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Eating GSXRs, Sh***ing CBRs
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Discussion Starter #1
So last year in the fall my ZX9R started having issues. Once it became cold and rainy, the bike became extremely hard to start. It would backfire while cranking. I put it away for the season. A few days ago, I got a new battery and it was warm and sunny. The bike fired right up and ran no issues for 3 days. This morning was 32f and when I went to start it, it would crank but wouldn't fire. After a few tries it backfired louder than I could ever imagine. I gave up trying to start it and rode the other bike.

After researching on the net, some of this, like problems in colder weather and the backfiring, is pointing me towards the valves being too tight. Does this make sense? Anything else, I should be looking at? The valve adjustment is a huge job for me and an expensive one if someone else does it. I want to be somewhat certain that it is the issue before dismantling my beloved bike.
Additional info:
Battery is good, spark plugs are good. Once it's running, it runs beautifully. No hiccups or stutters.
 

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ZAMM Fanatic
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2,732 Posts
How many miles on the bike, what is the MFR's recommended interval for valve adjustment, how long SINCE it's been done on your bike.

IF you don't KEEP them adjusted you can trash a $$$ motor!
 

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Eating GSXRs, Sh***ing CBRs
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Discussion Starter #3
40000 on the bike. Not sure how many miles since the last check. I'm way over though. I'm going to do it but I'm just wondering if tight valves can cause these issues.
 

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It's all fun and games until someone loses an eye
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Interval should be somewhere in the 6-8k range, so I'd say it's a good place to start.
 

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MODERATOR
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A tight intake valve can easily cause backfiring and erratic running as can a vacuum leak. Get a can of carb cleaner spray and spray near the rubber intake boots where it meets the cylinder heads and spray there: If the idle speed goes up, you have a leak.

Try some Techron fuel injection cleaner first as it could also be a fueling issue. Plugs next.

Sam:coffeescreen:
 

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American Legion Rider
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A tight intake valve can easily cause backfiring and erratic running as can a vacuum leak. Get a can of carb cleaner spray and spray near the rubber intake boots where it meets the cylinder heads and spray there: If the idle speed goes up, you have a leak.

Try some Techron fuel injection cleaner first as it could also be a fueling issue. Plugs next.

Sam:coffeescreen:
He's got to get it running first Porky for your test. Right now it's just backfiring. Interesting thing, I've only seen valves get tight myself although I know they can get loose. Just what I've seen. If you got that many miles and you've never done a adjustment, and you want to keep the bike, I'd work on those valves. But I'd also suspect the carb boots as Porky suggests.
 

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It's all fun and games until someone loses an eye
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8,668 Posts
He's got to get it running first Porky for your test. Right now it's just backfiring. Interesting thing, I've only seen valves get tight myself although I know they can get loose. Just what I've seen. If you got that many miles and you've never done a adjustment, and you want to keep the bike, I'd work on those valves. But I'd also suspect the carb boots as Porky suggests.
Yeah and when they are tight expansion only makes it worse.

If he's not wanting to do a valve adjustment, a compression test should tell him what he wants to know.
 

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Eating GSXRs, Sh***ing CBRs
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Discussion Starter #8
Once it's started it runs and idles flawlessly. No hiccups, no hesitation. If carbs were an issue, wouldn't it run worse? The valves are a definite, at this point in just trying to see if there is anything else.
 

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Retired twice: Navy and as a govt contractor
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Someone help me out here. Doesn't metal contract a bit when cold and expand when warm?

If that statement is true then wouldn't tight valves get tighter when the engine warms up ?
 

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Justa anutta Human......
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40000 on the bike. Not sure how many miles since the last check. I'm way over though. I'm going to do it but I'm just wondering if tight valves can cause these issues.
Yes it can.....
Most sportbikes need the valve shims checked every 10-15,000 miles depending how u run the bike....
High rpms...more often.....
I had my Ninja 650 ones done at 25,000 miles because i run it at lower rpms most the time...( 3500-5000 ).
The guy that runs the same bike at 5000-9000+ will have to have it done every 15,000 miles.
Mine were all good at the 25,000, but the mechanic did change out one because i told him if any was even close to being out of spec do them while it's apart.
Also a quality oil will make a difference in wear of any engine parts, and how often u change it.
Mine calls for 7,500 mile oil changes with dino oil.....
I do them at 5,000 miles with mobil 1 for motorcycles....
Hoping to my bike will run till 100,000 miles with no major issues....
33,000 now in less than 3 years....
 

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American Legion Rider
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Someone help me out here. Doesn't metal contract a bit when cold and expand when warm?

If that statement is true then wouldn't tight valves get tighter when the engine warms up ?
Yep. People with VTX's I heard complain about loose valves. I've just never seen it. So loose gets REAL loose in cold. But Porky's suggestion of checking to boots is good too. Wouldn't a carb leak be bigger in cold? Probably yes. I'd at least reach in there an tighten the clamps if possible.
 

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ZAMM Fanatic
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A) Doesn't metal contract a bit when cold and expand when warm?

B) Wouldn't tight valves get tighter when the engine warms up ?
A) Yes

B) It depends on the valve configuration, for instance an overhead cam engine versus a pushrod design. In different configurations the valves may wear and get tighter OR looser, and expansion due to temperature may help or HURT the situation.

In general when you hear valves/ lifters "ticking" it means they are loose, the gap is too wide, and all they need is adjustment.

When valves get too TIGHT they go silent, and then valves get burned and things go to hell rather rapidly.

A valve / lifter / rocker that is too tight prevents the valve from seating completely, so exhaust gas escapes between the valve and head and does horrendous damage quite rapidly. A misfire is often the first indication.

Hydraulic lifters, of course, eliminate the need for adjustment and greatly reduce maintenance costs. They ALSO cannot do the 10,000-16,000 RPM redlines of crotch rocket motors. Realistically 8K is about it for hydraulic lifters.

The future of lifters is some electro-mechanical lifter that self adjusts AND is capable of ultra-high rpm's. It is yet to be designed
 

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Retired twice: Navy and as a govt contractor
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11,493 Posts
I know and or understand all about the damage. What I don't understand is gap getting looser as everything warms up.

If the valve gap is to tight when cold who does it open up when warm?

cold - pops, snaps, backfires and doesn't start
warm - starts right up and runs fine
 

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Save them all!
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Yes adjust your valves, but I'm going to throw another possibility out there: Plug wires and caps. They can be very sensitive to cold and moisture when they start to go bad.
 

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Registered
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amother little known cause of backfiring, stuttering is water in the gas.
The tank gets some damp air in it, everytime you open the lid. It condenses on the inside of the tank, and when the fuel level is low, it gets in the reserve, the carbs are designed to handle filtered and dried air, and when the water gets condensed in the head it causes steam that gets caught in the oil, circulates, and causes untimely stutters. take a papertowel, roll it into a dip stick, and dip it into your oil when you bike is cold. If it looks like it has water above the oil line, change the oil, drain the tank, dry it out with a hair dryer and then try it again. a motorcycle head job is a real learning experience the first time through. Bring a pro on the trip with you
 

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ZAMM Fanatic
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Water in the oil, etc.

WATER IN THE OIL: Generally water in the oil gets "blended" in and causes a baby-poop brown, distinctive color / texture.

After you've seen it once...

GAS IN THE OIL: Far more common is gas in the oil, due to leaking carb bowls, which is pretty indistinguishable except for the fact your oil level keeps going UP and getting thinner and thinner.

SMOKE ON THE WATER: that's Deep Purple. Be careful with those flare guns.

 

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MODERATOR
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I forgot to mention something that I learned the hard way on one of my track bikes, back in the middle 60's: "Always look for the most simple explanation in any task."

My bike was race prepped and ready to go but when I took a practice lap, it would 'miss and cutout' from about mid-range on! I didn't race that day, loaded up and went home.

On mechanical things, especially motorcycles, I have a very experienced and logical mind when it comes to diagnosis---or so I thought. I started to go through the entire engine and saw all systems in my mind, before I got out the wrenches---then it dawned on me that the last thing I did was put in new sparkplugs. I'd never had a bad, new plug before but when I changed them out, the bike ran perfectly!

Lesson learned.:biggrin:

Sam:coffeescreen:
 
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