Rusted Out 1970 850 Spider Fix-Up

dllubin said:
Have you done a compression check or leak down test? That might tell you if you have a bad valve.
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Not yet. But, I do have the tools to do so. I did check the timing, and it seemed close enough to not be a problem. Will check the valves tomorrow.
 
Doesn't sound like it's running on all 4, could be spark related. Try a timing light on all 4 wires to check for firing, should all flash about the same.
Just before I considered my 850 dead, had to preheat/clean the plugs with a propane torch, reinstall quickly and push start it. Smoked heavily, but still ran.
 
Daniel Gibson said:
It is not your imagination. Raw gas is sputtering up as well. I get the feeling the carb is running super rich, but I am at a loss as to why. Anyone know of a good rebuilder for these carbs?

It may indeed be timing. I will check that next. I am trying to not think about cam issue yet! Thanks!
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May not be your problem but check to see if the primary and secondary barrels are closing completely. Many times the linkage binds up and causes "mysterious" problems.
 
Like all things its about going back to the basics.

First question, is the fuel pump the OE mechanical unit or an electric? If an electric what is the psi? It should be 2.5-3psi. If the mechanical, did you check the stroke of the pin? If it is too great a stroke then it can pump too much fuel. The stroke is adjusted by gaskets.

After that it is time to look at the float level. Have a look at the following:
https://fiat850.com/the-project/weber-30-dica-correct-float-level/
It isn’t entirely correct, I will cast around for the exact info from the manual or the sheet from the rebuild kit.

If it still isn’t right, I would go back through the entire carb again.
 
kmead said:
Like all things its about going back to the basics.

First question, is the fuel pump the OE mechanical unit or an electric? If an electric what is the psi? It should be 2.5-3psi. If the mechanical, did you check the stroke of the pin? If it is too great a stroke then it can pump too much fuel. The stroke is adjusted by gaskets.

After that it is time to look at the float level. Have a look at the following:
https://fiat850.com/the-project/weber-30-dica-correct-float-level/
It isn’t entirely correct, I will cast around for the exact info from the manual or the sheet from the rebuild kit.

If it still isn’t right, I would go back through the entire carb again.
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Mechanical fuel pump, from one of the one line fiat places. Seems to be working ok. But you are right about the basics. Time to check the carb again along with the other pieces of good advice I have gotten today.
 
You might want to check that the valves open and close the same distance on all cylinders; a worn exhaust lobe, and residual gas escaping when the intake opens, could spit back like this.
 
From the archive. The first two came from a carb rebuild kit from back in the 80s. The manual images are from Haynes which were effectively from the Fiat manual. Sorry for the poor image quality I need to get new software for my scanner, software updates are sometimes both more and less than one would hope.

F53196F2-9AC2-48EE-89E2-AD8CC17407D0.jpeg 05D3469F-F32C-4BD1-9A69-0E565CEC7F07.jpeg 63E33C7D-D452-489B-9056-B9B558178FC9.jpeg 1AA550E4-76D7-4748-8234-B8E39EFD6BD6.jpeg
 
I spent a couple of hours reading your post from start to finish the other day. Your level of commitment and clever low/no-cost problem solving on this project is commendable. Regarding the current poor running condition, I am solidly in the "perform a compression test/leak down test" camp. Until you know the basic condition of the engine you will chase your tail looking at timing/ignition/fuel issues. Personally I suspect a mechanical problem. In order to get a backfire through the carb, you have to be firing the cylinder with an intake valve open. This could be due to a broken valve spring or valve sticking in the guide assuming the firing order is correct. An old master mechanic said to me as a young apprentice "The more mysterious the problem, the simpler the solution'". I have found this to be the case every time I am presented with a head-scratching diagnosis.
 
72Fiat850 said:
Maybe a dumb question at this point but did you check the valve adjustment?
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Nope, not a dumb question at all. Here are the results of the compression test: 1 - 0, 2 - 120, 3 - 150, 4 - 150. I took the valve cover off, and the second valve on #1 appears to be adjusted too tight. Time to use this extra hour of daylight and go adjust!
 
Got it all put together, got it started and it sounded great! Took off the choke, and it stalled. Tried to get it started again and the solenoid kicked, but the starter would not engage. Two hours of frustration later, and it turned out the main power cable that feeds to the starter from the battery is not doing it’s job. It shows 12 volts, but if you put any load on it at all, like even shorting it to ground, and it drops to zero. Ran a test wire from the battery to the starter, and crank-o-matic. Someone has replaced this cable before, so I guess it is time again. Grrrr...
 
Congrats Daniel, looks like one of the valves wasn't moving like the rest...
You should be able to keep it running by pumping the throttle a little to squirt some gas from the accelerator nozzle to go with the extra air after you take it off the choke.
 
You might check at MWB for a used one. Alternatively as you truly are handy, you can build your own.

The issue tends to be less the cable but the terminations at the ends along with corrosion of the cable near those ends. If they reused an old cable with old terminations I can easily see there being a problem.

Each one of these weak points will be good for the rest of the life of the car as you knock them off.
 
Ok, now you all know I am ok with re-using old stuff as much as possible, but even I draw the line somewhere. Maybe the PO should have replaced this. I dunno, but I did, and that got me back in business.
7EC06C18-3337-41A0-B155-3BA786C1231E.jpeg


Some basic tuning of the carb, and here we are! A running engine!

Sounds pretty sweet! And no more mouse nests blowing out! Time to hook back up that overflow tank I fixed. And maybe...just maybe sneak it out for a test drive.
 
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