Hesitations

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tommu
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Hesitations

Post by tommu » Tue May 03, 2016 4:25 pm

I have probably driven no more than 100 miles since Colin's last visit. At that time we refitted some components, set timing, set mixture and (thoroughly) reset valve clearance.

I have a '71 Karman Ghia with stock engine and:

- Original, rebuilt DVDA distributer, DVDA vacuum pot attached, known good and all vacuum lines connected
- Original, rebuilt 34PICT-3
- Standard jetting for carburetor and car. (need to refer to manual for jetting)
- Stock exhaust with open pre-heat

We ran out of time after bringing everything together, tuning and test driving. We noticed a mild hesitation but didn't really have time to fine tune.

Symptoms:
- Starts fine
- Pulls away ok
- Hesitates slightly when changing gear
- After a stop, really hesitates. If I feather the throttle then build the revs I overcome the hesitation.

Pretty much everything I'm reading talks about manual advance distributers or other components as probably causing such issues. In my situation I'm guessing that only a minor change is needed. but I really don't know what. I'm worried that I'll make another well intentioned ham fisted effort and lose the tune altogether.

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dingo
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Re: Hesitations

Post by dingo » Tue May 03, 2016 7:42 pm

if your hesitation is upon accelerating, then check the accel. pump squirt is strong and well angled...of course, ignition timing as well
'71 Kombi, 1600 dp

';78 Tranzporter 2L

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

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Amskeptic
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Re: Hesitations

Post by Amskeptic » Tue May 03, 2016 7:52 pm

tommu wrote:I have probably driven no more than 100 miles since Collin's last visit. At that time we refitted some components, set timing, set mixture and (thoroughly) reset valve clearance.

I have a '71 Karman Ghia with stock engine and:

- Original, rebuilt DVDA distributer, DVDA vacuum pot attached, known good and all vacuum lines connected
- Original, rebuilt 34PICT-3
- Standard jetting for carburetor and car. (need to refer to manual for jetting)
- Stock exhaust with open pre-heat

We ran out of time after bringing everything together, tuning and test driving. We noticed a mild hesitation but didn't really have time to fine tune.

Symptoms:
- Starts fine
- Pulls away ok
- Hesitates slightly when changing gear
- After a stop, really hesitates. If I feather the throttle then build the revs I overcome the hesitation.

Pretty much everything I'm reading talks about manual advance distributers or other components as probably causing such issues. In my situation I'm guessing that only a minor change is needed. but I really don't know what. I'm worried that I'll make another well intentioned ham fisted effort and lose the tune altogether.
For fun, let me know what the timing is with a warm engine:
Idle
with retard hose on
with retard hose off
3,000 rpm hoses off

What is current idle speed, all hoses on, warm engine?
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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tommu
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Re: Hesitations

Post by tommu » Tue May 03, 2016 9:59 pm

I will check and report back.

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Randy in Maine
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Re: Hesitations

Post by Randy in Maine » Wed May 04, 2016 4:57 am

It would also be nice to know if both your heat risers are indeed getting toasty warm after a few minutes of running. Check with a gloved hand please.
79 VW Bus

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tommu
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Re: Hesitations

Post by tommu » Wed May 04, 2016 5:27 pm

Results are in.

Heat risers - Left very toasty, right toasty - hot to the touch.

Idle speed, all hoses in place, warm, before testing - 910 rpm

Timing:
  • 11 ATDC (TDC to right of degree mark) hoses connected
    4.6 BTDC (TDC to left of degree mark) Retard removed
    30 BTDC all hoses off and no more advance
Purely out of interest I measured vacuum, hoses connected, at idle. 31 cm hg.

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Amskeptic
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Re: Hesitations

Post by Amskeptic » Wed May 04, 2016 7:52 pm

tommu wrote:Results are in.

Heat risers - Left very toasty, right toasty - hot to the touch.

Idle speed, all hoses in place, warm, before testing - 910 rpm

Timing:
  • 11 ATDC (TDC to right of degree mark) hoses connected
    4.6 BTDC (TDC to left of degree mark) Retard removed
    30 BTDC all hoses off and no more advance
Purely out of interest I measured vacuum, hoses connected, at idle. 31 cm hg.
Your distributor advance weights are a bit sloppy, robbing you of some timing down off throttle. But we stay with the 30*, so now we need to ask the carburetor.
Please jack your idle speed to 1,000 rpm. Now adjust the mixture to lean drop-off (try for 25 rpm if you can glean it from your tach).
Test drive.
improvement? yes let is know
no improvement, increase mixture to "best idle + 1/4 turn rich"
Test drive and report back!
ColinDa*nRain
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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tommu
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Re: Hesitations

Post by tommu » Wed May 04, 2016 8:22 pm

Amskeptic wrote: Your distributor advance weights are a bit sloppy, robbing you of some timing down off throttle. But we stay with the 30*, so now we need to ask the carburetor.
Please jack your idle speed to 1,000 rpm. Now adjust the mixture to lean drop-off (try for 25 rpm if you can glean it from your tach).
Test drive.
improvement? yes let is know
no improvement, increase mixture to "best idle + 1/4 turn rich"
Test drive and report back!
ColinDa*nRain
I think this is point I screw up. I haven't got a feel for how much adjustment to make. Getting idle up to 1000 is straightforward. Adjusting for lean drop-off I find hard. How many turns of the score would you expect to make? And.. is clockwise lean and anti-clockwise rich?

Second question - does this lack of idle advance merit a replacement distributer?

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wcfvw69
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Re: Hesitations

Post by wcfvw69 » Thu May 05, 2016 7:17 am

On the adjustments, you turn it in to increase and out to decrease, both the enrichment and idle. Colin showed me to turn the screw 1/4 turn and hold monitoring changes. Many folks read that both the volume and bypass screws should be right at 2.5 turns out or close to it. My experiences is they can be out further to achieve best mixture and idle.

Your idle timing appears off to me. If you put it back to 5 ATDC at idle (which is factory spec), what does it do to the other timing readings out of curiosity? Obviously, the high RPMS should move the amount of the idle changes but I've seen it not always happen that way. My DVDA has a bit of wear on the weights and I have no hesitations. It's very smooth off idle to acceleration. Did you say this distributor has been refreshed? It's been apart, was all the old, sticky, hard grease was removed from the pivot plates and new grease applied?

Your symptoms to me appear to be carb/fuel related. What is the accelerator pump setting at right now? Is it centered or? When you look down the throat of the carb and pull the throttle, do you get a firm stream of fuel out of the brass nozzle? Where is the nozzle (stream of fuel) aimed at in the carb throat? When was the last time the carb was taken apart, cleaned and reassembled with a fresh carb kit? How old is the fuel in your tank? You said you have not driven it much.

Last question, is it a German Solex carb or an aftermarket one?
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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Amskeptic
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Re: Hesitations

Post by Amskeptic » Thu May 05, 2016 7:57 am

wcfvw69 wrote:On the adjustments, you turn it in to increase and out to decrease, both the enrichment and idle. Colin showed me to turn the screw 1/4 turn and hold monitoring changes. Many folks read that both the volume and bypass screws should be right at 2.5 turns out or close to it. My experiences is they can be out further to achieve best mixture and idle.
Sorry, I have to do some corrections here . . .

Enrichment:
clockwise (in) LEANER
counter-clockwise (out) RICHER

The number of total turns is immaterial. We do not adjust to published numbers written somewhere, we adjust to:
What Makes Your Engine Happy.
wcfvw69 wrote: Your idle timing appears off to me. If you put it back to 5 ATDC at idle (which is factory spec), what does it do to the other timing readings out of curiosity?
We cannot change the base timing of 30* BTDC @ 3,000 rpm,hoses off. We can note that the distributor wear is "stealing" idle timing, but the engine doesn't care what the idle timing is half so much as it cares about the highway timing. As we lose degrees down at idle, it is easy enough to just ask the carburetor to compensate with a bit more air flow.
wcfvw69 wrote: Last question, is it a German Solex carb or an aftermarket one?
I can't even remember, but we had photographs from last summer's visit:

Image


Image
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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wcfvw69
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Re: Hesitations

Post by wcfvw69 » Thu May 05, 2016 9:15 am

Amskeptic wrote: Sorry, I have to do some corrections here . . .

Enrichment:
clockwise (in) LEANER
counter-clockwise (out) RICHER

The number of total turns is immaterial. We do not adjust to published numbers written somewhere, we adjust to:
What Makes Your Engine Happy.
That's what I meant mister.. You unscrew the adjustment to allow more mixture in to increase the richness! :cyclopsani:
Amskeptic wrote: We cannot change the base timing of 30* BTDC @ 3,000 rpm,hoses off. We can note that the distributor wear is "stealing" idle timing, but the engine doesn't care what the idle timing is half so much as it cares about the highway timing. As we lose degrees down at idle, it is easy enough to just ask the carburetor to compensate with a bit more air flow.
Something is really odd about those numbers. To be at 11 ATDC at idle to achieve 30* all in mechanical? I think the OP should recheck his numbers and make sure he's looking at the correct timing mark on his pulley. I totally agree that the retard function of the DVDA can requires more airflow thru the carb to achieve a good idle. I'd have to think it would have to be REEALLLY sloppy worn inside those advance weights holes/pins to give those numbers.
wcfvw69 wrote: Last question, is it a German Solex carb or an aftermarket one?
Amskeptic wrote: I can't even remember, but we had photographs from last summer's visit:
I asked because all the aftermarket carbs suck number 1. Number 2, the 34-3 aftermarket carbs are all SVDA carbs as they have the smaller hole in the butterfly for the 7.5 BTDC timing/idle because they don't need as much airflow when the butterfly is shut at idle. Many folks struggle with making the SVDA carb work with the DVDA distributor. When they are running a SVDA distributor with a DVDA German 34-3, people solder the hole smaller and or pop a pop rivet in the hole and remove the center pin. This makes that hole smaller and the carb play well with the distributor. On the other end, if it's a SVDA 34-3 carb, it's hole is too small for the idle circuit for the DVDA retard timing.

If that was my engine, I'd double verify the timing is set correctly while looking at the timing move w/a timing light. Then, I'd really look at the accelerator circuit on the carb while making sure the spray nozzle is pointing at where the butterfly is opening and the side of the carb throat. It is not un-common for crap to get stuck in that accelerator pump circuit by one of the check balls.
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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tommu
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Re: Hesitations

Post by tommu » Thu May 05, 2016 11:08 am

I'm running the German Solex the car was born with, rebuilt by Tim at Volkbitz back in 2012. It has the larger bypass hole on the butterfly and has received several carb kits over the past couple of years! Spray jet is sitting in it's correct position. Will check accelerator pump. That's one adjustment I did try but to didn't make a huge difference. I resolved to attempt measuring pump squirt before playing with that again.

The gas is only a few months old. Pilot jet blown through. Fuel pressure known good. The hesitation is not always extreme. Keeping the revs up overcomes it. Pickup and pull away does not feel as sprightly as it should.

Timing was tested exactly as instructed. I do *exactly* what I'm told :-) 30* was measured with both hoses disconnected and plugged at the carb.

Distributer was rebuilt by these guys: http://www.philbingroup.com. The timing mark doesn't fluctuate much so I think the shaft etc is still good. This point is important because I destroyed the DVDA I had from Aircooled.net by leaving an extension nut from a billeted aluminium distributor clamp in place - and refitting a stock clamp. It pushed the DVDA I was using at the time to an adverse angle and wore the shaft. I may even have another good DVDA rebuilt by them.

I can try making a video of the degree pully as I check the timing if that helps?

In summary, I think I always hamfisted my way into adjusting valve clearances which in turn doomed any chance I had of catching a decent tune. Without realizing that I spent months reading thesamba and trying every half arse fix available - and some good ones too..

I am now trying to learn how to do this the right way. And I thank you all profoundly for helping me along this path.

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wcfvw69
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Re: Hesitations

Post by wcfvw69 » Thu May 05, 2016 3:11 pm

I've heard those distributor rebuilders are hit and miss w/their quality control. I've seen their rebuilt DVDA's listed on some Flaps sites and I think Rockauto. It appears they open the vacuum advance can and install new diaphragms in them. It would be interesting to see one of their rebuilds put to the test on a Sun distributor machine..

If the rest of your tune up and valve adjustments are good, I'd still be suspicious of the carb. I bought a swap meet German solex 34-3. I had Tim install new throttle bushings in it. I suddenly started to smell fuel and the carb was leaking gas from a tiny corrosion hole in the fuel bowl of the carb.. I had another used German 34-3 that I cleaned and rebuilt. When I installed it and a DVDA that I had just rebuilt, I had a hesitation.

I was pissed to say the least. I had checked the float level and squirt from the accelerator pump before putting it fully together. After driving it, I looked down the throat of the carb again and wasn't thrilled with the power of the squirt. I then looked at the adjustment of the accelerator pump and it was slightly set to the - side. I hadn't noticed it during the rebuild. So, I reset that to slightly on the + side and the hesitation was gone.

That's a trick that people who run 009's and 34-3's. It's a terrible combo and is know for a horrible off idle flat spot or hesitation. They fatten up the main jet and max the accelerator pump adjustment to try and overcome it.
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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Amskeptic
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Re: Hesitations

Post by Amskeptic » Thu May 05, 2016 4:30 pm

tommu wrote: The timing mark doesn't fluctuate much so I think the shaft etc is still good.
Distributor shaft clearance is only relevant if you have breaker points. Timing light scatter turns out to be primarily opened-up end play.
To get a picture of how this happens, imagine a stationary engine. Pretend that you can move the crank pulley back and forth a good half inch. The brass gear's horizontal travel would move the distributor gear back and forth. Now imagine it in a dynamic setting as the engine is running at 3,000 rpm, the crankshaft's back and forth movement would show up as timing scatter.

Feel free to add a little accelerator pump. All you have to do is note your initial setting in case you have to scurry back to it. You don't *have* to stay rigidly inside the book specifications as far as output. Imagine that you have worn intake guides, or a build up of intake tract carbon, for example. You can compensate with adjustments that exceed the carefully determined new-car-mustn't-violate-epa-regulations specifications.

Maximum timing is different. Then you are dealing with the laws of physics.
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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tommu
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Re: Hesitations

Post by tommu » Fri May 06, 2016 2:23 pm

I had some time to test some more.

Idle/Mixture:
- couldn't wind out past 930/940 rpm Turning CCW. So I screwed the bypass (big screw) in until the revs started dropping and then back out to the fastest speed it would idle at.

Mixture:
-Turned small (control) screw slowly CW until revs started dropping and idle became uneven. I slowly blacked out out CCW until the idle just became a smooth and a little faster. Test drive and the hesitation had gone! Acceleration pick up felt slightly coarse - but no bogging or hesitation
-Turned screw out CCW one qtr. Smoother but a little stodgy?
-Turned screw 1/8 back CW and it felt best there. Pleasant to drive again. Stop obsessing over hesitations and start thinking of all the other things that need to be tinkered with.

Timing
With that done I thought I'd test timing again. This is interesting..

with retard hose on - 11/12 ATDC
with retard hose off - 8 BTDC
3,000 rpm hoses off - 27/28 BTDC

Then oddest thing happened. I put the advance vacuum hose on and after almost a minute the Idle slowed down a little and idle timing dropped to TDC. So I took the advance vacuum hose off again, it stayed at TDC, I revved a few times, and timing jumped back to 10 BTDC after a while it dropped back to TDC. So adv hose on or off it eventually just heads back down to TDC.

What do I make of that ?

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