1985 XJ 700 rough running tough to start won't stay running

Hi folks,
ok past the title this is what I have done so far:
removed and fully cleaned the carbs 12 times
I have a yuasa battery on a smart charger (full charge)
cleaned the petcock
cleaned the tank
Replaced the intake boots
removed the canister (cali model) and plugged all the hoses
still not running
I have had this bike since about 2000, I have taken apart and cleaned the carbs a lot of times, I can't find any leaks in the boots (starter fluid method)
It could probably use a new air cleaner but the one in there is after market and not dirty
It will start for a few secs on full choke when cold, then die
it's acting like it's running out of gas
I have been perplexed with this for almost a year and missed the whole season so far. If anyone has any ideas please help!

 

Re: 1985 XJ 700 rough running tough to start won't stay runn

After you cleaned the carbs, did you set the float levels? Are the floats in the right way?
Check the fuel valve on the tank to make sure your getting fuel.
Do you still have the vacuum line hooked up to the fuel valve?
You could try running it on PRI for a test. See if it stays running.

 

Hi man, thanks for the reply.
Yup I have done all of that, the only issue with the petcock is that the rubber gasket is shot so it does not really close w/o the vacuum but it does not overflow or anything so it's no big deal.
Even on Prime it does the same thing, I have a clear fuel filter on the fuel line, and there's gas flowing through it. The vacuum line is still hooked up from the manifold to the petcock (even though it doesn't do anything due to the washer).
Still won't stay running
Thanks for the thoughts!

 

hrm, 12 times... maybe luckey number 13 will work , that sucks man.. I have a 700 and i friend something electrically, and i still cant find it... probably gotta get a new harness,
but as for your problem, no idea

 

Re: 1985 XJ 700 rough running tough to start won't stay runn

You say you have a washer on the vacuum line from the intake? Make sure tha thing is clear all the way through. I know mud wasps like to plug up just about everything from gas lines to bleeder valves. Try switching the vacuum line to number 2 cylinder.

Do you have good compression?

Have you replaced the vacuum/fuel lines? It sounds like it might be the pilot jets.

Do you have spark on all the plugs? Have you checked the plugs? I had an airhead that did something similar, and it was running way rich and fouling the plugs. Replaced the plugs, adjusted the fuel mixture and it was good. One other thing to check and it is an oddity|

the fuel mixture screws in front of the carb bodies, right behind the manifolds. Next time you have the carbs off, pull them all the way out. Ensure you have a manual so you can see how and what goes back in there. There should be a tension spring, an o ring and a very small washer. They all need to be in there to work properly. My airhead had parts missing off them and a pinched o ring. thing wouldn't idle to save it's life. Made sure all the parts were in there correctly, adjusted the mixture to roughly 3 turns and it was good. I'd make sure those pilot jets are good and clean.

I'd check the float levels too. Before you pull the carbs, crack open the drain screws to make sure you have fuel down there.

 

Hi Guys,
Thanks for the input! Yup floats are at the right level, I haven't changed the mix screws (still factory sealed) All the vacuum lines are clear and no holes and the plugs look pretty good and gapped properly. The pilots were my main concern for all of the cleanings, so they're clean as a whistle (whatever that phrase actually means; I have never cleaned a whistle). There is fuel in the bowls and I can see fuel in the line (clear filter between tank and carbs).

 

i'm confused (not unusual lol).
If the "mix" screws are still capped,how can the "pilots"
be clean,as they are one in the same?

 

Did you sort this problem as mine has similar problems

Daz

 

Re: 1985 XJ 700 rough running tough to start won't stay runn

the pilot jets are just next to the main jets in a similar 'hollow' tube. The fuel mixture screws are in front of the actual carb bodies just behind the manifolds.

 

Yeah the Mix screws are not the same as the pilot jets, they are the first thing to clog so I figured these were why the idle was dying after the enrichment was closed, but after repeated cleanings they are quite clean and I have a filter from the tank to the carb.
So far I haven't been able to figure this one out. When I do (and after I'm done making up for lost time riding everywhere) I'll post what I found out. Till then if anyone has an idea please chime in!

 

Did you clean out the enrichment circuit in the Fuel Bowls?? Take a B string from a guitar and poke the inside and squirt it with carb cleaner. Could not be getting aby fuel from the Fuel Enrichment Circuit. Just IMO

 

Remove the Inline Fuel Filter.
Try "Blowing" through it, ... to test its porosity.
Cheap ones get clogged when thy get wet.

 

Wow... it seems this thing is being troubleshooted to death here. After you start the bike are you keeping the choke on? Also, is it YICS equipped? You might need to clean the YICS passage out. just pull a good piece of cloth through it but one that doesn't have strings hanging off and won't lose fibers in the passage.
Also, try giving it a little throttle and adjusting the choke down once it starts. Your choke and idle mixture are on the same circuit and if you are flooding the engine it will sound like its running out of fuel. But you'll also smell the gas.

Ever throw the choke all the way up and the engine dies? Its a quick reference for me when tuning carbs. A quick wide open choke will kill the motor...

If you run it on 'pri' you'll be running rich unless you disconnect the vacuum line. Try clamping the vacuum line and just running it on prime. If your petcock is bad you will either have a blockage if the valve is stuck between positions, or you can be drawing in too much fuel if the passages are rotted and cracked. Clamping the vacuum line, or taking it off and capping the nipple and plugging the line, will allow you to run the bike on a gravity type system instead of the constant velocity. I did it for a while out of laziness. I hate rebuilding the petcock. Haha

Also, How is the gas you have in that tank? If it has been sitting in there for more than 3 months, get new gas. And use 93 octane. And if you can get the stuff without ethenol, do it. Those bikes were made at a time when gas was just plain gas. Not this low octane with corn addative, etc... I run shell 93 without ethenol

Remember it's a Yamaha. Its cold blooded. They don't warm up fast and I am sure anybody here can give you a hard starting story. Its a carburated Yamaha's life story. If you can get it running, don't let it die. Keep on top of it and your hand on the throttle... just try keeping it running. If your carbs were cleaned and set right, it might just need a good running.

Those jets do need extra special attention, though. Just as SLKid said, you have to poke a guitar string (exactly what I use...) through. You should be able to hold them up to light and see through them.

 

Re: 1985 XJ 700 rough running tough to start won't stay runn

Chuckles has some good things in there.

I think it's being re'd to so much because it's winter time and most folks have their issues sorted....

 

Hi Guys thanks for the input! Yeah I can see through all the jets, no guitar string needed. They're clean, actually the old gas theory might be on the right track, also the fuel filter clogging idea is a good one I'll try those and get back to you. Yeah the cold start issues are nothing new for this bike (that's why I eventually switched to a Yuasa battery). As of right now it is not starting at all but it was starting with the enrichment at about 3/4 but then would die... if I added throttle while it was running (even up around 3000) it would die...which makes me think: too rich. And that might be from running it on PRI but it never had this problem before.
Here are my thoughts: I will get new plugs, a new fuel filter, some new gas and try it again. It might be something that simple!
Thanks again for all the input folks!!

 

-float levels checked dry or with fuel using the clear tube method?

-bench sync'ed?

-VAC sync'ed? (I realize it's a bit hard to do if you can't get it to hold 1500rpm.)

-fresh gas, new plugs, as above.

 

Ok, new issue: I managed to get it running on full choke (enrichment) but it was running really rough, so a quick feel of the exhaust pipes and only the outside cylenders are runnign the inner 2 are cold. So my first thought was the coil (since the middle two share a coil) so I pulled the middle plugs and turned it over, nope nice hot blue/white spark. and the plugs were covered with gas so it's getting gas and spark (and compression) but not firing. Maybe it's the timing? But how can the timing be correct for the outer 2 and not for the inner 2?

 

Sounds like you've fouled the plugs to me. Clean em up with some fine sandpaper and let the gas on the plugs and in the cylinders evaporate. Plug in. and try again. If it still fouls em up, carb issue.
Uuuuse the Fiiiitz.
He brilliant and speaks the truth. Check your floats.
-Chris

 

I had the same issue with my bike. Come to find out it was the coil. It would put out a spark but not hot enough. Checked the resistance on the secondary, sure enough open circuit. When I changed the coil out it runs like a scalded monkey, and has not giving me any trouble since. I also cleaned/rebuilt the carbs a dozen time before this. You can have the carbs running like the finest Swiss watch, but wont do no good if you can't fire the mixture.

 

The Timing is FIXED.
The Timing is regulated by Electronic Impulse.

If you have a Situation where: "It will only run on Choke", ...

You have considerable work to do in order to have the Carbs supply Fuel to the Holes like they are supposed to do.

Thoroughly Clean your Carbs, including:
Fuel Bowl Enrichment Well Metering Ports.
Siphon Tube.
Emulsion Tube (Remove Main Jet & Washer -- Press Tube Out Top)
Remove Pilot Jets and Topside Pilot Mixture Screw:
> Flush Connecting Passageways.
> Flush Main AIR Jet Passage
Refinish:
> Remove AlumaOxidation from Bores
> Search "Clunk Test"
Also:
> See if Petcock Tower Filter is in Place.
> Pull Float Valve Body's and Clean "Beanie Screens"

Get yourself in a POSITION for Fine Tuning.