IDF wizards needed

DubCty · 2012-08-26T10:41:10+00:00

G’day guys (and girls) I have recently fitted twin 36IDF carbys to my 1850cc and I’m going through the tuning/jetting stage trying to get the most from them. I have a wideband air/fuel gauge fitted to the car to help out with the jetting side if things but im having problems with inconsistent running. I can the engine to operating temperature and set the idle speed and the car runs great for a few drives, but then all of a sudden the idle speed jumps up from 800 to around 1200rpm and the air fuel ratio leans right out with an impressive backfire problem when coasting, with a bit more driving ( about 10 minutes) everything settles back down and the engine idles and runs as it should. I have checked all the jets are clear, the timing is as it should be and I can’t find any air leaks in the system.🤪 The engine is an 1850ccTP with electronic ignition, mild cam, Italian 36 IDF’s run 32mm ventures with 150mains at the moment Any help would be really appreciated. Cheers AL

DubCty Slammed & Awesome Dubber

95 posts · joined Jun 2009 · 26 Sep 2012, 8:45 pm

#923851

Hey guys,
I finally got around to slipping some 47.5 and then 55 Idle jets into my carbs, I would of preferred 50s but I’ll have to chase some down. The 47.5s were an improvement again on the smaller jets but still running lean when accelerating up to 60kmh, I then tried out the 55s acceleration was great with the wideband sitting on about mid 13’s there was a slight dead spot around 3krpm but that’s not a concern atm. The only issue I have is that at idle (was sitting a little low around 500rpm.. will fix) the A/F mixture was off the scale rich (below 10). Ill pop some 50’s in this weekend and I expect this will help with the idle AF but should I be leaning out the mixture screws to balance out the rich idle? Also how low is too low for A/F mixtures i.e when will plugs start to fowl?

Cheers AL

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matberry Moderator Go hard or go home

8,114 posts · joined Mar 2006 · 26 Sep 2012, 8:52 pm

#923854

The A/F is rich only because you haven't got the idle mixtures right. The idle jets govern the progression circuit, the mixture screws are at idle.

Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
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DubCty Slammed & Awesome Dubber

95 posts · joined Jun 2009 · 26 Sep 2012, 9:07 pm

#923863

Thats what I thought, Ill see how the 50's feel and then work on the idle mixtures.

thanks Matberry your a great help.

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DubCty Slammed & Awesome Dubber

95 posts · joined Jun 2009 · 1 Oct 2012, 8:59 pm

#924480

At last I think the jets are right there is still a small dead/lean spot when accelerating but any richer and everything turns to S**T. I’ve set the mixture screws so that idle sits at around 12.5A/F. The cold start is ok but getting the car to start when its warm (after sitting for a short period) can take a while turning it over, are there any tips for improving warm starts?

Any help is really appreciated, AL

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