fuel lines/vacuum line on 78XS

[Espiritus]

Ok, folks. I have read and researched and printed and deleted everything that I can find on here about how to run those fuel lines and Vacuum line on my 78XS1100, standard, no-octy bike.

It is pretty confusing. The manual doesn't really help on the original standard! So, if anyone can do one definitive explanation, hopefully with a photo or two, I would really, really appreciate it! I might even send you a copy of my famous "hot buttered rum" recipe for when the weather cools!

When I removed the nasty inline filters, he had a forward facing nipple on the petcock attached to the #3 boot, and also one attached to the #2. He had fuel from the right side petcock running over to the #1 and #2 carbs; the left side petcock feeding the #3 and #4. There is no connection that I could see running from the #2 to any engine part (crankcase?) I will go look again.

I gather that there are two separate attachment places: one on the actual carb body and one on the boot? Is this right? Does the vacuum run off the carb or the boot?

Sorry for what should be a common sense thing, but I read where folks reversed them and I just don't want to do that.

Thanks.

[thewiz]

Many of us ...

like to criss-cross the fuel lines, ie., left tap feeds the right carbs and vice-versa. This arrangement leaves plenty of room to install inline filters and lots of extra hose to spin the tank backwards for syncing the carbs. The vac hoses go to the carb BOOTS. The ported vacuum port on the #2 carb feeds the vacuum advance. Hope that helps.

[dbeardslee]

Espiritus - the forward facing nipples supply the vacuum to activate the fuel flow. They attach to #2 and #3 carb boots. There should be a vacuum line running up from behind the timing cover that attaches to the #2 carb fitting. If you take the timing cover off (left side of engine, round housing, four bolts) you'll see a little gold-colored diaphram can with a vacuum connection that points in towards the engine. That's what connects via the vacuum line to the #2 carb. The two lower fuel lines coming off the carbs attach to the petcocks while the two upper lines are vent lines that attach to the airbox.

I agree with thewiz on crossing the fuel lines under the tank. If you try running them straight you may run into issues with kinked fuel lines and it just makes for a very tight fit that is generally a PITA. If you took the fuel line filters out I would strongly recommend replacing them with new ones - especially if they were crudded-up. These old gas tanks tend to be rusty and you don't want that stuff getting into your carbs.

[79XS11F]

Hey guys ... Crossing the fuel hoses is the standard fuel hose set up on the 78 standard bike. If the fuel petcocks are in deed the original units the fuel nipples face straight inward toward the engine with no downward angle. The left petcock fuel hose goes from the nipple inward and down between carb 1 and 2 and then over to the lower carb body nipple between carb 3 and 4. Right fuel hose goes inward and down between carb 3 and 4 and over to the lower fuel nipple between carb 1 and 2. The fuel hoses are like a slow "S" in shape.
Rob

[Espiritus]

Now you see the fuel routing problem

Hey, all. If you read the three posted responses to my inquiry you can see why I am confused about where and how to run the lines. The petcocks have two nipples, one pointing down, one pointing forward towards the front of the tank. The inline filters were removed only to get the chunkies out and to clean or replace. The top nipple on each petcock side was ran as a non-fuel line, one to the boot of the #2 the other to the boot of the #3. The bottom nipple was ran to a brass nipple that lies between the 1 & 2, and the other bottom petcock nipple was ran to a brass connection that lies between the 3 & 4. There IS a line running from the left hand side casing into the #2 that I have not touched other than to notice that it is undersized at the connection, and "split" to make fit.

My understanding is that the #3 boot nipple where the top nipple, left petcock is connected should have been capped and had nothing connected to it.

Criss-crossing the lines with the inline filters laying on top makes perfect sense. I believe, but am not certain, that this is the original fuel tank as it holds over 5-gallons and the next year was smaller (?). If there is some other way to discover this, please advise.

I went to the "Harbor Freight" tool store today to get a compression tester, feeler gauges, grease guns, torque wrench, etc. . .there was so much testosterone in that place that I started belching and looking for a beer. . .only my daughters quick action in supplying me with my menopause estrogen saved the day.

Smile. Tomorrow is the day that I figure out how to use all these macho items. Wish me luck and send photos.

Cam

[79XS11F]

OK .. so your fuel tank or petcocks are not 1978. They are 1979 or newer. The fuel hose hook up is still the same as I described .
Rob

[79XS11F]

OK try this ... The Right hand side petcock when your siting on the bike .... The forward facing nipple of that petcock is the vac line and it goes to the nipple on the BOOT for carb #2. The downward angled nipple on that petcock is fuel and the hose for it gets routed between carb #1 & 2, on the air box side of the carbs, and then over to the fuel bowl nipple that is between carb 3 & 4.

The left side petcock forward facing nipple is a vac line and it goes to the nipple on the BOOT for carb 3, The downward angled nipple is fuel and the hose for it gets routed between carb #3 & 4, on the air box side of the carbs, and then over to the fuel bowl nipple that is between carb 1 & 2.

Fix that split vac advance hose so the vac advance works properly.
Rob

[John]

If the petcocks are correct for the application, then the smaller of the two nipples, which should be the ones pointing forward, will be for a vacuum line attached to a carb boot, #2 or 3, depending on which side of the bike it is on, and the other larger nipple will go to the lower set of T fittings between #1 & 2 carbs, and between # 3 & 4 carbs. There will be some T fittings that are higher up, between the same carbs as the fuel inlet T's, and they are routed to the two small nipples on the top front of the airbox. These are the float bowl vent lines. They must be kept open, or the float levels will be affected, or worse, the carbs could flood out.
The small hose you saw on the #2 carb body is for the vacuum advance mechanism down under the left engine cover. It should not be split to allow it to fit over the nipple. The correct size for the vacuum hoses is 3/16 inch, and the fuel line is 1/4 inch.

[79XS11F]

Fuel Line crossover ... Your looking at the air box side of the carbs



Rob

[egsols]

Hey Rob,

Drain plug on no 2 needs a bit more polishing

[79XS11F]

Originally posted by egsols
Hey Rob,

Drain plug on no 2 needs a bit more polishing

LOL LOL Those carbs have not been polished yet. They are fresh out of a storage bin. GGG they don't even have matching fuel lines .. I would NEVER do that ... LOL LOL
Rob

[olebiker]

Originally posted by 79XS11F


LOL LOL Those carbs have not been polished yet. They are fresh out of a storage bin. GGG they don't even have matching fuel lines .. I would NEVER do that ... LOL LOL
Rob

Having seen your work I believe you.