Running fine then poorly all of a sudden, dead rich, 82 Turbo

Good morning folks,

I have been riding my 82 Turbo all summer and it's been doing great. The bike sat for 24 years and then after a little work was revived and I have put probably 800 miles on it this summer.

All good with boosting strong, no breaking up, choke works like normal etc. until last week when the bike didn't want to turn on with the choke. I got it to come on with the choke off and the throttle turned halfway to keep it barely running until it cleared out, revved up and still sounded like is was missing slightly. Not running as smooth and overly rich. Move the choke on and now its running really rich.

Now this bike has stock carbs that I haven't gone through and besides a new battery and plugs, the ignition is stock. Since the problem started all of a sudden like a light switch, I'm sort of suspecting electrical. What would be your first items to track down and start with? TCI? Coils?

I don't want to dig in to the carbs first because they are a bigger pain in the butt and like I said before last week, I had no issues. It certainly could still be carbs that break overnight but I want to start ignition side first.

Thanks for the help folks.

 

Sorry to say, but it's not an ignition problem.
Sudden and rich points my nose to thinking about the floats, float needles, and fuel pump pressure regulator.

 

Welp, this fall I guess I’ll pull them and try to track down all the turbo specific mikuni bits. I was hoping my symptoms sounded like a failing ignition component I can swap out easier.

 

If it seems like ignition, check fuel. If it seems like fuel, check ignition. At least that's how it usually goes for me.

 

Start a conversation with @chacal. He's already tracked them down for you.
Also, diagnosis first. Buy no parts until you know which ones are causing the problem.

 

Yeah I mean if it’s anything carb related, it’s getting a total overhaul because they are a pain in the ass. 4800 miles on a 37 year old bike with nothing ever touched with them so if it’s one rubber part I’m just doing it all.

 

For complete Turbo carb rebuild and some gaskets I recommend BDesigns. http://bdesigns.ca/Yamaha_Carb_Kits.htm. Compared to any other XJ carbs they aren't bad. The rest of the fueling system however...

I would second checking your fuel pressure regulator as well. If it pushes anything over 2 psi over boost pressure, you will flood the carbs in a hurry. Check all the fuel and vacuum/boost hoses.

Also, 4800 miles you're right to be skeptical of low miles. Expect to go into the valves. I got mine 10 yrs ago with 6800 miles, and when checking the valves I had to replace 7/8 shims.

 

I'm not skeptical in the sense that I don't believe the mileage to be accurate but just that it hasn't been run much and sat for a very long time albeit indoors. I'm planning on doing the valve adjustment and clutch when I dig in to the fueling issue.

 

Like a Ranger UTV i worked on for a cutomer....
Under 500 miles, looked mint, bought at auction.
Complaining of wierd sounds and poor handling....
Needed all 4 wheel bearings, brakes, ball joints tie rods...
Customer got pissed at me, calked me a liar, paid for inspection n took it home... Lol!
Easy to buy a speedo for an ATV run on a golf couse for 10,000 miles and looks mint

 

^^ oh yeah diffs need bearing n seal kits too...

 

Sorry I didn't mean skeptical that the mileage isn't real. I meant skeptical that low miles means an easy or quick fix.

 

Yeah no worries. I usually like to get things that have average miles for the year and steady use over really low miles because it wasn't used for a quarter century. Our winters are long and so for 5-6 months a year I get to take my time and catch up.

 

MAP sensor?