40IDS versus 40PMO and get 185HP

[Xavier PJB]

Greetings all,

I have dropped my 2.0S 1968 engine to do maintenance and revise the Weber 40IDS (they leak fuel/petrol/gas/essence)

SOooooo, I asked myself 3 things and value inputs of the community
1) do I rebuild my 40IDS to fix leaks and get / check factory settings (if anyone has them, mind it to share ?)
2) do I swap to 40 PMOs ? Any return on experience here ? (am sure there is)
3) my 2.0S is standard settings, measured on a rolling bench at 162HP, and wonder how to increase the output a bit, to let say 185hp ? Have in mind to replace the piston fo HC. I could not find the thread on the 2.0 optimisation.

Cheers
X
(Hope everything is ok with all of you)

[1QuickS]

Use 2.2 S pistons to get your 185HP with S-cams and 32mm main venturis. Install a twin pipe muffler & get some more. Staying with 2 liter then think GE60 cams, 34mm venturis and sport muffler and keep the revs above 3000 RPM and expect peak HP to be at 7000 RPM vs. 6600 for S-cams. S pistons are 9.8:1 so not much you can do by upping compression without twin-plugging. Also, the early S pistons have a steep crown that inhibit fuel burning at high RPM which is the reason for the IDS Webers with the High Speed Enrichment circuit, a feature the PMOs do not have.

OK, now wait for more sage input, I'm just a Weber guy offering what I know from my customer's experiences.

[Richy]

If the pistons are changed to 2.2's you will need 2.2 , or 2.4 heads .

[Xavier PJB]

Use 2.2 S pistons to get your 185HP with S-cams and 32mm main venturis. Install a twin pipe muffler & get some more. Staying with 2 liter then think GE60 cams, 34mm venturis and sport muffler and keep the revs above 3000 RPM and expect peak HP to be at 7000 RPM vs. 6600 for S-cams. S pistons are 9.8:1 so not much you can do by upping compression without twin-plugging. Also, the early S pistons have a steep crown that inhibit fuel burning at high RPM which is the reason for the IDS Webers with the High Speed Enrichment circuit, a feature the PMOs do not have.

OK, now wait for more sage input, I'm just a Weber guy offering what I know from my customer's experiences.

Cheers Paul, so IDS are great carb on a 2.0S ? Neither PMO nor Weber IDA ? I have "holes" between 2000 and 3000 rpms then full power until about 6500rpm. Above 2000, the engine is very sweet with no rattle at all, and my middle is 800 and turns nice. Am running a MDS6AL box and coil.

EDIT : forget my comment above. I have started to read your (extraordinary) tech articles on Weber, and that tend convincing me to keep my IDS
Paul, it is a real pleasure to read, indeed.

Cheers

[1QuickS]

Thank you for your kind comments regarding the Tech articles on my website!

A flat spot during transition (2500 through 3500 RPM) is easily remedied by modifying your Webers to have tunable idle air correction jets. These work in a similar fashion to the main air correction jets in that they allow the fuel delivery curve to be adjusted richer or leaner as RPM increases while maintaining a given idle jet size. In this way you can keep a reasonable low speed mixture with the 55 idle jet but the fuel delivery will increase toward transition which overcomes lean mixture issues, this situation would benefit by decreasing the 110 idle air correction jet size to 100 or maybe 90. This is an easy modification to perform.

Re-bushing your Webers is probably required to make low speed performance acceptable if they do not consistently return to a given idle speed.

I did have an odd stumble (right at 3000 RPM) on my 2.3 liter S-cammed hot rod which was cured by installation of full radius intake horns.

The IDS carbs were developed specifically for the 2.0 S engine. The race engines used 46mm throttle bores but had twin plug ignition and tall auxiliary venturis, the twin plugs allowed better fuel combustion than the single plug ignition on the S engine so the high speed enrichment tubes were not required. If the high speed enrichment tubes were required then they would have needed to be bent to clear the tall aux venturis.