new 1.7L type 4 dual carb engine won't idle, is it fuel pump?

[dlwilson]

So I have my freshly rebuilt type 4 1.7L engine with dual carbs installed in the bus, but I cannot get it to idle. If I hold my foot down I can keep it at high revs, but as soon as I let up it will die.

Before I installed it, it ran strong for 20 minutes on the bench at perhaps 2500 rpm for cam break-in, then ran out of gas, so I didn't have a chance to try it at idle on the bench. I do feel like it ran stronger on the bench, out of a gas can, than it does no.

It has dual carbs I bought from a Samba member who took them off a similar 1.7L bus engine. I have replaced almost all of the linkage from pedal to carbs, but I still don't like the feel of it.

The tank was cleaned and sealed by the previous owner. I put two gallons of fresh gas in the dry tank. The new, clear fuel filter I put below the tank looks pristine, with no crap at all in it.

It has a Chinese vacuum advance distributor. I set static timing, but am waiting on a friend who knows about such things to put a timing light on it. I have checked closely for vacuum leaks.

The mechanical fuel pump is the one that came with this engine when I bought it as a core. I didn't rebuild it. Could it be moving enough fuel when the engine is running at high RPMs, and not moving enough for idle at low RPMs? That's all I can think of.

Any other ideas? I hate to just throw a fuel pump at it.

_________________
1977 Bus, with 1973 1.7L engine (rebuild complete, install underway)

[busdaddy]

Do all 3 solenoids click?
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[dlwilson]

[busdaddy]

There's 2 on the LH carb, one for the idle circuit on the carb, and a second for the CIS carb that supplies the tube across under the air cleaner. The CIS carb is built into the LH unit, it's intake throat is the brass tube that sticks up and connects to the pizza slice with the elbows and bent tube.
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[Abscate]

Those vacuum block offs look sub par. Get something solid in them, with a clamp. I don’t think fuel delivery is the problem but you can diagnose by inspecting fuel level in the bowl
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[kreemoweet]

The role of the fuel pump is to provide gas at a certain pressure to the carbs, and it does this
no matter what the engine rpms. How much fuel enters the carbs is dependent on the carb inlet
valves and floats, which in turn are affected by how much fuel the engine is actually consuming.
So not your fuel pump: inadequate fuel pump output would manifest at high rpms, not low ones.
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[dlwilson]

I was able to work on it for a while tonight. These carbs only have one solenoid each, but they are operating. I found that the solenoids were screwed in loosely, and tightening them helped stabilize the idle. Then my buddy used a timing gun to set the timing to 10 degrees like Bentley says, and that made it idle reasonably well. But it won't make power.

It's really hard to get it to rev, and when it does rev, and I engage the clutch, it just dies. Like it's not making any torque. Or power.

I inspected the manifold vacuum blockoffs, and they seem well constructed.

It has a Chinese vacuum advance distributor, and we can see it advancing. We tried taking off the vacuum hose (and plugging it) and that didn't help. It backfires out of the driver side carburetor sometimes. It's not driveable.

I've never been a strong carb guy, and haven't touched one for many years. I do have the single Weber and intake that came with this engine, and I did soda blast it and put in a rebuild kit before I bought these carbs. I'm thinking about putting that on, just to rule out these carburetors.

Anybody have suggestions?
_________________
1977 Bus, with 1973 1.7L engine (rebuild complete, install underway)

[aeromech]

Good luck, you need it. I hate those carbs
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[orwell84]

Do you have all the hoses hooked up? I think the short metal hose from the brass tube on top of the carb has to be hooked up to the pizza slice as BD mentioned.

Not sure about the missing solenoid. There is a big one that I don’t see in your photos. Years ago mine stripped it bore and immediately the bus fell on its face. Same thing happens when one of those elbows splits or any of the gazillion hose connectors.

I hated them too when I had them. I recently had them rebuilt and going to try them again. We’ll see.

[busdaddy]

[Alan Brase]

[aeromech]

Okay, take what you just said and add in 48 years and replacement Chinese made parts.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Alan Brase]

[aeromech]

A vendor in Italy? When I was installing these carbs on a bus a couple years back the solenoids that were available domestically were hit or miss. Sure, I guess great quality parts exist somewhere but I don’t know where. Seems much easier to install some brand new Webers. I guess if you want an original bus and have the time, money, and determination you can do it
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Alan Brase]

Well the Webers don't even USE idle jet solenoids. You could just replace them with fixed idle jets and still be where the Webers are at. Totally do not need complete idle shut off unless perhaps with automatic to stop run on.
I don't see how putting Webers on is gonna be easier in the short term. I do have a brand new set laying here , but never considered using, I was so wowed by the big vents that CB sells.
I guess I got big VENT envy? I made a 912e conversion to an old SWB 911 once, used these carbs. took the vents out and bored them to about 29.5, I think. The owner loved it. I got the 911 engine. All good.
_________________
Al Brase
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[dlwilson]

I checked the emails I exchanged with the seller, and the carburetors are:

Solex H 32/34 PDSI 2 and 3 Carburetor set

Whatever that is. They have the upper balance tube, but not the lower. The upper tube can be connected to the brake booster, but for now I have it blocked off to rule out booster leaks.

For now, I'm thinking I'll try the single Weber, just to be sure the issue is these carbs.

[edited: but first I'll try busdaddy's suggestion of 7.5 BTDC]
_________________
1977 Bus, with 1973 1.7L engine (rebuild complete, install underway)

[dlwilson]

busdaddy is the man. 28 btdc has the bus driving out of my garage and driving down the street. yay. after a couple minutes it sputters and dies, but then it restarts after a couple tries. I think maybe I’m running the carb bowls out of fuel?
_________________
1977 Bus, with 1973 1.7L engine (rebuild complete, install underway)

[dlwilson]

busdaddy is the man. 28 btdc has the bus driving out of my garage and driving down the street. yay. after a couple minutes it sputters and dies, but then it restarts after a couple tries. I think maybe I’m running the carb bowls out of fuel?
_________________
1977 Bus, with 1973 1.7L engine (rebuild complete, install underway)

[busdaddy]

You could rig a temporary tank to sit on the rear shelf (outboard motor tank?) and gravity feed it, if it quits quitting you found the problem.

That 28 BTDC is revved until it stops advancing (hoses off) at 28 regardless of how much higher you rev, right?
_________________
Rust NEVER sleeps and stock never goes out of style.

Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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[Alan Brase]