Stock 1981 XJ750 Seca jetting question

On my 1981 XJ750 Seca, the mechanical s are all stock, including the carbs; 120 main jets, and IIRC, 40 for the pilots. I have the adjustments on the carbs turned *way* in, and still the plugs look pretty light to me, like it is running lean. I have the stock airbox, all new rubbers, new shaft seals, diaphragms good, carbs cleaned in the church of OCD Clean. The bike starts and runs perfectly, no complaints, except for plugs. I am at approx 2,000 feet above sea level; should I be using different size jets because of the higher elevation?

Thanks!
Skip

 

That's because you have the idle mixture screws turned way in. In is lean, out is rich.

I'm at 2,5oo feet and stock jets are perfect for me.

If you're pulling the plugs after allowing the engine to idle, then all you're ever seeing is the idle mixture.
If you're killing the engine at speed, and are seeing lean plugs, then something else is the matter.

 

^^^+1 What k-moe said start at 2.5 turns out (lightly seat mixture screw in and count the turns out hence 2.5 out ) start there and run bike for a few miles at 45 to 55 miles an hr. Stop bike pull the plugs and check color ideal should be a brown to tan , if not back out screws another half turn and repeat till you get it. If you can't get it better you may have incorrect float level or carbs need to be cleaned .

 

find a hill you can roll down in 4th or 5th, let off the throttle all the way. listen for the exhaust popping a little. this would be a little lean. turn the screws out 1/8 turn at a time until it gets better.
the mixture screws are sensitive, they won't all be set to the same turns out.
mine seem to like 2 and 3/4 out +/- 1/8 turn.

1/2 turn is like a whole bunch

 

It's a lot easier done with a color tune plug. If you have one turn the pilot screws in until you get a white flame (lean), the open until you get a blue flame. Then install new plugs and take a ride and then read the plugs. As needed adjust the pilot screws about the width of a dime and ride and recheck the plugs. Do this until you get the nice tan color on the plugs. (Installing new plugs makes it a lot easier to read them.)

 

Having done both (color-tune, by ear/plug reading) I'll say that which one is easier depends on what the person is comfortable with. A visual learner will definitely have an easier time using a colortune.

 

Hey guys... thanks for the replies. I think I was having an attack of 'old-timers' disease (either that or having three bikes going at once is too much ) What I *meant* to say was that the screws were turned out quite a ways. Colortune is a good idea. Maybe Ill look into that. I have been leaving the bike parked because it is that time of the year in AZ (already had a couple <120 degree days) and I don't want to cook the motor if it is running lean...

 

Good call. I'm not much a fan of cooking the rider either. It hits 105 and I'm done for the day.