechanic check it out.

The smoke looked white to me but I could be wrong.

I had asked the outgoing mechanic about the difference in smoke/exhuast between the motors on day one. He said it was fine and for better or worse he was on the boat playing with the subject motor last friday.

 

[BobP]

Can you describe "cement mixer" sound?

At idle or in gear?

Is it like tapping or knocking? Cyclical like that or random?

If so, does the rate change with rpm ?

Does it shift OK (normal) or balky?

 

[LI Grady]

Bob

It's tough to describe but I'll try. First it shifts fine although it has at times stalled going in/out of gear. The motor was running rich and very tough to start (although I never did try the Yamaha recommended re-start for a warm motor) and after last weeks adjustment doesn't seem to be stalling as much and starts right back up.

The noise is mechanical, almost like something is loose and rattling around. If it was an inboard I'd be looking for a loose alternater bor water pump bracket. Its that kinda noise. Nothing seems loose on the outside. It doesn't seem to get louder at higher RPM but it could also be drowned out by the motor.

At the helm you don't hear anything amiss (its a Marlin if that helps visualize the distance) and I'd say its not until you're at the transom/livewell area that you hear it.

 

[BobP]

I don't know, perhaps the timing is way off, oil pump better be supplying oil to the engine. I hope it's not a bearing or connecting rod coming loose due to lack of lube, compression will be fine. The fywheel nut is in place, right?

Hard to start but running rich ?

This should be standard fare no genius work for a Yamaha tech. Suggest you find another Yamaha mechanic.

I'd not run the motor like that since you may wreck the powerhead then it's end of story until $7K later.

The mechanic will find out exactly what the noise is and why. If he doesn't know, on to next mechanic, and so on.

Just like doctors, just move on to another until you get satisfaction.

 

[BobP]

I can recommend a few mechanics on Long Island, depending where you are. I have personal experienec with two of them, another was recommended by another member.

Just PM me.

 

[Grog]

I can't see the flywheel not coming loose, they're ON THERE. The main and rod bearings are rollers, it they're slapping something is going to grenade soon. The wrist pins are bushed and may be wiped. If the rings are shot and you have piston slap the compression will not be where it should be. Run some pre-mix gas through the engine and see how she works. When my carbs acted up, they were going lean not rich (it was also harder to start when cold). With the motor running slowly pull on the choke by the motor and see if it runs better with some choke (when warmed up). If it runs better, you're running lean.