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welleyes
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« on: 13 November, 2011, 03:50:05 PM » |
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Thank you for the help with tappets. They are done and we move to the next problem. The engine hunts horribly at low revs and if the idle is kept decently low, it stops. So far, no amount of adjustment to the carb helps. We have to admit that our expertise is limited to Amal, SU and Fish, so any suggestion would be gratefully accepted. It is a 36VI 2 which seems to have been a fairly common mod.
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welleyes
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« Reply #2 on: 14 November, 2011, 03:02:29 PM » |
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We should have made ourselves clearer. The car is unwilling to idle. On the road, it is very prone to stalling when stationary. A touch on the throttle to keep it alive, sends the revs too high and lifting off stalls it. With the car in the garage, there are two adjustments; the idle mixture screw and the idling speed screw which alters the stop point of the linkage. The idle mixture screw does not make much difference to the problem as the engine behaves about the same with the screw three turns out or one turn out. Rich mixture at idle often causes hunting but in this case it would seem not to be the culprit. The only way to keep the engine from stalling is to idle it too fast when it hunts like an old fashioned diesel in a trafic jam. Adjusting the idle speed screw does not gradually slow the idle down; it goes from revving too fast to stopping completely with nothing in between. We have a spare carb and the idling jet in both is a 65 suggesting that is correct. Are the jets common to other Zeniths? What are we looking for if we wish to change jet sizes?
It occurs to me that the butterfly spindles may be worn enough to let in air. Is that a possible cause of poor idling? If it were a SU, I would know my way around it and would also know who to send it to for rebushing the spindles. What we are really asking is if anyone has had similar symptoms with a similar carburetter and has fixed the problem. At the moment, there are three other pre-war cars here which tick over like gas engines but they use Amals and SUs which are simple, trouble free and well brought up. We have a reasonable amount of literature on the 36VI 2, but none of it is helping. The Zenith is taking the gilt off our gingerbread.
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lancialulu
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« Reply #3 on: 14 November, 2011, 08:22:37 PM » |
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Seems that if the idle screw doesnt make any difference then a strip down of the carb to look for a blocked airway is on the cards. Best if you have access to an air line....
Tim
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Its not the winning but taking part! or is it taking apart?
Lancias:
1955 Aurelia B12
1967 Fulvia 1.3HFR
1972 Fulvia 1600HF
1972 Fulvia Sport 1600
1983 HPE VX
1988 Delta 1.6GTie
1998 Zeta 21. 12v
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welleyes
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« Reply #4 on: 16 November, 2011, 01:46:21 PM » |
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Carb changed for spare which is definitely clean and with unblocked passages. It is better but it still shows the same symptoms. Adjusted to a sensible idling speed, it will run like that for fifteen seconds or so and then speed will change either to just above stalling or to a very fast idle. In other words, it is still hunting, but with a longer period.
Any suggestions will be gratefully examined. If somebody tells us that 36 VI 2s always do that, we will live with it, but it seems unlikely. As it is a fixed jet carburetter, the only wear point would be the butterfly spindle, wouldn't it? That however does not seem unduly worn.
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davidwheeler
Permanent resident
Posts: 1487
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« Reply #5 on: 16 November, 2011, 02:01:10 PM » |
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Sucking eggs and all that but you are sure there are no leaks elsewhere in the system? and that the distributor is in good condition? Having said that, I had a very similar problem in the Fulvia, cured by re bushing the carb. spindles.
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David Wheeler. Lambdas, Aprilia, Fulvia Sport.(formerly Appia and Thema as well).
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lancialulu
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« Reply #6 on: 16 November, 2011, 07:19:49 PM » |
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Try a stronger butterfly return spring. Wont compensate for worn bushes but certainlt closes the butterfly kept open due to worn bushes. Short term fix as if new bushes then get them done.
Tim
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Logged
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Its not the winning but taking part! or is it taking apart?
Lancias:
1955 Aurelia B12
1967 Fulvia 1.3HFR
1972 Fulvia 1600HF
1972 Fulvia Sport 1600
1983 HPE VX
1988 Delta 1.6GTie
1998 Zeta 21. 12v
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ben
Lapsed
Megaposter
Posts: 456
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« Reply #7 on: 18 November, 2011, 10:48:08 AM » |
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I would also check for broken springs in the distributor auto-advance mechanism.
To verify if throttle butterfly bush wear is the problem try sealing them with blobs of grease.
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GG
Megaposter
Posts: 572
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« Reply #8 on: 18 November, 2011, 12:19:05 PM » |
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Leak in spindle bushes is one source; ovality in venturi ( and thus poor closure) is less common but can occur in older carbs.
See if you can check if any of the interior air passages are blocked.
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« Last Edit: 28 November, 2011, 04:23:54 AM by GG »
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Appia C10, Flavia 2000 coupe, Fulvia Fanalone
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welleyes
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« Reply #9 on: 18 November, 2011, 05:06:58 PM » |
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Thanks for suggestions.
The original 36VI 2 is now back on the car and it is better. It still hunts, though. We will try to sort out the carb we have taken off before going back to the other one. A cursory examination does not show much wear in the spindles but when other jobs (on other cars) are finished, we will take a closer look.
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