weber jetting

[krispy_kgc10]

I just got my L28 installed in the skyline, from an L20a!! I had the webers, kinda, tuned down to suit the displacement, I have triple 45 dcoe`s. I was wondering what other people with 45s had for jetting and venturi? the block is a f54, flat top pistons with a p79 head...

thanks for the help.

[Dtsnlvrs]

The jetting differs with venturi size. There are several good books which can help you get into the ballpark. "How To Build & Power Tune Weber & Dellorto DCOE, DCO/SP & DHLA Carburettors" by Des Hammill, and Honsowetz's book "How to Modify Your Nissan/Datsun OHC Engine" Camshaft selection, headers, etc will all play a part in setting up the carbs. However for a starting point, try a 34mm venturi with either a 135 or 140 main jet and either a 155 or 160 air corrector. For Idles I would start with a 50F9 or 55F8.

[krispy_kgc10]

i have those books but its interesting to see what others are running...

[HS30-H]

What series of 45DCOE are they, and roughly what vintage?

This is very important data. No point in giving you pointers on jetting without knowing what exact model of 45DCOE carbs you are starting out with.

Alan T.

[Dtsnlvrs]

What series of 45DCOE are they, and roughly what vintage?

This is very important data. No point in giving you pointers on jetting without knowing what exact model of 45DCOE carbs you are starting out with.

Alan T.

Great point Alan, the series of DCOE, IE 45DCOE152 etc, will glean usefull information on proper jetting. When it is all said and done, it is possible to have 2 identical motors jetted differently. The later DCOE carbs made in Spain (45DCOE152) were more of an emmision design with idle air bypass screws for balancing airflow, and more progression holes in the circuit. FWIW I pretty much follow Honsowetz"s reccomendations, but I dont use nearly as large a venturi as he specifies. I like my cars to pull well right off the line, therefore, I use a 30mm venturi in a 40DCOE18.

[krispy_kgc10]

sorry about leaving that number out, there 45dcoe13`s Italians

[HS30-H]

The 45DCOE-13 was a 'conversion' kit carburettor, never used as standard equipment on a production road car. That means its internal spec might have been changed to suit the engine it was originally supplied for ( anything from a Mini Cooper 1275S to the Renault engine in a Lotus Europa ). They were most often fitted singly to four cylinder engines.

You don't mention it, but I presume these carbs came already fitted in Japan to the original L20A in your car? If this was done a long time ago then there is a good chance that they were originally supplied as a kit by 'Far East Trading' ( 'F.E.T' ) and therefore have been supplied with changed internals to suit the L-gata engine. That's a good thing; hopefully they will already be pretty close to what you need.

But personally, I would want to check and see what Accelerator Pump Rod stroke they have. The Nissan L-series 6 seems to like a 'short' ( 10mm ) Pump Rod stroke, and this improves driveability. No sense in messing with venturis, emulsion tubes and jet sizings when your Pump Rod stroke is too long.

They are easy to take out ( even with the carbs installed ) so I'd recommend you confirm what you have before going any further.

Alan T.

[bjhines]

Mine are DCOE 45 - 152s... late models with the plastic floats and air bypass needles... made in Spain...

125 Main, 180 air, 60F9 idle, 34mm chokes..

I tried 30mm chokes... it ran great on street.. It felt like it was missing high end HP.. even though I have A/F ratio meters installed and mixture was correct throughout the range...

I tried 36mm chokes.. the mains would not come on until 3300 RPM...

I ended up with 34mm chokes installed for mostly track use.. occasional street driving... It comes onto the main circuits at ~2800 RPM.. It never bogs on track(even with 3rd gear corner exits)... but it does surprise me sometimes with jackrabbit starts from stoplights...

I would bet that 32mm chokes would work just as well at high RPMs... but would get onto the mains sooner and more smoothly at low RPMs... I just ran out of patience... and I don't have any street tires right now anyway...