Stock KZ650 - flames shooting from carb vents

Hey there:

Stock 78 B2, the bike will start on full choke but dies as choke is closed.

There is a major backfire out of the carbs - gasses pulsing through the gasket on the top of the carb and flames visible through the carb vents.

Scarred the crap out of me yesterday.

I think that I have gotten myself in this mess when I tied to retighten the cam chain.

When I started the bike up after removing the points cover - rotating the bolt 2 revolutions and slacking the cam chain tensioner - it sounded like a chain saw.

I started the bike with the electric start - that was a bad move. So I have read in the Haynes manual.
Clymer did not mention it in my book.

So basically what can I expect or what do I need to do to remedy the situation.

Has anyone ever seen this before.

My biggest fear is bent valves from the cam chain jumping a link or to. Would that cause the the valves to be damaged and the combustion to leak back through the carbs?

Any info on how to proceed would be greatly appreciated.

I just had the bike ready to go to paint as I figured I had everything working and now this.

I rode the bike for about 2 km and then she died on me.

Now the flames are shooting out the carbs.

its never good when you have fire in the carbs,,,

since you have ran the bike, the damage may have been done.

1 check the cam timing to make sure it is correct,
2 if cams are wrong, redo the install
3 if cams are correct, make sure the plug wires are on correect
4 run a compression test on all 4 cyls, this will tell you if you have a major problem
5 if the compression is low, start ordering parts for top end rebuild.

I know that is not good news but its going to take the slow down and check everything again.

i've never seen fire out of a stock engine,i have a question for you was the engine running when you attempted to set the cam chain.

KOOL RYDER wrote:

... major backfire out of the carbs... tied to retighten the cam chain.
When I started the bike up after removing the points cover - rotating the bolt 2 revolutions and slacking the cam chain tensioner - it sounded like a chain saw.
I started the bike with the electric start....

Might be mis-reading, but am interpreting the reported history to mean that the valve cover was not removed, and the initial objective was a routine adjustment of the cam chain tensioner located behind the cylinders below the carb holders.

Am wondering if the cam chaim tensioner was loosened and not tightened before running the engine while the tensioner remained in the loosened position. This would allow the engine to run with zero tension on the cam chain (and perhaps sound like a chainsaw what with the ultra-loose camchain flapping and flopping all around). Am uncertain as to the extent of damage which might have resulted. If the camchain slipped a tooth or so -- ouch -- possible valve damage. But if it didn't slip a tooth, maybe just lots of noise without valve damage.

Would try again to adjust the tensioner. With lock nut loosened, loosen bolt, gently and carefully hand-rotate engine (stop immediately if any resistance is noted as this might be a valve contacting a piston or another valve), tighten bolt, tighten locknut. Hand-rotate the engine (stop immediately if any resistance is noted as this might be a valve contacting a piston or another valve). Assure plug wires are correctly routed. Only if the engine rotated smoothly and quietly while hand turning, try to crank the engine, but be prepared to immediately shut it down if any unusual noise is noted.

Often, a leaking intake valve which isn't fully seating because of too tight valve clearance may allow combustion to escape and fire back out through the carb.

Good Luck!

Edited to include loosening tensioner BOLT after loosening its locknut, and tightening the bolt before tightening its locknut. The bolt holds the tensioner internals in position, and the locknut merely keeps the bolt from loosening.

Is this still the same situation we were discussing several months ago? I'd have that valve cover off several months ago if it was me We asked a few months ago and I don't think we ever heard exactly what transpired. If you turn the engine clockwise with the 17mm wrench until the point right past the 2-3 mark, that's the place to stop turning, loosen the 6mm locknut, then the 6mm bolt on the tensioner, then tighten the bolt, then the locknut. Spring tension takes up slack and there's no way I know of that the chain could possibly get more loose than it was previously and at this point you are done and can start the engine electric or kick without any difference. Some potential mistakes include attempting to start the engine without securing the adjustment or turning the engine over backwards during the adjustment before tightening the tensioner. If either of these happened chances are you didn't jump a tooth or two, but 10 or 20 and major damage can result. On a KZ650 they are pretty foregiving and maybe you jumped teeth and did no further damage. It takes 30 minutes to remove the valve cover and look over the marks to see where you are so get too it

RonKZ650 wrote:

Some potential mistakes include attempting to start the engine without securing the adjustment or turning the engine over backwards during the adjustment before tightening the tensioner.

Ron, what effect does turning the engine backward have, meaning how would this make a difference? Just trying to learn here, for when I do this adjustment in the future.

Should you only turn the engine one way? So if you miss the mark just continue round the same way until it comes up again?

Ron, I see your point,but it sure does sound like it has jumped time,
ont thought may be that the tensioner has broken, either way pull the valve cover and run a compression check,

HerrDeacon wrote:

RonKZ650 wrote:

Some potential mistakes include attempting to start the engine without securing the adjustment or turning the engine over backwards during the adjustment before tightening the tensioner.

Ron, what effect does turning the engine backward have, meaning how would this make a difference? Just trying to learn here, for when I do this adjustment in the future.

Should you only turn the engine one way? So if you miss the mark just continue round the same way until it comes up again?

Should you only turn the engine one way? So if you miss the mark just continue round the same way until it comes up again? Imo, Yes and Yes. Am thinking the idea is to keep maximum slack at rear of camchain whereby setting the tensioner will have the most effect.

Good Luck!

If you turn the engine over backwards all the chain pressure is trying to push the tensioner back in its body and the slack is now at the front of the engine. This probably doesn't hurt as long as the tensioner bolt is secured, but still no good reason to do it ever. It puts additional stress on tensioner parts that normally have no stress. Always turning the engine only forward, there is never any back pressure on the tensioner and chain slack will always be in the rear, loosen the lockbolt on the tensioner, simple spring pressure takes slack out of the chain, tighten and you're done. So simple, but works great.

Thanks guys for explaining that.

Gents. Points are moot. either cam timings are off, or valves are bent. pssibly both. follow procedure, verify cam timing, then check valve clearances.if clearances are close, check compression/leak down. bent valves usually exibit excessive clearance and leakdown. if unable to do yourself, a shop should be able to for @ an hour's labor and give you numbers. comp. less than 150, or leak down over 10% chances are you've tipped some and or needed a valve job anyway.g, flames from carb are either from intake valves out of time or not sealing.G

You can also produce flames by mucking up the ignition so that the intake valves are open at the wrong firing timing. If you cross the black and green wires on the coils, put the rotor from a Dyna S on 180 degrees out or have the wires from the coils on the wrong plugs... FLAMES. Since there has been stuff going on in this bike's past I don't recall and wasn't really mentioned, I would also check the ignition to ensure it is set up properly.