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[Howard 612]

This sounds remarkably similar to my own experience. I feel my Monobloc is set up "almost right", certainly I have no performance problems, BUT I get a fairly frequent "missed beat" when opening the throttle about 1/4 or 1/3 on the exit from a roundabout. Only EVER on the exit from a roundabout, whilst leaning to the left. It's just one missed stroke and then she accelerates in the normal manner, it's quite an odd one. I'm sure it could be tuned out with the aid of a DynoJet run, currently trying to find this service in my area.

[Alan R]

Hi HOWARD ---- this is an oddity of fuelling because that float & chamber is off-set to the needle and main jet assy.---you get a temp. weaker one way and a temp richer the other. In the early days of racing ie pre-monoblock days--- you would see a twin-bowl set-up ie one chamber on either side ---- in order to combat this slight "glitch" in throttle response. The obvious answer was to surround the needle/main jet with the float assy----thus we get the "Concentric" idea that stayed with carb.design and was copied by all the major manufacturers until fuel injection took over. In films showing early models of a Spitfire doing a roll the eng. temporally stutters and a small,black cloud comes from the exhaust as the plane becomes upright. The early cabs.(Gravity fed) couldn't cope with inverted running and would temp. flood on becoming upright again. Later carbs had a crankcase-vacuum operated pump which kept the fuel supply pressure constant----much like modern fuel injection has.

[Matt]

UPDATE: I moved the clip down a notch and there wasn't much improvement so I moved it down another notch and I can really notice a difference. The problem now only exists from tick over (and therefore only when crawling along in first gear) when I open the throttle quickly she hesitates and will actually cut out if I don't let off the gas fast enough. When normal ridding though in second and third I can open her up fast at any time without her missing a beat and she's off... Like a rocket (for an Enfield anyway.) I'm happy with the results and can live with the remaining issue unless there's a simple explanation? Thanks again everyone.

[Matt]

Does having an engine running richer reduce the MPG? Or does a richer running and easier breathing engine (air filter/ exhaust etc.) simply mean that you have the option to burn more fuel as the engine is more efficient at producing BHP and therefor you MPG will only reduce if you use the engine to it's full capacity but you could output the same BHP as before and attain the same MPG? Does that make sense?

[Howard 612]

Thanks for that explanation Alan R, I kind of had an inkling something like that was going on, but your post makes it crystal clear. So all I have to do is keep the bike upright to avoid the misfire Simple! I might run more often with the Concentric on, I usually keep that one for when I really want to go fast, the Monobloc is more my "show" carb as it is right for the age of bike, but of course the Concentric is available with the larger throat needed for a tuned up engine.
P.S. sorry for hi-jacking your thread Matt.

[Jack]

Matt,are you happy with the float height?Too low can cause those symptoms.Also if you
can find an old projected tip plug you could experiment with those.I've read the theory
is to get the spark as close to the center of the combustion chamber in a hemi head,and
it helped cure hesitation on my 535. Jack

[Matt]

Thanks Jack. I did measure the float hight earlier today as per the tech notes on from this site. I think it said to be 23-24mm from the carb body. It was spot on. Projected tip plug? I have a couple of plugs from my 500cc Bullet. Do you mean to try them? Is that what projected tip means? They are deeper/ longer.

[Riggers]

Hi Matt. Glad you're getting things sorted. It sounds to me like you need a 2.5 slide to sort out the last remaining snag you have (altough you could try enrichening the piot air screw a jot). The slide cutaway controls throttle response from just off tickover until the Pilot Jet takes over. As you've got so close it would seem a shame not to finish the job off although new slides are a tad pricey. Regarding your question on engines running weak or rich etc, there really is no option but to have the motor running with the correct mixture. If you constantly run a weak mixture the motor will overheat with possibly disasterous results (seized engine etc etc), too rich and the resulting 'coking up' will foul the plug and eventually carbon up the valves combustion chamber. The very best mpg for the highest bhp will come from a mixture that's spot on. Good luck!. Tony.

[Jack]

Matt,projected tip is where the porcelian projects out from the threaded portion of the plug and
the strap is longer,yes it won't hurt to simply try it,if it doesn't cure it then no harm is done.
But it was a tip i picked up on and tried myself,and it's a positive improvement on the larger
motor at least.

[Matt]

Thanks again Riggers. I understand. Looking at the slides there are two available. "Standard - 2.5" and "Richer - 2" At £15 it's a bit much but not to bad. I would have thought that it's a bit drastic though seeing as all I did was replace the stock 350cc exhaust with a stock 500cc exhaust that I had knocking around. No air filter mods. Is there a way to modify the throttle needle perhaps? Maybe file one more groove with a scribe whilst the needle is in a drill so I can move the clip a little lower and raise the needle one more millimetre? It's only aluminium sin't it. That way if it doesn't work I can always put it back. Or does that just sound plain crazy? --------------- Jack. Thanks for the advice. I'll try it one day I'm sure.