The damn monobloc!

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dandabbler
Posts: 11
Joined: Tue Apr 12, 2011 1:03 pm
Location: Sunderland Tyne and Wear

The damn monobloc!

Unread post by dandabbler » Tue May 15, 2012 1:16 pm

Hello chaps, right well I'm just starting to get frustrated now.....I've had the engine running on my '66 175 Silver for maybe a minute but only whilst holding my hand over the inlet and the throttle on about a 3rd. This has worked with and without the choke slide down but release one or both hands and the engine dies!
The carb is Amal monobloc 375/60. Its been cleaned out and all new parts fitted with these settings;

Needle jet 105
Needle position 2nd from top
Pilot jet 25, 1 1/2 turns out.
Main jet 140 (although AMAL actually sent me a 100 and seemed surprised I wanted a 140 on the 'phone- is this because of modern fuel?)
Throttle stop is just touching the throttle slide valve
Pilot screw 1 1/2 turns out

When it does run it's sounding good and smooth and the exhaust is white initially but then starts to clear- so, what am I doing wrong (and don't say 'trying to get a monobloc to work!)

Cheers

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Bournemouth bantams
Posts: 12
Joined: Sat Dec 24, 2011 10:56 pm
Location: Portsmouth
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Re: The damn monobloc!

Unread post by Bournemouth bantams » Mon Jun 04, 2012 1:08 am

Hi
If the bike still runs when you restrict the air flow there must be an air leak else where. often the flange on the carg is tightened up to much this causes it to bow and air leaks past at he connection to the barell, check with a straight edge, and renew the oring seal.

"H"
Owner of Bournemouth Bantams. Various Two stroke machines. 1963 BSA Trail Bronc, 1963 Francis Barnett cruiser 80, BSA C11G, BSA C10L, and to my shame Honda 750 VFR

The Mighty Gusset

Re: The damn monobloc!

Unread post by The Mighty Gusset » Mon Jun 04, 2012 11:11 am

dandabbler wrote:So, what am I doing wrong (and don't say 'trying to get a monobloc to work!)


Hahaha !
There used to be a contributor on here who would have told you that all Amal carbs are completely worn out after 1000 miles and that all serious off-road riders fit nice reliable Mikunis.
He was a Right Arse !
BB is probably right, you've distorted the inlet flange (Ooooer - Flange !).

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Greenbat
Posts: 2748
Joined: Tue Feb 17, 2009 11:25 pm

Re: The damn monobloc!

Unread post by Greenbat » Mon Jun 04, 2012 11:20 am

Sheet of glass and fine-ish emery paper, and flatten the flange off. Then fit a new rubber ring.

dandabbler
Posts: 11
Joined: Tue Apr 12, 2011 1:03 pm
Location: Sunderland Tyne and Wear

Re: The damn monobloc!

Unread post by dandabbler » Thu Jun 14, 2012 11:17 am

Thanks chaps, a few small school boy errors were to blame, namely;

no air hole in my temporary fuel tank (bottle)- d'oh!

Also the collection of new parts supplied by AMAL aren't really that good;

The float and needle don't work when the washer is used with the fuel inlet, the float hits the top of the chamber before the needle rams home, so it's never going to stop the flow of fuel. Washer removal has solved that.
Washer on the main jet holder seems too big, fuel pissing out of the bottom, so I fitted a much tighter one which now works great.

So now with he engine idling nicely, tried it gingerly in the driveway...BANG, it jolted forward with the clutch still held in. Inspection revealed one solid, fused block of plates where there should be 5.
I'll give Surflex a call then.......

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