Quote from: mp183It turns out that the problem was caused by exhaust valves with no clearance. The symptoms I had: Hard starting, seemed like it started on one cylinder for about 15 seconds and then the other one would kick in. I could not set the idle. If I set it and ran it for a while the idle would shoot up to 3,000 rpm. This started to happen to me when I would be stuck in traffic for longer periods of time. I guess with a very hot engine the valve clearance changes. One more reason to get a bike with a water cooled engine.
Actually the valve clearance in motorcycle engines with overhead camshafts and aluminum heads increases as the temperature of the engine increases. The engine doesn't have to be very hot , the increase in valve clearance is immediate as the engine warms and proportional to the temp. A engine that runs poorly when cold will frequently run OK at normal operating temps and this is the same for air cooled and water cooled ones. Proper valve clearance is important to both.
This increase in clearance is due to the greater coefficient of linear expansion of aluminum compared to steel. As the head and valves get warmer, the head will grow taller faster than the valve grows longer. This lifts the camshaft away from the top ends of the valves increasing valve clearance. Any time your engine starts running poorly when it is cold and still runs well after warmed up, check the valve clearances first.
Great explanation. I wish I had known this earlier. I hope others read this. There have plenty of others that have had the same problem and most people giving advice jump in blaming the carbs.
How much does it cost to have someone adjust the valves? I actually have the exact same issue. It's hard to get her started, but once she's going she's fine, I think it might be the same issue.
Thanks
I cost me $185 bucks for the labor. They replaceed the gasket also which was another $23. That was showing signs of deterioration anyway. Might seem like a lot, but I'm glad I did it. I know I could have done it myself but life if too short.
Another good reason to do routine or scheduled preventive maintenance, even on a liquid-cooled bike. Valve adjustments should be made every 4000 miles. Oil change at the same time. Replace spark plugs, too. Clean airfilter. And if you can, synchronize your carburetors. When you lube your chain check the slack and adjust as nessessary. Check clutch cable freeplay. Throttle freeplay.
O.K., I'll stop preachin'
Valve clearance increases when hot... I have posted that for years... Even when the mailing list was the only one there for the GS back in 97-98 ... When I lived in Sacramento I did this experiment and ever since I burned my fingers doing this experiment... I have been running my valves tight... so tight you cant get a guage in there, and mine are rubbed down to under 1 thousandths... but the bucket spins... indicating the cam isn't on the bucket... That makes for a quiet bike with the usual clack clack toned down a bit. Compression tests dont make any difference... cos they measure compression hot... and that is what counts. On some bikes... the valve stems and face get hot before the head does... so a bike with tight clearance will strat fine and run fine for ~ 30 to 60 seconds... then a valve will stay open cos its hot now, and it will run like shaZam!... till its head gets hot.. .and then it will run like a dream... My virago was that way.
Cool.
Srinath.
I had a very similar problem. I did the valves myself and had similar results. If you had time I would recommend this job. It is a very satisfying feeling to know you saved money and learned something in the process. I'm glad your bike is running cherry now...
And that clack clack does get annoying from the valves. I get that sound in my bike. Sort of comes and goes now and then.
ASLAM.
Hmm... I'm having a similar problem. Once my bike warms up, idle > 4000rpm, lowsy gas mileage, and I adjusted the camchain tension once already but I'm hearing a sound again that might indicate that it's loose... all maybe things that could be caused by the same problem? I hope? =]
I checked the clearances and I know they are <.04mm, but I can't get an exact measurement. I'll have to get some really small shims to do a acurate reading with, I guess.
Thanks for the tip!
Anyone have a how-to for adjusting the valves? I have a 2002 that I bought new and I"ve put 17K miles on it. I've done all the other maintenance but have the same problem. I'd love to learn how to check/adjust the valves.
get a Haynes manual. if you buy it from Amazon by clicking on the Buy a Repair Manual (http://www.amazon.com/exec/obidos/ASIN/0892878339/ref=nosim/gstwincom) link on the top of the page, part of the money goes to support this site (but doesn't cost you any more).
I've been told that you can get small feeler blades at NAPA auto parts, but I can't swear to that. My valves (at 15K miles) were so far off I couldn't measure with the feelers I had, and had to get a 2.15mm shim (smallest) and measure from that to find out what size shims I should get.
Ordered new shims, should get them Wed... *crosses fingers*