77 kz650 issues

hey just bought my first bike new to this whole thing so I apologize for my ignorance in advance. I have two major issues that I need help diagnosing.

1. when I first star the bike it idles great around 1k and If I give it throttle in goes smoothly up and back down. but after riding for 5 minutes the idle wants to jump and stay at 3-4k rpms

2. at around 5k rpms in every gear it seems to top out and make this wapwapwapwapwapap reving sound and I feel like I loose all power to the wheel. runs very smoothly under 5k

any idea or suggestion are much appreciated

Welcome aboard. Does the bike have the stock air cleaner? If not, you may have a jetting problem. Also, you may have a vacuum leak causing the change in idle speed. I would test the carb holders for leaks - here's how:

Check the carb holders for leaks. They will eventually develop tiny cracks in the mating surfaces between the holders and the cylinder head that can cause them to leak at idle. These cracks cannot be seen with the carb holders in place. I suggest you try the following. Get the engine warmed up and temporarily set the idle as low as possible without killing the engine (lower than 900 rpm if possible). The lower the better because with the idle very low the slides are nearly shut and the vacuum inside the carb holders is at its highest. Then spray carb cleaner around the carb holders, especially where they mate with the cylinder head and where the carbs attach to them. Carb cleaner works best for this test as it doesn't leave an oily mess with WD40 or evaporate so quickly that it is not drawn into the leaks as can happen with propane or starting fluid (ether). If the engine dies or reacts to the carb cleaner, you need to replace the carb holders. Carb holder leak related problems are noticeable at idle but generally don't have much impact when riding because the throttle is open. If you find you need to replace the carb holders soak the screws with Kroil for a couple days before attempting to remove them, and use JIS standard, NOT Phillips, screwdriver bits, and this will greatly improve the odds that you will not break or strip a carb holder fastener as so many have done.

Also, here's a link to some info that should save you headaches and money when working on your KZ650. Ed

kzrider.com/forum/10-new-members/589649-...r-savannah-ga#594587

yea I figured I have a leak they look liked they have been patched a bunch new ones are already coming in the mail. why would the bike top out at 5k though. any idea I wouldn't think carb boot leak would do that. and no it had pods but It had pods before I bought it and when I first couple hours I rode it wasn't topping out like that.

I also noticed that it seems to drip gas from the one hose that's connected to the second carb from the left. not sure why that would be happening

The topping out problem could be the result of dirty carbs. Does the bike have an inline fuel filter?

Regarding the carb overflow -

Fuel coming out of the overflow hose (the little hose on the bottom of the carb) is the common symptom of the 3 possible problems described below. Remember - NO SMOKING or other activities that could ignite the fuel while working on carbs!

The float valve is not sealing. This may be (and probably is) just a matter of some minor dirt in the float valve and is very simple to remedy and can be done with the carbs still on the bike. Turn off fuel; drain carb by loosening big brass screw near bottom; and remove the 4 little screws on the bottom of the carb bowl. This will enable you to remove the carb bowl. You will then see the float. If you carefully remove the float you will see a stubby little needle that mates with a brass orifice; together, these two pieces are the float valve. Assuming there is no obvious damage to the needle or seat, use a Q-tip and some carb cleaner to clean the seat of the orifice and the needle. Be careful not to bend the tang that is attached to the float. This tang is the piece that the bottom of the float valve needle rests upon, and it determines the fuel level in the bowl, so bending it will change the fuel level. With the float valve cleaned it should no longer leak. To prevent a re-occurrence a quality inline fuel filter should be installed between the fuel tank and carbs. If there was damage the needle and seat should be replaced as a set; they are available.

The brass overflow tube inside the carb bowl is damaged. When you remove the carb bowl you will see a brass tube attached inside and rising toward the top of the bowl. This is the overflow tube and it leads directly to the overflow nipple on the bottom of the carb. Normally, the fuel level within the bowl rises somewhat close to the top of this tube. If the tube becomes cracked or separates from the bottom of the carb bowl fuel will flow through it and out through the overflow hose. Checking the condition of the tube is very easy after you have removed the carb bowl from the carb. Simply hold the bowl level and fill it up near the top of the tube with water or alcohol and see if it leaks. A slight crack in the brass overflow tube can be difficult to find. You can connect a rubber tube to the overflow nipple, fill the bowl with water, put finger over the open end of the brass overflow tube and blow in the rubber end and look for bubbles. If it does the best remedy is to replace it although some folks have found creative ways to repair them.

The fuel level is set too high. This condition occurs when someone has bent the float tang as mentioned above. This condition can be checked using what is referred to as the "clear tube test." The test involves attaching one end of a clear piece of flexible tubing to the carb drain hole and holding the other end of the tube above the bowl/carb joint. When the fuel is turned on it should rise in the tube to a level 2.5 - 4.5 mm below the bowl/carb joint. If the fuel rises higher than that level it may run into the cylinders or over the upper end of the brass overflow inside the carb bowl (mentioned above) in which case it will run out the overflow hose. This condition is corrected by removing the float and gently bending the tang to raise the float valve needle position. Doing this may take several tries before achieving the desired fuel level.

Correcting each of these three conditions involves removing the carb bowl. This task can be made easier if a short screwdriver bit is used, and depending on which carb you are fixing a mirror may help you locate the screws on the bottom of the carb bowl. Also, it is not a bad idea to have a new carb bowl gasket available in case the old gasket is damaged while removing the carb bowl. Ed

thanks so much so far. not sure if it has a fuel filter. I didn't put one on where would I look. appreciate all the info

would you recommend using a fuel filter if so which one?

Yes; I highly recommend using an inline fuel filter. Here's a link to what I use. There are less expensive ones out there too. Ed

www.kzrider.com/forum/2-engine/592889-19...orly-when-hot#636322

Hi markwood2868. It seems you have been pointed in the right direction. There are many knowledgeable people here on the forum and also a wealth of information already posted. I managed to return my 79/650 to running condition just by following advice and learning some things the hard way.

Carbs and leaks tend to be the basis of most RPM issues. I personally started my project with a full, part by part carb clean and moved to other areas knowing I had the carbs figured out.

I really got my engine running great after I started looking at points and timing. There is something called the timing advance sitting behind the point plate. And it has something to do with offsetting the timing based on engine speed (RPM). Sometimes these parts need to be cleaned and lubed to function correctly. I suggest a new set of points and condensers just to be certain they are new and working right.

I've also read that the choke part of the carbs sometimes cases a stuck RPM range. This is attributed to a passage in the carb being blocked up. Make sure your throttle cables are moving freely and the throttle itself.

Sounds to me like when you are riding a gust of addition air is pulling into the carbs/valves and causing the increase in RPMs. Check the airbox, make sure it is sealed, air filter and that all air hoses are good.

In the last 10 months I've learned plenty about my bike and still have plenty more to understand and wrench. But that's the heart of the experience. Wrench it and note the results and with some patience it will get you to the finish line.

update: just about any in line gas filter is better than no gas filter on a good old bike.

... just my 79 cents

Thanks again. Just got carb boots and fuel filter in mail. Gonna start there and clean up the carb that's dripping gas. All the information is greatly appreciated