| [ Total Views: 707 | Total Replies: 8 | Thread Id: 77162 ] |
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 alien8
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| posted on June 12th, 2009 at 09:44 PM |
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Flat spot problems. I'am stumped!
This is really annoying the hell out of me.
This is a run down. 34/3 German carb, New single vac distributor.
Idols great, couldn't be better. Points set and reset, checked and replaced, .4mm gaped. Dwell reads 50. Valves set to .6mm . Checked for carb and
manifold leaks. Checked fuel pump and throttle tube and tried all setting between + and - on the pump. Carb cleaned out and rebuilt three times.
Tried 130 and 135 main jets. Carb set as per manual guidelines. Air cleaner checked for obstructions. New condenser,plugs,leads rotor and cap.Then
rechecked with old ones. Coil checks out ok. Choke checked and works fine. Timed to 30 BTDC at 3000 rpm. Timing falls to about 10 BTDC at idol. Fuel
lines checked.
It runs great(no flat spot) for the first couple of minutes when the choke is closed but then it has a really bad flat spot as soon as you push the
accelerator after the choke opens. Have to rev the balls out of it to take off. Same problem happens when under no load. If you leave the accelerator
in that position the motor will stall. The flat spot can be adjusted out a little bit buy screwing the bypass screw all the way out but it revs high
between gear changes and fouls the plugs and blows black smoke. Way to rich.
Don't know what to do next except buy a new carb. Is there somthing I am missing? I am all out of ideas. This is really frustrating!
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dangerous
A.k.a.: Dave Butler Muffin Man
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| posted on June 13th, 2009 at 06:24 AM |
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Only thing that ops up is the valve adjustment of .6mm...which I am assuming is a typo and actually .006" (six thou).
Running well ON the choke, indicates that the engine is lean, when it flat spots OFF the choke.
Provided you have not mixed up the main jet and air corrector,
I would be more inclined to look at the idle jet and passage...(idle cut-off solenoid not restricting oening?)
and also the accellerator pump nozzle and pump stroke.
Most carbs run on the idle jet for some time before the main even operates.
And the accell pump can fill in lean spots at the crack of the throttle.
Before checking all that, it may be worth checking the float level.
This controls a lot of other functions with in the carb, like emulsion tube action.
| Quote: | Originally
posted by westi
That's mad Alan.
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alien8
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| posted on June 13th, 2009 at 09:21 AM |
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Yep typo .006 on the valves. Cheers mate that gives me somthing more to think about. I have checked the idol solinoid and clickety click. I am off to
tinker again. I was thinking last night maybe a problem with the pilot jet? Might try backing it out a little and holding it there. But I will check
the carb float again and the idol circuit.
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 Bizarre
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| posted on June 13th, 2009 at 09:30 AM |
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sounds like a leak to me
How white are your plugs ??
Try spraying fluid around carb, manifold boots and gaskets
Futue te ipsum!!!
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DylanTheDubber
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| posted on June 13th, 2009 at 09:59 AM |
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I had flat spot problem and i just put a bigger main jet in the carby and fixed it all, Some say the vw bug was set up a bit lean from the factory.
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Bizarre
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| posted on June 13th, 2009 at 10:34 AM |
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and some say you are compensating the air leak with extra fuel 
Futue te ipsum!!!
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1303Steve
A.k.a.: Steve Carter
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| posted on June 13th, 2009 at 11:03 AM |
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Hi
There are 2 basic 34Pict 3s. One is single vac advance, other is dual.
The dual can be picked by vac port pointing out the back of the car.
From memory and it was 20 odd years ago, the early dual vac carb had a huge main and air jet, the air was something like a 140Z, the main about 140,
don't quote me on these sizes, I may be out a little.
It was a economy mod to fit the early carb with the late single vac jetting, this was a 60Z air and a 125 main, again my memory is getting faded.
So check these jet sizes along with other suggestions above, also your manifold preheat after everything else has warmed up should sizzle both sides
if you lick your finger and touch it.
Steve
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alien8
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| posted on June 13th, 2009 at 04:06 PM |
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I was pretty sure it wasn't a leak. It idols really strong and smooth. But checked it again anyway. Rechecked the carb AGAIN. Its a single vac German
Solex. Seemed to all be in order. Checked the coil again nice blue spark and the two resistance measurements where within specs.
The coil is kinda old so I thought I would go get a new one anyway. I mean its only $50 more and it couldn't hurt. After all that it couldn't just
be the coil, right?
Problem gone, damn coil! Runs great now.
Thanks all.
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dangerous
A.k.a.: Dave Butler Muffin Man
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| posted on June 13th, 2009 at 08:05 PM |
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Wow, good to know it is solved!
| Quote: | Originally
posted by westi
That's mad Alan.
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