Gregory Bender

Carburetor rebuild - Dellorto VHB

Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models

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This is a series of photos I took during the assembly of the carburetors on my V1000 I-Convert project bike. These are Dellorto VHB 30 carburetors. But, the procedure is 100% identical for Dellorto VHB 29 carburetors. Thanks to Charlie Mullendore of Antietam Classic Cycle, Robert Hawkes, Steve Farris, Adam S., and Joe Tokarz for making helpful suggestions for improvement.

It is a very good idea to work on one carburetor at a time. That way, you can refer to the assembled carburetor as a pattern.

Parts needed

Consumable parts I always replace:

Consumable parts I replace depending on condition:

Disassembly

Disassembly is pretty much the reversal of assembly. So, just start from the last photo, and work your way up to the top.

Cleaning

Prior to these photos being taken, I had completely disassembled both carburetors and soaked all of the metal parts in a bucket of carb cleaner. With the parts out of the carb cleaner, I thoroughly rinsed them in a bucket of rubbing alcohol. Rubbing alcohol dries very quickly, leaves no residue, and - in my experience - does a good job of neutralizing the carb cleaner (though I'm not a chemist and haven't a clue whether or not alcohol neutralizes the carb cleaner, or simply dilutes it to a point where it doesn't matter). Use gasoline if you like, but I prefer rubbing alcohol. Even after cleaning, some of the brass parts appear discolored. Not to worry, they are clean and the discoloration really doesn't matter, as they will discolor again soon enough. But, if you like, a quick turn at a fine wire wheel (not coarse or heavy) will polish them up nicely. Just be cautious around the openings so that they are not enlarged and DO NOT WIRE WHEEL THE TAPERED NEEDLE AT ALL.

As an alternative, after soaking the parts in carburetor cleaner, Charlie Mullendore of Antietam Classic Cycle rinses them thoroughly in cold water, then hot water, and finally sprays through all of the passages with Berkebile 2+2 Gum Cutter.

Assembly

A bunch of carburetor parts!
A bunch of carburetor parts!

Photo courtesy of Gregory Bender.

Clean the jets

Here is a strand of wire I've pulled from a wire brush. The wire is stiff and strong, yet small enough to easily fit through the smallest passageways.
Here is a strand of wire I've pulled from a wire brush. The wire is stiff and strong, yet small enough to easily fit through the smallest passageways.

Photo courtesy of Gregory Bender.

The strand of wire next to a jet.
The strand of wire next to a jet.

Photo courtesy of Gregory Bender.

Insert the wire through the jet and spin the jet around a few times with your finger. Repeat with all the holes in all the jets: both main jets, both idle jets, both choke (enricher) jets, and both atomizers. Quick, simple, done. I learned this tip from my Dad, Tom Bender.
Insert the wire through the jet and spin the jet around a few times with your finger. Repeat with all the holes in all the jets: both main jets, both idle jets, both choke (enricher) jets, and both atomizers. Quick, simple, done. I learned this tip from my Dad, Tom Bender.

Photo courtesy of Gregory Bender.

As an alternative to using a wire from a wire brush, Joe Tokarz sent me his method:

I have an alternative wire for carb jet cleaning. I use stands of wire plucked from old control cables.

Throttle wires are the thinnest, and front brake is thicker.

The wire is stiff and has a natural ripple to it and that makes orifice cleaning easy. Just be sure to cut the end clean; no burs. The wire can be straightened with pliers if needed.

With this in mind I have been able to amass a supply of carb cleaning wires that will last for about 200 years.

Photo courtesy of Joe Tokarz.

Clean the passageways

Blowing compressed air through the idle jet passage...
Blowing compressed air through the idle jet passage...

Photo courtesy of Gregory Bender.

...you should feel air escaping from (a) the mixture screw hole, (b) two tiny holes in the throat of the carb (you've shown one - there's another closer to the atomizer hole IIRC) and (c) a small port at the inlet near the threads for the velocity stack (thanks to Charlie Mullendore of Antietam Classic Cycle for assisting in identifying air escape locations).
...you should feel air escaping from (a) the mixture screw hole, (b) two tiny holes in the throat of the carb (you've shown one - there's another closer to the atomizer hole IIRC) and (c) a small port at the inlet near the threads for the velocity stack (thanks to Charlie Mullendore of Antietam Classic Cycle for assisting in identifying air escape locations).

Photo courtesy of Gregory Bender.

Blowing compressed air through the main jet passage...
Blowing compressed air through the main jet passage...

Photo courtesy of Gregory Bender.

...you should feel air escaping from this location.
...you should feel air escaping from this location.

Photo courtesy of Gregory Bender.

Blowing compressed air through the mixture screw location.
Blowing compressed air through the mixture screw location.

Photo courtesy of Gregory Bender.

Blowing air through the vent...
Blowing air through the vent...

Photo courtesy of Gregory Bender.

...you should feel air escaping from this location AND...
...you should feel air escaping from this location AND...

Photo courtesy of Gregory Bender.

...you should feel air escaping from this location.
...you should feel air escaping from this location.

Photo courtesy of Gregory Bender.

Blowing air through the choke (enricher) jet passage...
Blowing air through the choke (enricher) jet passage...

Photo courtesy of Gregory Bender.

...you should feel air escaping from this location AND...
...you should feel air escaping from this location AND...

Photo courtesy of Gregory Bender.

...you should feel air escaping from this location.
...you should feel air escaping from this location.

Photo courtesy of Gregory Bender.

Blowing air through the vent...
Blowing air through the vent...

Photo courtesy of Gregory Bender.

...you should feel air escaping from this location.
...you should feel air escaping from this location.

Photo courtesy of Gregory Bender.

Blowing air through the choke (enricher) jet passageway in the float bowl...
Blowing air through the choke (enricher) jet passageway in the float bowl...

Photo courtesy of Gregory Bender.

...you should feel air escaping from this location.
...you should feel air escaping from this location.

Photo courtesy of Gregory Bender.

Accelerator pump, atomizer, main jet

Note: Some prefer not to disassemble the accelerator pump piston; choosing instead to consider it perfectly functional if they hear the plastic ball bearing rattle inside the accelerator pump piston.

This is the small plastic ball bearing.
This is the small plastic ball bearing.

Photo courtesy of Gregory Bender.

Place it inside the accelerator pump piston.
Place it inside the accelerator pump piston.

Photo courtesy of Gregory Bender.

Screw the spring holder into the pump piston.
Screw the spring holder into the pump piston.

Photo courtesy of Gregory Bender.

I keep the pump piston from rotating with a pair of snap ring pliers.
I keep the pump piston from rotating with a pair of snap ring pliers.

Photo courtesy of Gregory Bender.

Then I give the spring holder a bit of a snug with a screwdriver. It doesn't need much, just a wee little bit.
Then I give the spring holder a bit of a snug with a screwdriver. It doesn't need much, just a wee little bit.

Photo courtesy of Gregory Bender.

Now insert the assembled pump piston into the accelerator pump body.
Now insert the assembled pump piston into the accelerator pump body.

Photo courtesy of Gregory Bender.

Place the spring on the end of the spring holder.
Place the spring on the end of the spring holder.

Photo courtesy of Gregory Bender.

Slide it into place and screw on the main jet holder.
Slide it into place and screw on the main jet holder.

Photo courtesy of Gregory Bender.

Tighten the main jet holder to the accelerator pump body with a pair of wrenches. Just a light snug. There is no need for much torque at all here.
Tighten the main jet holder to the accelerator pump body with a pair of wrenches. Just a light snug. There is no need for much torque at all here.

Photo courtesy of Gregory Bender.

Now place the main jet into the main jet holder.
Now place the main jet into the main jet holder.

Photo courtesy of Gregory Bender.

Secure the main jet in place with a wrench and a screwdriver. Just a light snug. Don't get carried away and strip the threads, etc.
Secure the main jet in place with a wrench and a screwdriver. Just a light snug. Don't get carried away and strip the threads, etc.

Photo courtesy of Gregory Bender.

Place the atomizer into the main jet passageway.
Place the atomizer into the main jet passageway.

Photo courtesy of Gregory Bender.

Set the carburetor on end and let the atomizer fall to the bottom.
Set the carburetor on end and let the atomizer fall to the bottom.

Photo courtesy of Gregory Bender.

Use a wooden popsicle stick to push the atomizer into place. The wood is soft and you will avoid damaging the atomizer. I learned this tip from Charlie Mullendore of Antietam Classic Cycle.
Use a wooden popsicle stick to push the atomizer into place. The wood is soft and you will avoid damaging the atomizer. I learned this tip from Charlie Mullendore of Antietam Classic Cycle.

Photo courtesy of Gregory Bender.

You'll know it is seated properly when you can see it protruding here. Note: I am using the ice pick as a pointer, I am not poking anything.
You'll know it is seated properly when you can see it protruding here. Note: I am using the ice pick as a pointer, I am not poking anything.

Photo courtesy of Gregory Bender.

Insert the accelerator pump assembly into the main jet passageway.
Insert the accelerator pump assembly into the main jet passageway.

Photo courtesy of Gregory Bender.

And tighten with a wrench. Just a light snug. There is no need to start weight lifting just to assemble Dellorto carburetors.
And tighten with a wrench. Just a light snug. There is no need to start weight lifting just to assemble Dellorto carburetors.

Photo courtesy of Gregory Bender.

Idle jet

Insert the idle jet into its passageway.
Insert the idle jet into its passageway.

Photo courtesy of Gregory Bender.

And tighten with a screwdriver. Just a light snug. You should be getting a very clear picture by now that nothing on the carburetor requires much torque.
And tighten with a screwdriver. Just a light snug. You should be getting a very clear picture by now that nothing on the carburetor requires much torque.

Photo courtesy of Gregory Bender.

Choke (enricher) jet

Here is the contents of the carburetor kit. Notice that there are 3 small O-rings. The middle sized one is used for the choke (enricher) jet.
Here is the contents of the carburetor kit. Notice that there are 3 small O-rings. The middle sized one is used for the choke (enricher) jet.

Photo courtesy of Gregory Bender.


								I position the O-ring like this, and then push it over the top. I've found this method easier than trying to bring it up from the other end. Charlie Mullendore of Antietam Classic Cycle prefers to slip it up over the threaded end first, then work it over the larger end into the groove. Either way works fine. Charlie recommends using silicone spray lubricant on the O-ring to help it slip on easier.
								
								Note: Gary Frankel sent me information about the simple tool he made to make installing this O-ring much easier. Check out his tool for installing the enricher jet O-ring on Dellorto carburetors.

I position the O-ring like this, and then push it over the top. I've found this method easier than trying to bring it up from the other end. Charlie Mullendore of Antietam Classic Cycle prefers to slip it up over the threaded end first, then work it over the larger end into the groove. Either way works fine. Charlie recommends using silicone spray lubricant on the O-ring to help it slip on easier.

Note: Gary Frankel sent me information about the simple tool he made to make installing this O-ring much easier. Check out his tool for installing the enricher jet O-ring on Dellorto carburetors.

Photo courtesy of Gregory Bender.

Here the O-ring is in place on the choke (enricher) jet.
Here the O-ring is in place on the choke (enricher) jet.

Photo courtesy of Gregory Bender.

Insert the choke (enricher) jet into the body of the carburetor.
Insert the choke (enricher) jet into the body of the carburetor.

Photo courtesy of Gregory Bender.

And tighten with a screwdriver. Just a light snug.
And tighten with a screwdriver. Just a light snug.

Photo courtesy of Gregory Bender.

Float, float needle, float pivot pin

This is the float, float pivot pin, and float needle.
This is the float, float pivot pin, and float needle.

Photo courtesy of Gregory Bender.

Place the float needle into the clip on the float.
Place the float needle into the clip on the float.

Photo courtesy of Gregory Bender.

Insert the float needle into the carburetor body and position the float between the hinges.
Insert the float needle into the carburetor body and position the float between the hinges.

Photo courtesy of Gregory Bender.

Insert the float pivot pin.
Insert the float pivot pin.

Photo courtesy of Gregory Bender.

And push it through to the other side. USE YOUR FINGERS ONLY! There is no need whatsoever for the float pivot pin to be hammered or wedged into place. If the splined end gets stuck too far in, the pin is very difficult to remove. The float bowl will prevent the pin from falling out, anyway.
And push it through to the other side. USE YOUR FINGERS ONLY! There is no need whatsoever for the float pivot pin to be hammered or wedged into place. If the splined end gets stuck too far in, the pin is very difficult to remove. The float bowl will prevent the pin from falling out, anyway.

Photo courtesy of Gregory Bender.

Float bowl, float bowl nut

Now it is time to fit the large O-ring to the float bowl. It is easier to do if the O-ring and float bowl are warm. So, if you are working in the winter months, just take it inside the house and let it warm up.
Now it is time to fit the large O-ring to the float bowl. It is easier to do if the O-ring and float bowl are warm. So, if you are working in the winter months, just take it inside the house and let it warm up.

Photo courtesy of Gregory Bender.

Start in this corner.
Start in this corner.

Photo courtesy of Gregory Bender.

Then do this corner.
Then do this corner.

Photo courtesy of Gregory Bender.

Then do this corner.
Then do this corner.

Photo courtesy of Gregory Bender.

Up to now, fitting the O-ring has been easy. Now comes the tricky corner. If you roll the O-ring into place, it will immediately try to roll back out. You can fight it for eternity (or until the O-ring breaks) and it'll still want to roll out. The trick is to roll it in the opposite direction just a bit using your thumb and forefinger, and then roll it into place. This neutralizes any roll and the O-ring will stay nicely in place.
Up to now, fitting the O-ring has been easy. Now comes the tricky corner. If you roll the O-ring into place, it will immediately try to roll back out. You can fight it for eternity (or until the O-ring breaks) and it'll still want to roll out. The trick is to roll it in the opposite direction just a bit using your thumb and forefinger, and then roll it into place. This neutralizes any roll and the O-ring will stay nicely in place.

Photo courtesy of Gregory Bender.

Fit the float bowl to the carb. You may need to wiggle it in place a bit as you seat the O-ring on the choke (enricher) jet.
Fit the float bowl to the carb. You may need to wiggle it in place a bit as you seat the O-ring on the choke (enricher) jet.

Photo courtesy of Gregory Bender.

The float bowl nut and gasket.
The float bowl nut and gasket.

Photo courtesy of Gregory Bender.

Fit the gasket to the float bowl nut. Charlie Mullendore of Antietam Classic Cycle uses a little dielectric grease on the gasket to help it tighten down easier.
Fit the gasket to the float bowl nut. Charlie Mullendore of Antietam Classic Cycle uses a little dielectric grease on the gasket to help it tighten down easier.

Photo courtesy of Gregory Bender.

Screw the float bowl nut in place.
Screw the float bowl nut in place.

Photo courtesy of Gregory Bender.

And tighten with a wrench. A heavy snug is good here. You want the float bowl tight. But again, we are dealing with soft metals, so take it easy.
And tighten with a wrench. A heavy snug is good here. You want the float bowl tight. But again, we are dealing with soft metals, so take it easy.

Photo courtesy of Gregory Bender.

Idle speed screw

The idle speed screw and spring.
The idle speed screw and spring.

Photo courtesy of Gregory Bender.

Place the spring on the idle speed screw.
Place the spring on the idle speed screw.

Photo courtesy of Gregory Bender.

Insert the idle speed screw and spring into the body of the carburetor. Tighten it down a bit.
Insert the idle speed screw and spring into the body of the carburetor. Tighten it down a bit.

Photo courtesy of Gregory Bender.

You can see the end of the idle speed screw protruding through to the inside.
You can see the end of the idle speed screw protruding through to the inside.

Photo courtesy of Gregory Bender.

Mixture screw

The mixture screw and spring.
The mixture screw and spring.

Photo courtesy of Gregory Bender.

Place the spring on the mixture screw.
Place the spring on the mixture screw.

Photo courtesy of Gregory Bender.

Insert the mixture speed screw and spring into the body of the carburetor. Screw it in until it bottoms out. DO NOT OVERTIGHTEN! Just bottom it out gently. Then, back it out the number of turns specified by the workshop manual (generally 1 1⁄2 - 2 turns for the left carburetor and 1 3⁄4 - 2 1⁄4 turns for the right carb).
Insert the mixture speed screw and spring into the body of the carburetor. Screw it in until it bottoms out. DO NOT OVERTIGHTEN! Just bottom it out gently. Then, back it out the number of turns specified by the workshop manual (generally 1 12 - 2 turns for the left carburetor and 1 34 - 2 14 turns for the right carb).

Photo courtesy of Gregory Bender.

Slide and tapered needle

The slide and tapered needle.
The slide and tapered needle.

Photo courtesy of Gregory Bender.

Insert the top of the tapered needle into the bottom of the slide and push it through. I do it this way so that I avoid any potential damage to the tapered needle.
Insert the top of the tapered needle into the bottom of the slide and push it through. I do it this way so that I avoid any potential damage to the tapered needle.

Photo courtesy of Gregory Bender.

Place the needle clip in the position specified by the workshop manual (generally the middle).
Place the needle clip in the position specified by the workshop manual (generally the middle).

Photo courtesy of Gregory Bender.

Insert the slide complete with tapered needle into the body of the carburetor. Notice that the large flat area of the slide must face the intake manifold, not the air filter.
Insert the slide complete with tapered needle into the body of the carburetor. Notice that the large flat area of the slide must face the intake manifold, not the air filter.

Photo courtesy of Gregory Bender.

Carburetor top and throttle return spring

The carburetor top and gasket.
The carburetor top and gasket.

Photo courtesy of Gregory Bender.

Fit the gasket to the carburetor top.
Fit the gasket to the carburetor top.

Photo courtesy of Gregory Bender.

I like to slather on some grease in a hopeless attempt to keep the gaskets from shrinking.
I like to slather on some grease in a hopeless attempt to keep the gaskets from shrinking.

Photo courtesy of Gregory Bender.

Insert the bolts complete with wave washers.
Insert the bolts complete with wave washers.

Photo courtesy of Gregory Bender.

Insert the cable adjuster complete with jam nut.
Insert the cable adjuster complete with jam nut.

Photo courtesy of Gregory Bender.

Here is the throttle return spring. Notice that one end has the wire bent in toward the middle.
Here is the throttle return spring. Notice that one end has the wire bent in toward the middle.

Photo courtesy of Gregory Bender.

Insert the bent end into the carburetor top. This holds the spring in place.
Insert the bent end into the carburetor top. This holds the spring in place.

Photo courtesy of Gregory Bender.

Now place the carburetor top complete with spring onto the top of the carburetor. Note that the cable adjuster is positioned nearest the intake manifold, not the air filter.
Now place the carburetor top complete with spring onto the top of the carburetor. Note that the cable adjuster is positioned nearest the intake manifold, not the air filter.

Photo courtesy of Gregory Bender.

Hold the top down on top of the carburetor body and screw the top in place. DO NOT OVERTIGHTEN THESE BOLTS! They only take a light snug and are far too easy to strip. Be careful. I will also reemphasize, hold the top in its finished position and then screw the bolts in place. That is, don't use the bolts to pull the top into position.
Hold the top down on top of the carburetor body and screw the top in place. DO NOT OVERTIGHTEN THESE BOLTS! They only take a light snug and are far too easy to strip. Be careful. I will also reemphasize, hold the top in its finished position and then screw the bolts in place. That is, don't use the bolts to pull the top into position.

Photo courtesy of Gregory Bender.

Choke (enricher) assembly

Here is the choke (enricher) assembly.
Here is the choke (enricher) assembly.

Photo courtesy of Gregory Bender.

This is the sealing surface of the choke (enricher) plungers. New plungers have a flat sealing surface that has not been indented by years of constant spring pressure. While these may function fine, I will not reuse them. New ones are inexpensive and easily replaced. Adam S. recommends the following technique to extend the life of the plungers: One trick that I use, and it works fine, is to remove the rubber plug from the choke plunger, using a small dental pick. Flip the rubber piece over and you'll have a nice new sealing surface.
This is the sealing surface of the choke (enricher) plungers. New plungers have a flat sealing surface that has not been indented by years of constant spring pressure. While these may function fine, I will not reuse them. New ones are inexpensive and easily replaced. Adam S. recommends the following technique to extend the life of the plungers: One trick that I use, and it works fine, is to remove the rubber plug from the choke plunger, using a small dental pick. Flip the rubber piece over and you'll have a nice new sealing surface.

Photo courtesy of Gregory Bender.

The body uses the largest of the small O-rings.
The body uses the largest of the small O-rings.

Photo courtesy of Gregory Bender.

And fits in place like so.
And fits in place like so.

Photo courtesy of Gregory Bender.

Insert the assembly like this.
Insert the assembly like this.

Photo courtesy of Gregory Bender.

And secure in place with the screw.
And secure in place with the screw.

Photo courtesy of Gregory Bender.

Insert the cable adjuster.
Insert the cable adjuster.

Photo courtesy of Gregory Bender.

Place a rubber dust cap on the cable adjuster for the choke (enricher).
Place a rubber dust cap on the cable adjuster for the choke (enricher).

Photo courtesy of Gregory Bender.

And place the other rubber dust cap on the cable adjuster for the throttle.
And place the other rubber dust cap on the cable adjuster for the throttle.

Photo courtesy of Gregory Bender.

Banjo fitting and filter

Fit a new plastic fuel filter to the carburetor fuel inlet. Note: the filters do not come with the carburetor kit and must be ordered separately.
Fit a new plastic fuel filter to the carburetor fuel inlet. Note: the filters do not come with the carburetor kit and must be ordered separately.

Photo courtesy of Gregory Bender.

Here it is in place. The center of the filter usually needs to be pushed in place over the protrusion in the carburetor inlet.
Here it is in place. The center of the filter usually needs to be pushed in place over the protrusion in the carburetor inlet.

Photo courtesy of Gregory Bender.

Fit the banjo in place.
Fit the banjo in place.

Photo courtesy of Gregory Bender.

Select the smallest of the fiber washers.
Select the smallest of the fiber washers.

Photo courtesy of Gregory Bender.

Place it on the bolt.
Place it on the bolt.

Photo courtesy of Gregory Bender.

Insert the bolt into the carburetor body.
Insert the bolt into the carburetor body.

Photo courtesy of Gregory Bender.

And tighten to secure. You'll want to snug the bolt, but not over tighten. If fuel leaks from this location when you hook up the tank, check a couple things. (1) Did you fit a new plastic filter? If not fit one. (2) Is the banjo fitting bottoming out before it makes sealing contact with the plastic filter? I had one that did this. Drove me crazy until I figured it out. I fit a new banjo and it sealed immediately. Do be careful not to over tighten these bolts. The threads are somewhat easily striped. It is much easier (and cheaper) to replace the plastic filter and banjo than to deal with buggered threads. JUST ANOTHER QUARTER TURN IS NOT YOUR FRIEND!
And tighten to secure. You'll want to snug the bolt, but not over tighten. If fuel leaks from this location when you hook up the tank, check a couple things. (1) Did you fit a new plastic filter? If not fit one. (2) Is the banjo fitting bottoming out before it makes sealing contact with the plastic filter? I had one that did this. Drove me crazy until I figured it out. I fit a new banjo and it sealed immediately. Do be careful not to over tighten these bolts. The threads are somewhat easily striped. It is much easier (and cheaper) to replace the plastic filter and banjo than to deal with buggered threads. JUST ANOTHER QUARTER TURN IS NOT YOUR FRIEND!

Photo courtesy of Gregory Bender.