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Tuning my lean burn conversio from hell
https://slantsix.org/forum/viewtopic.php?t=37921		 Page 1 of 1
Author:  radarsonwheels [ Wed Nov 11, 2009 12:36 pm ]
Post subject:  Tuning my lean burn conversio from hell
I got a 1987 d150 this summer. I paid too much because it is really clean and solid and I was psyched to have a /6 833od pickup, especially since I have tons of parts for that combo already.

To make a long story short here's a list of parts that unexpectedly failed:
rear brake hard line
lean burn computer (replaced ign with points dist triggering msd 6a)
msd box fried up bought another
replaced carb with new 1945
better cold drivability pings bad when warmed up gets worse on highway
carb gasket started leaking air intermittantly replaced it
rebuilt and installed electronic dist. to get 15* gov
new distributor worked great for one day, stopped sparking
put points (to msd) back in w stiff curve
still pinging bad esp. on the highway

she still pings a little if I demand too much in upper RPMs.
11.5 governor 6.5 vac pot initial @ 2* both new black springs in dist

I'm inclined to rejet to 65-66 but that isn't what Im seeing on here. Am I on the right track?

Thanks for reading
Kevin
increased jet from 622 (2nd "2" upside down, holley tech says it's like 62.5) to 64h much better. Still pings but not unless you gas it good...[/img]
Author:  Doc [ Wed Nov 11, 2009 1:29 pm ]
Post subject: 
Quote:
... she still pings a little if I demand too much in upper RPMs.
11.5 governor 6.5 vac pot initial @ 2* both new black springs in dist ...
For this combo you need to run one light spring and one heavy spring, with a meadium size loop on one end.
Set the light spring tension so mechanical advance starts around 1100 RPMs and gives 24 to 26 degrees before the heavy spring "kicks-in" and slows the curve down for the last 6 degrees or so.
DD
Author:  bigslant6fan [ Wed Nov 11, 2009 10:43 pm ]
Post subject: 
He has my spring kit Doc,The black springs are the stiffest ones in the kit,using two of them results in a very slow advance rate that starts at 1,800 and ends at about 4500 rpm. I agree with you Doc,using the one stock spring with the oval shaped eye and one green spring from my kit might be best for his application,but I think some other things need to be checked.

I'd pull the plugs and see what they look like. I think the parts book call for too hot of spark plugs for the late 70s-80s engines. I often use one heat range colder.
I'd check for true TDC using the piston stop method to elliminate a possible slipped ring on the balencer.
Check for a mis-connected or stuck open EGR,or a plugged exhaust system.
And yes the culprit could very well be in the carb.Double check the float level-a 1/16 inch is a mile of difference either good or bad. Also, some of those 1945s have power valves that are controlled by both intake vacuum and a step-up linkage from the throttle,maybe the step-up linkage is assembled wrong preventing a richer mixture at WOT.
Author:  radarsonwheels [ Thu Nov 12, 2009 9:39 am ]
Post subject:  Thanks fellas!
I really appreciate the input.

When the EI distributor stopped working I initially thought it could be fouled plugs, because I have fouled plugs leaving the choke on on my harley before and it was a similar downward spiral of performance leading to stalling and not starting back up.

The first thing I did was check and change the fuel filter and check the plugs. They were clean, maybe on the lean side but no little metal balls on the ceramic. I did note that the strap wasn't melted but I didn't look to see how hot it was getting. I was just bummed it wasn't fluffy black because that seemed like an easy fix.

I removed all the vacuum lines except the charcoal canister and the choke thingy thats t'd to the air cleaner to let the choke close all the way at startup. (also kept power brakes, ported to dist, pcv) Do I need to block the egr port on the end of the manifold or is removing the vac. line enough to keep it closed? How about the air pump? It is no longer hooked up either. I just have no idea which stuff is purely mechanical and which stuff hooked up to the evil black box (RIP)

No egg smell so I'm gonna keeep my fingers crossed the cat isn't going bad. I'll check the plugs again after a couple trips to work and back to make sure I'm not sooting anything up with the 64 jet.

My truck EI distributor now needs another rebuild- the pickup is bad. That leaves me with the points distributor (triggering msd) and limited mechanical advance. I still have the springs that came in it though- an oval end one that only catches the end of the party, and a green one that looks like bigslantsixfan's green ones. I am thinking that 11.5x2=23 so the last 7* are missing from my curve right now anyway!

Thanks again for the input from the 'heavys'

Kevin
Author:  Doc [ Thu Nov 12, 2009 9:43 am ]
Post subject: 
Thanks for the input... it is great that someone is offering the Mopar style advance springs but as we know, the real challenge is finding the right spring combo (advance curve) for any given application.

I always have to generalize when it comes to dialing-in a distributor advance curve, just because there are soooo many variables but in general, a SL6 likes lots of initial advance 8 to 12 degrees) and not a lot of total. (28 to 30) Getting these settings is the easy part of distributor recurving.

Setting the spring rates is the harder part.
For a street application, where you need crisp, off idle, light load (1st & 2nd gear) throttle responce and then need to limit high speed- heavy load advance, I find that a "two stage" spring set-up gets you closer to the ideal curve.

As for where to set the rates, that takes some trial & error work but in general, the primary (light spring) should start working off idle and quickly give you 12 -14 degrees of advance.

The second spring should "hit" and slow the rate for the last 4-8 degrees. If the "looped" spring is set at the correct tension, it will be "working" at your highway rpm / speed so when you are "on the flats" and driving fast, you have more advance (mechanical and vacuum) but the advance starts to drop-back if you hit a big grade, load increases and the rpms drop a bit.
DD


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Author:  Reed [ Thu Nov 12, 2009 9:58 am ]
Post subject: 
If your catalytic converter isn't already clogged, it will be quick if you have disabled the AIR injection pump. Best to remove it or hollow it out.
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