fuel flow

[screamin deal]

I am not much of a mechanic, but I am going to try and fix my ride myself. My air box had fuel in it. My tank petcock valves were leaking a bit and I think I stopped that. I think that something else is wrong. There was way too much fuel in there for just my valves dripping. I am going to take the carbs off and make sure nothing is stuck inside. I dont have all the tools that I read you guys using , carb sync, valve shim etc... I have even less knowledge , but I am pretty lucky.While I have it apart I was thinking of going to Pods for air filter instead of the air box. Are the 54mm the right size for a 1979sf. Any info to help a mechanical moron would be greatly appreciated.

[egsols]

The fuel in the airbox is coming from your carbs. Either the float valves are leaking, which they do lots on the 79's, or your floats are sticking, or you have a bad float(the brass floats can get pin holed allowing fuel in which prevents them from "floating") or your float vents are plugged or a combination of the above. There are a lot of threads dealing with how to fix the valves and seats. Prom has suggested "lapping" the valves with a bit of chrome polish and several members confirm it works, maybe an idea.

Have a close look at the valves when you have them out and check them for signs of wear. If you see grooves on them then you may need replacements. If they aren't too bad, clean them up, perhaps "lap" them, adjust your floats, make sure nothing is binding and "bench" test them for leaks before you put them back on.

Again, do a quick search on this site to find the threads.

Many times just letting the bike sit for a few weeks can shelac the floats and valves enough to cause some binding and cause leaking, I know it has on mine.

Pods see http://www.xs11.com/forum/showthread...ight=54mm+pods

[prometheus578]

Well, not really lap them in....
If the needles have wear grooves, replace them.
Cheapest I've found online is Z1 Enterprises.
http://www.z1enterprises.com/detail.aspx?ID=310
And yes... these are the style of needles that you need.


As for the seats.. take them out of the carbs, remove the debris screen on the bottom and polish the seat's sealing area with Q tips and "Simichrome".
Other chrome polishes might work, too. Can't say that I've tried all of them, but the different ones I've tried have failed to smooth out the seat and stop the leaks.
I've used Simichrome to polish needle seats for years and have never been disappointed. Call around... most bike shops carry the stuff.

Pick up the tube, not the can. This stuff will last you forever!(Unless you're some sort of polishin' fool that has to have everything shiney)

[TopCatGr58]

Hey Screamin,

54mm is the size of the set of 79SF carbs I have, and it is also the size of the 81SH as well. There was some controversy about some XS's needing the 52mm size, and even though the 78E and 79F have the same carbs, they are different than the 79SF and more different than the 80-81 series. HOWEVER they all use the same part # for the Air Filter mounting boots, and I would think that IF there was a change in size, ie. the 78E/79F using a 52mm, then the intake boots would have been a different number for a different size, but they are ALL the SAME # throughout the model series/years.
T.C.

[bikerphil]

carb difference

the 78E and 79F have the same carbs, they are different than the 79SF
T.C.

Hey TC, what IS the diffrernce between the two, Standard and Special? Mine are identical.

[Axel]

Memory ?

On another board ,I heard of "lapping" with a golf tee and Autosol . Is this the same operation ? I think they cut the ball holder off the tee and mounted the pointy end in a drill press .

[TopCatGr58]

Hey Phil,

I was stating about the Yamaha Part #s for the entire carb assemblies, which are different for the 78E and 79F vs. the 79SF and 80-81 series.

The early ones are listed with 2H7, the 79Sf is 3H3, and on and on. SO....I was trying to determine where the 52mm pod size recommendations came from....but when I checked the airbox boots, those are ALL THE SAME#'s, and that told me that the early carbs should be 54mm not 52mm. I only have had access to the 79SF's and some 80 and 81's, and they all measured to 54mm, but wasn't totally sure of the very first carbs, especially since I had seen others post about needing 52mm pods for them!?

But now with your post, and Jesse's, having the early carbs available, and verifying that they are also 54mm intake ports, I can add that info with confidence in an upcoming carb tech tip.
T.C.

[Do Lee]

"The early ones are listed with 2H7, the 79Sf is 3H3, and on and on"

The 2H7 for the 78E, 79F & the 3H3 for the 79SF were for ordering replacement carbs with the stock jets. All three sets of carbs. bodies are
2H7.

[screamin deal]

new problem

I am an idiot. O.K. Boys and girls I have a new problem. Before I began to take my carbs off I thought it would be a good idea to start my bike with the air box off and see the actual leaking take place. When I did this it ran poorly and sputtered quite a bit . When I shut it off fuel poured out of my intake and appeared to be mixed with oil. Now my bike used to smoke a bit if I did not ride it every day and did not smoke if I did. I know oil and gas should not mix , but I don't know what is going on or how to fix. I am hoping I don't have to tear it apart because I am not sure I posess the skill to do this repair. Please advise.

[planedick]

Aounsa like

You may have leaked enough to fill your crankcase with gas to the point where it draws the mixture in through the crankcase vent and has contaminated the carbs so much that it appears to have oil mixed with the gas. Put the bike on the centerstand and check the oil level and sample it to see if it has gas in it. Your nose should be able to tell you!!! Stick something down the fill hole like a dipstick and pull up a sample to check. Some have been known to fill the crankcase with oil until it appears in the sightglass while the bike is on the sidestand...... causing the level to be WWAAAAAYYY overfilled.....

[Ivan]

not meaning to insult anyone's intelligence, but it is sometimes the obvious that escapes us.

You say there is oil and gasoline coming out the intake. Did someone make some premix fuel for a two stroke and put it in your tank?

Just a thought

[screamin deal]

gas in oil

Ok I checked my oil and it has gas in it. Two stroke mix solution not an option . I fueled up at the gas station, I leaked fuel into my oil somehow .

[bikerphil]

Leaky carbs will leak down past an open intake valve into the crankcase. Drain and change that oil before running the engine again. Gas in crankcase not good at all for engine bearings.

[screamin deal]

Thanks for the advice I will let you know how it turns out. Right now there are ten things a minute that keep me from getting to work on my bike. As an old friend of mine used to say " If it's not one thing, It's your mother!"

[screamin deal]

carbs are off

O.K. I found a minute to work on my bike and took off the carbs to fix my leak. I also removed the air box because I think I might go to pods instead. I have a question. If I do this where do I send the breather tube? And is there someone out there that can post a good picture of a pod setup? It looks like the battery will be showing alot. I need to see something to wrap my brain around. Thanks for all your help.