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View Full Version : How much vacuum should i see at idle?


xchipx
15-10-2010, 23:26
Still trying to diagnose why my car won't idle great/ cut out when braking.

At idle does 10inhg of vac sound pretty low?
Alex
16-10-2010, 07:07
That's fine, I think mines about the same :)
Tony Walker
16-10-2010, 09:18
Easy test, if you clamp the brake servo pipe and try it then( bear in mind that you will have no vacuum assistance on your brakes so they will be very hard to press and not work very well) If it doesnt cut out then theres a problem with the servo/pipework, if it does cut out id say check engine movement, engine earths, or king lead being stretched?
xchipx
16-10-2010, 14:55
Easy test, if you clamp the brake servo pipe and try it then( bear in mind that you will have no vacuum assistance on your brakes so they will be very hard to press and not work very well) If it doesnt cut out then theres a problem with the servo/pipework, if it does cut out id say check engine movement, engine earths, or king lead being stretched?


Just tried, doesn't make any difference sadly.

The engine even when car stationary does not idle properly ( but doesnt cut out ), when trying to drive in traffic for example in 2nd gear - the engine is constantly stuttering / rocking and it makes it jump out of gear. I doubt many people could tolerate it, but i am used to a honda crx with no interior/ sound deading / rose joints - motorway driving with no stereo. But i am hardcore when it comes to that ;)

On throttle and on boost there are no issues at all

Pressing the brakes when moving kills it though.

Not sure what a king lead is ?

Idle , when stationary, is constantly jumping from say 700 to 1300 non stop, popping sounds from exhaust too...

I think it might be an idea to tighten inlet manifold bolts etc, but i have no clue how to get the shield off ( under the carb ) its a lot bigger than on a 5


LAMBDA AT 1.8 at idle ( 25:1 afr )!!! I think that is extremely lean
modfather
16-10-2010, 15:36
king lead is the main lead going to the dizzy cap
michael tierney
16-10-2010, 20:09
mine has nearly 20 inches:)....vacuum that is,u might have a leak!!
Tony Walker
16-10-2010, 20:29
mine used to be nearly 20 too but i didnt want to say cause i havent driven it in a year so i could of been wrong lol.
Adam 005
17-10-2010, 12:11
have you got the small resticter in the breather system.if missing this can cause prolems
Andrew Cooke
17-10-2010, 12:15
LAMBDA AT 1.8 at idle ( 25:1 afr )!!! I think that is extremely lean

it won't be that lean as it won't run at anywhere near that.
jonnyshaw49
17-10-2010, 13:47
mine sits at 15 constantly at idle mate i run the cup breather mod with one way valve removed.
Slim
17-10-2010, 17:03
mine runs at -10 psi. I've always thought it was too low. Am i right? dont understand why. :( i reckon somthin is wrong :scratch:
Andrew Cooke
17-10-2010, 17:38
mine runs at -10 psi. I've always thought it was too low. Am i right? dont understand why. :( i reckon somthin is wrong :scratch:

10 psi is near as dammit 20in mercury
jonnyshaw49
17-10-2010, 17:48
Bad vaccuum is to do with valves and incorrect valve timing.check the timing is right pal
Slim
17-10-2010, 17:52
10 psi is near as dammit 20in mercury

pardon?? are you sayin -10psi is ok? (im reading this from the boost gauge right?)
Slim
17-10-2010, 18:04
Bad vaccuum is to do with valves and incorrect valve timing.check the timing is right pal

you mean cam timing? is this easily fixed?
xchipx
17-10-2010, 23:08
My problem just came on gradually , did not mess arund with any timing or anything like that so i cant see whats causing probs
Nick k
17-10-2010, 23:21
My problem just came on gradually , did not mess arund with any timing or anything like that so i cant see whats causing probs

Do you have a dump valve fitted? The diapham in it can split and cause a air leak?!
xchipx
19-10-2010, 19:34
I do but that would only affect throttle/wot
Alex
19-10-2010, 22:16
No....

Certainly worth checking :)
Shakes
22-01-2011, 01:28
did you get this sorted mark? im having the same problem, any help would be great
Tony Walker
22-01-2011, 09:27
dumpvalve doesnt just affect at wot, ur right in thinking its not after the throttle blade so shouldnt affect it but.... if the diagphragm is split it draws air up the vaccum pipe connecting it to the carb which is after the throttle blade and will affect idle and vacuum on closed throttle.
Matt Cole
22-01-2011, 09:30
mine has nearly 20 inches:)....vacuum that is,u might have a leak!!

:agree: All the C1j's ive had pulled nearly 20 inches. Check your manifold and pipework for leaks.
Tony Walker
22-01-2011, 09:42
:agree: All the C1j's ive had pulled nearly 20 inches. Check your manifold and pipework for leaks.


:agree: the two of mine that have been running also 20inhg
HAndy
22-01-2011, 13:12
my f7p is about 20inches on idle also with a 14.6 afr reading sitting between 950-1000rpm
Mart
22-01-2011, 13:25
Also depends upon which cam (ie, how hot) you have in situ.
Shakes
22-01-2011, 14:45
heres my boost gauge on idle my car is running rough on idle and when i brake to stop it cuts out, can someone take a look at the pic does it look like the right vac?
think i may have an air leak
Nick k
23-01-2011, 10:21
You might just have crap in your idle jet in the carb, give that a clean first and see how it runs. :)