I switched from TPI to carb and was having problems getting the tip in stumble out of the car because i was running an Elgin cam that was 224-234 @ .050, but had 71 deg of overlap (8" of vac in gear). After plenty of help i finally got it decent with carb tuning ( tube type # 37 squirter and blue cam in #2 position)and dist. tuning. For the dist i had to weld up the slot to only allow 15 deg of mechanical advance, and i used the crane vac advance canister with the screw all the way in and set to the lowest amount of travel or advance. That worked good I had 30 deg at idle which really smoothed out that cam and made it driveable. Then the motor spun 4 rod bearings..long story.

So in the rebuild i tamed it down a little with a nitrous HP cam 218-230 @ .050 113 LSA 108 ICL 48 deg of overlap(15" of vac at idle).( stock #31 squirter and blue cam #2 position) The car runs great, EXCEPT when i hook up the vac adv, to either manifold or ported, the timing goes back to 30 and the car runs rough, and starts missing as soon as the throttle is cracked open. It runs good without the crane vac can hooked up, but i thought it would run cooler and keep the plugs cleaner longer if i put the vac advance back on ? Do i just need to readjust the screw in the end of the vac can since i have more vac ? Or is this something to do with the MSD digital 6 ?


One more question, has anyone put a mechanical pump on an L-98 that was TPI previously ? I see there's a block off plate covering the hole, but is there a opening for the push rod ? Reason i ask is because I HATE that darn loud holley blue.

sorry so long and thanks for any help.


Mike

Something about your description doesn't make sense. If you tighten the spring all the in you are raising the amount of vacuum necessary to begin changing the advance. With 8" of vacuum, I can't see how you would have any effect at all by using the vacuum advance can.

The vacuum advance can physically rotates the trigger mechanism inside the distributor. I have seen problems caused by the mechanism being eccentric and creating problems with the air gap in the reluctor as the vacuum advance rotates it.

sorry , let me try to explain better.

the old cam had 8" of vac in gear. So i bought the adjustable crane vac canister and put it in my summit HEI and MSD digital 6 plus. I turned the screw inside the can so that i could get full advance with little vac. and hoked it to manifold vac so i had 30 deg timing at idle with 15 deg of initial and 15 deg of vac, this really smoothed out that old cam and made it tolerable on the street.

The new cam has 15" of vac and runs fine without the vac can hooked up with 15 deg of initial and 30 deg of total at 2500, but as soon as i hook up the vac advance the motor starts to run rough with the 30 initial and the vac hooked up, now if i hook it to ported it's ok at idle, but as soon as i crack the throttle open it starts to vibrate, miss and run rough ?

It's kind of tough to explain, sorry.

thanks for the help

Mike

Make sure the vac adv can's diaphram is not ruptured. Sounds like it could be a vacuum leak when the vac adv gets vacuum.

Pat i have thought of that and hooked a hose to it and sucked on it, I was able to suck what it felt like closed and then let my suction go and heard it close and hit the stop. Would this be good enough to check for a leak or is there a better way ?

thanks for the tip

Mike

That's how I check them. A vacuum pump with gauge would be better. However, if it was leaking enough to cause the problems you're having, it should show up by just sucking on the hose.

Someone on another board has suggested i get an old cap and cut a hole in it and see where the rotor actually goes to with a timing light while the car is running. They think the rotor tip could also be bent making it farther away from the cap and causing it to ark all over inside the cap ?
They made this statement below which i didn't know as true before,although that would explain why it runs fine if i turn the mechanical advance to 30 deg and more and it doesn't have that problem. I'll test tonight and let you guys know tomorrow.


Mike


***Because the vacuum advance affects the rotor alignment. The mechanical advance does not.***

***Because the vacuum advance affects the rotor alignment. The mechanical advance does not.***

How does this work? If the distributor cap remains stationary and the rotor is mechanically connected to the engine, the rotor must move in relation to the cap electrode in order to change the timing either by rotating the weight plate or the pickup and ring.

I'm surprised that you haven't refurbished the distributor since you've identified the problem as a timing problem.

sounds to me like you have to much total timing. a stock dist has at idle, intial plus vacuum which if the vacuum source was manifold, was 6 intial and about 18 vaccum total 24 which would fall off the second the carb started opening. if you have the can set so it takes almost no vacuum to pull on the timing it will be lazy to fall off and if you hook it up above the blades (ported) then it might be coming on with the little bit of vacuum it will see. tee a vac guage in the line and set the screw so that it takes at least 10 inches of vacuum to start it moving.
with having the dist recurved you want to limit the vacuum advance to about ten degrees, crane makes a nice little plate that goes under the screw on the canister for this.
when using even a mild cam i don't reccomend using manifold vacuum on the vacuum canister, it has a tendency to make a tip in problem worse, example- you give it gas to go, the advance falls off which will bog down the engine so you have to give it even more gas to cover the bog. better to use ported source so it will come on going down the road for better mileage and the engine is up in rpm so the advance fallin off when you give it gas has no bog effect.
if you have to use timing at idle to cover the rump rump of the cam you you will have problems up higher in the rpm range.

if you have to use timing at idle to cover the rump rump of the cam you you will have problems up higher in the rpm range.

How will you have problems higher up in the rpm range?

nova i have seen people put in 50 degrees intial to cover a rough idle ! and not care about total timing. a very good tuner can put in timing at the bottom end and take it out of the top end with proper recurving. and work with the vacuum advance by limiting it which very few people do.
with todays gas you must be very careful about to much advance. if you have steep gears or a loose converter and can get the motor up out of the 1400 to 2400 range fast (the problem area of which i write)you will not have the problems as much. but i have noticed a lot of beginners jump in and have so much problems (drivability in stop and go traffic, hard starting due to the timing) they lose interest in the hold go fast thing.

It's fixed, thanks to you guys for pointing me in the right direction.


I'll try to explain this the bast i can, but don't know all the parts exact names. I took the cap and rotor off and looked at the position of the two triangular ( magnets ? ) that come closer together as the advance works. I noticed as i pulled vac on the crane advance the two points went past lining up. I then used a stock one and when i pulled it with vac the two points lined up perfectly. I then compared the two advance cans and noticed that the crane slot was longer allowing more travel and the limit plate or adjuster goes to the initial side ( taking away the beginning point) which still allows over travel. Dave Ray sent me a pic of the limiting plate put on the other side to limit travel at the proper end. I used the stock one and only used half the limiter to get 10 deg of of vac advance. So I set 15 deg machanical initial timing with 30 total ( for the 100 shot pump gas) and hooked the vac advance to manifold vac and now have 25 deg when idleing, so if i have 30 mechanical plus 10 deg. vac i'll be at 40 max when highway crusing. So far the car runs great. I have alum heads and 9.8-1 static with 8.18 DCR and i run 92 octane

Mike

BTW, F-Bird i could actually see where the spark had been arcing under the cap on the weights.

Thanks alot to all you guys who helped me with this
:D :D

After a ride last night with the new tach i have come to the conclusion that my converter is a 3600 stall. I did this by cruising along at 1500 in 3rd gear and then go to WOT, the tack goes right to 3600 then stops and starts to climb as the car moves. It's a Midwest 10" converter

I don't know how to link it but the thread is at thirdgen.org go to forums and then the carburator section..it'll be close to the top under Mike 1985. The guy included pic's and other good tests too. I also have a pic that i can e-mail if someone could post it here to show what i'll try and explain below.

It's fixed, thanks to you guys for pointing me in the right direction.


I'll try to explain this the bast i can, but don't know all the parts exact names. I took the cap and rotor off and looked at the position of the two triangular ( magnets ? ) that come closer together as the advance works. I noticed as i pulled vac on the crane advance the two points went past lining up. I then used a stock one and when i pulled it with vac the two points lined up perfectly. I then compared the two advance cans and noticed that the crane slot was longer allowing more travel and the limit plate or adjuster goes to the initial side ( taking away the beginning point) which still allows over travel. Dave Ray sent me a pic of the limiting plate put on the other side to limit travel at the proper end. I used the stock one and only used half the limiter to get 10 deg of of vac advance. So I set 15 deg machanical initial timing with 30 total ( for the 100 shot pump gas) and hooked the vac advance to manifold vac and now have 25 deg when idleing, so if i have 30 mechanical plus 10 deg. vac i'll be at 40 max when highway crusing. So far the car runs great. I have alum heads and 9.8-1 static with 8.18 DCR and i run 92 octane

Mike