Technical Hesitancy

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Technical Hesitancy

AndrewRL

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Hi All

I've tried to search for the answer here but failed so far (I know it is there as I am sure I have read it!). So I am relying on a new discussion/post with apologies to the person who tuts and sends me the relevant link!!!

Owing to personal circumstances (house moves), poor Luigi hasn't had any attention recently but every couple of weeks or so we have been for a run and he has started OK and generally buzzed along well.

However, there is an increasing "hesitancy" especially when more under load (e.g. long uphill or long flat out stretches). It is like a very brief drop in power (sort of like a hiccup/hiccough or however you spell it) but will repeat a few times enough to make you fear the engine is going to stop. It can mainly be felt through the accelerator. He idles fine.

I'm hoping that it may just be that the timing is slightly off or, more likely (?), the tappets needing adjusting again so that I can sort it once I can get out my tools again. However, if anyone has any other thoughts they would be gratefully received.

Many thanks as always (and once removals are finished and we are unpacked I am sure I will be back to asking lots of questions!).
 
Andrew;
As well as carrying out the checks that you have already scheduled (timing, tappets etc.) check (a) that there are no little bits of muck in the float chamber---modern fuel has a habit of attacking, among other things, rubber seals (b) check that all the jets are clear and, (c) how old is the fuel? Modern fuel (with 'bio' in it) goes off a lot quicker than "pre-bio" fuel did
 
Thanks Mr Hobbler [emoji846]

I'll add the carb checks to the list too. A good education to do one at a time I guess to, hopefully, isolate the cause for future reference.

Fuel should be fine as we have been out on regular drives over the last year or so and so the fuel is fairly recent. I just have not been able to do anything else (servicing items etc) in that time and this hesitancy is creeping in. I'm hoping he can hold on and last for a couple more short journeys to our new home.

Cheers
 
So...eventually got round to tappets and timing and made a huge difference (had to wait until people wouldn't tut at me for breaking lockdown and going out for a drive for pleasure!). Still only 80% right though and the engine still hesitates/drops power briefly mainly at speed (every minute or so).

So I stripped down and cleaned the carb as well as I can.

Two questions came to mind which I know you can help with:
(1) the "choke" connection - when attached this is taut and pulling slightly on the mechanism (so possibly slightly in operation I guess); is that correct or should this be totally unstressed with the cable not pulling the mechanism at all?
(2) mixture screw - I know what this should do but I can see/hear no discernible difference whether fully screwed in, part out or virtually unscrewed. Does that sound correct or does it sound like an issue?

And, of course, if anyone can suggest any other causes for this "hesitancy" then I will be very grateful and I will carry on round things.

Thanks all.

Keep safe!!!
 
If the fuel enrichment device (aka, incorrectly, the 'choke') is open, even a small amount, this will effectively richen the fuel mixture which can (a) make the mixture screw innefective and (b) make the engine run rough (due to excess of petrol). You are correct in thinking that there should be a little bit of slack in the operating cable for the 'choke'.
 
So, I'm afraid I am not really any further forward :mad:

To the best of my ability (so there may still be issues here :( ) I have adjusted the tappets, checked the timing (manually/check bulb), cleaned out the carb, checked the carb for a flat bottom and top cover, checked the air filter etc for blockages and have new fuel.

Unfortunately it is getting worse and is virtually undriveable as power just goes at regular intervals. I have checked the Haynes manual and most of the potential causes seem to be covered by what I have done so far. The only thing on the list I haven't done is a compression test (and will need your help on process, suggested meter and what the results may mean :eek: ).

I am trying to get the car running OK so that I can get him to Middle Barton Garage for a couple of things but I am not sure it is sensible at the moment.

Anyway, hoping that I can attach a link to a video of the engine (and, yes, I haven't got round to removing the fuel filter yet) I am further hoping that someone may recognise the symptoms and be able to suggest what next (or if you think I should go back and redo one of checks/adjustments already done).

Essentially, starts up very well and idles OK - I'm holding the throttle a bit open at the start but leave it to idle around the 58sec point; around 1m15 I increased the revs and then around 1m43 it starts to "search"/hesitate and get really rough; at 1m58 it almost cuts out (throttle is open fairly constantly during this phase) but seems to sort itself out and finishes idling sort of OK again.

Apologies for bothering you all but I am at a complete loss on where to try next - fuel pump? plugs? points/condensor? Or does it look more serious?

Many thanks for any suggestions


https://youtu.be/vvm01mLAhzQ
 
mmm. I can see fuel being supplied in your clear fuel line so that seems to be well fed. What do the plugs look like. Any fouling, discolouration.
 
watching the video I can see bubbles in the fuel line between the pump and the carburettor.
Is the fuel pump drawing in air? It might be worth swapping to another pump if you have one.
 
I also noticed that air in the fuel line--a quick check of ALL fuel-line connections might be worthwhile, as well as changing any 'jubilee' clips in the fuel system for proper fuel-line clamps.
 
Andrew, I would go for the main jet which is easily accessible externally. In my experience you can get repeated blockages of this jet which will lead to issues such as you are experiencing. It only takes a few minutes and the worst that can happen is that you drop the tiny blighter on the ground.

Everyone focuses on dirty fuel, aged petrol and air-bubbles; the former is very rarely a cause of problems. Although fuel doesn't get a chance to age in my tank, our cheapo lawn-mower starts first time no matter how long the Scottish winter becomes. You would need a lot air-bubbles before the carb bowl was low enough to affect the running.

But I have found the jet can become blocked by small flakes of paint, rubber or other kinds of debris which maybe fall of the internal surfaces of the induction system or which get past the air-filter when you're doing maintenance. I had a bout of this problem when I tried to redesign the air-filter lid with a sealing-strip to stop it rattling.
 
Backing up Peter's suggestion (and my comment earlier in this thread), check the main jet and the float chamber. I had a situation where, despite having previously checked, a piece of black 'something' had got into the float chamber and was sitting on the fuel orifice to the main jet. Initially and at low throttle the engine ran OK, but when revved harder, "it wouldn't pull the skin off a rice pudding", which was a bit embarrasing because the car was sitting on the rolling-road at the time, and the machine was winning!
 
Bubbles in the feed line are normal i believe, every 500 i have seen has them, i solve this problem to my car by replacing the green hose with black:D:D.
Anyway it is better to discard this green hose with a better quality. I had a similar problem too and i found flakes of paint inside my carb blocking the main jet.
 
Thanks all...jets and chamber it is at the weekend. I thought that all was clear but will double check. Suggestions much appreciated.

A further related question....a couple of years back when I first stripped the carb I ordered a service kit that contained a new main jet so I have one spare which may be worth trying. However, at the time I could not budge the small jet/nozzle off the longer mounting part (sorry, no good with names!). Looking at the excellent details in an old Bambino post (photo copied here) I assume the two parts should come apart (which also makes sense as the spare part is just the small end piece). Any suggestions on how to get the old jet out of the holder without damaging the holder? Or can both parts be bought (I have only seen the small jet available)?

Thanks. I will report back :-o

tapatalk_1594125649612.jpeg
 
Any suggestions on how to get the old jet out of the holder without damaging the holder?

If you haven't had the jet out of the "holder" I think that increases the chance that it could be the source of the problem.

You need to get a really well-fitting, short screwdriver. place the hexagon of the holder in a 10mm ring-spanner and apply steady pressure on the screwdriver, turning anti-clockwise, knowing it will come out if the slot isn't badly damaged. Even better might be to gently put the jet-holder in a vice.

Look carefully when it's out and ideally get it cleaned out with thinners and then blown out with an air nozzle. Any blockage may be very small and if you have a particle in there, another may arrive soon after getting running again.:bang:
 
Agree with Peter about a well fitting screwdriver. I use a bit from a 1/4” drive socket set and select the one that is the best fit and use the small ratchet for the turning force preferably gripping the main jet holder hex head in a vice so you have more control. I have a tiny 4” long ratchet especially for work on carbs.
I don’t think I have ever seen new main jet holders for sale even though they were a common part on a number of Weber carbs at the time. I have probably got one in one of my spare carbs if things go wrong.
 
Thanks all.

Update...

I managed to remove the jet from the holder (very long story!) and fitted the new jet having soaked everything in solvent, waited for it to dry and squirted compressed air through. I also checked the float chamber again and it looks clean. Had a look for any obvious gaps where air may be leaking and couldn't see any.

Started well and set off for a drive....but no improvement [emoji2959][emoji2959]. Still sudden drops in power, awkwardly often half way across a junction, cutting out a couple of times. Usually it clears itself a few seconds later.

So I am afraid that I am no further forward [emoji15][emoji33] and it seems to be getting worse.

I'll go back to tappets, check all connections for plugs, leads etc.

Apologies for sharing my woes but please keep any suggestions coming...my love for Luigi is fading rapidly [emoji852]

I am sure it is something simple and may even be something I am doing wrong.

Keep safe!
 
Points, condenser, coil, rotor arm, cap, leads , plugs.

Recently I found a condenser that would fail as the rpms reached around 1500rpm causing no spark.
 
If you pull that thing we all call choke but its not a choke while engine is doing this, is there any difference?

Also even if this is not your problem consider to replace your points with a powerspark ignition system. No adjustments, no condenser, smoother engine operation and low cost.
 
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