Technical Carburetor Problems

[RobertM]

Hello everyone welcome to the next installment of 'Man tries to drive 53 year old car thousands of miles and has to troubleshoot things a lot'. Here is my current predicament. I swapped our carb out with a brand new Webber 26, without realizing that we had a 28 on the car already, so we're a little down on power but I can't complain too much about that because the car is running great.... for about 150 miles. Then we get a constant missfire with the car under load and it won't idle. So we limp it to the nearest auto parts store and I spend the next 6 hours in the parking lot taking everything apart and putting it all back together with new parts. I replaced the fuel pump, the plugs (and pretty much everything else in the ignition system was replaced within the past 500 miles at this point) I try a new coil, which ironically was bad out of the box. Finally when I'm about to give up I pull the new carb apart and take come carb cleaner and blow it through all the jets to see if that does anything for me. Sure enough I put it back together and the thing is running great, there was actually a bit of dirt inside of the chamber where the float lives inside of the carb so it actually made sense. I then get back to driving the car, and we end up covering a good 500 or 600 miles with a couple minor hiccups along the way but nothing really of note. Then out of nowhere the miss comes back, so I take the carb off and clean it again, put it back on and if anything it's gotten worse. So we hop in and try to drive it a couple miles hoping that whatever was giving us our issue might clear it's way out, but no luck there. So we stop again, I clean the carb again, reinstall it and now it's running even worse, it wont idle and it's backfiring when I try to give it some revs at idle, but it smells like it's just dumping buckets of fuel into the engine and it's hard to describe but it sounds like it's drowning the engine when I rev it, which we experience the last few times I've cleaned the carb.

All this is to say, towing the car from where we're at will be comically expensive and logistically challenging, it's something that I'm obviously willing to do as I've signed up for this... but I still need to get the car fixed whenever I get home so there's no since in not trying to figure it out where I am now, I will be here for around a week.

My plan is to get a rebuild kit for the webber 28 that we still have and go through it and make sure everything is good. and assuming that we get it working on the car again then I can pull apart the 26 as far as I possibly can and clean the crap out of everything and keep it in the car as a backup. I also plan on getting the smallest micron inline filter that I can (to put next to the tank, not next to the engine) and I'm probably going to buy a new tank for it unless I can find someone to clean the tank that's currently in it for a reasonable price and reasonably quickly.

Does anyone have any suggestions as to why the carb seems to keep sticking open and is dumping fuel into the engine, or if anyone has experienced anything like this themselves? I'll also note I've gone through and checked the ignition system and when I pull the plugs and rest them on the exhaust manifold for a ground I get a great spark on both of them consistently so I am 99.999% confident that we do not have any ignition systems issues... currently.

 

[bugsymike]

So a good inline filter, a thorough clean of carb, then check float height is correct and also when carb off, using a clean tube attached to the carb inlet (unless you want to taste petrol for the next week) blow through and gentle turn the carb over to check float jet flows and shuts off easily when carb is up side down and then flow returns as carb correct way up.
With older vehicles , a good quality replacement fuel tank is a sound idea. Then fuel line blown through to clear any residual muck, plus fuel pump cleaned also, then fingers crossed.
By the way was it you, on an earlier post that I advised regarding dirty fuel in old fuel tanks?
Just a thought and if it can be safely fitted , what about a marine plastic boat fuel tank under the bonnet as a temporary fix, they can hold around thirty litres and most boating /chandlers stock them . Though remember to open the vent in cap. You could run a new rubber pipe directly to the pump. Obviously make sure of all the safety aspects!

 

[RobertM]

So a good inline filter, a thorough clean of carb, then check float height is correct and also when carb off, using a clean tube attached to the carb inlet (unless you want to taste petrol for the next week) blow through and gentle turn the carb over to check float jet flows and shuts off easily when carb is up side down and then flow returns as carb correct way up.
With older vehicles , a good quality replacement fuel tank is a sound idea. Then fuel line blown through to clear any residual muck, plus fuel pump cleaned also, then fingers crossed.
By the way was it you, on an earlier post that I advised regarding dirty fuel in old fuel tanks?
Just a thought and if it can be safely fitted , what about a marine plastic boat fuel tank under the bonnet as a temporary fix, they can hold around thirty litres and most boating /chandlers stock them . Though remember to open the vent in cap. You could run a new rubber pipe directly to the pump. Obviously make sure of all the safety aspects!

You may have mentioned old dirty fuel tanks, I do remember that. The first time I had the carb apart the float was still good (it only has 700 miles on it now, and it was a brand new one not a reman). I have time to get a new tank ordered, or time to find someone to properly clean it out. and then I plan on replacing all the old rubber lines and blowing out any of the metal ones. I might try to get my hands on a good metal or glass inline filter to put in the factory location in the engine bay after the fuel pump as well. It's all odd because it's acting like the float isn't functioning properly but on two different carbs. It makes me wonder if I'm somehow making an error in the way I'm installing the top plate causing it to get stuck, but it doesn't seem like it would be something that's easy to mess up.

 

[bugsymike]

After rebuilding carbs I always used to do the trick of blowing to check the float valve was working correctly, although nowadays I get someone else to do it to avoid the taste.
I can't remember specifics re those carbs, but over the years have done so many I always check things like that.
There are Forum members here who will have precise details on setting them up.

 

[the hobbler]

After rebuilding carbs I always used to do the trick of blowing to check the float valve was working correctly, although nowadays I get someone else to do it to avoid the taste.
I can't remember specifics re those carbs, but over the years have done so many I always check things like that.
There are Forum members here who will have precise details on setting them up.

Silly question I know, but have you tried running the car with the fuel-tank cap OFF? It is not unknown for the top of an old cap to have the breather gum up, thereby the tank is slowly bulding up a vacuum which the pump is trying to work against. I have also known little pieces of muck get stuck in the idle jet on these carbs---whorth while giving that one a good blow out. Also,check that your 'choke' isn't staying on---this will cause the same symptomsas you are suffering. What colour are your spark plugs? From your description, it does sound like you are suffering a fuel problem. Might be worthwhile re-checking your tappet clearances---they are much more prone to closing-up on a 500 than on the later 126 engines---don't know why, but is so.

 

[RobertM]

Silly question I know, but have you tried running the car with the fuel-tank cap OFF? It is not unknown for the top of an old cap to have the breather gum up, thereby the tank is slowly bulding up a vacuum which the pump is trying to work against. I have also known little pieces of muck get stuck in the idle jet on these carbs---whorth while giving that one a good blow out. Also,check that your 'choke' isn't staying on---this will cause the same symptomsas you are suffering. What colour are your spark plugs? From your description, it does sound like you are suffering a fuel problem. Might be worthwhile re-checking your tappet clearances---they are much more prone to closing-up on a 500 than on the later 126 engines---don't know why, but is so.

I will be checking the clearances in a few days, all but one valve looked about right last time I checked, one exhaust valve was slightly too tight but I didn't have the correct wrench to fix it at the time. I have tried running the car with the cap off the tank, the inside of my tank was in fact pretty grimy and rusty so I pulled the trigger on getting a new tank and I will be replacing the tank, all the rubber lines, and relocating the fuel filter back into the engine bay, I got a metal one so no worries of it splitting. the plugs look pretty good but are a bit black. Also the trick of blowing out all the jets with carb cleaner was working well enough but I had to do it frequently enough that I wasn't even reconnecting the choke. I've also replaced the plugs roughly 5 times in the process of driving 2,400 miles they're cheap and easy enough that I keep doing it to rule them out as a possible problem.

As well as replacing the fuel system I ordered a rebuild kit for my Webber 28 carb so I will be taking it apart and cleaning it all up as well as taking apart my new 26 carb to clean everything, and my fuel pump has around 500 miles on it so I'll be leaving it alone for now.

 

[the hobbler]

I will be checking the clearances in a few days, all but one valve looked about right last time I checked, one exhaust valve was slightly too tight but I didn't have the correct wrench to fix it at the time. I have tried running the car with the cap off the tank, the inside of my tank was in fact pretty grimy and rusty so I pulled the trigger on getting a new tank and I will be replacing the tank, all the rubber lines, and relocating the fuel filter back into the engine bay, I got a metal one so no worries of it splitting. the plugs look pretty good but are a bit black. Also the trick of blowing out all the jets with carb cleaner was working well enough but I had to do it frequently enough that I wasn't even reconnecting the choke. I've also replaced the plugs roughly 5 times in the process of driving 2,400 miles they're cheap and easy enough that I keep doing it to rule them out as a possible problem.

As well as replacing the fuel system I ordered a rebuild kit for my Webber 28 carb so I will be taking it apart and cleaning it all up as well as taking apart my new 26 carb to clean everything, and my fuel pump has around 500 miles on it so I'll be leaving it alone for now.

Whilst I can't argue that the "non plastic" fuel filter won't split, putting 4th filter into the system could be counter-producrive fuel-low-wise

 

[the hobbler]

Whilst I can't argue that the "non plastic" fuel filter won't split, putting 4th filter into the system could be counter-producrive fuel-low-wise

Whilst I can't argue that the "non-plastic" fuel-filter won't split, putting a 4th filter into the fuel system could be counter-productive fuel-flow-wise. You already have 3 filters in the system----the fuel-tank pick-up (have you checked that the filter on the bottom of the tank-unit isn't blocked?), the top of the fuel-pump and lastly, a filter in the top of the carburettor. You do NOT need a 4th filter!

 

[RobertM]

Whilst I can't argue that the "non-plastic" fuel-filter won't split, putting a 4th filter into the fuel system could be counter-productive fuel-flow-wise. You already have 3 filters in the system----the fuel-tank pick-up (have you checked that the filter on the bottom of the tank-unit isn't blocked?), the top of the fuel-pump and lastly, a filter in the top of the carburettor. You do NOT need a 4th filter!

I think I'm a little confused, I have not checked the filter in the tank. That's probably a good idea. The part I'm a little confused about is the fuel pump and carb filters. On the Weber 28 and 26 the fuel line goes directly into the chamber with the float so I'm not sure where the filter would go there, and I haven't pulled apart the fuel pump but I'm not sure where a filter would be inside of it?

 

[the hobbler]

I think I'm a little confused, I have not checked the filter in the tank. That's probably a good idea. The part I'm a little confused about is the fuel pump and carb filters. On the Weber 28 and 26 the fuel line goes directly into the chamber with the float so I'm not sure where the filter would go there, and I haven't pulled apart the fuel pump but I'm not sure where a filter would be inside of it?

There is normally a small filter under the top cover of the pump and also under where the fuel line goes into the top of the carb.The filter in the tankis at the bottom of the fuel-pick-up tube---normally a long filter about 2-1/2tp 3 inches long.

 

[bugsymike]

How about the float height and operation of carb, obviously dirty fuel is a major issue, but wouldn't account for sooty plugs.

 

[Goldnrust]

How about the float height and operation of carb, obviously dirty fuel is a major issue, but wouldn't account for sooty plugs.

To add to this, we know the engine is modified and the 28 carb is not standard, so it's quite possible that the jetting could be wrong in the carb. Not so easy to solve on the road, but a clean carb with float height set is a good start!

I'm hopeful for you (Robert) that changing the fuel tank will solve the root cause of these on going issues. From what you've described, despite the extra filers, dirt was making it way into the carb repeatedly, and there were potentially other blockages. With a new tank, new rubber lines (I would advise blowing out the hard lines while you're at it!) and a cleaned carb then that's got to be a big step forward.

 

[RobertM]

How about the float height and operation of carb, obviously dirty fuel is a major issue, but wouldn't account for sooty plugs.

For whatever reason it seems like the miss is caused by having too much fuel, you can smell it and even some drops get sprayed out of the exhaust. like the float is getting stuck down. but we have had this issue on two different carbs now.

 

[RobertM]

To add to this, we know the engine is modified and the 28 carb is not standard, so it's quite possible that the jetting could be wrong in the carb. Not so easy to solve on the road, but a clean carb with float height set is a good start!

I'm hopeful for you (Robert) that changing the fuel tank will solve the root cause of these on going issues. From what you've described, despite the extra filers, dirt was making it way into the carb repeatedly, and there were potentially other blockages. With a new tank, new rubber lines (I would advise blowing out the hard lines while you're at it!) and a cleaned carb then that's got to be a big step forward.

We're also going to be rebuilding the carb so hopefully that clears up any of the issues. Now that I have two of them I hope to get both carbs in tip top shape so if I need to swap them around while on the road it will be quick and easy.

 

[RobertM]

Now to anyone who knows, this is a completely different topic, but I don't want to start another thread about it. how many gaskets is it possible to replace in the transmission without removing it or the engine. We have a pretty massive leak that I can't pinpoint but we loose about a quart of transmission fluid every 1,000 miles. I've ordered a gasket kit for it and I want to try to replace all the easy-to-get-to gaskets but I'm also considering removing the transmission alone, or more realistically the engine and transmission to get at everything. I have a good garage that I can work in and the parts for it are going to get here Thursday, and I'm not set to leave until Saturday morning. how long would you guys say an engine / transmission removal would take versus just trying to wiggle the transmission out. Or even removing the engine and replacing the transmission gaskets with the transmission still in place?

 

[bugsymike]

Now to anyone who knows, this is a completely different topic, but I don't want to start another thread about it. how many gaskets is it possible to replace in the transmission without removing it or the engine. We have a pretty massive leak that I can't pinpoint but we loose about a quart of transmission fluid every 1,000 miles. I've ordered a gasket kit for it and I want to try to replace all the easy-to-get-to gaskets but I'm also considering removing the transmission alone, or more realistically the engine and transmission to get at everything. I have a good garage that I can work in and the parts for it are going to get here Thursday, and I'm not set to leave until Saturday morning. how long would you guys say an engine / transmission removal would take versus just trying to wiggle the transmission out. Or even removing the engine and replacing the transmission gaskets with the transmission still in place?

If oil leaks are the only reason , personally I would steam clean the transmission, road test and put it back on the ramp straight away and identify the source.

 

[RobertM]

If oil leaks are the only reason , personally I would steam clean the transmission, road test and put it back on the ramp straight away and identify the source.

I don't think I'll have the ability to do that before I set off unfortunately, as the car doesn't run right now and I wont have it back up and running until the night before I leave. I can however do that once I get back home, so maybe the best solution is to run a thicker gearbox oil like a 80-145 instead of the 75-90. It typically only leaks when it's hot. A couple drips per day when cold or a puddle within 5 minutes when warm.

 

[bugsymike]

I don't think I'll have the ability to do that before I set off unfortunately, as the car doesn't run right now and I wont have it back up and running until the night before I leave. I can however do that once I get back home, so maybe the best solution is to run a thicker gearbox oil like a 80-145 instead of the 75-90. It typically only leaks when it's hot. A couple drips per day when cold or a puddle within 5 minutes when warm.

I can see the logic of thicker oil, but probably best to stay with recommended grade.

 

[Goldnrust]

For whatever reason it seems like the miss is caused by having too much fuel, you can smell it and even some drops get sprayed out of the exhaust. like the float is getting stuck down. but we have had this issue on two different carbs now.

To have the same issue on two different carbs does suggest the issue is elsewhere. Fuel spitting from the exhaust definitely isn't right though...

Transmission/Gearbox wise, there are seals round the drive shafts and the input shaft. I can't remember about the gear shift shaft or not. There is no gasket between the bell housing and the rest of the gearbox, just some liquid gasket.

The drive shaft seals are the only ones I think you could do with the engine and box still in the car. If you cleaned up the join externally, you might be able to stem the flow by running some beads of RTV around the outside of the join between the bell housing and rear of the gearbox? If its just a case of keeping the leak more manageable till you make it home?

If you need to do more than that, I would suggest pulling the engine, then the gearbox. It'll be the easiest engine removal you've ever done. Essentially you put the car on jack stands, pop a jack under the engine, remove the fuel line/wiring/cables/air intake hose, remove the starter, remove the 4 bolts holding the rear valance/cross member on to the body, remove the bolts holding the engine to the gearbox and slide the engine out. Took me ~45mins to pull the engine last time (2nd time doing it).

From there removing the gearbox is fairly straight forward, unbolting the drive shafts from the wheel hubs, removing gear linkage, and the gearbox mounts.

I'm sure you could remove and install it as one unit, but I can't personally lift the combined unit, whereas I can (just about in the case of the engine!) lift them separately, which just makes dealing with it on my own that much easier.

 

[the hobbler]

To have the same issue on two different carbs does suggest the issue is elsewhere. Fuel spitting from the exhaust definitely isn't right though...

Transmission/Gearbox wise, there are seals round the drive shafts and the input shaft. I can't remember about the gear shift shaft or not. There is no gasket between the bell housing and the rest of the gearbox, just some liquid gasket.

The drive shaft seals are the only ones I think you could do with the engine and box still in the car. If you cleaned up the join externally, you might be able to stem the flow by running some beads of RTV around the outside of the join between the bell housing and rear of the gearbox? If its just a case of keeping the leak more manageable till you make it home?

If you need to do more than that, I would suggest pulling the engine, then the gearbox. It'll be the easiest engine removal you've ever done. Essentially you put the car on jack stands, pop a jack under the engine, remove the fuel line/wiring/cables/air intake hose, remove the starter, remove the 4 bolts holding the rear valance/cross member on to the body, remove the bolts holding the engine to the gearbox and slide the engine out. Took me ~45mins to pull the engine last time (2nd time doing it).

From there removing the gearbox is fairly straight forward, unbolting the drive shafts from the wheel hubs, removing gear linkage, and the gearbox mounts.

I'm sure you could remove and install it as one unit, but I can't personally lift the combined unit, whereas I can (just about in the case of the engine!) lift them separately, which just makes dealing with it on my own that much easier.

To endorse "Goldenrust" comments. If you are going to take the engine/gearbox out, do them seperately. I am closer to 77 than I am to 76, and I can heave an engine out from starting to put it on stands 'till it is on the floor in 1-1/2 hours, but I must admit, it takes a wee bit longer to put it back! Make sure that there is a square of ply (or similar) between the jack head and the sump. Don't forget, if you are going to heave the engine out---disconnect the battery first.
To, again, endorse "Goldenrust", there are only 4 places that the gearbox can seriously leak oil; the 2 drive-shaft boots which CAN be done with the engine and gearbox 'in-situ', the gear-change rod seal at the front of the gearbox which sometimes can be changed 'in-situ'. I say "sometimes" because some gearboxes have a seal that can be removed externally, other 'boxes rely on 'O' rings inside the rear gearbox housing to seal the shaft. Lastly, there is a seal/bush unit INSIDE the bell housing through which the spigot-shaft passes through. If this is the cause of your leak, then the engine will have to come out. The little housing CAN be removed with the gearbox still in the car----but renew the housing COMPLETE (Mr Fiat, in Atlanta, part number---TM-500-047)---removing the seal from the housing can be a "reet booger" of a job! If you are not suffering clutch-slip,I would have thought that the chances of the 'spigot-shaft seal' being the cause of your leak is slim. When you last filled the gear-box, how much oil did you put in the box? The "fill" plug is also the "level" plug---you need to have the car as level as possible when topping-upthe oiland let it drain until it stops coming out---and make sure that the fill/level plug is tight when put back in (you wouldn'tbe the first person to have onlyput the plug back "just over finger-tight"!
To go back to your carb problem---you say that it is so rich that the car smells of petrol----what sort of fuel-pump have you got fitted? Is it the standard pump on the side of the crankcase, or has the previous owner fitted an electric pump? I ask this because the fuel-pump pressure required for the 500/126 engines is only about 2-1/2 psi. The float level should be 7mm; measured by holding the top of the carb vertical and measuring between the gasket and the float. The easiest way to measure the float height is to use a 7mm drill-bit (or the imperial equivalent) between the gasket and the float.
Lastly, could the pump be OVER delivering (if it is the standard mechanical pump). The pumpis actuated by a rod internally coming across the crankcase from the camshaft (small lobe on camshaft) to the pump. This rod should only stick out past ALLthe gaskets and the spacer 1.0mm to 1.5mm at THE START of its movement. The easiest way to measure this is to build up your feeler gauge to 1.5mm (60thou) and then put this against the pump's operating rod---the end of the rod and the feeler-gauge should be level.