82 maxim 650 runs great when engine is cold, horrible when it warms up

Hello all!

Been working on this 82 650 maxim I bought for my son so we can go riding together. Typical story. The previous owner said the bike sat for a few years. We have gone through the usual stuff from the top down. Most of this was done before I found this incredible forum. Gas cap vent good, tank clean, petcock cleaned and working properly, new gas lines, new intakes as the old ones were cracked badly, carbs cleaned, new carb kits installed, floats adjusted, valve clearances checked and all in spec, carbs synced as well as we could get them with it running the way it is.

The bike starts up and sounds excellent, then out of the blue after a few minutes it just runs like crap! It has a bad stumble from around 2000 to 3000 rpms, idle hangs badly, if you blip the throttle it nosedives then revs back up. I have read so much information on this forum (THANKS TO ALL) that its almost overwhelming. Pretty sure all my issues are carb related but its just odd. It seems to be running extremely rich and lean at the same time. all 4 plugs are covered in soot. Dry soot not oily as if its running extremely rich. Which it could be until it warms up and goes lean. I've checked for vacuum leaks using the spray while running method but haven't found anything. I will be pulling the carbs back off and going back through them. I did not replace the butterfly shaft seals, which I will be doing, and checking the starting enrichment circuit. Any other suggestions are greatly appreciated! Wondering if I may have a coil dying when it gets warm. But first things first! Making sure the carbs are 100% clean and set up correctly.

I will be taking my time with this although I would like to go riding with my son before the snow flies. Yes, its July and the temps are in the 90's, but here in Michigan, you never know. lol! So as I said, any help is greatly welcomed!

Thanks,
Dave

 

Just out of curiosity, see if you can get a different TCI to try

 

RICH, LEAN, or possibly even ritually UNCLEAN or OBSCENE: THE CARB REBUILDING FAQ:

Let us begin by warning you, though: an engine that is out of synch may perform AS IF it has a lean, or a rich, or a hanging idle, or a no-idle, or a run-away idle, or any variety of different conditions------if your engine (carbs) have not been synched, then that at is the #1 issue that you should attend to first, before you even READ any of the guidelines below and go and try to adjust and fiddle with things and change settings THAT AREN'T THE CAUSE OF THE REAL PROBLEM!!

And here are a couple of very good visuals of how a Hitachi or Mikuni CV ("constant velocity") carb actually works. For those of us who are not intimately familiar with these carbs, these videos provide a great basic understanding of what is actually "going on" with your carbs:









Question #1: Why Isn't It Running Right?:

Below is a semi-useful "general rules-of-thumb" list to help you recognize and diagnose fuel-mixture problems.

All of these descriptions assume that the carburetors are cleaned and operating properly, are stock (no jet kit), the valves are adjusted properly, and the engine has been synched.

If any of the above procedures, tasks, actions, or activities have NOT been checked or performed, then do them first, or otherwise all your other efforts will barely even give you "casino odds" at striking it rich and determining what the real cause(s) of your symptoms are......

Here are the 3 rules you should always follow whenever trying to troubleshoot [i[anytime[/i]:





Typical Symptoms and Causes of a Lean Fuel-Mixture Condition:

- Poor acceleration; the engine feels flat.

- The engine won't respond when the throttle is snapped open, but it picks up speed as the throttle is closed. (A too-large main jet also mimics this symptom.)

- Idle speed falls after you blip the throttle, then creeps back up.

- The engine runs hot, knocks, pings and overheats.

- A lean pilot fuel circuit condition can be responsible for a creeping or "hanging (high) idle", where rpm's are very slow to return to a normal idle speed, is often a sign of being set lean. Conversely, if the idle drops way low and then (maybe) slowly recovers is often a sign of an overly rich condition.

- The engine surges or hunts when cruising at part-throttle.

- Popping or spitting through the carb occurs when the throttle is opened. Or popping and spitting occurs through the pipe on deceleration with a closed throttle.

- The engine runs better in warm weather, worse in cool.

- Performance gets worse when the air filter is removed.

- Fuel levels that are too low will cause a lean condition.

- Pilot fuel circuit that are partially or completely clogged.

- Fuel jets that are too small for your application.

- Pilot mixture screws being set too far "in".

- In cases where an overly lean fuel condition is suspected, the application of a small amount of "choke" may decrease or eliminate the symptoms.

- Here's the main reason you don't want to run lean over an extended period of time:

http://www.xjbikes.com/forums/threads/head-gasket-1982-maxim-650.85273/#post-504365

A holed piston. Notice how it's right where the plug fires (the hottest point anyway, and made ultra-hotter by a lean fuel condition).



Typical Symptoms of a Rich Fuel-Mixture Condition:

- Engine acceleration is flat and uneven and loses that "crisp" feel.

- The engine "eight-strokes" as it loads up and skips combustion cycles.

- The engine's idle is rough or lumpy, and the engine won't return to idle without "blipping" the throttle.

- An overly rich pilot mixture is usually the culprit when the idle drops below normal then slowly recovers.

- The throttle needs to be open continuously to maintain acceleration.

- Black, sooty plugs, a sooty exhaust pipe and black smoke from the tailpipe that stinks of unburned fuel.

- Poor fuel economy.

- The engine works better when cold. Performance falls off as it warms up or the ambient temperature rises.

- Engine performance improves when the air cleaner is removed.

- Fuel levels that are too high will cause a rich condition.

- A choke system that is slightly hung open or has leaky plunger valves. Leaky valves can be determined via a measurement of vacuum using your synch sticks (or vac gauge) --- while watching the gauge, apply a small amount of downward force on the top of the plunger valve. If it vac draw changes, the plunger isn't sealing very well. Over time a small ridge may build up on the tapered brass plunger valve surface (Hitachi carbs) that may be possible to polish out, or a deformity forms on the rubber seals (Mikuni carbs) that may be possible to reform back into shape.

- Fuel jets that are too large for your application.

- Pilot and main FUEL jets being reversed.

- Pilot and main AIR jets being reversed.

- Pilot mixture screws being set too far "out".

- Main jet needle set at too "high" of a position (on some Mikuni models), or that has "risen up" within its head cap (on Hitachi models).

- A simple test for an overly-rich condition is to remove the air filter element, and see if performance improves. A very dirty air filter will cause an overly rich condition, AND, even if the filter was in good condition, the great increase in airflow accomplished by removing the air filter will tend to dilute an overly rich fuel mixture, and thus allow you to focus on determining the cause of that situation.



Some common causes of a high idle:

- Engine has not been synched, as each cylinder "fights" the others for dominance, it can lead to a run-away idle situation.

- A lean air-fuel mixture condition, which can be caused by a variety of problems......vacuum leaks, plugged or too-small fuel jets, etc. Old or "stale" gas may also cause a lean fuel-air mixture to occur temporarily (until the fuel is used up!).

- Mixture screws not properly set or adjusted.

- Vacuum piston sticking or stuck in a partially raised position.

- Idle speed screw set too high, or set to create a "proper" idle speed when the engine was cold (and thus results in a "high idle" once the engine reaches operating temps). The idle speed when the engine is cold should be modulated via the use of the choke (enrichment) control system, rather than cranking the idle speed screw up.

- Butterfly valves opened too far; synch screws out of adjustment.

- Throttle cable wear, adjustment, or throttle lever brackets installed incorrectly or interfering with other nearby objects (cylinder head fins, etc.).

- Choke (enrichment) circuit is stuck "open"....this can occur even if the choke lever is rotated to the fully closed position, if for some reasons the choke plungers are not fully closing (cable wear, cable adjustment, bent finger brackets, or installation problems). In addition, even if the choke plungers are "closing" fully, if the choke plunger valve face or its seat are worn or scarred, this will allow fuel to leak part the plunger and richen the mixture even if the plungers are closed.



Some common causes of a “run-away” idle speed:

If the idle speed starts building and building and eventually “runs-away” to a level that will grenade the engine without you shutting it off:

https://www.xjbikes.com/forums/thre...-no-vacuum-leaks-detected.120948/#post-607986


This is typically caused by an out-of-synch condition:

https://www.xjbikes.com/forums/threads/82-xj-650-startng-problem-surpise.46358/page-2#post-414262


After reading all of the above, you should by now know the solution……….. 



Why your engine seems to be schizoid:

A hanging idle---one that stays high and slowly comes down when decelerating---is a sign of lean mixture. The opposite case, where the idle drops dangerously low then rises, is a sign of rich mixture.

A bike that runs better when hot is probably lean, and a bike that runs better when cold is probably rich.

But sometimes a bike that can be adjusted "just right" when cool, but actually starts exhibiting signs of running lean (hanging idle) as it warms up. And if the idle speed is then re-adjusted while the engine is warm, but eventually falls and the bike dies (especially when sitting at a stop light). Or if the pilot screws are adjusted, then it's too rich when cold---all in direct contradiction of the above observations.

Experience shows that this is a sign of worn throttle shaft seals.....the aluminum carb bodies expand with the heat, but the steel throttle shafts---resting comfortably in a nice cool airflow---don't heat up and therefore don't expand. Once the shaft seals get old and hard, they no longer are able to flex and fill the gap.....so the carb starts drawing air around the shafts, leaning it out.



Why does my engine sometimes backfire when I first turn on the key (without attempting to start the engine)?:

- When you kill the engine, the intakes will still have some remaining (un-burned) air-fuel mixture remaining in them. Upon powering up the bike (turning the key on), the ignition system will apply 12 volts to the coils, thus charging them. Of course, that constant current is not good for the coils, so a few seconds later (if the engine is not started) the TCI shuts down the coils by grounding them (to protect the coils from overheating) which cuts the current to the coils and thus triggers a spark to the plugs. If there is enough un-burned fuel in the intake manifolds or the combustion chambers, and if the valves are held open by the camshafts, a backfire thru the exhaust header and/or thru the intake manifolds/carbs/airbox can result.



Why is my engine hard to start, and using the choke makes no difference?:

Most probably, the starter jets --- which are tiny, and are down inside the carb bowl ---- are plugged up with fuel varnish or the like.



Why does my engine run poorly (or is hard to start) after it is fully warmed up?:

This could be due to leaking throttle shaft seals (where extra seal-to-carb body clearance occurs after the carbs warm up and expand), or, it could point to valve shim clearances that are dangerously tight (the clearances close up after the engine gets fully warmed up).



Why are my plugs carbon-fouled (dry, sooty black deposits)?:

- Carbon fouling is the result of incomplete combustion----for any reason. It is most often associated with an overly rich fuel mixture (whatever the cause), but can also be caused by an overly lean fuel mixture (or poor spark, etc.) In a lean-mixture condition, most of the un-burnt mixture gets pumped out the tailpipe, but some fuel droplets remain in the cylinder and add themselves to the next intake charge. That's not a very precise way of metering the mixture, so when it's finally rich enough for a spark to ignite, that particular charge may be too rich, resulting in incomplete combustion and plug fouling. So carbon-fouled plugs can be due to rich or lean conditions.......your Colortune spark plug will tell you for sure. If you have a light blue or white-ish flame, intermittent flame, and/or intermittent flashes of yellow within an otherwise white-ish flame, then your fuel mixture is too lean.

And by the way.........if the spark that happens to ignite this overly-rich mixture is the "wasted spark" (which occurs in each cylinder at the top of the exhaust stroke, it will occur JUST AS THE INTAKE VALVE IS OPENING ---- so the backfire pressure wave may be directed back up the intake tract!



Why are my plugs oil-fouled (wet, oily black deposits)?:

- worn or broken piston rings, excessive wear or damage to cylinders, *leaking intake valve stem seals.

* while bluish smoke from the exhaust can be caused by worn exhaust valve seals, that situation will not foul your spark plugs. Consider what happens: oil pools above the valve guides, and coats the valve stems every time they rise. These stem "seals" really aren't seals, they are more like wipers, and their function is mainly to wipe off the excess oil from the valve stem. Now, when these stem seals get old and hard, they leave an excess amount of oil on the valve stem, which then drops down into the path of the exhaust gas flow as the valve opens and the oil is evaporated off, leaving blue smoke from the exhaust. But note that none of that oil ever enters the combustion chamber, so it can't foul the plugs.

Of course, any excessive oil coating an intake valve stem will end up going through the cylinder, but intake valve stem seals rarely fail on these engines. Unlike the exhaust valves, which are constantly baked by superheated exhaust gas, the intake valves are bathed in cool and moist (with gasoline) air.



Why is the inside of my carbs covered with a brownish-green goo?:

When fuel mixes with water and sits around for a while, this is the result. Nasty looking, nasty smelling, and you can bet that the tiny passages inside the carb body are plugged solid with this stuff! Definitely time for a full rebuild.......




What are my fuel levels supposed to be?:

Here's the Holy Grail on this subject:

http://www.xj4ever.com/setting fuel levels.pdf

And here’s a good visual guide to some problems that you might run into:

http://www.xjbikes.com/forums/threads/setting-the-floats-mikuni-not-gettin-any-readings-fixed.40395

and here’s a wonderful video from TurpentyneTV that shows the whole process in excruciating detail:

 

make sure the choke is really off. i like to see the fingers go down past the top ring of the plungers

 

I second the running semi-choked theory. My first suspicion was tight valve clearances, but you said they were all within spec. Make sure your choke is operating properly, and go from there.

 

Thanks for posting Chacal! I have actually been working my way through that list of information.

I should mention, this is a yics motor and I do have the yics tool installed.

The choke......I have the cable adjusted so that when the choke is in the off position the fingers are resting at the bottom of the shafts. So the cable isn't holding them open. Doesn't necessarily mean they are seating properly, which is why i'm going to pull the choke (enrichment) components apart and double check them. Actually the carbs will be completely torn back down because I want to install the shaft seals. I have to order them still so......may be a week or so........How do you order from Chacal? Send a pm?

Valve clearances.....this was my initial suspect. The valve clearances are as follows:

all intake clearances are .005/.127
exhaust 1 is .006/.152 exhaust 2,3,4 are all .007/.178

Per the side cover, the clearances are
intake 0.11-0.15 mm (0.004-0.006 in) exhaust 0.16-0.20 mm (0.006-0.008 in)

so exhaust 1 is on the edge, but still in spec. The rest are all right in the middle.

As to trying another tci - after I have complete confidence that the carbs are 100% then definitely i will be investigating spark. I see in the info Chacal posted that weak spark can cause the black sooty plugs so need to verify the spark circuit is working correctly also.

Fun Fun Fun! lol. I am confident that with a little guidance we can get this bike back on the road. It sounds soooo good till it warms up.
I will keep this thread updated as I work through all the above suggestions. Won't be able to get back out to work on the bike till Sunday or Monday.

Thanks again all
Dave

 

people have had trouble with some carb kits. remember what kind they are?

 

Exhaust 1 is not on the edge... exhaust 1 is out of spec.

I didn’t say anything about throttle shaft seals cuz you said carbs were all cleaned and new kits installed...... I guess I assumed you had gotten the seals and installed them. Since you didn’t, yep— id do them so you eliminate that source of vacuum leaks.

j got my kits exclusively from Len. I recommend you do too.

email him at: info@xj4ever.com

or just pm him

 

I purchased the carb kits from a local shop.No name on the kits. The kits contained all new primary and secondary jets, emulsion tubes and needles, float valves and seats, bowl gaskets, bowl drain screws, and mixture screws which I could not use. I have the extremely fine threaded mixture screws. The screws in the kit were coarse threaded. My mixture screws look fine so I wasn't concerned with it. All jets and needles were marked and are the same as what I replaced. Well.....they are marked the same anyway.

Keep in mind......as I said .......Most of the work I have done on this bike was BEFORE I found this site. lol. I am now aware that I should also replace the butterfly shaft seals and a few other parts as well, which I will be doing. Worked on many bikes over the years, just not one of these. I do have the Hanes manual, which I understand has a few discrepancies in it.

 

Please explain.

As a precision machinist for many years.....if a part or several parts have a set of tolerances they must operate in, and they are within those tolerances....they are good.

Are you saying that all valve clearances must be exactly the same? And since all are except this one its out of spec? I am seriously asking, not trying to be a smart ass.

I will swap out the shim if need be.

 

- well, you stated that exhaust #1 is .152—— (we ignore the third digit, so it’s actually considered .15, and even if we consider the third and round it off, it still would round down to .15)
- and we know in-spec is .16-.20
- so as a precision machinist, even at .152, we can see that it is already .008 out of spec. As a .15, it’s obviously out of spec.

no, the numbers across clearances don’t have to match. They just need to be with the specified spec ranges.

intake: .11-.15
Exhaust: .16-.20

In-spec is in-spec

dfox

 

Did you put the air jets in according to how they were when you opened the carbs up, or did you use the photo in the service manual as a guide?

 

After reading your post something occurred to me. The valve clearance measured .006 in. Which should be in spec according to the Hanes Manual. I wasn't even paying attention to the 0.152 mm. You are correct. So the Hanes Manual has an error or they are saying .006 in is close enough. Page 31 at the bottom. Under all other models it states Exhaust 0.16-0.20 mm (0.006-0.008 in) . I'm looking at it as I type. So which is correct? Man, Manuals, can't trust them. lol

 

Yes, according to how they were when I took them out. Did not use any photos as guides. That does not necessarily mean they were correct when i took them out. the bike had been sitting for a number of years. Who knows what the previous owner did or didn't do to it. I will double check them when I tear the carbs back down to install the shaft seals and make sure they are correct per the guide on this site!

 

Some of the manuals have incorrectly stated that .16-.20 for intake and exhaust. Again, that is incorrect.

HERE IS THE CORRECT RANGES:
intake: .11-.15mm
Exhaust: .16-.20mm

DO NOT MEASURE IN INCHES. Measure in MILLIMETERS. These bike are metric.

 

Good call, too—- some manuals have this incorrectly marked.

HERE IS THE CORRECT PLACEMENT:
BIG NUMBER GOES TOWARD THE ENRICHER PLUNGER

 

Mnay of the no-name complete carb kits are the Chinese kits and the float valve needle/seat is not correct for these carbs.....I think they are supplying the HSC40 (Virago) needle-seat set, which many (most?) mfg's assume is also correct for the HSC32/33 series carbs. But it's not, the difference in length/seat height/float type prevents the needle from positively sealing the inlet in the seat as the float "arcs" thru it's range of motion, thus sometimes cocking (or otherwise failing) to lift the needle up fully and seal off the inlet. NOTE the word "sometimes", we use this word specifically because we've had many instances of the carbs performing okay, and then out of the blue, 1 or more would start flooding and then stop, etc......kind of bi-polar. It was a real head-scratcher until we figured out the root cause......

You should start by verifying that the fuel levels in the float bowls are correct, and that the carbs aren't "flooding" (whether fuel actually runs out of the carbs is not the issue---although that is certainly a problem if it occurs!----as too high a fuel level will cause the fuel mixture to be massively rich).

Also, keep in mind that sooty plugs are a sign of incomplete combustion, not necessarily a truly "rich" fuel mixture:

- Carbon fouling is the result of incomplete combustion----for any reason. It is most often associated with an overly rich fuel mixture (whatever the cause), but can also be caused by an overly lean fuel mixture (or poor spark, etc.) In a lean-mixture condition, most of the un-burnt mixture gets pumped out the tailpipe, but some fuel droplets remain in the cylinder and add themselves to the next intake charge. That's not a very precise way of metering the mixture, so when it's finally rich enough for a spark to ignite, that particular charge may be too rich, resulting in incomplete combustion and plug fouling. So carbon-fouled plugs can be due to rich or lean conditions.......your Colortune spark plug will tell you for sure. If you have a light blue or white-ish flame, intermittent flame, and/or intermittent flashes of yellow within an otherwise white-ish flame, then your fuel mixture is too lean.


Abandon All Hope:
http://www.xj4ever.com/setting fuel levels.pdf

 

You guys are AWESOME! I did use standard feeler gauges, not metric. Thought it would be ok since the manual showed both mm and inch. No matter, I will be replacing the shim anyway.

Carb kit.......thinking about it after reading the carb rebuild parts required, I don't recall there being a washer under the float valve/needle seat when I installed the new one. But then again I don't recall there being one on the old one I removed. I will double check that. And it is quite possible the kits I put in are Chinese kits so there is that as well. Thought it would be a good idea to put all new stuff in since everything was nasty from the old fuel. Maybe not so good. lol

I did set the float levels both with the dry method initially, and the sight tube after. Did have to adjust them. I will have more answers after I tear them back down. Had a lot going on the past few days and have not made it back out to the garage.

So glad I found this forum! This bike will run again!......Oh yes, It will run!

Dave

 

It seems to me that the carbs are the most frustrating issue most of have--and it is made worse by trying to cut corners and not doing it right the first time. That was my problem! I order any carb parts from Chacal. Knowing that I am getting the correct part is worth the extra dollar or so it might cost, not to mention the accurate advice I get from him.

 

ok, here is what I am dealing with......pictures! Woo Hoo!

 

New jets that were installed.....float needles and seats..old left new right.........

 

old jets, needle, emulsion tube...i believe the old needle says Y-130

 

new needle.....and air jets. Air jets were just cleaned, not replaced.

 

Had I known, I would have ordered from him too! Lol! I just bought the only kits I could find locally.

 

Hope that they work out for you.

 

drop the needle into the seat and see if the tip of the needle is the same height as the originals when the bottom of the flanges on the seat line up
so if you put the seat in the carb, drop the needle in and look at the height of the plunger tip of the needle, old ones and new ones, same?

 

You end up adjusting the float tang anyway, if needed.....

 

if the new needle/seat is taller and you adjust the tang down the tang is pushing the needle sideways
if all it took was bending the tang, any needle would work

 

Depends how you bend the tang and/or the floats themselves.....

 

The difference in needle/seat height is the difference that makes a difference (!) as Polock points out. The sets that we offer are a correct match to the originals, which is why they don't leak....we used to (way back when) carry the "supposed to fit" needle/seat units, and all we ever got was complaints, until we figured it out. Unfortunately, since the mfg. of those "incorrect" parts (they're probably correct for some other model carbs, just not for the Hitachi HSC series) has never corrected their applications list, the problem continues. AND, to make matters worse, sometimes those incorrect units would seal up, for a little while anyway, or sometimes they would leak and then not, and otherwise behave in a somewhat random manner....i.e. carbs #1 and 3 would leak, but #2 and 4 wouldn't, and then #2 would start leaking, but #4 would leak all the time..........my conclusion was that the incorrect length (and/or other factors) would cause the needle to get slightly cocked in the seat as the float "tang" moves in an arc as the bowl fills-and-empties of fuel, and this arcing path is what would cause problems with the incorrect-length needles. It was an especially common problem to have people report that the units would NOT leak "on the bench" (and they would successfully set their fuel levels, etc.) but once on the bike, would leak randomnly (or continuously) on-and-off........and my suspicion is that the vibrations in the assembly when the engine was running was exaggerating the underlying length issue / problem (which is why the problem wasn't always seen "on the bench").