1985 Yamaha XJ700 Carburetor Tennis

Back and forth, back and forth. I have been in a long and frustrating tennis match with my carburetor since buying the machine about 2 months ago. 1985 Yamaha XJ700, 8,000 miles.

I knew nothing about carburetors, but thanks to this forum (you guys are amazing) and willingness to roll my sleeves up, I feel like I've gotten to know mine pretty well. I'm stumped though, and so I'm writing my first post hoping you can help!

Carburetor (Hitachi HSC33) started leaking about a month ago. Checked the floats and needle, cleaned the carbs right out. Readjusted the floats after clear tube test (this has been a royal pain incrementally adjusting back and forth every week). One of the float arms that holds the pin was broken, so I used Permatex gas tank repair stick to hold the thing in place and let it cure for 24 hours. Hopefully this holds up and doesn't effect float bowl fuel level too much or the float movement. Before putting back on the bike, float movement didn't seem effected. Spark plugs looked pretty good.

Noticed previous owner had different main and pilot jets in despite there being no noticeable modifications to the bike, (main jet 110, pilot jet 40) so I replaced with as close to stock jets as I could get (Main: 108, pilot 38)

The Problems:

• Unless idle screw is turned down way low, the motorcycle throttle will hang for a few seconds after releasing throttle. (possible vacuum leak, though when sprayed with starter fluid, bike does not rev up.)
• At idle, motorcycle will slowly lose RPM's until stalling. This was a problem before and after pilot jets were swapped out, and idle screw adjustments make no difference here.
• After a long ride last night and no issues, this morning the bike was leaking gas out of the carburetor AND AIRBOX. Very concerned here. (float stuck?)

Anyone out there in carburetor wizard land have some insight for someone new to carburetor repair and adjustment? Thanks ya'll, can't describe how much I've appreciated reading the wisdom you all have shared.

 

Did you replace the throttle shaft seals?
The fuel petcock is leaking. The floats should hold back the gas that the leaking petcock is providing but they don't.

 

Polock, I haven't replaced those. I was wondering if that might be the culprit after reading through XJForever's fuel systems FAQ. Thanks for the feedback. I'll look into this.

 

Start with the petcock.
Then pop off the clips on the outside of the outside carbs and have a look at those , I find those are the best. If their bad the others are worse.

 

Sounds like getting into and replacing Throttle Shaft Seals can be a pretty messy business unless done absolutely thoroughly and correctly, which involves pretty much dismantling the carbs. Should I even bother just trying to replacing the outer throttle shaft seals to see if it makes a difference?

 

The whole carb cleaning and tuning thing is involved, that's why everyone says do it all, do it the first time, do it right.
When you have to go back in, you do want to kick the dog . Look at yours maybe their fine.
Replace only 2? Don't bother.

 

That's what I figured. Felt like I was getting real close to fixing this carb gremlin, but back in I go! Thanks for the advice.

 

Do all you can first , but if you have to, you have to.

 

Think of it this way, you will become a master at removing and installing your carbs, you will go to Church* and be saved, and in the vein of Zen and the Art of Motorcycle Maintenance, your fingers will be getting a justifiable dose of yoga.

Be thankful you are doing this now, the warm weather makes your rubber boots malleable and promotes less grunting when removing and installing the rack.

*http://xjbikes.com/forums/threads/in-the-church-of-clean.14692/

 

you should try to find a carb body forto replace the one with broken post while you have them apart

 

Also replace the vac hose, fuel line and add a new in-line sintered filter. Rebuild the gas cap when you do the petcock. Hope this helps.

Gary H.

 

PO had different jets installed. The question is why. Does your motorcycle have the factory 4-2 exhaust system?

If so then the PO may have been upjetting to compensate for leaking throttle shaft seals. As everyone lese has said, tear the rack apart and do the full monty.

 

I think I would use propane rather than starter fluid when looking for air leaks.

I have an 85 XJ700N and when I rebuilt my petcock I couldn't get it to stop leaking until Chacal advised me to use a small socket to SLIGHTLY depress the metal flange to lengthen the reach and it has worked perfectly since then. (Slightly means you can't see much change at all, but it is enough) I also put a small washer under the spring -- another Chacal suggestion. I also decided to replace the float needles and seats and again at Chacal's suggestion used the solid brass needles and they have worked great.

I agree that you should keep your eye out for a replacement carb body. Your repair may work well, but I'd prefer to have a solid post.

 

Thanks for the advice everyone!

Here's a little update about where I'm at:

Carburetor: I'll keep my eyes peeled for a replacement carb body to deal with the float post issue. In the meantime, I drilled into both sides of the broken float post and put a sanded nail in between the two cut flat so that the broken ends meet flush, but snugly. I JB Welded the hell out of the nail on the inside, as well as the sanded down exterior. This will hopefully be a fix for the short-medial future.

Put back in a larger pilot jet to possibly compensate for the shaft seal issue (I put back in a 40 as opposed to 38) but it hasn't really helped. Still not sure why the jets were changed out when there doesn't appear to have been any mods to the stock bike.

Petcock: Nothing seems wrong here, though I didn't rebuild or clean the petcock past shutting on and off and playing with the valve while riding around to perhaps flush out any junk that had collected. The leaking issue must have been a stuck float needle or something, still kind of a mystery to me what happened there. The petcock has not been an issue since the one incident, though I did lower the floats a little. I've been shutting the petcock off after I'm done riding just to play it extra safe as well.

Throttle Shaft Seals: I checked the outside seals, and don't really know what a "bad" seal looks like. They didn't look rotted, or dry, or cracked. Haven't dived into the interior ones yet, though the symptoms of leaking seals are there (sputtering/dying idle not fixed by idle screw adjustment, hanging throttle at medium / high RPMs) How important is purchasing OEM here as opposed to aftermarket? I get that I'll want a good seal, but is shelling out $50 bucks for 8 OEM seals going to make a huge difference as opposed to finding some "Grab Bag" rings that will fit from my local bike shop?

Once again, thanks for all the help ya'll.

 

I suspect the post fix will work indefinitely if you were able to get the post to fit exactly at the brake. JB Weld is pretty good stuff.

A stuck needle valve will only leak if it gets gas and that comes through the petcock and fuel line. If you had any leak I would think the petcock was somehow involved, although I guess it could just leak the fuel in the fuel line as long as air was able to get in to relieve any vacuum. Shutting off the petcock could be just hiding the petcock problem.

 

Got a picture? When the time comes to remove the guts for the new bowl you'll have to bend the float stops with a pair of needle nose pliers to allow enough drop for removal of the float needle.

Gary H.

 

do those petcocks have a "off" position ?

 

Fuel doesn't flow when the petcock is in the "on" or "reserve" position unless the bike is running. Fuel will flow whether the bike is running or not in the "prime" position. Talk to Chacal about the shaft seals. Iirc he sells aftermarket seals but you may have to double the new wafer washers on the ends because they're slightly thinner than the oem washers.

Gary H.

 

Sorry for the confusion, I've got a fuel flow shut off valve on there too.

 

From what I've read, washers don't wear the same way so I'm thinking those are still good. Already talking to chacal! Great resource...

 

I'll try to take a pic after I get those seals and pull the carb again.

 

Update: I synced the carbs, and the bike is running much better. The only issue I am truly left with is a carb that continually leaks no matter where I adjust the float level. I have also traded floats, pins, seats, and seat washers with this carb and while the leaking was better for about an hour of a ride, it came back on the same carb.

It is worth noting that this is the carb with the float post that was broken, that I jb welded back together. Upon inspection, the weld seems to be fine, and I cannot see how the weld would infringe upon the floats movement, as it moves fine as compared to the other floats. I actually have this float set to allow slightly less fuel into the float bowl, and it still leaks.

I am at a loss! I cant figure out why it would be leaking. Could there be a blockage somewhere? If so, could someone help describe to me (like I am a five year old) how this could lead to the carb leaking? Please help!!!!

 

i think it was in www.xj4ever.com catolog under carb parts i read that there are adjustment washers for the float pins beacuse the float moves sideways and jams the float.
you could have some crud in the needle valve assembly
or setting your float lower...you are not getting a complete seal.
is it leaking where the diaphram slide needle seats in the top of the main jet ? you could just be looking in the wrong place for the cause.

 

The float needles have a very tiny piston at one end, with a very tiny hidden spring that allows it to spring back out when not pushed it by the tang, is it posible this spring is shot and the needle doesn't shut off the fuel supply for this reason? I have one with a weak spring and I noticed this is the carb with the hjghest float level, not flooding but very high.

Update: well, the said carb is flooded this morning so I have a similar problem...

 

Carefully inspect the tab the float needle spring goes around. If there are any burs it could catch and the needle will hang up.
The post has to be straight and square to the carb body. If the float pin is crooked enough the float could bind and cause problems too.
Pictures will help so we can see

 

If you're still interested in checking the throttle seals, here's a way. Open up the flow on a propane torch but don't light it. Wave the nozzle around the carb rack while the engine is running. If the revs increase, it's because propane is sneaking in through leaks.

 

Assuming that the carb bowl is not cracked, the only way it will leak is if too much gas is allowed into the bowl, which to me points to two possibilities: bad float setting which you have already addressed, or a leaking needle and seat. A leaking needle/seat results from a sticking needle or a worn needle/seat that will not seal. At this point with what you have already done I would order new needles and seats from Chacal. I got the solid brass set and have had no problems at all.

That being said, the fact that it is the repaired carb seems to imply that the repair might have something to do with it, such as pressing the needle at a slight angle causing it to bind or not seat correctly or possibly binding the float. But if you are absolutely confident in the post repair then it has to be the needle/seat since that's the only way fuel enters the carb.

 

What about swapping needle and seat with a carb that doesn't leak and see what happens?

 

And are you sure that the fuel valve body and the needle are still a matched set?

 

Mikuni carbs also have an o-ring that seal the float valve brass seat into the carb body (Hitachi carbs use a threaded seat which screws into the carb body and a crush washer). That o-ring can get worn out and/or pinched during installation that will cause a fuel leak even if the needle/seat is sealing properly and even if the carb floats are set correctly.

 

I don't think this is the issue. I changed the float needles around to test if something like that could still be the issue, but it's still happening from the same carb regardless of what needle. Sorry to hear yours is acting up!

 

Nothing wrong with the float tang. Changed the floats around on the carb to see if the issue would spring up in another carb, but it stays in that same carb. The float post is square enough to be able to remove the pin and float, and then put it back with just slight resistance, but nothing major. I'm led to believe the leaking issue doesn't have to do with the needle, seat, or float.

 

Thanks for the advice! I'll have to check that and report back.

 

Very astute observation! I know that I have the hitachi carbs, and I noticed that the previous owner had an old paper washer instead of the washers the other three carbs had. I thought this was the issue, so replaced the washer (and actually pulled the threaded seat and washer from another carb swapping into problem carb to see if that would fix the issue) and it seemingly had. I rode around problem free for about 25 miles, parked the bike, and when I came back, the same carb was spitting gas again

 

Thank you for reading through what I've done already and the response. I am starting to wonder if the repair to the post might have something to do with it, as secure as it still is. I may try to re-do this repair paying special attention to making sure it aligns perfectly.

The fact that I can swap out any of the seats/needles/floats in the whole rack into that problem carb and get the same result points to the idea that it isn't any of those things that are the problem.

 

Weird. I strung up the carb without the float bowl on and gave it gas. Closed the float manually. No leaking, but it did seem to be leaking gas from this area when the float was closed? What the hell could that be? Bad seal somewhere?

 

O-ring on that tube. Split the rack and see if the tube has replaceable o-rings or you may need a new Tee.

 

Know of any good how to resources for breaking down the rack? Haven't gone that deep into my carbs before.

 

Read this and check out the links within it - it should help you understand your carbs:
http://xjbikes.com/forums/threads/in-the-church-of-clean.14692/

You DO need to get 'that deep' into your carbs, otherwise you will be chasing your tail.
It all sounds intimidating, but certainly do-able. Ask questions here.

 

Thanks y'all! Definitely sounds like a weekend project. Not something I should get up and walk away from and forget where I put a screw

 

Took me a lot longer than a weekend (lots of pics and notes) - Hogfiddles does it in a half hour with his right wrist tied to his left ankle and a welding helmet on.

 

Just an update for some closure; replaced the bras T and O rings with help from chacal, and the leak is all gone. That's one issue down!

Synced my carbs and gave it a little colortune, and there is still the issue of the hanging RPMs and trouble maintaining idle. May have to change those Throttle Shaft seals after all!

 

You could have vacuum leaks around your carb manifolds.
Inspect them closely and use propane to see if the idle picks up or changes.
Cracked and stiff as a rock manifolds can be a source for vacuum leaks

 

...and much crying....and bad words....and....

But they can be patched up if they are cracked.

 

I'm convinced you're correct. While syncing the carbs, carb two wouldn't change its reading (even though 2&3 are together, yes?) No matter what I did.

Picked up some propane tonight and will test this weekend with a couple beers, just in case there are bad words and yelling at the sky.

 

1 and 2 are a pair; 3 and 4 are a pair.

The process is to synch 1 to 2, then 4 to 3, then finally 1 and 2 get synched to 3 and 4 (via the #2 synch screw).
3 is the baseline carb and can only be adjusted via the idle speed screw that is under and between the #2 and #3 carb.

 

Your kidding me????? I just read through all of this praying to get an answer and it stops here.

 

There are lots of answers in this thread.
I think that it would be helpful to know what quesions you have.

 

I prefer to balance 3 and 4 first, because 3 is the baseline carb. then I do 1 and 2. then I go back and check 3 and 4 again. Then I double check 1 and 2. once both sides are stable, then I do the middle one. Then double check them all. Funny thing is, it sounds like a long process, but it takes only about as long as it took to type this.

 

I'm having the exact issues he is having and was waiting to read if he fixed it or not