bogs out from being too lean, fixing causes other issues!

Ok, so I have spent a ton of time on here the last 3 months working on getting my 82 xj650 maxim into shape and I feel like I am really close, but I'm running into a head scratcher. Most of my problems Iv'e eventually been able to figure out using the search function, but I'm stuck on this.

Already done:
Rear brake replaced
Valves in spec
Carbs cleaned (4 times, clunk tested, float levels set using tube, every passage cleaned and recleaned)
good running sync (at least 5 times at this point)
All jets are stock
Bike airbox and exhaust are stock
SS brake line upgrade with rebuilt MC and calipers
valve cover/donuts replaced
new tires

Here is the issue: When I set my mixture screws to the point where the bike idles perfectly and smoothly (using Ricks 'old school' tuning method) the bike will bog/chug along until the RPMs get up to 4-5k. Very little power to be had. Plugs at idle are nice and brown, but are solid white with one small dot of tan when I do a chop at 4 or 5k. That happens with all mix screws about 2.5 to 3.5 turns out.

Now, if I turn them farther out, the bike rides great, no complaints at all BUT the idle is lumpy and uneven, even with my manometer showing they are all perfectly synced. If I do a chop at 4-5k they are still showing lean, although a little less so. This also makes it a bit harder to start, requiring me to use a little throttle until it can hold itself.

So what should I be looking at? I have flooded the carb area with starter fluid and propane with no response to engine speed. Emulsion tubes are squeeky clean. Slides have been polished up to 2000grit using wd-40 as a lubricant.

I need more mid range fuel right? Do I shim the needles? I don't want to sacrifice easy starting and a nice idle for a nice ride, I want both! I read in another thread that a stock bike should never need to be rejetted. So something is wrong somewhere right?

 

Re: bogs out from being too lean, fixing causes other issues

sounds like you got the two air jets in the top of the carbs backwards.

CN

 

Ya, it sounds like it is starving for fuel.
Did you do a colortune???

 

a color tune won't do any good if the jets are in the wrong place.

CN

 

I switched the air jets. The small jet was in the center and the larger jet was towards the outside. which is correct right?

Well, switched them all just for the fun of it. Upon switching them however, I instantly fouled all the plugs and it ran like crap. With the mixture screws turned all the way in it ran better, but still ridiculously rich.

So I'm guessing the air jets were right to begin with then?

 

The jet with the smaller hole goes in the center, yes.

 

I don't see anywhere in your story a word about setting your carb bowl float levels. If your bike is starving at mid to hi-revs, it may be caused byyour fuel level being too low in the bowls.

If it doesn't show at idle or low revs, it may be that your fuel levels are not horribly low, just enough to starve at higher revs.

 

Float levels are set using the clear tube method to right at the same height as the screws. 3mm below the carb body. Re-verified that last week after setting it the first time about a month ago, still dead on.

Should I try moving the level up a bit? I shouldn't need to though, in spec is in spec right?

 

I assume that you took your readings with the bottom of the liquid meniscus in the tube, not the top edges, it would make at least 1 mm difference...

 

Re: bogs out from being too lean, fixing causes other issues

Yes, I did. Followed the instructions over at xj4ever to the letter the second time around to be safe.

 

Do you have the proper spark plugs in there? stock air filter?

 

Bp7es, brand new all the way around. Gapped to .028

 

I have to say that I'm a bit puzzled...

 

Does the engine run fine when it's above 4k?
Do you get any popping from the exhaust on deceleration?

Have you checked that the coils are in good condition (not cracked, primary and secondary resistance is in spec)? Are the resistors in the plug caps rattling? Are the plug wires in good condition, and the plug caps grabbing into bright, shiny wire?

 

Well that's exactly the thing, it can work great at idle OR it can work great at 4k. When the mixture is set perfect or slightly rich for idle it will stumble when any load is applied. That starts at 1.3k, right after idle. Turning the screws out will eliminate the stumble, but ruins the idle. So yes and no would be the answer to your question, depending on the screw setting. No popping or backfiring though. I did cut back the plug wire a quarter inch and reinsert the cap but I haven't checked the coil resistance yet.

I'm thinking that this has to be a lack of fuel coming from the main jet or a vacuum leak that only occurs with engine load. Is that possible? Is there any leak that might occur ONLY when the engine has a load of it?

And if it is the coils, why would that present as a mixture issue off idle and up? Would that have something to do with having only a dot of color on the plugs, not color all the way around? Is Incomplete combustion a thing, and would bad coils cause it? If so, why would dialing the mix screws out seem to fix it (or at least make it drivable, it's still lean)?

 

Coils are one possibility, so they need to be checked to eliminate that possibility. A faulty coil will fire inconsistently and give you the same results as improper fuel delivery. Another possability is the TCI not advancing the ignition (or a faulty pickup coil causing the same thing). Adjusting the mixture can move the problem to a different part of the RPM range, which is why I'm asking about the electrical side of things.

I won't discount that it could be a carb issue, but you have had them apart several times already, so that is unlikely at this point.

 

let me ask what other bikes have you ridden? if your comparing it to a "V" type cruiser, this could be your answer.
these don't make the stump pulling power down low it comes to life about 4 to 5K and again around 7K on up.
really 3K is about all the lower you should ask it to make any power at all

 

K-moe, that had not occurred to us dude. Very excited to have something to investigate I haven't done twice already! I assume I can find those instructions to test the coils and pickup coils on this forum.

Polock, it's my first bike but when tuned to the "idle works" setting, the bike is unrideable, not just a lack of power. I've ridden a 50cc scooter that pulled harder!

 

ok then, lets try
your sure the jets are the right size.
the needle jet needle is the right # , like Y11 or Y13
no holes in the carb diaphragms
"hats" are on right
it passes the "clunk"test with flying colors
the choke plungers are all the way down, all the way

 

All the Jets are correct verified by crossreferencing the xj4ever catalog. In the right holes too. No holes in the diaphragms. Hats are on right as far as I can tell. The lips of the diaphragm doesn't stick in the groove so the hat kind of pushes it down. I am pretty sure they are all sealed up well. The tab is lined up too of course. Clunk tested, polished up to 2000grit. Choke is completely closed, no bent lifter prongs.

Now for the needles, here is a twist: when I cleaned out the pilot mixture screw passages I found the screws to be a coarse thread allow steel. According to xj4ever, those were only available on the
80 and 81 maxims. My bike is an 82. So maybe the needles were from another bike? Or from this bike but the carbs were from another bike? The currently installed ones are y-10. How would I verify those are correct for the carb bodies I have? The xj4ever catalog says the 10s are the richest needle, so that can't be it right?

 

i think 11's are stock for a usa 750, i think.
get in touch with chacal and maybe get a set that's original to that bike.
when jets get changed that far, tuning is more a art than science

 

I'd think faulty coils would cause the combustion to be incomplete, the result being like too rich, not too lean.

But it is quite simple to check coils, so why not eliminate that possibility?

 

I found this in another thread, a quote from BigFitz:

"Be aware of this: When throttle shaft seals dry out they can split into a series of little concentric rings, they can also ONLY LEAK when the throttle shaft IS TURNED to any degree, but seem (and test) just fine at idle. Just a thought, wouldn't offer it if I hadn't seen it..."

and then this from the xj4ever catalog:

"Thus as these shaft seals wear and harden, they can't always maintain a vacuum-tight seal in all conditions, resulting in a lean running condition once the engine is warmed up----even though they "seal" perfectly well at idle, or when the carb bodies are still cool. If the pilot screws are adjusted with the bike partially warmed up, it may appear to be richer than necessary when cool, and then running lean when hot, resulting in an incredibly confusing and frustrating situation to diagnose and remedy."

I'll check the coils, and then my next step is to replace the throttle shaft seals even though they appear to not leak at idle. Worth it? Do you guys think throttle shaft seals would have this dramatic of an effect?

 

Update, mostly solved it:

I really appreciate all the suggestions and help. I would have never got this far without literally spending maybe a hundred hours on this site.

I tested the ignition coils and found #1 and #4 spark plug caps to be out of spec, around 9k ohms. Everything else was dead on. I replaced those, and there was a noticeable change in idle smoothness. Did not fix the issue though. Checked the circuit all the way through and cleaned everything. Cleaning the kill switch gave me .4 V MORE at the coils!!

Noticed that the starter drops the voltage a lot (from 12.8 to 10), and read that could be from worn brushes. Replaced those.

I removed the carbs again, coated the intake boots in liquid rubber and also coated the joint with the cylinder head. I then replaced the throttle shaft seals and also replaced the idle jets with brand new ones and re-cleaned the all of the pilot passages with carb spray. I also replaced the float needles and seats and re-double-checked the float levels.

Seems to have done the trick, all plugs have a great color to them after color tuning. My guess is the throttle shaft seals or the boots only leaked when the engine was under load, or moving a lot of air. Still having a warm start issue though, that's been there from the beginning. Starts immediatley when cold but is really tough to start warm. I'm going to start a new thread and ask for help on that so it isn't too confusing with all the other stuff already thrown out here.

Thanks again everybody. I've got some parts I ordered from the bay before I found this site and XJ4ever that don't fit my particular model XJ, so to pay you guys back if anyone needs the following PM me and I'll ship them out to you 100% free.
- GONE - 4 pilot mix screws ultra fine thread (mine are the coarse thread)
- GONE - back brake pads for a seca(?), they are slightly larger than my maxim's
- GONE - valve cover gasket for the 80-81 models, it's that papery kind. Mine uses the rubber kind with the half moons built right in.
-throttle grip and assembly with some weird locking clamp system for cruise control you flip closed with your thumb (fits my bike, just don't want to use that)(needs a starter button)