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Old 02-11-2015, 07:05 AM   #1
blaine.hale OP
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PHF36 Del thread (guzzi lemans)

I didn't want to clutter Dave's thread too much so here's my own question thread.
I've read quite a bit about the PHF series Dels but they're still kind of tricksy to me. At least, compared to the simple Bings I'm used to. I figure, now that I have 2 bikes with identical carbs...it's time I gather the ADV knowledge in one thread.

Where I'm at: For the guzzi, I rebuild the carbs with the standard kit from MG cycles. Gaskets and o-rings. No new jets. The carbs have 25k miles on them and weren't worn or abused, I didn't know if that was justification for new jets. I'm willing to bet they wear down a bit quicker than normal due to the stock stacks on the LeMans. In my rebuild I did my usual PineSol soak and scrub then soda blasted and cleaned all that out again.
Installing them on the bike, there are zero cracks or leaks in the boot on the cylinder side. The pumpers definitely inject fuel (ask my eye about that.) No fuel leaks or overflows, it's actually the most leak proof carb I own. I usually set the slides with 1.5mm drill bits and start the idle mixture adjustment at a base of 1 turn out from flush. Cables are zeroed out with lots of slack to ensure no slide lift at idle.

The bike won't start cold with choke off, as normal. Flip the choke levers and it fires up instantly. Idles around 5k with choke on and around 3k with choke off. No amount of lowering the slide will slow the idle down. Changing the idle mixture to basically flush will sometimes slow the idle but not by much.

*Side note: I have the time set dead on now. I even retarded it a bit to see if that would effect idle. Nope.

What are you guys thinking? Worn out jets, clogged passage? Maybe choke circuit is clogged even though it seems to function and I've cleaned it out many times.
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blaine.hale screwed with this post 02-11-2015 at 01:51 PM
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Old 02-11-2015, 10:15 AM   #2
stainlesscycle
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Quote:
Originally Posted by blaine.hale View Post

The bike won't start cold with choke off, as normal. Flip the choke levers and it fires up instantly. Idles around 5k with choke on and around 3k with choke off. No amount of lowering the slide will slow the idle down. Changing the idle mixture to basically flush will sometimes slow the idle but not by much.

a couple of different things:
a - does the slide actually lower to shut - or is cable or slide hanging up slightly open
b - choke is not shutting properly/leaking fuel through
c - idle jet worn/wrong
d - pumps not working properly and leaking fuel through? phf has one way valve on it right - can't remember haven't worked on one in a while...



there's probably more things it could be....

also shutting the fuel screw and it not stalling may be a good sign on where to start....

it only takes one carb to cause the problem - when you shut down either fuel screw can you hear that cylinder cut out?
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Old 02-11-2015, 01:18 PM   #3
chris a
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What size idle jets are in her and are you sure that the throttle cables have enoufg slack ? PHF 32 wasn't the right carb for a Guzz but I suppose you allready know that ! I guess you have small valve heads.
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Old 02-11-2015, 01:27 PM   #4
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Idk why I said 32...they're the stock 36 with completely stock jetting as well.
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Old 02-11-2015, 01:55 PM   #5
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I run a set on my BMW race bike and even with the stock cam it needs choke to start from cold and sometimes when warm.
It will sort of idle at about 200o RPM
When I had the 336 engine it would not idle at all.
Does your Guzzi have a stock cam?
Could your idle jets be too small causing it run lean?

My 36's came off a Ducati 750 I think.

gleaned this off a Ducati Forum, might be worth checking against.
PHF36BD

Main: 155
Pilot: 60
Choke: 75
Needle: 261 AB1
Jet Needle: K-27 Clipped at 2nd lean position.
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Old 02-11-2015, 02:51 PM   #6
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Is the AR unit returning properly?
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Old 02-11-2015, 04:27 PM   #7
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There is clearly something not right but you already know that. A few good suggestions above.

Not all PHF 36's are created equal. The LM 3 came with lean burn type and had a different shroud in the venturi that meant jetting was totally different with much smaller jets needed. Probably not your issue as it is the LM 3 that normally suffered by those over jetting them.

5,000rpm with choke and 3,000rpm at idle? No, no, no. I can get mine to idle down to less than 600rpm but have it at 1000 where it is smooth and happy.

Just because the carb rubbers are intact doesn't mean it isn't sucking air. Vacuum port and inlet gasket need to be checked. Spray the intake area with WD 40 as the bike is running. If the engine note changes for an instant then you have an air leak.

My main suspect is that the slides are hanging up. Have you checked the connector cable from the bell top to the slide? Is it straight and does it allow the slide to drop to the stop?

Are the side pull levers working properly, springs intact and levers not hitting anything?

Nothing hard or tricky with a PHF. Download the Dellorto Tuning Guide. Its a simplistic guide so don't believe it fully. There are no valves or shut offs between the jets and circuits. All circuits are running at all times, just with less influence depending on throttle opening.

http://www.ducatimeccanica.com/dello.../dellorto.html
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Old 02-11-2015, 08:50 PM   #8
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I don't see how fuel flowing through a jet can wear it out. A water jet can carve steel, but that's a whole different thing. If the jets are stock, I wouldn't worry about them unless the jet needle rubs on the needle jet. But that would affect a different RPM range than idle.

I'm not certain from your description if you dropped the slides lower than 1.5mm.

I also don't know what is meant by the idle screws being flush. Were they screwed all the way to the seat and then backed out a turn? I don't recall if these carbs lean the idle mixture by running the adjusting screw in or out.

As for checking the pumps, do a search for setting them on the 90S. I don't recall specifically the quantity, but X number of pumps should equal X CCs of fuel.

I'll second the opinion that there's either an air leak or the carbs are still set wrong.
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Old 02-12-2015, 07:11 AM   #9
blaine.hale OP
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Is the AR unit returning properly?
I'm eventually going to go into everyone's comments and try them out tonight but I don't think I've ever heard AR unit before. Can you explain?
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Old 02-12-2015, 01:20 PM   #10
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from generally dealing with dellortos: not your specific type.. but usually:

you have two screws. there is no "idle mixture screw" one is an idle screw and the other is the mixture screw.

the idle which just stops your slide; i usually set this by ear: back it out all the way, then just screw it in until you hear a "thunk" and not a "ting" as it hits the end of the needle. then do half a turn in or whatever you want to set a base line. after you set this, always do both sides exactly the same. This screw should be much larger than the mixture screw and easy to identify as its set right at the base of your slide body.

then mixture screw just allows a set amount of gas through even when the throttle is closed: and its linear- so it will add the same amount of gas no matter what your throttle. If you close it all the way (all the way in), and your throttle is closed, the bike should sputter and stop.. as it "should" be getting no fuel at that point. This screw should be on the cylinder side of the carb and below the idle screw. If its on the other side, then its an air adjusting screw.. which I am less familiar with.

If it does not do this, then I'd think there must be something wrong with your mixture screws/circuit - something stuck in there - missing an o-ring or some such and its continuously feeding fuel in.

This could all be BS as i have not dealt with your particular carb, but all the dellortos I have work this way.
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Old 02-12-2015, 01:32 PM   #11
pommie john
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Quote:
Originally Posted by blaine.hale View Post
I'm eventually going to go into everyone's comments and try them out tonight but I don't think I've ever heard AR unit before. Can you explain?

Advance/retard unit. In the little distributer behind the cylinders on a Guzzi. It advances the spark timing as the revs increase. If it's stuck at full advance the RPM won't drop back to idle.

The first thing to check is that you've got slack in the throttle cables when the throttle is fully closed.
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Old 02-13-2015, 07:30 AM   #12
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5,000 and 3,000 are not good. You have gotten good advice..make sure the slide comes all the way down. The idle speed screw has the larger head. Take them both out and see if it still idles high. If yes, make sure the slide is closing. Check distributor advance as well, but if it revs with the idle screw out it's likely something hanging up the slide or an air leak.

Main and pilot jets don't wear, but the slide needles will saw into the emulsifier (needle jet) which will make it run fat from off-idle to WFO. You can replace both at the same time.
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Old 02-13-2015, 07:58 AM   #13
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Heh, just because every person is asking...Yes the slides close. No issues there at all. Plenty of throttle cable slack and I can pull the stacks and actually see the slides all the way down.
I'll be pulling them apart again tonight and posting a picture of all the jetting sizes and such.
I'm thinking I may need to hunt down an ultrasonic cleaner to make sure all channels are cleared out.

Removing the idle adjustment screws is a good idea. I did affect idle by turning them all the way in, but not by much. It would at least narrow down the issue slightly if I can eliminate them as the problem.
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Old 02-13-2015, 11:05 AM   #14
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Do you have an air leak? Put your hand over the bellmouths, if it keeps running, you have a leak.
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Old 02-13-2015, 02:37 PM   #15
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Originally Posted by blaine.hale View Post
Heh, just because every person is asking...Yes the slides close. No issues there at all. Plenty of throttle cable slack and I can pull the stacks and actually see the slides all the way down.
I'll be pulling them apart again tonight and posting a picture of all the jetting sizes and such.
I'm thinking I may need to hunt down an ultrasonic cleaner to make sure all channels are cleared out.

Removing the idle adjustment screws is a good idea. I did affect idle by turning them all the way in, but not by much. It would at least narrow down the issue slightly if I can eliminate them as the problem.

Turning them all the way IN would raise the idle speed, because that raises the slides.

Are you sure you are turning the right ones? The idle speed screw is the one with the big spring around it:

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