Fiat engine rough running..

[element]

Re: Fiat engine rough running..

Hi I understand you have adjusted the mixture screw and gained an improvement with the idle which is now satisfactory. On many Weber carbs the idle mixture jet (not the screw you've adjusted) has a small black o ring that provides a seal. If it's cracked it will suck in air along there and you may find that your idle will change again in the future . So before refitting the louvre panel remove it and check if it had an o ring & it's condition.

If you cannot find it in your Haynes etc then let me know as it's very likely that I have an exploded & labelled parts diagram for your weber carb

The nature of our Marlin cars is that they often spend a lot of time parked up.

The petrol evaporates and often leaves a clay type residue in the float chamber bowls, this in turn clogs up the idle and main jets. It is a good idea when the car is next being stored, to remove the top of the carb for an inspection and clean out with carb cleaner and also an airline.

Whilst the cars still in use .The Weber the idle jet can usually be unscrewed inspect the small hole in the jet isn't blocked and spray where it fits with carb cleaner and then blow through with the airline.

A blocked main jet will also cause the engine to run weak and cause the engine to run hot.

This used to be a common problem on the carb you have fitted.

I would also recommend checking the ignition timing is correct using a Strobe light as it may also be running too far advanced and pinking when going up hill which could damage a piston, as well as cause it to run too hot.

Thanks for this very useful information.. I'll check to see if the mixture jet (pretty sure I can find it; I have a wide selection of books here, including a Haynes Weber Carbs 79-91 copy) has the O ring you mention....

[element]

Re: Fiat engine rough running..

Hi Element,
I’m pleased to see the rough idle has been sorted.

For the oil leak Europa do an extra long “T” piece:

https://www.europaspares.com/oil-pressure-gauge-t-pieces.html

I don’t think you have room for that. I have also seen a straight take off at the engine with a short pipe to a nearby bracket or bulkhead mounted “Y” or “T” connector.

All of the connections I have seen like this are tapered pipe threads. Sometimes they can be tightened an extra half turn – but this has a risk of thread stripping which could be very very annoying. I know from experience that these tapered threads from different manufacturers look similar but are not the same. You can fit them and they look and feel ok when you tighten them but will leak under pressure. Perhaps, someone who is familiar with the Fiat engine can tell you exactly what it is.

I’m not keen on packing on this type of connector. It doesn’t seem like a sound engineering solution. If it is a tapered thread packing will defeat the purpose of the taper – to create a tight seal.
Paul

I bought the Mini Spares replacement oil pressure pipe & its identical to the one that was damaged, so I'll be fitting it tomorrow. Also got my copper washers too so I'll be able to adjust the orientation for the pipe on the T piece. If I have a problem in the plan, you'll all hear about it but I'm pretty confident it'll be good.

Also plan to replace the fixings for the louvre side wall with nice new stainless M6's & Nyloc nuts.. no more spring washers and rusty old nuts and bolts.
Tony

[Ye Ol Ripper]

Re: Fiat engine rough running..

Fiats used metric threads , bl mini's were imperial. However with regard to tapered fittings they are usually bsp.
I would therefore recommend before fitting, to check both the thread pitches in addition to the thread diameters are both exactly the same.

Use white household ptfe plumbing tape on the oil pressure fittings threads before fitting. That will stop it leaking without the risk of over tightening and stripping the threads.

[element]

Re: Fiat engine rough running..

Yesterday I took a friend out on a back road to show him why I have a Marlin.

On returning home the orange light came on and stayed on, as I was virtually home I ignored it and left it to cool down on the drive. Later I restarted with the intention of another similar run but the light again remained on. Then I saw the oil pressure gauge was at 0. Lifting the bonnet, I find a slight drip from the oil pressure gauge sensor tube valve fitting.. maybe it needs a wee turn more... It shouldn't leak as its like new...

[Ye Ol Ripper]

Re: Fiat engine rough running..

Rather than over tightening it and risking stripping the threads try using some ptfe pluming tape on the threads, ensuring that you don't cover the small hole at the end of the sender and refit.

In any event,a slight oil leak there wouldn't cause the oil pressure guage to read zero, the wire coming off the sender unit may have some of its insulation damaged and if it earths out(shorts) on the engine or metal work could cause the warning light to come on.

To verify this theory try removing the wire from the sender,with the ignition on earth it to the metalwork and see if it puts the light on.
Is it possible that something is blocking the electrical oil pressure senders hole that goes to the light?

It would also be useful to screw in another direct reading oil pressure guage into the fitting to see if there is a difference in the reading

[HairyDave]

Re: Fiat engine rough running..

I assume you did check the oil level. If you have oil and it doesn't rattle suspect the gauge .

[element]

Re: Fiat engine rough running..

I used ptfe tape when I fitted it. There is oil; perfect level, golden brown oil. I'll get into fixing mode tomorrow; tied up with other stuff today.

[stevejgreen]

Re: Fiat engine rough running..

Too much PTFE tape could insulate the oil pressure switch from the block.

[Ye Ol Ripper]

Re: Fiat engine rough running..

Too much PTFE tape could insulate the oil pressure switch from the block.

An easy way of determining that without actually undoing the oil pressure switch is clamp on the outside of the senders body with some wire and clamp the other end to the block or another suitable earthing point in the engine bay. If that causes the required change, then you would know if its the ptfe tape causing it.

[jon_cox]

Re: Fiat engine rough running..

Hi Tony
If I understand correctly then you have both an oil pressure warning light on and a mechanical pressure gauge reading zero pressure. In my experience, to have both systems showing the same result would mean that you actually do not have any oil pressure.
The oil pump in the twin cam is not usually a failure point but you should check it before anything else. When you were out for the drive did you perhaps hit the sump. This can dislodge the pick up pipe from the pump. Have you changed the oil or filter recently. Crap filters can cause all sorts of issues, sometimes even breaking down internally and blocking the oil flow. The engine should see about 50/60 psi at higher revs so I do not think ptfe tape could withstand that pressure to cause a blockage etc.
You do not say if the light and gauge read zero all the time no matter what the engine revs or only when at idle for example. If just at idle then this could be just a simple case of incorrect oil being used or blocked oil filter due to degradation of the internals.

[element]

Re: Fiat engine rough running..

I finally got the opportunity to look into the problem of the orange dash light & oil pressure at zero. The flexible nylon tube carrying oil is attached at both ends by a union which scres into the back of the dash instrument and into the tube extention body from the oil pump. At the latter there was a a bit of an oil leak. I tightened up the brass union nut a little more and then started her up. Light out and oil pressure reading correctly. So the first thought I had - that the nut had just loosened up seems to have been right; if oil can get out then air can get in and the instument wouldn't have any held pressure to operate. Perhaps there was sufficient loss of pressure that the orange light came on because of the same reason. Glad its working again.

[David]

Re: Fiat engine rough running..

Well done, always good to solve problem...