Author Topic: Del'Orto Blues  (Read 504 times)

Offline Kiwi_Roy

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Del'Orto Blues
« on: May 05, 2021, 07:33:18 AM »
My 72 Eldorado loop has always been a good runner so earlier this week I was surprised to find it wouldnít idle on both cylinders, the LH cylinder cuts off all together at idle. As soon as the throttle is opened it cuts back in, this makes it very noisy and unpleasant to ride.
According to the manual from Gregís site it has VHB 29 CD on the right and VHB 29 CS on the left, they certainly look like the manual anyway. I cant swear as to the jet sizes  but have no reason to think they would be different from standard, they certainly performed well over the years.
Both carburators had a good amount of gunk in them after being off the road for a year but a quick clean seemed to bring it back to normal.
After running well for several weeks the left cylinder started popping and missing when cold now it just refuses to idle properly. I have checked all the jets several times, spark seems normal checking with a spare plug.
The left carburator is extremely tight on the manifold, even when the clamp is loosened right off, it is all I can do to twist it around to create clearance for dropping the float bowl, Iím wondering if this has caused some distortion somewhere.
One thing I found is the idling screw ďCĒ has no effect on this side so Iím wondering if its something to do with that system, the jets all look clean but maybe there is something plugging a port somewhere.
The description of how this idle screw works is a bit skimpy, does anyone have a detailed diagram of these old carbs, the Del'Orto manual on Greg's site seems to refer to a more modern variety.
Is there any where I could purchase a refurbished pair of VHB 29s?
Thanks in advance for any help, Iím running out of ideas.


A link to the manual
https://www.thisoldtractor.com/mg_manuals/riders_handbook_850.pdf
Page 37 to 45
« Last Edit: May 05, 2021, 07:39:58 AM by Kiwi_Roy »
72 Eldorado
17 V7iii Special
76 Convert

Moto Guzzi - making electricians out of riders since March 15 1921

Online bmc5733946

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Re: Del'Orto Blues
« Reply #1 on: May 05, 2021, 07:42:20 AM »
If you are using resistor plug caps check those. Common problem, low rpm = lower voltage to coil = lower voltage out of coil = no fire through resistor cap, higher rpm = higher voltage from coil passing through higher resistance of the plug cap. The fuel injected bikes display this very well because of the leaner mixture present in the chamber at idle. I learned to replace them regularly  on customer bikes, cheap fix for bad idle. Someone once said, "Carburetor problems frequently masquerade as ignition problems and ignition problems frequently masquerade as carburetor problems." I have frequently found this to be true. ymmv

Brian
« Last Edit: May 05, 2021, 07:51:13 AM by bmc5733946 »
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Offline Kiwi_Roy

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Re: Del'Orto Blues
« Reply #2 on: May 05, 2021, 07:59:33 AM »
If you are using resistor plug caps check those. Common problem, low rpm = lower voltage to coil = lower voltage out of coil = no fire through resistor cap, higher rpm = higher voltage from coil passing through higher resistance of the plug cap. The fuel injected bikes display this very well because of the leaner mixture present in the chamber at idle. I learned to replace them regularly  on customer bikes, cheap fix for bad idle. Someone once said, "Carburetor problems frequently masquerade as ignition problems and ignition problems frequently masquerade as carburetor problems." I have frequently found this to be true. ymmv

Brian
Brian, funny you should mention that I just posted how i was unable to get the suggested plugs BP6ES, but had to settle for BPR6ES with resistors, yes I do have resistor caps also, copper leads though.
I will follow that line.
I have non resistor caps on order.
« Last Edit: May 06, 2021, 03:16:24 AM by Kiwi_Roy »
72 Eldorado
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76 Convert

Moto Guzzi - making electricians out of riders since March 15 1921

Online John A

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Re: Del'Orto Blues
« Reply #3 on: May 05, 2021, 08:32:52 AM »
I learned that itís better to not use both resistor caps and resistor plugs. Itís one or the other but not both. I donít recall the information source but maybe someone knows if thatís true. Resistance could get too high is the reason I suspect
John
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Re: Del'Orto Blues
« Reply #3 on: May 05, 2021, 08:32:52 AM »

Online Antietam Classic Cycle

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Re: Del'Orto Blues
« Reply #4 on: May 05, 2021, 08:57:28 AM »
My 72 Eldorado loop has always been a good runner so earlier this week I was surprised to find it wouldnít idle on both cylinders, the LH cylinder cuts off all together at idle. As soon as the throttle is opened it cuts back in, this makes it very noisy and unpleasant to ride.
According to the manual from Gregís site it has VHB 29 CD on the right and VHB 29 CS on the left, they certainly look like the manual anyway. I cant swear as to the jet sizes  but have no reason to think they would be different from standard, they certainly performed well over the years.
Both carburators had a good amount of gunk in them after being off the road for a year but a quick clean seemed to bring it back to normal.
After running well for several weeks the left cylinder started popping and missing when cold now it just refuses to idle properly. I have checked all the jets several times, spark seems normal checking with a spare plug.
The left carburator is extremely tight on the manifold, even when the clamp is loosened right off, it is all I can do to twist it around to create clearance for dropping the float bowl, Iím wondering if this has caused some distortion somewhere.
One thing I found is the idling screw ďCĒ has no effect on this side so Iím wondering if its something to do with that system, the jets all look clean but maybe there is something plugging a port somewhere.
The description of how this idle screw works is a bit skimpy, does anyone have a detailed diagram of these old carbs, the Del'Orto manual on Greg's site seems to refer to a more modern variety.
Is there any where I could purchase a refurbished pair of VHB 29s?
Thanks in advance for any help, Iím running out of ideas.


A link to the manual
https://www.thisoldtractor.com/mg_manuals/riders_handbook_850.pdf
Page 37 to 45

No mystery about how the idle mixture screw "C" works: turn it in to lean the mixture and out to make it richer.

A careful rebuild may be in order, paying particular attention to making sure all of the orifices are open.
https://www.thisoldtractor.com/moto_guzzi_loopframe_carburetor_rebuild_-__vhb.html

I've had to resort to driving the carbs off of the manifolds with a section of wooden dowel and a hammer. Drive the front edge of the carb where it goes onto the manifold, not anywhere else or damage could result. Smear the plastic sleeve and manifold with anti-seize when installing.

I learned that itís better to not use both resistor caps and resistor plugs. Itís one or the other but not both. I donít recall the information source but maybe someone knows if thatís true. Resistance could get too high is the reason I suspect

This ^^^.
Charlie

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Re: Del'Orto Blues
« Reply #5 on: May 05, 2021, 09:37:53 AM »
I learned that itís better to not use both resistor caps and resistor plugs. Itís one or the other but not both. I donít recall the information source but maybe someone knows if thatís true. Resistance could get too high is the reason I suspect

The ubiquitous NGK black plastic caps are (5K ohm) resistor types, right? Where does one purchase non-resistor plug caps?
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Offline Kiwi_Roy

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Re: Del'Orto Blues
« Reply #6 on: May 05, 2021, 09:46:57 AM »
No mystery about how the idle mixture screw "C" works: turn it in to lean the mixture and out to make it richer.

A careful rebuild may be in order, paying particular attention to making sure all of the orifices are open.
https://www.thisoldtractor.com/moto_guzzi_loopframe_carburetor_rebuild_-__vhb.html

I've had to resort to driving the carbs off of the manifolds with a section of wooden dowel and a hammer. Drive the front edge of the carb where it goes onto the manifold, not anywhere else or damage could result. Smear the plastic sleeve and manifold with anti-seize when installing.

This ^^^.
Thank-you Charlie, thats exactly what I needed especially the rebuild information, I ordered the parts straight away and will look for a bigger hammer LOL

Roy
72 Eldorado
17 V7iii Special
76 Convert

Moto Guzzi - making electricians out of riders since March 15 1921

Offline Guzler

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Re: Del'Orto Blues
« Reply #7 on: May 05, 2021, 11:10:25 AM »
The ubiquitous NGK black plastic caps are (5K ohm) resistor types, right? Where does one purchase non-resistor plug caps?
From NGK of course. I have a set of each, depending on which plug is handy.

Offline Tom H

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Re: Del'Orto Blues
« Reply #8 on: May 05, 2021, 11:17:15 AM »
NGK cap codes:




Ebay has the 1k and I think Amazon. Usually more expensive then the 5K.

The EVT at least breaks the rule of resistor plug OR cap, not both. Manual calls for both to BE resistor.

I had a VHB30 that the pilot jet passageway was clogged. Same type symptoms. I used a jet cleaning wire/welding tip cleaner to gently work through the passageway.

Tom
« Last Edit: May 05, 2021, 11:20:02 AM by Tom H »
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Offline leroy_can

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Re: Del'Orto Blues
« Reply #9 on: May 05, 2021, 11:26:26 AM »
 Sounds as if some little gremlin is in that idle circuit. My LMIV suddenly developed that symptom on a trip years ago and all I did was remove the screw completely and fire it up letting it spit and hack for a few moments then put the screw back to it's original setting. If the carb to manifold you mention is metal to metal as I suspect I would use fine lapping compound #320 to 400 grit to improve the fit. The same Clover brand sold for valve lapping is available in a variety of very fine grades. I used to get it from Acklands/Granger. 320 is my overall favorite not course enough to be gritty but still works fairly fast and is ideal for that sort of situation just taking down the high points.
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Offline guzzisteve

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Re: Del'Orto Blues
« Reply #10 on: May 05, 2021, 11:31:10 AM »
Roy,  If you back out the idle mixture screw, shoot some carb cleaner in & make sure it comes out the jet AND the carb throat. Use some compressed air. Reinstall to where you had it or thereabouts, 2-2 3/4 turns out. Should not be 3 turns or more.
You can still get straight plug caps w/wires all in one, most auto supplies have a rack of different lengths. All made up, much better crimps than making your own.
« Last Edit: May 05, 2021, 11:32:08 AM by guzzisteve »
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Online jwinwi

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Re: Del'Orto Blues
« Reply #11 on: May 05, 2021, 11:52:15 AM »
NGK cap codes:




Ebay has the 1k and I think Amazon. Usually more expensive then the 5K.

The EVT at least breaks the rule of resistor plug OR cap, not both. Manual calls for both to BE resistor.

I had a VHB30 that the pilot jet passageway was clogged. Same type symptoms. I used a jet cleaning wire/welding tip cleaner to gently work through the passageway.

Tom

Thank you Tom!
96 Blue Sport 1100 'Stella'
76 V1000 Ex Convert
73 V7 Sport
02 Suzuki SV650 AHRMA #646 SoT3

 'The days I keep my gratitude higher than my expectations I have really good days'. RWH

Offline Alfetta

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Re: Del'Orto Blues
« Reply #12 on: May 05, 2021, 12:56:30 PM »
Kiwi_Roy...

Is your scoot equipped with a radio ?
NO, It's not pronounced "moder goosy"

Offline Kiwi_Roy

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Re: Del'Orto Blues
« Reply #13 on: May 05, 2021, 07:17:37 PM »
Once again the calm voice of experience saved the day
I viewed the file Charlie attached which allowed me to prove the passageways.
I never actually found one plugged but I must have blasted something out because the bike is back to it's old sweet tempered self.
I followed your instructions on lubing the clamp and it's much improved.
Thanks again Charlie, my Wife says thank-you as well, I am safe to live with again.
72 Eldorado
17 V7iii Special
76 Convert

Moto Guzzi - making electricians out of riders since March 15 1921

Online Antietam Classic Cycle

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Re: Del'Orto Blues
« Reply #14 on: May 05, 2021, 07:32:02 PM »
Once again the calm voice of experience saved the day
I viewed the file Charlie attached which allowed me to prove the passageways.
I never actually found one plugged but I must have blasted something out because the bike is back to it's old sweet tempered self.
I followed your instructions on lubing the clamp and it's much improved.
Thanks again Charlie, my Wife says thank-you as well, I am safe to live with again.

You're welcome, happy to help.  :thumb:
Charlie

Offline Scout63

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Re: Del'Orto Blues
« Reply #15 on: May 07, 2021, 05:24:50 AM »
Itís always the soon to be ex-husband, and almost always a clogged idle jet. Tiny orifice, crappy gas and the bike has usually been sitting about three times as long as an owner claims. I used to ask sellers how long.  Now I just sniff the tank.  God I love the smell of gasoline.
Ben Zehnder
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