Hi folks. I'm new here but have been loitering around these forums for years, and look forward to interacting with like-minded people.

I have a 2009 Fatboy with the 96ci engine. Everything is stock on it and currently has 85,000 km on the clock (53,000 miles). It is meticulously serviced. Has new cam chain and tensioner, new check valve and line to pressure regulator, new pressure regulator, fuel filter, and fuel pump and all new hoses in the tank and has perfect fuel pressure. Has new battery, new coil, new wires and new spark plugs, battery cables are tight in good condition with good connections. New fuses, relays and starter clutch.

First start up is no problem when cold. It's when it gets up to operating temperature and I stop for petrol the problem happens. When I go to restart it, it cranks and turns over (sometimes very slowly) but won't start. I can smell gas from the pipes, can hear the odd small backfire but no smoke coming out the air intake. I can't hear anything odd around the compensator area.

If I leave it switched off for one or two minutes it will then reluctantly fire up. It always runs perfectly when riding it. Never misses a beat. I've tried hitting start before the fuel lines are primed but that does nothing. Sometimes when I get home I try to replicate the problem in the shed by turning it off, then try starting it and it fires up no problem! It's quite infuriating and has been doing it for years.

I thought maybe temp sensor, crank sensor, stock compensator (suspect #1), voltage regulator, bank angle sensor, injectors, sticking valve. It has thrown no codes.
At a bit of a loss really (financially and mentally).

I look forward to any ideas. Thank you.

 

My last Yamaha would turn over super slow once it was hot, It was the starter motor

 

Without codes to direct your search, it boils down to compression, spark, and/or fuel.....

Heat soak seems to be the trigger to your issue.....

Also the fact that it cranks over, but won't start, and then you smell gas... seems to point to a temporary loss of spark....

When a motorcycle won't start, only when hot, it can be due to a weakness in an electrical component. When a weak electrical component gets hot, the resistance increases, and the component will have a harder time operating properly..

Sounds like you have done most of the checks I would do... ie: battery and connections to start with.. I just want to double check that you've checked where the ground wire connects to the frame...? That one is missed by many people...

You have replaced many of the other culprits I would check next... spark plugs, spark plug wires, and then test the coil....

Assuming that all the parts you have replaced are good parts and installed properly, that leaves fewer possibilities...

Just for your future reference.... it sounds as if you were just throwing parts at it... If so, that is why I always advise to diagnose first, replace parts second.... If you find a part that checks out to have failed.... then you know it was the problem (or part of it) when you replace it... Should the problem persist, you can recheck the new part, it's connector, and/or its wiring before continuing on with your diagnosis... Sadly, sometimes new parts fail too... You don't have that luxury of knowing what new part to recheck, when just throwing parts at a bike, waiting for it to work correctly..

Next, I would pull and check the CKP (crank position sensor) next.... I have read of CKP failures without throwing a code...

When hot and not starting, you could do this CKP check. I have not used it yet, but copied this procedure form a post many years ago. It was written in response to some misinformation given on testing the crank position sensor..

"1. there is no batt voltage to the CKP, period
2. the pulse is not a pulse but a constant a/c voltage PRODUCED by the ckp sensor itself
3. the drop in a/c voltage caused by the missing tooth tells the ecm what part of the stoke the engine is on, and the slow down of the crank (upon compression), and lower a/c voltage tells the ecm what phase the engine is on.
4. the only way to test the ckp, is to UNPLUG it from the ecm, put a multimeter on the 2 wires, (R/B and B) and crank the engine. it should show 1-5 VA/C.
5. this is hit or miss, some ckp show good when they are not, but if it shows bad, it is."

There is also an ohms check for the CKP:

"If the internal resistance value is 200 to 1,000 ohms (depending on the reference value), the sensor is OK. If the value is 0 ohms, there is a short circuit, and in the case of M Ohm there is an interruption."

If you don't have the electrical diagnostic manual for your year/model bike, it's times like these it proves it's value... but even without it, I would google or search you tube to see how to test various components, before replacing them...

Electrical issues require a systematic approach, and persistence to solve... You are putting in the time & effort... you will figure it out...

Good luck with your continued diagnosis and keep us posted on your findings...

 

I just had a similar issue with my 05 night train, finally changing the engine temp sensor, appears to be fixed, ran great when I took it out yesterday, today I’ll take it for a good run and make sure

 

Thanks for your reply. The starter was tested when the starter clutch was installed and was working as it should. I probably should have mentioned this in my original post.

 

Thank you for your suggestions. They are all on point.

Indeed, electrical issues do require a systematic approach. While I have the ability to install new components on motorcycles I have always been a wee bit stand-offish and hesitant to perform electrical testing. Perhaps this is evident in my original post by the way I just throw parts at it. I've always been that guy who creates fires or electrocutes himself when testing. I have found on many occasions that one of mankind's greatest inventions and investments is the humble fire extinguisher.

However, I will try to test the crank and temperature sensors, retest the coil, plugs and wire and let you know how I get on.

 

That's great. And a cheap fix, too. Let us know how it goes over the course of the next few rides.

 

I was going to suggest starter clutch. I was having similar issues and replaced the starter clutch with an All ***** starter clutch. Did the trick for me.

 

 

I don't want to sound too excited but I think the issue has been solved. I replaced the engine temperature sensor and it wasn't the problem but looked as though it needed changing so that made me feel a bit better.

When I replaced the crank position sensor the problem went away. I couldn't believe it. I took it for a 50 mile ride then pulled over, turned it off, opened the fuel cap (issue seemed to happen mostly at petrol stations), then hit start and it fired into life. I must have tried it a dozen more times and no problem. I will keep posting updates even if the issue doesn't come back.

To access the temperature sensor I needed to remove the horn. Upon reinstalling I heard some rattling like steel ball bearings inside. I took the horn off and rotated it to get whatever was in there out. Four or five small stones dropped out. Going for a ride afterwards I noticed that the sound of what I have always thought was the engine tappets, was no longer present!

When changing the crank position sensor I noticed another wire above it. It has three white prongs sticking out of the fitting but there is no sign of a female connection anywhere. The wire joins up to others and heads to the rear of the motorcycle. Looking up the number on it it is a NAMZ Custom Cycle Molex male connector.
Does anyone know what that is for? I have added a photo for reference. Thank you.