Technical new problem

[doc18015]

Hi all, I completed repairing the oil leak successfully!!!! Now, the car runs up to about 3-3500 RPMs , then decides to miss and backfire. I think I set the timing correct by following the thread in which Bambino details static timing. My problem is when I attach a strobe light to the engine....I find the markings( Painted w/red fingernail polish) but way off the area where they should be . Is it possible the the car runs Ok to 3500 RPM but that the distributor is somehow off ? I re-did all steps, carefully making sure that #1 piston was all the way up, marked off the timing marks and dropped the distributor in so that the one point on the distributor shaft lined up with the blade of the magnetic sensor. It is tough starting it also.
Any suggestions??? Many thanks!

 

[Bambino]

Hey doc,

Sorry to hear that your little car is still malfunctioning. All other things being equal, it sounds like the timing is out and the advance isn't correct. I'm not familiar with your type of electronic ignition, but with the 123 ignitions the distributor is set with the crank at TDC, not 10deg BTDC as for the standard points ignition. This is because the initial 10deg advance is built in to the electronics. I guess I'd try setting it up both ways - at TDC and 10deg BTDC and see which one gives you the best response. Poor starting may also be a sign that the ignition is too far advanced.

For your information, I've attached the standard advance curve. As far as I know the inflection point at 3000rpm is the same for all engines. Therefore at 2000rpm, the standard ignition for the 500 F/L/R, 600 126 and 650 126 is, in total, 16.8deg advanced and reaches its maximum of 28.0deg at 3000rpm.

Have a look at the 123 website for more curves, though disappointingly, little explanation (http://www.123ignition.nl/). I don't know whether Magnetti-Marelli publishes curves for your ignition, so I guess as a last resort you could take it to your local dyno centre and have your curve mapped.

The timing and degree of advance is also determined by the camshaft profile and you would really have to know what has been done to your engine to get a curve that is appropriate.

At the very worst, you should be able to get the car started and running reasonably smoothly even if the curve isn't exact.

Chris

 

[doc18015]

Hi and thanks! Is it possible that the #1 piston is at TDC but on the intake stroke, not compression stroke? I have set it up at TDC (or what I thought was TDC ) and I cannot get painted markings anywhere near the arrow on the front flange/boss. Should the blade on the pick-up be in line w/the blade on the shaft of the distributor at initial setting? All was done this way. It runs like it has too much advance and after 3000RPM , poor timing. Backfires somewhat also at exhaust .

 

[Bambino]

If the timing is 360deg out (on the crank) the engine won't start. If it starts and runs, albeit roughly, you are at least on the correct part of the cycle when the spark plug fires. The issues are then timing, valve overlap, spark strength, condenser, plugs etc. I guess you've checked all of the usual stuff - good cap & rotor, coil is OK, HT leads OK, plugs clean and the correct heat range etc. etc. Do you know what sort of camshaft is fitted ?

Exhaust backfiring is usually a result of an overly rich mixture igniting in a hot manifold. Has the carburettor been adjusted at all ? A very rich mixture will also cause very rough running.

Nasty things like cracked heads will also play up when the engine warms.

And yes, the rotor should line up with the appropriate cylinder on the cap when the plug fires. If it doesn't the engine will usually not run at all.

You're close - at least it does run but you may just have to bite the bullet and take it to a car tuning shop and get them to look at it.

Chris

 

[doc18015]

Hello again and thanks! I spent about 4 hours playing w/the ignition /distributor yesterday(Sat). Here is where I am : Two markings(spots) on distributor; I have a spot where the car starts and runs well up to about 3000RPM, then begins to miss. I have a spot where when accelerating( feeding gas ) runs beautifully up to 7000RPM. Between the two spots , is a sort of OK start (does not turn over slowly as if it is too far advanced; but runs OK up to about 3500-4000 rpm. If i had my way, I would like to start /idle at spot #1 and for fast running at spot #2.
the advance was checked by induction light.....seems like it is working OK. The valve cover was removed and rockers checked for free play to confirm #1 TDC. A note of interest here is that I do not have valve clearence specs for the car. The #1 rocker indicated very little, if any play in the intake side and some play in the exhaust. The on-line manual is not very useful because this car has an ABARTH cam (grind unknown from PO ) . What should be the clearences for the valves? Are they set cold? I searched this forum and did not get any results.
Last, the Weber carb. is spitting back fuel (seems to flood on both sides) . I have not checked the float level , jets, etc. I assumed this to be fine from the PO recommendations( which at this stage seem flawed) .
Before going further, do you think that I should redo the valves (assuming i can get specs or suggestions for lash settings); pull the carb and go over???? I have always lived by the rule of one step at a time.....add to many variables and disaster results.

Any suggestions gladly tried. This has become a challenge of man over machine. I expect to win .

 

[doc18015]

So where is the spell check button?

 

[doc18015]

Hello, spent some time on the net and did download a Fiat 500 Haynes workshop manual. The valve settings are 0.6 . If I set up #1 cylinder cold( I assume) @ TDC, are valves adjusted equally ? Then rotate 180 degrees to do cylinder #2? if the cam is ABARTH as said by PO , will these settings harm it? Seems like a guessing game not knowing the cam grind, etc.

 

[Bambino]

Hey doc,

You are on the right track.

With both pistons at TDC, one cylinder will be at the end of the compression cycle and ready to fire and the other will have just finished the exhaust cycle. The cylinder that is about to fire will have a little free play in the rocker arms (the other cylinder will not) and the clearances can be adjusted. Once that valve pair are done, rotate the crank 360deg (180deg for the distributor) and do the other cylinder.

It is very important that these tolerances are set with the motor dead cold because as it warms up, everything expands a little.

If the tolerances are too tight, as the valve shafts, push rods etc. lengthen with heating, the valves may never close completely and you can certainly burn an exhaust valve (the ex. valves rely on the valve seat to dissipate heat).

On the other hand if the tolerances are a bit loose, the engine sounds a bit 'tappety' which does less harm then if the gap is too small - you lose a bit of power and the rockers wear out a bit quicker.

For a street motor, the camshaft profile should not overly influence the rocker tolerance. If you have a cam with a lot of valve overlap, the tolerances may need to be a bit tighter. In the first instance, I'd use the standard tolerance. It is the same for both valves.

The carby may need inspection and now would be a good time to do it. With the valve cover off, it's easier to remove. All of the downdraft Weber carbies fitted to these cars are quite straighforward and rebuild kits are available at not much cost. Float settings are published in the manuals and are usually included with the kits. The little IMB carbies fitted as standard are not great and I'm told that the DIC is a better unit. My only experience with this is using a Dellorto FZD as a replacement - a much better carby, but rare as hens teeth. Mine came from Sicily and I had to sell one of my children to pay for it

You're right to only do one thing at a time and furthermore, yes, it is only a machine and you will win eventually. Use it as a learning experience and try to maintain a sense of humour throughout

Keep us updated.

Regards,
Chris

PS: Getting a smooth and sustained 7000rpm out of one of these is a great effort. You may have a little valve bounce though as each valve is opening and closing about 60 times a second - OK for a DOHC engine but probably a bit of a limiting factor for a pushrod engine. You may need to beef up the valve springs (at least) if you are going to do this regularly .....

 

[doc18015]

Hello, It been high of 20 degrees F here so no work being done. I can heat the garage but need to have a weekend or day off. But I hear loud and clear, valves will be next .....set @ 0.06 cold; then , I will tackle the Weber . Neat little cars!!!!