weber blow through carb

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Dougs Auto
Posts: 23
Joined: Fri Dec 14, 2012 12:54 pm

weber blow through carb

Post by Dougs Auto » Thu Oct 26, 2017 10:28 am

Hi All

Does anyone know of how to keep the air fuel ratio up under boost other than modulator rings and turbo emulsion tubes.
Emulsion tubes did nothing to richen up the mixture under high boost ( 6 lbs) modulator rings did work but had to be so small to richen up the mixture that it killed the HP. I tried every e tube and jet combination that I had it allways runs rich on the low end and lean on the high end. there was no way to get the air fuel ratio at a constant. there must be some carb mods or changes that can be made that I am missing that will get me a constant Air fuel ratio. the carb is a weber ida 40mm the engine is a 2000cc single carb fuel pressure is boost compansated and remains the same through out the entire boost range .engine is on a dyno so load and boost is easy to control. any ideas how to richen up under boost without running to fat at low HP .

Thanks Dougs auto service

GARRICK.CLARK
Posts: 511
Joined: Fri Aug 26, 2011 12:01 pm

Re: weber blow through carb

Post by GARRICK.CLARK » Thu Oct 26, 2017 1:31 pm

1st thing is boost pressure needs to be higher in the float bowl than what is going down the carb throats.

Dougs Auto
Posts: 23
Joined: Fri Dec 14, 2012 12:54 pm

Re: weber blow through carb

Post by Dougs Auto » Thu Oct 26, 2017 4:25 pm

Hi All

Yup knew that thats what the modulator rings are for I have a half dozen pairs yes they raise up the float bowl pressure as they were designed to do. but had to make them so small to get any enrichment from them it cut down my top end HP from 145HP to 120 HP I bought a pair of 32MM made no Difference so I machined out my own an exact copy of the ones I purchased went down to 26 MM before I saw any AFR change then It killed my top end HP from the restriction. I think most think you pop them in and they work without testing the different sizes how would anyone know if they worked or not.

Dougs

Clonebug
Posts: 2954
Joined: Fri Feb 16, 2007 12:28 am

Re: weber blow through carb

Post by Clonebug » Thu Oct 26, 2017 7:25 pm

Extend your fuel bowl vent up into the top hat and bend it slightly towards the boost source.

Report back your results......;)
Stripped66 wrote:The point wasn't to argue air temps with the current world record holder, but to dispel the claim that the K03 is wrapped up at 150 HP. It's not.

Dougs Auto
Posts: 23
Joined: Fri Dec 14, 2012 12:54 pm

Re: weber blow through carb

Post by Dougs Auto » Thu Oct 26, 2017 8:27 pm

Hi All

one of the next steps was to raise and extend the bowl vent tube up and towards the air flow. Did discover a possible problem. the secondary venturies extend up and past the modulator rings narrowest point in my thinking putting them into a high pressure area above the modulator rings. research showed that a lot of the weber carbs venturies were well below the top of the carb, so a cut off .500 of the top of the venture this put it below the narrow point on the mod ring. another pull on the dyno showed good improvement my AFR stayed closer through the run and no loss in HP, Ran out of time today will switch to a 2MM smaller mod rings tomorrow and see if I can get the AFR a little better.

Dougs Auto

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