Problem Solved - guess what it was...

[RazorRacer]

The answer : the PO had put a tip of a pencil in the vacuum line to the vacuum advance of the distributor. It held off vacuum for a while, but not completely. After running for a while, the vacuum did engage the advance and the engine started hesitating.

I replaced this with a new vacuum hose and the problem got worse. I then tied the new vacuum hose in a knot and the problem completely went away. I guess the knot was better than the pencil tip!

I will arrange a $50 gift certificate for boom next week. But I would still like to know more about the vacuum retard and how it's supposed to work.

Congratulations boom - you the man!

[Kevin Stewart]

Razor racer thanks for keeping us intertained it was fun, enjoyed it, Kevin

[RazorRacer]

Kevin: just sharing my joy!

[Kevin Stewart]

the reason i was so intereted was i spent almost a year chasin a gremlin, the car would stall, for no reason, one day i got piizzed and was gonna find and did, it was a dirty plug to the cdi box, know the car is a joy to drive again, i have had the car five years and promised myself if it wasnt fixed by fall I was gonna let the kids hit with a sludge hammer for 10 bucks a pop, but as it goes i have converted it to a wide body c2 look and did a cab conversion, maybe a 3.6 with a g50 this winter, and heres wishing you many more happy days with her, i mean car, post a picture, would be nice to see what car we were all guessing at, Kevin

[RazorRacer]

G'night all.

[Kevin Stewart]

Great looking car, Kevin

[A Quiet Boom]

Cool, I thought I might be right but I couldn't find a reference to what the PO had done anywhere in your other posts. How did I know? Well I've been installing a 3.0SC into my '66 912, I had both the vacuum lines disconnected because I'm running carbs and the motor broke up just like you mentioned. My initial timing with the lines disconnected was way to advanced. I also noticed with my timing light that the mechanical advance is very fast bringing it's maximum advance in at less than 3000 rpms. This lead me to look at the vacuum advance/retard unit. Basically both units attach to the throttle body with one above the throttle blade and one below (can't remember which is which) this means that the one below the throttle has a vacuum signal at all times except WOT (wide open throttle) the line above the throttle only has vacuum when the throttle blade opens and I believe it's proportional to throttle position. Anyway my engine also "free revved" fine like yours and since we are running different types of induction but exhibiting the same problem I had to look at what the engines have in common. I'm running an MSD box in place of the stock CDI as well so I ruled out the CDI, ruled out induction and fuel problems which left only one possiblity the distributers advance mechanism. I figured either yours had a weak spring on one side or the other or their was a hole in the diaphram. To further investigate as well as complete my ignition system I removed my vacuum advance and welded the plates together as well as welded the mechanical advance together, in effect giving me a locked distributer with no advance curve at all in anticipation of my next step which involved installing an MSD timing computer. I set the motor for total timing at 32 degrees BTDC and took it for a test drive, my problem was even more aggravated leading me to believe that 3.0 motors are very touchy when it comes to ignition advance. I then installed my timing computer and set the initial timing to 10 degrees BTDC with the curve starting at 2000 and total timing in by 5500. The problem is all but gone! A little more tinkering and I think I'll have it but I also need to adjust my accelerator pump circuit to more closely match my engine. My main clue though was when you stated that moving your initial timing to 5 degrees ATDC the problem was almost gone.

Well I'm certainly happy that you've fixed your car and that mine is almost done. I also don't feel that I deserve a gift certificate for fixing your problem after the fact, I only wanted to share a little knowledge with you and others, but then again this board is supported by Pelican Parts so if you/I spend $50 it only helps insure that we maintain this great resource. Best of luck!

[A Quiet Boom]

BTW, try one more test on your engine. Reattach the vacuum retard line, make sure it's attached to the throttle body in the correct position and set your initial timing at 5 BTDC. Test drive the car and see if the problem has returned before you eliminate the retard function by disconnecting it or before you replace the unit. I'm guessing it's probably bad (since the PO blocked the line) but this would be a way to know for sure.

[Bill Douglas]

Good man Boom!!!

Razor, now that the 911 is going ok you may end up saving some money for an air ticket down under. Why not fly down in January or February and we could do some very nice surfs aound the Wellington district, then round it off with a few high speed runs up to the wine making areas to the north in the SC. Then combine it with a trip to fabulous Australia where Fishcop, Adam, Merv and the rest of the team will entertain you.

Bill SCWDP - south pacific region

[wckrause]

Wait a minute. How can you say your problem is fixed when you've disconnected your vacuum advance? Vacuuma advance is for better performance at low RPM's with an open throttle, it's not an emissions issue.

You've still got some work to do.

[Superman]

True. when you first open the throttle to take off, there is some retard going on, and even at lower cruising speeds because the vacuum advance wants to advance the timing too much. It helps prevent the kind of detonation that happens when you suddenly open the throttle at low engine speeds.

but of course, if you've put carbs on or something, then those (timing) curves will be affected.

[wckrause]

78SC's only have vacuum advance. Vacuum retard was put on in 1980 along with K-lambda. (I think)

[RazorRacer]

Yeah, I still want to fix the vacuum advance. But at least now I know what the problem is and I can drive at constant speed, now, too.

Hey, I'm even going to participate in the next track day at Texas Motor Speedway in September!

[RazorRacer]

Surfer dog, I have checked air fares and a roundtrip to New Zealand is around $3-4K. Are there any better rates then this?

[CamB]

Wellington to Houston return should be around US$1500 per person.

You should be able to find a cheap fare from Houston to LA (or any other hub with frequent flights to NZ - I have only ever flown to or through LA on Air NZ). The figure I have in my mind is usually ~NZ$2500 (~US$1150). However, it seems to be much cheaper to fly NZ-US-NZ than US-NZ-US. They are screwing you

Auckland to Wellington is less than NZ$300 (under US$150). Maybe even NZ$200.

[MotoSook]

Wahooo! Go Razor Go!

Not to take anything from Boom, but Joeycatt started the revolution on the advance. Good for all and Boom for the investigation. Without the testing, it's all speculation.

You guys are grreat!!