piranha-bro2
Hero member
- Location
- Melbourne
That's a bummer for you after all that work. I'd also be looking closely at the inlet manifold connection. I'm assuming it has good compression?
73 SF2 Renovation
- Thread starter Bikepirate
- Start date
Idealy borrow a couple of proven carbs, sometimes those idle passages are bloody hard to clear. I think Paddy mentioned at some time trying 3 or more turns out to see what that does. Big changes are easier to notice or at least they should be. Now who do I know that is great with Dels in Queensland?
Sometimes, unfortunately, the carbs are fit for the bin and cannot be unblocked.
You can still find 36mm PHF new albeit with a male mount, but hurry, they're fast disappearing.
Paul
I've got a couple of bodies seemingly permanently blocked, still a bit reluctant to dispose of them for good. I'll leave them and wait for some magic potion or process to materialise that might give them a chance. I can always have them tossed into my grave if not... 
piet
piet
Hi Bikepirate.
Assuming Idle circuit blockage issues....
Something to try (see caveat)...
Get it started and warm. Choke off. Rev it up and then splat the palm of your hand over the carb intake - leaving the small air entry hole to the idle circuit open if you can. The sudden large draw (low pressure) through the idle circuit can sometimes dislodge a bit of crap and pull it through. The caveat.... Do it at your own risk - all I can say is I have done it dozen's of times with no ill effect, but there is always a first time for mechanical disaster.
I assume you have applied compressed air both forwards AND backwards direction?
IMHO ultrasonic-ing has little chance if dislodging crap from the idle circuits on these carbs. I recommend you do not place total faith in it.
Sometimes guitar strings are your friends - twizzle twizzle. Study the idle route - as others have said, there are corners.
Assuming Idle circuit blockage issues....
Something to try (see caveat)...
Get it started and warm. Choke off. Rev it up and then splat the palm of your hand over the carb intake - leaving the small air entry hole to the idle circuit open if you can. The sudden large draw (low pressure) through the idle circuit can sometimes dislodge a bit of crap and pull it through. The caveat.... Do it at your own risk - all I can say is I have done it dozen's of times with no ill effect, but there is always a first time for mechanical disaster.
I assume you have applied compressed air both forwards AND backwards direction?
IMHO ultrasonic-ing has little chance if dislodging crap from the idle circuits on these carbs. I recommend you do not place total faith in it.
Sometimes guitar strings are your friends - twizzle twizzle. Study the idle route - as others have said, there are corners.
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Rob
Hero member
- Location
- Midlands, UK
^ wot he said.
Nylon guitar string, not steel.
Check the pilot circuit drillings really are clear, see item 1 on this document
Bikepirate
New member
- Location
- Brisbane Australia
Yes, I've lapped in the intake manifolds and installed new o rings.If you have to add fuel to keep it running then either the carbs aren’t adding fuel properly or there’s air sneaking in later. Sounds like the carbs are spotless now. Checking the intake manifolds was suggested earlier but you haven’t confirmed, apologies if you’ve already eliminated that
piranha-bro2
Hero member
- Location
- Melbourne
I have an inkling that the main area prone to blockage is beyond the small hole at the air filter side of the carb, which feeds the air into the idle circuit. Seems the blocking material is likely to be corrosion of some sort? Is there any kind of acid that would eat that but not the alloy?
Quentin,
Most blockages seem to be between mixture screw aperture and the tiny idle mixture supply bore to the front to the slide, exiting at the edge of the throat where the inlet stub attaches. Unfortunately, the passage has a kink in it along the way, making it impossible to pass a probe through it. Compressed air and/or chemistry are the only options... sometimes luck or magic can help. My guess it's some sort of lime scale, mixed with solid fuel residue and corrosion. Whatever it is, it's a bitch. The passage from the carb mouth to the idle jet and transition apertures, even to the mixture screw, are usually easy to clear with compressed air.
I guess a last resort would be to melt out the lead plug that blocks off the bore to the kink and to replace it after cleaning. Haven't attempted that one yet, may as well give it a go someday.
piet
Most blockages seem to be between mixture screw aperture and the tiny idle mixture supply bore to the front to the slide, exiting at the edge of the throat where the inlet stub attaches. Unfortunately, the passage has a kink in it along the way, making it impossible to pass a probe through it. Compressed air and/or chemistry are the only options... sometimes luck or magic can help. My guess it's some sort of lime scale, mixed with solid fuel residue and corrosion. Whatever it is, it's a bitch. The passage from the carb mouth to the idle jet and transition apertures, even to the mixture screw, are usually easy to clear with compressed air.
I guess a last resort would be to melt out the lead plug that blocks off the bore to the kink and to replace it after cleaning. Haven't attempted that one yet, may as well give it a go someday.
piet
piranha-bro2
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- Melbourne
Gotcha re the mixture outlet. And I reckon your idea of plug removal is a good one - surely easy to make a plug replacement and fit it. I'm too tied up setting up FCRs to think about it these days.
Bikepirate
New member
- Location
- Brisbane Australia
Thanks for that Haggis. I don't know enough about these carbies to know the idle route - do you know of an illustration from Dellorto that shows the path?
Bikepirate
New member
- Location
- Brisbane Australia
Haven't measured the compression as I don't have a suitable instrument but as the engine is fine when on choke can't imagine it would be this
Bikepirate
New member
- Location
- Brisbane Australia
Thanks for your input Paul. I fitted new fuel valves and adjusted the floats to the recommended dimension of 24mm but will check them again.
Bikepirate
New member
- Location
- Brisbane Australia
I may be able to borrow an engine compression tester! What should the compression be?
Alzero
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- DaNang Vietnam
If at all possible try to get a leak down tester. It will differentiate between rings, valves and valve guides
Float height on the PHF carb is 18mm.
24 is way too low. If that's the case, no fuel apart from through the choke jet.
Paul
Yep, 18mm with the float just sitting. Not compressing the tiny sping on the needle. There is a diagram showing how the carb should sit, I don't remember if its on the engine side face or the airbox side face off the engine alone allowing gravity and its own weight to close the needle.
Exmoor beast
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- Minehead,Somerset, ENGLAND OF COURSE
I had some uncleanable carbs,my mum cooked my Dellortos in a pressure cooker using the skillet to keep them off the pan floor- that cleaned them!I've got a couple of bodies seemingly permanently blocked, still a bit reluctant to dispose of them for good. I'll leave them and wait for some magic potion or process to materialise that might give them a chance. I can always have them tossed into my grave if not...
piet
Seems like an excellent idea.
Paul
piranha-bro2
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- Melbourne
With very similar issues to Teddy and his SF, can you be absolutely sure that the cam timing is correct? Have you owned the bike when it was running well and idling? Are you a long-term owner? As I mentioned in his thread, these symptoms cry out 'cam timing' to me.