Vac Advance from Carbi to Cap Problem

Submitted: Sunday, Jul 25, 2004 at 16:36
ThreadID: 14992 Views:1266 Replies:6 FollowUps:9
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I tried to set my timing today and found out that my vaccum advance for the ignition timing doesnt work. At least I think so. The timing does not move when I reconnect the vaccum hose. The hose for the vaccum to the cap has no vaccum you could feel with you finger while the car is in idle. On higher revs a tiny, slight vaccum appears. I traced the line back to the carbi and the connection there does not create a vaccum so I think the fault is in the carbi. Any chance to fix that without replacing the carbi or doing a major overhaul?

Thx,
Reisender
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Reply By: Bilbo - Sunday, Jul 25, 2004 at 19:42

Sunday, Jul 25, 2004 at 19:42
Rei,

You won't be getting a vacuum when the engine is idling - at least not one that activate the vacuum adv & retard. The vacuum adv/ret only works when you rev it really hard. Before that point in the rev band it's the mechanical adv/ret, located under the ignition distributor baseplate that does the job of advancing the ignition timing.

You could try GENTLY poking out the hole in the inlet manifold/carby with a piece of fine wire in case there's a blockage. It's a very simple system and there's not much in there that you can damage.

The final solution is to get a tiing light on it to check the amount of adv/ret. This is quite easily done by referring to a GOOD workshop manual and then checking it with a timing light. A mechanic would take about 15 to 30 minutes to do this.

Bilbo
AnswerID: 69584

Follow Up By: reisender - Sunday, Jul 25, 2004 at 21:00

Sunday, Jul 25, 2004 at 21:00
That is really confusing coz my manual for the Patrol/RB30 says that after connecting the vaccum hose again the timing should imidetly shift from 3 degrees to 15 degrees. So there must be a vaccum in idle for this engine or the manual is wrong.
The whole is an idea I also wa thinking of some carbi cleaner for the hole.
The timing light I have...thats where my trouble started when I tried to set the timing. Everything works till the moment I reconnect the hose and nothing happens (as there is no vaccum from the hose).
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FollowupID: 329870

Follow Up By: reisender - Monday, Jul 26, 2004 at 16:34

Monday, Jul 26, 2004 at 16:34
I found the problem. The preowner mixed up the vaccum hoses at the carbi. There are two connections and one doesnt create vaccum until high revs. Changed the connection and it works like a charm.
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FollowupID: 329971

Reply By: mr diamond - Sunday, Jul 25, 2004 at 19:48

Sunday, Jul 25, 2004 at 19:48
the vac advance on the rb30 runs on a set of ball bearing that seize up.
if your basically mechanically minded its quite an easy job or a good mechanic should be able to do it in a short time.
also on the mechanical advance the little spring can break pull your cap of and see how much free play in the shaft with the rotor button on it there shouldnt be more than 5mm or so before the mechanical advance starts to work
AnswerID: 69588

Follow Up By: reisender - Sunday, Jul 25, 2004 at 21:03

Sunday, Jul 25, 2004 at 21:03
I dont think the vaccum advance is broken or at least I am not at that point yet. The hose leadint to the vac advance unit does not suck/create a vaccum so there is my problem. When I check my timing I have to set it to 3 degrees and then reconnect the hose. Then it should automatically jump to 15 degrees but nothing happens. The hose does not suck so I thought thats where the problem lies. The hose comes from the carbi which does not create a vaccum either. Maybe the hole in the carbi for the vaccum is closed up...so i want to fix that first before I try anything else :o)
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FollowupID: 329871

Follow Up By: reisender - Monday, Jul 26, 2004 at 16:34

Monday, Jul 26, 2004 at 16:34
I found the problem. The preowner mixed up the vaccum hoses at the carbi. There are two connections and one doesnt create vaccum until high revs. Changed the connection and it works like a charm.
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FollowupID: 329970

Reply By: ianmc - Sunday, Jul 25, 2004 at 21:43

Sunday, Jul 25, 2004 at 21:43
Have you checked if the vacuum diaphragm is OK. Not holed?
Put screwdriver into distributor & push diaphragm rod to one side towards the vacuum line the put your damp finger over the line entry & remove the screwdriver.
Should be able to feel vacumm from stretched diaphragm on finger particularly when you remove it & watch to see if the diaphragm lever moves back.
Think it would be unusual for hole in carby to be blocked.
AnswerID: 69622

Follow Up By: reisender - Monday, Jul 26, 2004 at 00:28

Monday, Jul 26, 2004 at 00:28
My problem starts earlier. I do not have the vaccum coming from the hose while idling. So either my handbook isnt right or the carbi which should provide the vaccum isnt working 100%. I'll check tomorrow if the vaccum works on high revs then my handbook might be not right if not the carbi must be stuck with some carbon or so and I need a cleaning/overhaul.
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FollowupID: 329907

Follow Up By: reisender - Monday, Jul 26, 2004 at 16:33

Monday, Jul 26, 2004 at 16:33
I found the problem. The preowner mixed up the vaccum hoses at the carbi. There are two connections and one doesnt create vaccum until high revs. Changed the connection and it works like a charm.
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FollowupID: 329969

Reply By: Bilbo - Sunday, Jul 25, 2004 at 22:12

Sunday, Jul 25, 2004 at 22:12
Rei,

I'd hazard a guess that the manual that you have is NOT a genuine Nissan manual. Some of the "Gregory's etc" manuals are inaccurate.

For a start I would find it highly unusual to find an engine that has 15 degrees of ignition advance when the engine is idling. 5 to 6 maybe but 15 is a bit over the top. Max advance is at max revs, and most engines don't go beyond 20 to 30 maximum advance when flat out.

Bilbo
AnswerID: 69636

Follow Up By: reisender - Monday, Jul 26, 2004 at 00:25

Monday, Jul 26, 2004 at 00:25
Yeah I have a Gregory and Haynes. The Gregory one is the one with the 15 degrees the Haynes isnt that specific and just says to set it up to the adviced angle (for my engine 3 degrees) and then put the vaccum hose back and done ... hehehe. I'll check tomorrow if the timing goes up to 15 degrees when I rev it up (dont know why I didnt try that today - duhh). If it does so I am happy and assume the book isnt accurately written. If nothing happens the vaccum def. has a prob somewhere and I'll go thru all parts.
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FollowupID: 329906

Follow Up By: reisender - Monday, Jul 26, 2004 at 16:33

Monday, Jul 26, 2004 at 16:33
I found the problem. The preowner mixed up the vaccum hoses at the carbi. There are two connections and one doesnt create vaccum until high revs. Changed the connection and it works like a charm.
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FollowupID: 329968

Reply By: Savvas - Monday, Jul 26, 2004 at 06:29

Monday, Jul 26, 2004 at 06:29
It's been a while since I played with a carby.

But if I recall correctly, some carbys shutoff the vacuum advance at idle and only apply vacuum when the throttle opens. Do you have any driveability/economy problems?
AnswerID: 69664

Follow Up By: reisender - Monday, Jul 26, 2004 at 16:32

Monday, Jul 26, 2004 at 16:32
Yeah I had but I found the problem. The preowner mixed up the vaccum hoses at the carbi. There are two connections and one doesnt create vaccum until high revs. Changed the connection and it works like a charm.
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FollowupID: 329967

Reply By: Bilbo - Monday, Jul 26, 2004 at 17:31

Monday, Jul 26, 2004 at 17:31
Another happy customer from "SUPER MECH"................or I was, about 20 odd years ago. These days just changing a tail globe gives me the screaming s**ts. And don't mention actually cleaning the car,,,,,,,,,,,,,,,,,,,,

Bilbo
AnswerID: 69731

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