Re: R15 stalling when idling after being ridden. Help please

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Re: R15 stalling when idling after being ridden. Help please

Couple of things are possible:

• Issue with fuel pump, as you said rust in fuel tank and some debris could have stuck inside fuel pump.

• Change spark plugs.

Re: R15 stalling when idling after being ridden. Help please

Thanks for the reply. I just took out the spark plug and had a look. It looked dry and black. Doesn't it indicate a rich mixture? I cleaned it and put it back for now. What is the solution if I have a clogged fuel pump or line? I certainly don't want to face a fuel pump replacement

Re: R15 stalling when idling after being ridden. Help please

A pitch black plug definitely indicates rich AFR. Try cleaning the air filter. Air supply being interrupted could be a reason for rich mixture.
And, how's the engine temperature compared to a normal R15, while in operation?

Re: R15 stalling when idling after being ridden. Help please

Thanks a lot for the reply. Yes the plug looked black and there is a smell of petrol for at least a few mins once you start the engine. The ecu sends in extra fuel for cold starts masking any possible issues especially since the R15 doesn't have the O2 sensor feedback. So could the dark plug + fuel smell be indicating a timing issue causing a misfire/late ignition? The timing chain has never been worked on and I do remember getting a feeble grinding kinda noise from the engine which later disappeared.

The air filter was replaced two months ago by Yamaha. But I'll still have a look. Engine temperature I think is somewhat normal. Two more things that may be worth mentioning: 1) a wire inside the frame somehow got cut during a disassembly and the bike wasn't starting at all although the pump and starter were working. My local mechanic found it and fixed it with insulation tape. This happened a couple of years back. 2) The clutch bell was replaced during last service.

Please help me zero in on the issue. I'm trying my best to give you as much info as possible regarding the symptoms and service history of the bike. Thank you very much.

Re: R15 stalling when idling after being ridden. Help please

Just checked the air filter. It looks new. I'm surprised that there's no dirt on it after riding for a few months. Is there anything else I should check before I put everything back? Like the fuel lines or something?

EDIT: I just noticed some semi dry liquid in the air box upon closer inspection. It smells like petrol and I think it is petrol! I guess this is bad news in a fuel injected engine.

It's been two days since I posted the issue here. Sadly I'm not getting much help .

Re: R15 stalling when idling after being ridden. Help please

Bro, sometimes its just not easy to diagnose the real cause from textual understanding of the situation. i'm trying my best to understand...

I'm thinking where the petrol can come on the air filter. Its normally not meant to be there... Now, there are only 3 ways this can happen. 1. It got soaked when someone was cleaning/ handling it, 2. it came from environment outside, 3. it came from within the engine.

The 3 seems more likely to me, as I have known it to have happened before on other bikes, due to vaccum pipe being broken, or fuel pump being messed up for some reason.
Within point 3, one more (pretty rare) reason this might happen is that it could be oil's vapour coming from the breather pipe, which connects the crankcase to the air filter. Pardon my limited knowledge, as I was more on Pulsars and Dukes, so I don't remember if the R15 has this setup or not...


So, for now, check all the tubes and pipes around the Fi (behind the cylinder) for any leakage. Unfortunately, you might need to remove the fairings for this.

Because, from the reason you mentioned, I'm sure the problem lies around the Fi or before it.

@psr Sir, could you please help the biker brother? Thanks a lot.

Re: R15 stalling when idling after being ridden. Help please

First of all the stopping of the engine during a rest after riding for some time, and the black color of spark plug points to a combustion which is not ideal...
1. Is the plug black with dry deposit or wet deposit ? Dry indicates over rich AFR and wet deposit indicates oil leaking past the rings.
2. If it is wet, check the silencer outlet for wet oily deposit when it is cold..you can try putting a finger inside the opening ,rub it it on the inner side and inspect your finger to know of any oily deposit...if it is there then you have ring leak... this is a probability ,since you also have petrol/oil Vapour deposit inside the Air box, which is connected to the crank case breather. Small amount of oil /petrol Vapor deposit inside the Air Box is normal....it is the result of blow by...
3. If it is dry soot on the spark plug, check again the outlet of the Exhaust and see if the deposit you get is dry black coating..This can be due to a Throttle body not cleaned for long time, and also a Choke which is not operating properly(Not closing fully , and leaking fuel ,through choke circuit)..

If the Petrol tank is rusted, then get a new one...bad petrol and rust can pose many problems , and ultimately lead to engine failure...
Good Luck.

Re: R15 stalling when idling after being ridden. Help please

Thank you very much for the observations bro. Really appreciate it. I did have a look at the fuel lines under the tank when I checked the air filter and couldn't find any leaks or anything. Didn't check near the cylinder though. I'll do it today. Can the fuel come up because of a faulty valve or valve timing. Wouldn't it cause semi optimal combustion?

I changed the spark plug yesterday. The bike starts just as smooth as earlier without a hitch. But the smell of fuel while idling has kind of increased now .

Thanks for the reply sir. I hope you remember this old friend of yours . The plug had dry, black deposit. I put my finger in the exhaust and got some black powdery substance in my hand. The throttle body has never been cleaned I think .

There's fuel smell when the bike idles at cold temps. It's fuel injected so some fault is tricking the ECU with the AFR? Or could it be due to faulty valve timing? Is there anything else I should check?

Sir the petrol tank does have some rust in it but it is far from rotten. A new tank would cost me 7k. Can I clean it with wd40 or something like that?

The bike hasn't been a disappointment in the performance front. It accelerates quite well but as the speed mounts (above 70), I do feel some vibration from the engine. But it hasn't bothered me much as I can't usually do high speeds in the city and its suburbs.

Re: R15 stalling when idling after being ridden. Help please

Yes Mr.Saurav I do remember your name...
Happy you found only Dry soot on the spark plug and Exhaust tip..This just confirms, that your engine is running very rich...Possible cause is,
1. Throttle body not cleaned....The reason why this causes rich running is that the Valve overlap in any 4 stroke engine causes a little of the exhaust gases to come back into the inlet and because it is cooler, gets deposited..over time this blocks the small gap under the Throttle butterfly , which is there to let in some amount of air to idle...this means from start the engine will run rich, and when you close the throttle, no air reaches the inlet beyond the butterfly, and thus makes the AFR rich..this will make the engine suddenly rich and flooded. So naturally with more fuel and less air to assist burn, the engine will choke and die..Here is an interesting read....

THROTTLE DEPOSITS TROUBLESOME: CARBON BUILDUP CAUSES STALLING, OTHER COMPLAINTS - ISSUE ARCHIVES - Tire Business - The Tire Dealer's No. 1 News Source

Regarding Petrol tank, most modern tanks have Tin coating to solve rusting problem...so I don't know how your tank got rusted...the problem here is the rust has both very fine as well as hard solid material floating in Petrol...this may lead to choking of petrol lines, filter etc. But the worst part is it can damage the Fuel Pump by clogging it's inlet and pump will work without petrol going through it, thus making suction very high straining the pump and eventually killing it..
Another interesting read on R15 fuel pump....
Yamaha R15 DIY - Fuel Pump Repair - Team-BHP
Hope this helps.
Good Luck..

Re: R15 stalling when idling after being ridden. Help please

Thank you very much sir. Hope you're doing good. That was a very informative post. Really appreciate it. The throttle body has never been cleaned. That fuel pump cleaning procedure looks very difficult and dangerous. Is throttle body cleaning something I can do myself? I just don't trust the dealer. They'd say yes yes to everything but they never do it. I remember asking them to tighten the tappets and to lube the swingarm. They said it's not necessary and that it can get expensive if some faults are found .

The tank is not coated with rust but I do see some specks here and there at the bottom of the tank.

In the meantime I have raised the idling rpm to 1400 range (Yamaha recommends 1300-1500) although I don't think that was the cause. It was idling earlier at 1200rpm with the engine hot and radiator fan running.

Throttle body cleaning is the next step then. Thanks a ton sir.

Re: R15 stalling when idling after being ridden. Help please

there are two ways to do the cleaning....one is to remove TB and use carb cleaner spray to clean the muck , second method is to spray the carb cleaner into the TB and run engine for some time...the former can be done if you are technically inclined and have the tools and patience...it is the best method...the second is for technically challenged people , but comes with a dis-advantage in that, the muck is washed into the engine which burns it off. Downside is the muck may sometimes form a coating on the inlet Valve and become a carbon deposit over a period of time...
Another method would be to remove Air Box rubber snorkel , and while looking at the throttle body inside, prepare a petrol soaked piece of cloth , and while keeping the throttle open insert it carefully in the lower half of the TB and clean the deposit...this needs dexterity and careful action...
Here are some links to TB cleaning methods...

Cleaning Throttle Bodies - STAMP3

In ASC also you can remain by the side of the Mechanics while the TB cleaning is done to ensure that the job is getting done....
Choose whichever is acceptable to you..
Good Luck.

Re: R15 stalling when idling after being ridden. Help please

Thank you very much sir. Everything is starting to makes sense since you explained. I was wondering how the ECU could get the fuel ratio wrong under normal working conditions. The rich AFR wasn't what caused the throttle body issue but rather the dirty throttle body that did it. And since there's no O2 sensor feedback, fuel supply isn't regulated either. That definitely makes a lot of sense sir. Thanks!

Not sure if I can do the throttle body cleaning myself. I don't think I have the time or the technical ability to do a complete disassembly and reassembly of it. What I can try and do is that last method but even that'll be a challenge as I don't even know how to remove that horizontal inlet pipe in the air box.

I have one doubt sir. If I give it to the ASC and they do the cleaning without removing the throttle body, would an oil change afterwards prevent any potential damage to some extent?

Re: R15 stalling when idling after being ridden. Help please

Oil change is not required...the TB cleaning is simple and removes a little bit of deposit only and it will not get into the area where the oil circulates.
For TB cleaning you can also try one of the method mentioned ie., opening the rubber snorkel from the air box, and then spray either carb., cleaner or WD40 to the underside of the TB BUTTERFLY...https://youtu.be/41yFXjibtLY
Good Luck..