MM .. a much easier way to align the primary sprockets is clamp a long straight edge, I
That's what the longer of the two tools I made does and, like you say, it works great. I made the other one, with the dial indicator, because I couldn't keep myself from "improving" on a tool that didn't need improvement...
I have done something similar with my "goldieised" B31. The silencer is Goldie shape, the tapered section is empty, the parallel section has a perforated tube surrounded by stainless steel wadding. This is a similar configuration to the Burgess silencer and it gives me a pleasing sound
If it's not one thing, it's another. And another...
I replaced the missing throttle slide stop screw and took it on a ride. I seemed it might be a bit better, but it still started missing when I got to ~1/2 throttle on a rising road. Not quite the classic incorrect needle slot symptom, but close enough to suspect that was the problem.
With a combination of pencil, needle pliers, haemostat, and curved tweezers it's just possible to move the needle slot without removing the carburetor (which also requires removing the air cleaner box). It's also possible to drop the needle into the carburetor when attempting this and have to take the box off anyway. Sigh...
After retrieving the needle I lowered it one slot, to the topmost slot. At that point I noticed the carburetor was loose on the engine. Hmm. I snugged up the nuts but didn't move the needle back to its original position, and took it on a ride. It was hard to decide if there had been a change because it still started missing when I got to ~1/2 throttle on the same place on the rising road. Also, it seemed too rich at idle, i.e. when I closed the throttle it took a few moments for the revs to drop all the way.
When I got home I left it running on the center stand and tried to adjust the pilot mixture screw. I kept turning the screw in, and lowering the throttle stop to keep the revs from rising, until the screw was all the way in and the idle was the fastest. Turning the screw back out from there caused the revs to drop. With the idle fuel (presumably) completely cut off the engine idles best. Hmm.
Back in the garage I removed the jet assembly and measured the needle jet. It was 0.1065"-0.1066" when I assembled the carburetor a few months ago, but now is 0.1069-0.1070", i.e. it is larger by 0.0004"-0.0005". This counts as worn out since it is enough to cause significant richness.(*) Your results may vary, but this shows that my needle jet lasted just ~1200 miles before the constant hammering by the needle enlarged it to out of spec. Although I blame the enlargement on engine vibration, because it has an air filter and all those miles were on asphalt roads, under the microscope with a 0.106" plug gauge in it the bore is round whereas I expected some fore-aft (or side-to-side) ovalness.
OK, tomorrow I'll stick a new needle jet in it (measured for size), but what's the deal with the idle mixture screw? Twelve hundred miles ago it behaved as it should, with one turn out being the sweet spot for the idle mixture. Now it idles best when the position of the mixture screw should be keeping it from idling at all.
(*)It appears from my measurements that AMAL aimed for their Monobloc needles to be 2.50 mm dia (0.0984"). Fuel flows through the annular area between the needle and the jet which, until the taper begins, for a 0.1065" bore is pi x (0.10652 - 0.09842) / 4 = 0.001304 in.2. If the bore of a needle jet increases to 0.1070", i.e. by 0.0005", the annular area and gasoline flow increases by 6%. Mikuni spaces the slots in their needles to change the flow by just under 6% in the region where the taper is active, indicating that a change of this size makes an observable difference on the performance (the grooves in AMAL's needles change by 9%).
Last edited by Magnetoman; 11/13/171:00 am. Reason: added (*)
I have two bore micrometers for that range, although I only used one of them (the Starrett) for these particular needle jet measurements:
Starrett 78XTZ-100, range 0.100"-0.120", 0.0001" micrometer. Uses a split cylinder. Diatest with probe #14, range 0.091"-0.110", 0.0001" indicator. Uses a split ball.
To check/adjust the Starrett I have four ring gauges covering the appropriate range, with IDs slightly less than that of the needle jet, 0.09995" and 0.10000" and slightly more, 0.10845" and 0.11500". Once set using one of the ring gauges it gives the correct result for the other three to within the 0.0001" resolution of its micrometer.
As background, John Healy and I disagree whether a jet stamped '106' means its ID should be 0.1060" or 0.1065", but we each trust our own instruments and measurements, and it doesn't matter who is correct for what follows, so let's agree that we're both correct.
The rebuild of the Catalina wasn't finished when it came to me. When I had it essentially finished the bike ran badly at mid-throttle, acting as if too rich, so I dropped the needle one notch and that was all it took to make it run "perfectly." I adjusted the pilot screw and found the optimum position where it ran best with the #25 pilot jet, with the engine slowing down either side of that position, was one turn out from fully closed. I then put 250 miles on it myself including a short stretch on the Interstate and 20 miles up a mountain to 8000 ft. with the jetting acting as if it were perfect at all times. It had a 320 main jet.
My friend then rode it for the next 1000 miles so I don't have first-hand experience with how the performance deteriorated over that time. The silencer that was on it when it had the "perfect" jetting broke during that ride and I've now replaced it with a different silencer that could have more, less, or the same restriction as the old one. In a previous post I described what I found this week with the carburetor. In summary, it was loose on the flange, had lost the slide stop screw, started missing badly at ~1/2 throttle, and its needle jet was enlarged by 0.0005" beyond what it was 1200 miles earlier. Tightening the mounting nuts, replacing the slide stop screw, and lowering the needle by one notch made little or no difference. Also, now the position of best idle is with the pilot screw turned fully in. As of the end of yesterday the engine was still missing badly under load (on a rising hill) at ~1/2 throttle.
Today I installed a new needle jet the same ID that the current one had when the engine ran great 1200 miles ago. This definitely made a difference since the engine no longer starts missing at 1/2 throttle. However, now it does at 3/4. Lowering the choke while this is happening makes it run even worse, i.e. it is too rich at 3/4 or higher throttle. Since the needle jet should be contributing relatively little by this point I replaced the 320 main jet with a 300 (6% reduction -- maybe not enough to make a difference?), repeated the test, and got the same result.
Dejected, the bike is back on the lift as I await hearing from one of you who knows the solution. What have I overlooked? What could have changed in ~1000 miles to be causing these symptoms? I want to figure out what is causing this behavior so "replace the carburetor" isn't a helpful response.
Last edited by Magnetoman; 11/14/1712:31 am. Reason: added info. about the silencers
can you go even smaller on the main jet? Is the carb body cracked?
Great minds think alike. Having had a few hours to reflect on this my best guess is the silencer is much more restrictive than the previous one and so requires a significantly smaller main jet, and perhaps the body developed a crack that is letting air leak by the pilot screw.
I won't have a chance to check the main jet until Wednesday, but I'll head out with spanners and a jets from 200 to 300 in steps of 10. I'll have to hope that whoever lives next to that hill doesn't call the police before I sort it out. Assuming I get it sorted before I'm arrested I'll then take the carburetor off and check for cracks. If that turns out to be the cause of the pilot mixture issue I have what's needed to build another Monobloc for the bike.
As a quick check, can you temporarily fit the silencer from your other GS, one which you know the main jet size is correct. see if this improves or dis-improves and that would give you a direction for jet change, carb body choke size issue... etc
re the carb idle mixture change. an air leak seems to be the culprit, On a Monobloc the jet block/ gasket could be at fault, cracked body? . Or a blockage in the fuel supply to the pilot jet. The only owner lead change has been the silencer, maybe a temp refit of the old silencer if its still functioning would solve this part. The most obvious place for an air leak would be the mounting flange. Thing arent always that straightforward . Another possibility, float level, although I dont think that would change in a 1000 miles.
Last edited by gavin eisler; 11/14/1712:22 pm.
71 Devimead A65 750 56 Norbsa 68 Longstroke A65 Cagiva Raptor 650 MZ TS 250 The poster formerly known as Pod
can you temporarily fit the silencer from your other GS,
Originally Posted by gavin eisler
maybe a temp refit of the old silencer if its still functioning would solve this part.
By now the old, broken silencer is a few feet deep in some landfill, and swapping silencers wouldn't provide a straightforward answer since the Catalina has a Monobloc while the BB and Special Competition have Concentrics.
Originally Posted by gavin eisler
re the carb idle mixture change... the jet block/ gasket could be at fault, cracked body? . Or a blockage in the fuel supply to the pilot jet. ...The most obvious place for an air leak would be the mounting flange.
The air supply for the pilot mixture comes through a passage from the front of the carburetor, over the pilot jet, and up through a tiny hole on the engine side of the slide. An air leak at the mounting flange wouldn't explain the fact the idle increases continuously as the screw is turned in.
Originally Posted by gavin eisler
Another possibility, float level, although I dont think that would change in a 1000 miles.
Ah, the float level. It only will take two min. at most to check this and I don't know how long it would have taken me to think of it had you not mentioned it. Thanks. I'm pretty sure I put a brass float in it so there definitely is the possibility that it might have slowly filled with fuel and raised the level. I have a very full day today but will try to get into the garage this evening long enough to check the level. Again, thanks.
Another possibility, float level, although I dont think that would change in a 1000 miles.
Originally Posted by L.A.kevin
can you go even smaller on the main jet? ... Go to a 250 jet. Good luck, and tell us what you find.
Gavin gets my gratitude for mentioning "float level," and Kevin gets the award for being (nearly) prescient with the 250.
I measured the float level on the bike and it was fully 1/2" below where it should be. Thanks to the oil tank it's not as if you can take the float bowl cover off while the carburetor is on the bike so I removed it, put it on my test stand, and checked the float level again. It was still 1/2" too low. I tapped and jiggled the carburetor but the level didn't rise.
When I removed the cover I found nothing amiss. The float was completely free to pivot and it has a viton-tipped needle in it. I removed the float and shook it but there was no fuel inside (which would have had the opposite effect on the level, anyway). The platform on the float that pushes against the needle looked fine but, rather than try to figure out what was wrong with that jinxed float, I put in a different one (also brass), closed it up, and checked the level again. This time it was ~1/2 mm too low, which counts as within spec.
Yes, I know, I know, you should only change one thing at a time, but in addition to changing floats I moved the needle back up one notch, to where it had been with the previous silencer, installed a 280 main jet, and bolted it back together. As a reminder, it had a 320 main jet with the previous silencer.
After reinstalling the carburetor (although, without Loctite... just in case) and air cleaner, I put into a baggie the two spanners I would need along with a plastic container, vinyl gloves, and 260 and 240 jets.
It was rich starting at ~3/4 throttle with the 280, i.e. began missing and wouldn't let the engine pick up speed climbing a long hill so, after a second run to convince myself it really was the main jet, not the needle, I pulled over at the top of a hill on a side street in case I needed help re-starting the bike. Before shutting off the engine I checked the pilot mixture screw and it was now working as it should. The best position for it was 5/8 of a turn out with the #25 pilot jet so I could switch to a #20 if I felt like it. Or, leave well enough alone.
I drained the fuel into the container and poured it back into the tank and then swapped in the 260 main jet. It started on the first kick, but was still too rich.
I swapped in the 240 and it again started on the first kick, but this time the jetting was almost perfect. If I had a 220 I wouldn't have used it because the 9% change would have been too much. It's back in the garage where I'll install a 230 when I Locktite the fasteners, but then I'm done with it for now.
The major lesson from this is that, contrary to what I would have thought, even if the fuel level is way too low a bike can start and run reasonably well. A second lesson is that two silencers can require significantly different jetting. That said, circling my driveway with my helmet off, the present silencer really does a pretty good job making the Catalina socially responsible. My wife commented a couple of says ago that the bike "doesn't sound right." When I said it has a different muffler on it she said "Oh, that's what's different." I should have thought then to ask her what jetting it needed...
If the float level changed over the first 1,000 miles , maybe the tickler is over long and bending the float mech when depressed.
That's not the explanation. The Catalina starts best without the tickler so it only would have been used when my friend forgot this, the tickler doesn't even reach the float when the level is 1/2" below where it should be, and if the platform where the tickler hits it became bent down and also bent down the portion where the needle touches it, the level would have become higher, not lower.
There has to be a physical explanation for the fuel level (it's either that, or voodoo...), and I do like understanding why something happened even if the problem goes away, so after I wrote my previous post I re-examined the "jinxed" float. It has solder on the portion that makes contact with the needle, put there by some previous person to adjust the level. There's a depression in the solder where it contacts the needle. If instead of making contact there the float had enough, ahem, end float on the shaft for the needle to contact a higher part of the solder that would cause the fuel level to be lower. Why this might have changed in the ~1000 miles since I originally checked the level is an unknown. The brass spacer was on the end of the shaft as it should be.
A second possible explanation would be if somehow the float caught on the shaft before reaching its proper height. That seems a lot less likely since the shaft is smooth and there wasn't any hint of the float "catching" or dragging when I moved it by hand.
This would have been a nightmare to diagnose and fix had I not had the tools and spares to deal with it. As it was, my post on the 13th shows how frustrating it was. Ultimately, the things that were wrong, and what I needed to find/fix those issues, were:
-- loose mounting nuts; tightened -- missing slide stop screw; replaced with one I had in my stock of AMAL bits -- worn needle jet; measured with calibrated 0.0001" bore gauge and replaced with one I had in stock whose ID I confirmed with the bore gauge -- low fuel level in float bowl; measured with "tool" having clear Tygon tubing; replaced with another float from my stock -- insensitivity to pilot mixture screw; cured by curing the fuel level problem -- main jet significantly too large for the replacement silencer; diagnosed using selection of main jets from my stock
Had I had to order replacement items one-by-one as I discovered problems with them, assuming in each case that the latest problem discovered was the cause, this easily could have taken several months rather than a couple of frustrating days.
It took two runs today but the jetting is now sorted out. I ended up with a 220 main jet. The Catalina starts on the first kick, idles, and the jetting is great across the entire range. What more could anyone want?
With the Catalina now sorted out I drained the fuel and put the bike where the BB used to be, and put the BB on the "maintenance lift" (as opposed to the "restoration lift") where the Catalina used to be. I don't plan to do anything in particular to the BB, but it also just covered 1200 miles so it wouldn't hurt to look it over. However, I'll only do that whenever I'm delayed with the Ariel for some reason.
In case anyone finds the information useful, the carburetor is a 1-5/32" Monobloc with the following settings:
pilot 25 pilot screw 5/8 turn out slide cutaway 4 needle jet 106 (measures 0.1065"–0.1066") needle on 2nd notch main jet 220
p.s. for what it's worth, at some point in the past I acquired a Webco jet holder that has ~20 tapped holes for main jets. On my recent 1200-mile trip I had it along, stocked with 3 ea. larger and smaller jets for the BB and the Catalina so I could rejet, if necessary, in the evening should a change in altitude require it. I've now swapped for the appropriate six Catalina jets that are larger and smaller than the 220. I suspect the Catalina is now at the rich end of the range which means if I find myself on a trip at higher altitude I might have to drop down to a smaller jet and the Webco holder means I'll be prepared for that. Unless I forget it at home...
Last edited by Magnetoman; 11/19/175:51 pm. Reason: p.s.