Running rich

[bison]

Hi Folks,
My little TL is running really nicely, almost!. I just can't get the tickover mixture right, nor can I get it to stop running rich. I should mention it's the dreaded Zenith 28IF. I've cleaned it and blown it through at least three times, there is nothing blocked or damaged, the car only has 40K on it so the throttle spindle etc is AOK, no wear, no air leaks, tried spraying it and the manifold with carb cleaner, no change. Head and valves all excellent. The car runs really nicely, pulls well and evenly, but running rich. The mixture screw has to be at least 5 turns out for it to tick over and even then it's lumpy.
I have the jets in the air pipes from the rocker cover, 1.5mm to the manifold, 5mm from the rocker cover and the manifold hole is 1.8mm. Float height is correct. It does tickover slightly better with the manifold hole blocked off, but still has to have the mixture screw out loads and still runs rich.
Any ideas?, or does anyone know where I can get smaller jets?.
Cheers,
Alan.

 

[Charliemouse]

Getting it running right

I set up my Quatrelle at the weekend. I had the fortune that a friend of mine was at our garage - he apprenticed on Renault in the late 60's. He's set up more 4's than most - albeit he'd forgotten some things for a while.

The best piece of advice - and this was true "in period" apparently - was to ignore measuring instruments and do it by eye and ear. Thigs will be worn in your engine - with period oil this was true of 2/3 year old cars so it certainly will be now. Book settings are for starters.

I suspect if your carb is ok you have an ignition problem. The thought i have in mind when im setting up things with 40's and 45's - mainly race cars - is that "90% of carb faults are electrical".

Make sure your dizzy isnt sloppy (on the shaft). Make sure the points are good and have a strong spark. Gap them to book as a starter. If its been running rich for ANY length of time on modern fuel - fit new plugs. They just cant cope being wet with this stuff pretending to be petrol. Then slacken the dizzy and swing your timing. You should aim for the fastest running speed then back it off (retard) about 3-4 degrees.

The mixture screw should be 3 - 31/2 turns out as a starting point. Again - fastest idle - without hunting. When you rev it there should be no black smoke from the exhaust. final check will be for a nice dark gray on the plugs after a run.

Its hard to describe all this when you're used to setting up cars by "feel". But give this route a try rather than by the book timings etc.

Charliemouse

 

[angel]

From your description, I can understand that it actually runs lean. If it was too rich, you would have to turn the mixture screw all the way in to achieve a smooth idle, and moreover, if idle mixture is that rich to make idle lumpy, it would be accompanied by black smoke from the exhaust.

I have not seen any different idle jet for the 28IF other than 35, nor have I managed to find anywhere idle or main jets.

I would agree with Charliemouse, make a thorough check of the ignition system and its settings for start. Are you sure you don't have any air leaks? What happens when you plug the manifold hole may indicate a vacuum leak.
Also, are valve clearances correct?

 

[bison]

Hi Guys,
Just back in from the garage. Yes Angel, it is running weak at idle, but rich at driving speed. The reason for that is the main jet is a 94, and according to Mr Haynes it should be a 90, the idle jet is a 40 which should be correct. I doubled up the manifold to head gasket and made sure it was tight, no change, I flattened the carb face with 400 grit paper on a surface table and replaced the gaskets, no change. I then sprayed all the mating surfaces with carb cleaner, no change in the way it was running. It does idle better with the little manifold hole blocked, but then runs even richer when driving. The exhaust pipe is black and sooty. Ive already checked everything you mentioned Charliemouse, I tend to do things by ear then check them with strobes etc, usually I'm pretty close.
OK, seems like I need a 90 main jet, I'll open a new thread and see if anyone has one laying around.
Many thanks yet again people, I'll tell you how I progress.
Alan.

 

[Charliemouse]

I replied to your post for a main jet - I won't repeat that here. I wouldn't expect .04mm to make THAT much difference. Have you tried running with the air filter removed (when its not dusty obviously), or with a large diameter pipe to the filter from the front of the car? Both of these would tend to weaken the mixture at speed and confirm the diagnosis.

Yorkshire Carburettors are sometimes good with old/obscure spares - just talk to one of the older guys. (I was VERY careful what I said there ;-) )

Let us know how you get on.

 

[bison]

Good morning,
Yep, removed the air filter, definitely runs better, IE weaker. We're talking small amounts here anyway Charliemouse, the car is running really nicely apart from a slightly erratic tickover, pulls up hills like it never has, but the exhaust is sooty and I'm getting around 51mpg in and out to work, my last TL's, both of them, were around 60mpg for the same journey, certainly high 50's, and I probably drive slower these days, I guess you have to allow for the stuff they sell under the guise of petrol though. I like to try to get stuff running properly anyway, good fun in the garage. As if I don't have anything else to do!!!
Alan.

 

[angel]

Here is an old trick done here, when it was realized that 28IF jets were unobtainable and the R4 had to pass the (new back then) emissions test.

By threading a fine copper wire (from an electrical cable) from the jet's side holes through the metering hole, and wrapping the ends around the jet, as is barely visible on th photo, you can effectively make the jet size smaller, without having to solder and re-drill the jet. You will need special-and expensive-jet drills to do this job with success (as normal drills are not as accurate), so you can try the wire technique with no cost and hassle.

You can also try lowering the fuel level a bit (0,5-1,0 mm may be more than enough) by using a thicker sealing washer, or adding a second one, under the float needle valve.

 

[Steve Hennessey]

I think that 51mpg is a very acceptable figure!!! Just because the exhaust tail pipe is sooty does not mean anything - the only way to got an accurate result is by using an exhaust gas analyser.

The 28IF needs as much help as it can get, and if anything, the jets are too small and it sacrifices power. I chucked mine away and fitted the carb from a R5TL.

 

[bison]

Hi Folks,
Angel, what a great idea!, I ride old motorcycles and thought I had heard all the tricks for repairing and tuning them, but that's a new one, I'll give it a try.
Steve, c'mon, I'm a Scotsman!, I have a certain stereotype to live down to!, soot on the exhaust is a wasteful sin laddie, but then, I suppose the 28IF is the carb o' the Deil!
Oh and the plugs are black too, but you're right I'm sure, it probably won't pull as well, I'll try Angels idea though, nothing ventured etc etc.
Not that I want to give people a big head or anything, but I'm a member of a few other forums for my different vehicles, and this is by far and away the friendliest and most helpful, thanks guys.
Alan.

 

[jjad]

I agree Alan, this is the best forum I've ever come across.

Thanks Malcolm and everyone

 

[Steve Hennessey]

Steve, c'mon, I'm a Scotsman!, I have a certain stereotype to live down to!, soot on the exhaust is a wasteful sin laddie, but then, I suppose the 28IF is the carb o' the Deil!
Oh and the plugs are black too, but you're right I'm sure, it probably won't pull as well, I'll try Angels idea though, nothing ventured etc etc.
Alan.

Alan, you may find that those of us who run and moderate the forum have a wee bit of Scottish blood in us :eek:
Of course I understand the need for you to keep your jet size as low as possible - maybe a nail would be a better bet than a sprig of wire! Furthermore I hear that chimney sweeps charge an arm and a haggis to remove that blessed soot from exhausts.
Surely the cheapest way to do it would be to feed a couple of mice into the front pipe and ram a lump of cheese in the tail pipe

Job done!!!

 

[bison]

Do you think instead of the mice I could use the Hamster who runs my heater fan?

 

[Steve Hennessey]

ooooh - heaters use up petrol!!

There are other reasons why the carb would run rich such as a dodgy float needle valve. When I had the 28IF on my car I had the opposite problem and had to run with the choke pulled out about 25% otherwise it pinked. I'm more than happy with my conversion to the 32IF - at the time I could buy jets so I bought a range of them and tried each one out until I achieved the optimum performance.

 

[malcolm]

I can't figure out why it would run rich. The only times I've had the problem were down to the choke not fully opening (very common on the R4 and got me a R5 really cheap once), float chamber issues, the mixture jet out more than about 1.5 turns, or a previous owner attempting to sort out ignition problems by changing the carb for one that looks similar.

I'd not encourage anyone to set anything by ear. Fine tune by ear maybe, but it's nice to start off with everything as standard.

 

[bison]

Yep, it is confusing, however the only way the car will tick over is with the mixrure screw out about 5 turns so you're right that won't help the mixture at higher revs, and I guess that points to an air leak, but I've had the manifold off twice to check and doubled up the gaskets, checked and replaced the carb gaskets, blocked off the little air hole in the manifold. I also tried spraying carb cleaner on all the joins while it was running and the revs remained the same. I had a Mikuni motorcycle carb on it to try, lo and behold it idled perfectly, smooth and even, hhhmmm.
Alan

 

[Steve Hennessey]

Did you check the straightness of the carb flange?? 5 whole turns is a lot. I assume you've done a compression test and all your valve clearances are correct. If you have any leakage past an inlet valve this will affect your carb adjustments.

 

[bison]

Yep, cleaned and checked on a surface table, the head is just back on after being skimmed and the valves cleaned and ground in, the clearances done again, as per Mr Haynes, when the head was re-torqued down after 300 miles. I should say the car was like this the day I first drove it so it's not a new thing, and I'm pretty sure it's the carb, as I said, when i fitted the Mikuni to see how it would run it ticked over perfectly, smooth and as slow as I wanted. I checked the plug colour again and replaced the plugs on Friday evening, they were a good colour at last, only slightly rich, so really just the tickover problem, the car is running beautifully.
Off up to Oban on a field trip for a week so won't be reading the forum. Thanks for all the suggestions, I think I'll just have to live with it.
Alan.

 

[mr-reno-139]

silly question have you had the float chamber air vent filter out and cleaned it
mainly a problem on gtls as they run hotter because of electric fan not blowing constant air over carb
will need to drill rivet off first as there is a guaze mesh which ends up blocked with petrol residue and upsets carb operation

would of been tempted to leave bike carb on

 

[bison]

Hi Paul,
I blew through the little filter/breather when I first had a good look at the carb and it was clear. I was up North of Perth (Scotland) yesterday and sitting in traffic for a while, I'm sure the engine was slowly increasing revs, I think a pretty sure indication there's an air leak, but I can't find it , hohum, when I got motoring again and stopped briefly the tickover seemed to be back to what it was.
The good news is it's running really well and the plugs are a good colour.
Thanks,
Alan

 

[Charliemouse]

Petrol

Quote:
"Where do you get your petrol? I noticed some brands "work" better with the R4 than others. On Shell petrol I had a rough running engine with and without additive. With Total petrol I had no problems. It's all a matter of trying some out."

Not that simple I'm afraid. It all comes from the same refinery in the main. The important factor is "how long has it sat in the garage tank" - pick a busy garage, and "how clean the tanks are" - trial and sometimes error im affraid. We run race cars with pump fuel and even with the expensive varietites this is a minefield. We need race fuel at 99 RON plus though. The Renault Engine was designed to run on bat Sh1t and vin blanc... 88 is fine in the main. Water and crap in the fuel cause problems though...