Classic Carbs again

[Mick Taylor]

I'm working through my newly purchased Classic, all electrical gremlins have so far been evicted and it has a new Electrex R/R and replacement Ballast Resistor. The Battery is excellent, plugs new, charge rate good. Where the air filters should be, I found a piece of sponge!...little wonder it was running so rich, I have now fitted new choke O rings, set the jet height with a digital vernier and set the float heights by the book. They had been unequal and very low indeed. I suspect the sponge 'air filter' may have been a storage precaution.The bike now starts instantly from cold, but once warmed up the idle is very weak, it is very slow, about 600rpm and clearly struggling. The idle speed adjusters make little or no difference no matter how far they are backed out. (Is there a standard 'starting point' I can revert to?) The exhaust smells rich, I have marked the carbs and backed out the mixture screws by one complete turn...it is slightly happier but still far from right. I can hear noise from the air intake, but this bike stood for ten years so I don't want to condemn the engine yet until it has covered a few miles in case it is just a sticky apex seal that may free itself...and I can’t interpret the noise anyway, for all I know it could be normal and mean nothing.When I fitted the new choke O rings they were not a tight fit in the bore, barely even snug, which was surprising. It has new viton tipped float valves and the carbs are clean. I chickened out of changing the O rings on the idle air tubes as the access is so limited. I sprayed a little WD40 onto them while it was running and idle speed was unaffected; unlike the choke O rings, they do feel a smooth but tight fit. I’m concerned that the idle speed does not respond to the adjusters; the mileage is a confirmed 3,700 from new, but I’m well aware that means nothing if it has suffered mistreatment.I’m looking for any suggestions re carburettor adjustment please (or anything else) in case I have done something wrong or overlooked the obvious, all advice gratefully received..........Mick.

[Richard Negus]

Mick,If it won't idle with the air screws right out, and sounds 'suck suck suck' from the air filter (called chuffing as in "Chuffin 'ell, another warranty job!", I suggest you take off both of the air transfer ports and have look inside. Black oil, bits of carbon or, worse still, a grey mud of oil and aluminium all suggest low compression/ scored side plates.

[Richard Negus]

Oops, clicked too soon!That, obviously, is an F1 centre plate but the 'black finger of death' more or less confirmed that the engine had scored plates thus:

050207-22.jpg

A bit of carbon in clean oil is ok but, particularly for an air-cooled, I would always recommend running on synthetic two-stroke oil.If the transfers are clean, you should be ok to run it and see if it really is just a stuck seal and if it mends itself.R.

[Mick Taylor]

Hmm....I don't like the sound of that (or the chuffing) or the look of that side plate.There has been a slight change this afternoon, I wasn't happy with the way the new Choke O rings didn't seem to fill the channel on the choke assembly or feel like it was making a seal within the recess when inserted...so I pulled them out and to my great surprise found the new O rings which came from Burlens had expanded and were now about as tight as Nora Batty's stockings.....in any event they clearly weren't preventing fuel from passing into the body of the carb.I found some generic O rings of the same internal diameter, but slightly thicker. I fitted those and it is now a much happier motor......still not as I think it should be, but vastly better, it will now idle when hot at 800rpm and I can walk away from it without fear of it cutting out.......and it will re start.That said, I think it probably has the dreaded 'chuffing' problem, so I will give the next step a bit of thought.Mick.

[Richard Negus]

THIS is the photo I couldn't find earlier. All the symptoms you describe, carbs completely overhauled, perished air filter replaced, new plugs & HT leads - and no improvement. Started every time, hot or cold, and ran very well, but no idle even with the temperature switch disconnected so it runs full advance.Elbows off, black finger of death.

3120-02.jpg

Engine strip reveals a moly engine (!) with two broken pin seal springs, one on each rotor. No damage to the plates, so a full set of new pin seal springs and rebuild.Voila! she idles.R

[Interpol2471]

Hi Mick,The air cooled engines are not the quietest of things, mine always sounds like a bag of nails when cold, and what Richard has stated above is obviously perfectly correct being the Rotary Gold standard holder but first of all give it time before condeming. Give it a little comp2 and redex to soften things up and give it a try first, if the damage has already been done it is done but again as above Richard is right it may soten up and fix itself but without time you will not find out. Give it a run and get your mixture right first and if that does not work check your warranty with the Guru I find that mine works best at about 750-800rpm idle anyway as I dont like it too low as I suffer from the dreaded retard syndrome when pulling away and have to blip to get the revs up and advance everything.I hope all goes wellPaul

[johnbirchjar]

Hi guys,still on Classic carbs,my old girl has started to run even hotter than norm(even on the dampest of days,e.g. the run up to Skipton!)mentioning this to one of my biking buddies (who knows a thing or two about bikes) he sugested that because of the ethanol crap in petrol,the carbs may be running a bit lean,and to richen the mixture a tad,what do you think?and if so, am I corect in thinking the mixture screw is the cross headed screw in the main carb body,and if so,screw in or out to richen up? regards,J.B.

[Interpol2471]

yes the cross head screw is the correct one and you turn in to richen, you can adjust like a normal twin if you listen carefully you will find the sweet spot on each carb but mark your start point for reference. After tweaking you may find the idle increases and you will have to adjust. I have mine set so it runs a nice dark brown like a toasty colour. Also I find that mine runs best on C9E plugs are you running 8's?Paul

[johnbirchjar]

Thanks Paul,mine has allways run a tad paler than "toasty bark brown" more sort of "greyish? allmost white after a long fast run,and yes I have run on 8s for the last forty odd thousand miles,don,t envisage changing any time soon,ride safe,J.B.

[Interpol2471]

Go on John be a Devil and try the 9 I found mine was much nicer on them.CheersPaul

[johnbirchjar]

In what way nicer?J.B.

[Interpol2471]

Just ran better and cleaner, seemed to pick up snappier from idle and would idle better from cold. I also found the standard C9E ran better than the iridium plugs when cold too.RegardsPaul

[kanonkopdrinker]

I think if you regularly 'give it some stick' then the '9' plug is the safer option.The '8' is a 'hotter' plug and so more resistant to fouling if you potter around town a lot.I know of one chap who runs his Commanders on '7's ... but then he never goes above 60 ....My own IP2 is on '9's .... I wouldn't want to risk melting a '8' or '7' ...Okay, pebble thrown .... let's see where the ripples end up ....DC

[Dell Boy]

I ran 7`s when commuting into & riding around Central London all day but use 8`s now.Derek F.

[johnbirchjar]

I purchased a couple of 8s at the Ingatestone rally,so perhaps I will try 9s when I have worn those out,J.B.

[johnbirchjar]

And as a PS to the above,I don't think I have ever had a fouled plug,(I don't tend to "potter" much )ride safe,J.B.