Running Rich ... not sure what to do next?

After "trolling" this forum for the past several weeks, I have finally decided to post and see if you guys can help.

1982 XJ550 Maxim - recently purchased, was running but would stall/die as soon as the engine warmed up. Pulled the plugs and they indicated a rich running condition (black/sooty). Here are the things that I have done so far:

- Check valve clearances - they are to spec
- Pulled carbs, cleaned bowls, diaphragms, jets (main/pilot), soaked in carb cleaner
- Installed "spec" main and pilot jets (112.5/35)
- Vacuum synced the carbs
- Pilot Mixture Screws set to 2.5 turns out
- Removed "pod" air filters and installed stock airbox and air filter

This work got the bike running reasonably, and I have been able to take it on a couple of rides (thankfully). However, the bike tends to "bog" at low RPMS (<2.5k) when getting off the line. After 2.5k RPM the bikes runs great and pulls hard. I have tried to make adjustments to the Pilot Mixture Screws per the "by ear" method, but it is difficult to determine if this is helping (either I can't hear the difference or there is an issue with the screws themselves). Here are the things that I have NOT done and I am wondering what order I should tackle these in:

-set the float height
-clean out the Pilot Mixture Screw assembly
-re-clean the carbs
-purchase Colortune plug
-attempt another tune "by ear"

Not really sure what to do other than that. As it is, the bike is ride-able, but it is not as "pleasant" as I know if could be. Also, my MPG is quite low at 25 MPG.

Any suggestions?

 

You've pretty much got the order down, here's what I'd do:

What exactly did you soak in carb cleaner?
Know that until you break the rack and replace them, the throttle shaft seals and fuel rail o-rings are always a concern, but neither would cause a rich running condition if they failed.

 

Actually, I would move re-cleaning up the list, which would include pilot screws and enrichment circuit.

Then wet set the floats when re-assembling.

I would also add at the bottom of the list, after the colortune, do a running carb sync. It's much easier than doing it by ear, and you can make a vac gauge out of some clear tubing and some tranny fluid.

 

with the super-low MPG, it's screaming "float levels." Especially on a 550.

And you'll need to do your vac sync (YICS blocked) THEN ColorTune, and then re-check the sync.

After properly servicing the carbs and wet-setting the float levels.

Exploded Mikuni: http://xjbikes.com/Forums/viewtopic/t=31061.html

 

Perfect. Thanks for the advice guys. I am going to give it a try and I will post back here with the results!

 

OK guys ... the plot thickens. After listening to all of your advice here is what happened.

- Removed carbs, inspected and cleaned pilot screw assembly and enrichment plungers. The o-rings on the pilot screws were definitely stiff and presumably an issue. These were replaced.

- Dry-set the float height to spec, and then verified the fuel level with clear tube method. Seems to be in spec, unless I am missing something.

- Re-installed the carbs and did a running sync with YICS blocked (found a local shop who had the YICS tool and he did the sync for $20 ... not bad).

- Adjusted the pilot screws using the "by ear/ idle-drop" method ... as I do not own a Colortune plug. This is where things get interesting!

For some reason the bikes seems to run best when the pilot screws are turned completely IN. With all 4 screws in this position I can get the bike to idle at around 2k. Once I start to open up the screws even just a little, the bike seems to get "burpy" and "sluggish" on the throttle. So here is the question, if the pilot circuit is completely closed and the enrichment circuit is closed, then where is the extra fuel coming from? My only guess at this point is that when I was inspecting the carbs I noticed that the slide diaphragms were "slightly" stiff. There were no holes and they were still pliable, but on their way to being unusable. Could this be causing an issue if the jet needle is not seating properly in the main jet? Another thing with that part of the carb ... should the "needle retaining plate" be screwed in completely within the slide housing, or should there be a bit of "play" in that system? Fortunately I have two complete "spare parts" carbs lying around, and I am planning on looking to see if I have a set of slide diaphragms in better shape. Would it be worth my time to replace them? Am I even heading in a realistic direction? HELP!

Thanks guys!

 

If you are "idling" at 2k rpm, you aren't drawing from your pilot circuit alone. You have to bring the idle down to 1200 rpm (i think that's the idle for 550s). You'll need to open your pilot mixture screws (2.5 turns out) and lower your idle. If it bogs down, you're probably still lean, and crank all out another quarter turn. At some point, you should be able to get your idle down.

I'd sync again (since a sync at 2000 rpm won't do much for you at idle). Even sync without the YICS tool (this won't be the only time).

Then fine tune your pilots with the idle drop method. The key here is that you must be at IDLE, not 2k rpm.

Then sync again. YICS tool helps greatly with syncing. You may want to consider buying one, and a colortune plug. They will help GREATLY in tuning your bike, and are a good investment.

Chacal sells a parafin wax fluid that you can use to rehab your diaphrams. This will help things off idle, but shouldn't affect your idle. Also make sure your slides go clunk.

 

It's still screaming "float levels." Either that or your enrichment plungers aren't closing fully or are damaged (the rubber sealing "insert" in them) so it's dumping extra fuel. On a healthy 550, your mixture screws should end up at around just under 3 turns out, give or take.

I'd start with the float levels-- rack off the bike, level in all directions, and INDIVIDUALLY VERIFIED, WET, within the +/-1mm spec.

See: http://www.xj4ever.com/setting%20fuel%20levels.pdf

If they're for sure right on, investigate the enrichment plungers.