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Mk2 polo weber conversion flatspot
Eviljohn - 10/3/18 at 12:16 PM

Hi all. As above, 1983, 1043cc breadvan recently converted from stock carb to weber 32ibf, 127 main jet, still running points and condenser on dizzy until i get around to converting to electronic ignition. Stock air cleaner, changed from rubber to silicone vacuum hoses.
Since carb swap, i have a little flatspot on accelleration at low revs. When pulling away or changing down a gear. Possibly more accurate to say the flatspot occurs when the revs are low and i put my foot down or engine load goes up. Revs drop a little and engine comes close to cutting out. Doesn't happen so much if manual choke is out just a little. Is this a normal thing or is there something i can look at adjusting/fitting to stop it? Thanks for stopping by and any xp you can give.

davew823 - 10/3/18 at 01:30 PM

Just try moving the accelerator pump linkage down one hole. You need to increase the fuel at tip in. Davew823

[Edited on 10/3/18 by davew823]

Eviljohn - 10/3/18 at 07:14 PM

Will look into doing that. Thank you.

Eviljohn - 11/3/18 at 04:54 AM

Is the accelerator pump the little diaphragm bit with a screw in each corner?

Eviljohn - 11/3/18 at 05:32 AM

Quick google says yes. Thanks anyway.

Eviljohn - 11/3/18 at 07:46 AM

Kay, i found it. On the weber i have fitted, looks like a metal bar with a spring over the top of it, hooked onto the throttle spindle on one end, a long nut on the other. Is it a simple case of loosening or tightening the nut to adjust the accelerator pump, and of so, should i be loosening the nut to push the linkage closer/tighter into the diaphragm or tightening the nut to bring it out/relax it from the diaphragm?
Thanks again for any xp anyone is able to leave.

Dingz - 12/3/18 at 05:25 PM

It might be a too small idle jet, at low revs and openings fuel is supplied through the idle jet circuit during the transition to the main jet.

Eviljohn - 12/3/18 at 08:22 PM

After googling "weber flatspot", larger idle jet seem to be the most common cure. Gonna try adjusting the pump linkage first and see how that goes. According to the paperwork that came with the carb, the idle jet fitted is a 45. Looking to try a 50 if adjusting linkage doesn't work.
Thanks for getting back to me. Much appreciated.

Eviljohn - 12/3/18 at 09:02 PM

Out of curiosity, are weber idle jets pretty much the same, apart from the size of the opening? As in, if i just google "weber idle jet 50", will that be the one i need, or do i need to open up the carb and find a part number?

Dingz - 13/3/18 at 10:38 AM

It will only have a number on it ie 40. Dont know about the 32 ibf but the dgav/dgas are the same.

Eviljohn - 13/3/18 at 11:11 AM

Cool. Will bear that in mind. Thank you.

Eviljohn - 13/3/18 at 02:41 PM

I had time for a quick tinker today. I adjusted the accelerator pump linkage and it seems to have improved the flatspot for now. I did adjust the idle very slightly too but only marginally. Anyhoo, i'll see how it goes tonight and report back.
Thanks for your advice so far.

Eviljohn - 14/3/18 at 09:04 AM

Yeah massive difference! Feels more solid and just nicer to drive. Leaving the idle jet for now. May tweak the linkage again just a tiny bit.
Thanks for your help.