Idle Issue (I Think) on CB650

[WingNut]

 

I've got a CB650 that's over 10 years old, but it's only got about 4000 km on the clock and still looks practically brand new. So it's obvious I hardly ride it. I know, that's not good for a bike, but I just don't have the opportunity to ride it more often. It is what it is. 

 

Anyway, I started having a recent issue with the idle in a way. It just started happening the last few times I drove it. I realize it can be many different things as the cause, but I'm just trying to get a rough idea of what might be involved in repairing it. I'll end up taking it into Big Wing I assume, but trying to get a rough idea in advance if this is going to be an expensive repair or not. 

 

A friend who knows a bit about bike repairs told me the challenge can also be that some Service Centers might end up fixing a few different things, without really knowing what's the exact cause, and then you're spending a lot of money possibly repairing things that don't need to be repaired, before (hopefully) finally getting to the root of the problem.

 

Basically, when I first start the bike cold, the idle RPMs jump around (up and down) a lot, not normal. Sometimes it also stalls while it's warming up. Once it's warmed up a bit then the idol becomes a bit more stable and steady, but often when I'm driving in the low rev range of around 2500 to 4000 there's hardly any power when I first hit the throttle. I might even get on the throttle hard at those low RPMs and the bike doesn't respond for a couple seconds, but then suddenly lunges/jerks forward very hard. It's not fun. 

 

Ever since I got the bike, since it was new in fact, I always felt there was some small dead zones in the lower rev range when I would hit the throttle hard. But I always thought this was normal because I was trying to give it too much power at very low revs. So maybe the problem has always been there to some degree and I was just thinking it was normal. I don't know though. 

 

Any thoughts on what might be the cause though would be much much appreciated. If the ECU would show some error codes I guess that might also help the mechanics to diagnose the problem. 

[novacova]

The only time I’ve ever experienced anything like this was water in the fuel and air leak.

[London Lowf]

I had similar inconsistent running on my low-mileage (800 miles in the last three years) scooter back home in the UK - a new spark plug sorted it out. A cheap DIY fix and worth a try.

Edited Wednesday at 11:59 AM by London Lowf

[WingNut]

14 minutes ago, novacova said:

The only time I’ve ever experienced anything like this was water in the fuel and air leak.

Thanks. I already ran a couple of bottles of fuel injector cleaner through the tank. Didn't seem to make any difference. How would water get in the fuel tank though? 
 

An air leak would be in one of the hoses? Normally one connected to where?

[WingNut]

11 minutes ago, London Lowf said:

I had similar inconsistent running on my low-mileage (800 miles in the last three years) scooter back home in the UK - a new spark plug sorted it out. A cheap DIY fix and worth a try.

Thanks. Spark plug was my initial thought too. Could be that I guess, but seems too simple. I would have to have all 4 changed I guess. I wouldn't be able to DIY that though. 

[novacova]

21 minutes ago, WingNut said:

How would water get in the fuel tank though? 
 

An air leak would be in one of the hoses? Normally one connected to where?

You mentioned that you haven’t been using the bike much, alcohol in the fuel attracts moisture. Or perhaps water in the fuel at the filling station. 
 

There could be an air leak at the intake. The rubber boots get hot and can develop cracks/leaks. A way to check is to start the bike, get a propane torch (please don’t light it!) and blow the propane around the intake, if the engine starts to rev higher, then you found a leak. 

[WingNut]

2 hours ago, novacova said:

You mentioned that you haven’t been using the bike much, alcohol in the fuel attracts moisture. Or perhaps water in the fuel at the filling station. 

Thank you. Do you think there are any products made by STP or Liqui Moly available in Thailand that I can add to the fuel tank to dry out and remove any water from the fuel system?
 

2 hours ago, novacova said:

There could be an air leak at the intake. The rubber boots get hot and can develop cracks/leaks. A way to check is to start the bike, get a propane torch (please don’t light it!) and blow the propane around the intake, if the engine starts to rev higher, then you found a leak. 

I would feel a bit nervous spraying propane gas around or into the intake myself. I think there are 4 of the rubber intake boots though on my bike. So if the mechanics were to find an air leak at the intake and all 4 rubber boots need replacing, would this generally be a difficult and/or expensive job?

 

 

[novacova]

12 hours ago, WingNut said:

Thank you. Do you think there are any products made by STP or Liqui Moly available in Thailand that I can add to the fuel tank to dry out and remove any water from the fuel system?

Personally don’t use those products, many of them are alcohol based. Though some folks swear by them. & personally only use clear fuel, non ethanol fuel in the tank, the yellow nozzles @ caltex ptt & pt in the 600cc & 300cc since those two don’t get ridden much anymore.

12 hours ago, WingNut said:

would feel a bit nervous spraying propane gas around or into the intake myself. I think there are 4 of the rubber intake boots though on my bike. So if the mechanics were to find an air leak at the intake and all 4 rubber boots need replacing, would this generally be a difficult and/or expensive job?

Propane is fuel and won’t cause any harm. You can do the same with a can of carb cleaner. Personally I’d try to figure out the source of the issue first. 
Generally I work on my own vehicles, so not sure what it would cost you, maybe ~1500฿ for the parts? 

[WingNut]

37 minutes ago, novacova said:

Personally don’t use those products, many of them are alcohol based. Though some folks swear by them. & personally only use clear fuel, non ethanol fuel in the tank, the yellow nozzles @ caltex ptt & pt in the 600cc & 300cc since those two don’t get ridden much anymore.

Propane is fuel and won’t cause any harm. You can do the same with a can of carb cleaner. Personally I’d try to figure out the source of the issue first. 
Generally I work on my own vehicles, so not sure what it would cost you, maybe ~1500฿ for the parts? 

Thank you for the additional feedback. This morning I spoke with the service department at Big Wing. The guy mentioned a few possible issues, nothing air intake or boot intake leak related, but unfortunately some of the words he used to describe the possible problem also weren't familiar to me.
 

When you talk technical stuff in Thailand they often have their own reference words that they have created from English words which are then hard to decipher if you don't know the reference. One thing he mentioned was something about cut off it sounded like. I think that might be something electronic to do with the throttle control. A possible issue I read about online before was something to do with the Throttle Position Sensor (TPS). So maybe that's what he was referring to. Wouldn't be a really expensive repair I don't think. He also suggested spark plugs as a possibility.
 

He said the erratic idle I have when first starting the bike is not unusual if the bike sits a lot. But the power delay in the low rev range is not normal he said. Also, since the engine warning light isn't showing up on the display, he said there most likely won't be any ICU error codes that can be used to try and identify the problem. 
 

Anyway, I've got an appointment now for them to go through it and try and find the problem. Unfortunately the queue is about two weeks out from now, but there is actually no rush on my part. I don't drive it during the rainy season anyway.

The cost will only be around 320 Baht he said for them to try to identify the issue. Seems worth to me it rather than messing with it myself and getting my hands dirty. I can do simple things like battery changes and small adjustments myself, but this would probably be over my head anyway. And since it could be a few different possible things, it seems better to just take it in. Do you agree?

 

Anyway, I'll update this post again after I take it in to Big Wing to let you know what they find. Thanks again. 

[Agusts]

Also check battery voltage, see if it changes when idling is not stable. Someone mentioned it to me when I asked about this... 

 

I'm guessing the voltage is shown on CB650 dash display......? On my Forza 350 when idling the rpm needle just very slightly (maybe 100rpm) moves up and down - at all times, cold or hot, and the battery voltage disolayed also changes about 0.1v to 0.2v. I am told the battery is weak...! 

 

I don't have other symptoms and the bike starts okay, so not tackled the issue yet..., I personally think it might be other issues too.... Never seen weak battery does this on other bikes over the years...!? 

 

[novacova]

55 minutes ago, WingNut said:

One thing he mentioned was something about cut off it sounded like.

You think he meant the kill switch? The symptoms don’t seem to resemble.

The tps should throw a code.

As usual, difficult to diagnose without inspection. Hope everything works out for you.

 

[WingNut]

1 hour ago, Agusts said:

Also check battery voltage, see if it changes when idling is not stable. Someone mentioned it to me when I asked about this... 

 

I'm guessing the voltage is shown on CB650 dash display......? On my Forza 350 when idling the rpm needle just very slightly (maybe 100rpm) moves up and down - at all times, cold or hot, and the battery voltage disolayed also changes about 0.1v to 0.2v. I am told the battery is weak...! 

 

I don't have other symptoms and the bike starts okay, so not tackled the issue yet..., I personally think it might be other issues too.... Never seen weak battery does this on other bikes over the years...!? 

 

Thank you. I actually had a battery issue on this bike in the past after I changed a battery and didn't seat one of the cable screws properly. But symptoms were very different. Sometimes bike just wouldn't start or power would just cut. After I tightened the screw down properly the problems instantly went away. I doubt this is a battery issue though this time the problem I'm having now. 

[WingNut]

1 hour ago, novacova said:

As usual, difficult to diagnose without inspection. Hope everything works out for you.

Cheers. I agree. I'll keep you posted. I am starting to remember now that when I first noticed the problem late last year I had did some digging online and watched a few YouTube videos and various sources were pointing to a possible TPS issue. But I never investigated that possibility further. Then, I began traveling, and doing some other things, and kind of just forgot about it. So, now, six months later I am back at it. Hopefully I get to the bottom of it this time. 😊