1985 xj700 runs on 2 cylinders

New to the group. Need a little help. Just picked up a 1985 xj700. Cleaned the carbs. It is running on the left 2 cylinders. Will not fire on the right side. Got new plugs and nice spark at plugs.

 

Float levels? bench sync? vac sync?

All need to be done if not

 

If you have good spark on #3 and #4 then you should revisit the carbs.

In the Church of Clean

 

Carbs have been gone through 3 times know. Have set the float levels and synced carbs. Did a compression test on those 2 cylinders. It has 120 psi on each.

 

I forgot to say that this a xj700x. If it makes a difference.

 

If you have compression, and you have spark, but don't have fire.........

Are either #3 or #4 plugs wet when you pull them after trying to start?

When you cleaned the carbs did you Church of Clean them?


EDIT;

Now that we know which engine you have.

Compression values:

700-X and 750-X (water cooled) engines:

Minimum: 154 psi

Standard: 159 psi

Maximum: 165 psi

Max range allowable between highest and lowest readings: 14 psi


Have the valves been checked and adjusted to be in spec?

 

I have spend hours cleaning the carbs. The plugs from #3 an #4 are a little wet put not flooded wet. Some black residue on them. Have not checked valve clearances.

 

Did you read my edit?
Your compression values are 34 PSI too low in those nonfiring cylinders.
Check the valve clearances and put them in spec to see if the compression comes up enough for those two to catch fire.

 

Yeah I did see your edit. If you could tell the specs for intake and exhaust clearance that would be much appreciated. Thanks

 

For others that are looking: valve clearances can be found on a sticker that is inside the left sidecover, regardless of which XJ you have.

From Chacal's catalog:

ORIGINAL VALVE ADJUSTING PADS:

OEM VALVE ADJUSTING PADS, all sizes 1.20 through 2.40, fits all Yamaha XJ700-X and XJ750-X (water-cooled) engines.

NOTE: all XJ700-X and XJ750-X models use the following valve adjusting pad clearances:

Valve Clearance Intake: 0.11 - 0.20mm (= 0.004" - 0.008")
Valve Clearance Exhaust: 0.21 - 0.30mm (= 0.008 - 0.012")


The clearances are the same for all of the "X" engines.


IIRC you need a set of tapered feeler gauges since there isn't much room to work in that 5-valve head. Get metric ones, not SAE gauges that have metric equivalents. Otherwise you'll have to get used to rounding your measurements to the nearest hundredth.

 

Thanks much for the help. If the clearances are good. What are some other things I could check.

 

Redo the compression test with a teaspoon of oil in the cylinders and see what the new numbers are.
If the compression goes up you can try running some Seafoam in the oil and hope that you just have stuck rings.
At this point just check the valve clearances. Baby steps. Eliminate what the problem isn't, so we can find what the poblem is.

 

Just an update. All valve clearances were well with in spec. Is it possible to have a bad ignition module. Not sure were to go next.

 

It is possible to have a bad ignition module, but you said that you have good spark. The compression numbers that you gave for #3 and #4 are well below spec.
What are the numbers for #1 and #2?

One

thing

at a

time.

Let's focus on determining if you have a compression issue, and try to remedy that first.

 

The compression on #1 an #2 were a little less then #3-#4. 120psi should be enough compression to fire the cylinder. Is it possible to be out of time.

 

OK a little update. I still have not got it to run on cylinders 3-4. I need some more help. I'm at a complete loss.

 

If you have good spark and good compression then your mixture is off.

Unless your valves are out of spec I dont think anything else is required for an engine to run beside those 3 things

Do you have vacuum pull on 3 &4?

 

Yes I have vacuum pull on 3&4. I just rechecked the valves tonight to double check. Which they were in the of the spec.

 

I'm still going back to you having compression that is 34 PSI too low.
If you have spark on all four
and you have wet (but not fouled) plugs on #3 and #4
that leaves one thing....

Put a tablespoon of sea foam in each cylinder and let it sit overnight. Treat the oil with seafoam as directed on the can. Run the machine until the fog clears (do this outside). See if that improves your compression and allows #3 and #4 to fire. I'm betting on the rings being stuck.


Could it be out of time? Yes, but if it were you would not have a lack of fire in #3 and in #4. Cylinders #1 and #4 are at TDC at the same time. #2 and #3 are at TDC at the same time. If the valves out of time enough that #3 and #4 were each empty when the spark fired you would have bent valves. Spark timing is fixed and can only go out of adjustment if the TCI is bad. If the TCI were bad you would have intermitant, or no spark on one or more cylinders. This is wasted spark system, so all plugs fire at the same time and twice per crank revolution.

My only other suggestion is to put brand new plugs in #3 nad #4. It is possible that both of those plugs will spark at atmospheric pressure, but not at 120 PSI. This is not a common issue, but does come up from time to time.

 

Can you describe HOW you are doing your valve shim check?

Now, I am wondering if there may be a blockage in the fuel T that is preventing fuel from sufficiently reaching 3 and 4. Just a thought. But, if stuff is sprayed in there, it should at least fire for a moment. THAT points more toward plugs not firing under compression. We'll have to keep hammering on this a bit.....

Here's a dumb question---are you sure you have a Maxim X? Quite a few people think they have an X when they don't. It's a simple SIMPLE way to tell.........if you have a radiator, its an X--if you don't have a radiator, it's not an X. This is why I asked about the valve shims check.....the procedure for an X is vastly different than for the non-X.

non-X (airhead) - shims are big and on top of the valve bucket
X (liquid-cooled) - shims are much smaller and are a cap on the valve stem, are under the bucket, there are 5 per cylinder, and you must life the cams in order to check them.

Dave F