Early 850 Coupe upgrade questions

Discussion in 'Rear-Engine Fiats' started by tomnj, Jul 2, 2018.

  1. tomnj

    tomnj Old fogie stogie

    Location:
    Scotch Plains, NJ
    Hey guys! It's been a while, but chiming in to say I am still into old Fiat's all these years. My latest acquisition from about a year ago is a 1968 850 Coupe. It came with it's original 817cc (disassembled), so I promptly found a later 903cc donor car to put in the big 903cc:) More upgrades to follow, but ran into 2 issues with the engine swap, looking for advice/direction on these:

    1. FUEL/Carburetor: The later 903cc's 850's used a tank recirculation style fuel setup with the stock Carb. This means an extra tube going back to the tank... but the early Coupe's had a different fuel tank and did not have this return line, so I plugged it off at the carb. The car runs like this, but idle dies as soon as I take it off choke. Maybe this has nothing to do with the return line (could be just a carb issue), but just wondering how others handled this and whether they needed to change to a different Carburetor. If so, what is the best carb to buy and maybe upgrade power a bit?

    2. Charging: When I installed the new motor, I realized the regulator is different (because the 903cc uses an Alternator). I ordered the correct regulator, but having trouble with the 4 wires and where they go. Where can I find a good wiring diagram online? The manual I have does not have a good diagram.

    Picture of the engine and Coupe. The other 2 850's are (were) mine also.:) 903.jpg 850_trio.jpg

    Tom in NJ
     
  2. kmead

    kmead True Classic

    Location:
    Michigan
    Welcome Tom!

    A fine brace of 850s there.

    Some answers:

    Jeff Stich will be able to answer best as he is our resident expert on 850s.

    You can take the top off the old carb and put it on the newer carb if you so choose to get rid of the extra return port. As you have found it doesn’t absolutely need the return line to work. The later carb has larger throats and in combo with getting rid of some of the emissions regulation features and the early top give s good compromise with some changes to jetting.

    I think you will find that the stalling issue is not related to the change in carb specifically unless it had an idle cut off solenoid which would need to be powered from an ignition regulated source. In all likelihood it is some guck somewhere in the carb.

    My 1969 Sport Coupe came with a generator and its original 817. I changed over to a alternator, I am away from home right now and I don’t have the info handy for the conversion, when I get back next week I will be happy to post it up. I have yet to go for the big block :)

    The alternator cars added two relays for charge regulation and idiot light actuation. It’s complex and failure prone. I followed the wiring diagram from a 1970 or later Sport Coupe to make the conversion.

    It is my intention to go to a Denso type alternator with an integral regulator. I will post up the changes needed for that mod when I get there. Higher output, smaller size and greater reliability. Versions of this alternator are used on things like the John Deere Gator, Chevy Sprint and other small GM/Suzuki cars.

    Hope that helps a bit.

    Thanks for signing up and being part of our community.

    Karl
     
  3. Last edited: Jul 2, 2018
    kmead likes this.
  4. kmead

    kmead True Classic

    Location:
    Michigan
    71 and 13 are the relays you would need to add in addition to the proper regulator.

    I placed both relays in the engine compartment and used the existing wire to the generator light from the new relay to minimize the amount of extra wiring I had to do.
     
    Last edited: Jul 2, 2018
  5. tomnj

    tomnj Old fogie stogie

    Location:
    Scotch Plains, NJ
    Thanks for the info guys, this is all very helpful. We decided to use the old 30DIC Carburetor from the original 817cc engine on the 903cc for the simple fact that there is no emissions stuff on it. I am reviewing the jetting, but the sizes are remarkably close, as is the throttle body. I might just leave it as-is. It's possible any change in jets to the later carb had more to do with matching it to the emissions connections or even detuning it to meet emissions standards.

    On the same topic, do any of you see any benefit to polishing or porting the intake manifold? Isn't there some "alquati" manifold that racers of the day used? Is that available or even worth doing on an otherwise stock engine? How about petronix/electronic ignitions? Any suggestions there?

    I am still working on the regulator. Thanks for the tips about the relays.
     
    Chaostoy likes this.
  6. kmead

    kmead True Classic

    Location:
    Michigan
    You may want to carefully look at the jets on the 903 based carb, I am away and can’t look them up but I think they would offer a better mixture for the larger engine in the older carb.

    I woudn’t bother with the manifold.

    Pertronix would be a worthwhile update. I have one on mine, it so far has proven reliable.
     
    Chaostoy likes this.
  7. tomnj

    tomnj Old fogie stogie

    Location:
    Scotch Plains, NJ
    Hey guys, here's an update. The carb is done and the engine is running great. Still have 2 issues:

    1. It's overheating at idle after about 10 minutes. I installed hoses and belts and everything appears to be working (fan is in good shape along with the radiator seal/cover), including the overflow tank. No leaks that I could find and I added enough coolant (above the min line). So where do I look first? The radiator is old, but a low mileage one that looked to be in good shape and flushed with all new coolant added. The water pump is original with a new seal. I'm thinking maybe the thermostat would be first place to look? What is usually the culprit for overheating on these 903cc's? How would I test the water pump?

    2. It's not charging the battery. I am not reading any voltage level over 12V anywhere while it's running, even at the alternator brown wire. I am assuming the alternator is bad. It has a new regulator. Any way to verify a bad alternator?
     
  8. kmead

    kmead True Classic

    Location:
    Michigan
    Is the radiator the early type or the later type? The early radiator has a vertically oriented hooked inlet the thermostat housing would lead to. The later unit has its inlet facing towards the rear of the car.

    The early one can be difficult to properly purge of air and can cause overheating.

    Do you have any sense of what the real condition of the radiator actually is? A clogged radiator would be a reason for overheating. It would be a reason for overheating at idle.

    What size pulleys are on the car? Does it have the larger or smaller water pump pulley? A slower rotating pulley could be a contributor.

    Yes the thermostat could be the problem but it would likely be a problem at all speeds.

    Another issue could be the way you have the timing set. If it is too retarded it can contribute to overheating.

    The water pump head space of the impeller to the waterpump body could be too great and is not forcing the coolant to move efficiently at low speeds. This might be a contributor at low speed that would be less evident at higher engine speeds.

    As for not charging, well, it is a complex arrangement that if not properly set up could lead to no charging. I do have the troubleshooting manual for the 850 and will post it in a bit when I find the digital copy on my computer.

    Karl
     
  9. The radiator cap in the picture at top looks to possibly be a "Stant" type. Kinda hard to tell from the photo, but make sure you have the right Fiat cap on the rad. Also, get some engine bay pans put on the bottom of the car. They actually do make a difference. Also, a flush of the coolant line wouldn't hurt. I got lots of rust and what looked like mud outta mine when I did it! I just put a water hose on the pipe that runs to the heater, and gave it lots of pressure, reversed the flow to the other pipe, and repeated til it ran clear.
     
  10. kmead

    kmead True Classic

    Location:
    Michigan
    I just went back to your the image of the engine bay.

    Do you have an underpan for the side the radiator is on? If you don’t have the underpan, the fan will start cycling the hot air and the car will overheat, particularly at idle as there is no motion to stir and provide cool air to the mix.

    The fan pulls air from the engine compartment and then pushes it under the car, when it is just sitting there the hot air comes right back up into the engine compartment if there is not pan from under the radiator to the back of the car and from the side of the car to the side of the engine.

    There should also be one that goes from the exhaust side of the car all the way around to the pulley end of the engine to semi seal off the compartment on that side.
     
  11. kmead

    kmead True Classic

    Location:
    Michigan
  12. Jeff Stich

    Jeff Stich True Classic

    Location:
    Norco, CA
    1. Incorrect or failing radiator cap. This causes overheating due to the water/coolant mix boiling from lack of correct pressure in the cooling system.
    2. Clogged radiator cooling fins (external)
    3. Clogged radiator passages (internal).
    4. Thermostat stuck closed or thermo housing clogged with coagulated (jelly-like) old coolant.
    5. Clogged cylinder head internal coolant passages (coagulated old coolant/mineral deposits).

    Why not just reinstall the original generator & its voltage regulator, using the OE wiring connections?
     
    Chaostoy and kmead like this.
  13. tomnj

    tomnj Old fogie stogie

    Location:
    Scotch Plains, NJ
    You guys are the best! I fixed the charging problem using Jeff's suggestion of just going back to the generator (dynamo). I didn't even know it would fit on the 903cc, but the bracket is the same and so is the space. I used the wiring diagrams you guys sent me and re-wired everything using the old regulator. Checked the battery and it's charging it fine now.:)

    As to the overheating problem. I think it's the radiator cap, as Jeff said (its some aftermarket one with a pressure release lever, not a Fiat one), and I also need to install the engine tin as Kmead suggested. Thanks guys! I'll post more pics as I get them. Next on the agenda is brakes. Any big brake kits available for these that work with the stock 13' wheels?
     
    NM850 likes this.
  14. Jeff Stich

    Jeff Stich True Classic

    Location:
    Norco, CA
    No real need for this, as stock late 850 brakes work absolutely fine when all components are in good condition. If you want overkill, converting the rear drums to disc is a possibility.
     

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