Full Throttle on Starting (82 XJ650 Maxim)

So as of today I have a problem. I bought this bike a year ago, and have been trying to restore it to running. Nothing was inherently broken when I bought it, it had just been sitting in an outbuilding for (???) amount of time and the guy who sold it to me rediscovered it an hour before he had to vacate the property that he had just sold. In his desperation, he sold it to me for $250. It was a steal for sure, but the bike has fought me every step of the way.

Recently, after ensuring everything else was in working order (Aside from the front brake, but I'll probably make a separate post if I can't figure that out), I got to the carburetors. After opening them up and failing miserably to remove the jets, I figured this was something way out of my league and brought them to a professional.

I had them completely rebuilt with new parts, thoroughly cleaned, and made them make sure nothing in it was broken. After bringing them home and popping them into the boots, the engine finally ran for the first time. Only one problem: The second I press the starter the bike jumps to full throttle and screams until I shut it off.

I have adjusted the idle screw to no avail. It doesn't seem to affect it at all. I have checked the throttle and choke cables and ensured neither were pinched or being pulled. I have no clue what is happening here, and am at my wits end of what else I can do.

Any help would be appreciated.

 

have you ensured that the enrichment cable (choke) and the throttle cable go to the correct place.
I've read on here that the throttle cables gets run to the enrichment circuit instead of the throttle (did I make that clear?)

and awesome deal on the bike!

 

Did he do a bench synch , my opinion your synch is way off first thing to try back off the idle knob see if you can get it to idle down ...

 

I am pretty sure the throttle and enrichment cables are going to the correct places (The throttle is supposed to go to the mount on the throttle side of the carbs and the enrichment cable goes to the mount in the center correct?). The shop did do a bench sync on them. Like I mentioned in the original post, the idle knob has no effect on the problem. I have tried it all the way in and backed all the way out and it makes no difference.

 

The throttle cable connects at the center of the carbs between carb 2 and 3, the enrichment cable connects to the linkage between the 3 and 4 carbs. The throttle linkage can also get bound up when installing the carbs. It should be easy to tell if the throttle is connected correctly and not bound by opening the throttle fully (just over a 1/4 turn on the grip) and releasing, it should snap back and you should here the butterfly valves bottom against their stops.

 

That's probably what it is then. I was wondering why there was so much free play in the throttle and yet the enrichment cable was overly tight!

When I get home around 4 I'll flip them around and post the results.

Thanks!

 

With the bike off can you do a throttle flip? Twist the throttle and then let it snap back to the resting position. I think the term is "blipping" but I am not sure. That will help with the cables as well. The If you can take a look inside the carbs from the air box side ( know hard to do when they are on the bike) see if the slide tubes are down also. If they are stuck up this is not good.

 

Please keep all posts about this machine in this thread. Seperate threads just make it harder for us to keep track of your work and help you.

 

Alright, sorry for replying later than anticipated but I've been fighting with it again.

So I switched the cables around, and now the throttle actually feels like a throttle is supposed to feel.

Only problem is now the bike won't start at all, even with starter fluid. If you leave it alone for a while and then attempt to start it again it will lightly chug for a few seconds like it is about to start and then die off. After that any further attempts just have the starter turning over and over.

I've even tried giving it a little bit of throttle when attempting to start, and it won't start with that either, which puzzles me because the only change has been the swapping of the throttle and enrichment cables.

Not sure what to do from here.

 

Turn the idle speed knob clockwise a bit and try again. The choke cable holds the throttel plate open further than the throttle cable will.
Also turn the petcock to PRI for a few seconds to make sure that the float bowls are full.

 

Tried both of those things, and neither helped. Could the spark plugs have crapped out during this whole process?

 

All 4 at once? Hightly unlikely. If they had you would smell raw fuel in the exhaust.


Let's go back a few steps.
Did you bench synch the carbs after rebuild?
Did you set the idle circuit baseline?
Were the enrichment jets in the float bowls thoroughtly cleaned and chedked to ensure that a spray of carbcleaner into them would go across the room?

 

Carbs were bench synced.

Enrichment jets were thoroughly cleaned. Guy at the shop even brought up how dirty they were when I brought them in, and how they completely cleaned them.

I'm not sure how to set an idle circuit baseline, and I am also unsure if it is something the shop did.

 

The idle mixture screws are on the top of the carbs, just next to the enrichment plungers (if you see brass plugs then the idle mixture screws were not touched).
FOr your bike you will need to turn them to a soft-seat (do not tighten them), and then back them out by 2 1/2 to 2 3/4 turns.

 

Adjusted the idle mixture screws, and it still won't start on it's own. If I shoot some starter fluid into the engine it will start up, but immediately jump to 5,000 rpms. If I turn it off when it is in this state I can start it (to the same result) 1-2 more times before it just quits and won't start again.

 

Back the idle screw CCW a bit to lower the idle. You have been adjusting it so it is likely causing the higher RPM.

The fact it only runs on starter fluid suggests the float bowls are not full of fuel. Turn the petcock to prime and if you happen to have a clear fuel filter watch and see if gas is flowing - note freshly rebuilt carbs let's hope you do have a fuel filter installed. If gas is not flowing you can wrap on the side of the carbs with the palm of your hand to get the fuel flowing - it can be stubborn and may take several minutes of this to get the bowls full. Set the choke to full enrichment and give it a whirl.

You could also do a quick check of the carbs with the clear tube method just to be sure they are filling. Put the bike on the center stand and check at the center of the float bowls and the level should be close to the 3mm if the carbs were initially setup correctly. The process can sometimes even get the fuel to start moving.

 

air(idle) mixture screws (4) are for tuning carbs for the pilot jet circuit are on top of carb, as stated above set to 2-1/2 to 2-3/4 turns from soft bottom. do not adjust any more unless needed after checking plug color or buying a color tune tool.

on the back of carbs between carb 2 and 3 is the Idle adjustment knob ( throttle plate stop screw) this knob is what you adjust the idle to 1100rpms with not the 4 screws on top.

 

So I am considering taking the carbs off and checking that they are filling, but first I just wanted to add here something odd I found. The insane throttling issue only occurs if I spray engine starter fluid into the 3rd cylinder. All of the other cylinders just burn the starter fluid and then die.

Not sure if this means anything, but it seems important to note.

 

Check the caps on top of the vacuum ports, as well as the vacuum line for the petcock (usualy hooked up to the #3 vacuum port). You probably have a vacuum leak.

 

Checked caps, and they appeared original (Hard as a rock) so I replaced them with new ones. The same problems still persist. Even attempted disconnecting the petcock vacuum line and capping off the #3 vacuum port, and nothing changed.