Moto Guzzi National Owners Club
Moto Guzzi National Owners Club
Moto Guzzi National Owners Club
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Hey...How About Those Converts, Huh!?

Easily and with less than a $100, build a “Power Plus” Convert in your own garage

More Club members than we know have Converts gathering dust as a second or other bike. What a shame! What follows is a long overdue treatise on getting more-for-less out of that great motorcycling milestone, the incomparable Moto Guzzi Convert.

I say overdue because there are many Converts at rallies. However, too many of those are two-up machines pulling sidehacks or trailers, many wheezing along on stock mufflers. Overdue because I have been enjoying increased power in my own Convert for the better part of ten years now.

I have always admired the old Indians and the axiom “Power Plus” for their engine description. Power Plus Convert aptly describes any Convert modified as follows.

Guzzi automatics respond well to exhaust modifications. The mildly cammed Guzzi engine is the darling of motorcycle engine designs for so many reasons. Smoothness and simplicity come to mind. Another reason is the simple and reliable power gains that are available.

Have you ever tried to re-jet an already relatively highly tuned Japanese bike? Carburation can be incredibly complex. Others, like myself, have no doubt waded in over their heads on the promise of a simple air filter swap that required nothing more than a jiffy installation. Except for the fact that the modified bike wouldn't get out of its own way even with the promised “No re-jetting required” statement on the box.

So, let us start this story of greater-than-expected results and unexpected pleasant surprises. I will take a few side excursions along the length of this article, because of the writing effort that would be required to produce separate articles on related topics. The option of breaking the article into two parts may be a good one.

A couple years ago, my riding buddy Ray Dustrude was going to sell his early Convert because he wanted more power. He really loved the bike, but yearned for more power. The Convert's combination of light weight, abundant torque, midsize handling, simplicity and parts availability in a large touring bike at an affordable price is not to be found in any other brand. Also add in “shiftless-riding”, or perhaps “always-correctly-geared” riding, to the value of the Convert. It needs to be said that a Convert is different enough for most to not fully appreciate its merits on a single, brief test ride. A later, second test ride converts more riders. Convert test riders have briefly forgotten to put their feet down at a stop. The more the bike does the less you do. A day of touring with no shifting is neat. Say I'm sentimental, but to me the Convert is equal to icons like the VW microbus.

The concept of the free breathing, Power Plus Convert should (in my logic) be the most sought after bike on the entire used bike market today. But sadly, all Guzzis are still a secret.

Why there are no Guzzis to ride at AMA's Heritage Days, I can't begin to imagine. It actually makes me mad! If the new hydraulic-lifter touring model were to be included there to ride, Guzzi would need a dozen demo bikes to handle the crowds lined up to test ride the various models. Announce the demo rides well in advance and stand back. These bikes stand out simply for not being HD clones! The HD clone bubble will break. You heard it here first. How many manufacturers will be ready? Guzzi is 70% there. They only lack a dresser and a revolutionary automatic that the world is now ready for. Put money on it that a GW or other behemoth will soon have an automatic.

Anyway, Converts willingly pull sidecars or fold-down campers. Additionally, the fluid drive loads the drive train splines and needle bearings once per getaway rather than four times for a five-speed gearbox. Peak loads are also way down (i.e. hard acceleration).

The simple modification of a two-into-two exhaust gives increased torque, increased horsepower, increased gas mileage, decreased engine heat, and minimal cost. An even better two-into-one exhaust will also be discussed.

We installed two Cherry Bomb car mufflers on Ray's Convert. The results were impressive. He more than found the power he wanted and once again was singing the praises of the Convert. Ray's seat-of-the-pants impression from the stock mufflers (which can be plugged with a none-too-large finger) was that the bike was half-again more powerful than stock. That impression equates to adding the power from a third cylinder!

His mileage went from 36 mpg with stock mufflers to 40 mpg with dual Cherry Bombs. Additionally, the engine's heat went way down. That's more power with noticeably reduced heat! Though we never measured temps before or after, Ray used to complain of excessive engine heat. He says everything is fine now.

That was a couple of years ago. When asked for his impression of that muffler project on his bike as I write this, he stated that he could now pass cars with authority. Ray will ride 80 miles to eat lunch. But because he is always hungry, he rides pretty fast.

By the way, you do not downshift into low to pass cars. While there are two gear ratios, I always run the Convert in high. I only use low range for pulling the pop-up camper through campsites, because Paul Studer always bawls me out for being in high range. Also, I only shift at very low speeds while coasting. I use Low for two-up 0-35 mph sightseeing the Fall leaves, etc.

We did not autopsy Ray's old, original mufflers, but we were not aware of out-of-position, rusted internal baffles, etc. I am confident that 2-4 more mpg are possible with a two-into-one single Cherry Bomb system on Ray's bike.

We are not talking tiny gains here that need a dynamometer to be measured, but rather real seat-of-the-pants torque and horsepower increases with readily-apparent decreased operating temperatures and a useful gain in gas tank touring distance.

The higher rpms for given road speeds of the Convert, as compared to manual gearbox models, favor increases in both perceived (power) and measured (mpg) areas.

How is this so? Well, horsepower increases with rpm. Improved breathing at higher revs increases horsepower, at least up to the point where volumetric efficiency falls off. Simplistically speaking, the falling off is due to lack of time for effective cylinder filling to have had occurred.

Let me make a short detour with this: What seems less realized is that free-flowing exhaust need not be excessively noisy. I once removed the perforated tubular cores of aftermarket bullet-shaped Triumph mufflers. Then I stuck a large dowel (closet rod, etc) up into the muffler. Then 1/4-inch fiberglass mat, cut into 1-inch wide strips was carefully wound around the dowel. The mat was tamped down tightly using a 1/2-inch dowel. As the muffler body filled with compacted mat, the dowel was raised (in effect) as needed to stay above the rising level of the mat. This was accomplished seated in a chair, with muffler clamped between the knees. One end of the dowel is on the floor while the other end is just into the muffler body. As the body fills with compacted mat, the muffler body is pushed downward with a gentle twisting motion, thus exposing more dowel to guide the wrapping process. The secret here is to tightly force the mat to stay in position as you twist the body downward. This is accomplished with two 1/2-inch dowels supplying the downward push against the installed mat as the muffler body is twisted back and forth. Fat, arthritic persons can strap or bungee the mufflers between their knees. It can take half an hour to install the mat in one muffler body.

After your first attempt at packing two mufflers, you will be good at it, so feel free to pull the packing out and repack tighter, knowing you can get even more mat (more quiet) into the muffler.

The straight-through Triumph mufflers I packed were so quiet as to seem not possible. Much quieter than stock double-tapered, plate-baffled, and much larger (late-style) Triumph mufflers! Feel free to roll your own perforated tubes out of hardware cloth, stainless, or brass screen. The more open the better, but the more open the tube, the more the tube gets locked in by interference from the fibers. If tighter re-packing is desired, the longer the delay (riding) the more resistance encountered in removing the tube. Also, last year, I saw the Epco stainless-steel exhaust guy at AMA's Heritage Days. He is out of Germantown, Ohio. He is now retired from flying airline planes and wants to resume his custom exhaust business. Some will remember his ads from 60s, 70s and 80s motorcycle magazines. Header pipes usually stay pretty decent, so a quote for a pair of packable mufflers from this guy may be a good idea for some. Fiberglass mat is readily available from marine dealers or home improvement warehouses.

Back from our detour now and onto the issue of noise. I don't like noise as much as most motorcyclists seemingly do. I wear foam earplugs when I tour. The Power Plus Converts are louder than stock. Ray's Convert has become famous for its exhaust note. Ray's bike was at a local Honda dealer for a set of tires. Ray met a guy out riding who asked if his Guzzi was at the dealer lately. Ray confirmed that it was the bike. The guy said someone at the Honda dealership was starting the bike for all to listen to the exhaust. Club members and strangers alike tell Ray that his Guzzi is the best sounding bike they have ever heard. My own two-into-one system sounds to me like an underwater exhaust on a CrisCraft cruiser. Guzzi exhaust music is best heard as the bike pulls away from you, or passes you, and not from the saddle itself.

The inlet and exhaust systems were too restrictive in my Guzzi at higher revs. Ray's, I think Paul's, and my Guzzis have K&N air filters installed in stock air boxes. I think I raised the needles a notch, but it is hard to remember back as we are talking about almost ten years ago. Pilots (idle jets) were drilled next size as I uncrated the bike when new, a scant 16 years ago.

Interestingly, when I installed a single Cherry Bomb on my `86 Convert I realized more power even at takeoff. I didn't need to be at highway speeds to realize a performance gain. The single Cherry Bomb fed through a homemade two-into-one exhaust manifold really woke up my bike.

Let's talk about torque. Torque is less understood than horsepower, yet it is more important to the road bike. Torque increases only with higher cylinder pressures. Horsepower climbs with revs even though lesser than max cylinder pressures are present. Higher revs beyond the max torque rpm quoted for a stock machine result in lower cylinder pressures and the torque falls off. Torque falls off (the lower the rpm at which max torque occurs, the better) well before horsepower in good touring machines, working pickup trucks, etc. See maximum torque as being maximum effectiveness as well as maximum fuel mileage for an engine under load. Reducing both exhaust pressure and reversed pressure waves also increased torque at takeoff of several Converts so modified. My `86 Cal II Auto is noticeably stronger accelerating from a stop than it was with stock mufflers. It is also more enjoyable to ride at slower speeds, such as when two-up looking at fall leaf foliage. It literally feels as if it has been uncorked.

By the way, drag racing my stock `86 with a stock `75 Convert showed no performance gain of the newer machine. The winner was the lightest rider, no matter which bike he was on.

Machine differences are such that shorter riders would be better off on the older Converts due to seated height being lower to the ground. Taller riders may feel cramped, as I do, on pre California II automatics.

Looking for a good seat for any Guzzi? Forget about stock police saddles or aftermarket saddles. Look no farther than a Kawasaki police saddle. Not the easiest thing to mount, but the comfort cannot be surpassed from a stock saddle. Two have been bought separately at $140 each. I mounted the nose of the seat on a Tractor Supply farm gate hinge and supported the seat rear with Chinese-made, HD-copy, chrome barrel springs. Springs mounted to 1” by 2” bed frame angle steel. Use the shock hanger and the bolt forward of it to mount the angle steel to support the springs. Stacked washers fine-tune the height at the rear of the seat. Use plastic .410 shotgun hulls for front pivot bushings. I used a Lincoln buzz box to make it all up.

Another detour here. The new hydraulic lifter engine is going to go over big time! However, the new hydraulic lifter machine would be an even larger success for Guzzi if only they would bring back the same torque converter transmission as a model option. Everyone I know riding a Convert would rip their pants pocket off to get his or her wallets out to buy a new Convert. How about a new Convert with hydraulic lifters and an external oil filter “YES., YES.., YES..!!!” (Quote from TV girl washing hair in shower).

By the way, the new hydraulic lifter engine is so quiet that it sounds like it is water-cooled! I like the 5-speed given no choice of an automatic, but now is the perfect time to bring back the automatic. The engineering is already 97.5% completed! Sidecars are selling. 10% of new bike sales are to women. Power is way up in totally stock machines. For example; there would be no need to put different mufflers on the Jackal I was allowed to ride at Jack and Mom's Ohio Rally this year! It was both very quiet and very powerful. Apparently the same basic Italian-built fuel injection system on that Jackal is also used on Harleys. That can't be a bad thing! Please Guzzi, forget that V8 idea I had, just bring back the Automatic!

By the way, I rode my big brother's top-of-the-line full-dress HD for the first time at the Ohio Rally. What a horse! I was not prepared for what I found. The machine was simply way too heavy and way too top heavy for 25-55 mph sightseeing on Amish back roads, many of which are gravel. To say that I did not enjoy the bike at all would be too kind. A GW could be no better.

A free-breathing automatic Guzzi has no touring equal on steep, hilly, curvy postcard-scenery roads! It can't be lugged like my brother's HD, which always seemed to be in the wrong gear, and it doesn't overheat like my brother's HD. The HD can get really hot on the thighs. It was a handful! However, unlike his `90 Heritage ST that my automatic could outrun solo or stay up with when pulling identical Kompact Kamp pop-up campers, I can no longer outrun his new generation HD.

His yearly depreciation of the HD ST was $200. My yearly depreciation for my Automatic (I paid $4950 retail was $5700 in 1986) was $125 as declared on the bike value table in Motorcycle Consumer News. However, I would never sell it for the value listed, and my year has since dropped off the old age end of the list.

Ray, my sister and I wanted to check out the small fishing lake across the road from the Ohio Rally campground. I rode my sister's 90cc Honda trail bike as I can't walk for any distance. The neat thing was that Ray just rode his Guzzi diagonally down the grassy slope to the water's edge to talk to fishermen about the fishing. Having seen this, I said, “Ray, you sure wouldn't ride a dresser HD or GW down that slope.” Ray looked up at the slope, laughed, and said, “You sure wouldn't!”

Back to our Power Plus Convert story. Anyway, experience with $14.99 ($12.99 on sale) Cherry Bomb (the old Hollywood brand, I believe) mufflers has shown real increases in both torque and horsepower.

It must be remembered that most performance goals/gains in the outside world do not typically encompass all five of the traits listed in the second paragraph. However, the results obtained on mine, Paul's and Ray's automatics have achieved the five listed traits.

For example, stock I indicated 38-mpg solo. With a two-into-one single Cherry Bomb system I indicate 45-mpg solo. I always get 190 odometer miles solo before reserve. I have gotten 220 miles before reserve when out all day. To go that far, I fill almost to the point of overflow while on the sidestand. I like to ride at 55 mph, often slower. Two-up, I indicate 40 mpg. Solo, pulling my loaded Kompact Kamp pop-up camper at 65 mph, I indicate 37 mpg. I believe (without being certain) that carbs on the 84-86 automatics are more fuel-efficient than the square slide carbs on early automatics.

The two-into-one exhaust was made a week before a long ago West Virginia rally. The right header was chop-sawed at 90-degrees from the flange that goes into the head. This was repeated (several times at 90-degrees) until the RH header pipe segments would reach the LH header pipe. This resulted in a high up crossover, as dictated by the first 90-degree cut.

Interestingly, a rally attendee commented that the uneven length of header pipes would never work, as they were unequal in length. I said don't let the bike hear you say that, I'm 250 miles from home. Actually the mild cam is enhanced by the scavenging effect of the two-into-one header pipe. A much hotter cam, typical in high output engines, probably would never tolerate uneven header lengths.

Why do I believe the cam is enhanced? I always follow another Power Plus Convert when I ride. I simply hate to lead, as you have to pay too much attention to what you are doing in the lead position. I also daydream too much. Anyway, it is easy to synchronize my bike's rpms off of the rpms of the lead bike as it accelerates. With matching rpms, the bikes accelerate together, sounding like Sky King's twin engine airplane. The helmet reverberations or frequency harmonics sound like a British bomber. Anyway, my bike slowly pulls ahead as the lead bike levels off its speed on that given throttle opening. Works with both Ray's and Paul's bikes. I always have to back off to prevent passing the lead bike. I do not believe it is torque converter related. I believe it is caused by the scavenging effect of the two-into-one header. More fully extracted exhaust allows a greater inlet charge to be pushed in. My theory is that residual pressure is lower, thereby encouraging more fully filled cylinders, due to a greater differential pressure existing across the exhaust valves.

The double-walled header pipe was gas welded to join the pipe edges of inner and outer walls. The LH pipe was cut to roughly an egg shape as dictated by the RH pipe ID shape at the juncture of the two pipes. I was careful to get an optimum junction with no edges to later form hotspots. Why cut the RH pipe? This was intended to accommodate a sidecar. Typically however, the exhaust would flow down the RH side of the bike to avoid interference when changing a rear tire.

Tack weld on the bike. Weld with Mig or Tig. I used gas as it was all I had at the time. Do not paint welds, it will come off. Possibly there is good paint at hotrod shops. No one will chrome used pipes anymore, so I've been told. It helps to be somewhat of a craftsman to do this. I did not even know if the cut/re-joined header pipe (I had no spare pipe) would reach the opposite side when I started. You only have something like 4-5-inches of pipe left over. I relocated the transmission oil cooler higher. It should be mounted within a front crashbar for full airflow. This is also much easier to do. I will probably do so, someday.

On to mounting the mufflers. Leave the crossover full length. It serves us well to extend into the body of the muffler. This effectively kills the return path of returning pressure waves, which further lowers back pressure, thereby increasing scavenging of our minimally-valve-overlapped camshaft timing.

Have your muffler shop take two each 1.5-inch (I believe) diameter exhaust tubing about 20-inches long. The tubes are hydraulically expanded on one end to a sliding fit into the minimum obtainable ID Cherry Bomb inlet end. The tubing seams will start to split as the muffler man says, man it ain't gonna go dat big before it splits. But, if he incrementally stretches it bigger and rotates the tube at the same time, the starting-to-split tube weld seam will be inside the Cherry Bomb inlet and out of sight. You always use minimum diameter muffler ends that are straight. LeMans riders might use angled-end Cherry Bombs.

All these exhaust mods will wake up 4-5-speed gearbox model Guzzis too. I was going to save that tip till the end of the article, but I might forget to mention the angled-end muffler models.

We now need a sleeve shim to eliminate clearance and leakage between muffler and pipe. A pop can has a shoulder near the top. Cut two cans, just saving this shoulder on one end of about a two-inch long sleeve. This shoulder is very helpful in getting the muffler to go over sleeve and pipe. Trim sleeves to get rid of overlap on pipes. Overlapped sleeve ends will not allow the muffler ID to slide onto pipe end.

Cut pipes to length desired and then cut three slots (Dremel tool or hacksaw) in pipe end to allow a regular muffler clamp to tighten slotted pipe to crossover. I had bought flattened muffler clamps, but do not know if they would still be available. Possibly aircraft stuff. Brush a coat of thread medicine (anti-seize) on all parts. I use old BMW muffler hangers (I knew I liked BMWs for some reason) or make hangers from 1/8” X 1” steel available from home centers. Ditto for aluminum, which could also be used. Hey, no hate mail please. Just try to tow a pop-up camper with an other-than-new-design BMW twin and then get back with me!

The hangers wrap around the muffler bodies and are secured with a pinch bolt. The other end of the hangers are trimmed to length and bolted to a hole in the rear peg/muffler attach area. Slide mufflers aft as necessary to ensure no exhaust heat or carbon gets on your luggage.

Now for some obligatory fine print: My opinions are strictly that, my own! If you and your bike end up as a wispy puff of smoke over the horizon, don't call me. I simply won't answer the phone! Besides, I know how to read the rings. Just be a sport and save me your transmission, please.

Lets see some more articles of a technical nature in our Newsletter. How about Dale's Convert Ambassador seen at this year's Ohio rally? I felt lust for that bike. But I'm the guy they would look for first if Dale had somehow mysteriously disappeared without taking his bike. How about Nolan's Morgan replica? I would like to build a Morgan replica. I also want to put a Crosley inline four engine into a Convert transmission bike with a Pierce replica frame. Man, that new hydraulic-lifter Guzzi tourer sure looks too pretty to be real!

Okay, Jack Arnold, my task is done. Give my love to Mom!