Lean/Rich Mystery

---skip to second paragraph if you're not interested in the bike's past---

Hi Guys, I am new to the site. I bought my Maxim back in November, and took it for quite a few good rides before deciding to do some much needed maintenance. Changed the fork seals, cleaned the tubes and refilled with fresh oil - found rust all over the springs, and more water inside the shock tube than oil. Changed the brakes and flushed the lines - found some rust inside the master cylinder and nasty gunk along the way. Went to change the oil and found that it looked more like liquid tar than oil. Changed the oil filter after having to cut it off the front as the previous owner had damn near fused the bolt to the cap - replaced it with a nice 17mm (i think) unit off ebay. Checked the shims and replaced 4 of the 8. Removed the cracked intake gaskets and replaced them with some nice new ones - sealed with RTV silicone. Did a real nice job of sealing the rest of the intake boots with RTV silicone. Removed the carbs and did a FULL clean job - literally removed, soaked, scrubbed, shot with brake cleaner to dry and remove moisture, then reassembled; bench synced, and placed back on bike with K&N Pod Filters. I replaced the factory main jets with 118s and the pilots with 41s. Set floats (dry method) and double checked. Also, bike is running a free pipe - 4 into 1; loud and awesome as hell! I'll post some pictures once I start doing the cosmetic stuff.

Here's my problem.. the bike starts right up with a little bit of choke.. give it a bit more, and it revs to about 4000rpm and sits there comfortably. (not comfortable by me) Drop the choke back down to the original level and it hunts its way back down pretty rapidly and stays there. Let the bike warm up, remove the choke, and it dies. Bike runs pretty well when I first start riding it until about 4000-5000 rpm and then it just starts sputtering.. more throttle = more sputtering and erratic power behavior - can't quite get past that range into the high rpm range. So, I just ride it around as such keeping engine rpm below 4000rpm. Then as the bike gets hotter, it starts misbehaving very badly - backfires sporadically at low load; on deceleration it backfires like crazy. I come up to an intersection and it dies immediately. If I keep the throttle cracked just a hair it stays alive.

My dilemma is I can't figure out whether it's running rich or lean!!!

I checked the spark plugs - all 4 appeared to be carbon fouled (obvious indication of rich mixture.) So I turned the air/fuel mixture screws all the way in, same problem. Checked the plugs, still carbon fouled, so I decided to clean the deposits off with a wire brush wheel and adjusted the gap. Ran the bike two more times and checked the plugs. They were clean as a whistle!!??? Still fumbling. I don't know what to do.

My next step is to turn the screws all the way out and see if I can get the plugs to foul again, or maybe that is the right mixture..? I'll see how that goes, then I guess the last thing is to do a full sync of the carbs/cylinders. I was trying to hold off on that until I at least had the mixture somewhat close.

Thanks!!!

 

Did you wet set the floats ? Also did you rebuild the petcock? Then check for vacuum leaks by flooding the carb area with propane.

MN

 

Welcome to the forum! Have a look at this thread it appears to be a similar tale of woe!

http://www.xjbikes.com/Forums/viewtopic/t=38808.html

Oh and could you pls put your bike type in your profile....it will assist us in your future postings

 

-Wet set the floats.

-Finish your carb tuning: do a running vacuum sync, with YICS blocked (if applicable.)

 

Okay, so I had some time to do some debugging on Friday after work. Here's what I found while checking the plugs.... only 3 cylinders are firing!!! That might be part of the problem :lol: After some more inspection it was discovered that the ignition coil wire to cylinder 1 was severed inside the insulation - I guess it was barely making contact the time it was running. Anyone know where to get a good deal on these? I'd be looking to replace all 4 if they are reasonable.

Once I get this fixed I'll check out if I'm still having the same problems. Would this cause the engine to run rich for some reason? Unspent fuel being redistributed by YICS?

 

Where exactly was it severed? If it is at the cap, then trim 1/4" or so, and screw the cap back on.

 

That's exactly where it was. It looks like the connection is make by a screw that winds into the coil.. is that right? Seems awfully unreliable.

 

If a Bike runs with Choke, ... and Stalls without it, ... you have a Delivery Issue.
It NEEDS Fuel.

Generally, ... this indicates a Carb Cleaning is due.
It also means the Diaphragm Pistons may not be lifting.

Do a thorough Carb Cleaning.
Be sure to punch-out the Central "Nozzles" (Emulsion Tubes)
Flush the Fuel and Air Passages.
Refinish Piston Bores -or- Polish

Complete the process;
Float Heights
Bench Sync for Closed Throttles

Run and Fine Tune.

 

Take the air filter out and try it, sounds rich

 

Yes, it is unreliable. After a few times of removing and re-installing the screw on plug caps, it breaks. Trim 1/4" off the wire, and screw the cap back on. Then check the resistance on the wires and the coils.

As for the stumbling, sounds like you need to do a thorough carb cleaning and rebuild.

 

Sometimes there isn't enough slack to trim the wire.
In that case, use a length of solid copper wire and stuff the core of the spark plug wire.
The bare solid Ground Wire from household wiring makes a good Core supplement.
Clip the end.
Sand a point on it.
Stuff it as far as you can up the core of the spark plug wire.
Clip end.
Screw plug cap back on..

 

Tried this.. and it worked. Thanks, for saving me some $$. Checked the spark on all the wires at the plug. Looks good now.

I decided to go over the carbs one more time.. found/learned some new things.

1. I noticed the small needle (pilot circuit adjustment) on the throat (it's a little little guy that sticks out.. thought it was a piece of dirt at first), behind the butterfly, I adjusted 4 screws to be exactly the same, all the way in, and noticed that they were ever so slightly different. I might have to put a new order together thru Chacal.

2. The big thing that bothered me though, and I don't know why I didn't notice this before, but when the idle is turned all the way up, the butterflies are just barely open - less than 1/16". I know it's just under 1/16" because I used a drill bit (shank side) to bench sync them. Shouldn't the idle screw be useful for more than just the last couple threads? I'd say for 80% of the threads, the butterfly is dead closed.

This would make a lot of sense if my idle was set too low. (butterfly closed)

 

You might have a substitute Idle Rod.

Slip the Spring onto the Threaded-end of a Bolt.
Use a Washer and Nut to keep a short length of the Spring protruding over the end of the Bolt.

Grind 4mm off the Spring.
Replace the Spring adding a Nylon Flat Washer on to the Idle Rod before the Spring.
The Washer will allow the Rod to be turned a bit easier.

Use a bolt the same O-D as the Idle Rods Threads.
Don''t use the Idle Rod.
You don't want to risk shortening the Idle Rod.

 

I found the source of the issue!!

The main jet is usually tightly snugged up against the carb body.. my had about half a millimeter of play up and down. My guess was that air/gas was flowing thru there. Making it tough for the pilots to work properly at idle, and making the bike way too rich at full throttle.

Lesson learned!

Now to sync and move on to a few more cosmetic things.