weber carb question

[seniorchristo]

I purchased some size 50 accelerator pump jets for my twin cam trying to improve upon a low end hesitation. Yet the existing size 40 jets appear bigger than the 50's. I thought the jet size was proportional to millimeters. Not having a wire gauge to measure size, I guess it is possible the 40's were drilled out. Is the jet size proportional to the opening?
thanks
Chris

[SENC]

I'm fairly new to Webers, but I believe you are correct. I believe 40=.4mm and 50=.5mm. Was your low end hesitation at WOT or partial throttle?

[Craven]

Yes proportional but it’s 40 = 0.40 mm ( ie 100 = 1mm )
So 50 is just 0.1 mm larger or 0.004 inch.

[seniorchristo]

Ok thanks! The flat spot starts at 2000 rpm most noticeably when throttle is open quickly.

[Certified Lotus]

Chris, you need one of these tools for jet size measurement (I forget where I bought it, but’s it’s made in Germany)

[seniorchristo]

Thanks Glen. I'm going to order from Pierce Manifold.

[nigelrbfurness]

Did you check your float level height during your investigation into your flat spot? More than once I've found incorrect float heights to the cause of the problem you describe.

[davidj]

I too had hesitation at low speed and car would sometimes cut out when slowing down for junctions. I eventually traced the problem to the float height as well.

[mbell]

Standard pump jets are 35, so going quite a bit bigger. Assume you only get when increasing throttle noticeably?

[alan.barker]

Imho your problem is not the pump jet but the Idle Jet to stop hesitation.
Alan

[seniorchristo]

From what I've read I didn't really think it would be the pump jets but thought I would experiment. I've set float levels but may recheck using Keith Frank method. I have different idle jets but undecided whether to go richer or leaner.
Thanks,
Chris

[h20hamelan]

Might be worth drilling a bung for o2
I leave the sensor/sender in place, but only have the readable instrument in place for checking.
Do you have access to ColourTune?

[alan.barker]

What colour are the Spark plugs after a good run. You'll know straight away if it's weak or rich.
when you go up 5 on the size you can see the colour change on the Spark Plugs easy.
Alan

[seniorchristo]

I've used colortune to set idle mixture but didn't think to use for the progressive circuit. I have an O2 bung to install but I'm waiting to rework my exhaust. Never a lack of things to do on an Elan.

[alan.barker]

Colourtune is only for slowrunning mix tick over.
Alan