Hesitation/flat spot on pull away.

[AlanH]

So today I put aside to finally get to the bottom of this annoying issue on my bus. Well, I didn't manage.
SO the engine has been rebuilt and has since done about 7000km trouble free.
The vacuum advance was disconnected for the duration of the 7000km as I thought it was faulty.
I have had the distributor serviced.
Today I removed the carburettor and adjusted the accelerator pump to deliver around 1.5ml per squirt. I also made sure the squirt goes down straight through the carb and not spraying against the side of the carb.
I rechecked the timing, readjusted the carb and while stationary it seems good. I was confident and wanted to take the bus for a spin and lo and behold I still have the same issue.

So other things I could check although on installation they were good.
Heat riser to heat the carburettor blocked?
Distributor vacuum can not operating properly, possibly leaks.

What else, please give me something to work with.


Oh, BTW the distributor and the Carburettor are matched for a 1600TP.

[AlanH]

So today I decided to revisit some possible causes again.
First checked the vacuum canister, although distributor was recently rebuilt these things are old. Turns out it has a leak and cannot advance as requested. When I suck on it, it moves slightly and returns to the original position. Obviously needs to be addressed before continuing.

Anybody out there have a Vacuum cannister with a number 461 on it preferably? Big Please.

Old Vacuum cannister.jpg

This is an old cannister that was definitely bust so I opened it for interests sake.

Vacuum cannister.jpg

Currently on my distributor. Note both are 461 and one does get different numbers possibly length, size ... differences.

[AlanH]

113 905 205 AL = Bosch 0 231 146 101 and Bosch 0 231 146 102 with vacuum can 1 237 121 461

113 905 205 AL = SVDA, 7.5° BTDC, hose off, mech. start 1050-1250rpm -> end 22-25° at 3800rpm, vac. start 60-100mmHg -> end 8-12° at 200mmHg


From the JBugs website:
BOSCH DISTRIBUTOR NUMBER 0 231 146 101 0 231 180 001
VW PART NUMBER 113905205AL 211905205S
APPLICATION 1971-72 non-US Type 1-2 MT
POINTS 01011
CONDENSOR 02054
CAP 03010(a)
ROTOR 04033(b)
VACUUM CANNISTER (Short Number) n/s
VACUUM CANNISTER (Long Number) 1237121 461
VACUUM CANNISTER VW Number 113905271H
TOTAL ADVANCE CRANKSHAFT DEGREES 8°-12° @ 180mm Hg

(a) Originally the 1969-early 70s distributor with the tall cap/rotor were listed ast taking a 1235522183-113905074A distributor cap. -> Now superseded to 03010

(b) The 04012 rotor was used on many cars from 1969-73 and is sometimes still listed as the part for them. However, the 04033 has all but superseded it now and is shown in place of the 04012 on the chart.

[73type2]

Thanks for this, Alan. I have the same problem on one of my vehicles. I’ll ask Dave from FFR to get me a couple of canisters.

[73type2]

I saw this on an SA website:

[AlanH]

The ones on that site seem to be universal and not what is required for our distributors.
The vacuum canisters for our engines seem to be specific for the application, carburettor and distributor and engine.
In my case 1600TP with a 205AL distributor and 34 PICT 3 carb for a bus I require the 416 canister. It seems the advance curve is determined by the canister and centrifugal springs.

[Dawie]

Vacuum advance can spec was decided by VW in 1971 when dual port engine was introduced. Fuel was cheap so economy was of little consideration then. Emission requirements from some countries carried more weight. (More vacuum advance would cause increased Nox emissions.)

From my own experiments since the 80's, more vacuum advance, within limits, on an acvw engine, do not cause knocking/damage.
I used the vacuum canister from a Golf gti at the time. Spec was 15 deg at 180/195mm Hg. Still using that distributor today. I would even consider one with higher max advance but reached at higher vacuum.
(If we try to compress a partial vacuum of 50% by 7.5 times, all we get is 3.75:1. Should we compress a 25% vacuum 7.5 times, we get 1.875. Which is nothing.) At these low cylinder pressures, burn is so slow that we need at least 40-50 deg total advance. Otherwise mixture will be burning late towards exhaust stroke.

Critical setting is maximum total centifugal advance, (always set with disconnected vacuum hose.) The needed vacuum advance gets added on top once we reconnect the hose. (Disregard online info only applicable to vacuum retard USA-emission controlled vehicles).
Knock limit mainly affected by rpm, load, and cylinder head temperature. That's why one should never ever adjust timing on an aircooled engine by ear.
That said, VW timing spec was meant for when using 91 octane at sea level. In the old days we used regular low octane- 93 octane at sea level and 87 at highveld altitude. (There is a 17% power loss at altitude- partial vacuum compared to sea level). So nowadays when using lowest octane of 93 at highveld altitude slightly more advance setting can be used. Maybe 2.5 extra degrees or so. But remember to retard before driving down to the coast.

[AlanH]

Wow Dawie, thanks for that although most of it went over my head. I only have a timing light to see timing and no pressure /vacuum instruments.
I also do what alterative canister I could use and how many degrees they give. Maybe I should refer back to the list on JBugs.

[Tony Z]

get someone to drive behind you and watch your exhaust.
If you accelrate (and operate the pumpjet), if it smokes black, then you have too much fuel. If it is clear and it still hesitates, then its not enough fuel.

[73type2]

I bit the bullet and bought a vacuum advance distributor from Goldwagen for R800. So far it’s working quite well with the cheap carb I got off Amazon. Time will tell.

[AlanH]

Do you have the part No.?

[AlanH]

Think I found it. V0260 currently R682.61 excl. VAT and R785 incl. VAT.
Might just try the same since I haven't had any joy with a replacement vacuum canister.