Weird Rough Running Issues

[eosrules]

Hey Guys ! Does anyone here have this problem I'm having. If I let my bike(Kat 600) sit for a day or day and a half, when I start it again it runs VERY rough and gets better after I ride it for a while(10 to 15 mins) then shut it off, let it sit for awhile, start it again, then it runs a little smoother. I repeat the process, and it runs a little smoother and so on until it's fine. USUALLY it takes the length of a day to straighten out(going back and forth to work). Also, when running rough it will be rougher in lower gears, but when I get up to 40mph and over it smooth's out. When I slow down for a stop it's back to rough running until I'm back up to faster speed. Anyone have this problem and what did you find was the problem? Also any suggestion's from anyone. Thanks......Larry

[Kreylyn]

Sounds to me like contaminated gas, possibly floating debris as well....

Flush your tank, lines, and clean the carbs. Check for rust in the tank and remove if there is any.

Krey

[The CyberPoet]

There's a lot of possibilities here...

Rider Issues:

First, let's examine what RPM's you are riding at... The bike will typically run rough if you're riding below about 4k RPM -- this is an engine designed to run primarily between 4500 and 9500 RPM; below that it's lugging (you may well know this, but I don't know what your experience level or previous bikes were).

The second possible issue is fuel boil-off at the carbs, combined with possible fuel-passage contamination (gasoline remains left behind as build up in the smaller passages). If you tend to ride in very low gears at very high RPM's, running the engine quite hot, when you park, the fuel in the carbs could be actively boiling off, leaving behind crud (gummy residues). In such cases, when you start the bike again, the fuel in the carbs will be devoid of their lighter compounds and it will normally take as long as it takes to burn through the fuel already in the carbs to clear -- possibly longer, if the new fuel has to clear away the gummy residues (the residue issue would be helped by better, higher detergent fuels, and optionally some fuel-system cleaner designed specifically to clear fuel residues such as techron). Switching the petcock to PRIME for about 30 seconds before starting in such situations will also help, refilling any boiled-off fuel missing from the float bowls since shut-down (switch back to ON or RES before starting).
Water in the gas tank or in the carb bowls would potentially cause this issue to be even worse, and if you have any reason to suspect water, either drain the tank and carbs or use a chemical compound designed specifically to encapsulate the water and carry it out (e.g. - EthanolRx). If you find any significant amount of water, you need to check for and treat any rust you find in the tank (see The CyberPoet's "How to fix a rusty gas tank on your motorcycle).

The final possibility is one of the rider only taking very short trips (never letting the engine come all the way up to temp, required for the spark plugs to self-clean). If most of your riding is from cold-starts and only consists of a few miles, this can be a very serious basis for the problem, as the spark plugs could never be reaching self-cleaning burn off temps. Easy way to test -- take a longer rider (say 25 miles) and see if the problem is present when you start the bike again. If it is, you need to consider either a plug that self-cleans across a wider temp range (irridium plugs), or a plug designed to remove less heat from the engine (different temp range), or an ignition advancer (which will increase the speed the engine heats up in general).

Carb Fueling Troubles Only When Cold:

There's a couple possible reasons at the carbs, the primary one being the jetting being too lean when the engine is cold (feeding too little fuel into the air mixture). As the engine gets hotter, the fuel in the carbs gets warmed more, and what may have started cold as too lean can become an acceptable mix as the fuel vaporizes more readily into a finer mist. This issue is compounded by the fact that modern fuels (at least in the USA) are typically gasahol, containing up to 10% alcohol, which makes the mixture even leaner than pure gasoline and thus making the problem more likely to crop up with borderline jetting. Again, dried fuel residues in the smaller passages of the carbs (pilot jets) will also make the problem worse. Finally, using an non-OEM filter (such as a K&N or UniFoam filter) can further complicate the matter by not providing enough resistance to air flow to have a good vacuum level at the carbs, particularly at idle, where the engine builds the least amount of vacuum to start with.

To fix this possibility, you should consider opening your pilot jets up a bit more (compensate for the leaner gasoline standard now vs. to the design standard for the Kat -- 2-5/8ths turns out on the pilot jets), make sure there's no fuel residues or blockages in the smaller passages (fuel system cleaner called for again), make sure the idle is turned up high enough (model dependent: 98+ models should be 1250 RPM warm), and make sure that the air filter isn't the basis for insufficient vacuum (ditto any vacuum leaks).


Carb Fuel Troubles Related Only To Cold Starts (Choke & Plug-Fouling Issues):
If you need to use choke to start the bike, you may be giving it too much choke (rule of thumb is 30 seconds max, and only as much choke as required to keep the engine at 2k RPM, turning it down as it climbs on it's own).
Or the choke cable may be sticking (should take no more effort to use the choke than to bend a paperclip -- if it takes any serious muscle, the choke cable needs to be cleaned/lubed or replaced).
If the carbs themselves are particularly dirty or debris covered on the outsides of their bodies, the choke plungers (the parts the choke cable activates) may have debris on them, keeping them from reseating properly when the choke is turned off.
Use of the choke (actually an enricher circuit that sprays extra fuel into the carbs) loads up the spark plugs with extra fouling fairly fast because the mix is way too rich -- this is the reason Suzuki's guidelines is 30 seconds and 2k RPM max. Spark plugs are like self-cleaning ovens, burning off fouling once they come fully up to temperature, so if you foul the plugs to borderline operation (or foul a single plug fully), it might easily clear itself again after several miles of riding and the bike suddenly starts acting "right" again.

To fix this possibility, check the choke operation, lube/replace the cable as necessary, then start the bike and shut it down after a couple minutes. Now pull the spark plugs and examine them -- if they're wet or covered with debris, it may be time to replace them. Compare the spark plugs to this chart of spark plug conditions from NGK.

Old or Incorrect Spark Plugs:

The Kats are particularly finicky to spark plug condition. Many start-up problems can be resolved, at least temporarily, by changing out the spark plugs for new ones of the correct type. They are also notoriously picky about brands, not seeming to like generics and off-brands like champion, autolite, etc -- use NGK's.
Note that if the plugs are fouling for some reason (and not simply age), fresh plugs will give you a healthy start up the first time (or first dozen times, etc.) but will go down-hill and the symptoms will return rapidly if the underlying cause isn't actually found and rectified.


Crap Fuel:

If the fuel is over 30 days old, or came from a source that might have been over 30 days old without being treated with a fuel-stabilizer, drain it and replace it. Ditto if you bought fuel from a questionable source (did this problem start happening only after the last time you took on fuel?).

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PS - to save reposting this indefinitely, it's been added to the wiki here: http://katriders.com/wiki/index.php5..._Rough_Warm-up
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Cheers
=-= The CyberPoet

[eosrules]

Thanks CP ! You must have taken a nap after that response, whew !! One thing you mentioned did stand out. I drive to work everyday about 4 to 4.5 miles one way and back for lunch in town and never really run it hard and usually max of about 50mph. So the lack of distance and running hard may be contributing to problem. Bear with me now......I just don't understand how I can run it 7 days a week with no issues and if I don't run it for even half a day I will have rough running(as I did this morning but it cleared up much quicker). I'm sure your response touched on the correct solution. I will just have to check the things you mentioned and do the ones you suggest(plugs and so on). Thanks again CP ! Double Cheers.....Larry

[The CyberPoet]

I drive to work everyday about 4 to 4.5 miles one way and back for lunch in town and never really run it hard and usually max of about 50mph.

Suggest you get in the habit of letting the bike warm up at least 2 to 3 minutes every morning before riding off, and install an ignition advancer (which will warm the bike up quicker -- note, I sell them through my special offers thread here: http://katriders.com/vb/showthread.php?t=58596 ). Also going to suggest making sure you run about 7k RPM in 3rd gear or higher whenever feasible on the way to work/home (i.e. - on the short trips), even if it means traveling a gear or two lower than what you're used to (will heat the bike faster/more).

So the lack of distance and running hard may be contributing to problem. Bear with me now......I just don't understand how I can run it 7 days a week with no issues and if I don't run it for even half a day I will have rough running(as I did this morning but it cleared up much quicker). I'm sure your response touched on the correct solution. I will just have to check the things you mentioned and do the ones you suggest(plugs and so on). Thanks again CP ! Double Cheers.....Larry

New plugs and some techron fuel-system cleaner (plus solely buying high-detergent fuels from here on out) should help. If you're not using a battery charger at home, I'm going to highly suggest you start (Battery Tender waterproof 800 model is ideal for your needs), because the battery may not be seeing enough riding to keep fully charged either, esp. as it ages.

Cheers
=-= The CyberPoet

[eosrules]

Thanks CP ! Will do. You're the man !!.....Larry