82' XJ 750 carbs

I have built the carbs and they are back on the bike. I believe the float level is low since it will not run without the choke on, however, also I have a low idle which is a steady 350. Any suggestions on what it could be? One guy told me that some sort of air passage is blocked in regard to breathing, but when I built the carbs, I shot B-12 into all holes as well as air and looking though the manual does not show these "air" holes. Please help. would running it without the filter cause anything difference in the idle as well?

 

Could the "air holes" be vacuum holes should they be covered by rubber boots?

Have you pulled the plugs to see if your running lean? running lean will make a low idle bad throttle response running very hot.

Is the air box on or do you have pods? the air box is designed for those carbs its extremely hard for it to run without it for the slide diaphram to work properly and the jets are set for the box.Its not meant to run without it there jetted for it.Is the filter your referring to the air cleaner? or inline fuel filter.If the AIR filter is not in yes if would make a difference but not as much as a difference as it would with the whole air box not connected.

350 rpm is defiantly very very low. How did the bike run before the carbs were taking off was it worse than this or did it run a higher idle.Does it rev out?Is it bogging if its bogging your jetting is not set correctly.

It could be a possibility that you've got the floats set incorrectly it may be being starved of fuel.Start the bike and look over it and listen for leaks if its leaking and letting air in the idle would be higher. Sounds like you need to take them apart and bring everything back to spec and to check your float levels.

Thats my two cents on that.

-Tyler

 

I lost my connection so maybe I'll be repeating my reply.
I believe that the air holes that guy was referring to are the miso orfices located here and there.
I haven't checked the plugs yet but will check tomorrow.
The air box is on but does not have a filter in it.
The bike was not running when I got it. It is all original, and very clean showing less than 5k miles on the speedo. I had to do the carbs since the guy that sold it to me said he had messed them up. When I looked at them, I found a very badly damaged needle (on the slide) and had to buy another setup in order to correctly replace it.
When you say, bring the settings back to original what are you referring to? Everything is original including the jets by the numbers, and they are clean. I shot B-12 in ever hole as well as compressed air, so nothing should be plugged. I cleaned the jets in a ultrasonic bath.
Also I neglected to mention one other thing that is happening. While the bike is running, there is no leakage on the ground, but as soon as I shut it down, it begins to leak from the air box hose and will continue to leak for more than 15 minutes. I made the assumption that it was excess gas due to running on choke. I can do anything you tell me to do without assistence from a dealer but you will find my carb jardon had much to be desired. Thanks for your help.

 

I would suspect either your floats are set too high or you may have a bad petcock that is allowing gas to pass when the bike is off. Are you running the engine on the "pri" setting? If so, this allows gas to flow freely until you switch to "on" or "res".
In regards to your very low idle, It sounds as if the engine is flooding out.
Check the exhaust for black smoke. In either case, you are too rich somehow. That's my guess. Anybody else?

 

Please read the following it will help you get the carbs right and give you some insight.

You definitely have fuel issues - as Malcolm said you have to check you floats and petcock.

Clean enrichment circuit
http://www.xjbikes.com/Forums/viewtopic/t=8918.html

Clean carbs
http://www.xjbikes.com/Forums/viewtopic/t=2908.html

Carb Sync
http://www.xjbikes.com/Forums/viewtopic/t=2132.html

Bench sync
http://www.xjbikes.com/Forums/viewtopic/t=6366.html

Fuel filter
http://www.xjbikes.com/Forums/viewtopic/t=6352.html

 

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If the Bike will onlyu run with the Choke on ... there is a Fuel Related Issue of some kind.
1. Tuned too Lean
2. Needed to overcome Major Air Leaks
3. Fuel Supply Issue due to Mixed-up or Incorrect Jetting.

4. Haynes Misprint Jetting: AIR Jets incorrectly positioned.

Get this situation under control before you spend a lot of time doing Tuning when the Problem MIGHT NOT BE Tuning.

First step: Compression Test.

(The "Air Holes" are small, drilled, Air Metering Ports, drilled through the Emulsion Tube)


But, we need to deal with why there is so much drainage happening.
Complete Petcock Leak Test
Float Levels
Other stuff; too.

First, we need those Compression Numbers.
Plugs all pulled.
Battery Fully Charged.
Throttles Wide Open.

Good luck,
We'll get to the bottom of it.

 

On the petcock, I do not see a "PRI" setting, only RES, and ON, the only other word on the petcock is "FUEL" but it is a unreachable setting for the indicator. I will do a compression test tomorrow, hope a automotive compression tester connection will fit the hole. Thanks for your help.

 

Forgot to mention that I cleaned out the holes in the emulsion tube as well, I was very careful to clean everything internally to include loosening the drain in the bowl and cleaning out the tube that would allow me to check the float settings later. The only pain I will feel from all this is the "fun" I have doing the R and R of the carbs in the boots. Its just great that a person can come in here and learn so much. I hope that I'll be able to ask questions later on my other 16 bikes even though they aren't XJs. Is that a possibility?

 

Sure! We ought to be able to get that whole stable fixed and on-the-road by Easter Sunday.

Take that '65 Vespa-90 you ain't got running yet.

I put-in a call to the Pope at the Vatican to see if he had any Sainthood candidates needing to come-up with their second Miracle.
The Pope told me that Resurrecting the Dead is a Miracle currently limited to only one known performer.
Currently unavailable; but expected to return ... "In the future".

 

Wow, by Easter Sunny.....now that is a prayer I'd wear my knees out on.

When a guy wants fun, there is no reason to have limits.

You outta see that Vespa, what a honey. It has compression, there's a start. It needs everything, but I couldn't resist her, when shes runnin, a smile will be on everyones face when my 250lb form ridin her.

 

Ok, compression test done, both dry and wet. Numbers dry are: 1-135, 2-135, 3-130, 4-135 then Wet: 1-145, 2-148, 3-145, and 4-150. If the valves are adjustable on this bike some improvements might occur but obviously there is the ring wear but the compression is basically ok I would think. As for someone mentioning the PRI setting. I do have one and yes the bike only runs on that setting, probably accounts for the drainage and noticed today that it drains even when its running but moreso when its off. It will not run in the RES or the On position. What do I do next?

 

I think you said above that you were stock jets and stock airbox. So, I think I would start looking for a vacuum leak. Two things point me in this direction: 1.) only running on prime tells me that the petcock is not getting vacuum pull which is why no gas comes out in on and reserve. 2.) Running very lean / low RPM idle tells / needing the choke all indicate too much air is getting to the engine. On each of the four carbs by the rubber boots facing upwards, there is a vacuum port. On cylinders 1, 3, and 4, a rubber cap blocks this port. On cylinder 2, a hose connects from this port to the petcock. I would check to see if this hose is missing or leaking, and make sure all three caps are present.

Also, if you are leaking fuel when you leave the petcock on prime, one of your needle valves is probably no good. While this isnt a show stopper, be careful not to leave the tank in prime with the bike turned off. First off, leaking gas is a fire hazard, but also, the gas also leaks into the cylinders and down into the oil, turning your oil into a soupy mess that does little to protect the engine. It also causes the oil pan to be over full, which gives bubbles in the oil which is also very bad.

 

Sometimes the Vacuum Hose to the Petcock is NOT missing. I have found a wide variety of substitutions. All bad.
That Vacuum Line to the Petcock from the Manifold needs to be ACTUAL Vacuum Line.

A shortcut test for looking for a Vacuum Leak is as simple as hooking-up the Manifolds to Carb Sticks and looking for any NOT pulling some Mercury.

Run a Test on the Petcock.
If the Petcock is leaking-by the Gas in the Tank is going to keep leaking until the Tank goes dry.

 

One thing I can say for sure. The vacuum hose is connected to the carbs and is in good condition and is indeed a vacuum hose. What direction should the petcock lever be when it's off? The leak does stop at some point, but runs fairly heavy just after the engine is shut off. Right now, I have the petcock lever set at RES. Tomorrow I'll remove all the hoses and take the petcock through its paces and see if it runs all the time and where it shuts off. Also I'll check to see if all the rubber caps are on each of the carbs. All needle valves are new so it seems unlikely that one is bad. I was very careful when I put them in place. Thanks so much for your help on this.

 

On my carbs, I had good needle valves, but the tab on the float was bent a bit, such that the needle valve did not push up high enough to seal. As far as the petcock, there is no off. A good petcock is "off" when it is in "on" or "res" and the engine is not running and providing vacuum. There are 3 settings:

On: picks up from a higher point in the tank, fuel flows only when there is vacuum present

Reserve: picks up from a lower point in the tank, fuel flows one when there is vacuum present

Prime: fuel flows regardless of vacuum.

The petcock is a common source of trouble, so it is worth trying all the settings and making sure they work as expected. You can suck on the vacuum line a bit with either your mouth (if this doesn't bother you) or a vacuum pump like you would use for bleeding brakes.

As far as the vacuum leak, a good test for vacuum leaks is to get some sort of aerosol spray like WD-40 that is very flammable and spray it around things that are suspect (like carb boots) and vacuum lines while the engine is running. Be careful to not use so much as to cause a fire on the outside of the engine, but you will hear the engine rev up when you find the leak.

 

I'll check all that stuff today or tomorrow and let you know the outcome. It is amazing how ignorant I am to these common occurances as to vacuum having to be present and just how the system works. Thanks so much for making me aware of it. As for the needle valve tabs. I'm sure they aren't bent any more than normal, that is another thing I paid attention to but once we get through all this other stuff, I'll probably have to remove the carbs again (ugh), and re-adjust the float level. I guess I just want to see if the petcock and vacuum issues are present before I pull them. Probably I'll construct the 90 degree clear hose to check the float level in a running capacity before I remove them as well. Thanks again

 

One other thing I could do to find the vacuum leak would be to borrow and friend of mines "smoke machine". Its quick fixer when it comes to finding this kind of stuff. That's ok on bikes isn't it?

 

Ok, the tasks are done and the news is bad. Fortunately I have a Mity-vac, so I connected it to the vacuum line and gave it some pumps. Nothing.
No vacuum on the guage, big leak time. Second. I put more gas in the tank and checked the petcock. Gas comes out from all 3 positions, so I guess that means that I need a new one. I checked all the vacuum ports where the caps are, and they are all good.

 

Are you saying you tired to draw a vacuum through the vacuum tube?

that would never work - they system s not sealed at all.

 

I guess I misunderstood the last guy, maybe he was telling me to pull a vacuum on the petcock to see if IT is working properly. You can see from my last statement that the petcock works in all settings without vacuum so probably it's bad right? Or maybe he meant that when it has vacuum it should not work in RES and ON. I'll have to get clarification on that one.

I guess I'll have to get it running and spray WD 40 on it and see if I find a vacuum leak as he suggested.

Tomorrow is another day, gotta got to work.

 

Yes it should flow under vacuum in Res and ON - with or without vacuum in Prime.

If yours flows without vacuum in all positions it needs to be rebuilt or replaced...

 

My personal opinion regarding Leaking Petcocks:

Replace with New Petcock.
Old Petcock worked fine for nearly 3-Decades.
New Petcock should too.

Kit's may work fine. May leak worse than Old Petcock.
Aftermarket Kits are not OEM. NOT --> OEM!
OEM Kits available through Yamaha Dealers ONLY.
You can ONLY get the Real McCoy from a Dealership.
The Manufacturer DOES NOT supply Kits to any source other than a Yamaha Dealership.

The Kit + Time rebuilding Petcock is more expensive than a NEW Petcock.
If the Kit leaks -- you need to buy another Kit.

If the New Petcock Leaks -- you return it to the Dealer for one that don't!

 

Rick not to hijack but what is it that causes the leakage in rebuild kits and are you talking about external leakage or drips fuel through the pipe or both?

I have replace the lever's oring on mine but the rest was fine. I just have trouble visualizing what would be so bad in a kit to cause leakage?

I know you always say replace which is why I usually say replace or rebuild since I don't have a preference at this point :lol:

 

The last time I rebuilt a Petcock with a Kit ... it leaked.

I have to Press the Valve Disc to get the O-ring to seal-off fuel flow.
I spent entirely too much time "Monkeying" with the parts in the Kit to make it work ... it never did. We wound-up saving the job by using a salvaged Petcock.

Following that folly ...

I called the TAIYO GIKEN Company, makers of the Petcocks on Yamaha Motorcycles, to inquire about obtaining a sizeable Bulk Purchase of OEM replacement parts.
The TAIYO GIKEN response was: "No. We are under contract to supply the parts to Yamaha Dealerships ONLY!"

Asked about the possibility of a Bulk Purchase of Complete Petcocks in a quantity exceeding 4-Gross Units.
Again, the answer was: "No. Contractually bound to sell to Dealerships Only"

I surrendered.
If I can't get Genuine Parts in a Kit and the Real Kit is nearly half the price of a New Petcock ...

Became a "No Brainer" for me.
How do I repair a leaking 25-year old Petcock.
Very simple.
Just get myself or a client a NEW one.

 

Thanks - makes sense

 

I've found a couple friends that have some old ones and they are bringing them to me this week and I'll vacuum test them and hope that one of them will work. How much do they usually cost?

 

Honestly I have to say, your mileage may vary with the rebuild kits. Obviously rick's did not work, and I completely understand and agree with his reccomendation to just flat out replace the whole thing. When I first got my bike, I rebuilt the petcock because a replacement just wasn't in the budget (can't remember the exact price, but I seem to recall between $60 and $70 for some reason), and my rebuild kit worked fine. No leaks, haven't had any issues with it yet.

Now as for the rest of my bike i can't say the same .... but at least my petcock works!

 

I'll check with the dealer today and see how much his price and time to wait scare me.