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Discussion Starter · #1 ·
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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Discussion Starter · #3 ·
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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Discussion Starter · #4 ·
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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my KARMA ran over my DOGMA
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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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Discussion Starter · #6 ·
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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my KARMA ran over my DOGMA
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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 :D

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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Discussion Starter · #8 ·
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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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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my KARMA ran over my DOGMA
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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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Discussion Starter · #12 ·
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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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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Discussion Starter · #14 ·
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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my KARMA ran over my DOGMA
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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.
The limit screw should have no effect on the starting point of mech advance only the end travel. One good not worn or stretched heavy spring and one light and the mechanical should not move till approx 900 rpm.

Vacuum advance needs a limit too, crane plate shown, second or third notch gives approx 14 Deg max vac advance or make one.

Adjustment screw on can only changes tip in not limit. Turn it all the way in carefully and then back out 7 turns after you install limiter plate, start from there. You need to change the base timing each time after installing or changing the notch on the limiter plate as the limiter moves the reclutor in relation to the pickup. I think these have a vacuum advance of almost 20 out of the box, that is why skip does not want you to go there, you will kill the motor with too much advance.

You can try and dial the idle/carb in with vacuum advance connected to manifold, turn the canister screw in all the way so that the 10-11"wg engine vacuum pulls the can all in, dont try and set the idle with the vacuum advance floating in the middle of its range with this cam.

Also again I think you are going to need more than a 72 jet on the primary.

If the thing wont idle than with less than 40 deg advance then you have other issues, distributor mods to mech and vacuum advance may not fix this just lessen the problem. Has this motor ever ran right?

Look closer at the carb/fuel/air delivery
 

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my KARMA ran over my DOGMA
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These are pics of the crane vacuum advance limiter plate they are cheap, or if you can make one that will duplicate the effect of holding the end of the vacuum canister rod approx 13mm from the center set screw then have at er. This will give you about 12-14 total advance via vacuum.
 

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Discussion Starter · #19 ·
I think I have the springs and limit worked out on the mech adv now. At least I am very close. I am now in the process of fabricating an adjustable screw for the vacuum advance. Where should I start with the can adjustment, 7 turns out or all the way in?
Now it seems to idle pretty well. [email protected] 20, mech @14, but I still would like to see about 24-26 initial and about 10 mech. With 10-12* vacuum adv, this would give me about 34-36* at idle (manifold vacuum). This is the range where it idles really well and would give me 34 total,(initial plus mech.)
One problem still persists. When I drop it in gear, it wants to die. Am I running into the transition slot thing?
The motor is brand new and does not run bad. I don't think there are any issues other than getting the timing worked out and carb adjustment.
I can't take it out for a drive yet, as it is a roadster, the roads are wet with snow, and it is very cold. I will try the jet change before I take it out.
It is supposed to be in the 50's this weekend, and I should be able to take it out for a drive.
Thanks for your attention and help custom10 and cobalt 327.
 

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my KARMA ran over my DOGMA
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How many miles on this mill? are we working on a virgin?

dont need to fabricate a allen wrench for the can adjustment do you?

Its is cold here too, if I could dig out the C10 from under the snow I would send you my dist, but please dont mess it up. ha
 
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