xj 650 maxim sputtering on acceleration

1981 XJ 650 Maxim
The other day I was riding and noticed that the bike had started sputtering upon acceleration. The bike has pods (I know) and a 4 into 1 with a straight pipe, It has been rejetted and has #42 and #116 jet set up. I did the valve shims late last year so they should still be in good shape probably only 500 miles or so. I thought maybe I had a stuck float. I pulled the carbs and the #2 carb pilot jet was lose and no longer seated it was just floating around. So since I had the carbs off I went ahead and cleaned them. I did not split the rack as I also had done throttle shaft seals late last year.

One thing I did try on one of the needle jets was to polish it with a metal polish pad. It is similar to a scotch brite pad but made specifically for metal. So when I did that I saw that I did change the finish from smooth to a somewhat "less smooth" state. It went from shiny to a cloudy color. I stopped and didn't do anymore with that pad. I did wipe it down with liquid carb cleaner and put it back in. I didn't think I did enough to make it not operate normally.

I soaked all metal parts in carb cleaner for an hour. I did not soak the carb bodies or diaphragms in carb cleaner. I know it doesn't like rubber. I reassembled everything bench synced. The bike fired right up and then I vacuum synced. Bike still sounded sputtery. mostly when I rolled on the throttle. I had probably 40% less power. I went to the manual and checked for spark -yes. checked both sides of the coil. One coil was testing at about 11000 ohms and the other coil was at around 15000 ohms. I swapped out the coil with another coil that I had on a parts bike. Both coils now tested at 110000 reassembled and went for another test ride. Still sputtering.

Before I cleaned the carb and noticed the jet was loose I did have gas on the floor. I couldn't tell for sure where at on the carb it was leaking from. I assumed when I cleaned the carb that it was the pilot jet being loose and not letting the float to operate properly. However now that I have reinstalled the carb with everything tight I can see that it is still leaking gas and it is coming out of the # 2 pod filter. So I am wondering if running it wi9th that jet loose for about 10 miles home flooded the engine oil with gas and or caused piston damage. I do not have a compression tester and I am going to pull the carb again and replace the needle jet that I "polished" I will clean it all again and blow air through the passages and bench sync and vacuum sync.

Would anyone have any other ideas? I am going to do an oil change just to be sure there isn't gas in the oil tonight as well. Also would a loose pilot jet on one csarb cause piston failure if ran for 10 miles or so?

 

Did you wet set your float levels?

 

Not this time. I did about three weeks ago when I tried to switch out #42 pilots for #41 pilots. I didn't like the way it sounded, so I went back to #42 then set float height. That was three weeks ago, I did not do it this time, but I put the floats back in the same carb and didn't do anything with the tangs on the floats to change the height when I had them out. Carb is coming back off tonight though so I will recheck them to see if they have changed any. I suppose that loose jet flopping around in there could have affected the float setting especially with the bike running.

 

That was just the first thought I had about fuel coming out of the #2 pod

 

Ok disassmbled the carbs again and drained oil. The oil smelled like gas.put new oil in checked compression. everything was low but then I read that if you put oil in the cylinder then it will give you different results. I did that and the all compression was at 155 except cylinder 2 which was 180. I think I may have put a little more oil in that cylinder. Anyway, I know that 180 is high but it shouldn't be the cause of my sputtering.

I had a friend over that knows these carbs and we did quite a lot of adjusting on the float arms. we have them all measured equally and not sticking at all. We would find that after a few taps on the needle that they would sometimes stick. I also found a pretty small rip in one of the rubber diaphragms. It's very small and we went ahead an put a drop of gasket sealer on it. I think it will be ok. I reassembled the carb. I have not wet set the fuel height yet and will do that tonight.

I am going to go ahead and stick new plugs in it and this thing should be in pretty good shape. I might check the valve shims to see if they tightened up any since last season. I will report back with how it turns out.

 

I sure would like to know the end of this story

 

I will update it. I do think that I may have had a diaphragm not seated properly. There was one that had a little bit of a crease in it and I got that straightened out. ITs hard to tell if they are seated properly when you're pushing the spring-loaded hat down and screwing the screws back in. When I push up on the carb slides they all operate similarly. I think I had one before that was not sliding like the others. I assume because of the diaphragm not properly seating. Anyways I feel pretty good about it now and will report back if its fixed.

 

carbs to me are extremely hard to get right.I never have done a good job with them.

 

I have been guilty of this myself and last night after a little more tinkering I found that my diaphragm on the creased section was still not seating properly. I went back to "church" and read that had I put some vaseline on the grooves where the diaphragm seats it would stay when reinstalling the carb hats.

To whoever took the time to write out : the In The Church of Clean https://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/ , The Information Overload Hour https://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/, and the-ultimate-relay-switch-sensor-and-diodes-guide https://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/ , as well as the experienced moderators on this site and Chacal. Hats off to all of you. Sharing this information is keeping these bikes on the road a hell of a lot longer than our Yamaha shops. And you have done so in such a way that makes even the nobbiest noobs get it.

buy bike- do valve clearences-take carb to church- vacuum sync- color tune No shortcuts-then come at us with your questions. Its hammered into all the threads. But it is absolutely necessary. Thanks for keeping these bikes going

 

Did you get your sputtering issue resolved?

 

I didnt get everything put back together. I got a 4-1 exhaust and I took off the exhaust to change the oil filter. When I removed the exhaust I had 2 header gaskets to replace so I am waiting on that. But summarize how my problem came about here is what I believe has happened
1. Tried to step down 1 pilot jet size 3 weeks ago. didnt like it so I moved back to what I had. when reinstalling I didnt get one of the jets tight. During riding it came losse and jammed the float in the bowl flooding engine
2. When i opened carbs back up after that problem I must not have seated the diaphragm properly. It was creased on a small section instead of rounded all the way. took it out for ride and had sputtering. But this sputtering was caused by poor vacuum and not loose jet. Assumed I had a bigger problem. Not knowing about diaphram not seating. So I drained the oil. Yes it smelled like gas and I did loose some gas.
3. Tested coils removed one that was slightly testing out of spec and installed other coil off parts bike that was closer to normal Ohm out put.
4. Completely tore down carbs except breaking rack. New throttle shaft seals last year so didnt want to mess with them. Carb zestfully clean and bench synced
5. New Oil, Filter and Plugs
6. Carb reassembled with vaseline in grooves for the diaphragm seating.

Now waiting to get the gaskets for header and then gonna fire it up. Then I will vacuum sync. Not gonna count my chickens yet but very hopeful of a smooth running lil yamachopper next week.

 

Dude! Nice! You gotta think about going to this! There is a group of about 7 people that I know of that will be there. Love to get the numbers up. Not that we are the only ones there, but it's not a huge turnout

 

I would consider that. Thanks! Des Moines to Dubuque is a good ride on a hardtailed 650 but hey I just tuned it up right!

 

Mine is only strutted right now, eventually once I get the 750 on the road it will go in for backbone surgery and get hardtailed. Rode from Fort Atkinson WI to Dubuque IA and back last weekend. It was a good ride other than hwy 11 being rough as a cob

 

Man I just dont know. This thing is driving me crazy. Now it's acting like it has throttle shaft seals going out. Roll on the throttle and nothing. then all the sudden take off like a rocket. More so after a minute or two of riding. came back, It idles just fine. I start the bike up and it runs great in the garage. throttle responds pretty well on start up. Get going and then its like its dead at a stop light. barely rolls through a stop then it shoots off. All 4 plug wires are testing at 12.5k ohms. Brand new spark plugs. fresh oil, premium gas, bench synced and vacuumed synced carbs. Took the new plugs out. #1 carbon fouled.#2 bright white #3 and #4 looked fine. Cut the plug wires back 1/4 inch and reinstalled boots. I am going to upload a pic of the #2 plug. It looks like its abnormally lean right? This looks like a combustion issue right? I know the plug sparks I pulled it out and grounded it to the motor. Bad TCI? I know the carbs are clean. I am unsure if the gasket sealant on the pinhole in the diaphragm held. I know they were all seated. I set the floats and they were all within 3mm of the of the top of the float bowl (gasket area). It runs pretty good at speed. It just is a complete dog taking off from a dead stop. it would take me 3 or 4 seconds for the power to kick in. Then I would shoot off like a rocket...Please Help

The #2 cylinder compression is 180 PSI. That is the same cylinder with this lean looking plug. All fuel air mixtures are at around 2 turns out. Course thread screws. This feels exactly like throttle shaft seals as I had that problem 1 year ago. I dont see how they could have failed again...

 

Do yourself a favor and order a colortune plug from xj4ever if you don't have one already. Mine bike ran "ok" after complete carb rebuild, valve clearances corrected, new battery, etc, etc. After I put the colortune plug to it, it made all the difference in the world. I know I need to up the size of the pilot jets by a size but I'm still well within an acceptable range. Colortune, synch, colortune, synch, rinse and repeat. It may seem like a bunch of small little changes but when you add them all up it equals a sweet running XJ!

 

gasket sealer is not what you want to use to seal diaphram

180psi #2 is high but that could just be the tester what did the other cylinders read
650, 750 air-cooled engines:
Minimum: 128 psi
Standard: 156 psi
Maximum: 171 psi
Max. variance between lowest and highest: 14 psi

 

check your charging system output voltages

 

I have often read about using oil in your cylinder to help check the compression. My understanding is that your compression psi is tested without oil in the cylinder. Adding oil does not help you get an accurate reading. Adding the oil will only indicate if your low compression is due to rings or valves. If the psi increases when oil is added then it is your rings. If the psi does not increase then your valves are the problem.

 

Have you checked for vacuum leaks on the intake manifolds? Sputtering off idle and taking off is a pretty good indication of lean off idle situation. I will admit I had an old Kaw I was riding that did exactly that. Cleaned and adjusted the carbs multiple times, only when I checked the manifolds I realized they were leaking badly and replacing them solved the issue. You can spray brake cleaner on them and the gasket at the cylinder head when running and see if the idle increases. I've never had much luck with the propane test.

 

I will try brake cleaner. The intake manifolds are in ok shape. Some of them have some cracks but none that I have seen all the way through. I used some self-adhering silicone tape around all of them just to try and close up anything that might be sneaky leaking. Tried the propane and on tops and bottoms of all boots with no racing. Did it on the intake boots and the carb boots. I have switched out the TCI from my parts bike. No effect. I did recheck the fuel levels and I had 3 of them set to high. I have since adjusted and there is no change at least from standpoint of not responding to the throttle from a full stop. I have checked all plugs again and have adjusted the mixtures on the 2 cylinders that were rich or lean. They are better but still not perfect.

So here is my question to everyone. I am at wits end. I have had the carbs off this thing 5-7 times in the past 2 weeks. If this is an internal problem then I want to stop trying to diagnose something I cant find. My wife is, lets just say "annoyed" with how much time I have spent on it. To me, it sounds like either Throttle shaft seals (which I just replaced last year) a timing issue which I need to learn how to check, or the 2nd cylinder with the higher compression and the white spark plug. Yes the pipe is hot on the exhaust side of that cylinder. The compression number on that cylinder was 180 PSI. What should I check next?

I dont want to tear the carb rack apart if the throttle shaft seals are still sealed. They are not cheap and it takes a little while to get them. I worry that if I broke the rack and the seals were good I would damage them taking them apart and need new ones anyway. So I wanted to eliminate anything else first.

 

This where my fuel levels are currently

 

That's usually right, the only other thing could be a plug breaking down under load?
Also, you didn't mix the jets around did you, and put one weak one back in?

 

You can test these by spraying cleaner around them as well but I doubt they went bad already if properly installed.

Timing isn't adjustable on these but you can check it. If timing was off it probably wouldn't rev up well. Do you have the correct TCI box for the bike?

 

yes for sure. I have had this bike running for a couple of years and I have a spare parts bike. Both have the 4H7 markings on them and I switched them with no change

 

I put the jets back in that I had been running with no problem for over a year. Before I did i put them in the carb cleaner gallon and let them soak for an hour. THen I used a jet spike to make sure the passages were clear. I stuck them up to the light and they all looked good. I can stick my old plugs back in to see if that makes any difference.

 

Ok, for what its worth I can't see it being the shaft seals, sure ratty ones will make idle set up difficult and give poor repeatability, but really here, your issue is with the throttles open 30% or more right? So the air (or more accurately mixture) coming in is way more than could be leaking past your spindle seals.
Look at the jet numbers to confirm you haven't made a mistake, check the diaphragms and springs, recheck the emulsion tubes and put them back together for the last time hopefully. Shame there isn't a way to check flow through the pilot circuit to make sure there isn't something moving around in there?
Is there a clue in the lean plug symptom? Sounds like there could be?

 

Agreed on the lean plug clue. I have backed that out to enrichen considerably more than the other 3. I have seen a change in plug color but still looks lean and hot. That damn color tune would come in handy about now... I am wondering if there is possibly an obstruction on the enrichment circuit on that carb. Possibly an O-ring not seating properly. I started with all screws at 1 3/4 out as they are the course thread variety. #2 is about 2 3/4 turns out now with the carbon fouled one now out at 1 1/2 turns, and the other 2 are at the original 1 3/4

I will say though that I had throttle shaft seals affect this bike in the exact same way. Just a dog from a dead stop to take off then racing like a rocket. Sounds like a vacuum leak to me but for the life of me, I can't find it. Gonna try the brake cleaner, and if that doesn't work, then I will tear it down again. I know I got the one diaphragm with the pinhole that has a dab of gasket sealant on it. Maybe a lil piece came off and is gunking something up. I know that the diaphragms are seated I paid special attention to it this time. I think I will do another compression test.

 

decarbonize the cylinder if you have 180 psi the top of the piston could have a lot of carbon build up

 

can that be done without dismantling the engine? I am unfamilar with this process?

 

https://www.xjbikes.com/forums/threads/sticky-valve-transmission-fluid-fix-experiment-xj650.113347/

you could use seafoam but that is a little more volatile

 

If you could inject water in the right quantity that would do it - the trick being to get the engine hot, and not inject too much. Not enough won't do anything, too much will flame out the plug, and again not do anything, and has the risk of hydraulic locking the engine.
I've squirted water in with a hand spray bottle before now, the trouble is you need to be riding it along to achieve anything in my experience. Perhaps rigging up a restrictor in the suction tube from the inlet manifold to a water bottle is what you need?

 

Ok Here is the update. went out and compression tested all cylinders again. The first time I did this I had JUST put oil in. Within like minutes of testing it Those had the high numbers. When I did this I did not have the exhaust on or the carb.

Here are todays numbers
#1 100 #2 100 #3 110 #4 115
when I added a tiny bit of oil in the cylinder here were the results #1 140 #2 120 #3 140 #4 150
I also have the exhaust and carb on bike unsure if that makes a difference. TCI is not hooked up when starting. I do believe I put significantly less oil in cylinder I put about 1/3 of a cap of a quart of oil. I believe I would have higher numbers with more oil in there.

I sprayed brake cleaner all over the boots and throttle shaft areas. It did not rev the engine at all while idling. However when I stopped the bike and restarted with the vacuum sync hoses attached the engine was hanging up while revving. I would roll on the throttle and it would not come down to idle as quick as it used to. I am going to pull the carbs and dissasemble. zALl the way down to the throttle shaft seals. My buddy has an ultrasonic cleaner and I am gonna run it through them. I am Complete carb boot inspection as well.

On a good note the #2 spark plug is looking better after enriching it

 

#2 plug now

 

I am getting a set of new boots. I am getting new throttle shaft seals as well. I checked clearances again today and all are within spec. It very well could be the boots. They all had self adhering silicone tape around them. I have removed all the tape and inspected. There is one that looks like it could have some deep splits however I could not get engine to rev with brake cleaner or propane. I guess we will know when we get the new boots.

 

pics are of worst boot.

 

Try using the choke and see if that "richens" up the mixture a bit.....if so, then that points to some issue with the pilot fuel circuit (internal blockage, missing or damaged o-ring on the idle mixture screw, etc.).

Has the engine been synched? An out-of-synch condition can cause all sorts of issues that appear to be due to other causes.

Compression readings should be done with a cold engine, fully charged battery, throttle wide open, all spark plugs removed, air filter removed. If your numbers are correct, you have some issues with the piston rings or cylinder walls.

 

Engine sync? Is that the same as the carb sync or are you referring to timing? I think with my low compression readings I think I didn't add enough oil I did a teaspoon not tablespoon. I will check it again. I have a parts bike that has a good motor on it. My plan is to get the carburetor in absolutely pristine shape. If it doesn't fix it when I reinstall it then I'll move on to the motor do you need to split the cases in order to hone the cylinders? And do piston rings?

 

engine sync=carb sync

 

Thanks, and yes I throw the vac gauges on it every time. No colortune though.

 

Colortune REALLY helped mine after valve shims and taking carbs to church. Once I dialed it in with the colortune it runs so much better.

 

carbs have been completely rebuilt. I also have new intake boots and gaskets. new throttle shaft seals. Its now somewhat harder to start and its worse with the sputtering. I did bench sync and vacuum sync. I tried dialing in the fuel air mixture and when I richen it out it sounds like it starts tapping on the valve side. I take the fuel-air back to the recommended setting and the tapping goes away.

I am thinking I have a valve problem. I am going to move the carb over to the parts bike and see if I can fire it up and if I can See if it transfers over to the parts bike. If it does then its carb if it dont then its in the engine. I suppose a leak down test would need to be performed to determine if its piston or valve right? New to this level of troubleshooting so any advice on next steps would be appreciated.

 

Your compression is low and it's the piston rings or cylinder walls.

Forget about the amount of oil you used. Assuming you did as directed by @chacal (no air filter, throttle open, no plugs, etc.), you have low compression. That you saw a rise in compression after adding oil into the cylinder means that your compression is low because of the piston rings or cylinder walls.