Looking for some advice, opinions, guidance.

The background: I currently have a 1972 with a 1.7L engine.
Recently had help from a few guys here from the world and found a few issues:
Rust in cylinder 3. Honed out the cylinder to get movement.
Converted the dual Weber 40 carbs to L-Jet FI
Car starts but won't hold an idle. You can keep it above 2000 rpm and it will run; made an obligatory trip around the block just to say we did!
While adjusting the valves, my buddy noticed they appears to be in excellent shape (possibly indicating engine work done by previous owner), which along with the bad idle we are guessing may point to a carb cam.

The options:
I found a 1.8L nearby that I can pick up for a deal. Was running at the time it was pulled, but that was years ago. Been sitting in a dry AZ garage ever since. Car was running with the L-jet FI, so I doubt I need to worry about the cam, but of course you never know till you look.

Thinking of picking up the 1.8 and a big bore kit from another world member here in town.

Curious if anyone has thoughts on using the 1.7 or the 1.8 for the big bore kit. I believe the 1.7 would require machine work to accept the big bore kit. Is it worth it? I keep hearing people talk about preferring the 1.7 over the 1.8.


Conditions:
I am looking at using this for a fun weekend driver and I am on a budget. I know there are lots of guys on here that can do some really serious amazing work, but its just not in the budget for me right now. Not saying its not worth it (as was debated earlier today), just not in my budget for this project.

What do you think?

I believe you have to do some head work to build up the 1.7. The 1.8 won't require head work if you don't go over 96mm on the pistons IIRC.

Are you planning on reusing the heads or buying new ones?

There is no difference between the cases on any of the engines. The only reason some people prefer the 1.7 to the 1.8 that I am aware of is that they prefer the D-jet to the L-jet systems because of the finicky nature of the L-jet with regards to vacuum leaks.

I had heard that as well, regarding the head work required for the 1.7. But the 1.7 is supposed to have better compression than the 1.8, so I guess I am curious if it makes more sense to spend a few bucks for the machine work and keep the 1.7 with the big bore kit....

You are correct that the stock 1.8 has lower compression ratio than the 1.7. However, you set the compression by adjusting how much volume is left in the cylinder when the piston is at top dead center (in relation to the stroked volume). If you are building a new engine you have the ability to choose whatever compression you want.

Does anyone know if they make a higher compression piston for the 1.8 like they have for the 2.0?

I am no expert, but isn't compression developed from the stroke and the deck height and CC of the combustion chamber? I remember tinkering with my deck height by adding shims UNDER the cylinders to LOWER my compression.

I just rambled on about what I know about the types of CC conversions here at this post: engine ? post

it might help here. Lots of folks doing engine conversions this week!

With budget being the main drive, stick with the 1.8L. Everything should bolt up, and you won't have to worry about sealing those head vents that the 1.7L heads have.

The European-spec 1.8 ran higher compression by almost a full point--8.5:1. Don't know where you'll get those, exactly.

You can get pistons made with a variety of crowns. It will cost a lot if they have to make them just for you, though.

You can fiddle compression by flycutting the heads. Do lots of measurements to understand how much effect that has.

--DD

1.8 heads flow better than the 1.7 heads
you can put a "big bore" kit on a 1.8 up to 96 mm with no machine work required.

When you increase the displacement of a motor with larger pistons, you raise the compression ratio, so you will need to measure that and get the correct base cylinder shims to set your CR exactly where you want.

Rich

Hi JP... The 1.7 is already in the car & running, appears to be low miles on a rebuild, nice & clean inside. Why not warm it up, do a compression test to get a better idea of what you're dealing with, then re-focus your energy on getting the fuel problem sorted out. What you're shooting for is a low budget, dependable driver. If you fail with the FI, you can always go back to carbs. Maybe it is cammed. Just thinking what I'd do. Best wishes ... Terry