Recently Acquired XJ750 Problems... Help

Hello friends, I am new to the forum and recently picked up an old 83 XJ 750... I'm good with cars, but this is my first bike. I have some problems I'd like to show and I ask for any help possible...

I DID A VIDEO, POSTED BELOW

1) Engine oil pouring from airbox overflow when engine running... more revs, more oil. I believe the source is the crankcase overflow tube.

2) After blipping the throttle at idle, engine is stuck in high rev and will not calm down. Throttle cable does not appear to be stuck and this is a brand new issue that I caused today.

3) 2nd gear is gone, must bypass and go straight to third... suggestions?

[video=250,200]http://youtu.be/FyAChTP6EYQ[/video]

 

Suggestion 1: Don't run the engine until you complete the following suggestions.

Suggestion 2: Drain the fuel/oil mixture that is in the crankcase, clean the carbs (including fitment of new float needles and seats), Wet-set the floats, Check the petcock for proper operation and rebuild if necessary.

Suggestion 3: Check that the valve lash is in spec, and adjust as needed.

Suggestion 4: Prepare to either live with the 2nd gear issue, or find a used set of transmission internals to swap in to your engine (there are other fixes, but involve carefully cutting the dogs on the existing gears).

Suggestion 5: Undo the hard tail. That isn't a '37 flathead.

Suggestion 6: Get a seat.

Suggestion 7: Do whatever Fitz says that I didn't list.

 

Thank you very much... So you think by draining the crankcase's oil and refilling with appropriate amount that this leaking issue will go away?

The idle issue is such a brand new problem, was working perfectly fine not less than 10 minutes before I shot the video. Now it's impossible for it to go to normal idle.

Frustrating because I've always been able to trace issues easily with cars

Also... The guy that had it before me was making it I to a bobber, I recently ordered a LaRosa seat and mount for it, any other advantages of removing the struts and replacing them with the springs? I think it looks better this way but you are correct in that it is NOT a flathead.

 

The trouble is that there is fuel leaking past the petcock, past the float valves, and into the crankcase. If you continue to run the engine that way you'll ruin the crank bearings (along with most of the rest of the bearings). The idle issue is directly realted to the carbs being flooded with fuel.

The advantage of replacing the struts with shocks is that you'll have a bike that can handle. The XJ750 was one of the first sport-cruisers. It's meant to take the curves in a very spirited manner. Keeping the struts will look cool, but you won't be getting everything that the machine has to offer you.

 

Thank k-moe for all of your wisdom... Unfortunately, I am ignorant about these issues, I am wondering why there is fuel leaking past the petcock, and into the crank case... Why would this be? Simply drai ing oil and replacing with normal capacity will solve this?

I have never rebuilt a carb in the past so I am a little weary in how to approach this initially. I have the desire to learn, I have a manual, just need the confidence and direction.

 

Simply draining the oil and refilling will simply re-flood your crankcase with new fuel and new oil. You need to properly rebuild the carbs and set your floats to the proper settings.
In the bottom of each carb is a "bowl". Inside is a hollow float which, when the bowl is filled with fuel, will reach a level and close off the fuel flow. If the floats are not properly set, the fuel will continue to flow and flood the engine.

 

You can start here...

http://xjbikes.com/Forums/viewtopic/t=2 ... build.html

Then into the carbs.

 

Archi,

The pet rooster is vacuum operated, it seems to be working properly but once vacuum is applied when the engine runs, fuel is going down to the carbs, but not stopping when it should, overflowing the bowls into the crank case. The fluid that you see overflowing probably smells like gasoline not like oil.

To stop the issue you need to drain the contaminated oil and service the carburetors so the float valves will close when the bowls are full.
Here are instructions on how to set the float levels:
http://www.xj4ever.com/setting%20fuel%20levels.pdf

You won't be able to do this until to clean the carbs and make sure that the float valves operate properly.


If you have never serviced a rack of carbs here is a good document on what they look like:

http://www.xj4ever.com/inside%20your%20carbs.pdf

And once you are ready you must attend a service at the church of clean:
http://xjbikes.com/Forums/viewtopic/t=1 ... clean.html

Feel free to ask any questions, and do not ignore the advise. Cutting corners will take you where you are right now (previous owner did that for you)

Best wishes.

 

Again, NO. IT WON'T. Three different people have told you the same thing. Your carbs are leaking gas into the oil causing the level to increase. The problem will re-occur again and again until you properly service and adjust the carbs. Pay particular attention to wet-setting the float levels.

 

how come when my floats leaked (due to a rusty tank) gas would just leak out of the emulsion tubes or those hoses hanging out of the carbs on the 1985 xj700n and I would never get gas in my oil?

 

Not certain. Did you ever happen to stop at an empty crossroads and come across a beguiling stranger with hot-smelling breath? He may have been playing a fiddle...

 

nope for some odd reason... that only happens to you

 

I thought that happened in Georgia

 

Well after losing the first one, he swung up to New England for easier targets. Who knows how to fiddle up there?

 

so does anyone have an answer to why my crankcase never fills up with gas and why everyone else' does? should I start a new post?

 

first you have to fill the tank with premium, then put the petrock on prime.
next day you'll have your very own crankcase of gas

 

If the floats stick open on your bike the fuel gets dumped on the ground via the float bowl vent tubes (if you have the single hose-per carb setup. This does not apply to the two-hose per rack setup on the later 700)

 

hmm so a leaky float wont do it? if your float seals are working correctly then why would it fill up with gas? doesn't the gas have to seep past the float seals to get into the crankcase? even then wont the gas just leak out the breather tubes coming down from the carbs?

 

ok then leaving the petcock on prime with a full tank would not fill my crankcase up it would just leak out the float vent tubes right?

 

Joshs,

Your bike has breather tubes for the float bowl that will let excess fuel drop on the ground, but most (including the OP) do not. Two things must occur for fuel to get into the crankcase: A faulty vacuum petcock/ petcck left on prime/ manual petcock left on, and one or more faulty float needle valves (or a stuck float).

Leaving the petcock on, or on prime, will not cause fuel to get past the float needle(s), if they are working correctly and the floats are set to shut off at the correct fuel height.

For a working exampla of how a float shutoff system works, take the top off of your toilet tank and give it a flush. He has a differnt set of carbs than you do, and advice for him will not necessarily apply to you.

I suggest that you start your own thread so archifx can see replies to his problems more clearly. His bike has a different set of carbs from yours, so advice on his problem(s) will not necessarally apply to your situation.

 

thanks I appreciate your response that's exactly how I thought it worked I didn't mean to blow up his thread.

Archif I watched your video and looks like the revving problem is because your throttle cable isn't routed right or it isn't adjusted right so when you turn the wheel all the way to the left its pulling the cable making it rev but that is the least of your problems... quit running it and do what everyone has told you to do.

 

Thank you for all of the great advice. I am taking it... Here's the update. I drained the oil from the crank case and to my surprise nearly 2 quarts had come out before I saw any air bubble in the oil sight window. I did a video illustrating what I did...

https://www.youtube.com/watch?v=bd5FUOBD2Ik

Now I am off to the throttle issue, it's un rideable unless the choke is placed on halfway. Luckily, fuel was not dumping out of the air box, only oil

 

My guess is your petcock was working and turning off the fuel when the engine wasn't running. When it's running the excess gets burned instead of seeping past the rings and running into the crankcase.

If the petcock doesn't shut off the leaking float valves will fill the (not running) cylinders with gasoline which eventually leaks down into the crankcase. If you're really unlucky enough fuel stays on top of a piston to hydro-lock the engine and break things.