1978 Bus L loss of power --- PROBLEM SOLVED! ---

[renobdarb]

I'm havin' some issues with power loss in my '78 bus... It seems to run just fine in 1-3 gears, but when I shift into fourth it seems to flaten out and bog down, and just doesn't accelerate like it should... If there's even the slightest uphill (and I mean slight... doesn't have to be a hill, just a rise in the road), it won't accelerate and sometimes even slows down, even with the gas mashed down.

I've tried just about everything I can think of... I've adjusted the valves (twice), checked the timing, even installed a new SVDA distributor (was going to do that anyways), and checked the timing again. Same problem.

Results from a compression test told me the valves were between 92-110.

The only thing left are my carbs (dual Weber 44's). Could out-of-sync carbs cause a loss in power?

Seriously, this is really annoying me. Any help would be appreciated.

[Amskeptic]

seems to run just fine in 1-3 gears,
fourth it seems to flatten out and bog down,
even with the gas mashed down.

The only thing left are my carbs (dual Weber 44's). Could out-of-sync carbs cause a loss in power?

That and possible fuel delivery issues or clogged main/power jets.
Double-check timing at 3,200-3,400 rpm for 28-30*. Also bring the engine up to 4,000 rpm briefly to make sure the timing is not advancing still further. You want the top of the centrifugal curve to be 28-30*.

How does it pull in 3rd gear between 40-55 mph?
Colin

[renobdarb]

seems to run just fine in 1-3 gears,
fourth it seems to flatten out and bog down,
even with the gas mashed down.

The only thing left are my carbs (dual Weber 44's). Could out-of-sync carbs cause a loss in power?

That and possible fuel delivery issues or clogged main/power jets.
Double-check timing at 3,200-3,400 rpm for 28-30*. Also bring the engine up to 4,000 rpm briefly to make sure the timing is not advancing still further. You want the top of the centrifugal curve to be 28-30*.

How does it pull in 3rd gear between 40-55 mph?
Colin

Hi, Colin... thanks so much for the reply! This has been really frustrating... I just can't seem to track down what's causing this power loss.

Anyways, I took the 'ol bus for a test drive this morning. I checked and rechecked the timing... It's at 8.5* BTDC at idle (I live at 6,500 feet), and at 28* at about 3,400 rpm. I just installed a new SVDA distributor a couple days ago (I was having this power loss issue before that), and here's a note that came with the distributor:

A) 28-30 Total Advance (hose disconnected)@ 3500 RPM.
B) 38-45 Total Advance (hose connected)@ 3500 RPM.

Let it idle and re-check the timing, you can now use this timing setting to set
the timing at idle, though we do recommend you check the full advance settings
to make sure the SVDA is working properly at both idle and full advance.

Do NOT be alarmed if you do not get the full amount of vacuum advance coming in
right away; the vacuum advance diaphragm is new and is VERY STIFF, it make take
up to a month or two of driving (A month sitting in your driveway or garage is
not the same) to loosen up as it's used.

...so I'm assuming I'll get more advance once this thing gets "broken in"...

Anyways, back to the test drive. It seems to run pretty well in 1-3 gears, but seems to flatten out on the upper end of 3rd, say around 45 mph, and seems to hold the speed there. In fourth gear, it holds steady at, say, 60 mph on FLAT roads with no headwind, but if there's even a slight rise in the road or headwind it'll decelerate.

I also took it up a real hill, and I had to downshift and downshift and downshift again. Basically, I used to be able to climb this hill steady in 3rd gear and now I struggle in second. It just doesn't seem to be getting the power it should.

Thanks again, Colin, for your help. If I sound desperate and pathetic, it's because I am desperate and feel pathetic, because I feel like I've tried everything and just can't figure this out. The carbs are the only thing I haven't tried, so do you think my problem may be there?

Also, do you think this might be a fuel delivery issue, like with my fuel pump? It sounds like it's working fine... Also, I changed out all my fuel hose last summer, so I can't imagine they'd be clogged...

Any way I can talk you into swinging through the beautiful Teton Mountain Range on your next circut?

Cheers,
Brad

[Amskeptic]

A) 28-30 Total Advance (hose disconnected)@ 3500 RPM.
B) 38-45 Total Advance (hose connected)@ 3500 RPM.

seems to flatten out on the upper end of 3rd, say around 45 mph, and seems to hold the speed there.
Also, do you think this might be a fuel delivery issue, like with my fuel pump? It sounds like it's working fine... Also, I changed out all my fuel hose last summer, so I can't imagine they'd be clogged...

High elevations with performance carbs can be a real headache. The carbs do not know that the air has much less density than at sea level. Your symptoms are classic high elevation symptoms for an engine that is set up for sea level driving. You can take another 3* timing advance if you are consistently above 5,000 feet. You must remember to retard the timing back if you go down the hill.

The mixture is very likely to be terribly rich. Check plugs for black sooty appearance on the insulator that immediately surrounds the plug center electrode. The PIA here is that you might have to re-jet the carbs if the plugs are indeed black, and what do you then do when you go down the hill? Rejet the carbs again. Ask your Weber professional about jetting at high altitude. If you do not know what your current jet sizes are, you will have to investigate.

If your plugs are nice and tan (or even white which would suggest a lean condition) at the insulator immediately surrounding the center electrode, then we can perhaps ask if your pump is delivering adequate volume. This is not a pressure test. You can have decent static pressure that drops to zilch when you need volume, so find out your delivery specs and get a measureable container to see what the pump puts out in "X" time. Lack of volume is not a question of clogged hoses half so much as a clogged outlet from the pump or a clogged filter or a tired pump.
Colin

[renobdarb]

Colin...

After pulling all the plugs and not finding any blackish-residue, I was still simply baffeled at what the heck was causing this power loss. I was so sure it was my carbs. But then I got to thinking... This power loss literally occured in an instant, in that at one point I was driving the bus and the next time I drove the damn thing just wouldn't go. I sort of deduced that if the carbs were going out of sync the power loss would be more gradual. Then my mind went back to the dozens of times I read your last post, and two suspicious words poped out:

... tired pump.

Hmmmmm.. frickin' fuel delivery. I didn't beat around the bush and just ordered a new fuel pump. A nifty Carter rotery pump with a constant 3.5 psi output.

Long story short, I installed that little bastard and off we went! Simply incredible. I'd simply forgotten how well my little bus runs when everything is in order. After long last, problem solved.

Anyways, a ton of good came through all this... this broken fuel pump made me learn to:

- Adjust the valves
- Adjust the timing
- Install a distributor
- Hook up aformentioned distributor to carbs
- Do some serious-ass trouble shooting
- Install a fuel pump
- Install fuel pump relay (so pump isn't operating off coil)

Seriously, I feel like I'm about ready for anything. Thanks so much for all your time and help, Colin... if you're ever in northwest Wyoming, you have a driveway to park your bus.

Cheers,
Brad

[Amskeptic]

problem solved.
I feel like I'm about ready for anything.

Good. These are the posts that others can learn from,
real life problem solving. . .
Colin