I think I messed up with my carbs

My '83 Seca900 has ran ok since I bought it two years ago. The engine used to start quickly and to run smoothly. But I wasn't completely satisfied with the colour of plug #1 (a bit rich) so I thought I could do some adjustments.

Don't ask me why I did that, but instead of simply screwing a bit in the mixture sxcrew of the offending cylinder, I screwed them all in all and backed them out 2 1/2 turns to start with something I'd know for sure.

After that I decided to go for a ride to test my adjustments. The bike started as usual on choke and when a bit warmed up I took the street. First thing I noticed the bike started to fart a bit but ran almost ok when I give some more thtrottle. At the stop down the street, it quit on idle and hardly started again.

I managed to come back home, same scenario, engine ran smoother with half throtlle, but poorly on idle. THen it quit and never started again, except for 20 seconds today, but ran very rough, with farts and backfires. I noticed that headpipe #3 was cold, they others were a bit warm.

DO you think I dislodged some dirt that clogged most of the 4 mixture jets?

 

Did you use colortune? If that's the case, maybe you loosened a spark plug cap ( cap to wire) on number three.

 

I didn't touch the spark plug wires at all. The only thing I did was to install an auxilliary fuel supply during the mixture screws adjustment. I left my fuel filter on the line in the process, so there shouldn't be anything wrong with the fuel. ALso I blocked the vacuum line tight with my thumb, and the engine ran great then. It began to act weird only when I put my fuel tank back on and I hit the road . FIrst I thought I idn't connected the vacuum line tight enough, but it looked ok.

I'm a bit puzzled.

 

Did you count how many turns in it took to get the idle screws to seat? My thought is that they were out further than 2.5 turns to begin with.

 

I don't. Not if the only thing you messed with is the mixture screws.

Out of curiosity, what happens if you pull the vacuum line back off and block it again with your thumb?

 

Second this question... You DID run the screws all the way in and count the turns first before you took them all out, didn't you? So you could go back to "before you messed with it" baseline, right?

 

That's what I think too, but no, I didn't count )I can't believe how stupid I can be sometimes). Actually I tried to back #3 abd #4 a little more out but it didn't work.

 

I'll try it tomorrow.

 

Could it have something to do with your orings?

 

It is a possibility that I destroyed one or more mixture s crew o-rings, even if I was careful not to bottom them in too tight. MAybe they were too brittle.

 

If that were the case my question is why would that head pipe be cold???

 

Well, according to Chacal , it is possible an o-ring piece blocked the mixture jet passage, that could be the case for #3 cylinder. No fuel can pass, no combustion possible.

 

Yes it's possible. And you need to investigate and remedy if needed.

But what's for sure is you completely screwed your sync. Now you get to do it right.

-Valve clearances in spec.
-Make sure you have a good solid bench sync.
-Set them all at 2.5 ~ 3 turns out.
-Do a running vacuum sync, YICS blocked (if applicable.)
THEN mess with the mixtures as needed; but only by turning them 1/16 of a turn at a time and taking copious notes. This is where the ColorTune comes in handy. Then you re-do your vac sync and set the idle and you should be good to go.

One the bike is running right, "touching up" the mixtures based on plug readings is fine. But you don't need to make huge cranking adjustments on the mixture screws. And unless you can put it back from whenst you got it (and you can't) then it's do-over time.

 

Bigfitz

I did check the valves last spring, they are in spec.

Why should I go thru a bench sync? I didn't touch the sync screws. I don't get that one...please explain .

 

Because the sync adjustments are likely NOT exactly the same; the bike was vac-synced to the way the mixtures WERE.

You need a new starting point for the vac sync since you're starting from ground zero on the mixtures. And the starting point for a vac sync is to have all 4 mechanically as close as possible, then you adjust them away from that mechanical "sameness" based on the demands of each cylinder.

You have effectively "zeroed out" the mixture adjustments. A good bench sync "zeroes out" the vacuum sync adjustments.

 

I forgot to mention that I put a brand new vacuum hose with two good collars, to rule out this as a possible issue.

 

Fine, makes lots of sense, thanks.

 

Manual says to remove the carbs from the left hand side, do i have to disconnect the clutch cable anyhow?

Also, since the site migration, the Gamuru how-to links are no longer available, can anybody send me a link that covers this procedure, just to give me a chance not to do some other dumb moves...

 

I wouldn't totally discount debris contamination from the tank from removal and installation. Its possible you my have had a lot of debris in the bottom of the tank that got unsettled and ended up migrating into the carbs. Do you have an inline clear filter?

 

I thought it was a good thing to leave my fuel filter on the line during all the process. I make smart moves sometimes, not always dumb moves.

So if there are debris somewhere in the fuel system, they don't come from the fuel supply neither the fuel tank.

 

Sorry, my bad. I just saw, further up the thread, that you mentioned you left the filter in.

 

No problem , I did the same before myself!

 

Your saved links don't work, but the articles are still where they used to be. http://www.xjbikes.com/forums/index.php?search/3885/

 

Alright thanks k-moe

 

I just checked and when I copy and paste in the browser or simply click on this link you gave me, it doesn't work, I have an error message.

 

Are you looking for the bench sync procedure? It's located in the XJ DIY How-to-Instructions

http://xjbikes.com/forums/index.php?threads/how-to-bench-synch-your-carbs.6366/

 

Also, Len just updated most of the links in the information overload (thanks Len), which seems to cover just about every question one could have.

http://www.xjbikes.com/forums/index.php?threads/the-information-overload-hour.27544/

 

Thanks a lot Mr Rooster!

 

That probably happened at a time that Snowsherrif was working on the site. I tried earlier tooday and the link gave me an error, but it is working now. You can also just do a search for posts by Gamuru (that is what I linked to).

 

I removed my carbs earlier this afternoon. I had a hard time screwing out #3 intake boot collar, little bolt turned but it didn't have any effect on the collar. I sprayed the boot with silicone and managed to give the collar half a turn to have that bolt on top of carb, and finally decided to cut the little bolt out with jeweller's cutter, after I removed the choke bracket to give me some room.

I sprayed silicone on the airboots too so they easily went in the airbox and I had the carbs out five minutes later. I'll send pictures and infos of what I'll find later, maybe this weekend.

 

It sounds to me like you've not had the carbs off prior to this.

If that's true, then by all means, wet-verify the float levels, etc. LEARN those carbs. And learn to love them.

Above all, become PRECISE. Imprecise cranking on screws got you here. Aren't those Mikunis?

Mikunis don't require a carb doctor. They require a carb brain surgeon.

 

I haven't checked yet but I'm pretty sure they are Mikunis. This is the first time I removed these carbs, but I've done it a few times on my Maxim-X and also on my XJ750K. So I'm not in a totally unknown country.

While I have them off of the bike, I will open them to see how clean they are inside, to check the diaphragms for wear, I wil pay special attention to mixtuer screws and passages, I will wet set the floats for sure and of course bench-sync and run-sync them. Hours of fun...

 

I opened the carb tops this morning, the long springs, the diaphragms and the slides are in very good shape.

I also removed the mixture screws, little springs, washers and o-rings and they all seem to be ok except that the o-rings are a bit stiff and flat. I looked down in the 4 holes and didn't notice anything wrong, I could see the light I put close to the opened butterflies.

I will remove the bowls and check the floats and screens.

 

Removed the carb bowls this afternoon, nothing obvious except for some fine rust particles here and there, that probably were there when I bought the bike two years ago, I've put a fuel filter since. I cleaned the passages in the bowl with spray carb cleaner, it jerked pretty strong out of the passages so they should be clean.

I didn't check the float valve screens because I wasn't able to remove any float pivot pin though, and I didn't insist because I wanted to ask what is the general consensus as to what is the best way to remove them without breaking the posts?

 

Check this out:

http://www.xjbikes.com/forums/index...-removing-float-pivot-pins.47726/#post-424386

 

Man, that was quick!

Thanks a lot!

 

I just read it and my question is: why use an auto centering punch? why not just a punch of the proper size? There is nothing like a hole or a depression at the end of the pin you could center a punch in anyhow...

And what about using a piece of harwood of the right width instead of a piece of metal metal between the post while gently tapping with the punch?

 

I have never worked with the Mikuni carbs, but the suggestion for the auto centering punch would be the spring delivers just enough punch to knock the pin loose. Using a hammer and a punch one could easily get a bit aggressive and break the supporting post. I might also speculate that with the auto punch, you could actually support the post with one hand while driving the float pin with the other. It seems no matter how it is done, it could be a bit stressful, particularly on the inner carbs where it might be difficult to get a straight shot.

http://en.wikipedia.org/wiki/Automatic_center_punch

 

While I can see how using an automatic punch tool would work, I have always been able to use a standard punch and a small hammer to gently tap out any float pin I've ever come across. Don't go all gorilla hands with it and you won't have to worry about breaking the towers off.

 

+1 what shank said. Bikes are not cars. Just about all of the nuts and bolts, if not seized by time, can be made tight to spec (using the old 1/2 turn past snug technique) or broke loose by hand (with the aid of a breaker tool in some cases). And yes, imo torque wrenches are necessary.

Gary H.

 

Just remember, all auto center punches are not the same. So be careful

 

NOw I remember I have a very smal hammer in my toolbox, it doesn't weigh more than 4 ounces, would be perfect.

 

I haven't had much success with the float pins yet, but I'll let the penetrating oil do its job and try them again later today and tomorrow and the the day after if necessary.

Meanwhile, I decided to bench sync the carbs. I used the paper clip method at first attempt but I was not satisfied with the result, maybe my clips aren't the same size or I did something worng...

At second attempt, I use the first of three tiny holes in the venturi as my mark and adjusted all four butterflies so that I could see only half of that hole, As a result, I see the same amount of light at the bottom of the butterflies, so it should be a good start to have the bike running.

 

[QUOTE="quebecois59, post: 425823]
At second attempt, I use the first of three tiny holes in the venturi as my mark and adjusted all four butterflies so that I could see only half of that hole, As a result, I see the same amount of light at the bottom of the butterflies, so it should be a good start to have the bike running.[/QUOTE]

Imo best way to do it.

Gary H.