running great then revs drop

Hi There,
Had this problem for some time tried many and varied things to fix. Even had it to my mechanic.

She normally starts just fine, of late sometimes when pressing the starter nothing for a bit press a couple of times and she is up and going. Anyway that is not my main problem. She runs just great most of the time but say after 15 minutes of riding if I pull up at lights revs drop away to about 400rpm engine sounds muffled maybe running on only 2 cylinders?. I give her some throttle revs pick up and I am away get to the next set of lights same deal. If I let her cool down for a bit she will not do it for a little while but then sure enough start doing it again.

This is really annoying me now, it has affected my riding I am hardly riding at all knowing this will happen and of course I do not wish to cause anything to go wrong in a major way nor do I wish to be broken down on the side on the road.

I dont mind paying to have her fixed but to this point none of the mechanics I have been to can isolate the problem.

I have fitted another IC Igniter, new plugs and leads the mechanics have done most electrical tests and tell me all seems ok.

Any Ideas? It is really giving me the u know whats. I just want to ride.

Thanks :Brad

Check the "coil melted?" thread here. Wiredgeorge's post in particular.

I think it may be coil related. It's been known that a coil may be fine when cold, but as it heats up it developes a short inside. It would test ok when cold and then konk out miles down the road.

Is it associated with a loss in power, or does the bike respond normally other than a low idle?

If there's a loss in power, you might check the connections between the coils and the ignition -- the wires are joined with connectors about halfway down on my SR, right under the side cover.

One of the connectors was barely making contact and I had intermittent power and rev loss. Everything would be fine, then suddenly the RPMs dropped, idle was really rough, and 5000 RPM was barely able to maintain 50 mph, let alone accelerate. Then the wire would shift, make contact, and it would be back to normal again.

Check your connections, and take a voltmeter with you. If the bike starts behaving thusly, stop RIGHT THERE and check all resistances -- between ignition and coils, coil internal, spark plug caps, blah blah blah.

On a hot day, ride on the highway for 15 or 20 minutes hard. Then pull off and idle. If it dies right away, it could be your valve clearances.

If the clearances are out of tolerance (too small), the valves will not seal when hot because they expand. As the problem gets worse, the symptoms will be just as you describe. The only thing that helps is to let it cool off. The problem will only become more frequent until you adjust the valves.

This one gets a lot of people. The first assumption is usually carbs or electrical (which should be checked also). A compression test won't show it unles it's really bad. By the time a compression test can be done, the head is too cool to show the problem.

If it's been awhile since you checked the valves, then it's time.

Post edited by: loudhvx, at: 2006/02/02 13:44

Thanks Guys.

I will check out your suggestions where possible this weekend.

Cheers: Brad

Can anyone tell me more about faults with the ignition coils. My mechanical / electrical knowledge is limited but I can follw instructions and I am a logical thinker in relation to problem solving.

Valve clearences were adjusted only a couple of months back hoping it would fix this problem(Did not fix).

I took her for a ride today about 25 miles, problem occured about half way home at lights but I just added throttle to stop her from stalling whilst at lights. Got home as I was pulling into drive oil pressure light also flicked on while revs were still ok at idle or faster.

I am thinking maybe coils thanks to your suggestions, if one of my coils is shorting when hot would the bike still run with revs ok on 2 cylinders because if I add throttle it runs ok? Would you expect the oil light to come if I have been riding on 2 cylinders for a while eg: Not pumping oil through the engine efficently?

The bike dosent come to a screaming halt when the problem occurs it just loses revs at idle and sounds muffled so to speak.

If it is one of my coils can I test somehow before I replace I understand in order to test I would have to test whilst the fault is occuring. If I can test what test procedure should I use?

Thanks for all your feedback this has at least given me somewhere else to start looking. The weather is just great in Australia just now luv to be able to take her for a long problem free ride on the weekend warm and sunny weather is forecasted for both days.

Cheers: Brad

Weather great in OZ? I have a buddy (named Doode) from down under who is a volunteer fireman and he has spent his summer chasing wild fires! We are having the same problem here in Texas but I guess the winter here has been great for riding except it has been a bit windy some days... OK... to your problems...

First, I don't recall if you have Mikuni BS34 carbs or the Keihin CV34. In this case it doesn't matter but you should mention that in this post. I won't move this to the carb section where it belongs since you mentioned a starting problem.

1st problem: starter doesn't engage every time
OK... here is the problem, the starter solenoid is a relay that closes when you press the starter button. The reason is that a voltage is passed to the solenoid that triggers it. The voltage runs to one side of the button ALL THE TIME and then passes through the button when it is depressed (and back to the solenoid). The button consists of a brass plate as the contact and the button itself has a brass stud pressed in. If they are dirty or worn, contact can be bad. Similarly, if you kill switch is dirty or worn, the starter button will not get voltage as the power going to one side of the button goes through the switch. Also, on most KZs, the power OUT of the button goes back to the main harness via a connector located on or near the steering neck which OFTEN can come a bit loose and make the connection sporadic. To fix these problems, open up your right switchgear and clean the contacts on your kill switch and button and coat them in dielectic grease. If anything appears worn; especially the button, replace it. There are replacement button kits on eBay all the time. You would do well to clean the contacts (both sides) with contact cleaner on the connector mentioned and coat them in dielectic grease.. even bending the connectors slightly so they will remain firmly seated when the connector is connected and move the connector so the tank doesn't rub it loose.

2nd problem: idle drops real low after warm
Thing to understand here is that your idle must be set when the bike is WARM! Not when it just comes off choke. ALSO, perform a service fuel level check. Often when the carb's have a low fuel level, they will run out of gas at idle somewhat and the idle can drop; especially on an incline. Also make sure your throttle cable is adjusted properly. That is, it has some slack in it.

Thanks for your post wiredgeorge. I fixed the stater switch problem as per your advice thankyou (Yes very dirty button).

We have been in fire season and the past 3 weeks have been very bad with high temps and strong winds, however all the fires are under control now. I have a couple of buddies in the Fire Service and they have been kept very busy. We have had some days with consecutive days of 43 deg C. However 27 Deg C is forecasted for the next few days.

As for my carbies they are Keihin CV34. Maybe I did not explain my problem clearly enough sometimes the bike does it when cold sometimes when warm and sometimes not at all. I do not think it is the carbies or the idle setting. It idles at 1000 rpm when hot and I have had the carbies sychonized and serviced all seems good there.

On the other hand I have checked my coils with the ohmeter and found a problem there.

Primary winding both left and right ok at 2.8 my manaul stated between 1.8 - 2.8 is ok. However on the secondary windings the left side is good 12.5 manaul states between 10 - 16 is ok, however cannot get any reading on the right hand side secondary winding at all.

Charging system has been checked all ok 14.5 volts at 4000 rpm, so it sounds to me like the RH side ignition coil is shot????

Does this sound like any of the symptons I described above?

Thanks: Brad