Zenith Carby Gasket

[AustHaflinger]

My engine has been running really well but as the outside temperature is getting up it is having trouble idling even though it is adjusted up and runs beautifully when the engine is cold and when outside temps are low.

I have reset the mixture idle but the issue is still there.

I am just wondering if the heat from the carby heat tube is upsetting the heat of the carb on hot days. The carb it is insulated from the carby heater pipe by the gasket that the carb sits on - I understand that these come in various thicknesses and I was thinking that as I never had the original gasket, I have the wrong one on my carby. My car was not originally fitted with a standard carb and manifold which have been ditched and the correct bits put on.

So what sort of thickness is the gasket fitted to your Zenith carb - the gasket I have is about 1/16" thick.

Thanks

Garry

[heinkeljb]

Gary,

The parts book only shows 3 gaskets fitted there. two thin .5 and one 3mm, so maybe you need to fit the two missing ones? Would have thought they were plain gasket paper material types. The thicker one being a composite material to make it insulate better. There is one for sale on FleaBay uk at the moment which has a single oval hole in the middle rather than two separate holes, which may or may not add extra problems!

I would also make sure that he petrol pipe is not routed right next to hot things - wouldn't help.

You could always try putting another 3mm gasket in as well, worst thing that will happen is you will get some throttle lag. Best thing that will happen is you will cure your idle issue.

John

[AustHaflinger]

Hi John - yes I saw the three gaskets in the parts book but I thought they were options rather than you use all three. I have no local suppliers so I guess I need to order some from one of the regular suppliers.

This is the only thing I can think off as the idle jets were only cleaned last week and mixtures set and it runs fine when cold and hot but not when it has been running for a while in hot weather.

Cheers

Garry

[heinkeljb]

As I said, I think the two thin ones are just ordinary gasket paper ones, if so just get your self a sheet of gasket paper and cut your own!

Make sure you don't have an air leak on any of the lower Carb joints i.e. the Governor choke block to Carb, the Governor choke block to the insulating gasket, the gasket to the manifold mounting plate. Any of those joint letting in air will give you bad idle speeds.

John

[Goatwerks]

What you want is MBZ# 1800710681 Unimog 404 carb insulating flange(4mm) it replaces the bakelight and gasket combo originally used.
Keeps the fuel in bowl from boiling on warm days.

[AustHaflinger]

Keeps the fuel in bowl from boiling on warm days.

That is what I suspect is happening - no issues when running as the fuel flow is fairly high but when idling the fuel in the bowl starts to get hot. To support this when you pull up at lights it idles OK but the longer you are stopped idles starts dropping off until it stops - always starts first go though.

Cheers

Garry

[kerry460]

G,,day Garry
i just had a look , the fibre heat spacer is about 4 mm , i didnt measure it , with a paper gasket on both sides .
that fits with other comments .
you could also try some good fibre washers under the metal washers when you fit the carby

the type of fuel hose can have an affect also .
if you are using the so called fuel safe pvc hose ?? toss it and go to the propper black rubber type .

and i agree , positioning of the fuel hose can have a big affect

cheers
kerry

[AustHaflinger]

Thanks Kerry - I will visit the local Merc independent tomorrow and see if he has the thick gasket but he doesn't know much other that mainstream mercs and didn't know the the Zenith NDIX was even fitted to some mercs. But I might get lucky. I am using normal rubber fuel hose and an electric fuel pump.

I didn't have the issue this time last year as I had blanked the carby heater pipe so the carb didn't get hot.

Cheers

Garry

[Goatwerks]

Spacer used on all 6 cyl Zenith carboureted Mercedes M130 M180 sedan and truck engines, Also used on Porsche 356

[AustHaflinger]

Thanks for all the input. I managed to get the three gaskets from my local Mercedes Benz independent specialist.

After 500km of perfect running, the engine has all of a sudden gone out of tune and is down on power and will not idle well and is hard to start when hot. I suspect it is killing off the spark plugs again and the tappets have closed up again. When I put the carby gaskets in I will do a carby clean, re-route the fuel line, new plugs and redo the tappets.

Maybe poor workmanship on my part but I am finding that the Haffie is fairly high maintenance and does not hold tune well, even with electronic ignition.

Garry

[kerry460]

Garry , i cant understand why you are having some of the problems you are having .
the only one i could not get running right had a broken crank , it still ran and was driveable ,
did not run good !!!!!!

you have my phone numbers if you want to discuss it .
cheers
kerry

[heinkeljb]

Gary,

Before you do any of those things, check the points = gap, timing, condensor. if the heel of the points has worn, then the gap will close up altering the timing. That has the same effect as you are describing.

How far have you driven since the engine rebuild? It could just be down to things bedding in.

John

[AustHaflinger]

Thanks for the input - is now electronic ignition so no points or condenser - now done about 1200km since rebuild and timing, tappets oil and plugs all changed/adjusted at 1000km - also carby reset with new floats etc. Idle was good at 700rpm hot or cold and engine was running sweet and strong. Engine is now rough and having trouble idling.

I will redo the usual stuff when I pull the carby off to put the new gaskets in.

Cheers

Garry

[AustHaflinger]

Garry , i cant understand why you are having some of the problems you are having .
the only one i could not get running right had a broken crank , it still ran and was driveable ,
did not run good !!!!!!

you have my phone numbers if you want to discuss it .
cheers
kerry

Thanks Kerry - I have no problems getting it to run right, the issue is seems to be keeping it running right.

Yes I have your number and I will certainly give you a call if I continue to have issues - the main issues seem to be the engine killing standard spark plugs (the Iridium plugs are holding up though) and as we have discussed before the tappets closing up and causing valves to stay open with an associated loss of power as expected. I set them at your recommended clearance a while back so it will be interesting to see what has happened to the clearances in that time.

Cheers

Garry

[heinkeljb]

The other thing to look at which will be an ongoing thing just because of the positioning of the fuel filler cap, is rubbish in the fuel blocking the jets.

Try pulling the choke cable out a bit and see if things improve.

John

[AustHaflinger]

I have a dual filter system - the first is the glass bowl that slows fuel flow so that heavy particles settle the bottom - there is a little debris here. Between the glass bowl I also have a modern inline fuel filter and it is perfectly clean so the chances of dirt getting into the carb from the fuel is unlikely.

Well I started work on a few things - shock horror the engine oil was extremely low and for some reason the oil light was not working though the oil pressure gauge was showing 40psi - low but Ok. Climbing underneath showed why the oil was low - the new repro seal on the oil return pipe that takes the oil back from the heads has split. Crap repro parts. I will try to fix insitu.

Timing was spot on at 7 BTDC and when cold, starts first go and idles happily at 750rpm.

I took the carby off to put on the spacing plate - hmmm the stud holes are all about 1/2mm out - easily fixed and on it goes.
Hmmm the main holes are different sizes - one 32mm and one 34mm - both should be 32mm - so not the right bit but no real issue.

I then to go to bolt on the carb bit the manifold studs are too short so I measure the thickness of the spacer - is not 4mm but 7.8mm So I do not know what the spacer is off - I guess a dual throat carb with 34 and 32mm throats. Was in a package for the twin 32mm but is not the case. I could sand the spacer down to 4mm but I do not have the gear so I will just get 4 new studs 4mm longer than the originals.

Having the carby 4mm higher should not be an issue.

There is always something - it never gets boring and is always interesting.

Garry

[heinkeljb]

Gary, which side oil return pipe? Should be possible to repair with the engine in place, You will obviously have to take off the tin wear in order to get access. Do you have a nice dribble line all down your drive?

Shame about the Carb gasket, but as you say, always interesting! Sometimes it would be nice if it more straight forward.....

I think from what you said earlier, your issue is down to not putting the blanking plate in the Carb preheat pipe junction and that your new thicker gasket might manage the same result, but you can always fall back on the blanking plate if it doesn't work.

John

[HaffyHunter]

Hi Garry,

I've been following your thread and have a few items for you to consider.

1) Do you know what your engine oil temperature is running at now that the ambient temps have risen? You may have some over heating issues now that your "high output" engine is running at full potential with all the work you've done recently.

2) An extra 4mm of thickness in the insulator plate may give a clearance problem with the engine bonnet if you are using the stock air intake box. There is barely 4mm clearance with the stock configuration so adding plate thickness could become an additional problem.

3) Tropical spec Haf's use a blanking plate in the left side flange where the preheat tube joins the exhaust manifold to reduce carby temps. As I only drive my Haf in summer I've installed this plate and get more consistent idling after longer drives. Occasionally the idle would drop a little too much while waiting at intersections when the Haf was good and warm before installing the plate. There doesn't seem to be a downside to having the blanking plate installed as the Haf starts and warms up when cold as it always did.

Cheers,
Steve

[heinkeljb]

If you do have to fit the blanking plate, it would be nice if there was some sort of "shutter valve" that you could fit like a choke cable or the panel on the rear lid which you can put up or down easily.

How about a sort of "double" size gasket, one part with a hole in it, one part with out. You put a bolt in one mounting hole and have two other mounting holes, one for the section of gasket with the hole and one for section without the hole.
You then only have to loosen the one mounting bolt. Remove the bolt from the other mounting hole, slide the appropriate section of the gasket in to place and put the bolt back in a do things up.

Could be done when you do the switch from summer to winter oil change and when you switch back from winter to summer.

John

[AustHaflinger]

Thanks Steve and John - some old cars have such butterflys and are operated by a bi-metallic strip that opens and closes the butterfly depending on temps - though was one of the first to fail if I remember correctly. I had both mine blanked this time last year and did not have the issue I have now but the guy who tuned it all up said I would most likely have issues during winter so when I did the engine rebuild I took the blanks out.

So to address Steve's points:

No I don't know what the temp of the engine is running at - a future project is to put either a oil temp gauge in or a block temp gauge.

I checked clearance and it is OK. The spacer I have is actually made out of wood - a bit like particle board.

What you described about idle dropping off is exactly what has been happening to mine so I think we are on the right track.


The bits are all back together but when running, the oil pressure light was off but the gauge was only showing 10 psi at idle when it normally is 40psi rising to 60/70psi at revs. So some issue exists - so off with the sump and all OK and in with a new oil filter. I also reseated the pressure valve - back together but the oil gauge was still showing low pressure - however I revved it up to 4000rpm and all came good - 70 psi and back to 40 at idle so just needed a good rev - I think the pressure valve might have been sticking.

I have the idle mixture screws wound back to 1 1/4 turns which is about the position I had it before and tomorrow I will take it on a run on that setting and get the engine up to operating temp and then reset the idle mixture as per the handbook - then hopefully everything will be back to normal - fix the oil leak - some Toyota silicon sealant is compatible with oily rubber surfaces so I will use it to fix the oil seal insitu.

I fully service my Range Rover Sport TDv6 and my V8 Landrover 101 myself and do not have any of these issues that I have with the Haffie - both have twice the kms of the Haflinger though the 101 is from a similar era.

Fingers crossed.

Garry