Technical Engine help

[nickfox]

I am reaching out in hope of some knowledge.

I have a 650cc engine in my Fiat which I have owned

for a few years but cannot get it running well at all.

So far I’ve tried refurbishing the carb; cleaned fuel lines; new spark plugs and leads. I’ve tried adjusting the carb but nothing seems to make a difference.

The car won’t really run off the choke and if you drive it has very bad kangaroo petrol. It also gets red hot. Could it be engine timing? My next thoughts are to try a 123 electronic ignition.

I’m not very mechanical so any help much appreciated.

 

[smart51]

So it runs on the choke but not if you back it off. It suggests you're not getting enough fuel without having the choke on. Have you set the idle fuel mixture? Is your idle jet clean?

What carb have you got and what jets are in it? Are you sure the idle circuit is clean inside and flowing fuel? Have you set the float hight correctly?

Also, have you checked for air leaks between the carb and the head?

 

[nickfox]

Thanks very much for the reply.

Air leaks below carb - checked for that one and all good.

Carb is a Weber imb 28 which I cleaned and refurbed with a kit last year. All jets clear and float height good.

I was trying to adjust the mixture screw but it doesn’t seem to do anything which is strange. Could it be timing / condenser or do you think I’m best to keep focusing on the carb?

 

[smart51]

What size idle jet do you have? The adjustment screw gives you one jet size worth of adjustment either way. It might be too small to adjust in. Also, I believe the tube inside the carb that goes to the idle jet can get gummed up. It could be that.

If it idles OK on the choke but not off it, it seems like a fuel problem. That said, others on here have had weird problems that just go away when the condenser is replaced.

It will do no harm to check the points gap, though if it idles on the choke, you've got at least a fair spark.

Have you got a timing gun? They're not that expensive. You can rule out the timing by setting it with a timing strobe. There is another way. Paint a thin stripe across the bottom of the distributor on to the engine block in white paint. Slightly loosen the bolt that holds the distributor so you can turn it but it isn't loose. With a little bit of choke so the engine runs passably, turn the distributor a millimetre or two clockwise then a millimetre or two anti clockwise. If it runs worse when you turn it, your timing isn't bad. If it runs better, your timing is bad. Use the paint line to put it back where it was before you started.

A word of warning. Wear gloves, and not ones that will melt. The distributor and block get hot, but not nearly as hot as the exposed exhaust header.

 

[Goldnrust]

It does sound like you've checked the usual suspects for the carb/fuel side of things. Theres 3 parts to make an engine run, fuel air/compression and spark. I would say you've ruled the first out, so try the other two!

I'm not hearing much tappet noise in that video, was the car cold? Might be worth popping the valve cover off and checking the valve clearances?

Paying the money for a 123 ignition distributer, which if you search the forum you will find are not know for their reliability in the 500 application due to the heat that comes out of the thermostat flap, is a big outlay before you've done some checks on the standard ignition.

Certainly a new condenser is not a bad idea. I would also suggest checking the points gap and the timing.

To check the points cap, remove the distributer cap, and rotate the engine by hand till you can see the points open. You want to find when the points are at their widest, then use a feeler gauge to measure the gap. You are aiming for 0.5mm.

To check the timing you can use a timing light if you have one, or you can set the static timing a number of different ways. Tuning the engine over by hand you are looking for the points to start opening when the pointer on the crank pulley is ~13mm before (to the left) of the arrow on the crank case. There are various methods of checking when the points open, from as simple as looking at the points, though using a bit of thin paper (cigarette paper was often suggested back in the the day) between the points so you can feel the point at which they stop gripping the paper or using a test light or multimeter to tell.

 

[nickfox]

Many thanks for these responses.

My idle jet is 50; I’m going to try a new jet; valve clearances; condensor points and timing at the weekend - I will report back!

 

[nickfox]

Just an update - I replaced the idle jet; checked the valve clearances (there were none!) adjusted those; points and timing were good. It’s now running much better than it ever has - many thanks.

I’ll replace the condenser for good measure. Thanks again

 

[Goldnrust]

Good to hear you got it sorted. If there was no valve clearance, then that could well have been your issue!

If your condenser is ok, I wouldn’t replace it. They kinda work or don’t, rather than gradually loosing performance over time.

 

[fiat500]

Good to hear you got it sorted. If there was no valve clearance, then that could well have been your issue!

If your condenser is ok, I wouldn’t replace it. They kinda work or don’t, rather than gradually loosing performance over time.

....or hang on to the old one as a probably working spare.

 

[the hobbler]

....or hang on to the old one as a probably working spare.

Strange that your tappets had closed up---the '126'engine is not known for that (unlike the 500 where is quite common to find that the tappets have closed up) Tappet clearances on the '126'engines are:---8 thou Inlet and 10 Thou Exh---COLD