xj600 diversion 1993

Carb tech cleaned my carbs and tried to synchronize them. 1,2 and 4th carb were in 230-240 mm Hg range but 3rd was around 150 mm Hg. As he started to rise the value on that carb engine started to knock. Deep thumping sound was comming from the engine. He said that problem could be in brass ring in piston rod, piston or a piston pin that connects piston and piston rod. But most likely in that ring because it is soft metal.
I checked in parts list and repair manual and did not find any brass rings in piston rod.
Does anyone have some engine rebuilding experience or idea what to do?

tnx

 

-Quit listening to the "Carb Tech" guy.

-Don't worry about the actual readings on the vacuum gauges, comparison is what it's about.

-Get the valves adjusted first; then see how it does. I think somebody's pulling your chain. A tight valve will throw off vacuum synchronization.

 

Soumds like that carb tech had a different metal in mind, and not on your motor!

Brass is to soft a metal for piston pin bushings, and would quickly deform under the stress of opertation. Most pin bushings are made of a Bronze alloy for strength.

Do as Fitz suggests. Get the valves right first. Then bring the carbs in line.

Ghost

 

Tnx mates. I will chk valves tomorrow.
Any idea what caused that loud engine knocking while he was on carb 3?
Could it be that too much fuel/air was getting in the cyl and explosion was
too strong?


Live long and prosper

 

Update:
I've checked valve adjustments and they are all within 0.11-0.15 and 0.21-0.25.

what now?

 

Compression test.

 

Does the engine sound normal the rest of the time/when riding?

I owned the previous XJ600 model and they were very sensitive to carb balance - I know that is what was being set - which caused the primary chain to be noisy, especially on a high mileage engine.

 

@markie
well i did not try to ride it with something knocking inside. Reving to 3000 rpm did not made that knocking go away.
Carb tech then returned vacuum value to 150 mm HG and knocking stopped. XJ is now slow and there is a delay in acceleration. 3rd cyl is now not working as it should be.

@fitz
I did compression test last year and as I recall all was ok. will check tomorrow.

I've checked pilot screws on carbs and all 4 where set on just a bit less then 2 turns. ???? I do not know how they were before carb cleaning. Last year spark plugs had normal color.

PS How to check oil pressure in cyl head?

 

It could possibly be a diaphragm not opening properly -- maybe the carb mechanic didn't clean/polish the bores well. If the mechanic is trying to compensate for that by adjusting the synchronization, it's just not going to work. That could cause that one cylinder to fight against the others.

Just a thought.

 

I still think the "knocking" was primary chain slap brought on by an out-of-sync motor; or the "mechanic" cranked the adjustment so radically that it basically shut the cylinder down, which would make it knock.

It could also be throttle shaft seals on only one carb; a vacuum leak, or a carb that wasn't really cleaned as thoroughly as necessary. It only takes ONE acting up to throw the whole thing off.

Have we even discussed floats and float levels? I'm not sure how they work on those bikes, but they have them...

 

Floats are the same. Everything inside the carb bowl is just angled 45 degrees instead of straight down (since the carbs go up under the gas tank if that makes sense) They've even got a little line on the outside of the carb bowl where you're supposed to set em. Handy, eh?

Something is definitely out of sync -- and apparently it's not anything a carbtune can uncover. I've had a cylinder(s) knock and found that the idle mixture adjust screw for that cyclinder was a hair lean. A 1/8th turn and the knocking went away...

The carb mechanic has me suspicious of his handiwork.

 

UPDATE:

I've checked compression. 1st cyl 12 bar, 2nd 9 bar, 3rd 9 bar, 4th 9 bar.

Intake rubbers have lots of cracks. I've rearranged 3rd and 4th just to see if that will help improve vacuum on faulty 3rd cyl.

PS Why so much on 1st cyl?????!!!!!?????


Live long and ride a motorcycle!

 

Do you have a workshop manual? PM me if not. Haynes give the compression pressure as 10.6 bar - 156psi.

As long as the rubbers are not cracked all the way through, you should be ok but these can be repaired.

Lastly. If everything was fine before the carb cleaning - it must be a fuel/carb issue!

 

rubbers are so close to death. i'will order new ones.
i have manual tnx.
tomorrow i'll give him some fuel and friend will bring his vacuum gauges.
we'll see what happens

 

you were right mates, intake rubber on 3rd cyl was full of cracks and air was going trough. that is why carb tech could not sync that carb. he just put that cyl out of sync.

bike now runs great again.
tnx for help

live long and have a nice sunny weather.

 

Glad to hear it. Have fun!