128 accelleration problem (long post)

Jeremy128

Jeremy128

True Classic
Since buying the car last summer I have experienced an occasional issue. I assume its fuel related. When accellerating hard on highway entrance ramps, and at highway speed, when I get to around 80 the engine acts up. It will be running fine, Then it gives a quick sputter. If I keep my foot on the gas, it continues to do this every 3-5 seconds. I have to drop my speed to a bit above the speed limit. If I drop the speed a little to maintain a good speed (70-75) it is ok.When I creep teh speed back up, it will do it again. If I keep my foot in it, it wil die occasionally when I slow down.
For example, today I ran it pretty good, and it started this. I dropped it down just a little bit, and it was ok. I let off the gas while gettign off the highway. It died. It wouldn't start up again. I coasted to a stop, and turned it over a few more times. Nothing. Suspecting a fuel problem, I popped the hood, and checked the elec connections for the fuel pump. They seemed fine.
My fuel hose does run just over the heat shielded exhaust manifold with a clear plastic fuel fileter just above it. I was wondering if this may be aproblem? SO I moved it up, and kinda laid it over the heat shield at the base of the carb. Closed the hood, turned the key and it fired right up.
Could excessive heat from teh manifold be heating the fuel in the line and cause vapor lock?
Is this even related to fuel supply? I had the same problem when I had the 32 datr on it. I replaced that with a 34 datr, so I dont think its carb related.
Could this be a timing issue? Or a vacuum advance prob?

Earlier today, I adjusted the air mix. THen i noticed the idle was low, so I raised it a bit.
Any ideas, thoughts or advice would be greatly appreciated
 
Some ideas.

Well, since you have an electric pump, it is probably not fuel supply. Do you have a pressure regulator on the system? If so, make sure it is set to 3.5psi.

It is not vaporization. At 80mph, the fuel is running to fast to vaporize. Most likely, you are not able to keep the fuel bowl full of gas. I would check to see what size needle value you have in the carb. Remember, 80mph is practically wide open throttle. I have also seen needle valve begin to unscrew themselves and cause this same problem

Finally, check your float level as well.

Let us know.

Eric Armstrong
 
Hmm, Please excuse my ignorance in advance. I'm kinda new to old cars. I always had motorcycles. Bikes are much simpler than cars in many aspects. My carb background revolves around beating my head against the wall over a set of Amals on a 65 triumph.
I do not know if I have a pressure regulator. If so, how would I find out? Where would it be? The needle valve does make sense, except for one thing. I had the sme prob with the old 32datr, as I currently do with the 34datr. I guess it would make sense if they both had the same size, or too small of needle valve.
What would the odds be of having the needle valve unscrewing on both ?
Float level.... I guess the best way to adjust this would be to split the carb, and bend the float bracket so the float sits higher?
 
Jeremy...

I agree with Eric that it's unlikely to be heat related. At speed the fuel isn't in the system long enough to boil. Vapor lock typically takes place after the car has been sitting for a while in hot weather.

It does sound like a supply problem to me. If it was my car I'd tee a fuel pressure gauge into the supply line to the carb and tape it to the windshield (much easier to do in a front engine car than an X) and drive the car to replicate the problem.

Now, this is somewhat dangerous if you don't do it right so you need to make certain to use new quality fuel line and pad it anywhere it might come in contact with a sharp edge. You also need to make certain to carry a *large* fire extinguisher, just in case. And you obviously want to do this on back roads, not in dense traffic.

But IMO this is the quickest/easiest way to determine whether the problem is in the supply or the carb. Small aside here, but way back when we chased a similar problem on a 260Z for quite a while, rebuilding the carbs, replacing the filter, etc. We finally did as suspected above and proved that fuel pressure was dropping way off when the problem occurred, so we took another look at the system and discovered that one of the two pumps was weak (that car had an electric supply pump out back and a mechanical pump up front).

Don't recall the 128 well enough to know if there is a supply pump out back but I have some vague recollection of an electric pump in some of the 128s. I have an original repair book I could check if it'll help.

Anyway, checking dynamic fuel pressure is a definite go/no go test to isolate the problem. My test suggestion is decidedly "backwoods" for this day and age but it works and it's cheap, as long as you're careful in doing it.

As to your question about changing the float level, yes you either bend a limiter tab or the float tabs themselves, depending on what you're trying to accomplish. But I would not change the level as an experiment-- that's more dangerous than taping a fuel gauge to your windshield. It'd be fine to check the level against factory specs, and adjust as necessary, but I'd caution against raising the float level arbitrarily without confirming the root cause of the problem.

It's possible you have a "heavy" float-- one that has absorbed enough gas to decrease its buoyancy enough to affect the fuel level under heavy load. But in order to confirm that you'd need to compare the float weight to the factory spec. Before going to that effort I'd want to determine if the problem is in the supply or the carb.

However you choose to chase this, take your time and be careful. Don't turn the 128 into a barbecue pit.

HTH,

///Mike
 
Fuel problem.

Sounds like a fuel supply problem, a filter that is clogged or an old line that pinched off inside and detieriorating. Once the car engine dies, heat soak takes over and since there isn't any fuel or little fuel and the engine is hot and has been running hard, the little fuel that gets by vapourizes, creates a vapour lock and is difficult to start until enough cool fuel is ciculated in the lines and supplies the carb.

TonyK.

Grimsby Ontario Canada.
 
Jeremy128 said:
Since buying the car last summer I have experienced an occasional issue. I assume its fuel related. When accellerating hard on highway entrance ramps, and at highway speed, when I get to around 80 the engine acts up. It will be running fine, Then it gives a quick sputter. If I keep my foot on the gas, it continues to do this every 3-5 seconds. I have to drop my speed to a bit above the speed limit. If I drop the speed a little to maintain a good speed (70-75) it is ok.When I creep teh speed back up, it will do it again. If I keep my foot in it, it wil die occasionally when I slow down.
For example, today I ran it pretty good, and it started this. I dropped it down just a little bit, and it was ok. I let off the gas while gettign off the highway. It died. It wouldn't start up again. I coasted to a stop, and turned it over a few more times. Nothing. Suspecting a fuel problem, I popped the hood, and checked the elec connections for the fuel pump. They seemed fine.
My fuel hose does run just over the heat shielded exhaust manifold with a clear plastic fuel fileter just above it. I was wondering if this may be aproblem? SO I moved it up, and kinda laid it over the heat shield at the base of the carb. Closed the hood, turned the key and it fired right up.
Could excessive heat from teh manifold be heating the fuel in the line and cause vapor lock?
Is this even related to fuel supply? I had the same problem when I had the 32 datr on it. I replaced that with a 34 datr, so I dont think its carb related.
Could this be a timing issue? Or a vacuum advance prob?

Earlier today, I adjusted the air mix. THen i noticed the idle was low, so I raised it a bit.
Any ideas, thoughts or advice would be greatly appreciated
Click to expand...

Classic low fuel pressure problem. As suggested by others, put a gauge where you can see it. Anything below 3.5 PSI and the float bowl simply runs out of fuel at extended high RPM.

BTW, on my 128 Rally I run the stock North American electric pump (controled by the oil pressure) AND the mechanical pump. Niether pump by itself, even though my fuel pressure was within specs, could keep up with fuel demand I had while autocrossing.
 
And if it is not fuel pressure.....

Try replacing the coil with another one. A weak, but not failed, coil can be a bear to track down. Ask me how I know!

But at the high speeds, the engine is working hard and a drop off in the spark plug energy could cause the symptoms that you relate.
Ciao,
 
I was thinking that a fuel system whose tank vent valves and/or hoses were not otherwise up to snuff would contribute to a fuel delivery problem, too.
 
Thanks for the input guys! I think this is heading in the right direction.
The car is not using the original style fuel pump. It has one of the "chatter boxes". To make it worse, someone mounted it in the engine bay in a very odd manner. It is sitting on the shelf in front of th efire wall, and is mounted where the spare tire goes. I have never cared for the manner in which it was installed.
I was just out in the garage digging through some of my Spider spare parts that is carried as a break down repair kit. I found a brand new ACdelco electric Fuel pump that is designed for the spider as well as a 71-78 128. Is there any reason why this pump would NOT work on my 79 128? Also should I go ahead and install it to see if it helps? Or keep it in my stash?
I have also been thinking about the filters. I have a clear plastic type filter in the engine bay that apperars to be clear. Last summer, I put a metal style filter under the car beneath the rear axle. Im startign to think I should replace this. I have no idea how clean/dirty the tank is.
Is there a "sock"inside the tank? I was thinking that if so, it may be clogged, after all it would be 30 years old. If there, I was wondering if I should blow it out. Afterall, I have 2 filters in the line, so the sock would be useless.
 
The metal fuel filter is probably an FI filter...

which would be expecting 30-40 psi. If you only push 3-4 through it, I wonder if it would slow flow to the point it would cause a problem?

Pete
 
Will an electric fuel pump from a 71-78 128 work on my 79?
I picked up an adjustable fuel pressure regulator.
I just got home from picking up my daughter. AS I came to a stop, the car just died. Again I cranked it and nothing. Popped hood wiggled wires for pump, moved fuel line away from exh manifold. Closed hood, turned it over, and it started.
This has to be pump/pressure related. I think I am gonna try to install the pump I have with the reg.
 
Ya know...

I've preached this 1000 time and I'm surprized that no one else suggested it...

But I haven't seen/heard you say anything about pulling the emulsion tubes or metering rods? I believe I posted this before to you also.

Your symptoms duplicate what I have experienced several times before... before I finally replaced all the fuel lines and thoroughly cleaned my carb. It only take a little speck flying around in the bowl or stuck in a rod to cause all this trouble.

If indeed you've done all this... and I missed it... then let me bow out. I just hate to see someone purchasing stuff and doing all this stuff that will probably NOT solve the problem. I say all this with the best intentions...

Good luck...
 
Well, I did this a few weeks ago before putting the carb on the car. I made sure the jets, and emulsion tubes were clear. THe clear fuel filter under the hood appears clear.
I guess it wouldn't hurt to check em again. Im not spending alot of $. I bought the adjustable fuel pressure regualtor today. It was about $30. I have had the fuel pump since buying the spider in 07.
I am still wondering if a sock on the fuel pickup inside the tank could be causing this?
As I said previously, I've never been happy with the fuel pump that is on it. The way it was installed leaves much to be desired. So, I think I am gonna install the pump I have under the rear end, where the O.E. one is. I just need to verify if the elec connector still woks down there. I figure if I put the new pump there, and the pressure reg unde the hood where the current pump is, it should only help.
Call me stubborned, or stupid, Im still gonna drive the car until I do this. I just wont drive it with my daughter in it. In case I cannot get it running again. I had to walk home with my daughter last summer. Not fun!
 
Jeremy128 said:
Will an electric fuel pump from a 71-78 128 work on my 79?
I picked up an adjustable fuel pressure regulator.
I just got home from picking up my daughter. AS I came to a stop, the car just died. Again I cranked it and nothing. Popped hood wiggled wires for pump, moved fuel line away from exh manifold. Closed hood, turned it over, and it started.
This has to be pump/pressure related. I think I am gonna try to install the pump I have with the reg.
Click to expand...

Yes, the earlier fuel pump will fit your 1979. And if it's really an original one in new packaging you could probably sell it to a Ferrari owner for more than your Fiat is worth. I always put my known bad ones up, and usually get $65.00 to $100.00 for a fuel pump that says it's junk in the description!
I personally would not bother with a regulator until you know what your fuel pressure is. Go buy yourself a gauge.
And it sounds to me like your buzz box fuel pump is your problem, they always are too low on fuel pressure.
 
Thanks Chris. The fuel pump I have is not OE. I was talking aboutwhere the OE one is located. After reading your post, I should remove teh OE one and sell it. The replacement is an AC Delco pump.
As far as the regulator is concerned, I already bought it yesterday.
I think my dad grabbed a gauge for me while he was at work yesterday. I will find out today.
I have heard that it is better to place the pump closer to the tank, than the engine. Is this correct? THe chatterbox is under hood with only about 18"-24" of hose seperating it from the carb. COuld this add to the fuel probs I've been having?
 
Jeremy128 said:
Thanks Chris. The fuel pump I have is not OE. I was talking aboutwhere the OE one is located. After reading your post, I should remove teh OE one and sell it. The replacement is an AC Delco pump.
As far as the regulator is concerned, I already bought it yesterday.
I think my dad grabbed a gauge for me while he was at work yesterday. I will find out today.
I have heard that it is better to place the pump closer to the tank, than the engine. Is this correct? THe chatterbox is under hood with only about 18"-24" of hose seperating it from the carb. COuld this add to the fuel probs I've been having?
Click to expand...

Every instruction for an electric fuel pump that I have ever read stated to mount the pump as close to the tank as possible. But look at the stock mechanical location... It's not close.
You will never know if your fuel pump is the problem, or even if you are going down the correct troubleshooting path, until you check your fuel pressure. Tape the gauge to the windscreen & go drive it. Personally I would have my timing light connected and on the seat next to me at the same time.
 
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