Only getting 30-35mpg - what should I check?

[College]

Boxermania, sorry for the delay in the update but TTS took ages to sort it out and I have been away on work but I collected the bike yesterday.

TTS fiddled around with the bike for some time on their dyno and decided that the Power Commander was not working properly so fitted a new one. However even with the new one they tell me that things are not perfect in that the Y piece fitted is not a good design – slightly narrower bore than it should be and join is not swept – just a simple T junction. The result of this is that the back pressure is not as it should be and it is difficult to get the mixture in the two cylinders correct – one is slightly rich and the other too lean. It produces 72 bhp at the rear wheel. Their advice is to get a second hand ‘cat’ and put that on. They also said I should get the stick coils checked – is it a big job to replace them or is it just a plug in exercise?

Have not been able to test the fuel consumption yet which is where this whole story started but hope to get out at the weekend and see if it has made any difference. Had a quick run up the road last night and if anything seems to run the same as before. So much £ later not sure we are any further forward!!!

[boxermania]

Knowing little about your bike I will not take a position, but I don't buy TTS backpressure argument as it that were the case their recomendation to install a "second hand cat" will only add backpressure to the system and not correct the "Y deficiency", if there is one.

I will recomend that you proceed with the check of the stick coils, as they are prone to heat deterioration which will lead to failure and the behavior you are experiencing.

BTW, if you have a Y with a can (muffler) and a fuel nanny, the engine should be putting out right at 83-84 rwhp, (I went through the motions and documented the results) 72 rwhp is just about what one should see on a stock bike.

[spoon]

Just replaced my coil sticks and my milage went from about 38 mpg to 51 on the last tank. This is a bike with 24,000 miles on the clock.

[College]

Looks like I will be replacing the stick coils then - is this a big job or just a 'plug in' exercise? With 4 spark plugs do I have 4 coils to replace? Sorry about the numpty questions not as handy with the spanners as i should be!

[boxermania]

Not a big job, there are only two stick coils, they are on the upper plugs. Be extremely careful with the removal of the electric connector at the end, as they are fragile and have been known to give problems.

The part number for the stick plug is 12137680644 and the last time I checked pricing they were around $145 per. Shop around......

[College]

Thanks Boxermania - I will order one up abot £60 (and the liitle tool to pull them out?) and try it on both sides as it is probably unlikley that both will have gone?

[College]

Boxermania, bit of an update. Ordered up a stick coil (£60 plus postage from BMW Motorworks –nice people) and when it arrived took out the old ones. Well it was pretty obvious to me which was the duff one - as you know I am very highly competent with all things mechanical. One of them looked quite new and the other a bit corroded and tatty so that was chucked. Popped in my new one and off for a test drive. Bit disappointing as does not seem that different and after 50 miles topped up the tank and still only doing 30 ish mpg. Get home despondent. Think I might as well try the rusty old stick coil and manage to find it at the back of the shed where I had tossed it. Pop it in – getting dark and have to pick the nippers up in 30 minutes so only have a chance for a quick 10 minute run. Blow me different bike! Running much more smoothly, no occasional misfire and seems to pull a lot cleaner everywhere.
Hope to get out at the weekend and have a proper test run and check MPG but I think you may have cracked it! Fingers crossed – further update after the weekend.

[College]

Stick Coils it was now running sweetly and getting 45 MPG plus.
Now to tackle TTS and get a refund.

[loutusmaximus]

I've only just found this thread and I'm also in the 35mpg range.

I wanted to ask though, do you think my poor fuel economy could be down to my having a 33bhp restrictor fitted? I passed my test 15 months ago (UK) and I still have until December before I can remove it legally. I realise that it's not gonna race off because of that, but should I see more miles from a full tank when the restrictor comes off.

If it helps, I think the restrictor works by restricting the airflow into the carb so once I'm past 4000 rpm, it's not getting enough air and it won't rev any higher.