MonteCarlo Weber 40's Jetting...

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tired_guy
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MonteCarlo Weber 40's Jetting...

Post by tired_guy » Sat Jul 01, 2017 7:08 pm

I was wondering if some one could confirm that the current jetting i have in the webers is correct for the spec engine. The engine is a Guy Croft power unit on the receipt it states "fast rd spec guaranteed 130bhp at the wheels". I have no idea what its running cam wise or even compression wise so a little clarification would be helpful

On the whole the engine runs well, i have removed the carbs to replace the gaskets and give them a once over. Idles great, starts great(with choke), top end power is good the only issue i tend to have is slight reversion on one pot at around 2k giving a fluffy/dull feeling (cruising speed with light throttle). This was worse until i moved the timing back slightly.

This may well be fixed once i refit them with the new gaskets and after a good clean.

I would just like some one to confirm that the base setting of the jetting is good.

Starter Jet - 60F9
Main Jet - 140
Emulsion Tube - F21
Air Corrector - 150
Pump Jet - 35
Venturi - 22* (struggling to see anything on these units apart from what looks like 22 scratched in)
Aux Venturi - 3.5
Idle Jet - 60

I currently don't have any AFR readings (once back up and running i will)


Many thanks for your help
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Guy Croft
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Re: MonteCarlo Weber 40's Jetting...

Post by Guy Croft » Sun Jul 02, 2017 12:00 pm

think the emulsion tube is OK will check tomorrow..

The only jet alteration really needed is much bigger air correctors, go 180.

Sy chokes will more likely be 32 not 22mm but only measurement will determine for sure. 40 DCNF are OK on 32 but you'll get more top-end power on 34mm. The old ones may have been machined-out and marked with a scribe, dunno. Boring out is OK provided the aerodynamic shapes up-and-downstream of the controlling section is shaped as before...

Ignition timing should be 34 deg total (incl 10 deg static) at 5500, +/- 2 deg

Carb idle setting via mixture screws and balance is vital, also make sure the carbs are getting full throttle and the pump jets are not dribbling.

A sealed cold-air duct to the carbs is essential, no "if" no "but". Airbox on carbs with as much clearance to the carb bellmouth/intake as you can get, large bore trunking ( eg: dia 80mm) to a remote filter drawing cool air from somewhere. The Montecarlo is very prone to detonation if you induct at underhood temp. First signal is usually a blown head gasket and white smoke from the exhaust..


G
Guy Croft, owner

tired_guy
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Joined: Fri Jun 30, 2017 6:30 pm
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Re: MonteCarlo Weber 40's Jetting...

Post by tired_guy » Tue Jul 04, 2017 6:35 pm

Many Thanks for your response.

I will reassemble them with the larger air corrector jet and do some datalogging.
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