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Allan G, JER.Hill, Mark Parker, mdodds
Total Likes: 4
Original Post (Thread Starter)
#863228 11/15/2021 3:03 PM
by ziggy53
ziggy53
Winter has arrived here in the canadian west so it's time to contemplate the next project I'm wondering what the best options are for maximizing the midrange grunt of an a65. I am contemplating a big bore kit and or cylinder head work but would really like advice from those who have experimented with engine mods. I'm sort of inclined to see what is possible with the single carb head. Thanks.
Liked Replies
#863420 Nov 18th a 12:30 AM
by gavin eisler
gavin eisler
Thanks for the vote of confidence Nick. good things about the 750 big bore , 6kg weight saved, lighter B44 pistons ( less material from crown to gudgeon pin) and a dynamic crank balance make it smooth up to about 5.5 k with the stock balance factor, the stock chamber combined with the B44 piston tops gives a squish effect which helps the fuel burn.
at 9:something below 5 ish to one its an easy starter , the heavy flywheel really helps. On 21 tooth gearbox (One tooth more than normal) /47 rear sprocket gearing its in the sweet spot from 60 to about 90, stuff doesnt fall off or crack too much, the big downside is you need more brakes. Having thought a bit more about the outrigger bearing, maybe it is essential, before I fitted it I had a lot of bother with the clutch, ( it was shagged , new bits were fitted at the same time). Going up through the gears changing up at 5.5 gives enough poke to get past most stuff indecently quickly. I sometimes rev to 6 + but its not really any faster, the stock 30 mm carbs probably hold it back a bit at full chat, the flip side is the high gas speeds in the carb make it perform better, I had to fit 3 sizes smaller main jets , and a weaker needle jet it breathes harder faster gas lifts more fuel.Hardly ever needs tickled, starts of choke down to about 12 C. It does about 55 mpg cruising at 4- 4.5 K, seldom gets overtaken. At its best on hills, with twisty bits. It deals with A road tourist traffic without any issues, its my daily transport when the rain isnt falling, a very fun / practical bike. theres an overlong thread here if you want the gory details https://www.britbike.com/forums/ubb...els-5-speeds-a65-750-oif-1971#Post541665, theres about 10 years of evolution, the pics might not work until the end, some were hosted by phot =£$ cket, who went all wrong, the ones near the end should be OK.
2 members like this
#863382 Nov 17th a 09:43 AM
by gavin eisler
gavin eisler
The outrigger is not essential for road use, I used my bike with the big bore kit ( Originally Devimead barrels) for years without it, but in the great scheme of things while the motor is down for work its not that hard to fit and helps stop the mainshaft flexing. PES in the UK have something that might fit or you can modify an existing inspection plate.
1 member likes this
#863294 Nov 16th a 09:24 AM
by gavin eisler
gavin eisler
Search for Mark Parker's threads here to see what can be done with heads.
My 71 has great middrange. Heres the recipe,John Hill big bore Alloy Nickasil barrels, B44 pistons, stock stroke , end fed crank,2 off 30 mm mk 1 Concs,stock airbox , stock pipes, big inlet valves. Seven plate clutch with mainshaft outrigger bearing. The head was flowed by following MP's advise, flattened D ports, deeper bowls.put more stuff in than I took out
1 member likes this
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