Need help tuning 28/28 DFTA

Road-race engines and ancillaries - general discussion
timinator
Posts: 116
Joined: March 9th, 2011, 5:20 pm

Re: Need help tuning 28/28 DFTA

Post by timinator » November 4th, 2011, 6:07 am

Hi turbofiat,

I didn't know what a 32DFTA was. So off to the internet. There was a 32 DFTA OEM jetting table for Ford Fiesta (US).

Primary: 100/F22/250 _ idle jet 60 _ pump jet 45 _ pump bleed 40(1) _ needle valve 150

Secondary: 105/F22/250 _ idle jet 60

Float level 7/16

Hope this helps.

Tim

turbofiat
Posts: 67
Joined: November 30th, 2006, 10:09 pm
Location: Kingsport, Tennessee, USA
Contact:

Re: Need help tuning 28/28 DFTA (solved sort of)

Post by turbofiat » November 13th, 2011, 9:46 am

This is an update concerning the problem I thought I was having with my Yugo's 32/32 DFTA carb. The jetting had nothing to do with it. The problem was the ignition timing. I was trying an experiment about a year ago and it seemed to work OK in hot weather but shows up as bucking off cruise and backfiring in colder weather.

The other day I advanced the static timing from TDC to 10 degrees BTDC and now the car runs smooth as silk even in freezing weather. But the downside is the engine pings at 4K rpms under boost. Which I expected it to.

I have never been able to get the ignition timing spot on with this car. I am using a dual diaphram advance module from a VW Golf mk1. These modules were used to meet US emmisions by advancing the timing when cold so I don't think you'll find these used on VWs outside the United States.

If positive pressure is applied to the "advance port", the timing will retard about 3 to 5 degrees. It seems setting the static timing to 5 degrees BTDC is the happy medium but the engine still doesn't run as smooth as it does at 10 degrees BTDC.

Since Jacobs electronics no longer makes the Boostmaster which I am using on my 124 Spider, the other electronic alternatives are MSD, Crane and Megajolt. I'd rather use something simple if I could.

Based on what I have read there are two Bosch advance modules out there that can advance the timing and retard the timing up to 10 degrees. These were used on turbocharged Saabs and Volvos and maybe Porsches before knock sensors were used.

However the part seems to be elusive. Several Volvo suppliers say this part is no longer available and all Saab part suppliers are showing the same part number for turbo and non turbo models.

So in summary, I'd like to be able to advance the static timing to 10 degrees BTDC yet be able to retard the timing 10 degrees under boost.
Any ideas or suggestions?
124 Spider, Yugo,131

WhizzMan
Posts: 459
Joined: August 13th, 2010, 9:05 pm
Location: Amsterdam, the Netherlands

Re: Need help tuning 28/28 DFTA

Post by WhizzMan » November 16th, 2011, 8:31 am

Does your ignition have springs and weights? If so, you could limit the travel of the weights so max advance is limited. When under boost, this would help, but with little or no boost, you'd lose a bit of power. The only other alternative I know of is something like a megajolt. This is essentially only the ignition bit of a megasquirt EFI ecu. There must be plenty more, but I'm not familiar with them.
Book #348

turbofiat
Posts: 67
Joined: November 30th, 2006, 10:09 pm
Location: Kingsport, Tennessee, USA
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Re: Need help tuning 28/28 DFTA

Post by turbofiat » November 18th, 2011, 11:14 pm

WhizzMan wrote:Does your ignition have springs and weights? If so, you could limit the travel of the weights so max advance is limited. When under boost, this would help, but with little or no boost, you'd lose a bit of power. The only other alternative I know of is something like a megajolt. This is essentially only the ignition bit of a megasquirt EFI ecu. There must be plenty more, but I'm not familiar with them.
I considered limiting the advance weights and even tried this with my Spider about 10 years ago. The result was bucking under cruise, just like my 1500 in my Yugo.

I'm currently considering the Mallory Hyfire IV system. Unlike the MSD system, this is a stand alone system and will work with distributor type ignition systems. The wires from the magnetic trigger plug into the system.

The only difference between the Jacobs Boomaster I'm using on my Spider and this one is the Mallory unit requires an optional MAP sensor to tell it when the engine is under boost.

Still pricey at around $350 (including the MAP sensor) but less involved than the MSD or Crane units.

I found the Bosch distributor has the capabilty of retarding and advancing the timing allot more than required (such as up to 20 to 30 degrees) but I haven't found anything capable of doing both. The dual advance module I'm using from a 1.7 liter Golf that gives me 5 degrees retard is not even available anymore!

I've even considering trying to make a vacuum/retard module by splicing two advance modules together. Trouble is they are crimped together and not easily taken apart. I have seen photos of where people have taken them apart without destroying them but I haven't be able to do it. Not yet anyway.
124 Spider, Yugo,131

turbofiat
Posts: 67
Joined: November 30th, 2006, 10:09 pm
Location: Kingsport, Tennessee, USA
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Re: Need help tuning 28/28 DFTA

Post by turbofiat » December 30th, 2011, 12:37 am

timinator wrote:Hi turbofiat,

I didn't know what a 32DFTA was. So off to the internet. There was a 32 DFTA OEM jetting table for Ford Fiesta (US).

Primary: 100/F22/250 _ idle jet 60 _ pump jet 45 _ pump bleed 40(1) _ needle valve 150

Secondary: 105/F22/250 _ idle jet 60

Float level 7/16

Hope this helps.

Tim
Seems odd the 32 DFTA installed on the Fiesta 1600 and Yugo 1100 had virtually the same mains, emulsion tubes and air correctors but slighly larger idle jets.

As with most European cars sent to the US back in those days, we always got the largest engine options. I suppose being these engines were smogged to death and needed the extra displacement to make up the difference. All 131s were twin cams, all Yugos were either 1100 or 1300s, etc. Yugo 55s used the smaller 900cc pushrod engine where our 1100s made the same power.

This DFTA carb must have been a special universal US spec carb used on engines of less than 1800 displacements because it had ports for emmisions. I have plugged all of mine off which I realize changes the characterists of how it was to operate to begin with.

I ordered some larger mains (115,120 and a 125) the other day. Should take over a week to arrive from California.

Still not quite sure this misfire happens below 60F. Why the engine runs fine otherwise above that temperature. Unless I'm on the trailing edge of the primary main and the colder air just makes it worse.
124 Spider, Yugo,131

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