View single post by Esprit2
 Posted: 08-22-2014 02:52 am
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 573
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 First, do you know when the timing belt was last replaced? If not, replace it now before putting the car into general service. The belt is supposed to be replaced every 24k miles or 24 months (whichever comes first), and time is just as important as mileage.

If you'd like to get together sometime, I'll take a look at it. No promises, just another opinion. We can make certain the cam and ignition timing are right, then dig into the carbs a bit.

Which Webers? Including the dash number after the throat size... like DCOE40-151.

The problem with Webers is that neither J-H nor Lotus ever used them on their stock versions of the 907... both used Dellorto DHLAs instead. So with Webers, you don't have that history of factory settings to use as a starting point, and you're pretty much starting from scratch.

What jetting is in the carbs now? Matt Cooper at Eurocarb Ltd in the UK knows both Weber and Dellorto carbs, and he also knows the Lotus 907/ 911/ 912 engines very well. Perhaps he could comment on the current jetting. I'm a Dellorto guy, and could offer some more specific input on DHLA/ 907 set-up, but Weber jetting would be more of an exploration.

In the chart below, the first two columns are generic jetting set-ups by the standard Weber jetting formulas. The third column is what Charlie S. used in the otherwise stock 907 in his Lotus Eclat. Pete B's Yelodog is 2.2 liters, 11.1:1 compression, big cam, ported, 0.180 oversize valves... etc, etc... so probably not a good match for yours.

.......................................................... Charlie ..... Pete's
Weber Jetting: .. Power ..... Economy ... Seabrook .. YELODOG
Carb Size ....... 45DCOE9 .. 45DCOE9 .. 45DCOE9 .. 45DCOE9
Choke (mm) ...... 36 ............ 36 ............ 35 ............ 36
Main Jet ........... 135 .......... 135 ........... 120 ........... 135
Air Corrector .... 160 .......... 175 ........... 180 ........... 180
Emulsion Tube .. F16 ............ F9 ............. F2 ............ F3
Idle Jet .............. 55 ............ 50 ............ 50 ............ 50 (50F9)
Idle Air Bleed ..... F9 ............ F9 ............. F9 ............ F9
Pump Jet ........... 40 ............ 40 ............. 50 ............ 45

Charlie’s comments:
"If gas mileage is really important, the 45F8 idle jet can be used. Idle jets on Webers control the mixture from idle all the way up to and beyond 4000 RPM. With this jet, you get some slight lean surge and a definite hesitation when opening the throttle at 3000-3500 RPM. The 45F8 saved me about 2 MPG on long trips over the 50F9. If you want better off-idle response, use 55F8 idle jets. Again, you will lose another mile or two per gallon."

IMHO, Charlie’s set-up is rather conservative and biased more for economy that performance.

Pete posts here. Perhaps he will chime in.

Regardless, knowing what jetting is in your carbs now would be a good place to start. Open them up.

Dyno-Tech (Tim Moore, or it could be his son by now) off I-94 in the Hwy 280/ Cretin-Vandallia area knows Webers and could tune your engine on a chassis dyno.

DynoTech Automotive (Tim Moore)
(612) 379-4205
2090 Gilbert Ave, St. Paul, MN 55104
Dynomometer tune-ups - Power or Emissions
https://www.facebook.com/pages/Dynotech-Auto/138837712830146

Last edited on 08-22-2014 03:39 am by Esprit2