128 coupe hard starting when very hot

ghostdancing

ghostdancing

True Classic
in these hot summer days i experience hard restarting: must floor the pedal and go with the starter motor for too much time. should be due the gas evaporation in the carb, so (i figure) the long starter running it's needed to pump fresh fuel from the tank..correct?
do an electric fuel pump can mitigate the problem? any experience on this?
note that the car goes very well, carburation it's ok, ignition works well..
 
If you wire an electric pump to energize with the key in the "On" position, the pump will circulate fuel prior to turning the key to the "Start" position that cranks the engine. This means that it will fill the carb bowls prior to cranking. I have an electric pump on my 124 sedan and it does seem to help with hot starts. Not as much as I expected it to help, but it does help. My set electric pump up is a fairly recent addition and this is the first summer, so I have some experimenting to do to figure out the best starting sequence.

Keep in mind that when configured this way, the pump will keep running as long as the key is on. It is wise to add in an inertia switch to the pump power circuit in case of accident.
 
Jim you deleted the original mechanic pump..correct? can i mount the electric just for starting (and as plan B in case of original pump failure)?
 
I did delete the mechanical pump. I don't know how you would run the hoses to support two fuel pumps, but I guess it could work.
 
Must be the difference between US and Italian models. Most 128's that I have worked on and 124's had an electric fuel pump with dual relays and tied to the oil pressure sensor. If you can find all that, you could keep it stock Fiat. A lot of older cars have trouble with hot restart that use only a mechanical pump. I do not know if your fuel is different from ours. But follow normal practice. Electric pumps should be as close as possible to the tank. You can have both in the system as long as the electric pump is a pass though type so that the stock pump will pull through it. You could just use it as a priming pump when you have a hot start problem. Use a spring load switch so you don't accidentally leave it on. If you go only electric then do not just wire it to a hot wire. It needs to be on a relay. You can get it wired to oil pressure with relays as the stock Fiat set up. From my old VW days, I use the old CSI pump relay when I convert to an electric pump. Very slick set up as it uses the ignition pulse to run the fuel pump relay. Has a built in fuse holder. So if the car stops so does the pump. I like it better then using oil pressure.
On a related thought, does your carb have the inlet and return line set up? There is a tiny restriction plug in the return line that does not let too much fuel go back to the tank. If there is only a single inlet on the carb and you decide to go only electric, you might need a fuel pressure regulator, and /or add a return line back to the tank to vent some volume back so as to not over come the needle and seat. Good luck.
 
Getting old. Remembered something else. Does your Coupe have the thermo sensor in the intake like my 128 Coupe? Some folks disconnect them. I like them as they run the radiator fan until the engine cools down. I don't like them as they can run for a long time. You have to have a good battery. I have had folks tell me my car is still running as I walk away and come back many minutes later. I think that it was to help with heat soak on shut down. This is similar to that little fan set up in the X 1/9.
 
Tkagi, tnx or your inputs! i did not fully understood your write up (it's not a language problem: it's because i'm not so in the car tech yet: this is my first "hobby car", and my mechanic knowledge it's limited to old motorbikes..)

first of all: my radiator fan goes off when i turn off ignition key, so i guess no thermo sensor..

my carb does have inlet\return setup? yes: i see 2 hoses from the tank to the engine bay.. dont know if there is that tiny restriction plug on the return line: will have a look indeed

electric pump: it's hard to mount it close to the tank: it should be mounted under the floor (i feel it's not a not a good place to have it..)..so i guess must mount somewhere in the engine bay.. correct?

i'm thinking about this easy setup: electric "inline" pump fitted before the mechanic pump, with push button and relay direct from the battery (dont like hotwires): i can push the button for say 5 - 10 seconds for priming the carb, then turn the ignition key..is it feasible?
 
Every 128 I owned had a factory electric pump. Look under the car just ahead of the gas tank and see if your car has a mounting plate attached to the under side of the floor to attach an electric pump. Without getting all fancy with electric circuits, why not just wire in the pump to run when the ignition is on to see if this solves the hot start problem? If it does then you can make a more appropriate wiring circuit with whatever cut outs you want. Also, to keep things simple I would not run both an electric and mechanical pump, but that's just my way of doing things.
 
Carl, when i was under the car i only saw the 2 plastic hoses (coming from the tank and connected to the metal hoses that run under the carpet in the cabin).. never knew about an oem electric pump in the 128s..(but hear that some 124 and 131 had it).

an electric device in that position under the car will be safe enough?

what kind of pump should i look for? i made a quick search in the web and found pumps rated for 0,1 to 0,5 bar (70 - 100 liter\hour)
some are very cheap, other more expensive

another question: the excess fuel will be returned to the tank via the return hose..or there is the risk of gas mess somewhere in the system?

the "easy setup" for priming only it's intended just to see if the electric pump improve the situation..if yes, will think about original pump deleting..
 
With Weber carbs, the critical spec is the pressure, Webers like low pressure, no more than 4 PSi. Most of us use the Facet "cube" pump. Sold under many names and come in different pressure ratings. I don't think volume is a consideration, especially for a stock carb.
 
thank you Carl. do you know if i can put this pump over the fluid level in the tank, or must be fitted close to that level? is it an inline pump that let the gas flow when the pump itself is in off mode (mechanic pump running)?

..just back from some homework about the cube pump: is "solid state", so no motor spinning inside..more expensive then a motor spinning pump..is it better?
 
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I'd say that that is an OK unit for your car. Price seems good. Pressure is on the low side, but the volume is plenty, so looks good. Looks to be a rotary style pump. Some of the cheaper pumps are a clicker style where a little piston goes back and forth. Both kind work, but the type like this E-bay add are usually more reliable. When you go only electric, you are better off spending a little more to get something that is, hopefully, more reliable so you aren't stranded. Make sure that you protect the pump with a filter. The last pump I bought had a filter included so that the pump was protected. Try and mount this as close to the tank as possible. As Carl said most of the Fiats here, at least have a bracket just in front of the tank to mount the pump. There was also a guard that fit the stock pump. By design, nearly all electric pumps push well, but do not suck well. I know that some folks have run electric pumps up on the firewall and they will tell you that it is just fine. Consider that all cars with electric pumps have them located by or inside the tank. Outside they are at or below the tank. Just to check and see if an electric pump will cure your starting issue, mount and wire it anyway that you want and see if it helps. Just be careful. Make sure there are no leaks and keep an extinguisher handy.
Keep in mind that this type of pump is cooled and lubricated by the fuel. When they are high mounted, they can dry start and will not last as long. I recommend, if you do go all electric pump, remember not to run low on fuel as to starve the pump and shorten its life. I always add a tablespoon of ATF or marvel mystery oil. once a month to lubricate the pump when I am driving. I usually find those small soild state pumps are cheaper then the bigger motor style pump. They used to work great, but be careful as like so many things, they are not made like they used to be. The last one I tried failed early and left me on the roadside. But anything should work long enough to help you figure out the problem. Good Luck
 
Tkagi, i understood your write up: now many aspects of the problem are clear for me;

do you think that the "pierburg style" pump (the one of the ebay link) let flow the gas when in off mode (mechanic pump feeding the carb)? if yes i can try the "in series" setup (tank\filter\pierburg pump\mechanic pump\carburetor), so the main use of the elec. pump will be priming (and running only in case of mechanic pump failure)

in this way i think can avoid the security\inertial switch as the elec. pump will be on only for priming and emergency back-home run

i also found the attache scheme in an italian forum: it's more "complete" but also more complicated to build (and there is no security crash switch)
pompa eletrica.jpg


sdoppiatore: T joint tube
valvola unidirezionale: one way valve
rubinetto manuale: manual open\close cock
 
The 128 tank is under the trunk floor so I don't see an easy way to locate the pump above the tank. On 124 spiders we located the electric pump next to the gas tank in the trunk and usually located even or just above the top of the tank with no problem.
 
I think that the diagram is interesting, but I don't think it means to put it over the tank, just the way it is drawn. Fiat mounts them about level with the tank and they pull the fuel from the top. As carl said, it should work above the tank, but there is no place. I would not put it in the truck for safety. ghostdancing, can you post a picture of the area in front of the tank under the car? It would not be too hard to fabricate a mount for an electric pump. Could be all bolt on and removed it you don't want to use it.
But we are getting away from your issue. Any carb equipt car will suffer vapor lock if the under hood temperature are excessive. I have not followed your posts about your coupe. Has it been hopped up a bit? Any increase in hp results in more heat. My 128's have always had a thermo insulater under the carb. Does yours have that? Is the air cleaner stock? Is there a place to mount the stock sensor to run the fan on shut down? Is the engine operating at normal temperature? My 1300 runs just under the middle of the gauge, fan comes on just about the middle and goes off after barely a minute, and the gauge is back just under the middle. I know there are no actually marks on the gauge, but it seems correct. I think years ago I did check the temperatures with an infra-red gun and it was right where I thought it should be.
I don't mean to be wordy, but I have been around a lot of different cars and made my living repairing cars and there are many different things to consider here. For example, your car has a mechanical pump. How old is it? The mechanical pumps use a diaphragm that will stretch and internal linkages that wear after years of use. The fuel is "lighter" when the engine is hot and is harder to pump with an older worn pump. That restriction piece in the return line comes into play here, if you think about it. To make things worse, replacement parts can be terrible and fool you into thinking a problem is something else. When I first recommended a primer pump was because I was thinking about my old Studebakers. Some of us old farts like to keep things as they were, so some go to the trouble to try and use what was stock and use something like an electric primer pump to get things working and yet leave things mostly original, when maybe the smart and practical thing to do would be to just block off the pump and use an electric pump. Also, old cars like my Studebakers usually don't have that handy return line to bleed off excessive pressure
So, to keep it simple, maybe you get some type of electric pump, hook it up as best you can, wire to a switch and drive the little guy and when it won't start, try priming the carb with the electric pump. If that works, then we can consider how and where you mount it permanently. There could be other things going on, but maybe just try that. If your car was sitting in my driveway, I'd fix it for you. Let us know and good luck
 
well, about the condition of my mechanic pump i have to say that i didn't care of it since when i bought the car (last september, in the meanwhile i made about 3k km with the 128); have to say also that when my mechanic guy removed the oil sump, exposing the internals, said: the cam that acts on the fuel pump it's rather worn.. but nevermind, no problem at all.

in wintertime (i'm talking about mediterranean winter: no snow or ice here, temperature is around 10 °C) no problems: when starting the car after say 10 - 15 days form the last ride, some time is needed to pump the fuel, but when the 128 is used everyday she fires up instantly, so the problem showed up in these hot (30 °C and more) days

water temp gauge: it works, yes but i got not so much confidence in its reading: in wintertime is always on the cold side, now is in the middle, but the rare auto kick in fan events where always when the gauge was before the middle..i do have the manual fan switch , and i use it often (hills\traffic stops).. dont wait to see the gauge ater the middle (hot side)

i guess the correct behaviour of a fuel gauge should be: cold start, then after few kms become 90 °C, here the thermo valve opens, so the gauge drops when water start to circulate in the radiator, then again around 90 °C: it's exactly the behaviuor showed by my other car (1993 fiat cinquecento 899 cc pushrod)

in the 128 i never had this, probably i should have a look in the thermo valve..anyway never had overheating problems, the fluid level does not drop in his tank (i only once added some cc of distilled water, so far)

electro pump positioning: what about the right well in the trunk (where there is the filling tube)? the undercarriage zone is more exposed to water, dirt etc. and there is also the leaf spring.
 
Another check is when you go for a hot weather restart, remove the top of the air filter and with the engine off work the throttle linkage by hand while you look into the carburetor throat. You should see a squirt of gas from the accelerator pump when you work the throttle by hand as if you were stepping on the gas pedal. If no gas squirts out then you have no gas in the float bowl and you can continue on with the assumption you are cooking the gas out of the carb. As a data point you could also do this to a cold engine so you can see what that squirt of gas is supposed to look like.
 
Good advice from Carl. Here is a picture of my fuel pump under the car. Hope this works. I've never up loaded pictures before. If you decide to mount one down there, that is the way it could look. . If you want to do some technical checks, get a pressure and volume test on your pump when it is hot. Also a vacuum test from the intake of the pump. Be careful with spilled fuel. Good luck.
 

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tkagi, you also deleted the OEM pump, correct? on another forum of fiat enthusiast (T124 aussie forum) another friend says he mount the facet pulse pump in line (without removing the OEM pump), and wiring it for continous flow (ignition key on)..

do you have an inertial switch or other security system (i mean in case of crash, intended to stop the gas flow)?
 
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