Club126UK
Fiat 126 Chat => Fiat 126 Mechanical Problem Solving => Topic started by: dadandlad on January 10, 2016, 09:49:01 PM
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I am looking for ideas regarding the running of my Bis engine
I really struggled to find a cure for the rough tickover which turned out to be the O-Ring on the jet with the big flat head in the side of the carb duly replaced with a copper washer
The problem I have now is if throttle is held mid position it misfires
I set the timing static at 10 degrees BTDC and duly checked with timing light and vacume advance blocked, the timing marks align but does seem to fluctuate slightly either side of pointer
It has new points, condenser,spark plugs and leads fitted but still using original coil
The bob weights and springs in the distributor appear to be fine and there is no play in shaft
I have noticed the inline fuel filter i have fitted is never full, would you expect it to be ?
The carburettor has had all flaps and linkages set according to the workshop manual
I should also add the engine has been rebuilt so has good compression and all valve clearances are as they should be
Fuel or timing issue ?
Any ideas greatly appreciated
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Mine is doing a similar thing in that if i hold it half throttle it coughs and splutters but if i put a little bit of choke on its fine so mine must be a fuel issue but with using the car for work ive not had chance to look.
Try it with yours and see if it makes a difference.
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Hi Mark, check you have the vacuum pipes on in the correct place
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Cheers chaps
Pete I think you may have hit the nail on the head, from memory I think I have the throttle kicker connected to the carb and the distributor advance/retard connected to the manifold :D
I will have a look and play tomorrow evening
Mintex
If the above doesn't work I will give your idea a try
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Fingers Crossed ;D
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Well didnt get in till 7 this evening but i really wanted to play out
Checked the vacuum pipes and you was right Pete, Carb connected to kicker and Manifold to distributor :$
Started her up and she sounds a lot better smoother tick over and I can shut the choke a lot sooner
Still has a misfire at mid throttle though
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Still has a misfire at mid throttle though
Just a hunch :D
The problem maybe the transition from the 1st choke to the opening of the 2nd choke it could be opening too soon/late
Look for the Carb section in the manual it has all the measurements of the butterfly positions
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Cheers Pete
I set all the flaps and linkages the last time I had the carb off using drill bits as accurate measuring devices
The problem is in the first stage at the moment
I haven't really pushed it onto the second stage yet, still running her in and not too keen on over revving her with no load
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Right boys the plot thickens
Fitted electronic ignition and now runs really well on tick over and mid throttle position
When I snap the throttle open it bogs down and then picks up to wherever the throttle is held, at the same time it is coughing back through the carb
Classic symptoms of the carburettor pump either not working or not delivering enough fuel, looks like the carb is coming off again to do the fuel pump metering test.
It had a new diaphragm fitted when I rebuilt it so we will have to see what I find
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Do you mean backfiring through the carb?
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Do you mean backfiring through the carb?
Yes but Iam pretty certain its not a timing issue
The accelerator pump system is simply a mechanical fuel injector that provides enough fuel for a brief period of time for the engine to respond smoothly to the heavy wide open throttle demand. Its purpose is oh so simple and its function is oh so critical. And, when it isn’t working right, the dreaded “Bog†and the always dreaded backfire through the carburetor are effects of an accelerator pump system that isn’t equal to the task. The “Bog†simply means the engine is not receiving enough fuel when you go to wide open throttle. While there are other issues that may cause similar reactions within the carburetor, often the problem can be traced back to the accelerator pump system.
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I have that same issue, that my engine "bogs" down if I open the throttle too quickly. Does that mean my accelerator pump is knackered?
I find it can be dangerous when you pull out in to a gap in the traffic, and the car gulps in air for a couple of seconds and bogs down when you need it to accelerate. My way of dealing with it is to open the throttle more gradually and slowly until the revs rise up before bringing the clutch up to pull away.
Is this accelerator pump easy to fix and where do I get one from?
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Do you mean backfiring through the carb?
Yes but I am pretty certain its not a timing issue
The accelerator pump system is simply a mechanical fuel injector that provides enough fuel for a brief period of time for the engine to respond smoothly to the heavy wide open throttle demand. Its purpose is oh so simple and its function is oh so critical. And, when it isn’t working right, the dreaded “Bog†and the always dreaded backfire through the carburettor are effects of an accelerator pump system that isn’t equal to the task. The “Bog†simply means the engine is not receiving enough fuel when you go to wide open throttle. While there are other issues that may cause similar reactions within the carburettor, often the problem can be traced back to the accelerator pump system.
There's something i can't get my head round :headscratch: For the engine to backfire through the carb the petrol needs to be ignited, which can only happen if one of the inlet valves is slightly open?
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Sounds to be the same problem
If you remove your air cleaner you should be able to see the accelerator pump jet pointing down the barrel of the carb
If you operate the accelerator you should see a jet of fuel squirting down into the carb, if you cannot see a jet of fuel either the pump diaphragm is shot or you have a blockage
Link to carb kit complete with accelerator pump
http://www.ricambio.co.uk/69-fiat/72-classic-fiat-126-parts/149-fuel-system/1368-carburettor-overhaul-kit--fiat-126
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There's something i can't get my head round :headscratch: For the engine to backfire through the carb the petrol needs to be ignited, which can only happen if one of the inlet valves is slightly open?
Cheers Pete you have now got me thinking, pretty certain that my valve clearances are bang on but I will check them just for piece of mind
Certainly making the brain tick as I have not worked on anything with a carb for donkeys years but really enjoying myself :D
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Is this accelerator pump easy to fix and where do I get one from?
I've taken some pictures and done a small video for you to see what yours should do.
If you work the throttle with the engine off and look in the carb you should see it squirting a small jet of fuel in.
As dadandlad said if yours isn't working it might be blocked or need a new diaphram in the pump located on the carb.
Hope it helps a little :)
(http://i128.photobucket.com/albums/p161/suzuki998/Fiat%20126/pump_zpsli84nd8h.jpg)
(http://i128.photobucket.com/albums/p161/suzuki998/Fiat%20126/20160117_163620_zpseqoyja9i.jpg)
[youtube]https://www.youtube.com/watch?v=GEs1MS--GJw[/youtube]
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Thanks Dave for the photos I'm sure they will help other members :thumbup
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Thanks both of you I will check that out, the pictures explain it all :thumbup
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Well the plot thickens
Checked the valve clearances as per Petes idea to no avail all found to be correct
Accelerator pump working fine
Ordered a Ultrasonic cleaner from ebay and going to fully strip carb once again
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Bit of a strange one? Will it go on full throttle or are you still running it in?
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Still running it in but I have opened it up on to the second choke but not to the stop, so long as you give it chance to catch up it revs fine
I will keep plugging away at it
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I have asked on Retro Rides for help and in doing so could have stumbled on the answer
When I originally stripped the carb it had sat for years full of gunk
The accelerator pump jet was blocked solid and nothing I did would clear it, so I got online and found a shop selling said jet.
The original jet didn't have a size marked on it so I wrongly or rightly assumed one size fits all
Opinion seems to think it is running rich, made even worse by giving it a little choke
I have found a company selling the correct jet so hopefully this will cure it fingers crossed
If it cures it I will be kicking my own backside for a month
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Well the carb is off again and in lots of bits
I managed to find some info on the Weber 30 DGF online but fitted to a Panda 30 and it appears I have the correct size accelerator pump jet fitted
What I did notice though was the very low fuel level in the float bowl approx 6mm deep barely covering the two jets in the bottom
I have also purchased a Ultrasonic cleaning tank and had the carb in and cooking
I will post some pictures of the carb before and after so you can see the results
Should have the carb back on tomorrow night
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I didn't get chance to refit the Carb this evening but have rebuilt it once more
I did find a issue with it and if it works all will be revealed tomorrow
(http://i669.photobucket.com/albums/vv57/markm16/P1030278_zpsl6u9jpyw.jpg) (http://s669.photobucket.com/user/markm16/media/P1030278_zpsl6u9jpyw.jpg.html)
(http://i669.photobucket.com/albums/vv57/markm16/P1030282_zpspzoqvzxs.jpg) (http://s669.photobucket.com/user/markm16/media/P1030282_zpspzoqvzxs.jpg.html)
(http://i669.photobucket.com/albums/vv57/markm16/P1030283_zpsz1zkthkv.jpg) (http://s669.photobucket.com/user/markm16/media/P1030283_zpsz1zkthkv.jpg.html)
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Well where to start
Today refitted rebuilt carb and if anything its worse :cry:
Well I decided to start right from the very basics
Removed rear panel and bumper and stripped off timing cover to check timing of crank to camshaft all found to be correct so everything refitted
Checked valve clearances all found to be correct
Removed and examined spark plugs found to be very sooty
Started her up and checked timing again
For some very annoying reason it now runs and revs fine with only a very very slight hesitation when opening the throttle
It is so annoying that I dont know what the problem was
One thing I think is worth mentioning which I could see someone else falling into the trap of doing is
The big jet just to the right of the accelerator pump has a tapered seat which I can only assume seats internally, now if you do as I did and replace the O-ring with a copper washer the jet will not seat internally as in effect the washers jack it out slightly
What if any effect this would have I dont know
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So its running ok now.
A bit strange it's fixed itself but maybe are lucky and have one of them rare self maintaining cars..... you and me wish this were true eh lol :D
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Hi Dave
Yes it appears to be running fine and I really do wish I could put my finger on what it was
I think I will replace the spark plug leads with some high quality ones just as a matter of course, they are new ones that are fitted but of unknown make
At least I can move on now
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You said that the copper washer is stopping the jet from seating, well if it works the same way as an idle jet then that will allow too much fuel to flow through at a certain part of the rev range, running too rich. You also said the spark plugs are very sooty, which could be a sign of running rich.
If you're after quality HT leads, I fitted Magnecor ones to mine, I fit them to every car I own because they seem to last forever.
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I assumed that is what was happening with the copper washer and expected it to be a instant fix but it was actually worse
I tried her again yesterday just to be sure and seems to be running really nice
Magnecor are the leads I have been looking at , did you have to fill out the application form or did they already have the spec for them
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I bought my Magnecor leads from Ricambio actually. They are listed as being for the air cooled car, but I asked him specifically if they would fit the Bis so he opened a box and compared the lengths of the leads with a set of Bis leads and they were almost exactly the same.
Of course 1 lead (the king lead) is wasted because the aircooled uses 3 leads and the Bis only 2.
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Grrrrr back to running rough again
Revs up but misfiring and bogging down again
Swapped fuel pump no better
Distributor removed examined refit and timed up
As a last resort tried on the grottiest looking carb ever,one of the polish Weber copies, unbelievable runs perfect nice tick over revs cleanly and holds constant revs at any speed
So I have no idea what is wrong with the original carb