Spluttering at 3/4 throttle..... gs850gz. :-(

[Seana23]

Hi all.
Ive got pods, & 4-1 Harris race can...
Cv carbs.. Standard pilot jet... Needle up one notch... Main jets 130.s...
Runs ok at low revs...
On opening the throttle... Great acceleration then splutter, pop, splutter, bang, splutter....

Jus checked the plugs and 1,2,&3 are tan, 4 is black...
Im using BP Super so no ethanol...
No inline filter but a wee bit ov light rust in the tank.

Any ideas?
Thanx in advance.

Xxxx

[Steve]

Have not heard you complaining about this before, did it just start to happen?

What did you change just before this started?

It almost sounds lean. Try activating the "choke" while this is happening to see if it helps or hurts.

Are you running "Super" just for the 'no ethanol' part of it? Extra octane will hurt your engine more than it will help.

How much ethanol? Over here, there is a limit of 10% (so far). Some claim they can tell the difference in performance, I have not been able to verify that for myself.

.

[hampshirehog]

Are you running "Super" just for the 'no ethanol' part of it? Extra octane will hurt your engine more than it will help.

How much ethanol? Over here, there is a limit of 10% (so far). Some claim they can tell the difference in performance, I have not been able to verify that for myself.

Our Octane ratings are different to US octane ratings for some reason Steve but suffice to say BP Ultimate Super is 97 RON and BP Ultimate ('regular') is 95 so there's no issue caused by that. However, just to check Seana, there is BP Ultimate Super Unleaded 102 (sold under that full name) - make sure you haven't filled up with that (it's not sold at many places so it's unlikely).

Our regular petrol is running 5% or 10% Ethanol (depends on the brand and where you buy it), heading a towards a 20% EU target at some point. However, BP Ultimate has no Ethanol in it - it gets a dispensation for some bizzare reason under EU legislation. It's more expensive (but not a killer price, for us anyway, you would have a heart attack) and Seana and loads of other guys who have had trouble with dodgy tank sealants are running with it to avoid the sealant dissolving.

If she accelerates well when you **** it and then starts to cough and splutter after a few seconds that would suggest a fuel blockage in the tap or pipe somewhere. When you had to get all that Villiers gunk out are you sure you got it all? Some of it could be wrapped around your filter. Is it ok on full bore? If it is I'm wrong.

[Steve]

Our Octane ratings are different to US octane ratings for some reason Steve but suffice to say BP Ultimate Super is 97 RON and BP Ultimate ('regular') is 95 so there's no issue caused by that.

Yeah, I know they are measured differently, that is why I did not mention any numbers. The principle still stands, though, using a higher-octane fuel "because it has more power" or because "it's better gas" does not always work.

Octane is a measure of knock resistance, not energy content. Using a fuel with more octane than necessary for your engine can hurt, because it burns slower, so might leave deposits on the piston or valves, due to incomplete combustion.

Ironically, ethanol has a higher octane number than gasoline.

But ... that's a discussion for another thread, let's get back to getting Seana over 3/4 throttle.

.

[Seana23]

Thanx all.
Hmmm... I think your quite possibly right about fuel restirction... It has only just started happening, so maybe there still is some old "tank liner" in there, or maybe a film ov rust gathering on the filter....
I really must get some POR15 or Caswells to line the tank properly..i had a nightmare checking the plugs today, as number 2plug was very difficult to get back in again as i think the threads are messed up a bit... I got it in being careful and gentle yet forcefull.
I dont think it will take being taken out again without me having to Helicoil the plug hole!
Oh well, one problem at a time eh?

Ill drain the tank, filter the fuel and check the filter tomorrow.
Thanx again.
Xxx
Oh yeah, i think it was called BP Super... But i couldn't be 100% certain. Do'h!