1981 XJ550 troubles

Hi everyone,

This is my first post. Here's the deal. I bought an 81 550 Maxim a month ago. It sat for nearly 15 years and wasn't running having 13.5K miles and in OK shape. The PO had stored the bike with a FULL TANK OF GAS 15 years ago. That should give some idea to the mess I encountered.

Here's a list of the things I've done.

New air filter, stock replacement from OldBikeBarn.

New battery.

New plugs.

Petcock seems to be functioning and the gas tank was rinsed. I'm not totally sure how the petcock should be tested.

Cleaned, and I mean cleaned, the carbs (Mikuni). Including new float gaskets, valves, and seats. Drilled out the adjustment screw covers, just under 3 turns out. And, I have tried my best to sync to carbs with a homemade manometer when the bike turns over. So I think they're close.

Now, the bike will "run" with the choke on all the way, but it races to about 5k on the tach. With the choke all the way off, the bike will start with a little throttle then die shortly.

Two problems:

1. 3 out of the 4 exhaust pipes are hot, really hot. The number one cylinder is warm at best.

2. If I blip the throttle the RPMs race high for a few seconds and then fall and the bike dies.

Basically, I am at my very ledge of my mechanical knowledge.
Any help would be great. Thanks to all who post here. I have learned a ton reading through your posts.

Thanks,
CRAIG

 

Your main jets have to be clogged. You cleaned the float valves and seats so its getting gas to the idle jets but I bet the main jets are crud.

There are folks on this forum with far more knowledge and experience than me but I believe your carbs need more work. It'll be worth it in the end though.

 

Check you carb boots (these are the intake hoses going from your block to your carbs) for cracks or leaks. If your intake boots are sucking in air then your bike will act just the way you explained. I have encountered it myself twice and seen a few here with the same problem. If they are cracked then you will have to replace them.

 

Check those things to be sure, and then when they don't work, just go ahead and pull the carbs and clean them really well. My 550 was acting much the same way when I got it, and no matter what I did, nothing made it run any better until I cleaned the carbs. Now it runs perfectly. Just bite the bullet and pull 'em off. That's the only thing that will really help.

 

really problematic spots I found on my mikunis:

1. Pilot jets (the holes are so tiny that you have to use a very, very fine strand of wire to unclog them
2. siphon tubes (same story, although they're not as small)
3. rubber diaphragms on the top might develop tiny holes, so they have to be repaired or replaced.

main jets actually come out quite easily for cleaning - use a flat screwdriver that fits the slots on the bottom _perfectly_ ... unscrew, push the remaining part of the jet out. it will come out from the top (you have to have the diaphragm assemblies off). There are a bunch of tiny holes on the upper part of the main jet. Every one has to be spotless.

 

That's not the Main JET.
That's the Emulsion Tube.

The Emulsion Tube doesn't Meter FUEL.
It Meters AIR ... from the Main AIR Jet.

Still, it has to be cleaned and all the 16 -to- 20 Ports drilled into its Outside Diameter free from contaminant.

As previously mentioned.
Withdraw the Main FUEL Jet.
Remove the washer exposing the Emulsion tube bottom end.

You will likely have to drive the Emulsion Tube out after sitting for all those years.
Place a bolt with matching thread pitch into the threaded end where the Main Fuel Jets was removed from.

Begin with lightly tapping the bolt ... graduating to more force if its stuck.

Note: The Diaphragm Piston Assembly must be removed before extracting the Emulsion Tube. The Emulsion Tube goes OUT the Top.

Clean the Exterior with a ScotchBrite Pad -- Gray
Clean the Interior with 3 Pipe Cleaners twisted tightly and Carb Cleaner added.

Clean the Metering Ports by extending the Smallest Tool from a Welders Tip Cleaning Set in one side and out the opposite side.

While the Emulsion Tube is extracted ... Clean-out the Main AIR Passage by shooting Carb Cleaner directly into the Main AIR Jet and look for it exiting the Port where the air is drawn-in to surround the Emulsion Tube.

Once the Main AIR Passage is Cleaned ... Clean the Inside diameter of the Bore where the Emulsion Tube Fits.

The Twisted Brass Brush used for cleaning Rifle Barrels supplied to Infantry Soldiers makes a perfect tool for scrubbing clean the Emulsion Tube Bore.

 

Greetings!

im brand new here myself...

i chose this thread to start with because i have the same issues (or i should say i will SOON have these same issues)...

bought my 81 550 Maxim in 92 and ran the odometer up by 4K in about a year and half to 11,900...

parked it for the winter in 93 and tried to run it in 94. it ran only if the choke was full on but it acted like the choke was, full on...

i let it set for the next 13 years and am now in the process of treating it the way it SHOULD have been treated...

Rick and Stereomind, if i pull the carbs off and cant figure them out to reassemble them, can i send them to you for your assistance? without pics i dont know what it is im looking for for reassembly...

thanks for the forum. ill be spending a bunch of time here i think!

david

 

Rick, I dunno what is all the stuff called yet, I just know how to get it out and clean it

Ltdave, putting everything back is not as hard as you think. Just remember not to break the carb rack, and do only ONE carb at a time. If you have a digital camera, take pics as you go.

 

Don't do any damage.
You need a few special tools to work on Mikuni's

ALL the Jets and Muxture Screws are soft Brass.
You want to make yourself some screwdrivers that fit those slots with Absolute precision.

Otherwise, the wings on the Jets and Screws will move and the Body will still be stuck. The Wings will break-off leaving you to have to drill-out the part which would have come-out if the correct tool is used.

Particularly, the Pilot Mixture Screws. They will feel like they are moving but the top will give, leaving you with a nightmare of drilling-out and finding new Mix screws.

 

Thanks to all for the posts.

The Emulsion Tube. That for certain didn't get pulled and cleaned. Rick, thanks for the heads up on that one. That will be this weekend. I thought it was a straight tube. I'm positive there's goo in there.

I'm almost sure the jets are clear. I can see light through them and I can see the machined hole.

The manifold boots look cracked on the outside but they look OK on the inside. There goes next week's paycheck.

Is there any reason not to replace the outer screws of the carbs with Stainless? I stripped more than a few pulling them apart.

ltdave, feel free to contact me if you'd like. We have the same bike. I can always send pics or any info you need.

Thanks again,
CRAIG

 

uh oh... 8O

Rick has me worried now. im not that much of a mechanic and now im afraid i might bugger these carbs up...

do you want to take a crack these Rick? i would make it worth your troubles... :lol:

 

I have had those carbs apart multiple times on mine too. I am always going through them and every time I do, I find another another part that needs to be cleaned again. Even with an inline fuel filter in there. You might not have to buy new carb boots as you might be able to smear silicone on the outside to fill the cracks and let it dry. If you want new ones, go on eBay as I got a full set of 4 for $75 shipped.

Stainless screws would be nice on there. I am looking to source some for mine as there are more than a few float bowl screws that are close to needing help with a dremel... I'm just very careful with them.

I'd also be happy to look at pics if you get stuck.

 

The runway's foamed, Elle-Tee

I'll have the equipment standing by.

Let's do the maintenance and get you back on the flight schedule.