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1600 xflow - Which Weber Jets?
Kaino - 22/6/15 at 06:52 PM

Hi guys,

Just fitted a rebuilt 1600 xflow to my locost. The engine is standard other than a high torque cam fitted and vernier timing pulley which I have been assured is correctly set up.

I have a flat spot on the carb twin choke 32/36 DGV with choke butterflies removed. Only occurs just before opening the secondary barrel flap - it stumbles quite badly. Fine up to this point and through accelerating and great on secondary barrel/flap. Cleaned out and run fuse wire through all the jets and no difference. The carb ran fine on the engine before the rebuild, only change is the cam.

Should I change the jets?
Currently setup:

Primary Idle: 60
Secondary Idle 50

Primary Main: 140
Primary Air Connector: 170

Secondary Main: 140
Secondary Air Connector 160


Both Emulsion Tubes: F50

Any help greatly appreciated!
Thanks for reading

Sam_68 - 22/6/15 at 07:08 PM

quote:
Originally posted by Kaino...ran fine on the engine before the rebuild, only change is the cam.


You've answered your own question.

A cam change will need the carb jetting to suit.

Kaino - 22/6/15 at 07:19 PM

Thanks, but any idea to what jets or where I can find information on which ones to use?

Sam_68 - 22/6/15 at 07:50 PM

Even if we knew the full specification of the engine, it wouldn't be possible to say with any real accuracy.

The only way is to get it set up on a rolling road by someone who understands carbs.

Dingz - 22/6/15 at 10:37 PM

As it faulters when the second choke opens try a bigger idle jet in the secondary choke, possibly you could just try swapping them over for a start to see if it improves that area.

Angel Acevedo - 23/6/15 at 02:46 PM

It is either the progression circuit, maybe a progression hole plugged or too small an Idle jet which controls the fuel metering in the progression circuit.
You lose some metering ability with lopey cams as air speed on the ventury is reduced due to low vacuum.
Also you may alter acceleration enrichment cam to provide additional fuel on fast throttle opening.
Both will require some fiddling about and better done by someone who knows webers and has access to the engine running.
HTH.
Angel Acevedo

PS: Tis was studied on the weber manual some time ago... not dealt with webers lately....

SeaBass - 24/6/15 at 08:23 AM

Some good thoughts here to aid understanding...


http://datsun1200.com/modules/mediawiki/index.php?title=Weber_DGV_Tuning

[Edited on 24/6/15 by SeaBass]

steve m - 24/6/15 at 08:51 AM

link doesn't work

SeaBass - 24/6/15 at 10:40 AM

Fixed

Kaino - 3/7/15 at 07:30 AM

Thanks for the posts and replies, some good reading to keep me going and to investigate.

Will update when i get chance with the progress.

redturner - 6/7/15 at 09:14 PM

Your jetting is certainly out. Try these Primary Main...160, Secondary main...190 Primary air correction 165... Seconday air 160. The emulsions and pilots are ok, You should also fit a twin squirter...What cam are you using....Is the pump valve in the bottom of the float chamber been removed...

[Edited on 6/7/15 by redturner]

Kaino - 7/7/15 at 06:19 AM

Thanks,

They are quite different so will investigate in the next couple of weeks. It is fitted with the Kent high torque camshaft.