Classic cars forum & vehicle restoration.
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Clactonguy
Joined: 20 Mar 2018 Posts: 104 Location: clacton on sea
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Posted: Tue Apr 27, 2021 10:07 pm Post subject: spitting back through carb and stumbling. |
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suspected fuel supply issues in our rover P6B so removed both carbs and refurbed.. rebuilt and test= worse than before though did start easier. Suspect a problem made worse as jets replaced and no tuning of fuel/air flow. ..yet.
probably have to adjust 'jet' heights (SU carb) tomorrow and try again. such are lifes tribulations. |
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roverdriver
Joined: 18 Oct 2008 Posts: 1210 Location: 100 miles from Melbourne, Victoria, Australia
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Posted: Wed Apr 28, 2021 8:16 am Post subject: |
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Symptoms suggest a lean mixture. _________________ Dane- roverdriver but not a Viking. |
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Clactonguy
Joined: 20 Mar 2018 Posts: 104 Location: clacton on sea
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Posted: Sat Jul 24, 2021 9:21 pm Post subject: carb issues? |
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fuel supply tried using a 2 litre tank suspended above car and direct to carbs ( no fuel pump) fuel could be seen diminishing far too fast even at idle! mixture screws both set at 2 and a quarter turns out form. fully in. pistons freely move and drop on bridge and oil is in dash pots. def not lean .. if anything too rich on one carb. colour tune used one side =blue at idle to slightly red/yellow on fast revs ( OK) other Side not tested as it packed up! lifting pin same carb shows slight increase in revs and fall back to normal ( correct) lifting pin other side= no change ..so offside carb appears to be the faulty one. However it had been stripped and checked ..jet,needle etc and nothing untoward found even float setting was OK. bit of a puzzle at moment. |
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alastairq
Joined: 14 Oct 2016 Posts: 1955 Location: East Yorkshire
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Posted: Sat Jul 24, 2021 11:35 pm Post subject: |
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Is the throttle disc bar operating in a worn hole in the carb body? _________________ Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces. |
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lowdrag
Joined: 10 Apr 2009 Posts: 1585 Location: Le Mans
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Posted: Sun Jul 25, 2021 6:29 am Post subject: |
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Of no help, but after 25 years I sent my HD8's back to Burlen for a refurb. They came back gleaming, but the performance was worse. I could usually run without choke after a few hundred yards, but now the engine spits back if I don't keep it on a while. And the fuel consumption has increased by 10%. no matter what we have tried we cannot get them anywhere near the performance we had for 25 years. |
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alastairq
Joined: 14 Oct 2016 Posts: 1955 Location: East Yorkshire
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Posted: Sun Jul 25, 2021 10:27 am Post subject: |
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Does the OP have one of those cheapoh [Lidls is good] digital calipers?
I use a set of these to first set the jet heights equal. [with twin carbs]
CAre is needed as it's easy to tilt the calipers... I first set them level with the tops of the bridges. After having removed the dashpots and pistons.
Then I wind them down by the proscribed amount for a starting point, and check again they are as close to each other as feasible.
MAke sure the pistons move freely in the dashpots, but not loosely.
I then screw down the dash pots and check the idle mixtures [I don't even put the dampers in at this point...not needed.}
Use light machine oil in the dashpots..engine oil is too heavy, and may lead to weaker mixtures at bigger throttle openings.
Make sure the needles are centred in the jets as well [if not the sprung, later type]
Are the needles actually not bent at all? I had a box full of spare needles of various sorts, and a good 40% were actually bent.
Check the throttle butterflies for wear. the carb bodies wear overtime.
If wear is excessive, then the carb bodies can be drilled, & sleeved..there are kits available to do this.
A worn butterfly spindle can allow air to leak in. This will weaken the mixture [a bit] Sometimes only seen when the butterfly is actually opened up.
Check also for any air leaks downstream of the carbs, on the various manifold gasket face.
Vacuum leaks are possible too?
Also ensure the air bleed holes on the carb outer faces [the filter side] are not obscured by gaskets, or the filters themselves are mounted so these holes are not blocked. [[I have found filters for SUs where these holes aren't even drilled!]
Sometimes, when the floats in the float chambers are changed, the pivot spindles are wrong for the float design, meaning the floats either intermittently fail to close the needle valves, or the floats themselves jam in the closed position when the bowls are full. This might lead to the bowls emptying and causing a weak mixture.
Burlen went over to [ethanol resistant, so they tell me] plastic floats, but one really also has to have the float bowl lids that go with them a well. I have tried using plastic floats [one piece, not the ones with the brass strips rivetted to the tops]...with the older type of lid [to suit the spigot positions]..and there are problems with the positions of the float hinge holes, etc etc.] There ought not to be, but there are! Again, I have quite a few lids of varying ages....so I have had to mix & match to remain leak free, and jam free.
Not good to assume just because things are new, or renewed, that they are right as they come out of the box!
My Dellow arrived minus it's old blower, and on twin SUs..but these SUs hade been put together [not refurbed] in the USA, and US parts for SUs differ somewhat from those we find in the UK.
What a mess! All sorted more or less now. Just need to bush the throttle butterfly spindles when I find my round tuitts. _________________ Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces. |
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Clactonguy
Joined: 20 Mar 2018 Posts: 104 Location: clacton on sea
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Posted: Sun Jul 25, 2021 6:58 pm Post subject: backfiring. |
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carbs are low use and NO wear on spindles .mileage is approx 38K and believed to be correct ! wear on dizzy gear when removed for new full electronic unit shows hardly noticeable contact on gears .. suggesting ( it is original dizzy ) low mileage shown on odometer appears correct. compression test showed all good at approx 160 psi with 2 cylinders on nearside bank ( next to each other) at 150-155psi. oil injected each cylinder and recheck shows little on no increase in pressures suggesting valves are good and rings not badly worn. all issues came about after standing car for a year ( covid) and filling up with contaminated fuel ( Morrison are suspect here) . tank drained .relined after de-rusting. all pipes blown through . return restriction checked and clear. all plugs checked .each cylinder check with a strobe for firing pulses =good . coil =good. leaving suspect broken/sticking valve spring ? ( unlikely ) or carb woes. £400 to have carbs refurbished and fairly sure not needed as both had new kits .etc fitted. 3 years ago. nearside carb reacts to lifting pin .offside does nothing! engine seems to be running very lumpy and we suspect one ( carb) is simply not fuelling correctly . pistons fall freely ( clunk on bridge) and both set at same heights ( vernier calliper) found dizzy diaphragm not working ( wont hold a vacuum ) but that only affecst instant throttle response /advance. though might weaken mixture a wee tad if air leaking past! so far have had myself and a friend whom strips and rebuilds carbs ( for motorcycles) check it over .we are a bit stumped. we are wondering if we have a combination of part contaminated fuel ? and float level in one carb sticking! though when stripped it works well. needle is NOT bent and is running bias in jet ( correct) on both carbs. at moment acceleration is slower than a milk float ( v and power is down by about 50-70%? choke keeps it running at low speeds but has no effect when moving above 5mph. wife. looking to get rid of car now.. changed 2 plugs as despite coil showing firing on them an exhaust manifold temperature check on each cylinder found 2 with very much lower working temps.. so swap plugs and re-test = all balanced.so hopefully a road test tomorrow will see an improvement. |
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