"new" XJ might have problem

[TheDjost]

Hi gang.

I just got an XJ750. I haven'y had the chance to ride it yet, since I don't have the liscence for it. Will have in a month or so.

My question is this: How much blow-by gas is acceptable?

Today I decided to change the oil in the bike, since it had been stored in a heated garage for two years. All went well, except that I noticed that the #4 cylinder is not firing. The exhaust pipe stays cool to the touch, even after the others are way to hot to touch. First check I did was to run the bike with the oil filler cap off to see the amount of blow-by gas there was... And behold, a real wind (about as much air as you would be able to blow out a McD straw) of UNBURNED fuel/air mix.

Now there's a couple of possibilities:
1- piston rings -- most obvious
2- head gasket -- another possibility
3- ?

I havent't yet taken the time to check for good spark on that cylinder, but it seems unlikely(if not impossible) that excessive blow-by be caused by absence of spark.

If the blow-by is not normal, what would be the next thing to do? Compression test?

A bad ring would probably mean I'll be riding only next year. I hope I won't have to pull the engine apart, but if I must, then so be it. I've never had to take on apart... how much time the average weekend mechanic could expect to take to "rebuild" the engine. If it's got to come out, might as well do the whole job.

I'd like to have some of your opinions/experiences/advice, if you think I'm worthy with my "small" XJ750


-Justin

[mitch]

check the simple things first

justin, the blow by is normal i think if i take my filler cap off i get the same thing and i have put 4000 klms on my xj this summer .Did u check for spak at the plug, have u cleaned the carbs?To check the carb if u have fire at the spark plug squirt a little gas in the carb when the bike is running to see if that cylinder fires. Hope this helps, MITCH

[Jerry]

If the bike has been stored a couple years, don't get in a panic. Put in a new set of spark plugs. Clean the carbs. Do a compression check. Get a can of SeaFoam or somethig similar and run it through the crankcase and/or fuel system per directions on the can.

Any stored engine has at least one cylinder that will be exposed to the elements as one or more valves will be open. Chances are you have some stuck rings. There is a good chance they will work loose with some running time or treatment with the SeaFoam.

Pistons moving up and sown create pressure differences in the crankcase. This is not blow-by, but normall operation. That is why engines have crankcase breathers. Blow-by is gas escaping past the rings.You may have some of that as well, particularly if a few rings are stuck, but you couldn't tell how much by pulling the oil filler cap.

[TheDjost]

Cool, thanks for the encouraging notes.

I'll check for spark , change spark plugs, and then if the #4 still won't fire, I'll try the carb.

I'll take the bike to a friend's shop on friday PM (he does small engines like mowers, chainsaws) He should have a compression tester that I can use. That way i'll be very sure everything is runnung as it should.

Does someone know of a quick way of unsticking piston rings apart from a seafoam treatment? The bike already got a full can of a similar stuff in the gas tank. Maybe if I pull the plugs, pour a spoonful of gas in each cylinder, and turn the engine over by hand... could that help? Or maybe full strengh fuel system cleaner?

If time is the only answer, how much could it take? A couple of hours, days, weeks of running?

Like I said, I have a month or so to play with it... After that, it's on the road.


Thanks again!

-Justin

[Duster]

Stuck ring

Hi; I unstuck the rings on one cycl. of my 81 SX1100 by pouring a little Marvel Mistery Oil through the spark plug hole and just waited awhile before cranking with the spark plug out.

Duster

[uk1.1s]

Dead cylinder

Heard that storing an engine with a little diesel oil in the cylinder can help keep the rings from sticking - potential to try overnight maybe - but only use a little as it's likely to end up in the crackcases mixed with your oil.

Had a similar problem (dead cylinder) with a long stored XS1100 project which I managed to solve by changing the plugs and a bit of 'encouragement' by adding a small volume (about an eggcup full) of fuel direct into the plug-hole before replacing the spark-plug. The bike eventually got the idea and started trying to run on that side until eventually the problem cleared.

I may have even warmed up the plug in the oven whilst the wife wasn't looking as this tends to help the combustion process along sometimes (technically not sure how - but it's worked on old bikes for me before. Makes getting it back in the bike before it cools too much fun too - try leather riding gloves and beware of burning yourself too much

Good luck

[TheDjost]

Ok, here's what I did:

Last night I sprayed a LITTLE WD-40 in each cylinder and pushed the motorcycle around in first gear. Then I let it sleep quietly. This morining, I checked spark on all cyls and changed plugs.

Finally I started it, and it runs GREAT. It has trouble holding a steady idle without a tiny bit of choke, but I figure that is due to the fact that it's still running on an overdose of fuel system cleaner. When that is through, I'll feed it some premium gas and see how it goes.

Maybe I'll check the carb synchronisation, idle speed adjustment, etc. But I'll wait until I refill the fuel tank with "clean" gas to do that. The fuel system cleaner is probably throwing everything out of whack.



Thanks all of you for your advice, and I hope to be able to return the favor some time in the future.

-Justin

[mitch]

great another xs up and running

Justin ,glad u got it running but u should clean the carbs,check out our site ur carbs are different but it will give u the idea good luck and have fun ,Mitch

[fusionking]

I say if it runs great ............don't screw with it.

[Bill__Woods]

I would say "remove and clean the carbs now, cause you know you need to."
Get it out of the way

[TheDjost]

advice taken

I took your advice and tok apart the carbs.
They were a little gummed up inside so I cleaned everything with carb cleaner, a used toothbrush and compressed air. Now they're clean as a whistle.

Now I sure have to tackle a carb synch and idle adjust. What is the best tool for synchronizing the carbs? Needle guages, or murcury tubes?

-Justin

[xssiveone]

Re: advice taken

Originally posted by TheDjost
Now I sure have to tackle a carb synch and idle adjust. What is the best tool for synchronizing the carbs? Needle guages, or murcury tubes?

Basically I think the choice is yours. They both accomplish the same results, just one with mercury, one without. I chose not to mess with the mercury so I purchased a set of vacuum gauges from JC Whitney and am very happy with them.

Several good help tips on carb sync here.



Carb syncronizing

and here:

Pre-syncing the carbs