Valtra
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 posted on 25/3/12 at 11:52 PM |
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mishab plates? v nylon and o rings
Hi
My Fiat twin cam is still having poor running issues , no 1 cylinder is not getting fuel properly except under acceleration . It's running twin
40 Webers and I suspected vacuum leak as a squirt with "easy start" around the join has the engine running better , so I got some new o
rings for the nylon mounting plates which seems to have made no improvement (I'm using cup and rubbers to clamp) Is it worth trying mishab
plates instead ? I do know I have a good spark (Lumenition competition ) as i am testing with a colourtune plug , the only way to get any burn (blue
flame) is to wind out the mixture screw 2 or 3 extra turns but then instead of sounding like a tractor on 3 cyls it sounds like a 3.5 cylinder tractor
with unburnt fuel detonating in the exhaust. I'm getting set up with vacuum gauges to test the individual pressures as balance is likely to be
an issue , but it does seem to be one cyl that's at fault . I've had the top off the carb today and there don't seem to be any
blockages and the fuel level seemed ok. Compression was ok last time I checked . any suggestions greatly appreciated
Ian
"If it looks like it works and it feels like it works, then it works"
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JeffHs
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| posted on 26/3/12 at 09:20 AM |
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Balance is critical. I've got twin 40s on a Pinto and it took me ages to realise that the poor running was due to imbalance between chokes on 1
carb (bent spindle). not just between the carbs. I bought a vacuum gauge which highlighted the problem. I spent hours fettling no1 carb until I was
happy with it and it is now much better than no2 so that the imbalance has shifted to the driving range not just idle. I need to rebuild the 2nd carb
but I've made the car very driveable by balancing both carbs at 2000 rpm.
It means it's a bit rough at idle but as soon as the throttle opens it smooths up and is great all through the driving range.
Before I rebalanced at 2000, I could get a smooth idle but it would spit and fart at pottering about speeds only cleaning up on the main jet. I
quickly realised that for a road car about 90% of the time is spent on the idle jet so it wasn't much fun to drive.
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Valtra
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| posted on 26/3/12 at 12:47 PM |
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Thanks . Yes it may be that I'll get to some sort of compromise . I've got some vacuum gauges , now I just need the adapters to screw into
the carbs and I should have a better idea what's going on .
"If it looks like it works and it feels like it works, then it works"
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JeffHs
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| posted on 26/3/12 at 02:51 PM |
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If you don't have any luck with the vacuum gauges - try one of these - dead easy to use, just stick it up the air horn. If you will guarantee
its return, I'm willing to let you borrow mine, but I do need it back!
CARBURETTOR SYNCHROMETER BALANCER WEBER DCOE/DCNF/IDF | eBay
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Autosri
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| posted on 26/3/12 at 02:59 PM |
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Make sure one of the air bleed screws havnt come undone on one carb causing the massive I ballance
Have you tried listening into the venturies to see if they sound the the same using a piece of pipe
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Valtra
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| posted on 26/3/12 at 07:55 PM |
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quote:
Originally posted by JeffHs
If you don't have any luck with the vacuum gauges - try one of these - dead easy to use, just stick it up the air horn. If you will guarantee
its return, I'm willing to let you borrow mine, but I do need it back!
CARBURETTOR SYNCHROMETER BALANCER WEBER DCOE/DCNF/IDF | eBay
Hi Yes I was watching a few on ebay but they all go for a lot of dosh . Simple but effective . I've ordered some adapters from Morgan Carbtune .
so I should be ok . but thanks very very much for the offer and of course it would be returned if I took you up on your kindness. 
"If it looks like it works and it feels like it works, then it works"
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Valtra
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| posted on 26/3/12 at 08:00 PM |
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quote:
Originally posted by Autosri
Make sure one of the air bleed screws havnt come undone on one carb causing the massive I ballance
Have you tried listening into the venturies to see if they sound the the same using a piece of pipe
Hi yes I have listened down some heater pipe but it seems a bit "approximate" especially to my untrained ear (plus 30 years listening to
Radio1 in noisy tractors)
re air bleed screws . sorry to be a bit thick but I'm feeling my way here by trial and mainly error . where are the air bleed screws located ?
"If it looks like it works and it feels like it works, then it works"
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Autosri
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| posted on 26/3/12 at 08:14 PM |
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i know the feeling mate i am still getting my head round my set if you find some small pipe about 8mm id the noise seems more easy to distinguise and
put it into the aux venturi a small amount
i think there only on some models they are on around the 10 oclock position on the left carb and the 2 oclock position on the right carb and have
white caps on them i bought the type of gauge that has 4 seperate gauges on and there is a perfect place to screw them in its between the accelerator
pump jets and idle screw ithas a bung you can unscrew and screw your gauges then you can see all 4 at once
have you checked that all the jets are the same size
i replaced the misab seals and cup wahsers on mine and it made a massive difference on mine the old ones didnt really look bad just a bit perished and
afteer replacing them the idle and part throttle is much better
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Autosri
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| posted on 26/3/12 at 08:19 PM |
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http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm
look on the left carb find the idle control screw just to the right is an unmarked screw thats where you screw the vac guges in and the diagram shows
the air bleed positions
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Valtra
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| posted on 26/3/12 at 08:23 PM |
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quote:
Originally posted by Autosri
i know the feeling mate i am still getting my head round my set if you find some small pipe about 8mm id the noise seems more easy to distinguise and
put it into the aux venturi a small amount
i think there only on some models they are on around the 10 oclock position on the left carb and the 2 oclock position on the right carb and have
white caps on them i bought the type of gauge that has 4 seperate gauges on and there is a perfect place to screw them in its between the accelerator
pump jets and idle screw ithas a bung you can unscrew and screw your gauges then you can see all 4 at once
have you checked that all the jets are the same size
i replaced the misab seals and cup wahsers on mine and it made a massive difference on mine the old ones didnt really look bad just a bit perished and
afteer replacing them the idle and part throttle is much better
Thanks though my old Sunbeam Ti carbs may differ there is certainly nothing like a white cap on my carbs but will do some research .
Did find some m5 screws adjacent to the mixture screws that get a vac gauge fluttering so hopefully when I screw in some proper adapters I should get
a fair reading ( only 2 gauges but I should be able to cross reference )
All the jets were set up on a rolling road 3 years ago and the car ran sweet as a nut for 2 years (not many miles though admittedly)
"If it looks like it works and it feels like it works, then it works"
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Valtra
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| posted on 26/3/12 at 08:51 PM |
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quote:
Originally posted by Autosri
http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm
look on the left carb find the idle control screw just to the right is an unmarked screw thats where you screw the vac guges in and the diagram shows
the air bleed positions
Ah yes thanks there are some variations I believe but I've come across this article before ....clear as mud 
"If it looks like it works and it feels like it works, then it works"
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