Technical New Carb, new ignition points - still struggling to start without choke

[Toshi 975]

That float looks to be lifting a little too high in the float chamber to me. The jet you could not remove is the main jet. You should be able to shift it with a long well fitting screwdriver or at the very least get a piece of wire into it to make sure it is clear. I use a piece of steel guitar string. Or you could get a can of carb cleaner or WD 40 to give it a blast if it has the tube on the nozzle. You should see the fluid show in the carb Venturi when you do this.

 

[bugsymike]

I am sure some one may correct me but isn't the jet at the bottom of float chamber, that you cannot, remove actually the main jet, so if nothing else I would want to check it was clear and the actual jet size as I understand this carb design was used on several different capacity engines and make of vehicle.

 

[Toshi 975]

I am sure some one may correct me but isn't the jet at the bottom of float chamber, that you cannot, remove actually the main jet, so if nothing else I would want to check it was clear and the actual jet size as I understand this carb design was used on several different capacity engines and make of vehicle.

Hi Mike, just to get the record straight you are quite right on the first point, that indeed being the main jet. On fitment as far as I am aware the Weber 28IMB carbs were only ever fitted to the 126 engines but went through various stages of evolution in about a 28 year period starting with the 594cc 1st series126 models In 1972. The Fiat 500R models that shared the same engine and ran in parallel had a restricted Weber 24IMB because Fiat did not want the old 500 to be faster than the new 126.
Out of interest the 500 range apart from the 500R despite having different carb variations retained exactly the same jets & specifications, only the sport models were different.

 

[fiat500]

This is how I did it in 2014. I think the last time I set one up I used plastic, building spacers that come in different mm sizes.

 

[bugsymike]

Hi Mike, just to get the record straight you are quite right on the first point, that indeed being the main jet. On fitment as far as I am aware the Weber 28IMB carbs were only ever fitted to the 126 engines but went through various stages of evolution in about a 28 year period starting with the 594cc 1st series126 models In 1972. The Fiat 500R models that shared the same engine and ran in parallel had a restricted Weber 24IMB because Fiat did not want the old 500 to be faster than the new 126.
Out of interest the 500 range apart from the 500R despite having different carb variations retained exactly the same jets & specifications, only the sport models were different.

Thanks for that, what was odd that when I looked up for another guy in the States re jetting a 500, the model of carb he quoted had been used in a variety of larger engined four cylinder, older vehicles including the jeep I mentioned with much larger jets, but similar choke size. His also was a brand new pattern carb, which I am guessing, but could have been Chinese. Did they fit a Solex version on some early models?

 

[Toshi 975]

Thanks for that, what was odd that when I looked up for another guy in the States re jetting a 500, the model of carb he quoted had been used in a variety of larger engined four cylinder, older vehicles including the jeep I mentioned with much larger jets, but similar choke size. His also was a brand new pattern carb, which I am guessing, but could have been Chinese. Did they fit a Solex version on some early models?

None of the standard 500 and 126 air cooled models started life with anything other than the Weber carbs already mentioned but there were a number of variations available as aftermarket tuning mods or uprated carbs on variations like the Giannini versions.

The water cooled 126 Bis was fitted with a twin choke downdraught carb , Weber 30DGF. The similar code as the carb fitted to the Panda 30 but the Bis had restricted venturis. The twin choke Weber fitted to the Panda was superseded by a similar Solex. The Weber 30DIC is a tuning mod that has been used for many years with a suitable manifold.

Weber 30DGF on left, 30DIC on right, these two carbs along with the Solex are the only carbs I know of that share the same flange size mounting.
Variations or the 30DGF were also fitted to the Willis Jeep and some Citroens.

 

[The Panda Nut]

Just my thoughts. Its set too lean. Its telling you it wants less air / more fuel at start up. Check the air cleaner is sealed properly and not allowing excess air in.

I would also give the distributor a good clean-out and check its vacuum advance is functioning too.

As has been said it may be down to fettling, particularly as the engine is a hybrid.

Has the fuel you used changed recently?

 

[Cornish Ian]

Its a Spanish brought from an official Weber reseller in the USA. The car ran fine it’s the starting that’s the issue.
I’m trying to think what I could check without taking the carb apart. I’m thinking of starting with making sure there are no gaps in the gaskets, with some tape.

Many years ago I had similar symptoms when a small piece of the inlet manifold gasket went missing.
Good luck with it.

 

[bugsymike]

None of the standard 500 and 126 air cooled models started life with anything other than the Weber carbs already mentioned but there were a number of variations available as aftermarket tuning mods or uprated carbs on variations like the Giannini versions.
View attachment 419980
The water cooled 126 Bis was fitted with a twin choke downdraught carb , Weber 30DGF. The similar code as the carb fitted to the Panda 30 but the Bis had restricted venturis. The twin choke Weber fitted to the Panda was superseded by a similar Solex. The Weber 30DIC is a tuning mod that has been used for many years with a suitable manifold.
View attachment 419981View attachment 419982
Weber 30DGF on left, 30DIC on right, these two carbs along with the Solex are the only carbs I know of that share the same flange size mounting.
Variations or the 30DGF were also fitted to the Willis Jeep and some Citroens.

I have been trying to find the thread , it was an American on Fiat Forum having jetting issues with a Solex PBIC 32 carb on his 500 and when I checked online the carb was used on some CJ jeeps and also Citroen Traction Avants I believe, so a variety of jetting used for those, although as you say not a original fitting for a 500 aas far as you know. From memory he was some where high up near the snow line so maybe it was a mod someone had fitted?

 

[Toshi 975]

I have been trying to find the thread , it was an American on Fiat Forum having jetting issues with a Solex PBIC 32 carb on his 500 and when I checked online the carb was used on some CJ jeeps and also Citroen Traction Avants I believe, so a variety of jetting used for those, although as you say not a original fitting for a 500 aas far as you know. From memory he was some where high up near the snow line so maybe it was a mod someone had fitted?

That was the standard carb on the Giannini 35hp 590cc GT Special.

 

[turbo500]

Just my thoughts. Its set too lean. Its telling you it wants less air / more fuel at start up. Check the air cleaner is sealed properly and not allowing excess air in.

I would also give the distributor a good clean-out and check its vacuum advance is functioning too.

As has been said it may be down to fettling, particularly as the engine is a hybrid.

Has the fuel you used changed recently?

What's the best way to clean the dizzy? and can it be done in place or does it need to come out?


@peter, that's very smart, I hadn't though about measuring it that way.

I'll try and get to the main jet as well just to remove any chance of the carb being the issue moving forward.
Just to make sure, the correct starting procedure is always using the choke for a few seconds?

Also, another forum member mentioned that maybe the sparks are wrong, I'm pretty sure I've been using the NGK BP6HS plugs, and I noticed the 126 says to use the BP7HS. Until now the BP6HS worked fine (although I admit I've never done many miles with the car in the last years), I don't know if it would make a difference to switch?



Thank you all for your contributions, hopefully I can make the most of them and get the car to start

 

[dangfiat]

What's the best way to clean the dizzy? and can it be done in place or does it need to come out?


@peter, that's very smart, I hadn't though about measuring it that way.

I'll try and get to the main jet as well just to remove any chance of the carb being the issue moving forward.
Just to make sure, the correct starting procedure is always using the choke for a few seconds?

Also, another forum member mentioned that maybe the sparks are wrong, I'm pretty sure I've been using the NGK BP6HS plugs, and I noticed the 126 says to use the BP7HS. Until now the BP6HS worked fine (although I admit I've never done many miles with the car in the last years), I don't know if it would make a difference to switch?



Thank you all for your contributions, hopefully I can make the most of them and get the car to start

I too have been having problems with my '67 500F. I've been able to start OK (with choke for a bit), but it would stutter and cutout when I gave it throttle. Thanks to the good folks on this forum, I seem to have cracked the code! What I did:
1. Complain a lot, drink some wine/beer... gripe about it some more... play a few video games to relieve Fiat based rage
2. Replace all Ignition components (points/capacitor/leads/coil)
3. Try to sell the car to my neighbor after it still won't rev. Neighbor's dad tells me to stop trying to get his kid to buy my car
4. Break out the timing light, make sure it's timed correctly at the 1600 RPM idle. Still have troubles
5. Finally pull the carb and replace the jets, idle screw, gaskets and the spacer. Spray out the emulsion tube/etc with carb cleaner
6. Wait for the torrential California rains (surprise!! We're soggy here in Nor Cal the year!!)
7. Replace carb, making sure all is tight/sealed
...............
8. Forget to reconnect the fuel: spray it everywhere.. whoops!
.............
9. After 30 seconds of cranking with the choke on, it fires up and idles well with a few hickups
10. Drop the choke after 20seconds or so and DANGIT!!! THE CAR REVS!!!!!!!!!!!!
............
11. Drive around the neighbor hood like a madman grinning from ear to ear! Take the win! Kiss the wife! Drink a beer! Yay!

There are still some problems:
- the throttle sticks at wide open. Don't think it's the butterfly but the linkage somewhere (didn't before I rebuilt and I didn't touch the butterfly)
- Pops when I shut it down, going to double check the timing when I get idle adjusted
- See above, need to adjust idle after I readjust the timing... it's a recursive process

TLDR: Go back to the basics. If the carb is new, and the timing is OK. Just start it on the choke (a very normal occurrence, even EFI cars pump a little extra fuel in when it's cold (even on a warm day). Try to drop the choke after 20sec or so and see what happens

Also, don't give up. It'll work. This is a very informative and friendly forum, and they'll get your car going in the end

Good luck and let me know if I can help

Daniel

 

[the hobbler]

Update on this since it's been a few weeks and didn't get round to it until now.

I decided to remove the top of the carb because all signs point to that (I've checked coil, cleaned sparks, charged battery, rechecked points). Upon removing it there was a nice surprise covering the starter valve (looks to be some piece of extra gasket (Remember this is a brand new Spanish made weber).
I then checked all the jets, and nothing seemed to be obstructed. There was some gas in the carb, so I dried that out, and removed the trace sediments, the only one I couldn't get to is the one at the bottom of the float chamber.

Before starting it again, I'm going to measure the carb float to make sure; for the 28IMB its 8mm closed and 16mm open right? (measurement should include the gasket and closed is pushing the float towards the gasket, and open is it just touching the ball bearing of the inlet jet)

View attachment 419927
View attachment 419928
View attachment 419929

You don't 'push' the float towards the needle-valve for the 'minimum' adjustment----you just hold the carb. cover in a vertical position and it should just 'hang' at the correct measurement (8mm)

 

[the hobbler]

You don't 'push' the float towards the needle-valve for the 'minimum' adjustment----you just hold the carb. cover in a vertical position and it should just 'hang' at the correct measurement (8mm)

Another way to check the adjustment of the float, is to use the appropriately sized drill bit---slide the shank of it gently between the float and the needle-valve

 

[the hobbler]

Another way to check the adjustment of the float, is to use the appropriately sized drill bit---slide the shank of it gently between the float and the needle-valve

Lesson of the day---check brain and finger operation before you press the 'reply' button----you slide the drill bit between the GASKET and the float. Sorry about that--DOH! Put it down to the fact that I haven't had my porridge yet

 

[turbo500]

I too have been having problems with my '67 500F. I've been able to start OK (with choke for a bit), but it would stutter and cutout when I gave it throttle. Thanks to the good folks on this forum, I seem to have cracked the code! What I did:
1. Complain a lot, drink some wine/beer... gripe about it some more... play a few video games to relieve Fiat based rage
2. Replace all Ignition components (points/capacitor/leads/coil)
3. Try to sell the car to my neighbor after it still won't rev. Neighbor's dad tells me to stop trying to get his kid to buy my car
4. Break out the timing light, make sure it's timed correctly at the 1600 RPM idle. Still have troubles
5. Finally pull the carb and replace the jets, idle screw, gaskets and the spacer. Spray out the emulsion tube/etc with carb cleaner
6. Wait for the torrential California rains (surprise!! We're soggy here in Nor Cal the year!!)
7. Replace carb, making sure all is tight/sealed
...............
8. Forget to reconnect the fuel: spray it everywhere.. whoops!
.............
9. After 30 seconds of cranking with the choke on, it fires up and idles well with a few hickups
10. Drop the choke after 20seconds or so and DANGIT!!! THE CAR REVS!!!!!!!!!!!!
............
11. Drive around the neighbor hood like a madman grinning from ear to ear! Take the win! Kiss the wife! Drink a beer! Yay!

There are still some problems:
- the throttle sticks at wide open. Don't think it's the butterfly but the linkage somewhere (didn't before I rebuilt and I didn't touch the butterfly)
- Pops when I shut it down, going to double check the timing when I get idle adjusted
- See above, need to adjust idle after I readjust the timing... it's a recursive process

TLDR: Go back to the basics. If the carb is new, and the timing is OK. Just start it on the choke (a very normal occurrence, even EFI cars pump a little extra fuel in when it's cold (even on a warm day). Try to drop the choke after 20sec or so and see what happens

Also, don't give up. It'll work. This is a very informative and friendly forum, and they'll get your car going in the end

Good luck and let me know if I can help

Daniel

Haha Daniel, I think I would have given up today if it wasn't for reading you post last night. I can't believe it but it actually turned on. Funny story is I spent 2 hours checking the carb, pulled it off completely, check the jets again, checked the points, checked the spark plugs with a multimeter, checked the voltage regulator (found a dodgy wire but no clue as what it's for, hanging on by a thread for now), checked fuel flow, etc.
I cranked it for a good 30 seconds on several occasions, and nothing happened. I have a battery charger that I resorted to 3-4 times today. Eventually I started filming a video so I could post it here to see if while cranking anything stood out to you guys, and it started


I spent about 15 minutes trying to get it to run smoothly, but I'm not sure I've gotten there. In an effort to reduce the sooty sparks I had with the previous carb, I found this guide from weber https://www.carburetion.com/Weber/adjust.htm, and it helped, but I don't know if there's a better way.

I turned the mixture screw fully closed (clockwise) and it actually sped up the engine and was running fast. So I backed it out, and I went too far because when accelerating the exhaust gasses were slightly dark. So I ended up about a turn or so from closed (turning counterclockwise).
Idle I followed the guide of turning clockwise until it starts to run rough, and then back it out 1/4 to 1/2 turn.
Throttle linkage screw, turned out until generator light starts to appear on the dash.

The problems I'm finding, is when moving the accelerator linkage, the initial acceleration I notice a few hiccups, then it rises smooth. Letting go of the accelerator it goes back down to idle, and sometimes wants to turn off. I also noticed a few spits and pops.



The biggest win is that it actually turned on, and seems to turn on after a half second or so, compared to before when it used to crank for a few seconds with the 28imb. I think I will attempt to adjust valves to see if that improves, but first want to get her going.
Anyway, a little picture dump, maybe someone can spot any issues (anyone know what the green wire on the left most voltage regulator coil thing would be?it goes into the passenger compartment?)

 

[myoshik]

(anyone know what the green wire on the left most voltage regulator coil thing would be?it goes into the passenger compartment?)

I think the green wire should connect to the generator warning light on the speedometer.

 

[turbo500]

I think the green wire should connect to the generator warning light on the speedometer.

Thanks, am I safe working on the voltage regulator wires with the car off, or should I disconnect the positive of the battery?

 

[myoshik]

Unless I'm fault finding where a current is needed, I would always recommend the battery be disconnected. FYI, the thick brown wire (which connects to the red wire) on terminal 30 of the regulator is essentially a "live" wire coming right off the battery, via the starter motor - if that inadvertently comes into contact with ground it could cause trouble. The red wire connected to it generally powers all the devices that work even while the car is switched off (such as the dome light, the horn, starter motor, etc.).

 

[the hobbler]

Unless I'm fault finding where a current is needed, I would always recommend the battery be disconnected. FYI, the thick brown wire (which connects to the red wire) on terminal 30 of the regulator is essentially a "live" wire coming right off the battery, via the starter motor - if that inadvertently comes into contact with ground it could cause trouble. The red wire connected to it generally powers all the devices that work even while the car is switched off (such as the dome light, the horn, starter motor, etc.).

With regard to mixture adjustment---some times it works better if, when you have got the engine 'sort-of' idling OK, you turn the mixture screw ANTI-CLOCKWISE (i.e. OUT) until it runs a bit rough and then turn the screw back in (clock-wise) until it smooths out