Newbie needs help 80 XJ650

I recently bought my first bike that has come with a load of problems. I have ordered a Haynes Manual but am still waiting to receive it.

I will give you my first of many problems........

When I start the bike it starts up cold (seems normal) after it heats up the Idle will stay very high and to the point I have to shut it off or it will blow. I have checked the choke linkage and it is a little rough but still looks to operate. I tested this by making sure it released all the way at the carb.

What would be my next likely step and where is this step located? :?:

 

After it warms up make sure all the enrichment valves are closing. The cable might be holding them open.

Check the throttle cable is not too tight holding it open. You can adjust the slack at the throttle. There is an adjuster with a locknut.

Try adjusting the idle set screw counter clockwise(looking from the rear) located in the lower rear between carbs 2 & 3.

If none of the above, start checking for air leaks around the carb to head boots.

 

There are little rubber caps on the intake manifold boots, make sure 3 are covered and 1 is going to the petcock via rubber hose with no cracks. Side note; don't run on Prime. Spend a week reading threads on carbs, look at the stickys in this forum. Good luck & welcome

 

Thanks for the tips I will let you know how it goes.

 

Don't mean to threadjack, but what happens when you run on prime?

My bike's previous owner always kept the switch on prime, so I did as well. I rode it switched to "on" last week on the expressway, and the engine stalled after about ten minutes. (Not fun.) Put it back on prime and it's been fine since.

 

Fin your petcock needs a rebuild or the vacuum line running from it to #3 intake boot is either not connected or has a hole in the line. Prime allows the fuel to run from the tank to the carbs all the time. The stock petcocks have a vacuum shutoff that stops the fuel flow when engine vacuum goes away.

 

Fin, don't leave it on PRI when you're not riding. If you experience a stuck float it can fill the crankcase with fuel. Put it in "ON" because "on" is actually "off" in the absence of vacuum. (or in your case all the time, at least until you fix the petcock.)

 

Thanks bigfitz and wingnut. The lines were just changed, so I'm assuming the petcock is the problem. I have another one that I will put in once the weather gets better.

 

By the way, Prime gets the fuel from the same inlet as Reserve. So if you run out on Prime you're really out.

 

So where the heck should you run the thing on a bike working properly????

Keep it on ON?

Rob

 

If the petcock is working right thats were you run it. Long side of the leaver straight down. It will shut the fuel off when the bike is stopped and allow fuel flow once the engine starts to produce vacuum. You can test your spare by applying vacuum to the smallest port and see if it allows flow when you do. Same thing happens in the reserve mode only it lets fuel from the tank flow from a lower level. Prime lets the fuel flow from the same level as reserve but it never shuts the flow off

 

And it can't take much vacuum to hold that valve open. Think about riding up a long hill and you twist the throttle open without a downshift. There would be very little vacuum but the carbs would want maximum fuel flow.

Those carb sliders are what's maintaining that slight vacuum.

 

Yeppers. As explained above; and no, it doesn't take much vacuum to operate the valve.

I'm currently working on a complete dissection and rebuild article on the Yamaha vacuum-operated fuel valve (can't call it by the common name, it will get auto-edited.) Probably have it finished in about a week, stay tuned.

 

Awesome! Explained perfectly! And this would also explain why my carb bowls were filled to the gills when I took them off to replace my carb joints. Damn things spilled all over me. I was not pleased.

Good tip and look forward to the article Fitzy

Rob