1995 C85 Yamaha TLRT - Out of Ideas

[JoLin]

This motor hasn't been in the water in over a year (ran okay then), though it has been run periodically on muffs since then. I've rebuilt the carbs and replaced all the fuel hoses and fuel pump. Gave it a full tune-up, set idle timing (2-3 deg BTDC) and did a link and sync. All good, and it idles fine at 850-900 rpm on the muffs. Couple of weeks ago I took the boat to the ramp and splashed it.

1. As soon as the leg was in the water and exhaust back pressure came into play, the idle speed dropped by a good 300 rpm. I raised the idle speed and reset the timing accordingly until it once again idled at 900 rpm in the water.

2. When put it in gear, idle speed dropped way down again. It would chug along for 5-10 seconds before it stalled. If I advanced the throttle, it died immediately.

After stalling, the motor restarts immediately (first revolution of the starter) and runs okay in neutral.

I think the key to whatever is going on here is that the motor doesn't want to accept any load, even exhaust back pressure, without losing power.

I know the fuel and carburetion systems are good. This morning I verified the following:

a. Compression is good on all cylinders (95-100 lbs).
b. Using a DVM, I verified resistance (per the factory manual) of the spark plug cables, ignition coils, pulser coil, charge coil and lighting coil. All are very close or right on spec.(outside temp was mid-30's today, and the manual calls for testing at 68 deg.). I put a spark tester on each plug and got a consistent blue spark across a 7/16" air gap. That's the 20K volt marking on the tester.

I'm out of ideas. Anyone?

 

[robert graham]

Just curious, but do you have a fuel/water separator?.....are you dead sure all the carb jets are clear?....

 

[JoLin]

Yes, I have one and it's clean. I'm as sure of the carbs as I can be. It ran (and runs) fine on the muffs since I rebuilt the carbs and set everything to spec. I've rethought the fuel system, of course, but why would simply adding some back pressure point there? Throttle and ignition timing are all controlled by manual linkage- the engine doesn't 'try' to speed up on its own when load is introduced. I have to manually advance the throttle and timing to do that.

I never saw an outboard lose that much rpm just because the exhaust was now under water. I might expect a 50 rpm drop, but 300?

 

[99yam40]

good compression ,spark, timing , and proper fuel to air ratio is what is needed for proper running.
something is not right yet.
more fuel is needed to create more power so fuel/air ratio is my guess for now\
carb passages, adjustment, or air leak

 

[JoLin]

Grrr.... okay, guess I'm back to the fuel system again. This may take awhile (like months) but I'll try to report back once I've either done it myself or called a mechanic. I suppose if I'm going to pull the carbs again I might as well replace the intake manifold gasket(s), too.

Thanks, guys.

 

[robert graham]

My C90 got so it would shut off after idling for a few seconds....I removed those idle mixture needles form top of carb, sprayed carb cleaner into holes, replaced/reset needles....all was good after that....maybe a tiny bit of trash in there I guess?....don't take but a speck of dust/dirt to effect these carbs...good luck and keep us posted with what you find!...

 

[JoLin]

I'll just have to troubleshoot the fuel/air system the way I did the ignition. I guess I should be thankful that the (expensive) electricals came up clean. I've ordered new intake manifold and float bowl gaskets (I usually manage to pinch at least one of those), and some clear fuel hose that I can use to check for a vacuum leak between the tank and engine. It's all labor and little parts cost at this point, and I sure don't want to pay a mechanic for that.

The downside is that I'd hoped to tow the boat down to Florida permanently in a few weeks. I don't have a place to really tear into it there (condo), so I'm stuck until I get it running right. I'm also stuck now with cold weather in the driveway. Sux.

 

[robert graham]

Well, the good part of these troubleshooting adventures is that you learn so much in the process.....but hopefully you get it figured out before heading to Florida....We're heading down there Christmas through New Years....Amelia Island, Cedar Key, Tallahassee....gotta visit with the kin folks and fishing a lot!....

 

[JoLin]

This morning I disassembled the carbs and put the bodies and jets into a solution to soak overnight, before I blow everything out and reassemble them. I might just have stumbled onto the issue, however. When I pulled the float valve seat out of the lower carb, I thought I saw something sitting at the bottom of the hole. Couldn't confirm anything with a pick, but when I blew into the fuel inlet 'something' shot out of the hole. Don't know what it was, but it was in the right spot to cause a fuel restriction/blockage in that carb.

In any event, tomorrow I'll put them back together. Just don't know if I can confirm how the motor's running before I fly to FL on Saturday for 2 weeks. Whenever I do get everything hooked up I'll report back on my progress.

 

[JoLin]

Just wanted to wrap this up. I finished rebuilding the carbs. While they were off I inspected the reeds (all fine) and replaced the intake manifold gasket to eliminate it as a potential source of a vacuum leak. Now that it's all back together it seems fine. I hauled the boat down to the ramp. Didn't launch it, but backed down the ramp far enough to bury the leg. I now have a good idle with the leg under water, and I put it in gear and ran it up to 1500 rpm with no stumbling or stalling. So, after all that troubleshooting and rebuilding, seems the issue was whatever was plugging the fuel inlet on the lower carb.

 

[99yam40]

most of the time it is something very simple.
Good to hear you have it under control