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Venom tuning - from a distance!
#772920 05/07/19 4:26 pm
Joined: Aug 2011
Posts: 106
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The 61 Venom we just did a top end job on ran great on the lift, and tootling around outside the shop (through 1st/2nd gears) and when back with the customer, did 2 road runs - both over 100 miles. On those runs, he was under strict orders to not do much over 50mph, not to let the motor lug on hills - more keep running it up and down through the rev range.
He was having trouble starting it at home, though it was starting first kick on the lift, and on bringing it back for a post run check, we couldn't find anything amiss. More - it now takes a slightly different technique to fire it up than he's been used to. On picking the bike up this last Sunday, he fired it up outside our shop -- first kick, using the 'new' method, and was very happy. We told him the rings seemed to be seated correctly, and he could now start 'goosing' her a bit on rides.
Later that day, he called to say he'd taken the bike for a run at home (2+ hours from our shop) and it was doing some something odd.
Though it fired up quite readily - he said once warmed up and out on the road and at a normal cruising speed (50mph or so) when he opened the throttle, it didn't want to accelerate -- more just sort of baulked, then slowly started to pick up revs. Once he got back home (he wasn't far away) he said he pulled into the garage, and as he let go of the throttle, it returned to idle - but then started to 'hunt' -- revs rising and dropping without him touching the throttle. A couple of hours later, he again fired it up - and it reacted normally (though he didn't ride it again) just sitting and idling.
I have asked him to mark the throttle, to try and ascertain what rev range it is in when it is acting 'odd' --- which may tell us something. However - the hunting thing has me a tad miffed?
It has an AMAL Premier 930 on it - and though not sure of jetting, they came stock for that model, with a 200 main, 106 needle jet and #3 slide (not sure on the pilot jet)
Magneto was rebuilt (professionally), with new points/Brightspark Easy Cap etc.
Any thoughts?

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Re: Venom tuning - from a distance!
Brid Caveney #772977 05/08/19 12:20 am
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Air leak between a carb and head when hot ?
Air leak in the carb when hot ( air screw o' ring broken ) ?
Carb getting loose ?

Re: Venom tuning - from a distance!
Brid Caveney #772979 05/08/19 12:29 am
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Yes, that occurred to me too, but usually you'd get some popping-back symptoms with a carb air-leak.

Re: Venom tuning - from a distance!
Adam M. #772982 05/08/19 1:03 am
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Originally Posted by Adam M.
Air leak between a carb and head when hot ?
Air leak in the carb when hot ( air screw o' ring broken ) ?
Carb getting loose ?


Adam -- we just rebuilt the complete top end of the engine -- and it was put together very carefully. It's only done a couple of hundred miles 'break in'. It's a new 930 Premier, so I'm not suspecting any of those faults. In fact, with it running on a 'hang tank' when it came back in (after the 200 miles) we blew brake cleaner around the manifold, and it showed nothing.

Re: Venom tuning - from a distance!
Brid Caveney #773019 05/08/19 1:46 pm
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Is the ignition advance automatic or manual? If automatic, could the springs be acting up or the unit not retarding smoothly? If manual, is it a tight or loose cable advance? Could the lever have slipped from retard to advance or otherwise without the owner noticing? Timing have slipped a bit?

Ed from NJ

Re: Venom tuning - from a distance!
Brid Caveney #773480 05/12/19 5:03 pm
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I ran a 930 AMAL Concentric with a 270 main jet, needle on the middle groove, No air cleaner.
Bike ran fine at these settings


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