The Knowledge - Velocette Owners Club

in. With the cam timing right, these motors can fly.
# 5540 Please note my original text, all settings were to spec.The only way to time valves on a Velo is
with a deg disc, you can use the old valve rocking technique, but you need the disc to check the angle.
# 5541 I once had a very reluctant Viper. I found the petrol tap filters totally clogged. Cleaned them & it
flew!
# 5542 Fuel starvation was my bet, the obvious. Do the simple things first.
# 5549 Don`t forget the breather hole in the fuel tank cap. I have seen an occasion where when the
cap was turned to fasten it something inside the cap moved, or didn`t move, and covered the breather
hole.
# 5547 Did you change the ignition timing after moving the valve timing? You may have retarded the
valve timing and advanced (?) the ignition?
L # 5636 I have a few questions for Mac owners out there but I will start with what I have got so
you have the info. 1949 Mac m17 cam set to marks and confirmed to be good ( valve timing check
done) 276 pre monoblock carb ( new ) Advance set at 4* ( fully retarded, has BTH mag with ATD)
running 91oct. new valves and guides, new cam followers, fairly fresh bore ( @1000mi ) 18T sprocket I
suspect no exhaust baffle Now on to the symptoms Started with book specs for carb ( middle groove on
needle, 130main ) and was lean at WFO and at the top of the needle range ( white B7HS plug), put
needle up one notch and now get dark plug in low to middle range, still white at middle to top, kept
going up on the main jet with the same results only to get a VERY little color at a 160 main ( color was
around the base of plug and very bottom of electrode ( cap side)), suspecting float level I went WFO
and held down the tickler and did not get any adverse effect, even seemed to go better ( maybe
because I was hauling down the road with one hand wedged between the tank and motor). This lean
condition with such a large main jet vexes me, all I can think of is float level ( float is without leaks ). I
have a float needle from what I think is a velo 276 that sets a higher float level and I have installed it,
have yet to run it though. Could it be something that simple? When I look at a parts diagram from
hitchocks I see only two float needles ( top and bottom feed ) but I know that amal made different ones
( as evidenced by me having one with a higher float level). Has me scratching my head. as an aside I
was able to reach 60mph and a pitmans book I have states that as the max speed for the Mac but with
the white plug I think I will wait until I get the bike sorted before attempting to sustain a speed over 55
for any length of time, what kind of speed are you getting out of your Mac and how did you get there?
My goal with this bike is to be able to at least cruse at 55 for the portions of highway I am forced to take
to get to the B roads that I like to ride. Seems strange that I can easily hit 65 on my mostly stock Enfield
g350 and hold that speed for quite some time before worrying about the motor and this bike seems to
hummingbird out at 60, 55 seems to be pushing it right now. Sorry about the long post but this one has
me scratching my head.
# 5637 Not sure I can answer your questions. First, can you check that the new fuel level is the same
height as the top of the mainjet? If it was originally lower then that would weaken the mixture. Too high
and the carb will flood continuously (and it'll be richer). I have a 54MAC and use an NGK B6ES plug
with no problems. These are longer reach than an HS I think. My MAC will happily sit at 60mph with
plenty of go left. It has an M17-7 cam though. I have clocked it at 82mph before. An exciting (and
worrying) speed for an old 350. Yours is probably stopping at 60mph because its not getting enough
fuel. An old chestnut but you have checked the tank cap breather, haven't you?
# 5638 Look out! Regarding the plug question, NGK plugs with an "HS" designation are 1/2" reach -
i.e. thread length. Those designated "ES" are 3/4" reach. They are NOT interchangable. 1/2" plugs are
most commonly used on iron head engines, 3/4" on alloy heads, although I must admit to not knowing
which variation should be used on a MAC, whether iron or alloy. Easy enough to tell if you've got the
head off though!
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