Hi, wonder whether anyone can help. I have had some spare Dell Orto PHF carburetors ultrasonically cleaned and have refurbed them using dell orto seal kits. The bike idles well but has a flat spot immediately the slides are lifted such as when pulling away from standstill. Once past say 1/8 throttle the carbs perform perfectly. Any ideas what I should be looking for?
Carburettor Problem
- Thread starter mart430
- Start date
G
Grant
Guest
Did you renew the brassware?
Did you set the carbs up with gauges when refitted to the bike?
Did you blow through them with a high pressure air line after they came out of the ultrasonic bath?
Could still be some blocked airways in the carbs.
Did you set the carbs up with gauges when refitted to the bike?
Did you blow through them with a high pressure air line after they came out of the ultrasonic bath?
Could still be some blocked airways in the carbs.
Tippie
Hero member
- Location
- Dr?bak, Norway
Pickup from idle is slide cutaway. It sounds like it is a bit rich, you can compensate a bit with idle mixture.
You don?t say which model you have them on and what else is on it, ignition type etc. That symptom can be ignition related also amongst other things like synchronisation.
You don?t say which model you have them on and what else is on it, ignition type etc. That symptom can be ignition related also amongst other things like synchronisation.
Hi guys, in answer to your questions bike is a 500 Alpino with Sachse ignition and dyna coils all recently fitted. Standard air box. Standard size jets replaced but did not blow out with airline after cleaning so that may be the problem? Only other strange thing is that idle mixture screw has to be set at only 1/2 turn out for the bike to tick over properly regardless of idle jet size (tried jets from 55 standard down to 45, no appreciable difference)
Gravelroad
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- Location
- Central Europe
Did you check float levels according to the Dellorto manual? Float valves replaced or still the old ones?
Rob
Hero member
- Location
- Midlands, UK
Yep! Gravelroad's question referred to the float valves, not the floats
Gravelroad
Hero member
- Location
- Central Europe
Yep, the 1/2 turn mixture screw and the non-reaction on idle jet variation could be caused by fuel levels being to high. I generally replace the float valves on used carbs, then check for correct float levels. Take care that both sides of the floats are at the same height while adjusting the float level. Easy to achieve with an old credit card cutted to size, see picture below.
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It may be my fuzzy memory but look at the carb throat through the slide hole and see if there is a smalll hole in the floor of the throat just in front of the slide. There will be one behind the slide[toward the engine] which is the idle circuit outlet, and one just in front of the slide[toward the air filter] which is a transition port. It is fed by the pilot circuit and can get blocked without affecting the idle quality. It is there to richen the mixture as the slide opens before it starts drawing from the needle jet. I may be confusing it with a Keihin or Mikuni that has driven me nuts but it's worth a look while you have it apart to check/set the float levels
I have also used different sizes of interdental brushes (must have fine soft brushes, available from pharmacy stores) to clean channels and still some carburetor cleaner (additive to fuel) when the carbs are assembled.
Other problems not mentioned allready I have had with PHFs is once a faulty float (fuel went there inside), idle emulsifier tubes (should not be on SFC 1000, some confusion on documents) and original o-rings.
Here fuel has 5% of ethanol, and probably faulted the float and periodically those NBR o-rings supplied on original sets. On SFC 1000 the float number is 74501 (10 gram, adjustment 18?0.5mm), and with same number Dell'Orto is supplying 8.5 gram floats that withstand better ethanol (adjustment is 21?0.5mm, even Dell'Orto says these are not adjustable but they are). The new 8.5 gram floats give same responce than the elder 10 gram floats, then no other alterations should not be made. Nowadays I use Viton o-rings instead of the originals. I have the correct sizes documented for PHF 32 if someone is interested to know. Those work much longer with ethanol fuel.
Other problems not mentioned allready I have had with PHFs is once a faulty float (fuel went there inside), idle emulsifier tubes (should not be on SFC 1000, some confusion on documents) and original o-rings.
Here fuel has 5% of ethanol, and probably faulted the float and periodically those NBR o-rings supplied on original sets. On SFC 1000 the float number is 74501 (10 gram, adjustment 18?0.5mm), and with same number Dell'Orto is supplying 8.5 gram floats that withstand better ethanol (adjustment is 21?0.5mm, even Dell'Orto says these are not adjustable but they are). The new 8.5 gram floats give same responce than the elder 10 gram floats, then no other alterations should not be made. Nowadays I use Viton o-rings instead of the originals. I have the correct sizes documented for PHF 32 if someone is interested to know. Those work much longer with ethanol fuel.
piranha-bro2
Hero member
- Location
- Melbourne
I'm sure you'll track it down. At least you have that 'half-turn-out' issue, so you know absolutely that the problem lies in carburation, unlike other niggles and gremlins that can be very hard to cure.mart430 said: