Engine/carb issue with xj650 maxim '82, please help

Hello, I got this bike about a year ago (summer of 2019) and have been working on and off (since I have to be at school during the spring and fall terms) whenever I get the chance. Since getting it there have been an array of issues, some of which have been dealt with, but the bike has never run properly. I've browsed these forums but have not been able to find a solution, so I'll describe the current issues I'm experiencing and what I've already done to diagnose so far, and hopefully there are some new ideas on how to fix. To start off, the bike itself: Yamaha xj650 Maxim 1982 with aftermarket pod filters and aftermarket 4-to-1 exhaust (before I'm berated about having aftermarket exhaust/pod filters, the previous owner did it). I have bought an airbox but am hesitant to install after realizing that the full process requires taking off carbs, intake boots, starter motor, battery, cylinder head, and moving the engine forward an inch, all the while I'm not sure if this will even solve the problem(s).

SYMPTOMS:
The problems are as follows: bike has difficulty starting and only starts on mid-choke, and when it does start (usually after a quick squirt of starter fluid) it will do one of two things: If the engine is warm OR if I used too much starter fluid, the engine will jump to 5-6k rpm at idle (very loud and very scary) and stay there. When I throttle it in this state the engine rpms increase as expected. When I take off the choke in this stage the rpms also increase. every once in a while I'll ignore my natural instinct to kill the engine and watch it for a minute, and sometimes the engine seems to calm down a bit and go to maybe 3k rpm, but I have never observed it settle back down to a normal idle (1-1.5k rpm) after jumping up to 5-6k. In the second scenario, which is usually what happens the first time I try to turn the bike on from a cold start (and a bit of starter fluid, maybe a second-long squirt onto 2 of the 4 pods) it will struggle to run but will idle at 1.5k rpm. It usually dies after 5-15 seconds in this case, and if I take off the choke it immediately dies. Also, if I pull the throttle in this scenario the engine immediately dies (I assume it gets too lean). What I don't entirely understand is why in scenario #2 the throttle causes it to die whereas scenario #1 throttle increases rpm from 5-6k idle to 8k rpm as a throttle should. Maybe because when it idles at 1.5k it's already lean and opening the throttle immediately kills it with too much air, but in the first scenario the airflow into the engine is already so strong that it can more quickly atomize the fuel and suck it into the engine. I also noted that after pulling on the throttle at the 5-6k idle, it will hang a bit at ~8k rpm and slowly return to 5-6k rpm, which I believe is also a symptom of lean mixture. As for other symptoms I have little actual experience (this is my first bike), so my hearing isn't acute enough to try to "hear" whether the engine is lean or rich. If I had to say, the exhaust smells like gas (a fuel-rich symptom) but I could be wrong about how it smells, as I've never been shown what fuel-rich and fuel-lean exhaust smells like. Lastly, at the 5-6k idle the exhaust AND one or two of the exhaust headers is smoking. I'm not sure if this is normal at such a high rpm, but could be indicative of a vacuum leak at the header (I took off the exhaust manifold once to do an oil change, but when I put it back on I also replaced the old exhaust gaskets). I know there are some weird things that can happen with back-pressure of air into the engine if exhaust headers aren't on properly and this may be partly responsible.

WHAT I'VE TRIED
I did a carb overhaul with a kit I bought online, which included rejetting to the stock fuel jets, ie a #40 on the pilot fuel jet and a #110 on the main fuel jet, as well as gasket replacement, new needle jet, etc. I am considering purchasing a new set of main/pilot jets to account for aftermarket exhaust/pod filters, but I'm not sure that such a small difference (I believe the calculator I used said ideally I'd have a #42 pilot and #116 main) in jet size would change much/be able to cause the problem I'm experiencing. I have also tested for vacuum leaks after replacing the original crusty intake boots and their gaskets (between the carb and engine) and have not found any. I tested throttle valve seals, intake boots, and petcock-to-carb vacuum hose for any vacuum leaks by spraying starter fluid at each location and trying to start the motorcycle without result, meaning I shouldn't have any vacuum leaks. I have also done a compression test (good on all cylinders, between 93-100 psi for all four) and replaced spark plugs which I am certain are all firing. When I removed the original spark plugs I examined them and they all looked fairly normal, no obvious signs of overly rich or lean, but again I'm no expert. I haven't yet tried checking out the intake valves. I've seen a couple people say to check the clearances and do some other things but I have not done that. I have extensively looked at the carbs and boots. The only thing I haven't done with the carbs is adjust float bowl heights, but all are relatively close to each other in height (within 1-2 mm).

Please, please, please if you have any ideas help me out. Apologies for the long post; I've spent a lot of time fixing up this bike and I refuse to take it to a mechanic! I've learned a ton about motorcycle maintenance and repair through this process but I think there are a few small things that I've overlooked, and I'm sure a couple of you with extensive experience could help a newbie out.
Thanks in advance, Nick.

 

this procedure needs the motor running, you're listening for an increase in RPM's. What you've done does not prove or disprove anything.

a wet set is the only way to determine what the actual fuel level is. Have you done a wet set?

You're making some serious RPM's there. Are you certain the throttle cable is not holding your butterflies open?
Did you do a bench sync when they were off the bike?

Did you read the church of clean information in Chacal's pages.
I think ultimately you need to remove the carbs and dismantle them for a proper cleaning as per the church of clean.
As an immediate measure have a look at the linkage and determine they are not being held open anywhere, disconnect the throttle cable and rule out it is not holding them open.

 

The first thing to do is confirm that you have the throttle cable up to the throttle and choke cable hook to the choke. Second thing to do it's the check your idle knob between card 2 and 3 at the rear and possibly back it out some see if it is making contact with the throttle plate.
Allure pods on the bike the bike should run at normal RPMs etc on startup.

Make sure your mixture screws I said between 2 1/2 and 2 and 3/4 from a soft bottom.

replacing the air box does not involve everything you have written above. You do not have to remove the cylinder head you do have to remove the starter in the carbs. It is also not also necessary to remove the manifold boots. You will have to remove the motor mounts on the front of the motor and take the front long motor mount bolt out.
This should allow the motor to tilt forward. You want to warm up the airbox with a hair dryer and then try to slide it in you may have to heat the edges of the box to get it past the frame.

 

When you speak a float bowl heights is that the actual height of the float or are you talking about the fuel levels in the bowls?
Starter fluid will make the motor rev high and will also follow your plugs if you use it too often, check your spark plugs.

If you bought those cheap eBay kits to rebuild your carbs we're all four cops are done for around $40. I would suggest putting the needle Jets which I assume you mean the slide needles back on from the original parts. A needle jet set, those kits don't match any numbers but I seen the specs for the bikes I believe they are for newer bikes.
On the main Jets and the pilot Jets are they flat what do they have a countersunk face to them with a whole score for the Jets? Again some of the Jets that come with these kits a flat and some have the proper

 

On the bike is cold you'll need half choke to full choke to start it. the choke will make the bike go up to 3 to 4000 RPMs as it warms up.

 

Ok, after reading this today I took off the carbs, put the original needle jets back in and bench synced the carbs. I have read the church of clean and have cleaned my carbs thoroughly. I also confirmed that the fuel mixture screws had been at 2.5 revolutions from soft bottom and still are. I also ran the bike (after doing all this) with the throttle cable disconnected. It had difficulty starting so I sprayed a bit of starter fluid on the pods and it shot up to 5k again.

Could you elaborate on what a wet set is?
Next I'm going to try the vacuum leak test with the motor running and I'll also try messing with the idle knob to see if that does anything.

The jets have a countersunk face. I have not measured the float bowl heights, I was merely saying they all seem to hang at about the same level so I would assume they're all okay since no single one of them is severely deviated from the average height.

One other thing I thought about was the cylinder head. Based on evidence of a poor sealant job it's clear that the previous owner opened up the cylinder heads and must've done something with the engine or valves. As mentioned I have not checked the valve clearances or opened the cylinder head, is that something I should check out, and if so what would I look for?

 

...

correction. I put the original jet needle back in. The needle jet (which to clarify is the cylindrical piece with holes in it that sits in the base of the venturi of the carburettor) is the new one I used to replace. Next time I get the chance I'm also going to lower the jet needle (which "plugs" the needle jet) one setting to see if that reduces fuel flow during the super high idle. Will update this thread once I've done those things

 

Notes for a ~68 degree day:

tried lowering the jet needles to see if too much fuel entering the carbs was the issue, but it made no difference.

There is a hissing sound when the the engine is killed

Lots of smoke, unsure where its coming from (definitely the exhaust pipe, likely elsewhere too)

Noticed some popping sounds (lean?)

With petcock at prime and choke fully on, the bike immediately jumped to 7-8k rpm. With petcock at ON and choke off, idled at ~2.5k until throttled, then jumped to ~4.5k

On warmer days the bike immediately turns on without starter fluid (runs better on warmer days -> air thinner -> bike is running lean)

Began to spray (small amount) WD-40 into pods to test for a drop in rpms (for the vacuum leak test, wd-40 (I think) is supposed to lower the idle rpms) but nothing happened

Now the bike wont start, makes weird clicking sounds

Also, bike wont shift past 4th gear while off. Not sure if this is part of the design or an issue with this bike specifically.

This bike has always done weird things. The main issue now is that it won't start, and instead makes a weird clicking/rattling sound when I hit the starter. Again if anyone has ideas or advice it would be greatly appreciated

 

Anyone have suggestions for a good place to get '82 xj650 maxim compatible shim kits? Also if I plan on only doing this once or twice since I'll probably sell the bike eventually does it make more sense to buy individual shims? Gonna do a valve clearance test/shim replacement next week

 

www.xj4ever.com. Sells individual shims. And there is a shim pool here

 

IN THE CHURCH OF CLEAN

Replacing your Hitachi throttle shaft seals

Why you should replace butterfly (throttle shaft) seals.

Setting the fuel levels

She's lean, either from a vacuum leak or from running pods without rejetting (likely a combination of both). Throttle shaft seals are very likely shot.

 

I see you are starting to jump around a bit to find answers on the forum. There is nothing new posted here to tell us what progress you have made with the advice given? If you follow, read and then do the work the "k-moe" above suggested you will get the bike running.

When I first started rebuilding these bikes, I pulled the carbs off six times to get them the way they should have been the first time. So what I am trying to say is take the time to do the carbs right. The carbs being right will really make getting the bike running easy. The valve shims can be done after you get the bike running as that is just part of normal scheduled maintenance.

I recommend doing a bench scynch and to do a fuel level test with the carbs out of the bike supported in a vice or common setup. If you have fuel leaks from the fuel tubes it is so much eiser to see what ones are leaking from a bench then when the carbs are installed on the bike.

The hardest part for me to remember when I get a new bike project is to take the time to do the things right. You get so excited to get it to run and or ride that you might not take the time needed to so some of the things correctly compared to half A**ing it.

 

Ok, thanks. I'll do it again. I already did a bench sync but I'm definitely going to replace throttle shaft seals and set the fuel levels. Thanks "k-moe" for the pdfs, I'm going to follow those closely. It's true about getting overexcited, and I'll remember your advice to do it thoroughly the first time around. About changing the shims, I was hoping for advice on whether that could be a critical issue causing my rpm problem or just something for maintenance later. I will update soon. Thanks all

 

Valves being out of adjustment will not cause a high idle. But you do need to check the clearances. Lots of owners neglect that bit of maintenance.

 

So I took a look at the spark plugs to inspect them and they’re super dark, like theyve been carbon fouled. How can that happen with a lean mixture? These plugs were new when the high idle problem first arose so the coloration is related to the issue. Ill attach a photo below

 

Clearly not lean. A vacuum leak through the throttle shaft seals, or elsewhere, will cause high idle. In addition, your mixture (probably) needs to be adjusted, but you need to solve the vacuum leak first.

 

Going to do a throttle valve seal replacement, bench sync, wet set/check bowl heights, and then see what that does. Anyone know what the proper stock height for the jet needle is? I was messing with mine to try to fix my rpm issue but it might've made it worse. I changed from (of 6 height settings) the third lowest (fourth highest) up 2 to the second highest (ie letting more fuel through the main jet and emulsion tube I believe) and that made it worse. Will change back to the original height but previous owner might have also messed with those, wondering what the stock setting is.

 

Pretty sure the stock needles aren't adjustable. The multi groove ones usually come with aftermarket jetting kits.

 

Ok im in the process of taking apart my carbs and replacing throttle shaft seals and fuel rail o-rings. The butterfly valve screws (holding the plate to the throttle shaft) are pretty tricky, any thoughts on how to get them out?

 

The pdf writeup said to get loctite and anti-sieze fluid for this job. I know the loctite is for the self locking screws, is the anti-seize fluid (I have molybite) for any other non self locking screw?

 

I use a little heat and a perfect fit screw driver to break them loose. One of the others will chime in soon with more suggestions. Once I heat them up with a little torch, I put the screw driver in and apply pressure counter clockwise or in the loosen direction, if they don't move I tape the screw driver lightly with a hammer while keeping still applying the pressure.

 

a tiny dab on the mixture screws to prevent frozen screws a little dab on the bowl drain screws. framework screws get loctite.

 

How much should a change in fuel level in the carbs affect performance? I did a wet set on carbs 1 and 4 today and both were about 5-6 mm below the top of the carburetor body. For the xj650 carbs (hitachi HSC32) the level should be 3 mm +- 1 mm below the carb body. Im going to try readjusting so all carbs are below within tolerance, but would a low fuel level contribute to my high idle rpm/rich mixture? (see my earlier post w pics of the spark plug)

 

Update: this weekend I replaced my throttle shaft seals and fuel rail o-rings, then bench synced and did a wet set. Got my float heights to spec and I'm gonna throw it back on the bike next chance I get. Does anyone have a good trick for bench syncing? I try to use needles but I can't use the idle screw to get carb 3 butterfly open enough for me to fit a needle. I need something even thinner than that I think. Today I tried to do it by shining light through the carbs and lining it up by slivers of light but I doubt that's as accurate as using an actual object (I also don't have the money/time to buy or make a manometer).

 

Ok so after doing the wet set, throttle shaft seal replacement and subsequent bench sync, the bike is better but still has issues. When i can balance the choke level just right it will idle at 1-1.5k but has some lean issues (usually dies within 20 seconds, sometimes it remains there). Sometimes if theres too much choke the engine will rev up to 3 or 4k at idle, which is better than before (7-8k) but still not right. Any thoughts? Ive heard some people say that when the bike first goes on choke it may idle at 3-4k for a few minutes. I havent waited that long to see if the idle drops back down because the bikes starts smoking but maybe i should

 

you should be able to shut the choke lever off after a few minuts.
the choke lever will cause rpms to climb as bike warms up 3 to 4 k is not unheard of.

have you adjusted the throttle stop knob /Idle knob between the backside of carb 2 and 3? sounds like you have to turn it in some.
to properly adjust idle you have to ride bike 10 or so miles to get it warmed up.

choke dumps fuel into carbs,

 

I have not tried messing with the idle screw. I think it’s all the way out, so barely any air is getting in. I’ll try that but wouldnt opening the butterflys more let more air in and make it harder to start? Currently the bike is in the garage, i dont really feel its ready to be ridden in its current state of either stalling or runaway rpms

 

that is your issue.

when bench syncing carbs the idle knob is used to set carb 3 then the other carbs are set to 3.

if you look into the front of carb you will see holes in the top of the throat you open 3 untill the plate lines up with the edge of that hole.. cycle the throlttle a few times recheck . then repete proceedure for the other carbs so you see the hole.
when done back out the idle adjuster untill you see half of the hole. you are done.

there are 3 screws on the front of carb with springs on them carb 1,2,4 have them for adjusting the sync. the idle knob adjusts the #3 carb.
when you start bike and get it warmed up some you can adjust the idle knob in or out to set idle. then reset if needed when you can go out for a ride. set idle to spec 1050 rpm. you may want to go up to 1100rpm

 

air getting in is what draws the fuel into the motor

 

Out of curiosity is it the very first hole? or second?

 

first hole is where mixture screw protrudes it is the next set of holes and the one closest to front of carb
I think this is the hatachi carb yes it has silver(aluminimum disc)

 

Is the standard fuel mixture position 2.5 revolutions out from seated for the xj bikes? Ive heard 2.5 as standard for most bikes and I’ve been treating that as the norm for my xj650

 

It’s worse today than it was yesterday. It either doesnt catch or I use starter fluid and it goes crazy. Yesterday the high rpm’s were at 3.5k, today theyre at 6-7k. The temperature is also about the same, maybe a bit colder. I dont understand this motorcycle. No changes were made to it between today and yesterday but it changed its behavior. I tried messing with the idle knob but that didn’t help. If anything it seems that more air and fuel flow past the butterflies made this crazy idle rpm worse. I’ve done a wet set, fuel level check, throttle seal replacement, bench sync, jet replacement, carb clean, etc. Any more ideas?

 

yes the starting set is 2-1/2 turns from a soft bottom.

 

Was curious if you have made any progress? I am in the same boat as you, felt like had done everything right and I can still only get it to start with the choke on and it dies as soon as I shut it off. On top of that the starter motor engages about half the time I press the start button! If you find out what your issue is I would love to hear so I can check on mine. At this point I’m just going to clean all the passages in my carbs again since they are now bench synced and have wet levels set. Can’t hurt right?

 

Have you been having any electrical issues?

 

I’m curious—- what air jets are under the diaphragms and what positions do you have them in?

 

@NikoRx little progress, no electrical issues. Taping up the pod filters reduced the idle rpm to like 4-5k but not a solution. What is the issue(s) on your bike? I believe mine has two different issues: one is difficulty starting, and the other is a runaway idle. It's as if the bike is unstable and wants to do anything except idle normally. Very frustrating; I've combed forums and tried everything, pretty much now I just wait until I see something different I haven't tried yet.

@hogfiddles The air jets are all to spec except for one of the two under the diaphragm on all four carbs; I can't remember if its main or pilot but I know the stock size is 205 and mine are 195; a small difference which cannot account for 7k idle rpm.

 

The pods can mess things up a lot

 

Yeah but I dont think pods are enough to cause a 7k idle.

 

If it runs fast at idle it's pulling air in somewhere - simple as that. No engine will run without air. You should, if you've set the bench synch carefully by lining the plates up on the edge of the hole be able to get an acceptable idle straight off.
A running synch will be the icing on the cake.
If it runs too fast you've got air going in one or more butterfies - check all close fully against the light - are they centred properly? Set all carbs to the edge of the first hole, make sure all the enrichners are fully seated and none damaged. Check all the manifolds are sealed to the head and at the carbs.

 

195 for 80-81 205 82-82 pilot air jet.

 

Tomorrow I’m going to take the carbs off and try to line them up exactly as you have said. I know they’re all very similarly angled and close almost if not all the way in the body. I think the first time I used light shining through the carbs to synch them, instead of using that top hole as a reference point. I’ll be surprised but more than happy if that does the trick.

 

You see, that post tells me all I need to know. "Very similarly angled" and "close allmost if not all the way in the body"
Both these statements are not good enough I'm afraid. Each plate individually must close tightly on its own, every time without fail - have you managed to mix up the plates - they are not all the same apparently and definately only go in one way.
Once each plate is centred and closes fully you can then set no3 with the screw to the edge of the most closed hole. Then move out the rack on either side to the other carbs, and repeat. You need good light and eyes. Closing the idle screw should close all 4 together. Once happy set it one and a half turns open ( guessed starting point only, this will change once its idling). Make sure the manifolds are all sealed, the vacuum port plugs are all sealed and start it up with the enrichner. As it warms let off the enrichner, you may need to close down or open up the idle screw to keep the rpms tame as this goes on.

 

I finally am not having as much difficulty starting the bike (set the wet levels and did a proper bench synch) besides some electrical issues. my main issue now is that the idle runs away to 3k to 6.5K and I cannot get the choke off without it dying on me. I have done basically everything you have done and I do not have pods thankfully. I hear those are such a headache!

 

that top hole trick made a difference for me and I wish I would have done that first.

 

[QUOTE=" As it warms let off the enrichner, you may need to close down or open up the idle screw to keep the rpms tame as this goes on.[/QUOTE]
so I can slowly let off the enricher but cant fully turn it off, so you suggest to turn the idle screw to compensate for it? I havent tried that and if that is all I need to do that sounds easy enough!

 

Ok, thank you! Just to be clear, after getting the rack off the bike I individually tune each carb (starting at 3, and then moving outwards doing 2 before 1) so that the plate just covers the fuel hole at the top of the venturi? and then try closing them all the way with the idle knob and push it out about ~1.5 turns to get t to a starting point from which to adjust?
I really hope this solves my issue, and at the very least I think it will help. Honestly though do you think this issue could cause a 7k runaway idle? I'll post updates after

 

yes you start with three, you use the idle knob to get it placed over the venturi as is pictured earlier in this thread and then you go outward adjusting the others to be as similar to the third carb as possible relative to the venturi

 

You want to set idle mixtures right? How are you going to do this if its not idling? Actually, first off you want to get it running low enough to do a running synch - and whichever way you look at it that needs to be without the enrichener. If that means you need to tweek the idle control, then mixtures, then idle control - do it!
If you have no idea what the mixture screw settings are doing set them all the same and move them all the same, no more than 1/4 turn each at a time until the warm engine is idling.
Then do a running sync, and if you have a 4 gauge set you'd better be sure they give you the same reading on the same port - ie are accurate, or if not accurate - oh hell you need to back to back test them thats all.
Once you've done the running synch go back to the idle control, bring the speed to where it should be, do the running sync again, over and over. Then tweek the mixture screws, all together, to get the fastest smoothest idle. Then do another running sync (all this can be done together in minutes by someone who knows what their doing and is methodical, so dont let it put you off, and dont take shortcuts).
Finally, once you think you have it near right you should think about a colourtune to set the mixtures ( I hate them, never used one since I threw mine into the toolbox in dismay), I use my ear to listen for a drop, then by turning the screw the other way, a rise, and eventually a throbbing drop, then back to somewhere in the middle.
Oh, get a fan, even a desk one, to blow over the motor, otherwise if you're slow at this you will overheat the oil.