Dual Carb T4 Gutless and Lurchy at Low RPMs

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whc03grady
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Dual Carb T4 Gutless and Lurchy at Low RPMs

Post by whc03grady » Sun Feb 11, 2018 4:11 am

Is it possible for a backfire to destroy a vacuum canister?
Let me explain.
Ludwig's gas gauge doesn't work so we were guesstimating range. It turned out that Southern Idaho's headwinds did more of a number on his mileage than our guesstimate allowed, and we ran out of gas.
Tank filled, it still wouldn't start. (I'm guessing mere cranking isn't enough to truly spur the electronic fuel pump to life.) So I poured some gas in each carb. Some combination of cold, fatigue, jitters, and idiocy led me to dump about a 1/4 cup in the right carb; I was more judicious with the left. Naturally it backfired horribly and died, but then started. We made our way in town to the night's lodging.
The next day it was really loagy off the line, up hills--even little rises--anywhere except at the top of the rpm range. That is, when we nursed it up to a good speed or went down hills, all was well. Other than that, it was a dog. Hills formerly taken in 3rd were taken in 2nd, and in one case, 1st. Also, mileage was horrible: high single digits.
Could the backfire have destroyed the vacuum can, leaving us with nothing but mechanical advance?
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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wcfvw69
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Re: Gutless and Lurchy at Low RPMs

Post by wcfvw69 » Sun Feb 11, 2018 5:22 am

whc03grady wrote:
Sun Feb 11, 2018 4:11 am
Is it possible for a backfire to destroy a vacuum canister?
Let me explain.
Ludwig's gas gauge doesn't work so we were guesstimating range. It turned out that Southern Idaho's headwinds did more of a number on his mileage than our guesstimate allowed, and we ran out of gas.
Tank filled, it still wouldn't start. (I'm guessing mere cranking isn't enough to truly spur the electronic fuel pump to life.) So I poured some gas in each carb. Some combination of cold, fatigue, jitters, and idiocy led me to dump about a 1/4 cup in the right carb; I was more judicious with the left. Naturally it backfired horribly and died, but then started. We made our way in town to the night's lodging.
The next day it is really loagy off the line, up hills--even little rises--anywhere except at the top of the rpm range. That is, when we nurse it up to a good speed or go down hills, all is well. Other than that, it's a dog. Hills formerly taken in 3rd were taken in 2nd, and in one case, 1st. Also, mileage was horrible: high single digits.
Could the backfire have destroyed the vacuum can, leaving us with nothing but mechanical advance?
I'd check all your vacuum hoses on the engine to insure they are all in place vs. a vacuum canister diaphragm failure. You can also see if a spark plug wire is loose, came off a plug, etc. A strong backfire can knock something loose. Look over the entire engine to insure everything electrical or vacuum is plugged in correctly.

If you have a timing light and hand vacuum pump you could quickly check your vacuum canister and the distributors ability to advance correctly. Hook up the test light. Unhook your vacuum hose to the vacuum canister and plug it. Hook the hand vacuum pump to the vacuum canister. At idle point the timing light at the pulley. Apply some vacuum to the vacuum pump. The timing should advance and stay there after you stop pumping. If the timing advance goes back to idle after you applied vacuum and held, it would tell you the diaphragm is leaking. If that test passes, hook your supply vacuum hose from the carb/s to the vacuum canister. Now, rev the engine. Is the timing advancing smoothly? If not, consider it time for your distributor to be taken aparts, inspected and then lubricated.

Every 40+ year old Bosch distributor I've disassembled showed it desperately needed to be cleaned of decades of dirt, debris, old dry grease and carbon dust. The advance pivot plates can be sticky or even frozen too. If the parts are not excessively worn, lubricating them again with distributor grease makes the parts advance/slide and rotate again like when they were new.
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

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whc03grady
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Re: Gutless and Lurchy at Low RPMs

Post by whc03grady » Sun Feb 11, 2018 10:21 am

Also, the lines come off the left carb.
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Re: Gutless and Lurchy at Low RPMs

Post by asiab3 » Sun Feb 11, 2018 10:56 am

Did it backfire out the intake or out the exhaust? If you had the air ducts off the carb, the ringing in your ears would tell you which…

An intake backfire could theoretically take out a vacuum diaphragm. Since you have stock Solexes and have been an IAC customer for years, I'm going to assume you have a DVDA distributor with vacuum retard functionality. If this is the case, and your advance diaphragm ruptured but the retard diaphragm did not, your ignition timing would be significantly retarded throughout the engine power band, causing the issues you described. A "side of the road don't have a vacuum pump" handy test is to take the advance hose off the left carb at idle and suck on it. Idle speed increase? Your vacuum can will perform fine on the road. (wcfvw69 won't like this, but I have driven a few VWs that fail the vacuum pump test, but drive flawlessly on the road because the sheer amount of vacuum pulled on the diaphragm can still actuate the advance/retard enough to get me 400 miles home…)

If the advance line DID rupture, you could restore much of your power by removing and capping your vacuum retard port. (Unless you're crossing the Rocky Mountains, then just leave it unplugged until you get below 5,000 feet.)

Don't you have an electric fuel pump? I'm getting the feeling you need to carry a jumper wire to trigger your relay for carburetor priming! :)
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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whc03grady
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Re: Gutless and Lurchy at Low RPMs

Post by whc03grady » Tue Feb 13, 2018 11:19 am

asiab3 wrote:
Sun Feb 11, 2018 10:56 am
Did it backfire out the intake or out the exhaust? If you had the air ducts off the carb, the ringing in your ears would tell you which…
The air cleaner was all reassembled for the backfire. It was pretty loud.
asiab3 wrote:
Sun Feb 11, 2018 10:56 am
An intake backfire could theoretically take out a vacuum diaphragm. Since you have stock Solexes and have been an IAC customer for years, I'm going to assume you have a DVDA distributor with vacuum retard functionality. If this is the case, and your advance diaphragm ruptured but the retard diaphragm did not, your ignition timing would be significantly retarded throughout the engine power band, causing the issues you described. A "side of the road don't have a vacuum pump" handy test is to take the advance hose off the left carb at idle and suck on it. Idle speed increase? Your vacuum can will perform fine on the road.
Funny thing is, the idle had been high the whole trip. Except--and this is even funnier, and not related to the present issue, I suspect--when I'd fill it with gas. We weren't turning it off during refills (don't ask). I noticed that after the gas had been pumping for maybe 15 seconds, the idle dropped for a bit...but this wouldn't happen if it just idled--only while it was being fueled. Every time.
asiab3 wrote:
Sun Feb 11, 2018 10:56 am
(wcfvw69 won't like this, but I have driven a few VWs that fail the vacuum pump test, but drive flawlessly on the road because the sheer amount of vacuum pulled on the diaphragm can still actuate the advance/retard enough to get me 400 miles home…)

If the advance line DID rupture, you could restore much of your power by removing and capping your vacuum retard port. (Unless you're crossing the Rocky Mountains, then just leave it unplugged until you get below 5,000 feet.)

Don't you have an electric fuel pump? I'm getting the feeling you need to carry a jumper wire to trigger your relay for carburetor priming! :)
Robbie
I do, with the IAC-approved relay that turns it off when the engine's off. Colin showed me how to jump it for just such an occasion, but it was one of those things that was so simple, I was sure I'd remember it. Nope. I didn't wanna guess and fry something, so I did it the old-fashioned way.
wcfvw69 wrote:
Sun Feb 11, 2018 5:22 am
I'd check all your vacuum hoses on the engine to insure they are all in place vs. a vacuum canister diaphragm failure. You can also see if a spark plug wire is loose, came off a plug, etc. A strong backfire can knock something loose. Look over the entire engine to insure everything electrical or vacuum is plugged in correctly.
That was the first thing I checked. Nothing was loose, though some of the can end of the advance hose was a little cracked at the end. I trimmed it and reattached. No change.
wcfvw69 wrote:
Sun Feb 11, 2018 5:22 am
If you have a timing light and hand vacuum pump you could quickly check your vacuum canister and the distributors ability to advance correctly. Hook up the test light. Unhook your vacuum hose to the vacuum canister and plug it. Hook the hand vacuum pump to the vacuum canister. At idle point the timing light at the pulley. Apply some vacuum to the vacuum pump. The timing should advance and stay there after you stop pumping. If the timing advance goes back to idle after you applied vacuum and held, it would tell you the diaphragm is leaking. If that test passes, hook your supply vacuum hose from the carb/s to the vacuum canister. Now, rev the engine. Is the timing advancing smoothly? If not, consider it time for your distributor to be taken aparts, inspected and then lubricated.

Every 40+ year old Bosch distributor I've disassembled showed it desperately needed to be cleaned of decades of dirt, debris, old dry grease and carbon dust. The advance pivot plates can be sticky or even frozen too. If the parts are not excessively worn, lubricating them again with distributor grease makes the parts advance/slide and rotate again like when they were new.
I'll start looking into it.

Thanks to you and asiab3.
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Amskeptic
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Re: Gutless and Lurchy at Low RPMs

Post by Amskeptic » Wed Feb 14, 2018 10:02 pm

"and your advance diaphragm ruptured but the retard diaphragm did not, your ignition timing would be significantly retarded throughout the engine power band, causing the issues you described."

Not likely. The retard signal is blocked off the instant that the left throttle plate opens past the retard orifice in the throttle body.

Mitch, does it sit there and idle pretty? That answers a lot of questions if it does. If it idles poorly, check your brake booster elbows. They can get blown clean off or split along a seam if you had a backfire. Heck, check the brake booster hose to the one-way valve under the car, too. Check both idle cut off solenoids for clicks and as importantly a noticeable change in idle rpm when you carefully pull off the spades one at a time. Backfires can soot the interior passages of the carburetors and clog the cut-off jets.

The reason your idle drops while fueling is because you are blasting the fuel mixture with piles of rich fuel vapors getting forced into the charcoal tank that dumps into the > air filter box as the fuel displaces air in the tank.

I get woozy reading of people pushing their engines when they can hardly move the car. Major expensive damage can occur!

You need to be very careful with priming for a number of reasons, especially a big fire lit by a backfire.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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whc03grady
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Re: Gutless and Lurchy at Low RPMs

Post by whc03grady » Wed Feb 14, 2018 10:48 pm

Amskeptic wrote:
Wed Feb 14, 2018 10:02 pm
"and your advance diaphragm ruptured but the retard diaphragm did not, your ignition timing would be significantly retarded throughout the engine power band, causing the issues you described."

Not likely. The retard signal is blocked off the instant that the left throttle plate opens past the retard orifice in the throttle body.

Mitch, does it sit there and idle pretty? That answers a lot of questions if it does. If it idles poorly, check your brake booster elbows. They can get blown clean off or split along a seam if you had a backfire. Heck, check the brake booster hose to the one-way valve under the car, too. Check both idle cut off solenoids for clicks and as importantly a noticeable change in idle rpm when you carefully pull off the spades one at a time. Backfires can soot the interior passages of the carburetors and clog the cut-off jets.

The reason your idle drops while fueling is because you are blasting the fuel mixture with piles of rich fuel vapors getting forced into the charcoal tank that dumps into the > air filter box as the fuel displaces air in the tank.

I get woozy reading of people pushing their engines when they can hardly move the car. Major expensive damage can occur!

You need to be very careful with priming for a number of reasons, especially a big fire lit by a backfire.
Colin
It does sit there and idle as pretty as it ever has, albeit a little fast. It had been a little fast since long before the backfire.

I was stressed to the max, believe me, about pushing the engine, but was conflicted because it ran so well at the top of the gears and it was running so cool (outside temps in the low teens helped for sure). What expensive damage was it prone to? (Not doubting, just asking.)

I will definitely lightly prime by jumper instead of by sloppy pouring in the future. Can I be reminded (again) where to make the connection?
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Amskeptic
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Re: Gutless and Lurchy at Low RPMs

Post by Amskeptic » Thu Feb 15, 2018 7:34 am

whc03grady wrote:
Wed Feb 14, 2018 10:48 pm
A) conflicted because it ran so well at the top of the gears
B) What expensive damage was it prone to? (Not doubting, just asking.)

C) I will definitely lightly prime by jumper instead of by sloppy pouring in the future. Can I be reminded (again) where to make the connection?

a) If your engine is not feeling well, high rpm can mask sickness because rotational inertia becomes a more significant contributor to rotation. That is why we hear claptraps getting revved to high heaven to cough their way across countless intersections across America each day.

b) Expensive damage occurs when people drive over a loss of compression due to a tight valve or the bugaboo for us air-cooled folks, trying to keep going when there has been an overheat on a hill where the pistons accidentally expanded into the cylinder walls.

In your case, I think the problem is minor, but find it for sure.

c) Go to relay. It has four spades. Only one of them is perpendicular to the perimeter wall
(perimeter wall? Really? :geek: ) . . .
Yeah, so you bridge that spade (#30) to the one directly across from it (#87) and the pump will run.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: Dual Carb T4 Gutless and Lurchy at Low RPMs

Post by whc03grady » Mon May 07, 2018 5:33 pm

Since we here shall be exclusively focused upon Symptoms > Solutions, I'd better come here and fess up.

I was so intent on assuming a vacuum can failure, checking all the hoses' connections, that I failed to notice the frickin' linkage bar had come off the driver's carb (at green arrow). Not only that, it was contacting the terminal at the choke!

Twenty demerits for not paying enough attention. It runs well now.

Image
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Amskeptic
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Re: Dual Carb T4 Gutless and Lurchy at Low RPMs

Post by Amskeptic » Mon May 07, 2018 8:43 pm

whc03grady wrote:
Mon May 07, 2018 5:33 pm
Since we here shall be exclusively focused upon Symptoms > Solutions, I'd better come here and fess up.

I was so intent on assuming a vacuum can failure, checking all the hoses' connections, that I failed to notice the frickin' linkage bar had come off the driver's carb (at green arrow). Not only that, it was contacting the terminal at the choke!

Twenty demerits for not paying enough attention. It runs well now.

Image

Thank-you for being the first person in 30,877 posts to even acknowledge the system we have. And thank you for responding with a solution update within three months, better than most around here.

You like that 1972-only trick spring thing that keeps a pressure on the 1972-only synchronization screw? Get a 1972 bus. You have the simple elegant '73-'74 floating cross bar with a much more annoying synchronization link.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: Dual Carb T4 Gutless and Lurchy at Low RPMs

Post by whc03grady » Tue May 08, 2018 8:22 am

Three months because that's how long it took before I actually took a real look at it.

The green arrow should be shifted centerward, to the other side of that plate (or whatever you wanna call it). I couldn't find a picture of a '73-'74 unit.

I should also say, the bar wasn't completely disconnected, dangling there. It had shifted toward center enough to contact the spade at the choke (like I said) but still performed some tenuous operation of that carb.
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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satchmo
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Re: Dual Carb T4 Gutless and Lurchy at Low RPMs

Post by satchmo » Tue May 08, 2018 9:25 am

You do have a good spring under a plastic cup in the end of the passenger side of the throttle linkage crossbar, yes? These items take up the side to side slack in the crossbar, and keep it under tension as the distance between the carbs expands and shrinks as the engine heats up/cools down.

Satchmo
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First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

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Re: Dual Carb T4 Gutless and Lurchy at Low RPMs

Post by Amskeptic » Wed May 09, 2018 2:10 pm

satchmo wrote:
Tue May 08, 2018 9:25 am
You do have a good spring under a plastic cup in the end of the passenger side of the throttle linkage crossbar, yes? These items take up the side to side slack in the crossbar, and keep it under tension as the distance between the carbs expands and shrinks as the engine heats up/cools down.

Satchmo
I . . . think . . . he does. He might be sporting one of our Itinerant Air Cooled Kustom RTV nozzle cups.
Check for springiness, Mitch. If the cross bar "springs back" towards the left carb after a light pressure towards the right, you do have the spring.
Colin :geek:
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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