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[timktm]

Adjusted the idle mixture and boy does she respond. Cannot get it to stumble. Can't wait to see how it runs after a carb sync and another round or two of idle circuit adjustments! I noticed the petcock mounting screws are leaking a bit. A quick search on the forums looks like I should run the screws without the metal washer? I have new screws and new fiber washers. Any other tips to keep it from leaking? Sealant of sorts on the threads?
Thanks again,
Tim

[TopCatGr58]

Hey there Tim,

Aside from using just the fiber washers...the screws are supposed to have built in washer heads, there is also an Oval O-ring that seals the petcock to the tank. It's probably gotten flattened as well, and needs replaced as well. I've used regular neoprene O-rings from the hardware store, but VITON would be better and more fuel resistant. Not sure what the ones in the petcock kits are?

T.C.

[timktm]

I have new orings. I will try it without the metal washers. And the new screws have the built in washer heads.
Tim

Hey there Tim,

Aside from using just the fiber washers...the screws are supposed to have built in washer heads, there is also an Oval O-ring that seals the petcock to the tank. It's probably gotten flattened as well, and needs replaced as well. I've used regular neoprene O-rings from the hardware store, but VITON would be better and more fuel resistant. Not sure what the ones in the petcock kits are?

T.C.

[motoman]

I'm at 2 turns out now. Should I start there or start one turn out?

If all else(float/fuel levels,etc.) is correct, the later model carbs mixture screws should be no more than 1 1/2 turns out from lightly seated........tuned while idling.

[timktm]

Well, they ended up at 3 out. Maybe because it's cold out? Either way it runs good and throttle response is amazing. Carbs were pretty darn close but I got them closer.
Tim

[motoman]

Well, they ended up at 3 out. Maybe because it's cold out? Either way it runs good and throttle response is amazing. Carbs were pretty darn close but I got them closer.
Tim

Actual fuel levels(not float levels) is likely cause for the '3 out' instead of 1 1/4 to 1 3/8 turns out. Be sure and set those mixture screws at motor operating temperature with a fan in front of motor.

[timktm]

I did and actual fuel level.

Actual fuel levels(not float levels) is likely cause for the '3 out' instead of 1 1/4 to 1 3/8 turns out. Be sure and set those mixture screws at motor operating temperature with a fan in front of motor.

[timktm]

Well I don't know if the bike cares if it's 3 turns out or not. She flat out hauls the mail! No coughs, farts, pops, on top, on bottom, accelerating, decelerating doesn't matter. Did about a 30 mile test run. It is around 48 degrees here in Ohio today.
I had one casualty, a speedo cable. It was making all kinds of noise, squealing. I unhooked it and I did not secure it, fell down and got dragged throughout the ride because its smashed and damaged. I have to figure out whats going on with the speedo. Probably another reason the auto cancel doesn't work either. It handles pretty good overall and held tight and straight at speed. A few things I need to tweak but overall very happy!

[mack]

Plugs

Just watch your plugs and milage per tank. with the early carbs and correct jetting you should get 38-44 mpg with mixed driving. Adjust the idle mixture screws until you get a very light tan colour. The factory setting when new was 1 1/4 turns out. However over time, wear and different fuels this can change. My carbs on my SF run at 1 3/4 with the best colour and performance (each one slightly different but pretty close to that). My milage with two up is 38-41 but if I'm alone I can get as high as 45 at 60mph. The plug colour will tell the story.

[crazy steve]

Don't get hung up on mileage numbers; these bikes were never known for their fuel economy. My '78E only achieved 40 MPG once, it was usually in the mid 30s. If it drops into the low 30s or less during 'reasonable' riding, then you have tuning issues....

[timktm]

Yep, and I will set it up for best performance, not mileage. And so how does the mixture screw have any effect on mpg? I would think if it had any effect it would be minimal? A bigger factor would be pilot jet and main jet wouldn't it?
Tim

Don't get hung up on mileage numbers; these bikes were never known for their fuel economy. My '78E only achieved 40 MPG once, it was usually in the mid 30s. If it drops into the low 30s or less during 'reasonable' riding, then you have tuning issues....

[motoman]

Yep, and I will set it up for best performance, not mileage. And so how does the mixture screw have any effect on mpg? I would think if it had any effect it would be minimal? A bigger factor would be pilot jet and main jet wouldn't it?
Tim

Nope........mixture settings are utilized thru ALL rpm ranges. Main jets fuel is added to mixture as revs come above approx. 3500rpm under load.

[motoman]

Nope........mixture settings are utilized thru ALL rpm ranges. Main jets fuel is added to mixture as revs come above approx. 3500 rpm under load.

Better explained, assuming jetting(pilot/mains) are stock using stock intake, pilot jets flow thru all rpm ranges. A rpm increase and manifold vacuum drop dictate metering rod location that control main jet fuel flow. In other words, pilot jet flow will maximize with rpm increase, at which time metering rods will rise adding in main jet fuel flow to accommodate rpm increase(venturi velocity)and manifold vacuum drop. A stock intake set-up(heaven forbid pods unless you enjoy a jetting night-mare) and stock jetting is all that is EVER needed, no matter the elevation(less venturi velocity and a bit less vacuum as elevation increases). At sea level there is 20-21 in vacuum maximum. At 5,000 ft. elev. there is 18 in. maximum vacuum. At 10,000 ft. elev. there is 15-16 in. maximum vacuum. These are constant velocity carbs, so elevation has little to no effect on carbs. Running pods for intake DOES as does a 4 into 1 exhaust. Those Japanese engineers had it pretty well figured out and did intake and exhaust accordingly. Any mod to either intake or exhaust throws calculations out of wack, resulting in an actual power loss at some given rpm range from idle to red line range.

[BA80]

C'mon Brant, the IDLE MIXTURE SCREW is just that. It has an insignificant affect off idle.

About 1/8 off idle the pilot jet is what controls the majority of fuel flow, the main jet and jet needle come into play at 1/4 to WOT.

[timktm]

Clear as mud.