Issues with Type1 Dual Port - Idle

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Amskeptic
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Re: Issues with Type1 Dual Port - Idle

Post by Amskeptic » Sat Oct 10, 2015 10:46 am

asiab3 wrote: Continued from another thread...
hambone wrote: Best seems to be 30 deg. full advance, disconnect retard.
If I run it at 32 full advance, retard barely keeps the idle at 900.
If I run it at 28 deg. it doesn't like to idle after a run, and runs hot.
It also doesn't like to start after warm and shut off. I have to crank it a good 6-7 seconds before it catches, pedal floored "the Colin method".
When cold it runs rough for the first minute or so. I don't like it but it's the way it's been.
Hard to tell what to do, if it's the carb or the distributor. I've been chasin my tail here for a month. It seems to like higher advance...
Mr. Hambone?
From what i have gleaned, you have a pilot jet not seated because at some prior point, the engine would only idle with that jet turned out a crack, yes? Seat that sucker. You cannot get the balance of all of these interacting systems with any one of them compromised.

With the pilot jet seated, and the idle mixture subsequently readjusted to compensate, you will not have such a difficult warm start. You might find that this also improves your rough cold running.
IF seating the jet destroys all chances of getting an idle, you need to investigate why.
Low float level?
Incorrect main/air-correction jet?
Clogged passage?
Fluffy crap aftermarket base or top cover gasket squeezed into delicately calibrated holes?
Crushed pilot jet seat (due to overtightening) ?
Crap between the intake manifold and head (I have seen some doozies)?


I can tell if my mixture screw is adjusted incorrectly just by how the engine catches on a cold start. If it is too lean, my cold start may stall. If it is too rich, my cold start has a rough idle. If my timing is too advanced, the cold idle gets too fast before the choke shuts off. If my timing is too retarded, the cold idle has a temporary dip when the choke shuts off.

Regarding "likes more advance" vs "runs hot at 28*". Any time the timing is more retarded, you get more combustion heat dumped into the exhaust system. It only seems hotter at the apron, but CHTs show a cooler combustion chamber at relatively more retarded timing.
asiab3 wrote: Do you remember off hand seeing the hole in your throttle butterfly plate? DVDA distributors like this hole, and some carb rebuilders (Volkzbitz if you ask him to) will solder/rivet this hole shut to make it better with a 009/SVDA.

Is your big idle speed screw cranked WAY out? Good! You have my permission to really loosen it to get an idle. As long as the screw o-ring is still stiff enough so the screw doesn't back out, 'yer fine.
If we are going to attempt to control variables here, my first sacrosanct control variable is a precise valve adjustment followed by (for a SVDA or DVDA equipped engine) correct maximum advance (hoses off).
Dualport Type 1 max for me is 30*, preferred 28*.
Next variable to conquer is a functioning thermostat and air preheater system.
Then, proper float level, correctly indexed carburetor gaskets, proper jets, etc.
To test the vacuum retard range, you should do a temporary timing adjustment at idle to 7.5* just to see that the vacuum can can pull it down to 5*ATDC. Some advance cans have migrated from the dual carb buses into general circulation, they have a more intense pull down to 10* ATDC.
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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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Sat Oct 10, 2015 1:27 pm

Thank you Colin. Before I read this I went out today and played with timing. Weirdly if I time it with the vacuum hoses connected to the distributor - 30 deg full advance - I am able to connect the retard again and maintain idle and performance. If I time it (the correct way) with hoses disconnected and plugged I have issues. WTF I dunno but I will clean the glue out of that pilot jet and seat it and see what that does.
I did not consider a crushed gasket, that is subtle. The carb looks "new" but maybe sat a long time. When I have time I should just take it apart for a soak.
Thanks for making this a thread. OF COURSE Bus1 just fried the turn signal switch, it shorts out and smokes when I turn on the key. Always somethin, $100 new.
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Sat Oct 10, 2015 2:37 pm

Ok I went out there between the rain storms and seated that pilot jet. Guess what I can maintain idle now. How do you remember these tiny details with 1000 VWs in your head? It does seem to start quicker, but rumbles rough for a couple minutes until it "warms up". I have to give it a little gas pedal.
I will know more in the morning when it's cold. It seems to run well, in spite of the weird timing. The idle air screw is almost all the way out, if I retard the timing I know it will be too slow at idle.
The engine ran the same way with the 009. Maybe it's just a crappy aftermarket carb, oh that never happens. Jets, I haven't dealt with them before.
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Re: Issues with Type1 Dual Port - Idle

Post by Amskeptic » Sat Oct 10, 2015 2:50 pm

hambone wrote:Ok I went out there between the rain storms and seated that pilot jet. Guess what I can maintain idle now. How do you remember these tiny details with 1000 VWs in your head? It does seem to start quicker, but rumbles rough for a couple minutes until it "warms up". I have to give it a little gas pedal.
I will know more in the morning when it's cold. It seems to run well, in spite of the weird timing. The idle air screw is almost all the way out, if I retard the timing I know it will be too slow at idle.
The engine ran the same way with the 009. Maybe it's just a crappy aftermarket carb, oh that never happens. Jets, I haven't dealt with them before.
You may not time it with the hoses on. Period. If you are timing it to 30* with the advance hose on, you are actually retarding the range. With the vacuum advance hose on, the timing might normally be closer to 32-34* at 3,000 rpm, so setting it to 30 here is dropping the entire map a couple of degrees.

Aftermarket carbs have been calibrated for southern hemisphere cities which suffer smog. I do not know how we can read their jets, because their numbering is different than those listed in the Bentley. If you can find classic Solex jets with, for example, main jets of 127 or 120 or whatever stamped on them, you can compare our known jet orifices with the aftermarket carb jets by small drill or rod or even wire diameters.

Chloe was sold new with an insane 112 main jet. It now has a 117 and averages 20-22 mpg and 350-370 CHTs..
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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hambone
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Sat Oct 10, 2015 3:36 pm

It is raining buckets now, but tomorrow I will time it again. I will let you know the "baseline" we are at right now, at least it will run this way. Mebee that pilot jet was a fish in the pudding.
Is the 3000 RPM important? I just "floor it" and time it that way...
A question: how does the vacuum advance interfere with timing if the engine is at 3500+ RPM? Isn't that the mechanical-advance-only range? I am not questioning you, just curious. The whole idea of an advance curve is somewhat confusing. How poorly would an engine run without advance? Very mysterious though we deal with it all the time...How does moving the spark timing around via advance make things run correctly? 10 words or less.
I am struggling with this engine like the old days. It would be nice to have another carb to throw on there.
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bus71
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Re: Issues with Type1 Dual Port - Idle

Post by bus71 » Sat Oct 10, 2015 3:46 pm

Im throwing this out there based on my experience with the bocar carbs.
You may have done this already but there are 2 checkballs that must be removed to ciean these carbs. 1 in the floatboal and 1 under the brass pin on the side of the carb. These were somtimes stuck even when new. My theory on these was if stuck open; the carb would run rich and load up. there is probally something on the other site about this. I can put up a procedure for this if needed. The bocar on my bus works well after several cleanings over the years. Im running a mexican bosch 034 however. Hope this helps.

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dingo
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Re: Issues with Type1 Dual Port - Idle

Post by dingo » Sat Oct 10, 2015 7:26 pm

Bus1 just fried the turn signal switch, it shorts out and smokes when I turn on the key. Always somethin, $100 new

crack it open..youll see1,2 or 3 wires that have become unsoldered or chaffed and are shorting. Add small length of wire to each as neccessary and resolder to their correct joint. Make sure no exposed wires when all folded back together. very revive-able
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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Re: Issues with Type1 Dual Port - Idle

Post by Amskeptic » Sun Oct 11, 2015 10:07 am

hambone wrote:How does the vacuum advance interfere with timing if the engine is at 3500+ RPM? Isn't that the mechanical-advance-only range?
The whole idea of an advance curve is somewhat confusing. How poorly would an engine run without advance?
Because vacuum advance overlays the centrifugal advance, it can change the timing we are trying to read. Centrifugal advance is strictly speed-sensitive and answers to the simple laws of physics, i.e. at high rpms, the piston will drop away faster than the flame front, so we set off the combustion sooner to make sure that the combustion impact hits the piston 10* after TDC.
Theoretically,
At idle, the crankshaft rotates 13* in the time interval between initial spark, burn, and impact against piston.
At 2,000 rpm, the crankshaft rotates 36* in the time between spark and combustion impact against the piston.
Therefore, we start the spark at 3* BTDC at idle (to hit the piston at 10*ATDC)
Therefore, we start the spark at 26* BTDC at 2,000 rpm (to hit the piston at 10*ATDC)

There ^ is your reason for spark advance.

The upper limit of centrifugal advance is cast in stone, it is the point where compression stroke pressure meets combustion pressure. If the pressures get too high before our desired spark, spontaneous ignition of fuel can occur instead of the properly timed progressive burn we must have. This limit in our air-cooled engines is 28* at full throttle. At less than full throttle, the combustion and compression pressures are less because the cylinder did not get a full charge, so we can actually set off the spark earlier than the above 28*.

Overlaid to the above is vacuum advance, which **adds additional advance** (up to 40*) only under low/no load. It "knows" when there is no/low load because vacuum drops at full throttle exactly when we don't additional advance, and it increases at closed throttle overrun where we can afford to start the spark earlier for better efficiency, fuel mileage, and smoother transitions.

hambone wrote: Very mysterious though we deal with it all the time...How does moving the spark timing around via advance make things run correctly? 10 words or less.
At given load / speed, piston gets hit at correct instant.
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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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Sun Oct 11, 2015 1:40 pm

That is incredible. I feel all tingly from actually understanding this, it has been bothering me for some time! It's all math...and then it works in the real world, like a moon launch. Had no idea it had to do with piston geometry etc.
Okay then, here is where I am at today. First thing this bright morning I timed it to see what the "vacuum lines attached" setting actually was disconnected: 38 deg. Way too advanced. Well let's see if I can time it closer since I seated that damned pilot jet.
30 deg it will only idle at 700 RPM. But wait, at 32 deg. I can maintain the idle at close to 1000 RPM if I fiddle with the mixture and idle screws! And it runs well, not as jackrabbit jumpy but smooth all across the board. Still runs hotter than the singleport but it passes the dipstick test. It does indeed seem hotter at the exhaust. After it cools down we will see how the cold idle goes. I'm sure that 1-2 deg. of variation is possible with pulley marks, jumping timing etc.
The moral of this stupid story?
1. Pertronix manufactured 009s suck ass. I had to funky with the pilot jet to get the car to run.
2. Because of #1 all the other variables were thrown off causing all sorts of trouble
3. I still owe Asiab3 for this distributor in spite of all my fumbling bitching
Why do I need 2 identical buses anyway? Feel like a lunatic.
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http://pdxvolksfolks.blogspot.com
it balances on your head just like a mattress balances on a bottle of wine
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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Sun Oct 11, 2015 1:48 pm

P.S, thanks Dingo didn't see that at first. I was reading that the tracks themselves wear out but it is worth taking apart for a free look.
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http://pdxvolksfolks.blogspot.com
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Re: Issues with Type1 Dual Port - Idle

Post by dingo » Sun Oct 11, 2015 8:30 pm

yeah, it was in reference to your 'smoke in the cockpit' scenario
im sure the tracks do wear, despite forum members claiming that German made parts are immune to wear and metal fatigue
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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Re: Issues with Type1 Dual Port - Idle

Post by asiab3 » Mon Oct 12, 2015 11:24 am

hambone wrote:How poorly would an engine run without advance? Very mysterious though we deal with it all the time...How does moving the spark timing around via advance make things run correctly? 10 words or less.
MaBus1 has the vacuum-only distributor, correct?

"Rev MaBus1 up by hand with and without vacuum hose."

There's your 10-word story. ;) Just listen and "feel" the engine when you do it. You know the engine, and you'll feel an immediate difference.

hambone wrote:Still runs hotter than the singleport but it passes the dipstick test. It does indeed seem hotter at the exhaust.
Was there copious amounts of idling involved for this dipstick, apron, and exhaust test? With the retarded timing, the combustion will be so delayed that it will actually conclude in the exhaust system, heating up the exhaust "feel" quite a bit. The cabin heat is wonderful, too.

You don't owe me squat. Pass it on.
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Mon Oct 12, 2015 4:18 pm

Today. $%@#)%#)%
Adjusted the valves, most quite a bit loose.
Then it would only idle at 700 RPM. I have been screwing with this thing all day, the best I can do is a sickly 850 RPM with the fast idle cam slightly involved.
I am getting very frustrated. If the idle screw is out anymore it will fall out - but I need more screw! What the HELL is going on. At this point it must be the carb?
When I set it to run the best it just won't idle. It is running cooler now. But it still won't idle when cold and it still won't start correctly when hot. I am running in circles here to get nowhere. I set it one day, come back the next and it won't run the same way. It wants to be set rich to even idle at all, a couple turns past the "die out" spot. That is unusual, no?

BTW I took the turn signal apart, a fiasco #2 with stripped housing etc. All the wires were connected so I sprayed a bunch of electrical cleaner and worked it back and forth. No more smoke. Could a metal shaving gotten in there? Time will tell.....you should see my screw rig with piece of metal fuel line as a spacer........................

Anyone want a '69 Westfalia?
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Re: Issues with Type1 Dual Port - Idle

Post by asiab3 » Mon Oct 12, 2015 5:28 pm

At this point I need to see a picture of the throttle butterfly. The DVDA 34pict3 requires a hole in the plate, otherwise it will never pass enough air at idle. The 34pict3 carbs that run with a 009 or SVDA have a tiny or missing hole. I would not be surprised if the aftermarket carb did not have this, because no aftermarket company makes a DVDA.

(I sealed up my throttle plate hole in an experiment once, and I needed three extra turns out of the big brass screw to compensate for the "missing" air.)

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: Issues with Type1 Dual Port - Idle

Post by hambone » Mon Oct 12, 2015 6:16 pm

I am back fresh from the driveway to report that the hole is indeed there. The carb throat is very clean too; it is a new carb.
There is a chance that the engine sat for a while and the carb is just gummed up. Right? It was pulled from a wrecked Beetle, I'm guessing less than 10k miles.
When I first got the bus, it idled ok. Then I saw that the cutoff solenoid was loose (!) tightened it and then lost my idle with the 009. And the rest is madness. This carb seems to want more air.
I've never seen a carb 1/2 adjust, usually if they are gummy the adjustments won't do squat. Nor have I seen an adjustment change overnight! Should I blast the hell out of it with Gumout, or does that sound like a waste of time? Otherwise I'll have to rebuild it, and if it still doesn't work I haven't solved anything.
This is what I need, $200:
http://www.thesamba.com/vw/classifieds/ ... id=1715786
Oy.
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http://pdxvolksfolks.blogspot.com
it balances on your head just like a mattress balances on a bottle of wine
your brand new leopard skin pillbox hat

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