Clanking noise

[IT-simon]

Hey guys so i finished cleaning the carbs and re-jetting stage 3 dynojet, replaced fuel lines with clear ones everything is good but..., i actually haven't moved the fuel/air mixture screws on the individual carbs at all but i figured i didn't need to yet..

they problem i'm having:
exhaust #2 seems cold while the others warm up
there is a clanking noise (sounds like lifters on a car)

what i checked
spark plugs are new, i held it up and saw the sparks flying, it seems to be getting fuel, i'll move the mixture screws tomorrow.. the spark plug smelled like gas so i think it's ok on getting gas

i'm just worried about the clanking noise, i haven't changed the old oil because i wanted to add an additive to the old oil and warm it up before changing the oil, i figured i'd do that when it's running properly.

it is fresh gas though.

so if i mess with the air/fuel mixture screw and nothing changes, should i start taking the top end of the engine off and looking for loose stuff?

also when i turned off the engine, there was a distingished clank noise like a metal piece finaly stopped moving.

i'll be checking the thread tomorrow, thanks again in advanced

here is a blackberry video of the sound hope it helps.

http://www.youtube.com/watch?v=rBNWrvVkGT0

[almarconi]

When was the last time you adjusted your valves? You could have a loose tappet in there. Also check your cam chain and guides to make sure nothing is stretched or broken.

If you installed a stage 3 kit, the mixture screws will probably need to be about 3 turns out.

I would not use an oil additive unless its safe for a wet clutch. Just use a good quality diesel oil in there or a 5w-40 synthetic.

How did you clean the carbs? Complete strip and dip? If #2 is not getting hot, more than likely the carbs are still dirty. Did you check the plug wire and cap on that cylinder?

[IT-simon]

I have never adjusted the valves, i'll have to check for that loose tappet in there and check the cam chain and guides to make sure nothing is stretched or broken. (not sure how i'm going to do that but i'm sure i can do it.. lol)

when i get home from work tonight i'll check what the screws are turned to write it down then set them all to 3 turns out.

I wasn't sure about the additive but yeah i do remember reading about using specific oils for the wet clutch thanks for the imput there. >>Just use a good quality diesel oil in there or a 5w-40 synthetic.

I did strip and dip but everything was actually really really clean, the only thing that was dirty was a tiny bit of crap on the float bowl so i didn't bother taking the mixture screw off... everything else came out to be double checked, the boot assambly was loose (spring>metal piece>screw) i re-tightened it, put the plug back into the boot and just held it above the opening, started the bike and saw sparks flying without interuptions.
I just got the bike and it already had the aftermarket muffler and had no air box so i installed the pods, and went with the stage 3 dynojet, it's all i've done to the motorcycle so far, i'll be changing the oil as soon as i adjust the valve's and air/fuel mixture screws so i can warm up the oil before the oil change.

thanks again for the imput i'll let you know how it goes

[1948man]

Wouldn't hurt to put some Seafoam in the oil if you're only going to warm it up to change it. Air-cooled bikes warm up fast if stationary. Most would say the Seafoam isn't really necessary but it might help suspend some gunk.

[Steve]

... I did strip and dip but everything was actually really really clean, the only thing that was dirty was a tiny bit of crap on the float bowl so i didn't bother taking the mixture screw off...

Sorry, but if you did not remove the mixture screw, you did not do a FULL strip and dip.
You also need to remove the mixture screws to replace theh o-rings.
If you don't have good o-rings in there, all bets are off, regarding ability to properly tune the engine.

Besides a possible loose valve, that noise could be a bad carb sync. You said that #2 is not warming up like the rest. It's possible that it is closed farther than the others (higher vacuum reading) and is just not firing yet. The imbalance in firing pulses will make a rattle. If the noise gets less at higher throttle openings, it might be carb sync. If the noise stays the same or gets louder, it's probably the valves.

.

[IT-simon]

They sure do warm up fast.. lol helped me notice that the exhaust #2 was not warming up, but also made me worry, there is no temp gauge, how do you guys monitor the temperature? should i not worry about it? thanks

[TheCafeKid]

Hate to say it but that sounds like a blown conrod bearing to me....

[Steve]

Hate to say it but that sounds like a blown conrod bearing to me....

That was another possiblity that I thought of, but was holding back on that, pending the adjustment of valves and carbs.

.

[blowerbike]

damn man,
the piston's hitting the head surface.
i think josh made the right call.
a spun bearing lets the piston ride higher in the cylinder and make contact with the head.
if you rev it some the knocking sound should speed up with the RPM's.
80-82 GS750 common problem.

[IT-simon]

So after the scary comments what would be the best way to go about checking it out? should i change my plans of going home to fix fuel/air mixture on the carb to taking the top part off and checking for damage? i was afraid it'd be engine relateded (that's why i started the thread here..) would i end up having to take the engine off the frame or is this something i can do with the engine on the frame? thanks

[SqDancerLynn1]

Start with a compression test. You could also use a small dowel rod. hold it on the top of the piston. Get the cyl to top dead center turn the crank to see how far it turns before the piston moves. You could also put a oil pressure gauge on it to check the oil pressure. It 81gs750 is a plain bearing high oil pressure motor
Back to what has been said,?? What does the motor sound like
at 2K rpm ?? Carb sync, a dead cyl, clutch basket ?? ALL can make the engine very noisy

[blowerbike]

remove the head and flip it over.
look for the combustion/squish area that has all the carbon banged off.
or just look at the pistons.
you will see which one is bad.
the noise i heard is not a basket or starter clutch noise.
plus these models don't really have basket issues.
the only reason to disassemble is so that you can see what is wrong.
these engines are 100% not worth rebuilding when the crank is damaged.
you can purchase an 1100 16v. engine for less than the cost of rebuilding yours.

[chef1366]

If that's not an exhaust leak than
Uh Oh

[IT-simon]

I picked up a compression tester on my way home, but I work 4 12 hour shifts, i thought i would have time yesterday but nope, i had time to adjust the fuel/air mixture screws 3 turns out, but it didn't make a difference, when the bike starts it sounds fine but after like 5 seconds the clanking sound returns. I'll probably have to wait for Friday to work on it, thanks again.

[IT-simon]

I ran the compression test yesterday, and this is what i got
#1 135
#2 80
#3 99
#4 115

how much do rebuild kits usually cost?
i'll be opening it up tomorrow, since i have the day to work on it.
I still don't know exactly what i'm getting into but i have the service manual i'll post up any strange things i find.

i also found a lot of parts on ebay. (Cliff's Used Motorcycle Parts Place)
will combine them all and ship together.

http://stores.shop.ebay.ca/Cliffs-Used-Motorcycle-Parts-Place_GS-750_W0QQ_fsubZ103928014QQ_sidZ81151384QQ_trksidZp4634Q2ec0Q2em14?_trksid=p4634.c0.m14.l1513&_pgn=6

thanks