Fuel leak through main jet.

[Philofthenorth]

The carbs on my 78 special have a small amount of fuel coming through them. The right side more so than the left.To be clear it is the lower left hole in the carb that the fuel is coming from.The bike runs fine but the air filters are getting wet with fuel and the wife is complaint about the smell. Where should I start?

 

[angus67]

I think that's your air bleed for the main. Marked "M".
Have you checked your float height recently?

 

[5twins]

Yes, those are your air feed passages to the main and pilot circuits. The left one was marked with an "M" on the earlier carbs to identify it as the main feed but Mikuni stopped doing that on the '78-'79 carb set for some reason .....

If the fuel level in the bowls gets too high, it will flood up through the jets and out those air bleeds. The over flow pipe and drain nipple on the bottom of the bowls was eliminated on the '78-'79 carbs. There's no place for the extra fuel to go except out those air bleeds or in extreme cases, up into and out the main bore.

 

[fredintoon]

1) Turn OFF your petcock.
2) Replace you float needle and seat.

Hi solo,
good advice, Phil should also check the float levels.
But,
the '78 Special has vacuum operated petcocks that don't have an OFF position.
One only knows they ain't shutting off automatically when something bad happens.
IMHO one more reason to switch them out for manuals.

 

[5twins]

Folks might be interested in seeing how you did that, me included. I'm still running the vac petcocks and think they're great - as long as they're functioning correctly, lol. But I can see the need to make a change sometime in the future when they fail.

 

[fredintoon]

Folks might be interested in seeing how you did that, me included. I'm still running the vac petcocks and think they're great - as long as they're functioning correctly, lol. But I can see the need to make a change sometime in the future when they fail.

Hi 5twins,
replace with the swap-in manual gas taps from MikesXS
OR
file off the nubbin on the shiny plate so that the tap can turn vertical and cut the lever short enough to clear the tank.
Up is a true off and still lets the vacuum positions work.
What I did on my XS11 Standard was to dismantle both taps and swap the levers over.
This converts the flow pattern from prime/on/reserve to off/on/reserve.
I'd suppose the innards swap would also work on an XS650 that had two taps.

 

[5twins]

Swapping the innards side to side is documented on the 650 Wiki site. I thought maybe this was something different.

 

[Philofthenorth]

Thanks for all the input. My bike has a standard on-off-reserve petcock. Can someone point me in the direction of how to check the float level?

 

[Philofthenorth]

When I park it I leave it on.

 

[Philofthenorth]

Thanks. I'm putting the bike up for the winter before I go back to work on Baffin Island. So I probably won't be able to look at it till the spring. No room to play with the bike in my tiny garage in the winter. Should I just shut the petcock off and let the bike run the gas out.?

 

[5twins]

It's best to physically drain the fuel out of the carb. These carbs have drain bolts or screws on the bowls. With a small catch container under the carb, loosen the screw or bolt and let all the fuel drain out of the bowl. Make sure your petcock(s) is (are) off or you'll be draining the whole tank. I like storing mine with the carbs drained but the tanks full. Full tanks don't allow condensation to form on the inside walls. I use the plastic tops from liquid laundry detergent bottles for my catch containers. They're small enough to slip under the carbs but big enough to hold what fuel is in them.

 

[Paulrxs650]

Hi, I had exactly the same problem on another bike with the same carb. The bike had very fine crap in the tank, flowing into the carbs and not allowing the float needle to seat properly. I washed the tank out, put in an in line filter, inspected and scrupulously cleaned the carbs. The needle and seat, in this case were good, so didn't need replacing.

 

[Philofthenorth]

Hi, I had exactly the same problem on another bike with the same carb. The bike had very fine crap in the tank, flowing into the carbs and not allowing the float needle to seat properly. I washed the tank out, put in an in line filter, inspected and scrupulously cleaned the carbs. The needle and seat, in this case were good, so didn't need replacing.

The tank is new and the engine was rebuilt professionally within the last 300kms. So hopefully there is no crud coming through I will check when I open up the carbs.

 

[Philofthenorth]

Thanks I drained the bowl and shut off the petcock no more leak. I don't understand why women dislike the smell of gas so much. I find it quite pleasant.i guess up next is takem off and see what I can see. Thanks everyone for the help.

 

[Philofthenorth]

So I know it's not quite spring yet but I'm going to look into my fuel leak. Check the needle and seat. Can this be done without removing the carbs from the bike they are in there quite right and would have to cut he fuel lines to remove them. Can I just remove the bowl and check them from underneath?

 

[fredintoon]

Hi Phil,
WTF kinda fuel line won't just pull off the spigot, eh?
Cut the bastards if you need to because the only way to clean and inspect XS650 carbs properly is to take them off the bike.

 

[XSLeo]

www.amckayltd.com/carbguide.pdf is our carb bible.
Fuel line ain't expencive.
Leo

 

[grizld1]

The kind of fuel line that won't pull off is Tygon and just about any other kind you'd even want to think about installing: pulling just makes the line tighten up on the barb. To remove, get a screwdriver behind the end of the line and push it off.

 

[lakeview]

Welcome fellow Canuck. First, I feel your pain and there will be pain. The first couple times you take off the carbs, the only thing that will keep you going is your earlier investment in the pro rebuild. Search the threads for carb removal, it will get easier and it is the only way to do it right. Back the clamps off all the way and take off that big nut on the camchain adjuster. A little rubber friendly lube will help them go back on.
About the third install, you will do it in about ten minutes and you'll grin all the way out to the concession on your test run.