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Tue Nov 30, 2010 9:45 am

Wildthings wrote: 1977_L63H_P27 wrote: I have the original single vacuum distributor for the engine. Timing is set to max out at 30° BTDC.

That is with the hose disconnected from the vacuum can isn't it?

After I got her running good, I went back and did some checking on this. It was always my understanding that all the vacuum did, at least on a single vacuum distributor, was give the mechanical advance a little kick start off idle. This seems to be the case as I get the same reading @ 3400rpm with the hose on or off and plugged. YMMV!

Tue Nov 30, 2010 10:17 am

1977_L63H_P27 wrote: Wildthings wrote: 1977_L63H_P27 wrote: I have the original single vacuum distributor for the engine. Timing is set to max out at 30° BTDC.

That is with the hose disconnected from the vacuum can isn't it?

After I got her running good, I went back and did some checking on this. It was always my understanding that all the vacuum did, at least on a single vacuum distributor, was give the mechanical advance a little kick start off idle. This seems to be the case as I get the same reading @ 3400rpm with the hose on or off and plugged. YMMV!
Ever tested the vaccum pot on the distributor? how about your EEC valve?, if one won't hold vacuum neither will work and you'll be driving a toad.

Tue Nov 30, 2010 10:58 am

1977_L63H_P27 wrote:
After I got her running good, I went back and did some checking on this. It was always my understanding that all the vacuum did, at least on a single vacuum distributor, was give the mechanical advance a little kick start off idle. This seems to be the case as I get the same reading @ 3400rpm with the hose on or off and plugged. YMMV!

The vacuum advance and the centrifugal advance are two different systems that work independently of each other. Not sure where the idea came along that the vacuum gives the mechanical a kick start off idle, it does nothing of the kind. It mainly gives more advance at light cruising speeds. Test for vacuum as Bus Daddy recommends, you should have 12° +/- more advance at 3500 with the hoses connected than with them removed.

Tue Nov 30, 2010 1:05 pm

:oops: :oops: :oops:

Plugged port on throttle body giving me false readings and assumptions. My apologies.
EEC working perfectly as per Bentley testing procedure. Now I reset timing like so; Looking at Bentley, the highest setting they list for centrifugal advance is 26°. So that was my starting point. That gives me a 7-7.5° reading at idle and 36°@3500rpm with hose on. How's that sound?
Now my next problem is idle. I can turn the bypass screw until it's about to fall out and can only get 700rpm max. Any ideas? Thanks for all the help.

Tue Nov 30, 2010 2:50 pm

Lots of ways to look at this:

For a bus the normal range is typically considered to be 28-32° BTDC at 3500+ rpms with the hoses off, while the original T4 engines ran at 27° BTDC at 3500+. Many recommend limiting the timing at full mechanical advance to 28° to keep head temperatures down.

Using the specs available for a '77 at Old Volks Home then the timing works out to 28-33° hoses off at 3500+.

Full mechanical advance = Initial advance + Centrifugal advance.

28° = 7.5° + 20.5°

Total Advance = Full mechanical advance + Vacuum advance

40° = 28° + 12°

Tue Nov 30, 2010 6:29 pm

Well if I raise the centrifugal advance to 30°, I can get my idle in line. I just didn't want to run my new engine too hot. I'll try running the timing up a little at a time and split the difference between 28° centrifugal and 900rpm idle :P. Thanks again!

Sat Dec 04, 2010 2:58 pm

I can't believe my luck. All the idleing while getting her in tune and, the couple of trips around the block, left the bus on empty. So I decided to try the three blocks to the gas station and get some go juice. She died right as I got to the pump, after a smooth trip up there. She ran great, with lots of pep. I assumed it was out of gas and all would be well as soon as I put about five gallons in. Well, we all know what happens when we assume. Any way, now she starts fine, but only runs a few seconds. Sometimes you can rev her a little, but then she dies. I've put on a known good fuel pump, and tried another double relay with no better results. I pulled the fuel line loose past the CSV and ran it in a pop bottle. I'm getting about 8oz in 4 to 5 seconds of cranking. Could I have collapsed the fuel filter? Any other ideas appreciated.

Sat Dec 04, 2010 3:00 pm

Got the black wire from the DR connected to #15 on the coil?

Sat Dec 04, 2010 3:39 pm

Wildthings wrote: 1977_L63H_P27 wrote:
After I got her running good, I went back and did some checking on this. It was always my understanding that all the vacuum did, at least on a single vacuum distributor, was give the mechanical advance a little kick start off idle. This seems to be the case as I get the same reading @ 3400rpm with the hose on or off and plugged. YMMV!

The vacuum advance and the centrifugal advance are two different systems that work independently of each other. Not sure where the idea came along that the vacuum gives the mechanical a kick start off idle, it does nothing of the kind. It mainly gives more advance at light cruising speeds. Test for vacuum as Bus Daddy recommends, you should have 12° +/- more advance at 3500 with the hoses connected than with them removed.

Yes they are separate systems....but the vacuum advance on almost every system especially on ACVW...kicks in way before centrifugal. Most centrifugal advance systems on ACVW kick in between 1100 and 1500 rpm. The vacuum advance starts on some models with as little a 5" of vacuum. Mine starts at 8" of vacuum...which corresponds on 411/412 1.7's to about 950 to 1000 rpm with the throttle plate just cracked open past plugging the vacuum orifice.
This is why most people think that vacuum kickstarts the advance.

But...vacuum advance is virtually non-existent on most systems after the throttle plate moves more than about 10*....because the vacuum drops too far.
You can pick up vacuum advance again at part throttle at higher rpm ranges..and again at the same high rpm ranges that produce maximum centrifugal advance...which is why its not uncommon on some engines to see advances at 38-42* total at 3000-3500 rpm.
This is also why for instance on the high compression 411,412 and 914 1.7 with D-jet....that most of them came with an adjustable vacuum can to limit the total combined advance to prevent detonation. Ray

Sat Dec 04, 2010 4:42 pm

busdaddy wrote: Got the black wire from the DR connected to #15 on the coil?

Yep, and even checked on the wire connected to the starter solenoid. I just don't understand, running fine one minute and not the next. If I'd known it was gonna' cost me $500+ to switch back to FI, I wouldn't have bothered.

Sat Dec 04, 2010 4:43 pm

On a bus you are seldom going to see any vacuum advance except at light cruise. Lets face it the bus needs just about every last ratpower to get going from a stop on level ground, let alone to make forward motion up a hill. I used to run a vacuum gauge on my bus and know for a fact that the manifold vacuum seldom got above 5" of mercury on anything other than level ground or heading down hill. Maybe when you were winding out first gear at something besides full throttle you would see a higher vacuum for a bit, but in second and higher gears I at least tend to run pretty much dead to the floor until I reach cruising speed.

Sat Dec 04, 2010 5:40 pm

Got a fuel pressure gauge? Can you hear the pump run if you prop open the door in the AFM when the key is on?

Sat Dec 11, 2010 12:19 pm

Ummm, how exactly does this happen?

I finally got a break in the weather today, so I changed out the fuel filter. That wasn't it. Still started then died as if running out of gas. Sometimes, if you knew just when to do it, you could rev it up and it would run a little longer. So how does running one out of gas do this to the AFM? The way I found it was while trying to use a pencil to activate the pump, and I couldn't find anything to hit. I'll have to wait 'til monday to get an AFM. I'll let you know how it goes.

Sat Dec 11, 2010 12:27 pm

Likely damage by a backfire.

Sat Dec 11, 2010 1:51 pm

Wow, that's crazy. Mate up the two pieces and look for gaps. Check your intake plumbing for any fragments that may have broken off.

Sat Dec 11, 2010 2:37 pm

timo78 wrote: Wow, that's crazy. Mate up the two pieces and look for gaps. Check your intake plumbing for any fragments that may have broken off.

Already done! Nice even break. It is crazy!!

Mon Dec 13, 2010 7:19 am

Wildthings wrote: Likely damage by a backfire.

That has to be what it was, even tho' I never heard one. But why did that spring loaded center disk not protect the flapper? The world may never know :P

Mon Dec 13, 2010 7:38 am

1977_L63H_P27 wrote: Wildthings wrote: Likely damage by a backfire.

That has to be what it was, even tho' I never heard one. But why did that spring loaded center disk not protect the flapper? The world may never know :P
OK then, how about vacuum leaks (masked by richening the idle) lowering the flow through the AFM so the door is barely off it's stop, as the bus idles intake pulses make it constantly go tap tap tap tap on the stop, sooner or later small cracks develop until one day they join into one catastrophic failure?
How about a clear closeup of the crack? is it bright clean and new along it's full length? or are there discolorations in areas?

Mon Dec 13, 2010 12:16 pm

busdaddy wrote: ...
How about a clear closeup of the crack? is it bright clean and new along it's full length? or are there discolorations in areas?

Here's the one that has me curious...

Sorry, it's not as clear, but what could warp it like that?