Starting issues - a pattern developing?

Another sunny Sunday and another frustrating ride out. Given there seems to be a pattern (albeit just twice now) I thought i’d see if anyone else is getting the same.

I posted this on 6th April (around 14 posts in):
https://www.accessnorton.com/NortonCommando/reluctant-starting.27514/

What I didn’t mention was the restart issues were after filling up with fuel (it wasn’t empty as only took £11.


Today I rode some 12 miles and was planning another 100 miles so stopped off to add fuel, only took a gallon to fill it up. I go to start it, side stand was up, not in gear, not expecting any problems..... guess what, wouldn’t start at all. Had to push over to the parking bays.

Same as before, would start if gave it some throttle but mega lumpy, farting and banging, and if I came off the gas would instantly stall. I noticed black smoke this time. Tried a couple of turn off and back on again wondering if I could reset ECU, no change. I was 12 miles from home so had to leave the petrol station and try to get home, so just gave it a few thousand revs throttle and jerked and spluttered up the road. A few miles in it kind of cleared and was pleasant enough but still not right with the odd miss here and there. Amongst all this it’s still idling high 70% of the time.

So all in all not a great day again. I’m up to 260 miles now and can’t wait to get this all sorted. It really needs to be back to the factory, but would rather wait until the 600 m service as it’s 250 miles from home.

Why post here, i guess just interested if the filling up with fuel situation is connected at all. Bike probably been started 50 times now, but these two major issues where I thought it wouldn’t even get me home were both after topping up with fuel. Coincidence? Maybe,but I suspect not.

So it started with feeding some throttle . When stone cold are you having issues ? Only just after you been running it some and a quick stop at a gas station to top off ? So the head temp sensor comes to mind if its acting up this can cause some trouble for you . The two sensors The bike is still new under warranty ? I don't think they'll want you putting your own parts in . But I have been advised to replace the Head temp sensor and the cam sensor with Genuine Bosch . We have heard of new bikes having issues with these sensors but not recently. Back in 16-17. But these Bosch replacements are available and easy to install and they are a direct cross to factory parts. If you do a search you will find the p/n's. Also , If the O2 sensor or sensors are acting up you may have low speed mixture issues . Once the O2 sensors get up to temp they may stabilize and work well. Of course you need to have the system plugged in and analyzed to be sure. Try this , take a good long run next time before you stop for gas . Say 50 miles or more (get it up to full operating temp) then get your gas and see how it starts then.

Thanks for the reply. It starts fine when cold (well it takes 2-3 seconds on the starter button which feels too long) but no throttle is required. And to be honest for all the other hot starts it’s been fine too apart from these two occasions where i’d just added fuel a few minutes beforehand (always high octane esso fuel). Hence I can’t believe it’s a coincidence, possible, but unlikey.

Didnt help that some kind biker on 19 year old 90k mile GSXR saw me struggling and came over to see if he could help. He tells me his £1k bike has been trouble free for years. I’ve spent £18k and stuck in a petrol station twice in 3 weeks!

If I can limp on to 600 miles I will assuming i’m not going to cause any other problems. I’ll email the factory and ask them. You’re right, it’s under warranty so don’t wish to start changing parts. Would rather them see the high idling, try and replicate this starting problem, and get it sorted.

TonyA said:

So it started with feeding some throttle . When stone cold are you having issues ? Only just after you been running it some and a quick stop at a gas station to top off ? So the head temp sensor comes to mind if its acting up this can cause some trouble for you . The two sensors The bike is still new under warranty ? I don't think they'll want you putting your own parts in . But I have been advised to replace the Head temp sensor and the cam sensor with Genuine Bosch . We have heard of new bikes having issues with these sensors but not recently. Back in 16-17. But these Bosch replacements are available and easy to install and they are a direct cross to factory parts. If you do a search you will find the p/n's. Also , If the O2 sensor or sensors are acting up you may have low speed mixture issues . Once the O2 sensors get up to temp they may stabilize and work well. Of course you need to have the system plugged in and analyzed to be sure. Try this , take a good long run next time before you stop for gas . Say 50 miles or more (get it up to full operating temp) then get your gas and see how it starts then.

Click to expand...

Tony,

If the head temp sensor was bad, the ECU would see the head temp as low, correct?
On startup in this case the ECU would probably richen the fuel mixture to start a cold engine due to low temp voltage from the failed head sensor.

The only thing I can think of is that when filling up you are stirring up possible crap in the tank? If water or other contaminant I would expect it to sputter a bit but then clear itself once the water settled. Otherwise I can't see what opening the fuel cap can possibly do to affect the running. PS: I always start up on the sidestand in neutral but again that shouldn't a prob one way or the other.

When I had my bike serviced last month the head sensor was changed, the old variety (thin brass?) had a habit of breaking so Norton are fitting a stronger unit made from stainless, sorry don't have the part number.

Is the fuel system on these bikes pressurised?
Opening the filler would release the pressure and if the fuel pump is faulty then no pressure builds up to get the fuel to the chamber. Turning the throttle draws more fuel - possible compensation for a pump not fully working?

Fuel tank is vented so shouldn't be any +ve/-ve pressure in the tank.

BritTwit said:

Tony,

If the head temp sensor was bad, the ECU would see the head temp as low, correct?
On startup in this case the ECU would probably richen the fuel mixture to start a cold engine due to low temp voltage from the failed head sensor.

Click to expand...

Head Temperature Sensor Norton 961


Found a chart that shows what the correct values should be for a given temperature. Fits in nicely with what I measured, should be useful for anyone trying to fault find. (from iwilson post just re-posting it for you to see again) When you say bad (wrong resistance) ...


T [°C] R [Ω]

-40 45313

-30 26114

-20 15462

-10 9397

0 5896

10 3792

20 2500

30 1707

40 1175

50 834

60 596

70 436

80 323

90 243

100 187

110 144

120 113

130 89