81 xs650 won't idle/run consistently

[drummingpariah]

I purchased a non-running xs650 last year for $500 when I realized the PO broke the electric starter. A few kicks and some starter fluid and it kicked to life right away, and I thought I was in good shape. I bought it just before winter, and took it out for a few cold rides to find that it wouldn't idle consistently and didn't like to run after warmed up. I added some gas treatment to the tank, tossed the battery on the tender, and covered it up.

Fast-forward through the winter, where it didn't get much attention at all. I rolled it out this spring, and couldn't get it to run or idle at all. I pulled the carbs, and found that a diaphragm had torn, and decided to take it to a shop that had parts in stock where they replaced the slides/diaphragms and sync'd the throttle plates. They also replaced the coil and wires, since the wires were really old and crusty. It was running when I showed up to pick it up, so I decided to ride it home. After it warmed up, the idle started to climb, then climbed some more, then wouldn't stay below 4k rpm unless it was in gear.

That sounded like a lean condition to me, so I pulled the carbs down again, cleaned all the passages and jets carefully (cleared passages with a guitar string to be on the safe side), replaced the boots, adjusted the floats as per the Clymer's manual, and threw in a float rebuild from MikesXS as well. After reassembly, I fired it up and have a whole new problem. Here are the symptoms, in broad strokes:

1. The choke MUST be pulled out one stop or two to start
2. If one stop out, the idle sputters and is very low
3. If two stops out, the idle hangs at 3500
4. If no stops out, it will not start when kicked
5. The choke is EXTREMELY sensitive, moving it a couple mm will change the idle rpm by ~2k
6. There are no external vacuum leaks, not at the throttle plate, not at the boots, not at the caps or anywhere else.
7. The air filters look like the Green Giant's 3-year-old socks
8. Jetting is stock, exhaust is stock, airbox is stock
9. I've tried setting the idle mixture screws from 1 rotation out to 3.5 rotations out with no discernable difference
10. I have pod filters that I could install, but do not have larger jets on-hand, and have not tried them
11. I cannot run a compression test, as the electric starter doesn't work
12. I cannot run a leakdown test, I don't have a compressor
13. I believe (and have to continue believing) the bike has good compression, the exhaust pulse on both sides is strong
14. Spraying starter fluid into the RIGHT cylinder's airbox causes the idle to rise as expected
15. Spraying starter fluid into the LEFT cylinder's airbox ... just ... empties the can. No effect on the idle rpm.
16. This is my first xs650, and I've done my best to go through due diligence and problem-solve it on my own, but I'm at the point where I'm asking "Can this even be fixed?"

Here's how the plugs look after around warming up at idle (it doesn't run well enough to be able to ride it):

I'm no plug-reading expert, but that looks extremely rich to me. I'm open to ANY feedback, even if you're suggesting that I go over something again. I just ordered new orings for the idle mixture screws, since that could theoretically cause some of the idle issues I'm running into. I'm also open to any suggestions regarding ignition tuning; I haven't dug into that at all yet.

Thanks in advance, and I hate to miss out on this season because I can't sort out some basic tuning settings for my bike.

 

[DogBunny]

You can use the kicker to do a compression check. Hold the throttle all the way open during the test, and remove both plugs so that it kicks easier.
The results of your starter fluid test tell me that it's possible that only one side is firing. Check the headers for heat when you run it.
This is just a beginning, there's a lot that could be wrong.

 

[TwoManyXS1Bs]

Hey, drummingpariah, welcome to the forum.
Go to the 'tech' section, under fuel/carbs, and download the 'carb guide'.
Also, try doing forum search 'bleed', only where it concerns carburator air bleeds.

 

[drummingpariah]

Thanks for the welcome and responses, guys! I've been through the carbguide (http://www.amckayltd.com/carbguide.pdf), the Clymer's (which was pretty much useless for carb tuning), and used my carb diagnostic experience (again, not an expert, but I have some experience) chasing my tail on this.

I just finished kicking over the compression test and was surprised by the results. With no oil in the cylinders, the left was at 148 and the right at 149psi. That seemed too good to be true, so I tried twice more and only saw a +/-1psi difference between tests. I was running ~5 rotations on each side for each test. It seems like the engine itself is in good repair.

Both headers are warming up evenly, and both plugs have spark. The more I learn, the more I think the problem is with the carbs themselves. I feel like the best diagnostic data I have is the choke sensitivity, but I don't know where to go with that (yet).

I can add that the floats are filling properly now, draining them both into measuring cups showed the same amount of fuel in each.

 

[angus67]

sounds like idle circuits are plugged. and you need one up on the pilots.
What air filters are you using?Straight exhaust? You need to get the numbers off the brass in the carbs to see if they are still stock, wich I bet they are. then we can help.
Possible carb imbalance.

 

[xjwmx]

To me it sounds like it could easily just be the throttle stop screwed in too far.

After it warms up, screw the stop out so that it idles around 1500 and use it like that for a bit. In this kind of weather pulling the choke out to the half stop is good for starting. After a few min. push it all the way in. In the first few min. you can put it between stops to get it to idle at a reasonable place.

 

[5twins]

If you are dealing with an '81 and the BS34 carbs then your plugs are one step too cold and the wrong style. That could be part of (maybe even most of) the problem right there. You want BP7ES plugs. The "7" is one step hotter and the "BP" designates a projected tip. The tip sticks out more and into the combustion chamber more, and that makes it fire and burn the mix better. Also, the BS34s are very sensitive to having the float levels set correctly. Yours should have the plastic floats which should be set to 22 +/- 1mm.

 

[xjwmx]

If the idle gets too high, regardless of the cause, it will start to run away even higher because the advance has then kicked in.

 

[drummingpariah]

That makes lots of sense. Just to confirm, what I'm hearing amounts to this:

Set the idle to ~1200 while the choke is wherever it needs to be to run, then continue adjusting the idle screw while pulling the choke in.

I feel a little bit stupid for having not thought of that before, but it's always something simple like that. I'll update tomorrow after work.

 

[xjwmx]

^Not exactly, if you're referring to my suggestion. Let it warm up putting the choke wherever it needs to be to keep the idle around 1200 - 1500. After it's warmed up then push the choke all the way in. At that point it will be idling real high you say. Next back the idle screw out so that it idles around 1300 again. Leave the idle screw there from then on. At that point you might have a normal bike


I'm thinking that the people who put your diaphragms in would have also done some basic cleaning and checking. But may have left the idle screw too far in. In their haste to not let it warm up before they set the idle.

 

[drummingpariah]

No, sorry if I wasn't clear enough. Even if it's warmed up when I push the choke all the way in (open, no air obstruction) it'll stall. If I have the choke closed (maximum obstruction) it idles high (5k or so).

 

[xjwmx]

^Pushing the choke in turns the choke off. If it won't run warmed up with the choke off, then it could be the opposite problem - idle screw too far out

 

[retiredgentleman]

Problem is likely the pilot circuit, which includes the pilot jet. The reason the engine stalls without the choke is because the pilot circuit is blocked.

If you are test running the engine with the choke partially on all the time, you are running a very rich mixture, and that would explain the blackened spark plugs. All that extra rich mixture is not good for the cylinders.

You should remove both carbs to the bench. Turn them upside down, and remove the float bowls. Is the rubber plug in place that covers each pilot jet? Remove the pilot jets and compare the size markings, with what is stock for your bike, as listed in the carb guide. Are they stock? Carefully look through each pilot jet................the orifice is very tiny, but you should be able to see light through each one. Clear the orifice if its blocked.

 

[angus67]

the choke is a enrichener. it does not choke. I kinda wish these had real chokes, then no one would get confused. the gurus here still call it a choke because its easier to type. and the knob says choke on it. My Suzuki has an enrichener too, but it has the choke symbol on the knob. go figure. Easier to cast into the plastic part? less type spacing? who knows. But based on post counts we know that they meen enrichener, just to clear it up.
im still betting your pilot is plugged in that one carb. maybe the shop used a cheap rebuild kit, and used those crappy needles that come with them.
You should really learn how to do your own carbs. Its real easy once you figure out what passage goes where and does what.
When your done with all that carb cleaner, grab some good lotion for your hands.

 

[5twins]

It's never going to run right with B8ES plugs in it, period. Do whatever you like to it, rebuild the carbs, heck, rebuild the whole motor, lol.

 

[pristic]

Hi,

Try this: With choke PULLED (revving HIGH) and then as you push the choke back in increasing the revs with the throttle... does it stay running? Can you hold it STABLE?
If you can, when you hold it stable, look at the throttle stop screw and how far it is? I think like xjwmx said, it could be with the throttle stop screw being out too far.

In a way, none of this makes sense... look at it this way... if you had air filters removed and put your hand over the carb inlet... it would stall due to no air. In your case "Choking' the air actually increases the revs... hmmm

When the diaphrans were put back in were they oriented the right way? Is the vacuum hole TOWARDS the engine (look at the slide, there is a hole in it)
For pics see the jbm site here --> http://jbmindustries.com/Yamaha650.html


Choke all the way in and stalling in my mind means LEAN (too much air) so with my test above, you have the choke PULLED (max obstruction) and then REV the engine, you are opening the butterfly and allowing more AIR in, (plus more fuel)


When the choke is out its causing your 'rich' plug reading and to be honest the reading of the plugs on idle (no matter what the carbs are doing will not be accurate) technically they SHOULD be fouled if choke pulled and only idling.

 

[pristic]

It's never going to run right with B8ES plugs in it, period. Do whatever you like to it, rebuild the carbs, heck, rebuild the whole motor, lol.

Love it, didnt see they were 8's
Mine struggles with 7s and I run 6's

So flooded its running but with air it cant combust- is that what you mean 5twins?
A Hotter plug would resolve that but revving up to 5k seems strange right?

Cheers,
Peter

 

[pristic]

the choke is a enrichener. it does not choke.

Really??? ok, suddenly that would explain why SO many things that were supposed to work for me when tuning it made it worse, and when I try the opposite of logic it worked fine.

So it DOESNT stop airflow? (ie Choke) rather it adds fuel?
Dont they 'kind of' do the same thing though?
Enricher - more fuel + same air = richer mix
Choke - same fuel + less air = richer mix

I have just made my head explode

 

[TwoManyXS1Bs]

Pristic, I want to party with you man. You be a fun kinda guy...

The enrichner is a separate circuit that dumps fuel thru it's own large hole in the carb body.

Chokes are a second butterfly valve that restrict incoming air, their advantage is that they force the engine to draw lots of fuel thru the jets, which can help by clearing/flushing them. None of the XS carbs have chokes, but on those bikes running open/unfiltered carbs, you can do this same kind of forced jet flushing by placing your hand over the carb opening while running.

These `80-`83 carbs are like those maddening things I lost my cookies over back in the `70s, guys here referred to them as 'EPA' carbs. In the early carbs, the so-called 'mix' screw was really an idle fuel delivery adjuster. We just called them 'idle screws'. These later 'EPA' carbs have a completely different passageway arrangement, in that the 'mix' screw controls how much bleed air is admitted to the idle circuit, which is a true 'mix' term. When there is no change to engine idle when adjusting the 'mix' screw, start suspecting blockage of the air bleed.

 

[pristic]

Yeah mate, cmon down and we can have a great time!

I hear you, I spent hours tuning my 1976 Turbo Mini. Started with a HS4 - ok not too hard... then went to a HS6 when I worked the N/A motor.
When I went to turbo I got myself some UK goodies and a HIF44
So I tune it ok... start driving a while... throw on the lambda sensor and she is 11.2:1-12:1 off boost... great. Nail it, climbs a bit as expected then sits at around 12:1 or 12.5:1 - yay I think.
On the streets I notice AF while driving like a lunatic is spot on... perfect. Then I see the boys in blue (police) and 'cruise past them all' nice and easy, feather the throttle, no PSSSHHHT sounds etc... but my AF is out of control... 20:1 hmmm... nail it, she lights up the tyres and goes like crazy but the AF is perfect... ok, cruise - AH! 20:1
So, decide something is wrong with the lambda... cant be correct (duh)
Well, it wasnt :-S the mix screws as you stated above but there was also this 'lean off pipe' that went from the carb to the inlet manifold... tune and tune and tune and nothing helps... a mate who knows nothing about engines who was 'helping me' says - whats that one do. I say, nothing its for 'pollution' but actually makes pollution worse... WAIT A F-ING minute... it LEANS off the mixture when the throttle is just feathered... finally block them off and suddenly the 20:1 AF ratio in while cruising is fixed... the mixture screws did NOTHING in this thing except idle... they were IDLE mix screws... oh my ... that was fun.