xj 650 maxim sputtering on acceleration

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.