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So just double checked and I now have too little mechanical advance... getting 28 at 900prm with 36 total.. looks like I need to fix that first. its possible one of the weights is sticking
There should not be any mechanical advance stating at idle. Probably need heavier springs on the mechanical advance. Then you can set the idle timing to around 10 degrees. The idle timing and mechanical advance needs to be set up first, and then you deal with vacuum advance.
Example : 10 degrees initial advance. Mechanical advance starts above idle rpm sloping to 30 degrees at 3000 rpm to 34 degrees total 4500 to 5000 rpm
Vacuum advance adds to mechanical advance for 45 to 50 degrees at cruise rpm
I get that but I have two issues there.
1. the engine will not idle at 10-12 degrees it idles very rough when I advance it to about 15 and starts to smooth out at about 20 degree
2 now that I changed the weights to the mr gasket weights, no matter what it seems, I lost some of my mechanical advance curve... I just tried different springs and I get about 24 degrees base timing with 35 max mechanial.
right now I have another vac advance can on the way as the adjustment on mine does not seem to have any effect on vac advance. I am idling at around 40 at about 900 rpm but to make matters worse my mechanical tach cable interferes with my oil pressure sender so I did not have it screwed in while turning the distributor the second time around as my whole dist is advanced a bit more now with the new weights..
I'm half inclined to just buy a different hei tuneup/curve kit.
weird thing it its behaving the same as before even with the changes... after it warms completely up the rpms go from 1100 to about 600-650 when in gear and the whole car jerks when shifting into gear due to having the rpm way up at 1100 to avoid stalling. drove around and it seems fine once in gear no strange noises.
20° initial just to idle smooth is way too much! It shouldn't be able to restart after getting hot with that much timing, pinging, detonation, etc....Unless I'm missing something here, I'd go back to square one, verifying TDC on #1, looking for slipped dampner, was crank timing gear installed on a +/- keyway, etc! Most street SBC are going to be between 8°-12° maybe up to 14°.....factory is often a recommended 6° initial....my gut says something in the setup is not correct to begin with!!! Maybe I'm way off, good luck👍
You have been asked numerous times what the vacuum reading is idling in gear. I don't believe you have answered this
Sorry, It drops of course along with the rpm thats the whole issue im trying to correct. and the reason for the rpm drop im trying to correct. The vacuum drop to about 15 when the engine is fully warmed up and I put it in gear. if the engine has only been running a minute or 2 it typically just stalls when I put it in gear. this is why I recently replaced the trans modulator hoping it was the reason for the huge drop in vac and rpm when in gear but its not.
What does the vacuum reading in gear tell you? my understanding is when the rpms drop 400rpm it would expect to drop either way?
Last edited by augiedoggy; Jun 27, 2022 at 08:38 AM.
20° initial just to idle smooth is way too much! It shouldn't be able to restart after getting hot with that much timing, pinging, detonation, etc....Unless I'm missing something here, I'd go back to square one, verifying TDC on #1, looking for slipped dampner, was crank timing gear installed on a +/- keyway, etc! Most street SBC are going to be between 8°-12° maybe up to 14°.....factory is often a recommended 6° initial....my gut says something in the setup is not correct to begin with!!! Maybe I'm way off, good luck👍
ok so I hear that, I ive also been told by others that some builds want more timing at idle so I dont know what to believe. I do not have the stock engine. nothing radical but 64cc alumium heads, .040 quench and flat top pistons so if anything I would think I could get away with less timing.
I went through this last year. I even pulled the timing cover to verify the cam is installed correctly. I'm going to pick up another timing gun because honestly I dont know what else to check. I have checked for TDC with the heads off and its correct, checked for vacuum leaks double checked the msd sticker on the balancer to be sure its for the 8" balancer... I am at my wits end with this issue and I agree something is not right I just dont know what it is.
Ive only managed to limit my mechanical advance by changing the weights which is not what I wanted to do. I normally like to stick it through and figure things out but at this point I may just take it to my mechanic and ask him what im doing wrong.
Last edited by augiedoggy; Jun 27, 2022 at 08:43 AM.
Ok so ive been messing with the springs also put a slight dab of grease on the slides under the weights, I also went back to ported vacuum which allows me to shift into gear and back to park with much less increase/decrease in rpms and clunk. with the car idling at 900prm I am at 20 degrees this allows me 35 degrees of mechanical timing which all comes in before 3000 rpm. vacuum is 15 inches at 900rpm (with no vac advance) according to this chart i'm ok with 20 initial so I should be ok right? My numbers are somewhere between curve #7 and #8 currently. I did notice I have like a 1/16' or play in my distributor shaft from left to right almost as if my cam gear and distributor gear are not meshing tightly enough but the teeth on the gears both look of and I had initially adjusted the cam button for very little play. I imagine this could be effecting my initial readings slightly.
I hate to be the turd in the punch bowl but if you still have a stock torque converter with that cam you will need a looser one. Something in the 2200-2500 range.
I hate to be the turd in the punch bowl but if you still have a stock torque converter with that cam you will need a looser one. Something in the 2200-2500 range.
According to comp the stock 2000 rpm converter was fine. This was one of the reasons I went with the 270 and not the 276 HR cam. plus if I set the mechanical advance to 20 and put the dist on ported vac it shifts into gear fine. The issue there is there is too much advance at light cruise.
I did make headway. I discovered my adjustable vacuum advance is not stable between 15 and 17inhg and in fact does change when tested with a vacuum gun. Still waiting on the replacement I ordered last week.
Any chance your springs in your dist. are too light/weak and the few hundred RPM change going from park to drive or drive to park is causing the mechanical advance in the dist. to change and make your idle unstable?
Pat
Any chance your springs in your dist. are too light/weak and the few hundred RPM change going from park to drive or drive to park is causing the mechanical advance in the dist. to change and make your idle unstable?
Pat
Agreed^^^^, have you tried the heaviest springs!? Springs shouldn't limit advance, just how fast it comes in.👍
edit: I've experienced in the past lighter springs just being to weak, allowing the weights to "flutter" around! I really wish someone would make a "legit" spring and weight kit, where the weights are precisely balanced and weight matched and like 8 different springs rates and some bushings that were actually designed just like the factory ones and actually fit!!!!!!!!
Any chance your springs in your dist. are too light/weak and the few hundred RPM change going from park to drive or drive to park is causing the mechanical advance in the dist. to change and make your idle unstable?
Pat
no I tried different combinations of weights. it might have explained the stumble I was recently getting when accelerating though. that doesnt explain the main issue though which is a huge reduction in timing and rpms when going into gear. I am pretty confident this is a vacuum canister issue now.
Agreed^^^^, have you tried the heaviest springs!? Springs shouldn't limit advance, just how fast it comes in.👍
edit: I've experienced in the past lighter springs just being to weak, allowing the weights to "flutter" around! I really wish someone would make a "legit" spring and weight kit, where the weights are precisely balanced and weight matched and like 8 different springs rates and some bushings that were actually designed just like the factory ones and actually fit!!!!!!!!
the weights were the limiting factor not springs but if they are too stiff they do indeed limit advance.
