04 yamaha 4 stroke vibrate stalls at idle

[99yam40]

As said before
leak down test will tell you where the air is leaking by at.
that air going in has to come out somewhere
intake, exhaust, crankcase, water tube
If cylinders and pistons look good then valves would be my guess
or rings stuck or broken

[TownsendsFJR1300]

I'm betting he didn't do the leakdown test (or doesn't know how).

If you can't get a spark plug wire on the correct plug, jeez oh pete...



Just a side note, related. I had a weedeater, 2 stroke, about 135 PSI compression, ran like crap, couldn't get past half throttle.

Another weedeater(2 stroke), did a compression test 195..Humm..

There's no valves(reeds) on these engines (piston/port only).. Put the leadown tester on the 135 motor, you can hear the air rushing past the rings( the head IS part of the cylinder).

Pull the top end off, piston ring(just one total), was so carboned up, ok getting somewhere...

I had another machine for parts(very similar but this piston had two rings), nice and clean. Swapped piston/rod, cylinder/heads, runs like a top!! I still have it as a spare it runs so good..

Point being, even with 135 PSI compression, the leakdown test was VERY OBVIOUS there was an issue up top...

[99yam40]

I have removed the ring and cleaned the grove and ring on a leaf blower to get the compression back up from only 90 psi. It is amazing what carbon will do

[TownsendsFJR1300]

I have removed the ring and cleaned the grove and ring on a leaf blower to get the compression back up from only 90 psi. It is amazing what carbon will do

Oh yea...

My neighbor gave me this Ryobi when he moved and said he pulled the top end apart and it was clean.. (NOT!)

I probably could have gotten by with the original piston/ring but I knew the other was in good shape (PO tore up the crankshaft end) and would rather have two rings..

So now its a troybilt/Ryobi or Troyobi!

A good tip to help, especially if the machine sits, put some "Seafoam" down the cylinder and crank (no start-thru spark plug hole). If a 4 stroke, I make sure its at TDC and both valves are closed(to keep moist air from entering thru a valve). The Seafoam helps protect against rust and over time, hopefully help loosen up carbon.

[rudderz71]

Latest update is the yamaha rep is heading over this week to put his eyes on the issue. I am preparing for the worse at this point. The side that is bad is if you are looking at the back of the engine, the port side of the engine is where the problem lies. If thats the problem and they call for that to be replaced can you just buy that side and if so how much roughly am I looking at? Just trying to prepare my wallet. This quite possibly is the worst run of luck/experience I have ever had

[TownsendsFJR1300]

The engine block is one piece, you can't replace half of it. IF the block looked good, that leaves the head (and valves) and the the piston/rings.

The head isn't super hard to pull, repair. Piston rings entails pulling the head and at least part of the lower block to access the connecting rod bolts(a bit more time consuming).

I would inquire, (depending on what he finds) IF it was mechanic induced and go from there.

BTW, do you know if anyone ever checked the valve lash?? Your circumstances shouldn't have affected them however a valve not closing fully would cause low compression. Again, a leakdown test would have shown that valve leaking(if it is)

If you click on the "Purchase Yamaha Parts" in RED above right, type in your engine info, you can look at the block, head, etc and get an idea whats on the transom of your hull. Just so when the rep is there, you have some idea what he's talking about.

Good luck..

[rudderz71]

I think at this point I am going to give them till Wednesday afternoon. If there is no update on a Yamaha Rep coming then I am going to pull the boat. The leak down should show where the issue is. Pretty simple at this point. It has to lie in that port side cylinder assembly. Take it apart and clean evalutate after leak down and replace that whole assembly, worst case. Not sure what the rep is going to do anyways. I am sure he is not going to fix the engine himself. But what do I know. At this point I just want my boat back

[rodbolt17]

keep blowing cash.
but did you LOOK on the wall for training certs???????????????

[rudderz71]

I know right ....
Yeah sure did they list 3 certified techs and have yamah plaques on the wall

[rodbolt17]

then your looking for advanced 4 stroke and electrical systems certs at a minimum.
5 star is a video course.

master tech certs would be better.

troubleshooting is actually a simple process.
it IS a process.
it starts with can the cyl mechanically seal? leakdown test. compression test is a teat on a boar hog on a 4 stroke outboard.

while doing a leakdown test the tech should carefully inspect the spark plugs as they will tell a story.

second test is can the ign PRODUCING devices make spark?
then can the ign CON*****ING devices CONTROL spark?
if the above passes then simply fix fuel delivery.

to do the above however it takes a working knowledge of exactly what each subsystem does and how it affects the others.

that's where training comes into play.

[TownsendsFJR1300]

It'd be interesting to know just what the REAL COMPRESSION is itself, 30 or higher. Seems like lots of smoke being blown about..

Obviously, the leak down will tell a bunch, but when you can't get the basics of the engine from the tech, sheesh...

For the Op, IMO, do the leak down test and see what tyou find (please post it!) and wait on the Yamaha rep. How many hours on the engine since the last valve clearance check?

Once you start tearing down, I would think the rep would rather have the engine assembled.

Rod, even with the wires crossed for a couple of hours, I don't see how that would damage/lower compression (if its even low) on a cylinder.

[rodbolt17]

crossed wires would make it run like crap but other than that probly wont hurt anything.

just as an example from the real world.

had a customer bring in a clean old 2001 F80.
2 other techs had monkeyed with it.
compression numbers written on the cam cover
1 145
2 140.
3 145
4 138.

who here would buy those numbers and continue on ??????

[Nautical]

Appears to be a lot of conflicting/ misinformation. ? ?

[99yam40]

I would think firing a cylinder with a valve not closed could burn a valve/seat,
But who knows for sure until test results are known

Just to give Rod an answer , 7 psi difference does not look bad to me

[rodbolt17]

on the above F115, motor was bad.
leakdown on #4 was 85%.
my first clue were the green flakes on the plug center electrode.
corrosion had eaten under the head gasket and was allowing water into the cyl.'

and that is the difference between a compression test and a leakdown test.
other than a leakdown is faster.