One cylinder not firing

Good Morning All,

I have been working on my 1982 XJ650 Maxim and ran across an issue.

The bike is an 1982 Maxim with YCIS motor.

When I pulled it apart it was only running on 3 of the 4 four cylinders.

I took the carbs apart and cleaned them with the soda blaster and ran them through the ultra sonic cleaner and couple of times. There were bench synced before being put back on the bike.

My problem is that it still is only firing in 3 of the 4 (#1,#2 and #3 are good) (#4 is the one not firing).

I have verified that I am getting spark. I open the barb at the bottom of the carb and there is fuel in it.

What could the issue be? I am a little lost on what to check next.

 

How's compression? When the bike runs, can you tell if #4 pipe gets warm if you hold it above idle? Just wondering if the main jet works?

 

I have not checked the compression. The pipe does not get warm at idle, I can try to see if it gets warm with the throttle opened up.

 

This might work to test it. Take the cap off the inlet stub where you attach a vacuum gauge to. If you can get a piece of tube and spray some engine start in there and crank the engine to see if number four runs. If you have pods remove number four and spray the engine start in there. It does look like a carburettor problem or tight valve clearances on four.

Would this work? Spraying the engine start into the the opening the YICS tool fits into on the right side of the head then replacing the plug and try and start it?

 

Did you clean all of the cold start jets in the float bowls? Perhaps right one is blocked? The jet is in the bowl and this brass tube takes fuel from the bowl into the inlet for cold starting.



When l first got my bike l didn't know about the above jets. I did the valve clearances still it would not start on all four. I cleaned the carburettors and still had the issue. Then someone on here told me about the float bowl jets. Cleaned them and it started and ran great.

 

I did make sure to blow out those tubes when cleaning the carbs. I can try putting the putting starter fluid in the vacuum gauge hole. Thanks for all the advice.

 

Yes just a small amount of starter fluid is all you need to check if it ignites on four. An inlet valve could be the problem also.

 

Do you mean you blew out the tube that goes into the bowl well? There is a small, pressed in jet in the bottom of the well that needs to be clear and usually requires a very small wire (guitar string for example) to manually clear. Shooting carb leaner in the well should result in the cleaner shooting out from the bowl bottom hole. Also a strong flashlight aimed into the bowl bottom hole should illuminate the jet hole when observing down the well. There is no shortcut.

 

Have you checked to make sure the float level is correct? Might not be getting gas to that one.

 

Have you checked all the fuel levels in the bowls?

oops. Just saw That I’m repeating the question from the previous reply.

 

Good Afternoon Everyone,

Here is an update.

I have not checked the compression yet.

I did pull the carbs off and took the #4 one apart. I took the fuel jets out and made sure that they were clear, while they were out I blew air through all the holes and felt the air coming out. I also blew out the tube that is attached to the bowl and made sure it was clear.

While the carbs were off I put a flashlight in the intake and exhaust side to make sure the vales were opening and closing and they looked good.

I also did the trick where I took the vacuum cap off and shot starting fluid in there to see if I could hear a difference, I thought it sounded different but I am not 100% sure.

Also I did rev it up and the pipe got hot once it got higher into the rpms. It sounded better after revving it up as well.

I think it is getting there, I might need to check a few more things.

 

Are the pilot air jets and passages clean on four?

 

I did not check them while I was in there, at least I can take the top off with the carb on. I know there were clean when assembled.

 

Better spraying carb cleaner through them. The air passages could be the problem.

 

Next update. The jet in the bottom off the bowl is clogged. I am trying my best to clean it out. Would anyone have a bowl they would be willing to sell if I cant not get it un clogged.

 

You can do it! Use a piece of guitar string, nice and stiff. You can try acetylene torch files too. Even a sewing needle to pick into the clog. If you use something that bends, like a guitar string, you can also attack it from the bottom of the bowl. To be clean you should be able to shoot a jet of carb cleaner out the other side. A strong flashlight in the bottom of the bowl will show you a nice round hole in the well if cleaned thoroughly, but a smaller jagged hole if not.
The clog is why the cylinder is not firing right at idle but just at higher RPM's.

 

+1 what @Huntchuks said. You can do it. It's a pain, but you can do it.

But if for some crazy reason you need a replacement bowl, I'm sure somebody around here has one, don't worry about that.

 

Put the bowl in a pot of boiling water for 10 minutes and once dry and cool check with flashlight if it's clear. Use carb cleaner through the jet.

 

A bread twist tie is a good size wire to use too. If you don't have any of the above tools at hand. As stated above, you can do it, just your time and if you are not using some good B 12 chem tool I would get some. That stuff really works well for these carbs. Might be a little hard on your hands, but does clean very well.

Stick with it, you are so close and then she will run the way she should.

 

Alright everybody. I believe I have solved the issue.

I borrowed a compression tester from my dad before tearing the carbs apart and made sure there was compression and we were good (120 psi)

Took the carbs off again again, found the right size guitar string (it was a #40 jet so I found some that was .37mm in dia. and it fit well)

Ran it though the jet till clear. Cleaned out the tube as well since I was in there.

I think it is firing on all 4 now. I just need to get them synced and find/build the rest of the exhaust.