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Sat Aug 22, 2009 11:09 pm

Bones 53 wrote:
where can I drill for the vacuum advance line? Should the vacuum be drilled into the manifold instead of the carb.

Thanks for all the help guys

Never use manifold vacuum for a distributor.

Sat Aug 22, 2009 11:12 pm

you have 3 areas to look at

You need to jet with the airfilter on. If the airfilter acts even a tiny bit as a choke - fresh oil on it etc, you will see differences. I could see jetting differences between a wire mesh grille and an air cleaner when I raced years ago.

You need to verify your fuel pressure.

Can't use 110 to jet then drive 91 and expect the same results. Each one has different properties including the speed at which it burns. I've had this argument with others but simply put, by burning slower, pressures develop slower so there is less risk of detonation. I doubt if you are detonating at 34 degrees but I would set it at 30 to 32 until this issue is resolved. You may have seen higher EGT temperature with the slower burning fuel also as burn may have extended into the J tubes.

Sun Aug 23, 2009 8:56 am

what does the snail gauge read at idle? Should be 5-7.

at your elevation, your idles should be 52-55 for the 48s, and 50 for the 44s.

You have either

Idle jets that are bigger than the 45 you think they are (common, since MANY companies drill jets a lot), or your choke pistons are not closing.

Sun Aug 23, 2009 9:12 am

Thanks John

I'm going to put the 44's on. I think the throttle response will be better. The snail gauge reads low 5. at 850 RPM idle. What I found on the 45's were they were smaller than 45 and that threw me for a loop.

These 44's don't have the vacuum port like the 48's do. There is a small brass screw next to the air mixture screw - can this be used for a vacuum line?

Sun Aug 23, 2009 9:46 am

you aren't fixing the problem. The extra fuel is coming from somewhere. You still haven't specified all the specs (venturi, emulsion, idle/main/air). You are making a mistake by changing carbs so quickly. You have the wideband, USE IT

your snail gauge is reading something I would consider NORMAL, so throttle settings are ok. If it's reading 13:1 at idle, adjust the idle mixture since it's improperly set.

Sun Aug 23, 2009 9:57 am

These 48's had the progression holes "opened up" to 110,100,100,100 from 105,90,90,90,85 going from top to bottom. I don't know if this is where the xtra fuel is coming from. The 44's progression circuts haven't been touched.

Both the 48's and 44's have 38 mm vents, f-15 etubes, I have tried 40, 45, 50, 52 and 55 idles, 140 to 145 Mains , 165, 180 and 200 airs.

The 44's do have the CB spray bar though. i've never tried the 44's they came with the CB kit.

Sun Aug 23, 2009 10:06 am

The progression holes can be a source of trouble but if it worked on the dyno and not in the car check to be sure the throttles are closing all the way. If the cable is holding one open a tad then the air rushing past the progression hole may be pulling fuel. The butterflys should close on the progression holes. The first hole should be covered by the butterfly. If any portion of it is open when you are at idle you will be using it. What you want is that the progression hole is exposed as you barely crack open the butterflies. This way it goes from the idle circuit to the progression circuits immediately.

Sun Aug 23, 2009 10:09 am

If all 4 barrels are reading 5-5.5 the throttles are closing all the way.

That's messed up that the progressions are opened up, it's gonna screw everything up, but you'll have to use way smaller idle jets than normal; you may need 35s, which don't exist, you'll have to make them. Try 40s next.

Sun Aug 23, 2009 10:27 am

I tried 40's and it would not run. I just looked at the 44's I have and there is no take off for the vacuum. Has anyone drilled for one with success? I have the Mallory unilite with the vacuum advance and would like to be able to use it. I have the 48's off the car. The throttle plates are closing fully and the progression circuts are covered by the butterfly.

Sun Aug 23, 2009 10:55 am

whatcha mean it won't run? It's 10s with 45s and won't run with 40s? That makes no sense. You'll have to back out the idle mixture screws when changing to a leaner idle jet. I still say your pistons are stuck open or the extra fuel is coming from somewhere. Are the idle air bleeds CLOSED? (They should be)

Sun Aug 23, 2009 11:12 am

When I tried the 40's I did need to open the idle mixture screws a lot and even then putting a small load on it driving up a 2% slope and the car just quit unless i reaved the sh*t out of it. Air bleeds are close. Are you saying the needle and seat - is that what you mean by the pistons?

Sun Aug 23, 2009 11:13 am

no, the "choke" pistons present above the pump diaphragms. If they stick open it will be pig rich. A lot of guys drill/tap the galley and use a setscrew to HOLD the piston closed, since a backfire can kick it open and it can stick.

You CAN'T be that rich with 45s, then too lean to run with 40s. Something else is up.

Sun Aug 23, 2009 11:19 am

I need to clarify that the 40's actually measured 37. I next purchased some more 40's and used a 1/64th bit to make 39's. That's what I have now

Sun Aug 23, 2009 12:12 pm

I just checked the choke pistons. They are closed. The spring pressure seems sufficient. I've heard of them bouncing open and closed before but I thought that was in off roaders which is the reason they drill and tap to keep them closed.

Sun Aug 23, 2009 6:43 pm

I changed the carbs to 44's. First started with 45 idles 140 M 200 A. From idle to 3 K it's at least in the high 12's / low 13's

At WOT From 3-5 it was 15-17 and from 5-6 it was a pig and way lean 17+

Next went to 145 M 180 air still lean from 3-5 15 -16 and it would run but still lean from 5- 6500 - 17.

Next tried 155 M 200 A and still lean at both 3-5 and 5-7 with the AFR being 15-16.

Can the advance be increased to help with the idle to 3 range and retarded to help with the 3-7 range? I know I'll need to richen up the main circut but I would like it better in the idle circut.

Also is it common for the LM to read kind of scattered? I notice it fluctuates a lot like being 12.5 then runs up to the high 13's and back again. It seems like it could be misfiring but doesn't sound like it at all.

Also I notice that when just cruising at 2400 or so the AFR is rich like high 11 but if I slowly depress the pedal it goes into the high 12's low 13's. Seems opposite of what it should be.

I also saw that using compression down a steep hill the AFR was mid 14's.

I tapped the top of the chokes with 3/8 x 24 flat hex head allens so I know the chokes are not leaking.

Any ideas / suggestions?

Sun Aug 23, 2009 7:29 pm

with 44s and 36mm venturis, you jetting should be almost perfect with

F11
36
50
140
220

floats set to 10mm. Tuning a SH engine is a biatch IMO

Sun Aug 23, 2009 7:41 pm

Thanks John I see what you have said all along about the SH heads.

The floats are set at 11 / 30. I have 38 vents(cb kit), F11, and tried 50's too rich, 45, and 47(too rich) as well as 140/ 200, 145/ 180 and 155/200 all too lean.

Sun Aug 23, 2009 8:32 pm

you are lean because you are at 11mm and 200 airs.

Change to 10mm and 220 and re-tune.

Sun Aug 23, 2009 9:05 pm

Thanks John I must have something wrong in my thinking. Wouldn't the 220's lean it out more by bringing more air in?

Sun Aug 23, 2009 11:58 pm

this is discussed in detail in the wideband tuning thread