81 xs650 won't idle/run consistently

Yeah, maybe I should cobble together several tons of junkyard bikes/parts and bunches of derelect $50 `67-70 muscle cars, get a boat, and that would pay for the trip.:D

Nice rant. If you want to see my blowout, try forum search "digressing" or "regressing".

To the OP: Sorry for the hijack, but carb problems are flourishing on this forum, and understanding these things, with the various versions, syndromes, previous owner gimmics, and such, it's a wonder anybody's able to fix them easily...
 
Hahaha. Yeah sorry to the OP. Lets just say twomany and I are absorbing some of your frustration.

:)

Back to the topic at hand. No more shenanigans from you twomany! :)

Peter

Posted via Mobile
 
No reason to apologize guys, I feel a little bad for even asking carb questions, since there really IS a plethora of threads about it already ... but logic wasn't explaining what's wrong and I needed extra eyes/brains.

I'm going to try to get some results today, but I did something to my neck sleeping last night, and can barely move. Hopefully this crazy-neck-pain will go away with some heat and advil, and I can play with the idle screw a bit.
 
I used to get those same 'next morning' neck pains! Found it was bone spurs from calcium deficiency. Been doing liquid calcium supplements, don't get spurs anymore...
 
This is a first for me, but I was nearly in tears when I tried to get out of bed this morning. Ibuprofin is definitely helping to make it bearable, but I'm not particularly excited about climbing all over a bike today.
 
Whoa! You married?? I had the same problem then found out it was the Mrs trying to choke me at night. I'm too stubborn to lose. Even in my sleep :)

Advil helps but I found Nd doc confirmed in a hospital once that one paracetamol And one ibuprofen at the same time nails pain fastest. Perfectly ok to take together. It's the second dose you need to work out time etc.

Get better and let us know how it's all going.

Peter.

Posted via Mobile
 
On all the BS carbs, 38 or 34 the idle mix screws work the same way. If you look in the carb by the throttle plates you will find several tiny holes. At idle some are covered. The pilot air vent in the carb bell lets air flow down into the carb to mix with fuel coming up through the pilot jet. The pilot jet delivers this air fuel mix to the idle mix screw and two of the holes. The mix screw controls the amount of air fuel mix that flows through the last hole.
At a idle most of the air fuel mix delivered to the engine flows through the one hole controlled by the mix screw. You need to back down the idle speed as low as you can so it is running on just the air mix hole. Then you will hear the effect the screws have.
Now once you get the mix right and bring the idle back up to normal the throttle plate starts to uncover the other holes. This lets them add more air fuel mix than the screw controlled hole can deliver. As the throttle plates continue to open, moire air fuel gets delivered by the other holes until vacuum starts to lift the slide. At this point the needle starts to lift out of the needle jet. The needle and needle jet start adding more air fuel mix to the engine.
There is a main jet air port in the carb bell too. This lets air flow down into the carb and mix air into the fuel at the main jet. The needle jet draws this air fuel mix up more and more as the needle lifts farther out of the needle jet. Once the needle is mostly drawn from the needle jet the main jet takes over to supply air fuel mix. The pilots and mix screws control the idle to about 1/4 throttle. about 1/4 throttle is were the needle and needle jet start to work. At about 3/4 throttle the mains start to work on up to WOT.
The "choke" being an enrichener, when pulled out adds extra fuel to get the rich mixture for starting. Once started you shouldn't need the "choke " to keep it running.
In your case this is not happening. Pull the carb, take out the air mix screws Using a spray carb cleaner, insert the straw in where the mix screws were. Spray, cleaner should come out the holes by the throttle plates. Also if you spray cleaner into the pilot jets it should come out the holes by the throttle plates. If you are not getting cleaner out all those holes the passage is blocked. Keep at it till cleaner comes out all three holes. A bit of carefull probing with a soft wire can help. I use a tie from a loaf of bread. Strip about a 1/2 inch off one end. This leaves a very thin, soft wire.
Leo
 
pristic said:
Whoa! You married?? I had the same problem then found out it was the Mrs trying to choke me at night. I'm too stubborn to lose. Even in my sleep :)

Advil helps but I found Nd doc confirmed in a hospital once that one paracetamol And one ibuprofen at the same time nails pain fastest. Perfectly ok to take together. It's the second dose you need to work out time etc.

Get better and let us know how it's all going.

Peter.
Click to expand...

Looks like it was a pinched nerve and pulled muscle. Now I'm starting to feel a bit better and can even turn my head a little, so I'm going to spend a little time working on the bike. HOPEFULLY I can have it running for tomorrow morning so I can take it to Deerfield Leathers (http://www.deerfieldleathers.com/latest-news/2013-wild-ride/), otherwise I might be forced to borrow my friend Laurie's cb350 (I need to get one of them, they're SO MUCH FUN).

XSLeo said:
On all the BS carbs, 38 or 34 the idle mix screws work the same way
...
Leo
Click to expand...

So much great info. I can't thank you enough for taking the time to break that all down. THAT is how the 'faq' posts should be written.
 
It 'runs' but needs a little more fine-tuning. I think I can take it from here though, at least now it works. The problem really was just the idle speed being way way off. I backed it out all the way, started it with full choke and held the throttle in place so it'd idle. Tightened down the idle screw to meet with where I was holding the throttle, and started slowly backing the choke out (or rather ... in ... backing the enrichment circuit in ... aw hell, I pushed the plunger in toward the carbs) while adjusting the idle piece by piece.

Right now, I have a halting idle at around 1600rpm and it dies when it feels like it, and barks/backfires when I burp the throttle a little. I might just call this close enough to ride out to Deerfield tomorrow, instead of taking the cb350.

 
look up dead cylinder method. sounds like idle mix screws are off. they are the small one on the top of the carbs.
 
angus67 said:
look up dead cylinder method. sounds like idle mix screws are off. they are the small one on the top of the carbs.
Click to expand...

I've searched around a bit, and thought this would be a sticky or something along those lines in the carb section. I also dug through the Clymer's manual, but haven't found a start-to-finish howto. However, I think I understand the broad strokes already. Please correct me if I'm wrong:
  1. Pull one plug, reattach it to the plug wire, and ground that plug to the engine (so the ignition system isn't damaged)
  2. Start the bike. If necessary, raise the idle until it runs on the one remaining cylinder.
  3. Adjust the idle mix screw on the cylinder that's in use to get the highest idle possible, adjusting the throttle stop to keep that idle sane
  4. Once the idle mix screw is adjusted to the highest idle spot (I assume the leaner end of the idleal zone), switch and repeat for the other cylinder
  5. Reinstall both plugs and unscrew the throttle stop until the idle is around 1250rpm (according to Clymer's)

In theory, that should get both carbs to roughly the same tune. It doesn't seem like this would work for throttle syncing though, that would really require a vacuum gauge.

I took the bike out for a short ride today (around 20 minutes round-trip) and it was MUCH better than before, but there's a fair amount of popping on deceleration, especially on the right cylinder. The idle starts to sputter if I'm at a light long enough, and burping the throttle causes revs to hang slightly (only for a second or so though). I'd like to install these pod filters I have but that'll require rejetting, but rejetting a bike that doesn't already run well seems like a bad plan.

Afterthought
I also changed the plugs out to BP7ES' but can't say for sure if that helped or hurt.
 
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Drummingpariah sounds like you made it long enough to experience old age.
Welcome to the club it gets more interesting. Bumps, spots, tweaks and twitchs like you've never had the pleasure of appear overnight like that.

On to the carb problems.
The hanging idle and decal popping are classic lean conditions.
You've done some homework and supplied good info on what you've done.
I could just say your carbs need cleaned, but you have had them off and done a fair job of cleaning so will think I'm being a smart arse.
IMO you will need to clean them again because of the varnish in the passages.
The paths between the pilot jet (that you cleaned and sized) and the 3 holes in the throttle body(again you cleaned them by poking/probing).
I'll venture to say there isn't anyone, 5twins included, that can get a wire of any type run through the passages so you are limited to a chemical cleaning and blowing out with compressed air.
You will need to do this from both ends. Remove the pilot jet and the mix screw so you aren't trying to blow the crud through the little feed holes.
When replacing the mix screws run them down to bottom and back out 3.25 turns.
And don't think the fact you have to clean them 4,5 or 7 times reflects on your cleaning abilities it just takes time to get some of these carb sets clean.
If you have some miracle fuel additive(sea foam comes to mind) you might try letting some set and soak in the passages for a bit to help dissolve the varnish.

On syncing a piece of plastic hose tacked/taped to a stick with an oil in it is cheap enough and quickly done. No special gauges needed.
 
Yep, I'll turn 30 later this year, with any luck. I think my body is punishing me for lack of activity lately (my schedule hasn't allowed me to get to jiu jitsu in a few weeks now).

Just because I've cleaned the carbs carefully, it doesn't mean they're necessarily clean. I didn't pull all of the jets either, so there's still more I could do. They were pretty gunky when I first got them, and I'm sure there's still some varnish breaking loose.

I'm running mystery oil with the fuel right now and have had bad results when I tried to mix it with seafoam previously, so I'll try seafoam in the next tank of gas.

3.25 turns out would be richer than the current 2.5 turns out, correct? Once the rain lets up a bit I'll take it out for another ride and see what the plugs look like during the popping conditions. I'll do my best to get some photos as well.

Unfortunately, all this progress I've been making has me really excited, and I may end up having to make some rear rests and controls, a seat, and clip-ons or ace bars. Of course, I know how quickly that would snowball into a huge project, and I'm holding off as long as possible so I can just keep riding 'till I have it right.

Overall, I'm pretty happy so far.
 
Your mix screw settings are probably a big part of your popping and hanging idle problem - they're set too lean. Yamaha never gave a spec for the screws on this carb set because they were E.P.A. mandated, set at the factory, and capped over so you wouldn't fool with them. From owner experimentation and reporting, we have arrived at our own spec - 3 to 3.5 turns out. Set them in any leaner than 3 turns and you will usually experience the problems you have. Set them to 3.25 turns as WER suggested and the popping and hanging idle will most likely be cured, simple as that.

Well, I'm glad to see you finally put the proper plugs in. They will make a difference. Honestly, those 8's never would have run right. They would always be dark, maybe even black, and misfire or even foul out eventually. They're just too cold.
 
When I mentioned sea foam I was suggesting using it only to soak and soften the varnish in the passages so it will turn loose and blow out. Rubbing alcohol will do the same but you have to have all the rubber bits out(mainly thinking mix screw o-ring). Alcohol isn't nice to rubber.
 
Makes sense to me. It looks like the rain is starting to let up, so I might be able to do some testing tonight. I've been trying to find a screwdriver bit that fits the idle mix screws without having to pull the tank, but to no avail. I used to have one of those double-ended bits that was PERFECT (just long enough to have something to grab onto but not so tall that it hit the tank, and just the right width to get a good bite on the mix screw) but it went mising at some point. Right now, I'm just using a long-handled flathead that requires pulling the tank any time I want to make adjustments. I bought a stubby screwdriver, but the tip is too thick for the idle screw slots, and a bendy screwdriver, but it doesn't flex enough to clear the tan on the left side. Anyone have a known-good solution to this?

Something like this would be ideal, I think ... but I don't want to keep buying things that I'm not sure will work, and this shaft looks too wide to actually reach the screw head:
http://www.amazon.com/Screwpop-Tool-Chrome-Black-Bit/dp/B0032IVVI2
31shXEasVWL._SX385_.jpg
 
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That looks a lot like what I had before, but it had a philips head on the opposite end (which was a bit of a pain). I don't actually want a holder/driver; If you need extra leverage on an idle mixture screw, something's really wrong.

Ordered, should arrive on Wed ... just after the time I expect to have these carbs dialed in a bit better.
 
Rode in to work this morning, the right cylinder feels about perfect but the left is popping and maybe even a little backfiring out the exhaust. I think a sync may be in order, as well as dead cylinder mix screw settings.
 

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