Pantah 500 Carbies

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redorca10
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Pantah 500 Carbies

Post by redorca10 »

Hello brains trust,
the original Dell'Orto PFH 36 AD & AS carbies are playing up big time on my Pantah 500SL. I have cleaned them and replaced obviously worn parts and rebuilt them. I am considering replacing them as the plug keep getting fouled after 10-15 mins of riding. I have had two mechanics look at them and other than head scratching, haven't been able to fix the problem. The bike has been totally rewired by a professional, the timing is spot on. If I was to replace them, would you suggest sticking with the same sort, or are there better alternatives out there? Cheers, Alistair.
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Craig in France
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Re: Pantah 500 Carbies

Post by Craig in France »

Hi Alistair,

Personally, I would persist with the carbs you have. After all, Dell 36 PHFs have worked satisfactorily on Pantahs, and continue to do so, over many millions of miles now.

I suspect you're not getting the set up correct. Rich running is, for example, a classic consequence of getting the float height wrong. How are you setting the float heights? Do you KNOW that the enricher circuit is properly closed? How worn are the slides?

(I imagine you're following the original specs for jets/slide/etc? And that you haven't altered anything else on the bike? Are you still using the original air filter arrangement, for example?)

And finally: Where are you in the world?
ducadini
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Re: Pantah 500 Carbies

Post by ducadini »

the original Dell'Orto PFH 36 AD & AS carbies are playing up big time on my Pantah 500SL.
So did they work fine before ?
I have cleaned them and replaced obviously worn parts and rebuilt them.
What are "obviously worn parts"?
I am considering replacing them as the plug keep getting fouled after 10-15 mins of riding. I have had two mechanics look at them and other than head scratching, haven't been able to fix the problem.
The bike has been totally rewired by a professional, the timing is spot on.
Rewired, timing spot on, how about the advance ?
If I was to replace them, would you suggest sticking with the same sort, or are there better alternatives out there?
On some circuits we raced with slightly enlarged and modified 32's, just better down low and a bit worse in high revs. But that means some more modifications.

Are the rubber plugs in the enrichment plunjers ok ? and do they seat completely ? Enough slack in the cables ?
Needles in the correct position ? And what happens when You lower them ?
Rewired, are the pickups connected correct ? IIRC, the advance doesn't work if those wire are switched, giving a less than complete burn.

ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri
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redorca10
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Re: Pantah 500 Carbies

Post by redorca10 »

Hi Craig in France,
Thanks mate, your rationale about keeping the carbs makes perfect sense.
They are with a mechanic now, who has checked the floats - which are fine (I'm reassured), jets are new.
I've got pods on the carbies and have been running a set since the 90's with no problems.
I'm in Melbourne (Aust).
Cheers Alistair


[quote="Craig in France" post_id=24039 time=1634891712 user_id=50
Hi Alistair,

Personally, I would persist with the carbs you have. After all, Dell 36 PHFs have worked satisfactorily on Pantahs, and continue to do so, over many millions of miles now.

I suspect you're not getting the set up correct. Rich running is, for example, a classic consequence of getting the float height wrong. How are you setting the float heights? Do you KNOW that the enricher circuit is properly closed? How worn are the slides?

(I imagine you're following the original specs for jets/slide/etc? And that you haven't altered anything else on the bike? Are you still using the original air filter arrangement, for example?)

And finally: Where are you in the world?
[/quote]
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redorca10
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Re: Pantah 500 Carbies

Post by redorca10 »

Hi Ducadini,
Thanks for the reply,
No, so I dismantled, cleaned (gummed up) and rebuilt -this is the part that makes me nervous, me rebuilding. :|
Worn parts - pump diaphragm, gaskets, lever choke assembly, all the rubber washers, banjo filter etc
I'll pass your suggestions onto the mechanic and duck the spanner that he throws at me :lol:
Many thanks
Alistair

ducadini wrote: Sun Oct 24, 2021 7:16 am
the original Dell'Orto PFH 36 AD & AS carbies are playing up big time on my Pantah 500SL.
So did they work fine before ?
I have cleaned them and replaced obviously worn parts and rebuilt them.
What are "obviously worn parts"?
I am considering replacing them as the plug keep getting fouled after 10-15 mins of riding. I have had two mechanics look at them and other than head scratching, haven't been able to fix the problem.
The bike has been totally rewired by a professional, the timing is spot on.
Rewired, timing spot on, how about the advance ?
If I was to replace them, would you suggest sticking with the same sort, or are there better alternatives out there?
On some circuits we raced with slightly enlarged and modified 32's, just better down low and a bit worse in high revs. But that means some more modifications.

Are the rubber plugs in the enrichment plunjers ok ? and do they seat completely ? Enough slack in the cables ?
Needles in the correct position ? And what happens when You lower them ?
Rewired, are the pickups connected correct ? IIRC, the advance doesn't work if those wire are switched, giving a less than complete burn.

ducadini
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Craig in France
Paso 750
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Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: Pantah 500 Carbies

Post by Craig in France »

H Alistair,

As Ducadini has said, as well as getting the float height right, it's important that the rubbers at the bottom of the choke pistons are sealing correctly, when the cables are hooked up.

Easiest way: simply fit new pistons. You can muck about with trying to flip the rubber seals over; but life is short and new pistons are not expensive.

Then to test: with the carbs on the bike and the cables hooked up, remove each float bowl and put a straw/thin tube on the bottom of the pick-up tube and try to blow up it. Obviously, it shouldn't be possible, at all ...

Next: you need to work at what throttle position you're running rich. This will identify which circuit in the carb is misbehaving.
Note: to do this, it's critical to not confuse throttle position with engine revs! They ain't the same ...

So take the bike out on a lonely road and run it for a mile or so at constant throttle position. Do it at no more than 1/4 throttle, less if you can. Remove the plugs and see if they're fouling. If they are, then this indicates that it's the idle circuit and/or the cutaway in the slide that's causing the problem.

And if you haven't changed the slides from standard, then everything is pointing to the idle circuit. Which means:

1. Float height (again ...). Sorry to bang on about this, but it's THE most common error. The float valve should be JUST closed when the distance between the bottom of the float and the carb body in the horizontal position is 18mm. Details in the Dell'Orto manual, page 10.

I STRONGLY recommend using a gauge to measure this dimension, not a tape or rule (Steve sells one such gauge or you can make your own). And personally, I gauge the moment of the closure of the float valve by (again) attaching a tube to the petrol inlet and gently blowing down it while taking the measure.

2. The air drilling at the front of the carb that delivers air at idle. Can be a PITA this one.The little daring is reduced internally - see illustration fig 18, page 13 of the manual - and may be partially blocked. Squirt some carb cleaner down the hole at the front of the carb - one of the 3 you can see, air intake side. Not the middle one, not the one that isn't properly drilled, the other one.

Here's a bit more guidance. Not my own work, but the words of someone much more experienced than me:

"Checking the galleries with carb cleaner.

The easy way to check the galleries (with the carbs on or off the bike) is:
1. Remove the pilot jet and the mixture screw.
2. Using a can of carb cleaner with an extension tube fitted, put the tube up the hole where the pilot jet goes. Cover the mixture screw hole with a finger and squirt cleaner while looking for a stream coming up into the venturi, just in front of the back edge of the slide.
3. Now put the tube in the mixture screw hole. Cover the pilot jet hole with a finger and squirt cleaner whilst looking for a stream coming out between the slide and the engine.
4. Now put the tube into the little air hole under the main carb air intake (not the "middle" one: the one on the side). Squirt, and look for cleaner in the venturi."


3. Too large an idle jet. Modern fuels can have an influence on this, as can the fact you're running pod filters. But don't start with this, however tempting it may seem ...
Buy some smaller jets and try swapping them over. But don't go crazy! A couple of sizes, no more. I think you should be running 65s? Go down to 60, no more.

HTH

Craig
duccout
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Re: Pantah 500 Carbies

Post by duccout »

I will jump in here with my experience of a 500 Pantah. I bought a new 500 when they came out and found the carburation very rich, with rough running and black plugs. The brilliant US magazine Cycle tested the 500 Pantah at that time and plainly stated that the carburation was way too rich also. Mine was obviously rich just off idle, so I tried the usual adjustments of smaller pilot jets and lowering the needles, but it made no difference, so, I took a file to the slide cutaways and opened them up - problem solved! The bike then ran correctly with no more black smoke or sooty plugs.

I'm not suggesting that you file your slides, but a pair with a larger cutaway would be well worth trying, and I would go up half an increment.

Good luck,

Colin
fab
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Re: Pantah 500 Carbies

Post by fab »

that is very interesting Colin,
what size slides are you running
and how much did you file away on the cutaways ?
my bike has the same symptoms and i have tried everything to get it to run leaner at idle
ducadini
860 GT / GTS
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Re: Pantah 500 Carbies

Post by ducadini »

Before You start filing away : does anybody have acces to the measurements of 32 Dell'Orto slides ?
IIRC (they are TOO difficult to get to now) they have the same diameter, and there could be different cutaways.
In the partslist of the 650 Alazzurra, the USA part has indeed less cutaway than the EU slide (50 instead of 60).
Also check the ramp for injection (that's the number behind the 50/ ).

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri
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