See full version: 1988 Yamaha 90 HP Compression Numbers
Thanks for everyones info I did notice this year I could not get the tach over 4300 rpms WOT but like I had said the motors really runs well. I beleive it should top out over 5000. This has got me scraching my head I got another new compression test with the same results.
Maybe it is slowly wearing out as stated earlier. Thanks again to ALL here
like the others have already said, decarb the motor to see if that will bring compression up. maybe just carboned up rings [links]
Can I please get some help identifying compression number on my 88 Yamaha 90 hp outboard. I just did a compression test with the motor warm and all plugs out. I got between 80 and 82 on all 3 cylinder. I understand that I am looking for all cylinders to be in the same range.My question is I have see used Yamaha 90 hp motors for sale that had number over 100? Could this be an issue? Not a ring but crank seal etc? The motor has been running very well and appears to have plenty of power mounted on a 17 ft Boston Whaler and moves it well. I have had to Boat for a few years and I do know the cylinder head was replaced but other than that I have kn knowledge of a rebuild or any other work. I just want to make sure if I have an issue lurking I can get a grab on it in the off season.Thank you for any help you can provide.
Re: 1988 Yamaha 90 HP Compression Numbers
Re: 1988 Yamaha 90 HP Compression Numbers here
This question is almost too involved to answer in simple form. The most general rule of thumb that I can provide is that most 2 stroke engines need to be above 100 psi and within 10% of each other. Johnson and Evinrude made a Looper, or 90 degree engine starting in 1985 that would generally read 85-100 psi on the cylinders, which was fine. The readings still need to be within about 10% of each other, and the closer all of your readings are, the better. Older OMC outboards (Johnson and Evinrude) came off the line around 150. After they’re broken in, they’ll generally sit around 120-130. As they get below 120, even if they’re still even, it’s a sign of worn rings. Mercury 75-115 inline 3 and 4 cylinder engines (1987-2006) run around 115 when broken in. The older Mercury engines would usually be between 120 and 130. Pull start engines will run anywhere from 90-115. Like I said, this is a very involved question.
Compression is created within the cylinder when the piston moves forward and back. During the stroke, the piston pushes air toward the cylinder head, which creates pressure. This is measured in psi, or pounds per square inch, and we refer to it as the compression reading. 4 stroke engines make compression differently than 2 stroke engines, but the principle is the same. On a 4 stroke engine, most mechanics and dealers will perform a leak down test, to see how much pressure escapes over a set period of time. On a 2 stroke engine, a compression check is sufficient. more
This is the first how to instructional that I’ve written and I’ve chosen compression as a topic because I think it’s the most important check you can run on a used outboard. About 6 years ago, a young man showed up asking me to diagnose and fix his outboard. As always, I started with a compression check. In the course of about 90 seconds, I advised him that his engine had a scored cylinder. The kicker to the story is that he’d already been to a certified shop mechanic at a local marine repair business and they had rebuilt his carburetors as well as installing a new waterpump, impeller, gear oil, and plugs. In short, he’d spent about 600 dollars at that shop tuning up a blown engine. I don’t know everything but I surely know that spending 600 of his hard-earned dollars on a blown engine was not his idea of a good boating experience. The learning experience that I’d like to impart from that story is that a 30 dollar compression gauge (sold at any auto parts store) can save you a lot of heartache when looking at a used outboard or preparing to service one.
The most common issues that will cause low compression: here
Yes - If you have a set of battery cables and a battery, you can ground the negative lead to the block and use the positive (red) lead to jump directly to the starter post. This will jump the starter and spin the flywheel. [links]
Outboards require 3 basic things, and this instructional could well serve as a primer for things you may want to check for when buying a used outboard. Those 3 things, in order of importance, are compression, spark, and fuel. If you have those 3 things and they’re working correctly, your engine will run. After those 3, most everything else comes down to the lower unit.
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The standard prop for most engines is a 19 pitch. I believe this will be the best prop to start with your application. Just remember that the goal with any prop selection is to get to the recommended wide open throttle RPM range when the boat is trimmed out with the usual load (Weight) in the boat Remove all spark plugs and take a compression reading in each cylinder.<br />Readings should generally be above 100 Psi on all, and within at least 10 PSI, best within 2-5 from eachother. Most healthy crossflows are around 125, loopers around 140. Some V6 s have compression around 95, though We offer current Johnson Evinrude OEM parts, the largest selection of old stock OEM parts and quality discount aftermarket parts by Sierra Marine, Mallory Marine, CDI Electronics and more. Choosing the Correct Parts. Your Johnson Evinrude model number is the key to finding the correct parts for your outboard motor
View and Download BRP Evinrude installation manual online. Evinrude outboard motor pdf manual download. Also for: Evinrude e-tec 300, Evinrude e-tec 250hq, Evinrude e-tec 200hql evinrude e-tec 150, Evinrude e-tec 130, Evinrude e-tec 90, Evinrude e-tec 60, Evinrude e-tec 50 13. Fits motors with thru prop exhaust only. 17. E-TEC motors 25-90 hp, remote control starting 2010, require neutral cable assembly #1547. 19. Also fits E-TEC H.O. motors. 20. Not compatible with G2 motors. 21. Uses 7 7/8 impeller and liner in place of 7 5/8 impeller and liner. 22. Also fits 48 Special. 23. Also fits 88 and 112 Specia . The diameter, pitch, rotation, OEM number, HP is provided from the manufacturer and completely fits the 115 Yamaha engines here
Johnson/Evinrude. Most Johnson Evinrude lower unit prop shaft seals are pulled out from the outside. This means that they will be easily pulled out by utilizing one of the two methods. The thing about these seals though. Is that they have a thicker metal frame to them. So they are harder to bend with the screwdriver Johnson and Evinrude. 396962 0396962 Johnson Evinrude 1988-2001 Swivel Bracket 50 60 65 70 HP 2-Stroke. Johnson Evinrude 1993 & UP 2-Wire Fastrac Power Trim 75 80 85 88 90 HP 2 YR WTY! 331400-1 Sea Dog Line Stainless Steel Louvered Vent 9-1/8 X 4-5/8 NEW We also had several stainless props on hand. The Triton needed a new prop, as you'll see in the photo gallery. (The logs on the Coosa River are a mean breed, especially when it comes to aluminum props.) The Tracker showed up with a 20-pitch (20P) Mercury Laser II prop, the go-to for many small-HP Merc owners Repeat this step until the prop is back to lining up correctly with the mark you made. Tighten the prop nut, and hopefully, this fixes the problem. #2. Cracked Hub: Remove the propeller and examine the prop hub. If you notice a crack, replace just that part. Set the new prop hub in place, slide the prop on, and tighten the prop nut. #3. Loose Nut