| Author | Topic |
|---|
Location:
Brisbane
Registered:
July 2004
|
|
18R_GU vacum advance
|
Sat, 18 December 2004 08:36
|
 |
|
anyone have one they wanna sell? im not too sure if thats wats wrong with it, but when i accelerate, it just sits there for bout 2 secs, then takes off? anyone able to shed some light on this? Cheers
|
|
|
Location:
Gold Coast
Registered:
October 2002
|
|
Re: 18R_GU vacum advance
|
Sat, 18 December 2004 09:11
|
|
|
what makes you sure its the vacume advance?
|
|
|
Location:
Brisbane
Registered:
July 2004
|
|
Re: 18R_GU vacum advance
|
Sat, 18 December 2004 09:20
|
|
|
ive had a few people tell me thats what it might be. Anyone think otherwise??
|
|
|
Location:
Brisbane
Registered:
February 2003
|
|
Re: 18R_GU vacum advance
|
Sat, 18 December 2004 09:26
|
|
put a timing light on the engine and see if the vacuum advance works
e.g. sudden opening of throttle should spike advance - likewise, sudden choking of engine from WoT to nothing should retard the advance.
you can do this in the garage
you could also remove top from dizzi, attach long pipe to vacuum advance and use your lung power to suck on the pipe and look for movement of the advance-arm-thing.
i'd make sure it's actually buggered before replacing it.
cheers, charles.
|
|
|
Location:
Adelaide
Registered:
June 2003
|
|
Re: 18R_GU vacum advance
|
Sat, 18 December 2004 11:23
|
|
If you're driving an 18rgu, I don't reckon it's the vacuum advance that's the problem.
Very easy to tell though.
Itf it i the vacuum advance, when you take off the tube at idle, your idle speed should drop, that is if you have it connected to manifold vacuum (where it should be to work).
What your problem is from my experience is with the carbies. If your part numbers are 88254 and 88255 generation numbers then I know what the problem is.
These carbies did not have the accelleration pumps adjusted correctly from the factory. They do not work!!!
Can this problem be fixed?
Absolutely, all you have to do is rip off the carbies, examine the accelleration pump push rod (from the throttle shaft to the lever beneath each carbie.
Take off the little pin and add a few small brass washers (hardware store) between the pin and the spring.
This is a simple fix and if you know how long the pumps are supposed to work for (a little over a second) you can set them up correctly, like they should have done from the factory.
More washers = longer discharge time and stronger squirt.
Also check the direction of your accelleration pump jets (the flathead screws near the idle mixture adjust screws.
They should shoot straight through the manifold into the ports.
Note: There is a flat locating side on the jet, this mush align with the flat side in the hole it goes in. Small adjustments can be made carefully with pliers (there is a little slack)
If the problem isn't this then I'll be really, really surprised.
Every set of these carbies I've seen has effectively had no accelleration pump because of this adjustment issue.
Good luck with it, it can be done comfortably in a day.
Make sure that the pins you put back in are made from something tough, soft ones (twitching wire) wear through and the springs get lost!!
Steve M
|
|
|
Location:
Brisbane
Registered:
July 2004
|
|
Re: 18R_GU vacum advance
|
Mon, 20 December 2004 00:41
|
|
Thanks heaps Steve and Thechuckster! ill give all this a try and let you no how it goes. Cheers 
|
|
|
Location:
Brisbane
Registered:
October 2002
|
|
Re: 18R_GU vacum advance
|
Mon, 20 December 2004 08:26
|
|
|
make sure u have the correct plugs and a working coil
|
|
|
Location:
tallahassee FL usOFa
Registered:
May 2002
|
|
Re: 18R_GU vacum advance
|
Mon, 20 December 2004 15:17
|
|
the vacuum advance really retards the ignition timing when accelerating. lower vacuum = less advance.
opening the throttle lowers the vacuum until the rpm's catch up, and only then it will be advancing any more then it does at idle.
WOT = almost no vacuum advance.
down shifting/engine braking gets the most advance out of it, but it's useless for the engine at that time.
accelerator pump??????
static timing & mechanical advance.
|
|
|
Location:
Rocklea qld
Registered:
February 2003
|
|
Re: 18R_GU vacum advance
|
Tue, 21 December 2004 08:18
|
|
|
flat spot in the carbs????
|
|
|
Location:
Sydney
Registered:
September 2004
|
|
Re: 18R_GU vacum advance
|
Wed, 22 December 2004 07:46
|
|
| allencr wrote on Tue, 21 December 2004 02:17 |
the vacuum advance really retards the ignition timing when accelerating. lower vacuum = less advance.
opening the throttle lowers the vacuum until the rpm's catch up, and only then it will be advancing any more then it does at idle.
WOT = almost no vacuum advance.
down shifting/engine braking gets the most advance out of it, but it's useless for the engine at that time.
accelerator pump??????
static timing & mechanical advance.
|
I think you have it the wrong way around. Why would you want to retard timing on acceleration??
less vacuum on the unit allows it to spring back to a more advanced state then when your off the throttle the increased vacuum works on the actuator to retard timing.
This is going off a Nissan CA20E with a vacuum advance module...IMO they should call it a vacuum retard module 
|
|
|
Location:
Rocky Mountains, Canada
Registered:
May 2002
|
|
Re: 18R_GU vacum advance
|
Wed, 22 December 2004 11:57
|
|
| SilverGhost wrote on Wed, 22 December 2004 18:16 |
I think you have it the wrong way around. Why would you want to retard timing on acceleration??
less vacuum on the unit allows it to spring back to a more advanced state then when your off the throttle the increased vacuum works on the actuator to retard timing.
|
Nope, he has got it correct.
Vac advance is there to advance the engine while cruising only.
Sure it does it at idle (ive seen some that dont though), but thats just a side effect.
If you dont have vac advance while cruising, the car feels like crap and you chew a lot of fuel.
Ive played with this stuff quite a lot...
|
|
|
