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#1 |
Registered User
Join Date: Apr 2016
Location: Vancouver BC
Posts: 5
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Points dist timing issues
Hey guys. I've got a '69 Sierra grande with a 350 in it and still have the original points distributor. I've been fighting a rough, unhappy idle since I bought the truck. It idles like it has a really aggressive cam in it.
I rebuilt the carb and that helped a little, and I threw a timing light on it and tried to follow factory spec, timed initial at around 10° and 3000(ish) rpm at around 36°. Problem is, the idle runs like sh*t unless I manually turn the distributor until it's at about 20° advance, at around which point it smooths right out. Anything past about 14° is a really hard start when it's warm, and I'm a little afraid total advance would be way up anyway. I've also noticed that the idle timing doesn't change whether the hose is connected to the vacuum advance or not... Should it? I feel like the vacuum advance should bring it from the initial 10° starting value up to around 20° or so at idle (high vacuum) to smooth out the idle. I've also connected a vacuum gauge and it floats right between the low end of "normal" and the top end of "late ign timing" when at idle. 20° pushes it to the middle of the green "normal" range. ![]() |
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#2 |
Registered User
![]() Join Date: May 2013
Location: WEST PALM FLORIDA
Posts: 1,174
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Re: Points dist timing issues
Sounds like you need a vacume advance canister ,they go bad and are cheep and easy to replace , set the idle advance with the canister disconnected , you should be good to go
__________________
68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive |
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#3 |
Registered User
![]() Join Date: Feb 2016
Location: Weatherford Texas
Posts: 306
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Re: Points dist timing issues
It sounds like your distributor vacuum is hooked to ported vacuum instead of manifold vacuum. At idle, ported vacuum is zero or very near zero.
Conversely, manifold vacuum is high at idle which will allow you to set your base timing correctly, then the advance will add more timing to smooth out your idle when you hook the vacuum line back up. It's an age old debate about whether ported or manifold vacuum for the distributor is proper and manufacturers have set it up both ways over the years. What you're describing though, that it idles better with an extra 10 degrees of advance over spec, is a scenario where manifold vacuum is ideal. Set your base timing to spec, add in about 8 degrees of advance when you plug in your vacuum hose. Smooth idle and overall total timing is still good at higher RPM. |
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#4 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,607
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Re: Points dist timing issues
Your points gap is too wide or the points are worn out.
And you need a vac pot. Likely easier to swap in a hei distributor. No problems with points then, a hotter spark, smoother idle, etc. |
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#5 |
Registered User
Join Date: Apr 2016
Location: Vancouver BC
Posts: 5
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Re: Points dist timing issues
It is hooked to manifold vacuum, i have checked with the vac gauge (edelbrock 1406, driver side port, shows vac at idle and the other doesn't). I guess the vac canister must be gone. It looks like the original canister. It *should* add advance at idle, correct?
I don't have a dwell meter to properly set points. I did it using a trick I found on the forum here by turning the Allen key counterclockwise until the engine dies, and then turning it back 180° and that is roughly 30° dwell, where it should be? Isn't there a lot of rewiring involved in switching to HEI? If I need to buy new set of points, A new vac canister, and a dwell meter then maybe I should just get an HEI... |
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#6 |
Registered User
![]() Join Date: Feb 2016
Location: Weatherford Texas
Posts: 306
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Re: Points dist timing issues
If you have your distributor hooked to full time manifold vacuum and your timing doesn't change by 8-10 degrees when you hook the line up, your vacuum can on the distributor is ruptured. Which is a vacuum leak, which further aggravates the poor idle.
As far as getting a new vacuum advance canister, Rockauto shows three different brands to choose from (Delco, Wells, and Standard) for about 8 dollars each (69 GMC w/a 350 engine). I'm sure things are different in Canukistan but surely the local parts stores won't whack you too badly when you ask the price. Converting to HEI requires the distributor itself, new spark plug wires, and hooking up a new larger gauge 12v power wire to the distributor. |
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#7 |
Registered User
Join Date: Mar 2013
Location: Campbellsville, KY
Posts: 888
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Re: Points dist timing issues
Since you're sure it's connected to manifold vacuum it sounds like the advance canister is bad. It's your call, but once they're right I have no problem with points ignition. Dwell meters aren't that expensive and IIRC my '67 owner's manual says to check the points every 12,000 mi. Though I do mine every thousand or so, just 'cause I'm always tweaking something else lately - jetting, timing, etc.
__________________
Alex V. ------ 1967 C10 Suburban, 350/NP435, Green/Green, PS, PB, HD cooling, charging, shocks, and springs. 1985 GMC C3500 SRW, Sierra Classic, 454/TH400, white/blue. |
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#8 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,607
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Re: Points dist timing issues
Easy to wire in a hei. Just need a 12 gauge wire to an unfused spade on your fuse box.
Only problem with an hei is the size. Tight fit back there. Plus cost if you buy one new. Likely a couple hundred bucks for the hei and new plug wires. On your carb drivers side is manifold vac, the other is ported. Pop the distributor cap off and hook a hose to the vac pot and use some lung power to pull the arm on the pot. I've seen them pop off the plate inside. The end of the arm is bent into a 90 degree angle and sits in a hole in the plate. Easy thing to check. If you keep the points and need a dwell meter, just pm me your address and I'll send mine over. |
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#9 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,628
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Re: Points dist timing issues
I adjusted points in several vehicles over many years and never used a dwell meter, just set the gap with a feeler gauge. Not the best way perhaps but it always worked.
That said, I would switch to HEI. Yeah, there's not a lot of room, but it fits. Installing it with the cap removed makes it easier. New hot wire and larger plug wires have been mentioned, and the plugs (same as stock) need re-gapped to .045". There are several how-to threads on the site, and I ran across this a long time ago: http://rmcavoy.freeshell.org/HEI.html
__________________
- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#10 |
Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,717
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Re: Points dist timing issues
Could also be the balancer has slipped on the inertia ring making the mark not in the correct location. There were some motors that actually had the tab in a different spot for a different balancer.
__________________
44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
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#11 | |
Registered User
Join Date: May 2016
Location: richmond va
Posts: 265
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Re: Points dist timing issues
Quote:
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#12 |
Registered User
Join Date: Dec 2009
Location: bisbee, arizona
Posts: 1,529
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Re: Points dist timing issues
sometimes the timing marks on the balancer are not correct for the indicator thingie on the timing chain cover.
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#13 |
Registered User
Join Date: Apr 2016
Location: Vancouver BC
Posts: 5
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Re: Points dist timing issues
Well a buddy just gave me his old gm HEI distributor and plug wires after upgrading to an MSD billet thing, but it looks like the vacuum advance on it is shot as well, since I can just blow air through it. I guess since I've got it now I might as well fix up the HEI rather than the points distributor.
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#14 |
Registered User
Join Date: May 2014
Location: Matamoras, PA
Posts: 397
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Re: Points dist timing issues
I went with an MSD distributor with the digital ignition box and never looked back.
Been running strong for almost 10 years now. Noticed the difference the second it fired up. And that was after an HEI. |
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#15 | |
Registered User
![]() Join Date: May 2013
Location: WEST PALM FLORIDA
Posts: 1,174
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Re: Points dist timing issues
Quote:
__________________
68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive |
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#16 |
Registered User
Join Date: Apr 2016
Location: Vancouver BC
Posts: 5
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Re: Points dist timing issues
Just as an update, I dropped the HEI dizzy in and got a new vacuum can for it. Even with the old, worn-out cap and rotor, it runs like a new truck. Lots of power, very smooth, no more rough idle. Feels like a later model EFI truck. Way more power and acceleration. Can't recommend this enough, and it was a really easy swap just like everybody said it would be.
The only difficulty I had was the spade connector that goes into the firewall fuse block had to be spliced onto the new wire because the spade connectors at the auto parts store didn't fit all the way through the hole into the contact. So I have about 1/8 of an inch of the fusible wire left, which I don't think should be an issue for the moment - but does anyone have a source for the GM long spade connectors so I can eliminate the old wire completely? |
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#17 | |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Points dist timing issues
Quote:
If you need a ton of initial advance, give it initial advance and limit the mechanical. Don't connect vacuum advance to manifold vacuum. Odds are the throttle blades are open too far. I'd wager the fuel mixture screws do nothing. If the cam is big enough, you wind up drilling holes in the throttle blades to get enough air moving without uncovering the transfer slots. I'm not an expert on giant cams - maybe in that case it makes sense to run vacuum advance off manifold, but never in a normal application.
__________________
1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#18 |
Registered User
Join Date: Dec 2009
Location: bisbee, arizona
Posts: 1,529
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Re: Points dist timing issues
I alays put a vaccuum advance from a 75 corvette in there.
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