Wierd Vacuum Problem

[Guest AWhite]

I have a very strange ongoing problem with a hesitation when i put my toe down.

 

Ok here's what ive done. I got a standard cheap mechanical vacuum guage to test for vacuum (i have one in the car but couldn't guarantee it's working). I connected it directly to my carb, a DGAS with no plastic things in between and get little or no vacuum at idle (POOR - red section) , it climbs as you rev the engine until it hits drive section then drops down to poor again.

 

So I tried to connect it to the manifold replacing the brake servo pipe, the vacuum goes into the idle section which is right and drops to the left as I rev the engine which is right.

 

So I block that pipe with my finger and assume that a gasket is leaking between the carb and the manifold. So I clean all gaskets and apply some blue hermatite gasket sealer. Same problem. Connect it back to the manifold and it is ok again.

 

I have replaced the carb recently to a DGAS previously had DGAV and had same problem.

 

So my question is: If it's ok at the manifold and not at carb and the gaskets are ok. Same with old carb. I've ran out of ideas. Anybody know what the hells going on?

 

Thanks for help guys.

 

Andy

[Peter Bell]

Hi Andy I am not sure what you are asking. Is it that you are not getting the vacuum readings you thought you should? where abouts on the carb are you fitting it? Or is it the hesitation during the transition stage of the carb? Does your dgas have a LOVE diaphragm? (low vacuum enrichment) What cam are you running?

Peter

[Guest AWhite]

Standard 2litre pinto no mods at all other than a DGAS.

 

There is only one vacuum connection on the carb. I just connected that straight to a vacuum guage and it read wrong (idled in red POOR section and climbs to right when pressing pedal). If I connect straight to the brake servo connection with guage it reads right (idles in IDLE section and drops to left with throttle).

 

Sounds confusing but somewhere between inlet manifold and carb all the vacuum is getting lost. Thought it might be gasket inbetween carb and manifold but that is correctly sealed now.

 

I think i'm just gonna get a t piece and connect it straight to manifold.

 

See any problems with this setup.

 

Thanks again,

 

Andy

[Longboarder]

Sounds like the vac connection is wrong side of the butterfly and the main air leak is through the two big holes (chokes) in the top of the carb. I wouldn't play with the servo connection. Drill and tap into the manifold below the carb and connect there.

 

Nigel

[Peter Bell]

Hi Andy the DGAS has one vacuum connection for the vacuum advance on the cam side (when fitted to a pinto) of the mounting flange, there is another on the opposite side for the love diaphragm, if fitted, and mine has another one between the two chokes behind the gear quadrants. I have blanked off this one, I assume you had connected it to the dizzy connection? either of the mounting flange connections should give a good reading.

Peter

[Guest Simon cooper]

Hello Andy,

You are on to the wrong pipe connector. You are connected to Vac Advance take off which does not suck until the throttle is open.

There is not direct take off for manifold vacuum that I can remember on a DGAS. You have to read manifold vacuum. so tap a moded bleed niple into the manifold if you have to have a gauge.

I suspect acceleration enrichment as your problem and not an air leak. Air leaks cause idle problems and not hesitation. I accept you have changed the carb, but when a carb has been standing a while, the alluminium oxidizes and white powder acts like cement and blokes pump jets.

Look down the throat of the carb with engine off and look for a powerfull squirt from the jet. The favorite on the DGAS is the bolt that passes through the centre of the jet works loose and instead of a squirt, you get an "Ouze" down the carb wall. Strip it5 and clean it. This crap also builds up in the diaphragm so strip it all down and clean the whole shooting match with celulose thinner and start again. There are no short cuts.

If enrichment is not the problem, then your timing is so far off it is in next week.

All the best.

Simon

[Guest AWhite]

Thanks Simon,

 

God you know your stuff. There's a lot for me to go on there, I let you know how it goes.

 

Andy