Carburetor conundrum Guzzi content

[ccoli]

I know that most fuel related issues are electrical,  however.
Bike is a Cal 3 with 36mm PHF Dellortos.
Right side works great, mixture screw works as expected ...all good there.
Left side runs fine off idle eg throttle open to any extent. Not so at idle.
Left side will fire somewhat if the idle speed screw is ALL the way in and the mixture screw is likewise ALL the way in. If I pull up on thr choke it runs better,  still not great.
Ultrasonic cleaned, gumout cleaned. Multiple times. Compressed air through everything i can find. Reassemble and it acts the same. Exchange plugs, floats and needle valves. Same. 
What next? Exchange Jets? Coils? Torque heads and set valves?
Not my bike so unknown history. Very low mileage machine,  7k.

[Canuck750]

If the PHF 36 are new Dellorto units they are a lean burn carb and to achieve an idle the pilot jets need to larger than the old PHF 36. I have installed new PHF 36 Dellorto’s on my 1975 Ducati 860 and 1973 Laverda SF1 and with stock jets (50) neither bike would idle and only started on choke. The Ducsti forum explained that a 65 pilot (minimum) would cure the problem and it did! The mixture screw is a fuel screw, out for rich and in for lean. If you can turn the mixture screw all the way in and the bike keeps running the pilot is too big. If you have to turn the screw out more than 3 turns the jet is too small, this from the Ducati Bevel forum and the advice worked for me.

[nc43bsa]

Switch the carbs.

If the problem follows the L carb to the R cylinder, the problem is in the L carb.  If it doesn't, the problem is not in the carb.

[SED]

The PHF 36s on my LMIII have an atomizer below the idle jet. It seems like a great trap for corrosion - could it be blocked?  It is worth proving that there is communication between the idle needle and the idle and transfer ports in the carb throat.

[moto-uno]

  And if you have a can of WD-40 handy , don't be afraid to spray it all over the intake area of the poor running side , this will
show you if part of your problem may be an air leak .  Peter

[Turin]

My 850T had running issues when I bought it. someone had rebuilt both carbs at the same time and put two main jets in in one of them. 

[Peter from Sch'dy]

I had a similar problem with a convert. Turned out valves on poor running side were tight..worth a look anyway.
Good luck!
Peter

[jwinwi]

I had a similar problem with a convert. Turned out valves on poor running side were tight..worth a look anyway.
Good luck!
Peter

With unknown history, valve lash is a good place to start. Not saying it IS ignition related but what system is it? Points, Dyna, Dodgyplex, Motoplat?
EDIT: Idle mixture screw should be about 1-1/2 turns out, right? All the way in is the leanest setting...

[guzzisteve]

What distributor does it have? Bosch? Dyna? Guzzi's electronic ign?

Does it have long tip mixture screws? You can trim them back to VHB size. Works better.

All good info on carbs here. Wouldn't hurt to check valves.

[ccoli]

Ignition is a Digiplex. Bike built 4/93.. PHF main and idle Jets have different threads so can't interchange like a VHB. Will check valves first as it's cold and I do have spare gaskets handy. Swapping carbs would be difficult as they are designed for right and left. Might try Swapping idle and pilots. Mixture screws are not the long ones and the right side is about 1-1/2 turns out.
Unfortunately schedule may not allow for much wrench time for a couple days.
Will certainly keep you posted.

[guzzisteve]

Put a timing light on the side w/miss make sure it's not skipping from ign. It is a Digiplex after all. 93's are pretty good usually.

[Chuck in Indiana]

I've never heard of a problem with a Digiplex as long as it's getting power. <shrug>

Unfortunately schedule may not allow for much wrench time for a couple days.

Yeah, yeah. You headed off to some exotic locale?

[chuck peterson]

Cal 111, w 36 phf

The needle valve, that is spring loaded, was getting hung up

Worked…didn’t…..worked….didn’t

Fuel flow on that side worked…didn’t…worked…didn’t

The tiniest spring inside that needle valve forked things up for several months as i…

Chased everything else. Timing, points, plugs, cables, floats, gaskets, overflow tubes, slides, needle, voltage, coils, grounds, and anything else I could find within arms reach

Frustrated on the sunny driveway, I casually pushed on the float needle valve thingee…clickclickclickingstuck

“Oh, it’s spring loaded..”

“and it sticks, too…”

Low fuel in the float bowl?

My first effort of motorcycle repairs…check everything else first so it’ll be your final possible solution

[pressureangle]

Verify that the rubber on the choke plunger isn't disintegrating from age and ethanol. Dellortos have a very weird reverse-flow choke fuel path- you may think that raising the choke adds fuel, but they are designed so that when you raise the slide enough they stop drawing fuel through the choke and draw air instead. No other carb I've seen works this way.

[ccoli]

Ok i got a little done before I left for the big city. Milwaukee to pick up mail and attend a Rhett Miller show tonight.
Checked valves, right exhaust was a little tight. Otherwise not bad. Torque heads, the did snug down a bit.  Set all valves. Checked spark, seems consistent. Choke tips look good, super low mileage bike and owner says, no ethanol. There were some metal shavings on the timing sensor.
Chuck; BTDT on my Spiii with something over 150k miles the spring valve came apart causing intermittent problems,  you'd think things would last longer than that 👌.
Sprayed more cleaner...
Still won't fire at low RPMs. Taking a break for a few days. Then I think I will try Swapping Jets side to side. Pick up a couple more cans of carb cleaner.

[ccoli]

I think I am insane. I keep trying the same thing and expecting a result of some kind.
Been through 2 cans of gum out and blown air through the passages. Rechecked Jets, floats. I still won't idle correctly on the left side. It will fire if I choke it or pull the mixture screw out entirely. Took it out for a short ride and it runs wonderful above idle.
Lost most of the mercury from my carb stix in a moving accident.
All of this frustration while I'm taping and mudding drywall in my new workshop. Fun and games.
PS Jets are 130 main, 60 idle and 70 pilot.

[Chuck in Indiana]

I think I am insane.

Realization is the first step.   
<sotto voice> Hey man.. I just scored a fair sized jug of mercury. Want me to bring some to help a brother out to the Wisconsin rally?

[lucian]

left float level too low?  The fact that you have to wind the idle screw all the way in and choke that side tells me it requiring more air flow to lift fuel at idle . Like RK mentioned, you can check bowl volumes , make sure you close the petcocks first.  Personally I would check the left float level and be sure it's floating and not sinking/leaking.  It's important also that both slides are resting on the idle stop screws and not hanging by the cables as RK stated.

[John A]

Realization is the first step.   
<sotto voice> Hey man.. I just scored a fair sized jug of mercury. Want me to bring some to help a brother out to the Wisconsin rally?

You beat me to it, I was going to offer some of my stash at the rally!

[Scout63]

Did you pull the idle jets and mechanically clean out the holes?  Spraying or ultrasonic cleaning won’t work. Usually a #78 drill bit or .016” guitar string will fit most idle jet holes.  When the bikes sit these are the first to clog.

[jwinwi]

Chris, have you set the idle mixture screw to 1-1/2 - 2 turns out? Most likely not the whole problem but you said it and the idle speed screws were all the way in.

[ccoli]

Float volumes seem good and I did swap the oats side to side. No problem with fuel flow to the carbs. I will use the tuna can method to verify them, but it might be a Nevada rally coffee cup instead 😉
I do not have nor know what a jet brush is. So no did not use one.
I can see through all the Jets except for the accelerator pump check valve whichI can blow through one way.  I have to think some passage in the body is clogged.
Yes John or Chuck i would love to have a new stash of mercury,  I will look into how much volume I need.
The right side carb adjustment is about 1-1/2 turn out, the left side does little or nothing between all the way in and all the out as in removed.
So yes there is slack in the cables and the idle speed screws are lifting the slides
Slides cannot be reversed like on a VHB.
I'll try  cleaning again and hope for different results 😅 do have some old guitar strings if it comes to that.

[guzzisteve]

Got to be in the body, Chris. I got one of those newfangled carb sync sticks w/stainless rods in it cause I got low on mercury.

[F-Fred]

Chris, I have a DS left-side 36mm body from a Cal III you could borrow and swap out?  It's been soaked in my bucket of old-school carb cleaner (methylene chloride).

[ccoli]

Guess I forgot to pray to Carlo.
Problem still unsolved.
Today I
Verified fuel bowl volume. Same on both sides.
Clean body, idle and pilot jets. Used another can of gum out. Couldn't find guitar strings so I used sewing needles. Thought I had found a plugged passage. Reassemble and fire it up same old sh#$. Tried something different by removing the choke completely. Leaving a big air hole above the pilot. Ran better than ever.
The cable on the affected carb seems a little tight in not much free play.  Changed it out with one that was a tad longer. Idle speed screw does move the slide, so it's not too bad. Might disassemble the splitter to soon if I can get some more free play. Not the biggest problem here.
Fred, I may have to try my left carb from the Spiii but its 170 miles away. Thanks for the offer.
May just put it all back together so the owner can bring it to the Wisconsin rally. It runs fine other than Idle.

[ccoli]

Another interesting fun fact is that the aftermarket exhaust system has no crossover. Think it might be Bub.
I also cleaned up a section of the woods. Burning the brush and dead trees and composting the old leaves, in case you think iam spending too much time on this. Need to get back to mudding drywall in the workshop.

[SED]

Have you tried squirting extra fuel in the throat of the offending carb at idle to see if it starts to run?

Two ideas.  Some (all?) PHFs have an emulsion tube under the idle jet that could be easily blocked.  Maybe it is clogged?  Guzziology suggests they can be removed and not affect the running. 

Also, having been warned away from using wires to clean jets I resorted to using round, hardwood toothpicks.  Push it into the jet and it will compress a small amount to the size of the jet.  Twisting the toothpick will polish the jet and you can insert it from the other side too.  Just don't break it off in the jet! 

Good luck.

[Chuck in Indiana]

Guess I forgot to pray to Carlo.
Problem still unsolved.
Today I
Verified fuel bowl volume. Same on both sides.
Clean body, idle and pilot jets. Used another can of gum out. Couldn't find guitar strings so I used sewing needles. Thought I had found a plugged passage. Reassemble and fire it up same old sh#$. Tried something different by removing the choke completely. Leaving a big air hole above the pilot. Ran better than ever.
The cable on the affected carb seems a little tight in not much free play.  Changed it out with one that was a tad longer. Idle speed screw does move the slide, so it's not too bad. Might disassemble the splitter to soon if I can get some more free play. Not the biggest problem here.
Fred, I may have to try my left carb from the Spiii but its 170 miles away. Thanks for the offer.
May just put it all back together so the owner can bring it to the Wisconsin rally. It runs fine other than Idle.

C'mon, pal.. idle is controlled strictly by the idle jet circuit. It's not rocket science..  

[ccoli]

C'mon, pal.. idle is controlled strictly by the idle jet circuit. It's not rocket science..  

And I'm no rocket surgeon! Decided to run to Milwaukee to get the left carb off the SPIII. Convenient night for a little party in town as we just won the NBA TITLE! Go Bucks!