[tedheath]

Hi I am a first time Royal Enfield owner and newbie on here.
My 2016 4600 kms Classic starts fine first kick and goes fine at first. However after about 1 km usually the same place every time it starts backfiring very loudly.
I mean loudly like gun fire people start looking then it slows down almost dies after a few minutes its away again no problems. Sometimes I have pushed it home and it starts again!
Things I have mucked around with are:  air filter it had a K&N but it was badly fitted the owner threw the original in with the bike which I refitted another thing was the muffler I took out the baffling material and got it rechromed I couldn't quite get all of the original material back in but pretty close.
I was an aircraft engine specialist including piston engines in the RNZAF for 27 years but I dont even know if its a fuel or ignition problem.
It would seem something getting hot sending a signal I guess.

[Haggis]

A new NGK BPR6ES is a good place to start.
I have had two RE that behaved in a similar manner.
My thinking was that its the cylinder head oil temp sensor.
This tells the ecu if the engine is hot or cold and the ecu will enrich the mixture for cold starts.
Is it keeping the mixture rich for too long and starting to foul the plug or is it leaning off too early before the engine is warm enough??
As you say, it soon clears itself and all is well.

[muezler]

Hoi Tedheath.

Did you take a look at the spark plug for deposits / gap?
Or check the cylinder head bolts.

Edit: sorry...was 49 sec too late with my post

[Narada]

I would start here, since I'm a big fan of keeping it simple when troubleshooting. 

It is very common for the negative ground wire to break, often only inside the insulation at the battery terminal. Replacing that terminal has cured many such problems. 

One other culprit for intermittent power loss is the kickstand safety switch. Unplugging it down by the kickstand solves that one. 

Of course, you then have to be sure your kickstand is up before riding...I hear lowered kickstands while riding can be painful! 

I believe most of us, including myself have unplugged ours...

The back firing sounds to me like your getting extra fuel in your exhaust while engine is off, then it's exploding when power returns...

I would first solve the cutting out, then be aware that your fuel mixture / exhaust may have a problem. Btw... Loose exhaust connections, like at the silencer, will cause backfires during deceleration on any bike.  Good luck!

[tedheath]

Thank you very much for replies. After putting up with the bike dying at the same spot on the road for last two years found the problem thanks to reply here.
Disconnected the oil temp cylinder sensor went for a blat no problems. Next day put it back on backfiring and slowing down almost to a stop clearing and away again. Disconnected sensor again this morning no problems so I will leave it off till a new sensor arrives if its still does it with new sensor I will snip the connector off.
Thanks for help and replies.

[Haggis]

You can test your sensor if you want.
You can see the resistance drops as it warms up.
Hopefully a new one will sort it.

Specification:
Operating temperature : –30º C to +120º C
Operating Voltage : 5 ± 0.5 V.
Resistance Value w.r.t. Temperature
–20º C –– 18.8 Kilo Ohms
+ 40º C –– 1.136 Kilo Ohms
+ 100º C –– 0.1553 Kilo Ohms

[Narada]

Glad you seem to have found your problem tedheath! Sorry if I mislead you.

Haggis, do you know what years of Bullets came with these potentially failing sensors? I've removed and replaced mine while playing with my lump, but otherwise, never gave it a second thought! 

[Haggis]

I think all the EFI are fitted with the engine temp sensor.
The newer abs bikes have an air temp sensor as well.

[Ove]

Mine failed on a 2019, after only 2,000 miles. The dealership has them on back order for the UK, but Hitchcocks have them. £30ish IIRC.

You can check for the fault code, which will tell you it's the sensor.

[tedheath]

The Check Engine light did not flash so I guess there is no code?

[Ove]

Ah, ok. If I remember right, the engine code wasn't easy to track down, not in the manuals / Haynes workshop book. It might only be on the later Euro4 models? Can't explain otherwise. Glad you're sorted anyway.

[Haggis]

On the euro 3 the MIL code for a malfunctioning circuit in the oil temp sensor is, one long and one short.
The sensor just stops working correctly but that doesn't bring on the light or a code unless the sensor fail completely.