81 Special II back to life after 28 years! fixed broken float tower, won't idle

[mrodub]

I recently bought this bike and brought it back to life. It only has a little over 100 original miles on it and has been stored and covered for almost 30 years. The motor isn't even broken in yet. The PO bought it, had a MINOR crash, and never rode it again. I couldn't believe it when I saw the mileage. The title says it was purchased NEW in 83. The last inspection was 84 and the sticker is still on the fork.
After I replace a few cosmetics, this thing will be near showroom condition! I will post some pics on this thread soon.

I pulled apart the carbs and found a broken float tower that the PO epoxied. He tried getting it running a few years ago admitted he got in over his head.
I ended up sending the carb and tower to Jim French to get it micro-welded for only $25 plus hipping to Georgia. It was well worth it and Jim is very helpful. I highly recommend him.

I'm not sure if this has been posted on this site so here's the info.

http://forums.sohc4.net/index.php?topic=111096.0


I cleaned the carbs thoroughly with spray cleaner and blew compressed air through all the jets. There was quite a bit of crud in there but I'm fairly certain I cleared all the passages. Both sets of floats seemed to be working properly. The bike fired right up and ran well but it won't idle. I have the idle screw all the way in.
I don't understand why the pilot jet has the plug. Can someone please explain this.

Is this a common issue and is there an easy solution?

Thanks

 

[wrench234]

i recently brought my 81 back to life after sitting for 27 years same deal minor crash then parked. its funny you mentioned the broken float tower,as my carbs were gummed really bad and i broke the float tower trying to get the pin out i bought 2 rebuilt carbs from ebay for 83.00 and bike runs great. maybe i could have tried the microwelding. just rode the bike around the block runs good.

 

[mrodub]

Wrench234: It's cool we both have such nice low mileage bikes. What's the mileage on yours? I wish mine would run great...

I'm still trying to get this thing to idle. I would really appreciate some input from the experts here. What would be the first thing to check? I thoroughly cleaned these carbs and it runs really good besides not idling.

 

[jmd_forest]

Your carbs have an idle circuit that is possibly fouled with dirt. There is a hole at the bottom of the float bowl that feeds through to the hole in the back edge of the carb that the brasss dip tube fits into. If this is clogged or fouled you will get erradic idle. Also, the dip tube has a TINY hole in it near the carb body that must be clear. Additionally, the main jet has many many tiny holes that all must be clear, the throttle shaft seals must actually seal and not leak air, the entire enrighment circuit must be spotless. Another common problem with idle is the idle mixture screw tip gets jammed and broken in the carb body, you might want to check and verify yours is OK. When I bought my son's 81 400XS, the PO had dicked with the carbs and the o-ring seal at the bottom of the mixture screw was missing. Additionally, you need to check the manifolds between the carbs and the engine body to make sure there are no cracks and that they are sealing correctly. Make sure the carb diaphrams have no holes.

In other words, you need to get a very detailed and thouough guide to cleaning and rebuilding your carbs and go through the entire carb in exquisite detail. These carbs must be SPOTLESS clean with NO air leaks to work well.

After rebuilding and bench syncing both carbs (and setting the timing which the PO had also managed to misadjust) the bike ran pretty smooth throughout the entire RPM range.

 

[xschris]

How do the plugs look?

 

[wrench234]

mine isnt as low mileage as yours it has 7900 on it in 83 when the guy i got it from bought it the title shows 5800 miles looks like he put about 2000 on it in 2 years before he laid it down and parked it

 

[arfstrom]

Mr Odub, under the link at the top has some common topics, that have been discussed, the link goes to the tech section. http://www.xs400.com/tech.php From here your carb is a Mikuni, This is just one forum chat that disscussed indepth carb problems. as you browse this website, you will find all of us that have had carb problems, fall into 2 categories, those of us who taken off the carb and sprayed a little spray, or those of use who have boiled the carbs multiple times, and have the bike running good. So I have used a dremmel, to Air, to soaking in carb cleaner, to finally boiling in a light acid such as lemon juice. (vinegar is okay too) most wives dont complain too much if you use lemon juice on the stove as you boil your carbs for 20 minutes to 2 hours. Eventually I had discovered my last problem with the bike running properly was that my checks for float operation did reflect a leaking float. So it took a few more times of taking my carbs off, and checking "one more thing." There are posts by Fubar that are vary detail, and Hughmade. (spelling), (don't be afraid to cheat, look under this box, at the end of the page, there is usaully 5 to 6 links based on the tags, and subject of message, to help bring to you to something that might be the same problem you are experienceing. Then click on it anyways if not, then the next link might have the next step, or go to the Tags, and search based by tags. Good luck

 

[mrodub]

I appreciate all your input so far. With two little ones, it's hard to find time to get out in the garage.

I considered dipping the carbs in Pinesol or lemon juice but I didn't want to destroy the finish because they look almost brand new. The GUNK dip would be my next choice but I believe that also eats away at the finish (do you know of any other finish-friendly dipping options?)
Therefore I tore them apart and thoroughly cleaned them with spray cleaner but I must have missed something. The thing fired right up within seconds with NO CHOKE and as long as I kept the revs up, it ran smooth from mid to high range.

XSChris, these are your floats and pins and I don't think they leak.

JMD Forest, that's a good call with the idle circuit. It makes perfect sense, those passages are very small. I will tear them down again and triple check everything.

Arfstrom, I will dig deep into past threads. thanks


What's the best way to get the anti-tamper cap off the idle mixture screw (aka pilot screw, not to be confused with pilot jet)?

I don't understand why the pilot jet is plugged at the bottom. Can anyone explain this?

 

[arfstrom]

What's the best way to get the anti-tamper cap off the idle mixture screw (aka pilot screw, not to be confused with pilot jet)?

Its on Top when its on the bike, I was able to remove it by carefully using a handheld drill, with a drill bit, just smaller than the size of the plug. As it started to go into the soft metal, it started to spin, then I was able to pull back the drill, and viola. I have seen posts where others have used a smaller drill bit, and then used a small nail to pry upward, and etc. I didn't need a lot of power, or anything. good luck
Tobie

reason, Yamaha thought this wouldn't need to be changed anytime in the future, just plug it, and no one will think to mess with it. and that it was set to meet emissions standards as well. (the metal plug)
The rubber cap I forgot why

 

[jmd_forest]

To unplug the pilot screw, drill a tiny hole through the top, being careful to NOT drill too far and ruin the top of the pilot screw. Pilot screw is brass and it doesn't take much to screw it up. Screw a small pointy screw itno the hole you drilled and pop out the plug by pulling on that screw. I would suggest soaking the pilot screw in PB Blaster for a few days after removing the plug before attempting to remove the pilot screw.

I also don't understanfd why the pilot jet is plugged inside the float bowl. However, new rubber plugs came with my rebuild kit and I simply inserted them where they were supposed to be. Agasin, after an extremely thorough cleaning of ALL jets and orifices and circuits and needles, and absolutely everything else, I did replace the throttle shaft seals, the pilot needle o-ring, and reused the existing diaphrams (which I beleve were replaced by the PO)., the bike ran and idled nice and smooth. If using replacement diaphrams note that there may be no orientation tab on the new diaphram but the slide piston must be oriented correctly anyway.

Another thing to think about is that if your valves are seriously out of adjustment you may have trouble idling.

 

[arfstrom]

I considered dipping the carbs in Pinesol or lemon juice but I didn't want to destroy the finish because they look almost brand new. The GUNK dip would be my next choice but I believe that also eats away at the finish (do you know of any other finish-friendly dipping options?)

I think thats why everyone sided with the lemon juice, its easy to pull the carbs out of the juice, and then rinse it right away to prevent the juice from doing more damage to the finish. The juice just needs enough acid, and the boiling action creates additions forces that we cant replicate with just blowing spray around. I think that vinegar is more acidic, so most of us just go with the lemon. I suspect just boiling water will do more, cause your getting dynamic fluid into the passages , and its going re-hydrate, and if it breaks down the gunk, the that was left to harden 28 years ago. My wife left her bike in a garage in 2003, and the fuel turned to varnish, I had thickly coated varnished carb, and the Front brake Master cylinder had turned into a cake mix. all dehydrated. Good luck

 

[jmd_forest]

When boiling the carbs in anything, remember that there are a number of small rubber and plastic parts in the carbs such as throttle shaft seals, enrighment circiut seals, pilot screw o-ring, and I believe some models have a plastic jet. I would make sure these items were removed before soaking/boiling. I made the mistake once of just pulling a carb off and dumping it in a gallon can of GUNK. After a day or so of soaking every rubber part in that carb had turned to goo.

 

[arfstrom]

I had thought about mentioning that, Like those Idle mixture screws, those o-rings been sitting there compressed for the last 31 years or so. Yea, They are flat, see if you can order new ones since your in there playing with them, and any other gasket/o-ring/seal.
Tobie

 

[mrodub]

I finally got out to the garage and tore down the carbs... again! Sure enough, I missed a couple things.

The passage in the float bowl itself was still partially clogged in one of the carbs.

My biggest mistake was not removing the needle jet from the carb body and just spraying carb cleaner through it. I popped them out and they were caked with 30 year old gas. Every tiny hole was clogged.

I went through an entire can of carb cleaner. I sprayed every passage until I saw it come out the other end, blew compressed air through it and then I did it again.

I DID NOT touch the idle mixture screws, I was hoping to get away with not having to drill out those caps and f' up the screws.

The bike fired right up and now it will only idle with full "choke". When I open the throttle it'll rev up to 3000-4000 for a few seconds and then rev back down slowly. I know it's not a sticky throttle cable because I'm actually opening the throttle by hand.

I checked float height was ~25mm on both. These are the brass floats and according to the manual, height should be 32mm. This seems very high with the way these floats are shaped and the stopper tabs up against the towers. I feel like I'm missing something.

I'm ready to just break down and soak these carbs. Could I get a consensus on the best way to dip them without destroying the finish. I think I'll boil them in some Pinesol outside on the grill.


Any ideas guys? I'd appreciate it.

Sorry for the long post.

 

[arfstrom]

Advise not to pinsol
http://www.xs11.com/forum/showthread.php?t=29211

Advised to pine sol
http://www.xjrider.com/manual/pine_sol_carb_cleaner.pdf
http://www.jeepforum.com/forum/f8/pine-sol-carb-cleaning-1396279/

So okay for my 5 minutes I spent googling this pinesol and carb. Let me google that for you. http://bit.ly/RedtxO Only problem doesn't resolve your first fear. Its going to effect plateing. What does that mean? probably nothing. You can see my carbs via the photo album. I dont recall seeing any damage following the lemon juice program. The Pine sol appears to not damage rubber items thou. since I have no experiences, I did google it for you, so you evaluate for your self, Seems you really want to. So go for it. as from what I read, there are ney sayers, as well as "This is the best thing in the world" so keep the dilution ratio, and have fun.
Tobie

PS I used my turkey fryer, and if your in the twincities, I can make arrangements, and invite you to come over to do a carb fry !

 

[HoughMade]

I used 1/4 vinegar to water for boiling. I removed everything that I could. However, at boiling temps- 212 degrees, a bit more or less, I wouldn't be too worried about rubber and plastic. These thing set next to an air-cooled engine running at temps higher than that their whole lives.

Now, I hate to say this, but the revving and not returning to idle is a classic lean symptom. Assuming everything is clean (a huge assumption), there is no way to cure this but to richen the idle mixture which was set too lean for good performance at the factory so it could pass emissions.

Now, back to the assumption. Did you spray cleaner through all passages so that you could see three distinct streams of cleaner coming out the three tiny holes above the throttle plate? You usually have to cover the idle mixture hole with your finger to see that. Did you cover those holes and see a strong stream out the idle mixture hole at the needle? If you didn't see these two things, you don't really know if the passages are clear. Maybe, maybe not.

Good luck.

 

[xschris]

You will need to get at the idle mix screws so you can richen up the pilot circuit. Compressed air and carb cleaner should do the trick for cleaning most of the time. I soda blast all the carbs I sell and use if they are very dirty. If you boil you will have to replace the shaft seals and they are a bicth to deal with most of the time.

 

[mrodub]

Thanks for the replies!

It seems like it's starving for gas because it'll rev up with the "choke" but the throttle response is slow.
Do you think this could be float-related? The float height was ~25 mm and the manual says it should be 32 mm. I don't see how I could bend these things to gain 7 mm.

I'm still going to boil them (vinegar or lemon juice) and see what happens.

 

[mrodub]

Also, the plugs were both nice and black.

 

[xschris]

You will need to be able to adjust your pilot circuit by turning out the mix screws. You will never get it right until you do it Start at 3 turns but go no more than 4 if you need more bump up the pilot jets to 45 then start a 1 1/2 turns out then more if you need it. The plugs would be black if you are using a lot of choke and not running the bike on the road to burn off the carbon. Did you replace the rubber plugs that go over the pilot jets?