Webber I do this or Webber I do that, my Hesitation Remains

[brandon]

Since having the head (Webber) rebuilt this past winter, I have had quite a few challenges getting the car to run well.
The head and initial setup was done by Dave Puton at Britian West (Brantford Ontario). He?s highly recommended in the area, and I?ve always had very good service from him. He knows our engines well, and owns some Lotii himself.
Initially the trouble was wet fouling of the plugs within 10 ? 15 minutes of them being replaced or cleaned. I?m using NGK BPR5ES which I know are a very hot plug, however it?s certainly never been a problem before. We were on the stock idle jet (45F9?), and slightly richer than stock Main (can?t remember which one). The car was ?smoking? quite badly and reeked of fuel, both out the exhaust and on the plugs when they were removed. This past weekend I finally managed to get back out to Britain West, and we quickly found that the idle jet was way too rich, so it was leaned out to a 45F4. This immediately cleared the ?smoking? issue, and the car now idled quite well without the fouling.
Unfortunately, it has developed a horrible hesitation when just starting to touch the throttle. When starting from cold, the car virtually stalls out and is a hairs width from undrivable until it warms up. Even when warm the hesitation is serious, and makes it difficult to drive. We?ve gone through just about every combination of jets available (spent 3 hours on it) and no difference. Jets are currently:
Idle 45F4
Air jet 205
Emulsion F11
Main 125
Pump jet 60

The car idles very smoothly at around 850RPM, and pulls well if I get into it. I have since changed the NGKs (which looked quite good when removed) to a warmer Champion RN9YC. If anything it is now running worse. We are at a loss.

Any recommendations???

Brandon

[rgh0]

There are many potential issues
I would check fuel level and throttle plate position as the first couple of checks.

Have a look at the Weber tuning white paper on the yahoo group sidedraft_central

cheers
Rohan

[Craven]

Hi,
Changing from 45 F9 to 45 F4 you have increased the air jet dia from 1.00mm to 1.4mm, your small throttle opening problems are indicative of weak mixture.
Ron.

[brandon]

Thanks Rohan, Ron,

We checked the float level and all is well. The carbs are well balanced, so I assume the throttle plates are in good order (I'm not certain about this though).

Ron,

I believe we moved up 45 F5 etc. and it would make a difference, but then would be running overly rich again. I've attached (I hope) a picture of the plugs. Cylinder 1 on the right, through 4 or the left. #1 looks moderately rich, but all else seems to be good. Would the plugs not indicate a weak mixture? I'm a bit of an amateur(with Webbers) here, so please excuse me if I'm off the mark.

I'l take a look at Sidedraft central.

[Craven]

Hi,
If your engine is in standard tune? then you should be considering WHY it won?t run as it should rather than changing the jetting, you may well be dealing with a fault condition.
Ensure the choke/ start circuit is not contributing to the excess fuel.
Ron.

[carrierdave]

Read the white paper as Rohan mentions, get the float heights correct and then check air flows in each carb and ignition timing.
Once that's set up I used a colour tune to adjust the idle mixture screws to get the correct mixture, it's this with the above that gets the engine running.

I think your pump jets are too large and with mains at 125, your air correctors should be around 175/180 - but both of these only come into play above 2500rpm.

I got to this point and had a stumble at about 2800 - 3000 rpm, F15 tubes did the trick.

Dave

[seniorchristo]

I have a similar problem with my S3. Going to a leaner idle jet will lean out the progression stage, possibly causing a stumble until the main jet kicks in. Once ignition timing is set properly I would suggest going back to the original correct jet and trying to set idle mixture again.
Chris

[MyLotus]

Had a similar problem with my restored S4. Check out p. 54 of the Shop Manual (attached). It worked for me.
Good luck,

Alain

[brandon]

Thanks for the suggestions.
Does anyone have a copy of the white paper? I'm not really looking to join the yahoo group if I can avoid it.

I suppose I'll start the process again based on comments here and some other threads:

1) Check and set timing.
2) Check and set float height.
3) Check fuel pressure, and regulate if necessary (I'm still on a mechanical pump).
4) Re-install "standard" idle jets.
5) Check and set balance and generally follow the white paper.
6) Report back with results.

[Spyder fan]

I don't run Webers anymore, but I remember having a similar issue and going around the houses with idle and main jets.

The extreme hesitation experienced and general lack of get up and go issue was cured with a new set of alloy pump jet washers. They are tiny little things, often overlooked when you change pump jets because they adhere to the old jets you take out.

http://www.burtonpower.com/pump-jet-all ... etp1w.html



Good luck, I hope the fix is this simple for you.

[ceejay]

Something that is often forgotten with the webers fitted to the twink is how old they are now, take in all of the above re jets etc, but also have a think about what the internal galleries and cross drilling's might be like inside the carb body.
Take a close look at the outer weber carb body and you'll find several lead plugs that are used to seal the galleries and cross drillings.

Several years ago I had similar problems with the webers on the S2, so I removed them from the engine, then stripped them completely and carefully removed all of the lead plugs so that the galleries and cross drillings could be properly cleaned out, this action is not required on new carbs, but worth looking at with old webers.

You will be surprised at how much crap you will drag and blow out of these little crevices. Over time petrol and moisture will react with the die cast alloy and the metal will corrode, that's the white crud you see on old aluminium, and if it becomes really bad it will restrict the flow of the gallery... A bit like Cholesterol build up in unhealthy veins of a human.

I'm not saying that this is what your webers may be suffering from, but with many old things, you have to think about things that you cant replace like the galleries in the fuel system of the weber carb.
A very strong carb cleaning agent may help to clear the crud, but unless you can actually clean and check the cross drillings etc, you wont really know what state they are in.

Removing the lead plugs is a very painstaking and slow job to get it right so that no fuel will leak after the job is done, and some care needs to be taken so that no excess pressure is placed on the alloy carb body metal when replacing the plugs. You can DIY the job as long as you know what you are doing.
Then once you are sure that all is clear inside, then you can start chasing correct jetting, air correcters, etc, etc and whatever else is required.
If you are wondering where to get lead plugs...just cast your own.. not hard to make a split die from two bits of metal clamped and drilled with holes where you can pour molten lead into, the taper on the plug can be created by spinning the cast plugs in a drill or lathe chuck then use a fine cut file to shape the plugs.. fiddly yes, but it can be done, it simply depends on how much patience you have.
Have a think about it - Happy hunting.

[vstibbard]

Also worth checking that the cold start (Choke) which is in essence a carburettor of its own on Webers is working correctly as if the pistons are not seated they allow fuel to flow which will impact tune and in particular low speed running, I had this on a recently rebuilt set of original carburettors!

Bearings, seals, spindles, needle valves, etc had all been replaced and yet it had large drops of fuel visible in two of the inlet manifold tracts! Turns out one of the pistons was sticking and the gear to lift the pistons where not correctly aligned, which held one piston up, both issues on the rear carb!

Before finding the problem I replaced the 50 year old carbs!

V

[Hawksfield]

Brandon

The white paper

[Ian T]

I will say thank you JH for that - what an excellent read.

I have a conflicting fuel level in my carbs, with the floats correctly set at 8.5mm (brass), the fuel sits at just over 31mm from the top of the bore. I hadn't thought of an optical dipstick, but will now order some acrylic rod and get one or two made up - so simple. Why my floats float too much I have no idea!

Symptoms for my engine are lumpy running between about 1500rpm to around 4000rpm.

If you've used an AFR gauge, where in the exhaust system did you fit the sensor?

Cheers,

Ian.