guzzibob
GT Reference
The "big valve" motor referred to here is the 1000cc motor with 47 mm intake, 40 mm exhaust valves that came with 40mm PHF Dell Orto carbs, & went on to the LM IV & V, '91 1000S (not the '93 version), & some early Cal III's. Some but not all Guzzisti feel these motors are more prone to needing top end work than others. All I knew when I bought my 1000S was that seat of the pants to me it clearly had more top end than the so-called mid-valve motor that replaced it & went in to the '93 1000S & a number of other models at the time, & since that is what I wanted I made sure that the 1000S I got had this motor. To me it also has plenty of mid-range, esp when rejetted properly. As it it came, it was jetted miserably, & almost unrideable from 5000' on up-a clear problem in the mountains near LA with Angeles Crest highway going up to 8000'. More on that later.
Like I said, some feel this motor is more prone than other Guzzi motors to valve train/top end issues. Mine, despite not being ridden gently by any means, has not been. However, as I approached the 70k mark, I have been noticing increased signs of oil deposits on the spark plugs, in both cases clearly on one side, but not the other-sort of a half moon pattern. The bike has still been quite happy to rev to red line near sea level, & done better at altitude as I worked on improving the jetting bit by bit. However, it was getting more sensitive to altitude & being lugged, & as I improved jetting by making the bike less grossly rich at high altitude that of course made it leaner lower down, & more prone to pinging on long uphill grades in hot weather. Finally the oiling on the plugs got bad enough that I had to replace them earlier than the 6k interval specified to prevent the thing from bogging down more & more unless it got a lot of warm up time, & throttle applied very gingerly. Replacing the oil soiled plugs made all this a lot better in the short term, but clearly it was time for a complete top end R&R, so at 74,000 miles off it went to the good folks at Moto Guzzi Classics, where it has been going for service most of the time I have had it.
They replaced all 4 valve guides & both exhaust valves (the intakes were fine). Rings measured technically still (barely) within useable limits, but since the heads were already off, it would have been foolish not to replace them, so they did, along with the usual gaskets & o-rings. Heads were bead blasted, resurfaced, reused valves & valve seats cleaned up, rocker feet dressed as well. Back together, torqued, run, retorqued.
Got it back, & the thing clearly runs better than it ever has, & declines to ping at any altitude I can reach locally & under any conditions this time of year. No doubt keeping oil out of the combustion chambers & cleaning out 74k worth of carbon deposits both contributed to the new lack of pinging. This is the first time it has had a properly sealed combustion chamber AND the benefit of my ongoing jetting experimentation. Worth noting, this bike has had a Dyna ignition in it for as long as I have had it (from 900 miles on), & the last time I even bothered to check the timing was at about 40k, or 34,000 miles ago. Also note that at 74,000 miles, this is the first time the heads have ever been off the bike. Wish I could have said the same for my small valve (& supposedly lower maintenance) T3 at that mileage.
Getting back to rejetting the 40 mm PHF's, this is what I have evolved to, on a bike with stock airbox but K&N air filter & stock mufflers with the end caps drilled a bit but otherwise left alone, & no other performance mods:
AB 266 atomizer (tried 265, 268 (stock))
60/5 slide (stock-too expensive to replace, & no need-transitions just fine just off idle)
65 idle (tried all sorts of jets with combos of other things from as low as 48 to as high as 70)
128 main (stock was 145, ridiculously fat, tried 152, 140, 135, 130, 125, 122)
K19 needle, clip in third of 4 from the top position (tried k4, k3, various clip positions on all 3)
At these settings as equipped this big valve 1000S now runs great, pulls redline anywhere from sea level to 8000', pings nowhere, still pops a bit on the downhill decel.
Now that i have the top end R&R'd, I may try slighlty larger (68/70) idle jets to try to decrease the decell popping, may try slightly different mains (125/130) just to see what they do now. I'll not touch the needle & atomizer, they effect way more than the maybe subtle changes I may try to get from here on out; it's running too good to mess with that much again.
When I started this I found a fellow Guzzisti who had a LM IV set up not too differently than mine who lives at 3700', often rides up to 8000', used his jetting as a starting place. Got a bunch of idle/main/atomizer jets & needles, ran up to Newcomb's Ranch at 5000' (remember when I started this the bike was ok at sea level, wretched from 5000' on up), changed ONE thing at a time, ran up to 8000' then back down to 5000' or sometimes lower, changed one other thing & then did it again-over & over. Really easy to changs these bits at the side of the road, just by tilting the carbs & undoing a couple of things to get in there. Used the Dell Orto tuning guide-a totally invaluable resource-to guide my experiments by helping me understand what throttle range is affected by changing which bit, & what parts were available-esp re needles, which affect things over a wide range in 3 different ways depending on which dimension is altered. It's been kinda fun-but it does take a lot of time & patience. Fortunately, jets are cheap, about $4 each, atomizers $11, needles $10-12, slides $70 (these are all prices for each-& you see why I am reluctant to experiment with slides). I have gotten them from MG Cycle, & herdan.com. And you don't need any computers or machines or anything else to mess with these. Just time & patience.
Like I said, some feel this motor is more prone than other Guzzi motors to valve train/top end issues. Mine, despite not being ridden gently by any means, has not been. However, as I approached the 70k mark, I have been noticing increased signs of oil deposits on the spark plugs, in both cases clearly on one side, but not the other-sort of a half moon pattern. The bike has still been quite happy to rev to red line near sea level, & done better at altitude as I worked on improving the jetting bit by bit. However, it was getting more sensitive to altitude & being lugged, & as I improved jetting by making the bike less grossly rich at high altitude that of course made it leaner lower down, & more prone to pinging on long uphill grades in hot weather. Finally the oiling on the plugs got bad enough that I had to replace them earlier than the 6k interval specified to prevent the thing from bogging down more & more unless it got a lot of warm up time, & throttle applied very gingerly. Replacing the oil soiled plugs made all this a lot better in the short term, but clearly it was time for a complete top end R&R, so at 74,000 miles off it went to the good folks at Moto Guzzi Classics, where it has been going for service most of the time I have had it.
They replaced all 4 valve guides & both exhaust valves (the intakes were fine). Rings measured technically still (barely) within useable limits, but since the heads were already off, it would have been foolish not to replace them, so they did, along with the usual gaskets & o-rings. Heads were bead blasted, resurfaced, reused valves & valve seats cleaned up, rocker feet dressed as well. Back together, torqued, run, retorqued.
Got it back, & the thing clearly runs better than it ever has, & declines to ping at any altitude I can reach locally & under any conditions this time of year. No doubt keeping oil out of the combustion chambers & cleaning out 74k worth of carbon deposits both contributed to the new lack of pinging. This is the first time it has had a properly sealed combustion chamber AND the benefit of my ongoing jetting experimentation. Worth noting, this bike has had a Dyna ignition in it for as long as I have had it (from 900 miles on), & the last time I even bothered to check the timing was at about 40k, or 34,000 miles ago. Also note that at 74,000 miles, this is the first time the heads have ever been off the bike. Wish I could have said the same for my small valve (& supposedly lower maintenance) T3 at that mileage.
Getting back to rejetting the 40 mm PHF's, this is what I have evolved to, on a bike with stock airbox but K&N air filter & stock mufflers with the end caps drilled a bit but otherwise left alone, & no other performance mods:
AB 266 atomizer (tried 265, 268 (stock))
60/5 slide (stock-too expensive to replace, & no need-transitions just fine just off idle)
65 idle (tried all sorts of jets with combos of other things from as low as 48 to as high as 70)
128 main (stock was 145, ridiculously fat, tried 152, 140, 135, 130, 125, 122)
K19 needle, clip in third of 4 from the top position (tried k4, k3, various clip positions on all 3)
At these settings as equipped this big valve 1000S now runs great, pulls redline anywhere from sea level to 8000', pings nowhere, still pops a bit on the downhill decel.
Now that i have the top end R&R'd, I may try slighlty larger (68/70) idle jets to try to decrease the decell popping, may try slightly different mains (125/130) just to see what they do now. I'll not touch the needle & atomizer, they effect way more than the maybe subtle changes I may try to get from here on out; it's running too good to mess with that much again.
When I started this I found a fellow Guzzisti who had a LM IV set up not too differently than mine who lives at 3700', often rides up to 8000', used his jetting as a starting place. Got a bunch of idle/main/atomizer jets & needles, ran up to Newcomb's Ranch at 5000' (remember when I started this the bike was ok at sea level, wretched from 5000' on up), changed ONE thing at a time, ran up to 8000' then back down to 5000' or sometimes lower, changed one other thing & then did it again-over & over. Really easy to changs these bits at the side of the road, just by tilting the carbs & undoing a couple of things to get in there. Used the Dell Orto tuning guide-a totally invaluable resource-to guide my experiments by helping me understand what throttle range is affected by changing which bit, & what parts were available-esp re needles, which affect things over a wide range in 3 different ways depending on which dimension is altered. It's been kinda fun-but it does take a lot of time & patience. Fortunately, jets are cheap, about $4 each, atomizers $11, needles $10-12, slides $70 (these are all prices for each-& you see why I am reluctant to experiment with slides). I have gotten them from MG Cycle, & herdan.com. And you don't need any computers or machines or anything else to mess with these. Just time & patience.