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GreenSwede

New headers with smaller primary tubes - Mixture to rich?

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Just replaced the headers, threw out a spaghetti style thing with larger primary tubing than the TEP 4-1 I now installed. (can´t remember measures)

It seems it´s running a bit rich? Hesitation on throttle and a bit of rumbling on deceleration.

So I´m thinking:

Am I wrong in thinking that the smaller tubing actually evacuates the exhausts quicker (on std engine) than the larger tubing did? At least on low revs?

Can a change of headers create such a noticeable change, that I have to adjust mixture? Anybody noticed this?

The damp autumn weather could be part of the cause, running a 32/36 with just the chrome filter top, no pre-heating of air. But even the other day, with cool dry air it seemed to be running rich.. A bit more so tonight, with damp and misty weather.

And yes, an adaption of the stock air cleaner is on the (probably)-to-do-list.

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You have a similar setup to me. I have a TEP header (ceramic coated) with 2" exhaust and a 2.5" rear muffler. My car is electronically fuel injected and I had to add fuel to the upper end, say above 80kPa, and especially at WOT. I really need to go to a dyno...

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Dear Ola,

please tell us the:

Primary Main Jet Size ________

Secondary Main Jet Size ______

Primary Air Correction Jet size__________

Secondary Air Correction Jet Size _______

Float Level _______

using an electric fuel pump ? pressure_____ psi

how is your ignition timing set? _____________

_________________________

_________________________

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Am I wrong in thinking that the smaller tubing actually evacuates the exhausts quicker (on std engine) than the larger tubing did? At least on low revs?

I believe you're on the right track; smaller tubes offer greater velocity, which increases the evacuation of the exhaust flow at low/mid rpms. It happens on cams grinds with lots of overlap, but perhaps the stock cam has enough to be affected as well.

As for jetting, there is no secret recipe that's ideal for every engine, location or the corrected altitude for every day (it's a good sign that you're in tune with how the car feels in different conditions - keep notes). -KB

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Maybe the change in design AND the tubing size in combination did it.

But I'd start by confirming that everything ELSE is good-

timing float level, etc, and then do a plug chop-

find a good steep hill, drive hard to the top and switch off

as you crest the peak- then take a look at the plugs.

They can tell you a LOT.

Not as much as a wideband o2 sensor can, tho...

t

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Thanks, all!

I´ll see how much I´ll get done before winter.. And, it´s not quite broken in yet, so for now I´ll pass on the hill climb testing.

And, of course, I have no idea of the performance at WOT.

I´ll fiddle a bit with the mixture this weekend.

Dear Ola,

please tell us the: (Your precription, I believe. Will check the records.)

Primary Main Jet Size ________

Secondary Main Jet Size ______

Primary Air Correction Jet size__________

Secondary Air Correction Jet Size _______

Float Level _______ Can´t remember the specs, but as it should. In august anyhow.

using an electric fuel pump ? pressure_____ psi Mechanic, std

how is your ignition timing set? _____________ (By the book. In august.)

_________________________

_________________________

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