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Old 11-27-2012, 09:22 AM
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383 hesitation

I have been lurking a long time, but this is my first post.
I have just installed a new 383 from Skip White Performance in my 1927 T roadster and am having some small problems.
Specifications: Long but maybe helpful

Car:
2280# with driver
3.55 rear gear, (Frankland quick change)
26" rear tire
TH350C w/ 2500 stall

Engine:
440 advertised HP using 93 octane premium pump gas
383 SBC
Flat top forged pistons w/ 2 valve relief, 10.8-1 CR
210CC procomp aluminum, 64cc, 2.02/1.6
Howards roller cam:
Lift: w/1.5 rockers .530/.545 (1.6 rockers installed)
Adv dur: 286/294
dur @ .050: 233/241
LSA: 110
Procomp Hi-rise air gap intake
QFT SL-750 carb vac.2ndary
jets 72 front 82 rear
idle air bleed 70/39
hi speed bleed 31/31
pri nozzle 35
needle and seat 110
power valve 6.5
HEI ini 24*, mech 10* total 34* no vacuum advance
Autolite 5224 plugs @ .035
1-5/8 lake style headers into 2-1/2 exhaust in front or rear tires
10-11" Hg @ idle

PROBLEMS:
ROUGH IDLE: White says not to use the vacuum advance. Motor seems to want more advance at idle. Why not use the vac adv to increase the advance at idle.
BUCKING OR SURGING at cruise speed. ???????
HESITATION at hit of throttle. ??????? bigger squirter????

I think I have searched out and read everthing to do with timing on this site. This has been very helpful, but I have had the timing all over the place and have not been able to eliminate the surging or hesitation. It must be in the carb. I am not a very good carb tuner. I know there are a lot of very knowledgable people participating in ths forum. I would appreciate any help you guys can give me Thanks in advance.
Jim

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Old 11-27-2012, 10:16 AM
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fuel pump and fuel filter is what?.
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Old 11-27-2012, 10:38 AM
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Fuel pump is Gm Hp mechanical regulated to 5.5#. Fuel filter is a large fram cylinder that I used to use for alcohol on my 434ci dirt late model (new filter). There is no restriction. It is mounted before the fuel pump. There is no filter between pump and carb.
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Old 11-27-2012, 11:22 AM
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Sounds like a vacum leak. Hesitation is caused by many thing but you used the word surge. That is usally what is the cause of surging issues.
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Old 11-27-2012, 12:15 PM
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Thanks for your responces, butI thought at first there might be a vacuum leak. I shot starting fluid at the intake runner to head joint and around the carb base at idle. The idle speed never changed. The very slight surging or bucking occurs at 55 mph steady state cruising. The hesitation comes at any speed, then kick down throttle.
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Old 11-27-2012, 12:28 PM
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Why not use vacuum advance is right? this can help with throttle responce to some degree and/or reduce hesitation. More advance may make the surging worse however at cruise. Try a 76 jet.
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Old 11-27-2012, 01:02 PM
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Thanks custom10. I will try jetting up. I have jets on hand.
I searched your other posts and see that you have the same distributor that I do. You stated in one of your posts that it is was easy to adjust the mechanical advance on these. I have been trying to limit the amount of mech. adv. on mine by inserting a small allen head bolt in the hole just inboard of the rotor mounting hole. Changing nothing else, It makes the adnance work backwards!! When I hit the throttle, it actually retards.
How are you limiting the mech. adv.?
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Old 11-27-2012, 01:13 PM
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Well that does not sound right,,,hmmm

I can attach a pic of mine with the small screw closest to the center on the right side as the one that does the limiting.

You can see another larger flat head machine screw on there, ignore this it was for a pointer I attached. I was measuring the travel of the rotor plate in mm to determine how much advance was added at the crank vs the pointer travel on the HEI base circumference, sometimes I have too much time on my hands

Sorry the pic is small, maybe you can zoom in? I am dumb when it comes to pic posting on here.
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Old 11-27-2012, 01:22 PM
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Yes that is exactly the place where I put the allen head bolt. I figured that should limit advance to about 10*. When I set the total timing to 34 at about 2500rpm, then put the limiting bolt in, it hits 34 at about 2500, then at 2800 to 3000 the timing retards to 31-32* Very strange. I can't figure it out.
Its cold here and I have the garage stinking. Got to run the exhaust fans awhile. LOL
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Old 11-27-2012, 01:23 PM
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Do you think that the nut on the bolt swinging past the magnets may be having an effect?
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Old 11-27-2012, 01:35 PM
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Quote:
Originally Posted by jaw22w View Post
Thanks custom10. I will try jetting up. I have jets on hand.
I searched your other posts and see that you have the same distributor that I do. You stated in one of your posts that it is was easy to adjust the mechanical advance on these. I have been trying to limit the amount of mech. adv. on mine by inserting a small allen head bolt in the hole just inboard of the rotor mounting hole. Changing nothing else, It makes the adnance work backwards!! When I hit the throttle, it actually retards.
How are you limiting the mech. adv.?
You can use more initial timing, as much as needed, actually. At some point the starter might begin to drag when the engine's hot, but w/the cam specs you have, that shouldn't be a problem because it doesn't need a ton of initial- I'd use 18 degrees and go from there.

Then limit the mechanical timing advance so the total stays within reason. You shouldn't need more than 34 degrees or so, possibly less, depending. Surging is sometimes a symptom of too much timing. You can take some mechanical timing out of it by changing the screw, or turning it if you've ground it like a cam lobe to give more or less mechanical advance depending on how the screw is turned.

If you're using a GM HEI, the limiter screw is placed in the hole like shown below (photo courtesy of 69-CHVL (Vince G) of Team Chevelle). Ignore the screw shown that locks the timing in place. Click on image for more info on ignition advance and the HEI distributor in general:



BTW, there's no reason you cannot use vacuum advance w/this cam/combo. Limit the amount added by it to about 10 degrees. If manifold vacuum doesn't suit the engine, try ported vacuum.
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Old 11-27-2012, 01:52 PM
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The screw goes in first, then set the timing to the desired advance with the motor at 3500-4000 rpm.

17mm rotor plate travel on pointer measuring the circumference as I mentioned gives about 14 deg at the crank if I recall my science project data correctly.

The screw should not interfere with the reluctor/pickup operation.
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Old 11-27-2012, 01:59 PM
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thanks cobalt 327. I have tried this, but as stated in posts 7, 9 and 10, something is not working right. At 18 initial the idle is very rough. It wants more tha 18 to idle smoothly. If I put 40+ in it it idles smoothly. I also can't seem to get it to idle below where the mech adv comes in. If I idle it below 1000 rpm, it just dies. If I put stronger springs in it, the advance comes on too late.
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Old 11-27-2012, 02:53 PM
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Quote:
Originally Posted by jaw22w View Post
thanks cobalt 327. I have tried this, but as stated in posts 7, 9 and 10, something is not working right. At 18 initial the idle is very rough. It wants more tha 18 to idle smoothly. If I put 40+ in it it idles smoothly. I also can't seem to get it to idle below where the mech adv comes in. If I idle it below 1000 rpm, it just dies. If I put stronger springs in it, the advance comes on too late.
Be sure the timing line on the damper and the timing tab are accurately showing the timing in the first place- there were several different tabs and timing lines used through the years, and if these get mixed together the timing can look like one thing, yet be something different.

More on that here, including a link under Resources for determining top dead center.

Use a stiffer spring on one side if the idle is causing the mechanical to start advancing.
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Old 11-27-2012, 03:06 PM
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TDC has been verified. I just tried stiffer springs. It's getting better. Need stiffer springs yet. It seems that with the mech adv limited, the advance comes on quicker than before limiting. I'm slowly getting there.
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