Lifetime timing belt - I don't think so!

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Lifetime timing belt - I don't think so!

RalphM

Active member
Joined
Nov 26, 2020
Messages
334
I always thought that the VV cut fuelling on the over run to a point were
when the throttle was opened the engine got a does of very weak mix
this caused a spit back and any fuel in that hit the hot engine and
WWWooooommmmmp
 

mj2k

Amateur spanner twirler
Joined
Oct 10, 2021
Messages
614
I always thought that the VV cut fuelling on the over run to a point were
when the throttle was opened the engine got a does of very weak mix
this caused a spit back and any fuel in that hit the hot engine and
WWWooooommmmmp

Could be, it was an oddity of the VV though, Dellortos and SUs definitely didn't do that. I seem to remember reading somewhere they fitted a bigger steel air filter surround in the USA with the VV, presumably that was to act as a fire break 😲
 

DaveMcT

Well-known member
Joined
Sep 14, 2009
Messages
18,496
Two stroke was even simpler with many having no moving valves
Check out the Rotax Etech 800/850. It's a twin cylinder direct injected two stroke that makes 160bhp with strong mid range, better fuel consumption than four strokes of similar power and it easily meets the stringent US EPA clean air regulations.

The engine breathes clean air so needs less oil to lubricate cranks and bores (no petrol washing effect). Injectors use speaker coils that squirt fuel AFTER the piston ports have closed. Inlet has reed valves exhaust has a variable geometry valve so you get a low height port at low revs for high torque and a high port at high revs for power. Maintenance costs are mono worse than for strokes (less to go wrong) and as they dont "chunter" (four-stroking/hunting on bad mixture) like the old strokers, the bores don't self destruct.

The old style 2 stroke was really only happy on wide open throttle engine. Drop the throttle and you get the hunting, chattering and piston slap the makes so much ring-a-ding noise. Direct injection solves that as there is no fuel in the cylinder unless its injected and never any fuel in the crank case.
 
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