79 Bucking, Sputtering,Spitting ????????????

[JEEPER]

I have a 79 that has been a probable since it was new. The dealer couldn't find the probable, so in about 1986 after Fiat left he US, Fiat paid an X dealer to rebuild a used carburetor and install it on my car (housing was defective). The X dealer even put an electric fuel pump on it to eliminate vapor locking, if that was the problem. The problem when the car was new was only when you went somewhere and restarted the car and it was still warm. You would start it and all of a sudden at about 40MPH or so it starts acting up. I live on a road that has a 35MPH speed limit. When I go the 4 miles then get to the 55 MPH speed limit and I accelerate the problem starts. It bucks, sputters, and spits(major whip lash) until I take my foot off the accelerator and gently press the accelerator.It smooth's right out. When the car was new I thought it was vapor locking. Once this stops it'll run smooth until you shut it off for awhile then restart it again.The car has been tuned half a dozen times over the past 35 years and the problem persists. I guess that I am just so sick of this problem that I want to fix it if I can. Wires, have been replaced a couple of times. I think it is carburation, but I don't know that, however it has done this through 2 carburetors. This car has 22,000 miles on it and is completely factory stock except for the electric fuel pump. Any help would be appreciated.

[majicwrench]

Good news, if it does this consistantly it can be dealt with. Needs to test some things. If it was in my shop first thing I would do it T a fuel pressure guage into fuel line, then secure to wiper arm. Now go create the problem and see what fuel pressure is doing while it is acting up.
Keith

[bobplyler]

What was the replacement carb? Original?

[JEEPER]

Good news, if it does this consistantly it can be dealt with. Needs to test some things. If it was in my shop first thing I would do it T a fuel pressure guage into fuel line, then secure to wiper arm. Now go create the problem and see what fuel pressure is doing while it is acting up.
Keith

Keith I am not disagreeing, however I have had this problem with mechanical OEM fuel pump and original carburetor and electric fuel pump and replacement carburetor. I took it out today, buck, spit and sputtered when I was able to open it up after 35 MPH. I jumped on the highway at 75 and she turned 3800 RPM smooth as could be(in 5th ). When I got off at the exit and stopped when I hit 4500 RPM it started all over again(buck, sputter and spit). It seems 3500 to 4000 RPM's is where the problem starts. What do you mean secure the wiper arm and why?

[JEEPER]

What was the replacement carb? Original?

bpbplyer, It was an OEM core they rebuilt. The reason for not giving me a new one is that Fiat didn't have one because they went to FI in 1980.

[AriK]

What Keith means is secure a fuel pressure gage to your wiper arm so that you can monitor it while you drive. I can't believe you are troubleshooting a 35 year old problem. There are enough experts here to finally put this to rest. Don't despair, the worst is over.

[seabeelt]

Is it at the same rpm regardless of gear and load? Wonder if you don't have a dizzy problem
R/

[majicwrench]

SO you can power thru the problem?? Then yes, it is not likely lack of fuel.

So next, what IS your fuel pressure?? These things need very little pressure.

Me, I'm one of those guys that think the factory knew what they were doing. I'm not fond of hang-on electirc pumps.

Still good news, sounds like it happens consistently. Not that familiar w a 79 carb, but I might be tempted to remove bowl vent line and see if it makes a diff.
Might remove vaccum advance line and see if it makes a diff.
Might hook up a timing light, arrange it so you can see flash from drivers seat, see if flash is nice and steady when issue happens.

[JEEPER]

Good news, if it does this consistantly it can be dealt with. Needs to test some things. If it was in my shop first thing I would do it T a fuel pressure guage into fuel line, then secure to wiper arm. Now go create the problem and see what fuel pressure is doing while it is acting up.
Keith

Keith, I installed a tee jut before the fuel filter. The gauge I am using is a 50 PSI with 1 PSI increments. I have good flow on the fuel line coming off the tee, however the gauge does not read. I tested the gauge with the blow gun off my air compressor and it read fine. Do I need to get a special gauge?

[So Cal Mark]

you need a gauge with a much smaller range-0-12 psi. Your stock pump will only put out 2-3psi, an electric a few more than that

[JEEPER]

you need a gauge with a much smaller range-0-12 psi. Your stock pump will only put out 2-3psi, an electric a few more than that

Thanks Ordered a 0-15 PSI gauge this AM (lowest I could find)

[JEEPER]

SO you can power thru the problem?? Then yes, it is not likely lack of fuel.

So next, what IS your fuel pressure?? These things need very little pressure.

Me, I'm one of those guys that think the factory knew what they were doing. I'm not fond of hang-on electirc pumps.

Still good news, sounds like it happens consistently. Not that familiar w a 79 carb, but I might be tempted to remove bowl vent line and see if it makes a diff.
Might remove vaccum advance line and see if it makes a diff.
Might hook up a timing light, arrange it so you can see flash from drivers seat, see if flash is nice and steady when issue happens.

I am borrowing back my timing light so I see if it flashes nice and steady(will post).

[Nathanchilman]

I battled a similar problem as yours and here is what I tried.
New electric fuel pump 2.5 to 4.0 psi
Blew out lines, adjusted float, pulled cleaned and red coated tank
Rebuilt distrubutor it's converted from points previously
Rebuilt carb 32 adf

All no help other than things that needed to be done
Replaced fuel pump again with a 4-7 psi and inline regulator set at 3.5 psi
Problem hasn't occurred again in 100's of miles.
It was starving for fuel

Good luck

[TRSmith99]

My wife's 77 Fiat was having the same problem. Its a "stock" setup (sans the CA SMOG items). The symptom we experienced were VERY similar to what you describe. Around 40mph (especially uphill and after's the engine is warm) the car would sputter and spit and buck. Downshift or upshift (different RPM's) and the car would kick-in and accelerate smoothly.

For 2 years we tried to resolve this - new gas pump, carb adjustments, transmission/clutch inspection, drained the gas tank, on and on.

Well....
It got fixed with the most recent trip to the shop. We recently moved. New town = new mechanic. As this was the first visit, the new mechanic went through the car with a fine tooth comb and gave a list of items/observations to be repaired/fixed/adjusted. One of the items was to replace the gas lines from the gas tank to the carb as they were decaying. When we picked the car up, the mechanic said that he replaced the gas lines, removed a gas filter at the gas tank, and "flipped" the fuel pump so that the gas line feed would sit "lower in the tank".

We've put ~200 miles on the car since the repairs. Not a single buck, sputter, or spit regardless of how much we've tried.

Just thought I'd share....


T-

[JEEPER]

Good news, if it does this consistantly it can be dealt with. Needs to test some things. If it was in my shop first thing I would do it T a fuel pressure guage into fuel line, then secure to wiper arm. Now go create the problem and see what fuel pressure is doing while it is acting up.
Keith

15PSI gauge came yesterday, I am using 3/8 fuel line 3 feet long with 1//4" tee and I am only getting 1PSI. I even let it idle and pulled the gauge out of the fuel line until I had a good flow of gas into a container then pushed the barbed fitting into the fuel line and no increase still 1 PSI.