Tag: Fuel pressure

I always have had several projects of some description on the go, whether they be small electronics (ESP32, Arduino etc.), 3D printing or slightly larger; such as a classic car in pieces. I am also that guy that people come to know as a car/bike guy and they random ask if I am interested in old vehicles, not because I often need a vehicle myself but because I will take opportunities to get bargains ready for friends and family when they find themselves in need. (I like wheeler dealing and always find better bargains for others than myself)

Which brings us to August this year when my younger brothers partner informs me that as a surprise for my brother for her birthday she is going to do her CBT. He has been riding for about 10 years and she often goes pillion with him but thinks she might enjoy it even more if she had her own bike. This was rather fortuitous as 48 hours earlier Owen, a good biker friend, had made me aware that his mothers old YBR125 was once again up for sale, and he just needed it gone from his garden.

I have known Owen and his twin brother Patrick since I started riding having met them at the old Southampton motorcycle club, ever since we have all been friends as a little circle of bikers. They are good lad’s to know in a storm, as it were, being the first ones round to lay in the dirt with a spanner when you’re really in the shit and you need a vehicle running the next day.

The YBR in question was their mothers which had been purchased nearly new back around 2009, she didn’t take to biking so it sat in their garden. Getting regular MOT’s for a while and being used as a backup bike when one of the lad’s bikes was off the road. That was until about 4 years ago when it stopped wanting to run properly…

At the time they had diagnosed the fuel pump a not uncommon issue on these bikes, and had ordered an aftermarket replacement. A sunny Sunday I just happened to be round there catching up whilst they replaced it in the garden, however after replacing it the bike would now start but didn’t want to remain running. After I had left another issue had been theorised with the TPS after some static measurements but it had never been fixed.

As with so many little projects like this it sat for a further couple of years before his mother was happy to part with it for a sensible figure for such a project and was due to go to another friend in the group, however after a failed attempt to collect it in the back of an estate car and then to further collect it his loss was about to be my gain.

I took a look at the bike in it’s gardened state half the panels off and various things randomly disconnected, a collection of bolts lay in a side panel and a top box elsewhere in the garden. Owen told me the classic line of “It just needs a new battery and starter solenoid, then it should be had to get running”… I looked at it and knew that it wasn’t in terrible condition and had much life to give but also any number of things could now have become wrong with it after it hadn’t been used for the last 4 or so years, not being in the position of needing the bike leaves you with a clear focus. To me the risk level of this project and what it might need / cost and what it’s worth once running made it clear that I needed to get it cheap, £150 later and a elbow bump and it was mine.

The next challenge was collecting it, earlier in lockdown Ryan another mate within the biker group (he is in the process of trying to get his license) had been unlucky and been made redundant. However in a stroke of luck he had found a new calling as a motorcycle mover – Transportmybike – a few messages and a sweet mates rate deal was done to get the bike from Chandlers Ford up to my garage in High Wycombe.

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Knowing that the starter solenoid and battery were definitely gone, I got those on order straight away along with a Haynes manual so that i would have them there ready to further diagnose when the bike arrived. I am pretty handy at most things but from experience if it is available it always pays to have the right information to compare to hence the Haynes manual.

After fitting them I had an FI system error code flashing on the engine management light, looking at the connections that were loose and the state of them I was note surprised. A little contact cleaner and few cables reconnected and that error was gone though it took me longer to realise the fuel pump connector was not connected than I would like to admit. No remaining error codes and the bike now cleanly cranking but not starting the real troubleshooting would need to begin.

I checked the oil and a few other basic things with my father being a useful extra set of hands, with a little break cleaner in the bore the bike fired into life. It was possible to get it to run after letting the pump prime a few times but it would never continue and would not rev. Given the bike had been sat and there was signs of rust around the petrol tank inlet the prime suspect was dirty fuel of some sort causing issues and not enough fuel getting through to the injector.

The fact that it had fired and run was enough to give me confidence to get on and order the rest of the bits I figured it needed to be fresh and ready to go back on the road. So we proceeded to de-rust the tank and whilst I was waiting for that and the new tank seal to be ready I ordered a bunch of other parts and cracked on with getting them fitted.

So as it stands:

• New Starter Solenoid
• New Battery
• New Fuel Pump & Filter – Aftermarket
• New Fuel Pump Seal
• New Michelin Street Pilot Tyres
• New front brake pads
• Brake fluid drained and replaced
• New DID Chain and JT Sprockets
• New front left indicator
• Tank de-rusted

And the bike still didn’t want to run and keep running! So I took a step back and went back to the troubleshooting and now have a new likely candidate for the cause of the non running. My workings as it were:

AIR

The air filter is clear and has no problems passing air, I have had the throttle body and injector out and there is nothing restricting the flow to the bore.

Spark

I have removed the spark plug and cranked over the engine to check for a clean clear strong spark, no issues seen however I had a new plug to go in which also has been tested and fitted without showing an issues sparking. However this does not stop there being a timing issue as the spark timings are controlled by the ECU.

ECU

I have no way to establish that this is good or bad at at current however it is not giving any error codes and I have checked the performance of these sensors/voltages against the values in the Haynes manual:

(Note that for most of these sensors even if they were flashing error codes the bike should start and consistently run)

• Throttle Position Sensor – (Previous suspect from Patricks investigation – there was a concern over this jumping value suddenly causing the ECU to kill bike but I have not been able to replicate this.)
• Air Intake Pressure Sensor
• Air Intake temperature Sensor
• Injector Impedance
• Injector Voltage Feed

Most of these tests require the Throttle body to be connected to the bike and powered, particularly the TPS as it uses some electromagnetic field to detect position. Testing these took the longest as its not easy to get a good electrical connection on a sealed connector, in the end I resorted to sharpening an old set of Multimeter probes so they would cleanly pierce the outer insulation of the cables and get clean measurements.

Compression

I have misplaced my compression tester however a finger over the spark plug whole indicates good pressure and given there is enough compression to get it to start it is unlikely that the rings etc have any issues. It is still possible that this could be an intermittent sticking valve but it is unlikely given the behaviour seen.

Fuel

It’s worth noting that the investigation for some of these areas and double checking has taken place over a couple of months, often checking certain things more than once. What is difficult is that some of these items the specific test is not easily possible either single handed or without specialist equipment.

I have removed and cleaned the injector and confirm that it is fires into a loose pot, however I have no reference for what the exact spray pattern or amount of liquid should be.

I have also disconnected the hose from this and pumped directly through the pipe into the pot. This is the smoking gun that I have so far missed, my prior experience is with gravity feed non fuel injected vehicles. I am not used to expecting tones of pressure and I figures as I did have fuel there and it’s a small CC bike surely it should run even if not right.

This assumption may be my failing as checking the Haynes manual and some online sites I note that there is a fuel pressure regulator and it is built into the setup inside the tank. This should give 35 PSI however testing this is easier said than done.

Diagram of the system:

However now I look at it it would seem clear that the fuel coming out of that pipe is unlikely to be at 35PSI and that when the pump re-primes it doesn’t seem to take very long (suggesting the regulator maybe blocked with rust in some way and it is getting up to pressure in the wrong section). Given I have replaced the pump and the filter, and these had been replaced in the first garden session originally 4 or so years ago that really only leaves the regulator and hoses as being the remaining parts.

Therefore I have ordered a second hand hose and will swap this first (unlikely but just in case) then cut it in half to enable me to make a hose with which I can measure the pressure coming from the regulator. If this is low then the tank will need to be drained and the regulator inspected, the catch being here that Yamaha only sell the pump as a complete assembly for £270 that includes the fuel level sensor the regulator, pump and filter.

There is no way to get the regulator on it’s own and I have already paid once for a new pump and filter… this leaves the only cost sensible option as finding a suitable second hand pump complete unit on ebay.

My diagnoses is not infallible however if it is not this then that really only leaves things like the ECU, to really diagnose any further I would likely need a known running donor bike that I could swap parts between to confirm what was wrong.

So that brings you up to date, hopefully I will have some time over January to test this theory and either confirm or deny a diagnoses. I had hoped to have had this bike done for October however as long as it is running and ready for the new season in April it will serve it’s purpose.

Current Total	£528.85	Received	Fitted	Notes
Purchase Cost	£150.00	1	1
Moving Cost	£55.00	1	1
Haynes Manual	£12.69	1	1
Battery	£25.00	1	1
Starter Solenoid	£15.00	1	1
Fuel Pump Kit	£22.00	1	1
Fuel Pump Seal	£14.00	1	1
Front L Plate	£5.95	1
Rear L Plate	£6.99	1
Indicators	£15.00	1	1
Front side undertank trim	£9.95	1
Battery retaining strap	£5.99			Bought in error, it was the toolbag strap that was damaged / missing
Rubber sheet to make Fuel cap gasket	£7.69			Didn’t work, in the end used rubber grease on the original seal
Tank to Injector Hose	£10			Second Hand Ebay
Service Items
Oil	£7.88	1
Spark plug	£2.99	1
Brake Fluid	£4.09	1	1
Front Brake Pads	£12.29	1	1
DID Chain & Sprocket kit	£31.26	1	1
Tyres	£99.08	1	1
Sprocket lock washer	£7.00	1
Fuel Tank Derusting
Bilt Hamber Deox C	£15.00	1	1
Bilt Hamber Surfex HD	£2.00	1	1	fag packet estimate
Bilt Hamber Korosol	£2.00	1	1	fag packet estimate