Tuning Carb base leak

[FR85]

Hi All,

Previously I had some backfires through the exhaust when I eased up on power or was going down through the gears. I sorted this out with retarding the timing.....or so I thought.
Recently on a drive the car started misfiring, down on power, bucking ect and when that cleared I was back to the backfires.
I quickly redid static timing, going to have a look at this again as it was a bit rushed with the time I had. I'm going to try and move the coil as it's in the firing line of the thermostat opening and it does get hot. Method used was per the 126 Haynes manual, rotor pointed at the engine for cylinder one, 13mm before tdc on the timing marks.

I also noticed fuel bubbling at the base of the carb once I'd shut down the engine, I have a new bakelite spacer to go on it so I'll fit this also. I sprayed some starter fluid at the base and the engine didn't rev up so I don't think air is being pulled in at the base.

So, what else could be causing the backfires on deceleration? Points gap perhaps?
How tight should the 10mm nuts at the bottom of the carb be and after a couple of heat cycles should these be tightened down again?

It's a 650 with a 28 carb running condenser and points and an old Bosch Blue Coil, I've read some horror stories about newer coils so I'm going to try and continue with the old one as it seems good.
I did notice some carbon burns on the centre of the rotor in the cap so I'm thinking my over all issue is spark/ignition. I am lacking a timing light so I'd be heavily reliant on static timing. Car is running and idling perfectly but it's when it's out on a run and things get hot that the issue becomes apparent.

Thanks all!

Gavin

 

[bugsymike]

Air leaks on exhaust can cause an exhaust backfire, most commonly on the over run down a hill.
I would try and get a timing light as retarded ignition can contribute, correct timing is important on any vehicle.
I am old school, so prefer points and condensor ignition systems as they can usually be repaired at the side of the road cheaply unlike electronic systems which often requires a tow truck, so I think you are making the correct decision there personally.
Re carbon burns on centre of rotor arm, I assume the carbon brush on a spring is still in the distributor cap, as that usually makes good contact with the rotor arm so no burns, often just a shiny spot.

 

[FR85]

Air leaks on exhaust can cause an exhaust backfire, most commonly on the over run down a hill.
I would try and get a timing light as retarded ignition can contribute, correct timing is important on any vehicle.
I am old school, so prefer points and condensor ignition systems as they can usually be repaired at the side of the road cheaply unlike electronic systems which often requires a tow truck, so I think you are making the correct decision there personally.
Re carbon burns on centre of rotor arm, I assume the carbon brush on a spring is still in the distributor cap, as that usually makes good contact with the rotor arm so no burns, often just a shiny spot.

I don't think it's in the exhaust, I fitted a new one with gaskets and the black paint turned white with heat and there is no burn or smogging at the joints. Will tighten everything up again.
I had an electronic ignition and it died so like you I said points and condensors are in the car at all times.
I'm going to have a look at getting a cheap and nasty light and see how we go.
I'm also going to get a new coil, cap ect as I genuinely feel the problem is with ignition and spark.
Is there a rough torque spec for the carb and the Bakelite spacer?

I've an 18 month old so it's finding a day to dedicate is the major problem!

Thanks Bugsymike

 

[bugsymike]

Re the exhaust just get a bit of cloth and see if you can stop the engine by holding cloth over tail pipe tight, it usually shows an leaks.
I still have a couple of old timing lights, main thing is a powered one as you get a brighter light and mark your timing points with tippex or white paint to stand out. Personally I have never bothered with ones that alter the advance shown, you can always use a protractor to mark the degrees of max advance if necessary. One point due to lower quality fuel octane rating these days, after setting timing always road test when warm pulling up a hill under load to ensure no "pinking/preignition".
Re the distributor cap, see if the old one has any tracking marks inside or outside where it may be shorting. I don't know if you have a weak heart but I often used to run my hand around the cap and leads whilst running to see if I got a belt from it shorting. We used to have an 80 year old who could stop an old Austin with the visible copper terminals on the leads by putting his hands across all four spark plugs.
Don't know about any torque settings for carbs, I would just run the nuts up , then just a little bit further to compress the gasket slightly, anymore risks distorting the flange. You can always retighten/check in a few days if necessary.
I am past the 18 month olds, the last of my five children were twins which didn't give you a lot of sleep, but they are in their thirties now, so I have seven grandchildren, the youngest of which is roughly 30 months.

 

[FR85]

Re the exhaust just get a bit of cloth and see if you can stop the engine by holding cloth over tail pipe tight, it usually shows an leaks.
I still have a couple of old timing lights, main thing is a powered one as you get a brighter light and mark your timing points with tippex or white paint to stand out. Personally I have never bothered with ones that alter the advance shown, you can always use a protractor to mark the degrees of max advance if necessary. One point due to lower quality fuel octane rating these days, after setting timing always road test when warm pulling up a hill under load to ensure no "pinking/preignition".
Re the distributor cap, see if the old one has any tracking marks inside or outside where it may be shorting. I don't know if you have a weak heart but I often used to run my hand around the cap and leads whilst running to see if I got a belt from it shorting. We used to have an 80 year old who could stop an old Austin with the visible copper terminals on the leads by putting his hands across all four spark plugs.
Don't know about any torque settings for carbs, I would just run the nuts up , then just a little bit further to compress the gasket slightly, anymore risks distorting the flange. You can always retighten/check in a few days if necessary.
I am past the 18 month olds, the last of my five children were twins which didn't give you a lot of sleep, but they are in their thirties now, so I have seven grandchildren, the youngest of which is roughly 30 months.

That's a good call on the exhaust, I'll see if I can kill it with a rag.
I'm not afraid of electric shocks, I work in the live music industry where I seem to average maybe three shocks per year! I did run the car in the dark to see if I could see any arcing but nothing.

On the way from FD Ricambi is:
New Coil (Marelli bk 2)
Cap
Rotor
Plug leads
Carb gasket kit (already have bakelite spacer)
Valve cover gaskets
Exhaust gaskets

I was going for the Black Friday 10% off promo, I entered the code but forgot to press the "gift" button so watch out for that one!

I have points and condensors on the shelf in the garage.

I'm going to try and move the coil to the air filter side also.

An old school mechanic said he'd come and time it for me with his strobe once I have the rest done. Just need to find the time!

 

[Goldnrust]

As well as the ignition checks, I’d consider testing whether it might be running lean on closed throttle, by either richening the idle mixture a bit, or even just pulling the choke a little, and see if that stops the popping on the overrun.

If it does, that might point back to your original idea of air leaks around the carb, or simply that you were a bit lean on the idle mixture.

 

[FR85]

Update to my situation, last night I ran the car and held a damp cloth over the end of the exhaust and it just about killed it so I doubt it's down to leaks there.
Today I fitted the bakelite spacer along with new gaskets and while the carb was off I checked the base for true flatness and alas the base of the carb needs skimming and it's rocky on a sheet of glass.
Also, it's own spacer was a mile out, I thought I had levelled it enough the last time but in comparison to the new one I failed miserably!
It's own carb is a 28/5, I had a rebuilt 28/1 on tye shelf off a spare 600cc lump so while its jetted differently it's base was true so that's now installed, I could be wrong but I'd say the difference will be minimal. It's running on choke but a bit hesitant with the choke off so I need to adjust the idle/mixture a bit. Also gapped the valves while I had the carb off.

I fitted a new cap and rotor also, it's own rotor had blackening on it. I didn't fit a new coil as I'm toying with the idea of moving it away from the stat opening, just need to source a long coil lead.
I didn't look at points or condenser as spark is there and I cant say if the popping has ceased because as mentioned i need to do some carb fettling and it's too wet to bring for a test drive.

Something I was shocked at the other night, I accidentally unplugged my lamp I had over the engine while it was running on fast idle, the headers glow red, didn't expect to see that and I'm delighted I killed the light by mistake, I've a new found respect for those little engines now, they put up with a lot! I've run it in the dark before to look for leaky lightening but I'd never noticed the red pipes.

Final bit of splendid news, I noticed a little bit of an oil weep from behind the the tinware on the thermostat side just above the dipstick so I'm assuming pushrod tubes are on the way out. Pulling the head was inevitable as someone before me rung the no 1 sparkplug hole, drilled/tapped and put a helicoil in. Hence I bought the previously mentioned 600cc engine for the head and I've spotted another 499cc complete engine and box local at nice money so I might pull the trigger on that in the new year. Can never have enough spares.

 

[smart51]

In the 2000s I worked on a rolling road for the Dodge Viper factory. They sit the car on it and test the ABS, then the gearbox, then the engine. Part of the test is driving it at 90MPH for about a minute. The car has side exhausts and is run without the bodywork. The cats glow red, then white, then go sort of translucent. Now that's getting hot.

The rolling road is sat in a pit when installed so the car can drive on it. In our workshop , it sat on the floor for assembly so the car's wheels were about head height. The Americans came over to see it before we shipped it. As I wrote the software, I had to be the test driver. There was a crowd of about 20 watching. After the low speed tests, it was time for the speed run. As I passed 30 MPH, they all took about 3 steps back in unison. Those wheels look fast when your eyes are level with them.

 

[the hobbler]

In the 2000s I worked on a rolling road for the Dodge Viper factory. They sit the car on it and test the ABS, then the gearbox, then the engine. Part of the test is driving it at 90MPH for about a minute. The car has side exhausts and is run without the bodywork. The cats glow red, then white, then go sort of translucent. Now that's getting hot.

The rolling road is sat in a pit when installed so the car can drive on it. In our workshop , it sat on the floor for assembly so the car's wheels were about head height. The Americans came over to see it before we shipped it. As I wrote the software, I had to be the test driver. There was a crowd of about 20 watching. After the low speed tests, it was time for the speed run. As I passed 30 MPH, they all took about 3 steps back in unison. Those wheels look fast when your eyes are level with them.

It would seem that you have the perfect opportunity to build yourself an 'enhanced ' head; 2mm larger inlet valves (and seats), smooth out the both the inlet and exhaust port and match them to the gaskets (smooth on the 'inlet', polished for the 'exhaust') The inlet port can be opened up quite a bit where the carb bolts on and there is a ridge in the inlet port, just behind the valve-seat needs to be removed. Have fun!

 

[fiat500]

Something I was shocked at the other night, I accidentally unplugged my lamp I had over the engine while it was running on fast idle, the headers glow red, didn't expect to see that and I'm delighted I killed the light by mistake, I've a new found respect for those little engines now, they put up with a lot! I've run it in the dark before to look for leaky lightening but I'd never noticed the red pipes.

If you really want to worry, get a thermal-imaging camera on it; this is my exhaust immediately after starting up from cold, having lain idle for two months. (the engine, that is!)

 

[FR85]

At the end of my tether with this yoke now.

I previously mentioned I popped a different carb on this, a 28/1, I had it idling lovely, albeit still backfiring but now it'll only run on choke/starting device.
I gave the carb a couple of taps either side in the event it was a sticky float but no, still the same.
It's now backfiring through the carb and exhaust as on the down run when I gave it a rev from the engine bay I can feel a "put-put-put" on my hand from around the air filter BUT it may have always been doing this unknown to me.

I've checked the points gap and they are about .5mm, been through valve clearance.
I'm going to look at swapping out the condenser and coil as it got new rotor, cap and leads so at least at that point I could say all that end is new and taken care of.

These are a horrible little carb when they want to be, the 30DIC I put on my 850 was less hassle and they are known to have a reputation. If I'd another and a manifold I'd do the same to this and be done with it!

 

[bugsymike]

At the end of my tether with this yoke now.

I previously mentioned I popped a different carb on this, a 28/1, I had it idling lovely, albeit still backfiring but now it'll only run on choke/starting device.
I gave the carb a couple of taps either side in the event it was a sticky float but no, still the same.
It's now backfiring through the carb and exhaust as on the down run when I gave it a rev from the engine bay I can feel a "put-put-put" on my hand from around the air filter BUT it may have always been doing this unknown to me.

I've checked the points gap and they are about .5mm, been through valve clearance.
I'm going to look at swapping out the condenser and coil as it got new rotor, cap and leads so at least at that point I could say all that end is new and taken care of.

These are a horrible little carb when they want to be, the 30DIC I put on my 850 was less hassle and they are known to have a reputation. If I'd another and a manifold I'd do the same to this and be done with it!

It's not "spitting back" through the carb, like a valve not sealing?

 

[FR85]

It's not "spitting back" through the carb, like a valve not sealing?

I'm going to pull the air filter pipe off it and run it and see what it's doing.

At least when it goes it'll be full of new parts!!!

Thanks Mike

 

[FR85]

So tonight I changed out the points, coil and condenser, wouldn't fire. The new points are grounding somewhere because I'm getting continuity when they are open and closed, have had them in and out twice and I cannot see where they are grounding.
I started to question myself on circuits and breaking circuits so I went over to my 850 and started playing with it and sure enough the beep on the meter stopped and started when they opened and closed.

So after halftime the score is, Beru Points 1:0 Gavin and we're not going to extra time tonight.

Old points back in tomorrow and try again

 

[bugsymike]

So tonight I changed out the points, coil and condenser, wouldn't fire. The new points are grounding somewhere because I'm getting continuity when they are open and closed, have had them in and out twice and I cannot see where they are grounding.
I started to question myself on circuits and breaking circuits so I went over to my 850 and started playing with it and sure enough the beep on the meter stopped and started when they opened and closed.

So after halftime the score is, Beru Points 1:0 Gavin and we're not going to extra time tonight.

Old points back in tomorrow and try again

On the old points if the contact area is what my old lecturer described as "blue and pitted" back in 1969 , this can be due to a duff condensor as it's job is to prevent arcing at the points by allowing a quick collapse of the electrical current when opening and shutting the contacts rapidly. Others may describe it better.
It can definitely cause a misfire and poor running , though not so sure re spitting back in the carb, air leaks at manifolds can do that or as I mentioned inlet and exhaust valves not shutting/ burnt out/ sticking etc.
I had a three cylinder Vauxhall Corsa 1.litre that actually melted the plastic inlet manifold around the injector ports due to a known by Vauxhall fault of valve stems sticking, this was on a very low mileage car always Dealer serviced.
The salesman at the dealership offered to sell them a new car and "give them" £500 for theirs, he was probably in a position to get Vauxhall to make a whole or part contribution to that repair given it was barely out of warranty, needless to say the owner whose dad was an old friend of mine did not buy from Vauxhall and bought a BMW Mini instead!

 

[FR85]

On the old points if the contact area is what my old lecturer described as "blue and pitted" back in 1969 , this can be due to a duff condensor as it's job is to prevent arcing at the points by allowing a quick collapse of the electrical current when opening and shutting the contacts rapidly. Others may describe it better.
It can definitely cause a misfire and poor running , though not so sure re spitting back in the carb, air leaks at manifolds can do that or as I mentioned inlet and exhaust valves not shutting/ burnt out/ sticking etc.
I had a three cylinder Vauxhall Corsa 1.litre that actually melted the plastic inlet manifold around the injector ports due to a known by Vauxhall fault of valve stems sticking, this was on a very low mileage car always Dealer serviced.
The salesman at the dealership offered to sell them a new car and "give them" £500 for theirs, he was probably in a position to get Vauxhall to make a whole or part contribution to that repair given it was barely out of warranty, needless to say the owner whose dad was an old friend of mine did not buy from Vauxhall and bought a BMW Mini instead!

The "old" points only went into it about 100 or so miles ago after a little electronic ignition went on the fritz.
Ever since then I've been suffering the pop pops.
I've read online that folks have had popping issues all lead back to the condenser and a change of that sorted it or indeed put a new one in and it made it worse.
It's true that newer made stuff is worse quality and I'm now wondering if the new condenser I put in was duff out of the box and causing the continuity across the points.

 

[fiat500]

So tonight I changed out the points, coil and condenser, wouldn't fire. The new points are grounding somewhere because I'm getting continuity when they are open and closed, have had them in and out twice and I cannot see where they are grounding.
I started to question myself on circuits and breaking circuits so I went over to my 850 and started playing with it and sure enough the beep on the meter stopped and started when they opened and closed.

So after halftime the score is, Beru Points 1:0 Gavin and we're not going to extra time tonight.

Old points back in tomorrow and try again

Have close look at the pivot tube of the points. From somewhere, I once acquired a set of points that strangely, had that part made from steel. This meant that the points were permanently grounded to the baseplate. Somehow, the engine was able to run well for a while, but one day it conked out.

I used to have a pre-war car that had this arrangement; part of the designed setup was an insulated washer that was placed over the pivot-post before fitting the points.

 

[FR85]

Have close look at the pivot tube of the points. From somewhere, I once acquired a set of points that strangely, had that part made from steel. This meant that the points were permanently grounded to the baseplate. Somehow, the engine was able to run well for a while, but one day it conked out.

I used to have a pre-war car that had this arrangement; part of the designed setup was an insulated washer that was placed over the pivot-post before fitting the points.

The pivot tube on the set I put in last night is made of a hard white plastic. The Marelli set that came out had for anything like a leather kind of make up.

I'll actually have a look and see if I could fit a small fibre washer underneath as I've two sets of these points so a remedy would be good.
Thanks for that idea!!

 

[bugsymike]

Have close look at the pivot tube of the points. From somewhere, I once acquired a set of points that strangely, had that part made from steel. This meant that the points were permanently grounded to the baseplate. Somehow, the engine was able to run well for a while, but one day it conked out.

I used to have a pre-war car that had this arrangement; part of the designed setup was an insulated washer that was placed over the pivot-post before fitting the points.

There is a lot of poor quality pattern parts around for many vehicles these days.
Going back to points set up, as an apprentice late 1960s it was common to go out on breakdowns Monday morning where over the weekend the proud owners after washing and polishing their cars would then feel the need to service them, after all if that "oily erk" at the garage can do it, how hard can it be?
On inspecting the car often you found no spark and on checking the "brand new points" , speak to the customer who would assure you that no one has opened the bonnet since the last service by the garage, however a few minutes reassembling the points correctly with either fibre/plastic washers or terminals reconnected correctly the car would miraculously burst into life.
If questioned, we would answer the cause of the problem was "The nut loose behind the steering wheel"

 

[FR85]

Evening!

Tonight's proceedings went as follows:
Old points back in (only about 150 miles since reverting back to points from an electronic ignition that failed)
New condenser, leads, cap and rotor.
Mixture screw all the way in and back out 3 turns, points set to about .5mm and confirmed to be happening with a test light.

Car started and it's noticeably more lively!
Ran it on choke for 5 minutes to bring the battery back around and eased off the choke, brought up the idle screw and have the mixture have a turn back in and it's idling nicely.
From the engine bay when it was warm I gave it a good rev, held it for 8 seconds and it started to fall and I'd to fettle the throttle to catch it and return it to idle. If I didn't do this it would just die, found this out the next time.
It's popping through the carb and there is still popping through the exhaust as it's falling.

I put a strobe on it set to around 12 degrees and while there is a slight wander through hunting, it's not a complete train smash.

I also remembered this carb has 125 jets in it, came off a running 600 126 engine.

Am I up against timing or fueling do we think?

Based on the info I've provided should the dizzy go clockwise or anti clockwise?

Sorry this thread has taken a turn but I didn't want to be creating lots of them and have answers and suggestions in a few different places!

Hope 24 is treating everyone kindly!