Zenith carb not idling

[gren_t]

Hi Chaps, I've had a poke through old posts and many have had the same issues I'm having at the moment but no clear answers so here goes...
I've had issues with Hemi running erratically stalling and poor idle, the carb was in a mess and leaking petrol from the baseplate shaft - the seals in there were split and hard though there is no play - I suspect it's been machined and bushed in the past.

I've replaced the plugs for a hotter range, replaced the coil and HT leads, points and condenser & set the timing to as near as I can get to the settings in the manual, but the poor idling and running was still there so I've decided to strip and clean the carb and rebuild it with new gaskets and pump etc.

All good so far however now it starts and will not idle it, it seems to start and then the engine will rev up or run away for a bit and then seem to flood stutter and then the rpms drop off to a stall.

I did find one of the springs for the idle mixture screws was snapped and shorter so I'll have to source a replacement, but does anyone have any ideas before I go tearing into it again.

I feel a full rebuild with new jets coming on...

cheers.

[heinkeljb]

Sounds like the mixture is going lean due to no fuel coming in then dies because of no fuel. So things to check, floats - make sure they are dry inside, they can split and allow fuel to accumulate inside.
The other thing you can check is to take the fuel pipe off where it joins the Carb. Turn the engine over with out ignition and see how much fuel your fuel pump is actually sending to the Carb.
Clean the idle jet by blowing air through them to make sure the holes are clear. look at the Idle jets when you take them out, as they can have a ridge around the bottom where they have previously been screwed in tight instead of just gently to find the matching taper in the Carb body. If that it the case, getting a stable slow idle will be very difficult. You would need to re-cut the bottom seal which will affect the size of the hole into the carb body which in turn will affect the running of the engine on idle.

The idle jet adjusters should be screwed in till they just touch the bottom of the hole, then both turned out 1/2 a turn each. Get the engine warm, at least crank cases hot enough to not want to keep your hand on them.
Adjust the throttle stop screw so that you engine is reving quite high but stable.
Now turn the idle jet adjusters 1/4 each either clockwise or anticlockwise to get the fastest engine speed you can.
Drop the throttle stop down a bit until you get the slowest stable tick over.
Now repeat turning the idle air adjusters a little bit either clockwise or anticlockwise to get the fastest stable engine idle you can. you might have to do this several times to get it right as it will change when you start driving the Haf around as this will change the engine temperature which has a direct effect on the engine idle speed.

John

[jhon]

Yep, I agree with what John has said, particularly the cleaning of the two idle jets. These can get blocked with fine particles very easily. I found that the petrol hoses were breaking down (maybe to do with E10 fuel) and allowing fine rubber particles in blocking the jets and giving issues similar to what you have. I'd clean the jets, then it would happen again in a short time.
Fitting a quality in-line filter just before the carb cured that particular issue.
If it runs a bit better with the choke on it's likely blocked jets.
Worth checking and eliminating as a potential cause.
Good luck with it!

Cheers,

John

[AustHaflinger]

The other issue is that people screw in the idle needles far too hard and this causes the ends to deform or ridges form - which changes the shape inside the carb. I suggest you puy new needles and put them in - - they only screw in until they stop - no further. You might be able to get just the needles but they do come with some carb rebuild kits - the Porsche kit has them.

[gren_t]

Hi Chaps, thanks for the replies.

the carb has been thoroughly cleaned in an ultrasonic cleaner, I've checked all the jets and apart from the slots being well used they all appear clear.
the Idle mixture screws are in good condition apart from the springs but I've ordered replacements anyway.

I'll check the floats in case they they are leaking but appeared to be fine when I stripped the carb down.

I'll persevere with trying to set the idle

[heinkeljb]

Hi Glen,

The needle on the left does appear to have some sort of damage tothe tip. This might be enough to give you some of the issues your egine is souffering from. The springs won't have any effect on the running of the engin eas all they do is keep some pressure on the threads to stop the needle for unscrewing themselves as the vibrations form engine running / driving tend to undo any thread unless it is tight!
So unless the spring does absolutly nothing whent the needle is screwed in until it stops at the bottom, no real need to replace other that it is likely to be cheap so why not?
If you can get a good view down the holes they screw in to and see if you can see a nice taper on the hole at the end. That might give you an insight into what teh cause of you bad idle is.
As mentioned above, Running with choke might improve things, if it does then the air ways the Idle air travels down is restricted somehow and even though you cleaned the carb once, it could well have collected something the moment the engine started. Put a filter in before the fuel pump and one after the fuel pump.
I have a can of compressed air used to clean computers with, can be bought from offic esupplies place if you can find them online. I take the Idle needles out. Use the compress air can with the straw it comes with to blow the needles clean AND stuck down each hole to give a blast of air down into the carb.
That normally get the engine running again without the choke.

John

[AustHaflinger]

The needles in the pic are the Porsche ones - the Haflinger ones have a smaller diameter knurled end - doesn't matter though as the needle itself is the same.

[gren_t]

Ah that may explain why the base plate looks different to other Haf carbs I've been googling I wonder if the porker carb had seals fitted in the butterfly shaft.!

[heinkeljb]

Have you actually check the number on the jets to see what size they are? It is possible that as above you have the Porsche version of the Carb or even the Pinz version and the previous owner didn't change the jet sizes for the smaller ones used by the Haflinger.

John

[gren_t]

Well I've had some time to fiddle over the weekend and I found the l/h idling air bleed "screw" was partially blocked, while I had the top off I thought I'd check everything again.
The main jet was a 107.5 rather than 110 as identified by the parts book and has been a little mullered with a screwdriver also the starter jet should be a 190 and I have a 100 fitted.
Pilot jets are correct at 45 but I think I'll replace all the jets anyway.
The engine now starts on the button however Idle is still way too high though more or less stable, any attempt to lower the idle results in it farting and burping before dying off.

another wait for parts ....

Thanks for the replies chaps it's much appreciated

[heinkeljb]

Hi Glen,

The sequence of having high idle revs / stable idle then adjusting the needle screws is one you have to repeat several times and you really need hte engine at working temperature. Getting it to idle at a nice slow speed whilst cold will result in it ruuning very fast once it warms up.
The other thing is as none of the tolerances are completely acurate, you have to make "very" small adjustments to the positions of the screws. Does sound like your Carb was played with by a previous owner in an attempt to cure running issues which were probably not Carb related. i.e. valve clearances not right or spark plugs wrong heat. Possible even rings not sealing well.
Keep at it, you find a compromise you will accept at some point.

John

[gren_t]

OK I have it idling sweet as a nut, I replaced the jets with the correct NOS items.. Many thanks James @ Haflinger parts.

I had a long think about what was happening and a look at the parts drawing showing the path of the idle fuel.. and found I had put the gasket between the base and the carb body wrong way around. doh...!

gasket turned around and 5mins fiddling and the idle is sorted.

thanks for your input chaps.

[heinkeljb]

Well done, glad you found an issue which when corrected made things work corrctly. Nothing worse than lotsof fiddling and somewhere along the line it just starts working - you never really know what was wrong and what cured it.

John

[jhon]

Ah...a moment. Great that you got it sorted!