wide band tuning.

Posted By: mopfried

wide band tuning. - 09/24/13 02:00 AM

I am finally getting around to tuning my 440 in my 74 scamp. Im running a BG 850 DP. I can get it to idle at 13.8-14.1 but crusing around the hood it will be in the high 11 to mid 12's on the wide band. I pull 12-13" vacuum at a hot idle. Im not sure what power valve or jets. It is a little lean with the secondarys open. 13.5 or so. It is rattleing a little so I cant stay into it.

.. So does it sound like the primary jets are too large and the secondarys too small?

Posted By: YO7_A66

Re: wide band tuning. - 09/24/13 02:28 AM

Tune your idle first (13.8-14.1 should be close), then tune the transition (idle feed restricters or Idle Air Bleeds/ 11 to 12 is rich for most WOT readings), then your main circuit (primary jets/primary High Speed Air Bleeds, pv and pvcr's), then last the WOT (sec jets/hsab's).

I would suggest that you write down the iab's and idle fuel restricters and let us know what you have. Either the ifr's need to be reduced or the iab's need to be larger to lean our your low end cruise a/f.

Posted By: DaveRS23

Re: wide band tuning. - 09/24/13 02:28 AM

Disconnect the secondary linkage and just tune the primaries, first. After you get the primaries where you want them, then hook the secondaries back up and tune them.

Sounds like the primary mains need to be smaller and then the PVCRs opened up to get that fuel back under load. Just make sure that the power valve is not adding fuel at cruise.

I usually tune the cruise mix with the mains (assuming that you cruise on the mains). Then start drilling the PVCRs till I get in the 13 range. I do the final tuning at the track to see what ratio the MPH likes.

Posted By: DaveRS23

Re: wide band tuning. - 09/24/13 02:31 AM

I would agree with Dave on adjusting the cruise mix if your car does not cruise on the main circuit.

Posted By: RapidRobert

Re: wide band tuning. - 09/24/13 02:41 AM

Quote:

It is rattleing a little so I cant stay into it. and the secondarys too small?

first I'd go to a slightly heavier dist spring combo to stop the pinging. Might richen the sec jets a bit at least to get it into the normal range

Posted By: Cab_Burge

Re: wide band tuning. - 09/24/13 07:38 AM

Which type and grade fuel are you using now? E10 with 89 octane, non ethanol 91 Octane or what

How much timing and which brand and heat range spark plugs are you using

Lots of ways to cause and prevent pinging and detonation

Posted By: mopfried

Re: wide band tuning. - 09/24/13 11:53 AM

Fuel here in central Ohio is ethanol swill... I'm running 92 octane. I set the base timing so as to get the highest vacuum reading I could last night and didn't get the light out to see what it is. I know its high cause its hard to crank over... even with 10 deg dropped out with the Mallory box's start retard. I'm just starting out... I know my total is way high... The unilite dist is very adjustable.
I am using A/C plugs but don't remember the number 43 maybe?

Posted By: RapidRobert

Re: wide band tuning. - 09/24/13 12:23 PM

I'd get the highest vac you can then drop back 1" in hg then change the total

Posted By: Cab_Burge

Re: wide band tuning. - 09/24/13 06:54 PM

Quote:

Fuel here in central Ohio is ethanol swill... I'm running 92 octane. I set the base timing so as to get the highest vacuum reading I could last night and didn't get the light out to see what it is. I know its high cause its hard to crank over... even with 10 deg dropped out with the Mallory box's start retard. I'm just starting out... I know my total is way high... The unilite dist is very adjustable.
I am using A/C plugs but don't remember the number 43 maybe?

I'ne never used the highest vacume method to set the initial timing, I start at 14 to 16 BTDC at a very low idle, under 1000 RPM and then shoot for 34 to 36 degrees on Mopar BB and 426 Hemi by welding up the advance slots in the distributors that need that done to set the total timing (less total timing(30 to 32) on Mopar SB)

I try to lean the idle and transition circuits out to have 14.2+ AFR and I like to use a the coldest spark plug I can use that will not foul out with that tune up

Works good, last a long time

BTW, pinging and detaontion is hurting your parts

Fix it now