View single post by Esprit2
 Posted: 11-27-2021 06:19 am
PM Quote Reply Full Topic
Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
 Disappointment is a function of expectations. Some JH owners are running DHLA 40 carbs with chokes as small as 32mm. There seem to be more JH owners who want more low end torque and driveability, while more Lotus owners tend to be biased toward improved top end power and performance. One thing is for certain, you can't have both, you must choose.

Smaller throats and chokes favor low end torque and driveability (J-H used DHLA 40 carbs).
Larger throats and chokes favor top end power and performance (Lotus used DHLA 45E carbs).

Since you already have DHLA45 carbs, that precludes the J-H priority of tuning for optimal low end torque & driveability. You're starting out in the Lotus school of tuning, at least in terms of your small throat size. Perhaps that was someone's attempt to detune the 45 carbs, but 34 chokes are pretty small for 45 throats... ie, not a combination you would normally see.

So, what is it you want to get out of your JH 907? Low end torque and driveability, or top end power?

In Lotus own first 907 powered car, the 1974 Elite 4-seater, Lotus went with 38mm chokes. That heavily favored top end power. Lotus marketing hadn't really accounted for the berzerker boy-racers who where rat-racing around in Elans and Europas would not be the same people who would buy the 4-seater executive express. Early buyers complained heavily about the car's lack of low end performance, and the need to rev the engine. Duh!

For the second model year, Lotus over reacted and went wtih Spec 3, 45E carbs, and 35 chokes. The customers were then pleased with the low end performance, but complained about the loss of top end power. Yeah, double duh!

For the third model year, Lotus finally got it about right with Spec 5, 45E carbs with 36mm chokes. They stuck with Spec 5 through the rest of the 907's Euro/ROW production run. Only when the 2.2 litre 912 came out did they go with Spec 9 and 37mm chokes.

All of those Lotus set-ups 45 or 45E carbs, and were a hotter state of tune that the J-H 40 or 40E carbs with 35mm chokes.

So, again, what do you want your engine's personality to be like?

If you wish to stick with your DHLA 45 carbs, and are willing to accept a more sporty state of tune, then I recommend Lotus Spec 5 The 36mm chokes are about right for a near stock 2.0 liter 907 with DHLA45E's, and a 'sporty' personality.

Tag Number . . Front . . . 5295A
. . . . . . . . . . . Rear. . . . 5294P
Carb Type. . . . . . . . . . . DHLA 45E
Choke . . . . . . . . . . . . . 36 mm
Main Jet. . . . . . . . . . . . 160
Main Air Corrector Jet . . 230
Main Emulsion Tube. . . . 7772-8
Idle Jet . . . . . . . . . . . . 50 (Too lean! Try 55-58 range)
Idle Jet Holder . . . . . . . 7850-7 (Lean to Rich . . –5, –10, –9, –4, –1, –3, –6, –7, –2, –8).
Float Weight (grams). . .10 gr
Float Height . (mm) . . . 16.5 - 17.0 mm
Float Needle Valve . . . . 170 .
Pump Jet. . . . . . . . . . . 38V 42H
Starter Jet. . . . . . . . . . 70
Starter Emulsion Tube. . 7482-1 .
Power Jet. . . . . . . . . . . None
Slow Running Speed . . . 900 - 1000 rpm
Idle CO Level (hot) . . . . 2.0 - 3.0%

Paulreese1 wrote:
(Snip)... So given a peak power @ 6500 RPM? should have:
Chokes 38 mm
Main Jet 152
Air Corrector 202
Emulsion 7772.5
Idle Jet 55
"IF" you went with 38mm chokes (I'll bet you wouldn't like them), then I would recommend the following:
Main Jet. . . . . . 142
Air Corrector . . 110
Emulsion . . . . . 7772.5
Idle Jet . . . . . . 55L
In other words, Lotus Spec 1 (that Elite customers complained about).

Regards,
Tim Engel

Last edited on 12-20-2021 11:43 pm by Esprit2