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Tune-up of a dell'orto DRLA 40 center mount on 1915cc
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domxs
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PostPosted: Tue Feb 16, 2021 6:24 am    Post subject: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

Hi,
My name is Dom and I run an off road buggy with a 1915 engine with engle 100 cam and 9:1 CR, 35.5 mm inlet valve diameter (stock) heads. The engine is not used over 4500 RPM. It uses a renovated DRLA dell’orto central mount.
Venturi size 28 (best torque), idle jet 55, emulsion tube 2, air jet 150 main jet 140, float level 5 mm. The manifold is a CB perf with heater allows the manifold to run at least at 90 F temperature. The AFR is relatively good around 12 to 13 at mid and full throttle between 2000 and 4500 RPM, My issue is that at low RPM about 1400 to 2000 RPM it goes very rich around 10 AFR from 1/3 to full throttle position.
I have been trying many configurations on air and fuel jets, can't get rid of this low RPM enrichment. The annoying thing is that the engine is used quite a lot under these conditions, fuel consumption is very high and cylinder washing may become problematic.
Thanks for helping,
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Dougy Dee
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PostPosted: Tue Feb 16, 2021 6:34 am    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

Sounds like your Pump Jet is too large. You could try backing off the the volume.
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domxs
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PostPosted: Tue Feb 16, 2021 8:12 am    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

Hi Dougy Dee, thanks for helping, the issue is not during accel, so I am not sure it is related.
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modok
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PostPosted: Tue Feb 16, 2021 5:25 pm    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

This aircooled engine is not designed to be running at full load at low speeds.

Need to re gear the transmission so you are not trying to cruise below 2200rpm

Very nice trick that your engine CAN pull strong at very low rpms, but just because it can.... doesen't mean it should.
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evanfrucht
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PostPosted: Tue Feb 16, 2021 5:37 pm    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

Stock vws are pretty rev happy, it's bad to lug them.

Another part of the reason for wanting to keep the RPM's high under load so that the fan is spinning fast enough to cool the heads sufficiently.

DOWNSHIFT
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modok
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PostPosted: Tue Feb 16, 2021 6:31 pm    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

With that said..... I'm not saying it IS 100% right, they usually aren't.

According to my rules of thumb,
30.5 would be the smallest venturi worth using with the 1.5" tube intake manifold.
Going up to a larger venturi size improve your problem or at least be a better match overall. Worth a try. You could drop the fuel level 1or2mm, you could add a high hole to the e-tubes.
I had to make an entirely different emulsion tube to make it right. First pic in my gallery.
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domxs
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PostPosted: Wed Feb 17, 2021 12:12 am    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

Thank you modok for answering!

I have 30 mm venturi that I can try, could even re-bore it a little to match the 30.5 mm.
Concerning the emulsion tube I guess you refer to this picture: https://www.thesamba.com/vw/gallery/pix/1876028.jpg
If so, I will try your proposal asap.
Now the other thing is that I am rebuilding EMPI heads with 40 mm inlet valve. Would this change the setup in any way? I am guessing the filling will be better at any rev meaning more torque and increase air speed around the venturi.
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modok
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PostPosted: Wed Feb 17, 2021 12:45 am    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

This one
https://www.thesamba.com/vw/forum/album_page.php?pic_id=656422

I think 37.5mm intake valve is best match for the stock aluminum end castings. Maybe too big is no worse than too small, I don't really know, it's up to you.
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domxs
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PostPosted: Wed Feb 17, 2021 2:42 pm    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

modok wrote:
This one
https://www.thesamba.com/vw/forum/album_page.php?pic_id=656422

I think 37.5mm intake valve is best match for the stock aluminum end castings. Maybe too big is no worse than too small, I don't really know, it's up to you.


I will have a try to copy your emulsion tube config, looks promising to me!
thanks
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domxs
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PostPosted: Tue Feb 23, 2021 5:59 am    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

first emulsion tube done
Image may have been reduced in size. Click image to view fullscreen.
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domxs
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PostPosted: Fri Apr 09, 2021 4:33 am    Post subject: Re: Tune-up of a dell'orto DRLA 40 center mount on 1915cc Reply with quote

Hello,

A little feedback about the emulsion tubes: The erased most of the issues of enrichment at low RPM, so thanks MODOK for helping. I would also share that I run oil from the oil filter tubing through the inlet manifold instead of the exhaust gases. That provide us, when the whether is cold, a perfect heating.
I might try to level down the fuel by 1 or 2 mm as recommended by MODOK as well as trying 30 mm venturis. I'll let you know.

Thanks again for your help,
Domxs
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