New 20 ounce tumblers available now! Forum donation credit with purchase. https://www.wildguzzi.com/Products/products.htm#Tumbler
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. ymmvBrian
My 72 Eldorado loop has always been a good runner so earlier this week I was surprised to find it wouldn’t 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 Greg’s 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, I’m wondering if this has caused some distortion somewhere.One thing I found is the idling screw “C” has no effect on this side so I’m 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, I’m running out of ideas.A link to the manualhttps://www.thisoldtractor.com/mg_manuals/riders_handbook_850.pdf Page 37 to 45
I learned that it’s better to not use both resistor caps and resistor plugs. It’s one or the other but not both. I don’t recall the information source but maybe someone knows if that’s true. Resistance could get too high is the reason I suspect
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.htmlI'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 ^^^.
The ubiquitous NGK black plastic caps are (5K ohm) resistor types, right? Where does one purchase non-resistor plug caps?
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
Once again the calm voice of experience saved the dayI 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.