Does this make sense - fixed 90 TLRD coughing

[murray8144]

So a few weeks ago I completely rebuilt my carbs. Prior to that, my engine barely idled, it was terrible, and no surprise I found tons of gunk in my carbs. I didn't touch my fuel pump, lines, or fuel tank during the carb rebuild.

After the rebuild, the engine ran perfectly. Would purr at idle. I took it out for a shakedown run last wed, and again, great idle. But after a few minutes of wide open running, the idle was a little shaky. Nothing like before the rebuild, but coughing every few seconds, stalling, etc.

I assumed that since I didn't replace my fuel pump, fuel lines, or clean my tank that I had jossled loose some more gunk during the high speed run that had found it's way into my carbs again. Planned to take them apart again...

...but today i read a few places that said that coughing at idle could indicate a too lean mixture. Now this engine's idle setting is 1 1/4 turns, which is where I had the screws the whole time. Today I turned the screws IN to find out where I had them, then backed them out to 1 1/2...AND THE ENGINE IDLES FINE. it even idled fine after i put them back to 1 1/4.

so does it make sense that just turning the idle mixture screws would somehow break loose some kind of blockage? there is no doubt that before messing wiht the screws, the engine idled like crap, and after messing with the screws, it idles perfectly. no change in the screws setting, all three are at 1 1/4.

thanks for your input.

[99yam40]

yep, sounds logical.

[rodbolt17]

yep.
half azzed jobs ALWAYS give half azzed results.
that much gunk in the bowls should have been your first clue that the pump and lines and everything else needs cleaning/replacement.

[throrope]

murray8144

I'm no expert. IMHO, that sounds like some dirt was dislodged after you assembled all. I had near the same until after the third try when I ran a brass wire through both ends of the pilot (or idle) jet path. In case you try, I'd also avoid removing the jets, they're easy to break.

If you're fuel hose & bulbs from the tank to the engine are more than five years old, I suggest replacing all. Per our manual, Yamaha reformulated materials to withstand ethanol, but the accessory mfgrs started later. I found our lines disintegrated in the middle of Pamlico Sound. Also, if you don't already have one, I suggest adding 10 micron water separating filter. I use Sierra's without a drain bowl. The kit we use was 30 or 35 bucks online and came with a spare. The hole job costs less than a tank of gas or a failed trip.

Hope this helps, good luck and keep us posted.