Jets or...? HELP!!!!

Need Carb help... I picked up what appeared to be a MINT 1982 Seca XJ550 with approx 3000K original miles on it back in June/July. It basically looks like it just came out of the factory crate. It's been sitting in storage as I was having a new home built with no time to play with it. Now I'm trying to get it tuned (since it ran like hell when it was delivered). Come to find out, it won't run at all without full choke and even then it wants to run at an approximate 4K+ RPM. I had a local mechanic go thru the carbs. He said they were all gummed up despite looking new on the outside. Now they are all spanky clean but the problem remains.

The bike appears to be stock with the exception of a MAC 4 into one exhaust. As the mechanic was going thru the carbs he noticed that it appears someone had previously gotten into the carbs as one airbox boot was not properly re-installed and some screw heads are a little boogered up. He suspects maybe the jets were changed. Does anyone know what the factory Mikuni jet #'s were/are for this bike? I know some exhausts need re-jetting but my understanding was that this MAC unit does not. I'll eventually be replacing the MAC with a NOS Kerker 4 into 1 I've been able to dig up.

Any other suggestions to get this gem running again properly?

Any and all help greatly appreciated!

 

Main jet is a 112.5 and pilot jet is a .35.

 

Cool! Thanks Much!

BTW.. where did you find that info?

 

On the XJCD. It is a CD containing the shop manuals with, (Yamaha's permission) and a compilation of info and how to's from the XJ gurus. Only costs $10 and is worth much more. There is a link on how to order it on this site.

 

The mechanic now tells me that if carb cleaner is sprayed on the choke portion of the carbs while the engine is running there is a surge. So it appears that there is a vacum leak from one or more of the rubber caps that seal the choke shaft (starter set?). A quick check with a local dealer tells me that those seals are discontinued. Are there any carb rebuild kits that would include all rubber parts such as these? (it wouldn't hurt if the jets were included also)

 

The rubber seals are to keep dust and grime out, they do not seal the choke circuit. The plungers that move up and down seal the choke circuit. However, there are intake boot seals in that area too! Make sure the clamps are tight on the carb side of the intake. Also check the intake boots for cracks.
Since the carbs have been cleaned it would have been good to know that the pilot mixture screws were set to 2.5 to 3 turns out. It sounds like your idle jets are either clogged or the pilots screws are set too lean. Not enough fuel getting in through the idle circuit so opening the choke lets fuel in through the starter circuit. But an air leak would keep even that fuel flow lean and cause a high idle, which is the most likely problem since the carb cleaner is getting into the intake tract.
There are no carb kits that include jets. The jets just don't wear out. They just need to be cleaned. But the jets are available from motorcyclecarbs.com.
So make sure the clamps are tight and even that the carbs are all the way into the intake boots. Then we can check the pilot mixture screws for proper setting.

 

The intake boots & gaskets were replaced as they were cracked (we assumed that was the root of the problem but like I've mentioned, despite new boots the problem remains). Agreed it seems that there may be a remaining air leak, the question is where?

At this point the carbs are being pulled again to verify the jet numbers and put that issue to rest. I'm confident that the carb internals, including jets, are clean. Are there any diagrams that show the location of the pilot mixture screws? I'd expect a lean air/fuel mix would show via the plugs but they actually appear to be very dark (sanity check... doesn't that indicate too rich a mixture?)

BTW... I will be running a K&N filter and a MAC 4 into 1 exhaust (later switching to a Kerker 4 into 1). Are the stock jets a good match for this setup or should I be looking for something different?

 

It doesn't matter how Clean the Carbs are if the Diaphragm Pistons are sticking.
You need to check that!

Search: "Clunk Test" in out archives.

The Diaphragm Pistons are housed in a finished aluminum bore.
The bore surrounding the Piston gets tight with aluma-oxidation.
A "Dust-like" substance similar to rust ... but, ultra fine.

The oxidation will cause the Piston to bind or hesitate or actually stick right in place.
That behavior needs to be eliminated by refinishing the bores.
(Outlined in my Post in our Archives)

I take the process a step further, these days, and actually polish the bores for maximum performance.

 

I upped my main jets from a 120 to a 122 just for the K&N filter. With a header I would assume at least another jet size. There should be some info and advice that comes with the header so go with what Kerker says.
Rick has a good point so check that the carb pistons move smoothly and drop free with a clunk. I would also make sure the choke is all the way off. Open it could let in the carb cleaner as the mechanic found out. It is also possible that the carbs are just enough out of sync to cause this. Since you are pulling the carbs off check them with a static or bench sync. Simply put this is checking that the butterflies are open the same amount at the bottom when the throttle or butterflies are closed.

 

Both MAC and Kerker say no re-jetting "should be" necessary. I wish I could remember what I did with my original bike I had setup this way 25 yrs ago.

 

After 20 Years, you need to know the Diaphragm Pistons are rising and falling with no drag on them. I can't imagine anyone with our style of Carbs not needing to check Diaphragm Piston movement.

The close tolerances get even closer when the Bore gets oxidized and the Piston cannot rise and fall with the slight changes of pressure that occur during open and closed throttles.

In the same manner ... the Bores of the Enrichment Valves will shrink due to oxidation. Enough to make the so-called Choke Valves stick open and cause for a Rich running condition.

At the very least, some ScotchBrite Pad should be used to burnish the Bores clean and get the oxidation off the Inside Diameters and allow the Pistons or Valves to have NO Problem moving up and down.

 

Since the carbs are being pulled out again, I'll make sure everything moves freely. I'm pretty sure the guy working them has already done this but it won't hurt. The whole bike looks like new but we've already caught some rubber rot. I can't imagine there is any oxidation from what I've seen but I know what you're talking about and we'll take a look.

 

khornet, it seem you biggest problem is letting someone who claims to be a mechanic work on the carbs while you relay info back and forth. It's best to do all the work on your bike yourself so you know it's done correctly rather than depending on some high school drop out to do it.

 

You've got that right! But believe me, if I thought I had a clue as to what I was doing with a set of carbs, I would do it myself. It's been much too long since I've tinkered with a bike. I've still got an ounce of confidence this guy will figure it out. When that is gone, I'll dive in if nececssary and hope I really don't screw it up.

If only I still lived in Phoenix/Glendale, I'd let you help me!

 

We are about to that point in time where the Dealerships might NOT be the best place to bring your Bike for a Carb Cleaning.

Why?

Because it takes too much time for the job to be done RIGHT!
Taking them off.
Tearing them down.
Cleaning the whole deal right
Putting them back together
Getting them back-on the Bike
Doing the Syncs and Mixture settings ...

This is NOT what a Dealership Tech wants to do with his Money Making Day.

The Technician can complete Work-Orders on several Bikes in the time it takes to get them off and take them down.

Several more completed Work Orders (at full rate) in the time it takes to really clean the carbs quite thoroughly.

He's losing money on your Old XJ Bike.
Combine the factors that make the Job even more difficult:
Soft steel fasteners
Stuck Jets
Mangled Pilot Mixture Screws ...

The sight of your Bike to a Latter-Day Service Tech sends shivvers down his spine.

That's why they don't want to mess with your Bike at the Dealership.
The Owner is pee-owed you are hanging on to the old bike and not doing business for a new one.
The have to order whatever you need and keep your bike "In the way" of progress.
The Techs get pee-owed having an antique mess their schedule up and begrudge the guy working two bikes at a time while he's pulling your carbs.

And so the story goes ...

Your bike means a frustrating day of getting backed-up on his weekly gross.

You need to be able to do your own Carb Cleaning and Tuning.
A little practice and expenditure for what you need to make the job easy
will get your bike tuned-up better if you take the time and do it yourself!

 

Long story... but the guy working this comes highly recommended by local bikers & the local dealer. He is an ex-dealer mechanic who is disabled and still does bike work at his residence to make some extra cash. I'm confident that he has the know how and ability to get this done and that he is being meticulous about the work. I ended up working this with him since there's not a single local dealer within driving range that will touch ANY make bike over 10 yrs old (supposedly for liability reasons) and since I don't have the time myself to get to this anytime in the near future.

He just called me with news that he confirmed that the carbs still have the factory jets. He's going over the whole set once again to make sure he didn't miss anything. The current game plan is to take the carbs off my other (running) Seca and put them on the bike currently having issues just to be certain that the issue is not something else. Conversly we may put the problem set on the running bike to make sure the problem moves with them.

You can bet that while both sets are off everything will be closely inspected for drag, etc per the recommendations y'all have provided so far.

All comments continue to be greatly appreciated.

 

pilot screws are located under the plug in the pic. If this has not been removed then the carbs are not clean. Under the plug there is a small screw. Turn the screw all the way in and count the number of turns it takes to bottom it out. This should be about 2.5 turns in. Be careful not to overtighten it. Then back it out all the way and remove it. There should a spring rubber o-ring and a small washer on it. Make sure all these parts come out. Then spray some carb cleaner in the hole with the straw installed and see if any cleaner comes out of the small ports in the carbs by the butterflies and the stem that goes into the bowl. If none comes out, then they are clogged. To unclog these small holes just keep spraying some carb cleaned down the holes until all the crud comes out. You may have to let the carbs sit for some time to get these ports to unclog. Kind of a soaking. Good luck. Read Ric-o-matics cleaning you carbs the whole nine yards post. It is a great post full of great information.

 

Sorry... where do I find that post?

 

http://www.xjbikes.com/Forums/viewtopic/t=2908.html
Right here. Great reading.

 

I see all this mention of Hitachi being the most widely used carb on these bikes but of the 3 Seca's and one Maxim I've owned, they ALL came with Mikuni's. ?????