Poor TR6 Throttle Response

Bigpete

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Today, 10:05
Joined
Aug 5, 2022
Messages
6
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Age
62
Location
Fort William
First Name
Peter
My Ride
Trident 660 and Steve McQueen replica rickman Metisse
Afternoon all, Ive a Metisse desert racer with a Tr6 engine, single amal carb, electronic ignition with approx 400 mile on a rebuilt engine.
The bike starts really easily and runs fine up to half throttle and then goes flat as a pancake. I suspect fuel but have had the carb of , cleaned and checked . All seems fine so any thought as to what else it might be, should say its also had a new foam filter which has been lightly oiled and E5 fuel with octane booster and lead replacement additive. it doesnt do a huge mileage and has sat for a while.
Cheers
 
You might want to look into changing out the jets and retuning it after.
 
Has the motorcycle had any mods? If you do go the jet replacement route, get a set with different sizes. You might be needing something a different size to what’s installed.
 
Tr6 engine, single amal carb, electronic ignition
runs fine up to half throttle
Not sure how anyone can start to offer any sensible advice based on such vague information ...

"TR6" was a model designation used from 56 to 73; however, a 56 engine is completely different from a 73 engine.

Which "amal carb"? Concentric? Monobloc? Which size?

Which "electronic ignition"? Make, model?

Which gear? Most TR6 had four gears, some 72, all 73 had five. Nevertheless, easy to retrofit a 4-speed cluster into cases bored for a 5-speed.

Mark the twistgrip housing with one mark you can see riding the bike. Mark the twistgrip adjacent to the housing mark at: throttle closed, 1/4 open, 1/2 open, 3/4 open and fully open.

Ride the bike, noting the throttle position where "goes flat" occurs in each gear:-

. same throttle position in all gears = carburation problem;

. same rpm - or, no tachometer, not the same throttle position in all gears = ignition problem.

For clarity, the above starting diagnosis is not mine, originally posted on A.N. Other forum by someone with much more experience than me ...
 
Last edited:
all of the above, plus check fuel flow.

is the tank vent in the cap clear?

will your fuel tap run 300 ml per minute out the carb drain plug?
 
and try it without the foam filter.
 
Not sure how anyone can start to offer any sensible advice based on such vague information ...

"TR6" was a model designation used from 56 to 72; however, a 56 engine is completely different from a 72 engine.

Which "amal carb"? Concentric? Monobloc? Which size?

Which "electronic ignition"? Make, model?

Which gear? Most TR6 had four gears, some 72 had five.

Mark the twistgrip housing with one mark you can see riding the bike. Mark the twistgrip adjacent to the housing mark at: throttle closed, 1/4 open, 1/2 open, 3/4 open and fully open.

Ride the bike, noting the throttle position where "goes flat" occurs in each gear:-

. same throttle position in all gears = carburation problem;

. same rpm - or, no tachometer, not the same throttle position in all gears = ignition problem.

For clarity, the above starting diagnosis is not mine, originally posted on A.N. Other forum by someone with much more experience than me ...
Hi Rudie, great advice thanks and yes it definately feels like carburation but ill do as you suggest.
Hard to tell what year the engine is as its a Metisse rebuilt unit from the states and restamped for registration by the builder Gerry Lisi, from that as well the electronic ignition system wasnt fitted by me and is unmarked/stamped with the manufacturers name.

STEVE MCQUEEN™ DESERT RACER SPECIFICATION​

POWERTRAIN

Engine: Fully reconditioned original 650 cc T6 Triumph
Transmission: Reconditioned 4 speed Triumph
Carburettor: Amal single concentric type R930/23
Exhaust: Twin up-swept chrome pipes
 
Hard to tell what year the engine is as its a Metisse rebuilt unit from the states and restamped for registration by the builder Gerry Lisi, from that as well the electronic ignition system wasnt fitted by me and is unmarked/stamped with the manufacturers name.
While "T6" is not a Triumph model code, the Steve McQueen™ Desert Racer webpage images show a late TR6 engine - crankcase vent from the primary is very late 69 onwards, cylinder head/rocker boxes are 71 onwards. Does your bike's engine match those images?

electronic ignition system wasnt fitted by me and is unmarked/stamped with the manufacturers name.
All electronics under the original points cover (circular chromed cover on the timing chest)? Or only some under that cover, separate but connected 'black box' elsewhere on the bike? Post some photos?
 
Obviously the more detail the better, but for me, goes flat as in no spluttering, coughing , lurching or surging, I would probably check timing first, making sure it's advancing as it should. Over retartded ignition tends to start really easily and run out of power quickly.
 
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