SOHC.co.uk Forums > CB750
CR750 Running (or not running!) issues
CR750:
--- Quote from: moorey on December 05, 2018, 12:56:10 AM ---[quote author=CR750 link=topic=17651.msg152447#msg152447
I had this reply from BP :- dated 2014
Thank you for your email concerning the fuel sold by BP.
In "most regions" of the UK our Ultimate Unleaded dos not contain any Ethanol at present (South West UK excluded).
This may of course change in the future as the specification allows up to 5%. If there will be any changes, these will bw shown on the pumps and at the stations.
BP ultimate will never have more than 5% ethanol until January 2017 when it could be increased to 10%
dated 2018, Shell & Ethanol. in the UK, Shell regular unleaded and Shell V-Power unleaded are likely to contain some ethanol, but it will not be present at more than 5% (in accordance with current UK specification requirements
--- End quote ---
So this contradicts your original post on ethanol percentages then.
No Not Really
I honestly don't think the Petrol Companies themselves are giving us the true content of ethanol in their fuel .
also I do know is its a waist of time asking the petrol station attendants about ethanol content I don't think half of them will know what it is..
why don't you try contacting the petrol companies above by email or letter & see what info & figures you will get
[/quote]
Ask the retailer it's on their spec sheets what they receive from the distributors . I asked the girls on the tills who didn't know the content but said they would ask and took my number. A day later I got a call from Sainsbury's head office with the information. It's not a secret and I didn't pluck my figures out of thin air..... neither did i
Quote:-
I also enquired about it at our local Sainsburys petrol station last year & I was told it had at least 5% ethanol in the super unleaded. I personaly would not buy any supermarket fuel for my bikes.
https://www.esso.co.uk/fuels-faqs
philward:
Had some time over Christmas hols to try and cure a intermittent popping/misfire on the overrun and tick over – to no avail!
Bike runs fine when accelerating and on a steady throttle but pops at tick over and when de-accelerating at lower revs. Its only on number 3 cylinder.
At the start of this post, I had problem of starting (suddenly) and the misfire – as per previous posts (and your help) cured the starting with the D7 plugs but mis-fire remains.
Plugs all between sand and brown (not black) – although not really had decent run
This is my thoughts
Can’t be ignition and coils as fire on 1 - 4 and 2 – 3 at once. Done compression test and 135 on all 4 cylinders (off kickstart as no starter motor fitted). Plugs new and moved caps on 2 and 3 with no change.
Just used a colortune and at tickover number 1 & 4 bunsun blue and 2 & 3 nearer white - adjusting airscrew on 2 & 3 makes no difference to colour of spark (although engine tone obviously changes slightly) – its more difficult to see flame colour on number 2 & 3 due to having to look via a small inspection mirror (colortune mirrored tube hard to fit due to Boyer coil setup in the way) – hence I might not be able to accurately assess colour.
Just taken carbs off tonight to re-check number 3 carb. Thought I’d carefully check the fuel level in float bowls and removed bowls with fuel still in. Noticed that 1,2 and 4 has same level of fuel but number 3 had lower fuel level by 3 – 4 mm! I’m guessing that this may be the issue - weak mixture causing the popping (although no issues on accelerating?)
So, to increase the fuel level, I think I should decrease the float to body measurement by 3 – 4 mm?
Your opinions much appreciated!
MrDavo:
In my experience popping and banging on the overrun, but otherwise running ok, sounds like an air leak into the exhaust, perhaps at the head / pipe joint.
Worth checking first before you play around with float levels.
philward:
--- Quote from: MrDavo on January 08, 2019, 11:36:21 PM ---In my experience popping and banging on the overrun, but otherwise running ok, sounds like an air leak into the exhaust, perhaps at the head / pipe joint.
Worth checking first before you play around with float levels.
--- End quote ---
Thanks Dave - I'll check this weekend. The header to head joint design is very basic on the the race exhaust so quite probable
Sent from my Moto G (5) using Tapatalk
andut:
Phil,
Popping on the overrun / idle is a classic lean mixture symptoms and the lower fuel level in the chamber is an excellent place to start - sure that will go a long way to fixing yout problems.
Andy
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