Yamaha Pro 50, ironing out the kinks

[Pat Gidley]

I have a 1990 Pro 50. Motor had been problematic with bad compression on one cylinder, so when I got the opportunity to buy a parts motor (bad lower unit) for a steal, I grabbed it. I had my mechanic swap the power head, and things seem to be running well overall. Definitely better than the old powerhead.

Now, I was out on the weekend, first time with a few people in the boat. I couldn't get the boat to get up on plane, wouldn't go about about 4000 RPM. So I checked the specs and sure enough the timing on the box wasn't getting up to 25 degrees. I decided to go through the service manual and set everything to spec.

All went smoothly, synced carbs, adjusted throttle control etc. Set the idle screws to 1 7/8 turns out. They were set at 6 turns out initially. Started up, and it stalled. Motor will run by bringing idle speed up to around 1000 RPM, but it runs rough and will die out. Backing out the idle screws to 4 turns smooths things out a bit. Work was done in the driveway, so I'll take it down to the ramp tonight.

Things to verify: See how top end is. Should I be able to get up to 5500 RPM with myself and wife in the boat? Its a 16' Mr Pike Deluxe.
Should idle be 800 RPM with the air screws at spec, or is it normal to need a few turns out with an older motor?

Where to start checking for causes of the rough idle: I have a spare fuel pump, can swap that out. Then rebuild carbs? Order a kit, or just clean and inspect?

Thanks for your help, you guys are awesome.

If anyone needs spare parts for a 1990 Pro50, I have stuff kicking around now.

Pat

[TownsendsFJR1300]

I would check the carbs first off. It doesn't take much with the crappy fuel to clog up a jet, especially the smaller engines with smaller jets...

I would remove ALL the jets and visually look thru them. Just a spray of carb cleaner in the carb body does NOT cut it.

You should see 5,500 RPM at WOT normal conditions.


Did the engine EVER rev up to 5,500 or is this a new issue?

[Pat Gidley]

The previous powerhead would run up to 5500 with these carbs, which has me suspecting its an adjustment issue. That was last summer however, so things could have gummed up in the meantime. I did run it out of fuel in the fall.

So jets to remove are the two that are accessed under the float bowl. Should I remove the float and inspect as well?

I have a spare set of carbs that came off the new powerhead, but when I was inspecting them they seemed pretty rough. Someone damaged one of the jets (the screwdriver slot) so I was thinking of doing a full rebuild on those and swapping them over. Is that worth the 90 bucks for a kit, or am I better off cleaning mine? I can go through them with copper wire and carb cleaner, then link and sync again.

Its storming out right now, but if it passes Ill take it out tonight and see what the RPM at WOT is. If that's all good then I just need to sort out the idle issues.

One thing that is kind of interesting is how different this powerhead sounds than the old powerhead. Much smoother and quieter overall.

[TownsendsFJR1300]

I don't know the exact model # for your engine but for that year and HP, here's a parts fisch for the carb;

Jets 20, 21 and 23 need to be checked. The float is very likely ok

1990 50ELD Yamaha Outboard CARBURETOR Diagram and Parts

If you look up and to the right, in RED, "purchase Yamaha parts" you can enter your model # and bring up whatever part/section you need.

And BTW, running the engine dry of fuel is better than not, BUT it still leaves a little bit in the bowl that WILL varnish up. The idle issue is likely related the the idle jet being clogged as well..

Run some of Yamaha's "Ringfree" thru the engine. It cleans the fuel system and top end. Its not cheap but works extremely well. I would, in your case, run it at 2-3x's the amount recommended. It won't hurt anything.. I run it in every gas powered engine I own.

And should you put the engine up for "awhile", simply drain the carbs with the drain screw removed from the float bowl(s)... No more gummed up jets..

Please post back how it goes/what you find, etc..

[99yam40]

did you have your mechanic do anything except just pulling and installing the power head?
Did he not start it up on the old motor and make sure it ran properly before or after the swap?

If motor will not run with everything set to factory specs the there is a problem and you should not be running it to see if it will get better,
you will toast another powerhead

I would not buy a carb kit until I opened the cabrs up to see what was needed, just a waist of money if you can reuse most of the things
and jets along with some orings do not come with the kits.

[Pat Gidley]

Ok I will check those jets and clean everything in general and report back what happens at spec settings. The motor is a 1990 Pro 50. I looked up the rebuild kit - its 90 bucks. Might order it anyways, be good to have all new gaskets and eliminate a source of problems, and if I open them up and they look fresh, I'll hold on to it for the future.

The previous powerhead had been converted to run on pre-mix, as it had the leaky oil pump issue, and was a bit of a pile in general. So when my mechanic swapped the power heads, he told me it would run rough until I got the fuel cleared up. We're into the second tank of clean fuel and its still being problematic. Much better than ever before, mind you, just a little stally.

I'll work on it tonight and post back tomorrow.

[99yam40]

Is he the one that turned the pilot screws out that far to try to make it run?

If these are the carbs that toasted the cylinder on the other motor and you did not clean /solve the problem that caused the cylinder to drop compression, you may have already hurt this one too. never hurts to make sure the cylinders are all sealing well right now

[Pat Gidley]

We were under the assumption that the bad oil pump had caused the compression issues. There was also a bad lower bearing that cleared up a lot of the problems. This new powerhead I got has a lot less hours on it, although they both run.

So I take it by your concerns that the pilot screw should be pretty close to spec, and if its not, there are other issues afoot? Getting it to run by backing out the screw too much can cause damage by running too lean? So I guess I should stick to the 2-turns out range and see if I can get it to run via the idle adjust screw, and if it won't then its dirt in the carb.

Should I take it back to him and get him to overhaul the carb? He is a very experienced yamaha tech, but he tends to work fast and is very reasonably priced but I wish he were more thorough. Wouldn't mind paying extra to not have to bring it back again, know what I mean? So I'm trying to learn this stuff myself, that way I know whats been done.

[TownsendsFJR1300]

Yes, you shouldn't have to have those screws turned out so far. You sound like your very capable of looking into the jets in the carbs.

The one jet may be under a small aluminum plug, make sure you get to that one too..

He may be good (doesn't sound it if he adjusted those out so far) but if he's in a hurry as you mentioned, the carbs DO take some time. I can't tell you how many small engines (mostly mowers/weedeaters/generators) I've cleaned carbs. My brother in law ran his 8 HP B&S generator dry of fuel. A month later, he tried starting it. Nope. I pulled the float bowl, the main jet (clogged solid in a MONTH), cleaned it out, FIRST PULL it started..

As noted earlier RING FREE will help clear out crap in the carb. Yours sounds like it needs disassembly, then run the RF..

Take your time. And I agree with 99Yam, a rebuild kit is most likely NOT needed. Its rare, very rare, I rebuild (the small weed-eaters yes) the carbs.

Just a good cleaning and regular use of a fuel stabilizer and RF..

[99yam40]

We were under the assumption that the bad oil pump had caused the compression issues.

Usually if not enough oil it will get bearings first.
lean fuel air ratio or overheat will get piston

[Pat Gidley]

So I stopped on my way home From work and borrowed a compression tester from a buddy. Confirmed compression is good, 110 on each cylinder. Plugs were wet coming out, although I had been running at idle and messing around yesterday.

I pulled the carbs and did a thorough cleaning. Jets are in good condition, they look quite new compare to the other set of carbs. Fished the holes with some copper wire. I did notice a bit of crud in the bottom carb, hoping that was the issue.

It's thunder and lightning right now so just waiting that out. Glad I tore into this (assuming I can get it going) as I do enjoy working on small motors. My experience to date has been mostly with small snowmobiles and my ATV. I found this yamaha intimidating at first but now that I have a shop manual and have done a lot of reading on here I'm feeling more comfortable.

Once this rain stops I'll set everything to spec and see what happens.

[TownsendsFJR1300]

If your just killing time right now, (if you haven't already), pull the float bowl drains and prime the primer valve to help flush out the fuel system. Just in case some debris is in there.

Please post back your results..

[Pat Gidley]

Okay, the rain finally let up and the bugs came out.

I got everything back together. Noticed that when syncing, the bottom carb was getting hung up on the throttle cam, so I let that one off too (they don't tell you that in the service manual). That got them all closed up tight and synced nicely. Set everything as per manual, and it fired up, but stalled out pretty quick. I didn't see anywhere where to start the idle adjust screw, so I started it backed out all the way. By bring it in 4-5 turns I got it to stay running, but idle was high, around 1000 RPM. Brought it down to 800 1/4 turn at a time and managed to get it all the way down to 600 RPM without stalling, but once it stalled it wouldn't idle nice, so I brought it back up to 800 RPM. It was running a bit rough still so I backed the pilot screws out a half turn (so 2.5 turns from seated) and it smoothed out. Idling at 800, carbs picking up at the specified point on the control box.

Tomorrow I'll trailer it down to the lake and make final adjustments. Any pointers on what to do there? Should I leave the pilots where they are and just adjust the idle adjust screw till I get it to idle at 800 RPM? What about in gear, should that be around 600? Wish I had a digital tach, I only have the old analog one.

If it stalls out, adjust pilot screws 1/4 turn out at a time?

I'll also pick up a bottle of Ring Free and use that. I have some seafoam around, is that any different?

Thanks for the help, you guys rock.

[TownsendsFJR1300]

Seafoam works OK (I do use it) BUT its NOT nearly as effective as the RF. Much better than nothing.

The RF should make a noticeable difference. You do have to run it a bit for it to clean the carbs up so don't expect it to run GREAT right away.

As for the idle, if it idles at 600 in gear and doesn't stall that's fine..

I would run the RF (as noted earlier) at least 2-3 times the amount recommended. That much more does make a difference.

Once it does it thing, it should be MUCH easier to get your screws/ adjustments where they should be..

Just as a side note re RF. My 2001 Toyota SUV, 16,000 miles(yes 16k) had the idle raise about 3-400 RPM's above normal. I put in 3x the recommended dose of RF and ran that. The idle eventually dropped back down to 600 in gear (from about 900). I didn't do ANYTHING ELSE..

Obviously, I was getting some fueling issues. Its never had the injectors cleaned, etc, just 14 years of use/wear and tear. MUCH cheaper than paying $100 plus for an injector cleaning. Runs like a top..

[Pat Gidley]

Thanks Scott - I'll definitely pick some up today. Its Canada Day tomorrow, and the Yamaha dealer is right beside the beer store .

16,000 miles is an amazingly small number of miles on a truck that age. I have a diesel VW Golf with just over 16,000 miles already and its a 2015! My 2000 F150 has 281,000 miles and still going strong, although the body is rusting away. How is the body on the Toyota? They're great trucks, but they don't seem to hold up to the salt up here. Next truck will likely be a Tacoma.


So here's my plan - I like to have a plan so that I don't get down to the lake and just start turning screws:

Add 2-3x recommended Ring Free, then launch the boat, start it up and keep it going with the fast idle lever till it warms up. Restart/adjust idle adjust screw until it will stay running. Go for a cruise at 1/4 throttle up to half, verify that there are no dead spots. Cruise up to WOT and verify top end RPM. Once I've burned through the majority of the fuel with the Ring Free, I'll adjust carbs back to 2 turns out and readjust idle screw to get idle at 800 in neutral, 600 *****ing. Adjust air mix +/- 1/4 turn to smooth things out.

Let me know if you'd do anything differently.