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Vacuum Leaks

 
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Oggie
Green Cloverleaf


Joined: 06 Mar 2008
Posts: 869
Location: Whitehill

PostPosted: Tue Jun 26, 2018 1:58 pm    Post subject: Vacuum Leaks Reply with quote

Hi Chaps,

Anyone ever suffered a Carb vacuum leak and know what the symptoms were?.
The Net isn't proving any answers via carbs.

My car has developed a problem whilst under acceleration which is the same symptom I suffered at Shelsey Walsh a few years back which I thought I'd cured via carb strip down and re-build with new Weber carb parts. The car after hard acceleration is fine through to 3rd gear then starts or feels like a misfire and will barely accelerate. The videos to my symptoms starts on the Video run 2 and again on run 3, I thought it is fuel related so have replaced all the jetting, fuel float needles and accelerator pump diafram.

Run 2 Video Link.

https://www.youtube.com/watch?v=3gxr-m5vGqE[/u][/b]
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Edward
Alfa 33


Joined: 21 Sep 2003
Posts: 341
Location: Bristol

PostPosted: Tue Jun 26, 2018 11:12 pm    Post subject: Reply with quote

.....and you are certain it is the carbs / vacuum.

I always find that what you may think is the obvious - is occasionally not the obvious. I would have perhaps said bad earth / fuel pump, but then I think on your car it is mechanical fuelling is it not?

What about distributor arm and cap. Are they clean and fresh. I have had similar problems in the past in this area.

To me I would be suspicions of the fuelling / vacuum - but I would also be suspicions of the electronics.

Perhaps take to an engine tuner and see if you can get it to mimic / do the stalling thing on rolling road. Doesn't Adie have any ideas? That way you could at least try and look at /wiggle things / change obvious things to rule out what may be the problem. Could it be engine earth affecting spark plug operation, plug leads, plugs, distributor, mechanical fuel pump, vacuum lines (as you say) carb float position, fuel pressure regulator (do you even have one of those on carbs), fuel pipe pinched, fuel pick up in the tank, tank over pressure / lack of venting causing fuel feed starving etc. There are loads of things that are worth working through. Can you put a fuel pressure gauge on the fuel feed to make sure you are getting fuel? Is there any way you can take the tops off the carbs and watch the fuel filling the bowls - but then I guess the float hangs downwards from the top plate. Hmmm....

Would be interesting to know how you get on. Sounds to me like loads of suspicions investigation required. One thing I have found that works well in the past is even the local AA/RAC man (strangely) the local friendly MOT garage - asking about / getting them on the subject of emissions or at worst case one of the mobile engine tuning specialists. On my mini cooper I had a small air leak on a carb gasket. I had spent ages trying to find a similar problem .... he found it in minutes. Doh!

Actually is your car dizzy or Omex? similar? I had a problem recently and it was the position of the crank position sensor. Move it 0.1mm closer - poor running at high revs - solved!
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RFlower
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Joined: 17 Feb 2004
Posts: 522
Location: S of France

PostPosted: Wed Jun 27, 2018 9:58 am    Post subject: Reply with quote

An AA man many many years ago showed me a quick and good way to find a vacuum leak.

With the engine at a fast idle, get your oil can and squirt a small amount of oil on and around gaskets and anywhere else the engine could be drawing in extra air.

Even a tiny amount of oil sucked in this way will produce clouds of white smoke from the exhaust.


Another cause could be fuel starvation on acceleration or cornering due to fuel moving back or sideways in the float chambers or in the tank, especially if the tank level is low.

I would also suspect the fuel filter in the tank, especially if it is still that perforated plastic bag fitted originally.
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Dick Flower, Nr. Carcassonne. '94 Trofeo 1.4 ie (F), '93 Imola 1.3/1.4 ie (now for parts) (F), '91 1.7 ie (GB)(spare car), '86 Sprint 1.5 QV (F). '87 VW Syncro camper (F), '96 Audi Avant 1.8T (F)
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Oggie
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Joined: 06 Mar 2008
Posts: 869
Location: Whitehill

PostPosted: Wed Jun 27, 2018 2:38 pm    Post subject: Reply with quote

Gents as always I appreciate your input and some of your suggestions I have overlooked, so far to date I have ordered a new fuel pump as I use an external unit, I have 2 filters one pre pump and one before the carbs neither are showing any dirt or debris but I will drop the tank to check the pick up as it could be a simple intermittent blocked outlet. I have filled the tank which again made no difference

I have checked the flywheel sensor and it hasnít move so possibly rule that out, my main suspicion is the petrol tank breather may not be venting therefore creating a vacuum which possibly closes the fuel lines enough to cause the poor running and would explain why after decelerating for 6 to 8 seconds then allows me to accelerate again. I did try to blow air through the fuel line before the pump to the tank to see if there is poor venting but fuel spewed straight out the fuel cap area again suggesting I may not have a vacuum issue.
I run a coil pack so have no dizzy
The issue I have is Iím the only one being able to observe the problem without having to pay Ahm or a mobile mechanic to run the car on a rolling road, not even sure they would be interested in looking at it now as servicing work pays better than old fashioned spanner work anyway I digress. Iíll attempt a few thing this week and see how I get on. Peace out.
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RFlower
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Joined: 17 Feb 2004
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Location: S of France

PostPosted: Thu Jun 28, 2018 10:18 am    Post subject: Reply with quote

I just noticed you said you have a fuel filter before the pump.

I think that might not be a good idea; the fuel is lifted only by spring pressure on the pump diaphragm, whereas the cam pushes it the other way.

The slight increase in resistance caused by the filter could have a large effect on the flow rate, especially when accelerating hard or when the filter is partly blocked by the debris inevitably found in steel tanks.
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Dick Flower, Nr. Carcassonne. '94 Trofeo 1.4 ie (F), '93 Imola 1.3/1.4 ie (now for parts) (F), '91 1.7 ie (GB)(spare car), '86 Sprint 1.5 QV (F). '87 VW Syncro camper (F), '96 Audi Avant 1.8T (F)
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Johnpm1967
Alfasud


Joined: 21 Jun 2013
Posts: 87
Location: Tewkesbury

PostPosted: Thu Jun 28, 2018 2:24 pm    Post subject: Reply with quote

Ok one weak thought as I had a similar issue.

Definitely only have one filter post pump. But check that all supply pipes in engine bay are nice smooth runs no tight curves or kinks.

I had it where the filter had moved a little and so the supply pipe was a little bent restricting flow.
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Edward
Alfa 33


Joined: 21 Sep 2003
Posts: 341
Location: Bristol

PostPosted: Thu Jun 28, 2018 5:38 pm    Post subject: Reply with quote

....and more.

I had a poor starting problem and thought it was the crank position sensor. Nope - turned out to be the plug where it connects onto the wasted spark coil pack. I was getting intermittent starting and when I wellied the car it would go fine as I think the voltage increased suitably to run the coil pack. At certain revs it would die. Found the problem by wiggling wires, then did a continuity test and found the only just touching / broken cable.

Always worth a wiggle.... Smile
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Oggie
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PostPosted: Thu Jun 28, 2018 8:59 pm    Post subject: Reply with quote

Hi all,

I took the tank out last night and its clean with very little debris, breather pipes didn't seem to be kinked but the one way vent/valve was in effective that in you could blow either way both times with resistance so for now I have left it off and run the breather up around the filler neck.

I have replaced the fuel line to the pump which incidentally recommends a pre filter?, the filter is a new un-used run of the mill unit I had laying around but I only fitted this after the car started to have the symptoms.

Now waiting on idle mixture screw o-rings to turn up as one has snapped trying to put it on the new idle screw Rolling Eyes. The only other thing I may have to change is the fuel line from the pump outlet to the fuel pressure regulator as I have a suspicion it may be too soft even though it was rated as a decent braided fuel line. It may be the weak point if the tank couldn't vent properly. Fuel pressure is set to just under 3 psi which is fine for the IDF carbs.

Hopefully once back together I can check again at the weekend.
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Oggie
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PostPosted: Sat Jun 30, 2018 4:31 pm    Post subject: Reply with quote

Spent a few hours on it today, replaced fuel pump which runs better than the last unit, removed pre-pump filter , new clips and replaced the fuel pressure gauge. Ran the car up and gave it a quick tune/balance and the problem is still there under load. The fuel pressure drops quite quickly under full throttle and i suspect its either the 12v pump supply or now the fuel line from the pump to the regulator , at least I know whats causing the problem. I'll replace the wiring to the pump or at least run a direct feed from the battery to start with before I rule the current harness out. I'll keep you all posted.
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BigAl
P4


Joined: 06 May 2003
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PostPosted: Sun Jul 01, 2018 10:03 am    Post subject: Reply with quote

Hi Iain.
If the fuel pressure drop isnt the cause, have you tried replacing the spark plugs, I have heard of new ones failing when under load.
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Oggie
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Joined: 06 Mar 2008
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Location: Whitehill

PostPosted: Wed Jul 04, 2018 9:13 pm    Post subject: Reply with quote

Right, got a sneaky few hours in this afternoon, replaced the 12v feed and went direct from the battery isolate switch rather than the ignition and sure enough it seems to keep pressure at full chat so hopefully problem solved, i'll re-wire via a relay or at least a fuse as the fuel pump switch I fitted is ineffective and have some new braided PTFD fuel line and a new regulator to go in on Saturday. Thanks for the suggestions they all help.
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Oggie
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PostPosted: Fri Jul 13, 2018 10:13 am    Post subject: Reply with quote

Spoke too soon FFS, going to spend another day on it tomorrow failing that I'll book it in to a local rolling road specialist who should be able to pin point the problem. Rolling Eyes
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Johnpm1967
Alfasud


Joined: 21 Jun 2013
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Location: Tewkesbury

PostPosted: Fri Jul 13, 2018 10:55 am    Post subject: Reply with quote

What a pain
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Oggie
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Joined: 06 Mar 2008
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PostPosted: Sun Jul 15, 2018 12:20 pm    Post subject: Reply with quote

Spent a few hours on it yesterday morning methodically going through the complete tank /fuel lines/pump/ new pressure reg to the carbs and eventually taking out the main jets using a gadget similar to what surgeons use to look around peoples bodies (cheap item from Lidl of all places) and found quite a bit of dirt sat where the main jet sits flush to the idf carb housing, gave all 4 a thorough clean re-assembled and new spark plugs now changed and reverted back to the F16 emulsion tubes from the F11 versions, went down a few sizes on the air jets to 180 from 200 so all I can guess from this was the car started to lean out under load, also temperature checked the manifold outlets on idle and piston 1 was showing signs of being 10 to 15 degree's C higher anyway took the car out, no misfire under load , rev range back to normal in all gears and with no hesitation. I'm one relived owner at the moment for the time being but would like to change the engine for a 16v unit (anyone have a complete one for sale?). and keep the 1.8 8v for a complete re-build.
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BigAl
P4


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PostPosted: Mon Jul 16, 2018 11:50 am    Post subject: Reply with quote

Sweet
Give me a call about 16v engine
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