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seekingserenity
14th Feb 2008, 06:34
Any Zenith Stromberg carb tuning experts here? I'm struggling to get mine adjusted properly and could do with a bit of advice. I'm playing this one by ear....

Firstly, backfiring and jerking at low revs. I've tried both weakening and strengthening the mix - either way I still get the occasional "fart" and have to keep the revvs high on the smallest hills. Mix is a bit stronger this morning so not as bad - but don't want to go too strong because of fuel-consumption problems. Started better with the stronger mix. How do I find the right balance?

At the same time there's power issues. Hitting the choke on a hard hill gives just a small boost of power sometimes - what should I be doing to the carb instead of having to rely on choke? This weekend we tried to get up a gentle slope in a parking lot. It didn't work. At all. Nearly burnt the clutch out trying! :eek:

I've been fiddling with idle speed along with mix. When I strengthen the mix the revvs go down - is this right?

Will probably come up with more questions later... but these are ones I need to sort out as soon as possible.

Thanks.

TEMPL4R
14th Feb 2008, 08:10
Put engine oil in the damper, it slows the piston rise a bit more than thin oils.

Chris

harro
14th Feb 2008, 15:34
Do you have the manuals for the Zenith? if not I can send you some in pdf.

The carb is the original one of the vehicle? with the correct needle too? (heard of a guy in holland who found out the previous owner had tried to run the six-pot on a carb from the 3,5ltr V8... doesn't work :-)

I'm not an expert but could the mixture be to lean? (lack of power, increase when choke is applied)
Are the needle and valve ok?
Six-pots will never be very fuel-economic, but 1ltr on 6 km should be possible with the engine in a 'normal' condition...

Any change on measuring CO? I don't have the official figure but 2,5 is said to be acceptable...


Harro

Rich_P
14th Feb 2008, 17:54
Something completely different but all the same in relevance to an engine's running. Have you got it timed up correctly?

Whether or not they're any use, I'll list the timing positions anyway.

8.8:1 comp, 6 Degrees BTDC (95 Octane Fuel).
7.8:1 comp, 2 Degrees ATDC (90 Octane Fuel).
7.0:1 comp, 2 Degrees BTDC (83 Octane Fuel).
7.0:1 comp, TDC (80 Octane Fuel).
7.0:1 comp, 2 Degrees ATDC (78 Octane Fuel).

Also according to the manual, engine numbers starting with 346 are 7.0:1 compression while engines beginning with 345 are 7.8:1 compression. It also states that if lower octane fuel levels are unavoidable while using the 7.8:1 compression, then the timing can be retarded to a maximum of 6 Degrees ATDC.

Hopefully this will help. :)

RobGell
14th Feb 2008, 23:49
You should be able to tune the mixture by use of the lifting pin under the dashpot which lifts the piston inside manually for this purpose.

With the engine at full temperature, ease the pin in so as to lift the piston off its resting place on the choke of the carb. If you undo the dashpot lid and leave it loose, you can see how much you are lifting the piston.

If the revs fall away to a stall, it is too lean. If they run away it is too rich. Balance the mixture so that you get a small increase in revs when you just ease the piston up a bit, then see how it goes.

bvudzichena
15th Feb 2008, 11:24
Guys,

You know me as being brutally honest. You also know that I don't beat about the bush and say what needs to be said.

Well, Michelle went to work in my Disco this morning, leaving me to fit the main petrol tank. I had to rush out to get some hose for the tank breathers and decided to take Olivia.

With hindsight I should have walked. There's something seriously wrong under that bonnet.

As you may or may not know, I've done a lot of the repairs and upgrades to Olivia. But at the end of the day, it's Michelle's truck, so I've mostly kept my nose out of the engine bay, only advising her as to what I thought the problems may be and what possible solutions would be.

Starting the engine was relatively simple, but getting the engine to actually move the truck forward was another story. There is a huge amount of splutter, backfiring and gurgling when you put your foot on the juice pedal, so much so that I had to ride the clutch to get the truck to move over a set of traffic lights where the junction was on a slight incline. When I'm driving down the road the truck lurches and jerks for no reason. The engine also sounds as rough as a bear's @rse and - as I keep on saying - there's just no torque.

I don't know how much of this is down to the carb, how much is down to points timing, how much is down to valve timing and how much is down to cylinder compression (or lack thereof). To the best of my knowledge, Michelle's not had the rocker cover off since buying the truck.

The oil pressure gauge never goes above 2 bar.
The oil temperature gauge sits around 110 degrees celcius.

The truck started running very hot in December (the start of our hot period). I took the truck down to the radiator guys, they did some tests and concluded that the radiator is partly blocked. I haven't had the nod to remove it and get it sorted yet, so I removed the diaphragm from the thermostat - meaning water flows through the working parts of the radiator all the time. On a cool day like today the temperature barely gets above "Cold" - even after five minutes of idling.

I'm seriously thinking of putting the spare thermostat back. Is it better for the engine to be running "hot" rather than "cold"?

Could someone who knows his or her way around these engines and carbs please help with a step by step set of instructions as to what Michelle needs to do to get the truck to move forward in a manner that one would expect from a 2.6l, six cylinder engine.

As things stand, this truck can't pull the skin off a bowl of custard. I had to use low ratio to reverse up our little driveway today as the engine kept on stalling in High One :eek:

Rich_P
15th Feb 2008, 13:08
As things stand, this truck can't pull the skin off a bowl of custard. I had to use low ratio to reverse up our little driveway today as the engine kept on stalling in High One :eek:

Interestingly, the retired Police Officer opposite my house says the same thing about my 2A's sister vehicle back when they were in the Police. The sister vehicle was a late 2A 109-inch SW with the 2.6 engine. :rolleyes:

I think the 2.6 also has a slight tendency to burn exhaust valves out if it is not running right. I personally would say to perform a compression test on each cylinder before continuing to try to get it running properly, as after all if there's something wrong internally that needs attending to then it's going to be impossible to get it to run right.

seekingserenity
16th Feb 2008, 10:02
Thanks for the input guys. Busy taking that carb apart - for the FIFTH time! :eek:

But there's quite a bit of carbon build-up inside - what would cause this?

Tuning by the book today, then checking other parts in the process - HT leads etc. Hope this time the thing works OK.

K&S
16th Feb 2008, 17:15
My recollection of the 2.6 is as follows. On our police station in Salisbury we had two land rovers. A 109 hard top with 2.25 engine and a 109 pick-up with the 2.6 engine. Being a 19 year old my choice was obviously always with the faster more powerful vehicle.

My choice always the 2.6 engined pickup. There used to be a farm we visited on our farm patrol where the house was at the top of a hill with a driveway akin to going up table mountain. The 2.25 could never make it up. It was parked at the bottom of the drive and we walked up. The 2.6 was always able to make it to the top.

Both were series IIa vehicles and in fact the 2.25 had led a better existence as far as abuse is concerned.

So Michelle and Bvudzi you can expect greater things from that engine.

harro
16th Feb 2008, 17:20
Michelle, from what bvudzi described I wouldn't expect the carb to be the only problem... I think these are rather 'sensitive' engines (for Land-rover standards) as there were originally designed for a rover 'family-sports-car' (the P4) and the design goes back to the early fifties when service-intervals were normally every 5000 km including adjustment of valves and such...
I don't know if you can find anyone around who knows his way with old petrol engines and has the right tools (like I said, it's an old Rover engine, but these carbs were also used in various other cars like early volvo's) Let him check the valve-clearance (exhaust-valves are really a pain in the @ss because they're difficult to reach) the timing, stroboscope required (if that is spelled correctly?) and adjust the carb to the right CO-value... Personally I think the investment of getting the expert to have a look at it will pay itself back in the end...

Also check the oil-pump and make sure the oil actually does reach the inlet-valve rockers... Engine oil and filter have been replaced? And maybe also sort out the cooling-problem first, these engines really like to chew on valves when running hot. It took me a few hours flushing that engine (in every direction I could think of) to get most of the rusty water out...
Did you replace the fuel-filter? Although apparantly there is fuel reaching the carb...

As long as the rear chrankshaft-seal is ok (no large amounts of oil leaking from the bell-housing?) and the compression is ok-ish then there's no real need for a complete overhaul yet. valve-seals are most likely gone anyway but they require the head to come of which often leads to a complete overhaul in the end... (you can buy a lot of oil for that money)
These engines should run smooth with a lovely six-cilinder sound and lots of torque to make up for their thirst for petrol...

cheers Harro

TEMPL4R
16th Feb 2008, 18:24
It's not the 2.6 F head engine we have here is it, it's the Australian OHV engine isn't it?

When you fit the top back on the carb, do you make sure the little lugs on the diaphragm rim edges fit into the indents in the body and piston? It won't lift if the piston is in the wrong way.

Chris

seekingserenity
16th Feb 2008, 19:16
It's not the 2.6 F head engine we have here is it, it's the Australian OHV engine isn't it?

When you fit the top back on the carb, do you make sure the little lugs on the diaphragm rim edges fit into the indents in the body and piston? It won't lift if the piston is in the wrong way.

Chris

Chris, yes - the lugs are in right, and the piston's lifting smoothly. What's an F head engine? OHV engine? Got no clue!

This engine apparently (says my Expert) is the one that started out in the 2a.

seekingserenity
16th Feb 2008, 19:18
So Michelle and Bvudzi you can expect greater things from that engine.

Believe me, I do! Bvudzi's not so sure.. :rolleyes: Tomorrow the quest forward continues, as I think the carb's as good as I'll get it at the moment. Took a test drive and she's running a lot better than yesterday, but not yet completely smooth - so it's on to other things down the power line - dizzy, HT leads etc. (as soon as my hand stops throbbing - injury put an end to work this afternoon)

seekingserenity
16th Feb 2008, 19:25
Let him check the valve-clearance (exhaust-valves are really a pain in the @ss because they're difficult to reach) the timing, stroboscope required (if that is spelled correctly?) and adjust the carb to the right CO-value...

Also check the oil-pump and make sure the oil actually does reach the inlet-valve rockers... Engine oil and filter have been replaced? And maybe also sort out the cooling-problem first, these engines really like to chew on valves when running hot. It took me a few hours flushing that engine (in every direction I could think of) to get most of the rusty water out...
Did you replace the fuel-filter? Although apparantly there is fuel reaching the carb...

As long as the rear chrankshaft-seal is ok (no large amounts of oil leaking from the bell-housing?) and the compression is ok-ish then there's no real need for a complete overhaul yet. valve-seals are most likely gone anyway but they require the head to come of which often leads to a complete overhaul in the end... (you can buy a lot of oil for that money)
These engines should run smooth with a lovely six-cilinder sound and lots of torque to make up for their thirst for petrol...

cheers Harro

Thanks Harro. Working through things bit by bit. The carb's the starting point, and a good few of the things you mentioned are on the list for tomorrow. There was a Rover engine expert in the area at one stage - but he's since disappeared and we haven't found another. So it's a bit of trial, error and learning how to do it myself.

We've had the engine running cool enough lately, it just took a while to warm up at times - but put in another thermostat today and will keep an eye on things. It's opening at quite a high temp, and I know that could get worse with town driving on a hot day. Our "roadtrip" to Cape Town last week saw some high temps heading up the mountains, though running cool enough on the long road. We've kept the old thermostat handy - it's been "modified" a little...

Did an oil change recently along with an oil filter change. Fuel filters have been done recently too. So it's going to be an investigation of other bits to see if there's another factor at work here too.

For now I have to say I'm happy with how the carb seems to be doing at the moment - no more backfiring or jerking/stalling at low revvs. I think it should be set about right, but did have to set the idle speed down after a test-drive.

Rich_P
16th Feb 2008, 19:52
Chris, yes - the lugs are in right, and the piston\'s lifting smoothly. What\'s an F head engine? OHV engine? Got no clue!
F head configuration is the inlet valves are located vertically above the piston, while the exhaust valves are located in the side of the block. In short, inlet overhead, side exhaust.

Whereas the OHV is Overhead Valves, both the inlet and exhaust valves are in the head and are above the pistons (like on the 2.25 Litre engines).



This engine apparently (says my Expert) is the one that started out in the 2a.
For European/GB spec, that would be the 2.6 Litre Rover straight six (which is an F head type engine). Although not really knowing what the export models were fitted with engine wise, I'm curious to know more about this Australian engine Templ4r talks of.

Is it the Holden engine you're talking of Templ4r?

TEMPL4R
16th Feb 2008, 20:25
I can't find a picture Rich, but it's based on the E series SOHC engine but for some reason is called the R6. There was a 2.6 version in OZ.

Look here and use the links.

http://en.wikipedia.org/wiki/BMC_E-Series_engine

Most older members will remember the 1500 and 2200 in the Maxi and the Princess/Ambassador.

Chris

K&S
18th Feb 2008, 15:46
In South Africa there was a version referred to as the R6 in the later stages of the series 3's life. It had the same front as the Stage 1 that came out overseas (our overseas, your home land :) ). This was before I arrived in South Africa so although I've seen a few I don't know too much about them.

Whereas the Stage 1 was fitted with a V8 this was fitted with the R6 six cylinder 2.6 engine but I don't know its specs.

K&S
18th Feb 2008, 15:52
Michelle with the octane fuel being available today and that engine being very low compression you can afford to advance the timing by about one to two degrees without harming the engine. If you hear the motor "pinking" under acceleration then retard the timing very slightly.

Remember that when that engine was made one would have bought regular for it (the same grade we used for petrol lawn mowers) whilst the higher compression motors used super.

Getting a tiny bit more advance out of the timing usually helps with a slight gain in power.