Needle Jets. Where to get them?

[TopCatGr58]

Hey Marty,

It sure could be, if the vac. adv. is hanging or not properly or fully advancing during cruising speeds, then you are not running at the max. fuel economy timing setting, and therefore could be wasting gas!

You may not need to totally replace it...although I know you like to install new parts when possible, but it may be just a matter of cleaning, regreasing the old unit. But it might be quicker and easier to just swap one out, and then you can take your time to refurbish the old one IF it can be.

But remember, if you're running all thru the mountains and not on flat superslabs, then you may be getting appropriate mileage for your riding environment, running up and down hills is not so good on mileage.

T.C.

[jetmechmarty]

I went to Birmingham and back last weekend. 30 mpg is my current best. I'll exhaust all ignition possibilities before I get in the carburetors again.

I'm using the bike daily for my commute. I should use the XS650. It goes twice as far on a gallon of gasoline.

[jetmechmarty]

Hey Marty,

It sure could be, if the vac. adv. is hanging or not properly or fully advancing during cruising speeds, then you are not running at the max. fuel economy timing setting, and therefore could be wasting gas!

T.C.

As usual TC, you made a good call! I've had a bit of a stumble when the throttle is just cracked open. It's most noticeable in top gear following traffic at 45 mph. I took the mechanical and vacuum advance mechanisms apart. I cleaned them, lubed them, and reinstalled. The stumble is gone! I just had a ride in traffic up over Blood Mountain then back over to TWoS and back home. Now, it wants to wheelie exiting the turns!

I'll be riding the bike to/from work all week. That should tell me if there's any improvement in economy.

[jetmechmarty]

Just a far-fetched idea, but have you checked your timing and mechanical advance? I had trouble starting as well, it was related to both for me.

I fixed that, so it moves like butter now. We'll see what happens.

[GLoweVA]

Alright Marty, It's been a week, How's the mileage?? Did lubing up your advance fix your low MPGs?

[jetmechmarty]

The stumble is gone. It feels like it runs great. My commute every day is 5.9 miles. My gas mileage was even worse this week at less than 25 mpg.

I just started the bike after it sat in the parking lot for five hours and the temp went from 29 to 39 deg f during that time. I mashed the start button and got instant VROOM! No choke. That ain't right.

[GLoweVA]

SOunds like it's still too rich. To be able to fire it up without the choke when it's this cold, then yeah, too rich. (like having the choke on all the time)

How do the plugs look?

I gotta ask, right size jets in there?

[jetmechmarty]

SOunds like it's still too rich. To be able to fire it up without the choke when it's this cold, then yeah, too rich. (like having the choke on all the time)

How do the plugs look?

I gotta ask, right size jets in there?

Plugs 1 & 4 are brown. Plugs 2 & 3 are tan.

All the jets are genuine Mikuni. The idle jets are stock size. The mains are 115 across. The main jets used to be 110, 120, 120, 110. Maybe that was better.

I hesitate to mess with the carburetors yet. I need to exhaust all other possibilities. I should replace the coils. Mine are over 34 years old.

[BA80]

The 2 center cylinders will run leaner because they run hotter than the outer ones. Yammi ran a little larger jet on 2 & 3 for a year or two for that reason but decided that it really didn't make that much difference.

[jetmechmarty]

The 2 center cylinders will run leaner because they run hotter than the outer ones. Yammi ran a little larger jet on 2 & 3 for a year or two for that reason but decided that it really didn't make that much difference.

I'm starting to believe the folks that wrote the Clymer manual did not make a mistake. They purposely call for 110, 120, 120, 110 jetting. It's beginning to make sense to me.

What went wrong that I no longer need the choke?

[motoman]

Possible enricher circuit is leaking fuel by it. BTW, the G and H Specials had 110's across all four. The Standard of those two yrs. had the staggered main jetting.....less predominent on the H by then, but some still did. Just depended on the mood of the assembler I guess. But it was dropped on most H's by then. Some even had a tad shorter diaphram springs on the center two carbs. The Canadian version of the Venturer even had adjustable metering rods........go figure.

[jetmechmarty]

I jetted mine fat because my plugs had been scary white. JeffH went through the carbs and made it run perfect. This after I had been in them over and over. The only thing I did after he set them up was adjust the mixture screws and sync. I did both with a Morgan tool. The improvement from Jeff's bench sync was barely noticeable. Cold starts required the choke. Now, they don't.

[jetmechmarty]

I hate to admit this, but I just discovered that my timing was retarded. I reset it. We'll see. I tested the vacuum advance a while back. I checked the mechanical advance this evening. It works.

[bikerphil]

Marty, you may like the way the engine runs with the timing advanced a few degrees higher than the factory spec, much more pep off the line. You will have to lower your idle a bit though. Too much advance and you will hear pinging under heavy throttle opening, then just back it off a hair. GL

[jetmechmarty]

fixed

This is a very old thread. I finally fixed my 25 to 30 mpg. I replaced the emulsion tubes and slide needles. Now 40 mpg!

XJ4ever.com has correct reproduction needles and emulsion tubes.