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Engine Stutters and low rpms

18K views 44 replies 7 participants last post by  erikmathewmalone8787  
#1 ·
Recently my bike has been acting really weird. When I go to start it, it starts up without an issue, but it idles pretty choppy like it’s starving for gas or something. When I’m riding it, during low rpms it’s very choppy and studders. The sound of the engine sounds like it’s carbed or something. The second I hit higher rpms, the sound goes back to normal and it the bike accelerates like now. This issue only happens at low rpms though.
 
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#4 ·
I actually tried that this morning but no luck. Last Thursday, I noticed there was a grinding noise coming from my stator, didn’t think too much of it so I rode the bike all day. In my mind,I just assumed that once the bike warmed up and the oil was flowing, it was stop the noise. Well went I went to ride the bike back home, it cut off on me right at a traffic light. When I went to start it, it wouldn’t turn over. After letting it sit for 10-15 minuets, it would start at all. Luckily it cut off right in front of a motorcycle repair shop, so I was able to push it there. I had the guys take a look at it and was told that the screw holding the stator broke off and that caused the stator to come loose. He was able to clean the area and screw the stator back with a new screw. After that fix, the bike rode fine all day. I went to fill up my tank and drove it about 20 miles to my friend’s house. I parked my bike outside and the next morning went to drive back home. The bike started without any issues but when I was roughly 5 miles from my house, that’s when it started acting the way it is now. I thought it might have been bad gas, so I went out and bought Seafoam to add to my tank. Almost at a half tank now and still having the issues. I’m not sure if this could be something caused by the stator? I would think that isn’t the case, because it starts up okay without any issues.
 
#9 ·
I can't see the attached image, but if it's the crankcase breather hose, I can't see how it can be causing any running issues, although it would allow crankcase fumes, which are pretty toxic, into the environment and might also allow ingestion of debris into the crankcase, both of which are bad. I'd still advise double-checking with the routing diagrams in the service manual, to make sure the routing is correct, unless you have reason to be sure.
 
#10 ·
I’m 100% sure it’s th crankcase breather hose. What I don’t get is how this just happened over night. I rode th bike all day without any issues. Next morning, went to ride and almost made it home and then this starts. I took in consideration what someone said about the charging mechanism possibly being comprised and put the bike on a tether so that the battery would be completely full, but still having the same issues. Idk, after getting gas the previous night, that’s when I noticed the issue. My tank is almost on empty, so I’m going to run seafoam in it again with another fresh tank of premium gas and cross my fingers. It’s really weird because on low RMPs is where the issue is. Once I get into the higher RPMs everything is back to normal. When it idles, it sounds like it’s carbed and not jetted if that makes sense.
 
#12 ·
Thanks for reposting the photo Samantha. As I've said, I don't think the breather hose being unplugged had something to do with your problem. I find it strange that the engine operates fine under higher loads. That would imply some problem with fueling, that is specific to low-load operation and the only things that come to mind are the IAPS, which you have tested and perhaps the primary injectors (although I've no idea if clogged primary injectors for instance, would allow the engine to run fine just because the secondaries have kicked in).

How and when does it transition from running badly to running fine? (Always at the same engine speed? Is the transition gradual or sudden, etc.)
 
#13 ·
It’s really all about the rpms. When I let it idle, it sounds rough. It seems the second I go past 4K rpms it instantly goes from sound like shit, to normal. It happens suddenly. I’ve been running seafoam through the gas take like crazy. Is there something I can do it clean the injectors?
 
#14 ·
I generally am suspicious of Seafoam and similar products. They seem to me to border or fall into the snake oil category, but I may be wrong. I also find it curious, that your problems happened to start right after your stator trouble, but perhaps it is just a coincidence. I can't imagine how they would be related. You can take your injectors to a shop to have them cleaned, or, if you want to do it yourself, I'm sure you'll find plenty of methods on the Internet, although I can't comment on how effective they'll be.

I still find it hard to believe that the primary injectors will be clogged up enough to prevent idling (which takes very little fuel) but this doesn't affect engine operation at higher loads at all. Does it always clear up when crossing 4k rpms, irrespective of the throttle? I wonder if your model has some other subsystem, which gets switched based on engine speed. You don't see FI flashing on the dash, do you?
 
#15 ·
No FI code at all. This morning, I figured I would give disconnecting the IAP one more time to see if it would help. Only difference is that I actually ran the bike with it disconnected and of course that threw a code out. I powered the bike off and reconnected the IAP and the bike actually sounded normal. The throttle response was back to normal and I thought it was fixed. After letting it run for a couple minutes, I powered it off again to so that I could run upstairs to grab my gear and take it for a test drive. When I came back downstairs and powered it back on, the problem seemed to have come back. This time it’s not as bad as it was before, but it’s still there. I think I’m just going to bite the bullet and take it into the shop.
 
#17 ·
Yes, that is correct. To further clarify, the bike idles right at 1300 rpms. It just sounds like it’s starving for gas or air at low rpms. While cruising under 4/5k rpms it sounds horrible, but the instant in crosses into higher rmps it’s right back to sounding normal. I was able to get a video while riding, but can’t seem to figure out how to post it on here.
 
#20 ·
It sounds like it's not firing on all four, both when idling and when under 4k rpm, but then again, if it didn't, I wouldn't expect it to idle at the proper speed, at least not if the K6/7 doesn't have an ISC valve, which I think is the case. Given that it suddenly starter running properly at idle, after you reconnected the ISC, I suppose it's not the injectors, at least not a case of the primaries being gummed up, as they wouldn't be likely to clear up for a few minutes only. This leaves some sort of control failure as the most likely cause, only you're not getting any codes thrown and it's not the IAP.

Have you checked your charging system, or at least checked your voltage at idle and at 5000rpm? Perhaps it's struggling to keep up at lower speeds due to your recent incident. Low system voltage, can cause all sorts of weirdness.
 
#21 ·
It may be a coil. I had a similar incident with a yamaha right after washing it and getting water into the area where the spark plug goes in. The bike ran like yours. I identified the bad coil by using a temp gun at the headers. One exhaust pipe was running much cooler than the others. So the bike was mostly running on 3 cylinders. It is easy to check.
 
#24 ·
You should borrow a temp gun from somebody, or try placing a drop of water and see how it evaporates. But if one cylinder is different you would verify this with a temp gun anyway. Also you could pull the coils and test them individually. I don't know how to do it but you could probably find out in your manual or do a search.
 
#25 ·
So in theory, couldn’t I just take turns unplugging each coil one by one to isolate the one that’s bad? Right now, we’re suspecting that at least one of the coils isn’t working probably, so if I remove the power to one that is working properly the bike will idle/behave worse than it is now. If I figure out the one that’s not working, and unplug it the condition of the bike will remain the same. I hope that makes sense?
 
#26 ·
To check the battery, all you need is a DMM (probably what you call voltage meter, but it measures more) and knowing how to use it. It doesn't have to be very expensive, just decent, but almost anything will do for most applications. See a couple of tutorials/videos on how to use it for voltage measurement and see what you get. You would normally expect >12.6V with the ignition off and the battery properly charged. At idle it should be more, but not more than 15V. At 5000rpm, it should be between 14.5-15.5V.

I'm a little confused about the rest. Assuming the coil came into the picture because of my comment that it's not running on all 4 and that "heat gun" means an IR temperature meter, presumably to be used to measure the temperature of each exhaust pipe, note the following. A faulty coil would likely throw a code (also that depends on the mode of failure, as is the case for faulty injectors) so I'm not saying it's the coil necessarily. It isn't necessarily running on less than 4 cylinders either, as engine sounds can be deceptive. In order to see if one cylinder isn't firing you can do the following: With the engine *cold*, start the bike and let it idle for a couple of seconds. About 5-10 should do it. Then shut it down and *quickly tap* each exhaust header with your fingers. Don't let them touch for more than a split second, for obvious reasons. If one is significantly colder than the others, or even entirely cold, you should notice.

Even if it is running on 3 though, the most important question is why. Whatever it is, it must be intermittent, engine speed related and probably related to that stator failure (barring a coincidence, which is always a possibility). A coil, or injector failure doesn't sound likely, as it doesn't match on two of the three counts.
 
#29 ·
So I took your advice and turned the bike on for 10 secs and immediately turned it off and felt each header to see if there was a difference in temperature and I could not feel one at all. They all seemed equally hot. I guess I just have to wait until my DMM comes in tomorrow to check the charging system.
 
#27 ·
Definately do the tests for your charging system. The manual is easy to follow on the procedures for checking the stator and the R/R. I used a $10 DMM from harbor freight and it worked perfectly to help me find my problem.

Also check your plugs and the coils. It's possible that a plug is bad. Could've happened to go bad at the same time as the stator, maybe got fouled when the bike died on you, or any other reason. I did a lot of mechanical work on cars before I started riding bikes and I've seen a fouled plug run better at higher rpm.

Also you should have run enough seafoam through it by now. Do your next check with just premium gas in the tank.
 
#31 ·
Read my thread here https://www.gixxer.com/#/topics/824316 .

Mine was the exact same issue originally. Then I crimped on some connectors and it was fine until they corroded and caused too much resistance.

I just removed the connectors and soldered my stator directly to my rectifier which is the best electrical connection you can have there. Much better than even the factory connectors. No more problems for me.

I also made my own relocation bracket which was really easy and very beneficial. I wanted to post a how to but I can get any pictures to post. Even when I resize them they come up as a broken link. And they are saved in the right format too.
 
#33 ·
Lol I’m going to be 100% honest. I don’t think I’m that advance to try and solder those wires together. I’ll rather just replace the connectors. Are the ones I posted in my previous post the correct replacements? Like I mentioned in my previous post, even if this isn’t the issue itself I definitely need to replace the connector regardless.

A note on connections: generally an electrical connection has to have sufficient surface, if it's going to have low resistance. Besides beefy lugs, this also means clean and tight mating surfaces, as both of these affect the effective contact surface for obvious reasons. Both ways of achieving a connection, i.e. electrical connectors and solder joints can be made effective, but care needs to be taken with each. A connector has to be of adequate size and proper type and care needs to be taken when crimping the lugs on, to ensure that the crimp is tight enough to compress the strands of the wire and maximize the contact surface.

Similarly, a solder joint needs to be made so that the solder has wetted both wire ends (.i.e. penetrated between the strands) and that the wire ends make contact along a sufficient surface, which is completely saturated with solder. It's easy to twist the wires loosely together and apply some solder, when they're still cold, which just forms a beefy-look jacket around them and is inadequate both mechanically and electrically. And of course, even a good solder joint has the shortcoming of making maintenance tasks harder.

So, what were the exact voltage numbers then, and how were the tests carried out?
When I tested the battery with the bike off, the voltage was roughly around 12.54 V. When I turned it on at idle, it shot up to 14.6 V. When I raised the rpms to 5k, it fluctuated between 14.9 - 15.1 V. When I tested the stator resistance, I changed my settings on my DMM to omes which gave me a reading of 1. I took the positive lead of my meter and inserted it one of the legs of the connector and took the negative lead to the negative pole of the battery. The numbers didn’t change at all, which I understand to mean there is not an issue. When I tested the stator voltage output, I switched my DMM to AC and inserted the positive lead from my DMM into one leg of the stator connector and the negative lead into another leg. The reading I got at 5k rmps was around 80 V. Just wanted to point out that these test were done using the connectors coming from the stator.
 
#32 ·
A note on connections: generally an electrical connection has to have sufficient surface, if it's going to have low resistance. Besides beefy lugs, this also means clean and tight mating surfaces, as both of these affect the effective contact surface for obvious reasons. Both ways of achieving a connection, i.e. electrical connectors and solder joints can be made effective, but care needs to be taken with each. A connector has to be of adequate size and proper type and care needs to be taken when crimping the lugs on, to ensure that the crimp is tight enough to compress the strands of the wire and maximize the contact surface.

Similarly, a solder joint needs to be made so that the solder has wetted both wire ends (.i.e. penetrated between the strands) and that the wire ends make contact along a sufficient surface, which is completely saturated with solder. It's easy to twist the wires loosely together and apply some solder, when they're still cold, which just forms a beefy-look jacket around them and is inadequate both mechanically and electrically. And of course, even a good solder joint has the shortcoming of making maintenance tasks harder.

So, what were the exact voltage numbers then, and how were the tests carried out?
 
#36 ·
I'd say first figure out what's causing your problem, with minimal interventions, that could complicate matters before you do so. Then fix what needs to be fixed and make sure it is fixed. If the voltage at the battery is >14V while the engine idles choppily, then I don't see how that, or the charging system might be the issue.
 
#37 ·
Figured I'd add my two cents:

First off, the manual is your friend for troubleshooting(as others have already recommended). We tend to skip over it, but half the answers are in there.

So i had something similar to this on my k6 750. I haven't heard the video/sound clips you posted but will take a look later tonight. For me my fix was simply to replace the spark plugs. The bike was around the mileage of needing them, so i randomly started there and got lucky. Spark plugs and coils a bit of a pain to get to (not really... a pain for me due to using tiny long hex keys..and then having to torque these by feel rather than a wrench, since i cannot afford to buy tiny accurate instruments/tools and it wasn't a deal breaker if i) but its a simple thing to check and if you are checking your coils, you are practically there.

That being said, i do agree with dpapavas on not adding new problems before fixing the one at hand. good luck and keep us posted.
 
#39 ·
It sounds like it's not firing on all four, both when idling and when under 4k rpm, but then again, if it didn't, I wouldn't expect it to idle at the proper speed, at least not if the K6/7 doesn't have an ISC valve, which I think is the case. Given that it suddenly starter running properly at idle, after you reconnected the ISC, I suppose it's not the injectors, at least not a case of the primaries being gummed up, as they wouldn't be likely to clear up for a few minutes only. This leaves some sort of control failure as the most likely cause, only you're not getting any codes thrown and it's not the IAP. Have you checked your charging system, or at least checked your voltage at idle and at 5000rpm? Perhaps it's struggling to keep up at lower speeds due to your recent incident. Low system voltage, can cause all sorts of weirdness.