Vapor Lock

[JohnHSpider]

My 16 year old son and I have a '72 Fiat Sport Spider 850 and live in Texas where it is 95-105F this time of year, the car is his daily driver and the product of his own sweat, elbow grease and yes a few tears too. But he doesn't trust the car for trips beyond 20 mins due to vapor lock issues that kill the engine while driving down the road. We live in a large city and I'm worried that it will die on him and he would get rear ended, smashing all our work. I'm looking for advice on ideas we thought of and new ideas we haven't thought of yet.

Diagnosis: I put a glass fuel filter in so we could observe, and the fuel in the line between the tank and the stock (mechanical) fuel pump does vaporize. The line has to go near the exhaust as far as I can tell, since the exhaust and the fuel pump are on the same side of the engine.

Fixes that we have tried so far:
- 1 way valve near the firewall (prevents vapor from pushing gas to tank and might speed up condensation and recovery) = recovery now down to about 30 mins
- Insulate the rubber fuel line (aluminized insulating tape) = added a few mins of run time but didn't stop the issue
- Re-route the fuel line (went under the edge of the engine compartment side wall, around and up to the fuel pump) = bad answer, lost 15 mins of run time, have restored to the previous routing
- Additional insulation of fuel line (several layers of aluminum foil) = added a few mins of run time

Fixes that we are thinking about:
- the car is missing the "Engine Protecting Panels" which might help airflow, but they are pricey and I don't want to spend the money to find out that they only make it worse (right now the engine bay goes straight through to the ground).
- Give up on the original fuel pump and get an electric and route it onto the other side of the engine (my son wants to keep it as original as possible and we both want it to be reliable)
- Other routing paths for the fuel line
- Other methods for insulation
- Some form of "heat shield" to deflect the heat off of the exhaust

I'm really at a loss as to what to try next. Any advice you all can give would be appreciated.

John

[SteinOnkel]

Ahoy, John.

The exhaust manifold and fuel pump are on the same side? This is news to me, but I have a slightly later (1978) model.

What I have found is that it's usually not the fuel in the lines that starts boiling (remember, it's constantly pumping and moving along), but rather inside the fuel bowl where it "sits". You then get positive pressure that your pump can't overcome and the car stalls.

Get a phenolic spacer for the carburetor. AR sells (shitty) ones. Go ahead and get yourself some of that rubber-cork gasket material sheet, nice and thick, 1/4" Then Grab the spacer and make yourself two nice and thick gaskets.

Also, do you have a return line? I have found the best fuel filter by far for carburetor applications is the stock one for a 1978 Jeep Wagoneer. Costs $6 at your local parts dealer and has a built-in pressure regulator as well as three ports (one in, one to the carb, one to the return).

That approach worked a treat on our 1962 Studebaker and our 1978 Fiat. Both run crappy California pump gas wi/ stock fuel plumbing and mechanical pumps. No issues.

Cheers
Steiny

[JohnHSpider]

Thanks Steiny,

The Weber 30 DIC carb on it has a return line built in, but if it didn't then I would be looking for just such a filter. It seems that it keeps the fuel cooler having the return line, so I'm glad it is there. He does say that he can hear the fuel boiling in the carb for a few seconds when he shuts it off, so the spacer may be exactly what we need. I will have to find a lower profile air filter, as what we have is not stock and the prior owner put a nice dent in the engine lid when he closed it the first time with this air cleaner. I ground down the wings on the wing nut and it hasn't hit since. These small rear engine cars don't leave a lot of vertical space.

Thanks again, I will post back after it is installed and let you know if it solves the issue!

[18Fiatsandcounting]

Steiny, good thoughts and keep in mind that this is an 850 spider, not a 124 spider. Very different.

John, I think all your past ideas have been good ones, and pretty much along the line with how I would approach it. Your proposed ideas are also good. At this point, it may just be that the 850 spider was not designed with TX temperatures in mind, although I would think a car would not have vapor lock at 105 degrees, unless at really high altitudes. I know it's not the same car, but the only time I ever experienced vapor lock in my 124 spider was climbing the pass out of Death Valley CA one July, where it was 127 oF in the valley and the pass I was climbing was 5000 feet. The car did make it.

Anyway, I think the electric fuel pump would probably fix it, but I see your point about keeping things original.

One thing to try: Gas additives, or just a different brand/grade of gas. I'm normally not a fan of the various "snake oils" sold to cure everything, but maybe a product specifically designed to minimize vapor lock would help.

Finally, avoid high octane fuel and fuel with ethanol, as both are more prone to vapor lock.

-Bryan

[JohnHSpider]

I got to thinking that surely the gas line doesn't belong where it is. So we got to poking around and located a small hole in the fender well, and now it routes (with the insulation) through the fender and is protected from the heat by the driver side wall of the engine bay. This has made a dramatic improvement as only a small amount of hose is exposed to the heat (from its hiding place to the fuel pump). We put the filter so that it is behind the access port and can be cleaned/changed as needed. My hope is that the new routing will result in cooler fuel being delivered, enough so that it does not boil in the carb.

We do plan on adding the spacer that Steiny suggests, but I'm still looking for a low profile air cleaner. My son is thinking that K&N might make something that is shorter but still has appropriate airflow to keep from choking the engine. Since we don't have the original air cleaner housing we'd might as well get something improved, right now it is a round Edelbrock lid and a home made lower piece to make it fit, but it does look out of place in a small Italian car.

I will ask him what gas he is running. That is a good thought as it never had this issue when I was filling it up, even with the old route of the fuel line. Maybe switching brands or grades could give improvements. We talked through the idea of higher octane, and I told him that is usually for higher compression engines and it wouldn't give him noticeable results with his engine. He didn't seem to believe me so this could be the change that caused him to have issues that I didn't when i was driving the car. I was running regular unleaded from a brand name I've come to trust in other vehicles.

[18Fiatsandcounting]

It sounds like you've already addressed the issue, but the type of gas could make a difference. Note that I may have misspoke when I suggested avoiding higher octane fuels. Higher octane fuels have less volatile compounds than "regular", which makes them less prone to pre-ignition and detonation (pinging), and also less risk of vapor lock.

Anyway, try some different brands of gas and octane ratings and see what works best.

-Bryan

[JohnHSpider]

I forgot to mention in the previous post:
Altitude is not an issue for us, his house is approximately 80 feet above sea level, and the only "hills" that we have around here are overpasses on the highway.

We will experiment with brands and octane ratings. Thanks for clarifying Bryan!

[SteinOnkel]

I only have anectodal (n=1) evidence for this, but my other car (11.5:1 compression ratior) hates cheap high octane fuels. It's Shell, Chevron, 67 or bust with that thing. Any of the cheapo brands water down the fuel too much and it starts to ping and knock.

Your engine can benefit from it, but not without bumping up the ignition. Which I wouldn't do, seeing as y'all like to keep things original.

Ah...the 850 has the engine in the back.

Many moons ago, when we ran my brother's 914 on carburetors, it too had vapor lock issues (surprise surprise on an air-cooled high performance engine). It needed the works - insulation on the fuel lines, electric pump and carb spacers.

[JohnHSpider]

Yeah, the rear engine is a first for me. Other small cars like MGB that I've had behaved more in my Chevy and Ford background.

This is my first Fiat to own, but likely not my last now that I have become familiar with them. They are designed to be worked on, with good access and very thought through. I've been impressed with this little car.

As part of fighting with the car, we recently went to an electronic distributor and coil. It has been a very beneficial update, but my son asked that we keep the old ones in case he wants to go back at some point.

I don't know the compression, but I would not expect it to be as high as 11.5:1, since this is very stock.

I bet that 914 was a pretty fun car!

[SteinOnkel]

Yeah, the rear engine is a first for me. Other small cars like MGB that I've had behaved more in my Chevy and Ford background.

This is my first Fiat to own, but likely not my last now that I have become familiar with them. They are designed to be worked on, with good access and very thought through. I've been impressed with this little car.

This is the exact opposite of my experience with my 124. Huh.

As part of fighting with the car, we recently went to an electronic distributor and coil. It has been a very beneficial update, but my son asked that we keep the old ones in case he wants to go back at some point.

First thing I did as well. I binned all the old stuff, nobody ever goes back to points

I don't know the compression, but I would not expect it to be as high as 11.5:1, since this is very stock.

You think so? My Fiat is at an abysmal 8.3:1. You can run 85 octane fuel in it if you want.

I bet that 914 was a pretty fun car!

It is now that it has programmable efi. Those carburetors were terrible.

[JohnHSpider]

I'm betting mine is in the 8:1 range. Certainly nothing high performance driving the higher octane... but if it gets it to stop vaporizing I would try it.

The 850 is so simple. Removing the seat is as easy as sliding it forward off the rails. When we pulled the engine and transmission, instead of renting a hoist, I took off the rear bumpers and the center rear panel and just rolled it out on a floor jack. We put it back in the same way. The drum brakes are an easier design to deal with than my 67 Impala had, and the front discs are super easy.

There are a few spots where my fat forearms won't get into, but my son is still thin and fit so he can get his arms in there. The hard part for me is that the car is so very low to the ground. When I get under it I have to decide which way I want to look before I get under there because my nose hits the bottom of the car if I try to turn my head. Other than that, I am finding it super easy to work on.

[18Fiatsandcounting]

My only experience with an 850 was a friend who had one, a tall guy who I seem to recall could stick his arms out the window and almost touch the ground, given how low the car was. Could be an exaggeration on my part, though.

At any rate, you may be interested in what wikipedia says about the 850: https://en.wikipedia.org/wiki/Fiat_850

If you read about the spider, it says that the engine size was reduced to 817 cc (50 cubic inches) when it was introduced to the US market, in order to meet the less stringent emissions requirements for that small an engine. To compensate, the compression was raised to 9.2 to 1, thus requiring premium fuel.

So, maybe your 850 really does need premium fuel?

-Bryan

[JohnHSpider]

[quote="18Fiatsandcounting"]If you read about the spider, it says that the engine size was reduced to 817 cc (50 cubic inches) when it was introduced to the US market, in order to meet the less stringent emissions requirements for that small an engine. To compensate, the compression was raised to 9.2 to 1, thus requiring premium fuel.

So, maybe your 850 really does need premium fuel?

I think that it might need the premium. On the Wikipedia, ours is the 903cc engine "Sport Spider" made in the later years. It is great, but in the US there are only about 250 left in operational condition. (sorry I'd put the web page but I don't recall where I read that) This makes it nicely rare, but a real pain to find parts for. My son wanted a unique car and he got one for sure.

His next tank of fuel will be premium, and I learned that he has been filling up at a crap gas station that I assume has higher water and ethanol content. I bet when we get back to better gas a lot of this will improve.