Also Check Out

© 2014 Message Forums
April 21, 2018, 05:30:06 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with username, password and session length
News: Welcome to! Please register in the Forum to post messages or view attached photos.
  Home Help Search Login Register  
  Show Posts
Pages: [1] 2 3 ... 6
1  General Category / Tech Corner / Re: Reprise of: New bike a Republican? (aka my bike doesn't lean LEFT). on: April 17, 2018, 09:55:18 AM
Hi Bill, what is the hole on the left chamber wall at the same level as the "crude hole"? From a manufacturing perspective how the heck did they drill the "crude hole" if it's orthogonal to the jet tube. There is very little working space.

The crude hole is drilled at a downward angle intersecting the passageway holding the pressed-in jet, so no problem with manufacturing access. The hole to the left is the float bowl vent which connects to the vent hoses marked "6" in the manual and with a label on the hoses themselves. When I lean my bike way over to the left the idle stays the same until finally at a very extreme angle gas runs out of those vent hoses and the engine dies!

2  General Category / Tech Corner / Re: Reprise of: New bike a Republican? (aka my bike doesn't lean LEFT). on: April 09, 2018, 07:12:21 PM
By the way I just tested my bike and found that with the choke ON it runs the same whether vertical or leaned over, Since I only have a side stand it's always leaned left when warming up. I have to lean it over to at least 45 degrees to make it die - that is the same with choke on or off - and that happens because gas is pouring out of the carb vent hose because of the extreme angle. So no help here except to say that the stalling while choked and leaned left is not normal, or at least not universal.

3  General Category / Tech Corner / Re: Reprise of: New bike a Republican? (aka my bike doesn't lean LEFT). on: April 09, 2018, 10:25:04 AM
Thanks James. OK I was wrong about the bystarter jet, it is actually on the left side of the carb meaning they are submerged deeper in fuel when the bike is leaned left. So I'm not sure what is going on, but would still want to check float levels and all passageways in the bystarter circuit, especially the very tiny hole in the jet. Possibly the mystery hole is above the fuel level and therefore takes in air to help atomize the bystarter mixture, but when leaned too far left and with float level too high the hole takes in fuel making the mixture too rich?

4  General Category / Tech Corner / Re: Reprise of: New bike a Republican? (aka my bike doesn't lean LEFT). on: April 06, 2018, 11:37:39 AM
I'd really like to know, as my bike does it too.

Guessing it's one of the small channels in the carbs relating to the choke circuit which is blocked so that one or more carbs get no extra fuel at certain lean angles. Solution in that case would be a long soak in an ultrasonic cleaner.

I can tell you that replacing the seals doesn't fix it. That said, I'd still recommend getting a set of viton rubber seals at if you're planning on splitting the carbs, they are cheap to buy and you'll definitely find at least one split and perished seal while you're in there.

Is there a connection or red herring regarding the other symptom of the engine slowly fading to 0 RPM when I'm stuck at a stoplight: choke off, fully warmed up, upright, throttle closed? The fan did come one during one of these bouts but doesn't seem to by directly responding to the fan being on (which could suggest an electrical issue).

Further, the RPMs can be kept alive (increased to say 2k RPM) by application of choke.

If a choke enrichens the mixture (right?) does that mean my bike might be improperly adjusted lean?

I'd go with the red herring since when the bystarter valves are closed they are not supplying any mixture, assuming their rubber seats are not damaged or one or more is mis-adjusted to stay open slightly. That is always possible. The brackets that actuate the valves are individually adjustable on the rod, and adjustment can be made just by pulling the air box. On the dying at idle, I would first go through the carb synch/mixture screw adjustments assuming the screw limiters are already removed from the float bowls.


5  General Category / Tech Corner / Re: Reprise of: New bike a Republican? (aka my bike doesn't lean LEFT). on: April 06, 2018, 11:31:18 AM
Hi Rick,

I'll take a stab at this. The only effect I can see that leaning the bike could have on the richener system (bystarter valves as Honda calls them) is one of changing the fuel level in the float bowls. Or more precisely, making the fuel level shallower on the right side of each float bowl. When I had my carbs apart for seal replacement I took photos and traced all the circuits, but unfortunately I deleted the photos by mistake! But what I found is that the bystarter valves have their own fuel and air supply, separate from the main and slow jets. The bystarter jets are pressed into the carb body and not removable with a screwdriver. They are offset slightly to the right side of the float bowl and have an extremely small opening - I had to use a single strand of very fine copper wire to probe them, as well as spraying cleaner and compressed air through to confirm they fed the bystarter valves. But here is the odd thing: in the carb body just above each jet there is a rather crude hole communicating with the passageway the jet goes into. Damn I wish I had the photos. I have no idea why there would be a precise tiny brass jet metering fuel into the bystarter circuit but also a rough drilled hole just above the jet adding fuel to the same passageway. Those rough holes would normally be submerged in fuel when the bike is upright, but when leaned left they might be above the fuel level. And if one or more of the tiny bystarter jets were clogged, possibly the system would still work when upright but not when leaned left. So I would want to check those pressed in jets as well as carefully checking float levels.

Without the photos I am just going by memory here and might have some details wrong. Maybe if someone has a carb apart and can post up some photos of the inside of the float bowl I can point out the details above. Anyway, my money is on some effect of the sloping fuel level on fuel supply to the bystarter system.

6  General Category / Photo Gallery / Re: Dash and CeeBee went to Brno and even got back! on: March 31, 2018, 09:48:11 AM
Wow Dash, those are some fantastic photos and your narrative really conveys the flat out fun you had. I look forward to watching the video clips later today. It's so cool to see a CB-1 in its element.

7  General Category / General Motorcycle Discussion / Re: Introduction on: March 26, 2018, 11:26:21 AM
Welcome, I look forward to following your progress!

8  General Category / General Motorcycle Discussion / Re: So, these 400 cc bikes on: March 22, 2018, 11:37:28 AM
Each configuration has its own charms. Some you can get along with, other you can't. If only I had space for 2 motorcycles... Sad

No, two is not enough, you also need a dual sport!

Oh, and while you're at it, a nice little tiddler!

9  General Category / General Motorcycle Discussion / Re: So, these 400 cc bikes on: March 21, 2018, 08:15:20 PM
I had a 650gs single. Not the same as that bike, put it was enough to inform me I don't like big single cylinder bikes. Definitely try before you buy!

Yeah, but big singles have their own unique personality. Variety is the spice of life, I say we need both singles and multis!  Grin

10  General Category / Tech Corner / Re: Syncing carbs & adjusting idle mixture on: March 18, 2018, 04:20:10 PM
I forgot to add that mixture screw adjustment is only really possible if the limiter stops have been ground off the float bowls or the flag caps removed from the screws.

11  General Category / Tech Corner / Re: Syncing carbs & adjusting idle mixture on: March 18, 2018, 04:02:38 PM
Thanks for the comments all.

Nice writeup Spurlock!  Now if you please, finish by detailing Honda's very hard to grasp(to my mind anyway) idle drop procedure and this will be a perfect set of instructions.  Grin

Sugs, the link at the top of my post listed the steps involved in the idle drop procedure, but I'll try to put it in my own words. Basically you are using changes in idle speed to tell you whether idle mixture is optimum or not. First step is to set them all to the book setting (2-1/2 turns out). Then you begin backing out all four screws at once, 1/2 turn at a time to see whether rpm increases. If so, reset idle speed and back them all out another 1/2 turn, etc. Stop when you no longer get a speed increase. You have now done a gross adjustment of all screws to get them in the ballpark, but you do not yet know whether each individual screw is in its best position.

So the final step is to apply the test to each carb individually. Reset idle speed, then turn #1 mixture screw back in 1/2 turn at a time, pausing between each turn to see if rpm changes. keep turning in (leaner) until you see a 50 rpm drop in idle. Then back the screw out one full turn, which is what the manual calls the "final setting". Repeat this process with carb #2, then #3, then #4. In this way you are using the feedback of idle drop to achieve a consistent mixture setting on all carbs.

At this point I would want to reset idle speed and confirm that carbs are synced since throttle plates might be in a different position than when they were synced. For instance, if mixture was off enough to cause poor idling, then the idle speed knob would have needed to be turned in to achieve desired idle speed. But after correcting mixture, the idle would have been too fast and the knob turned back down, closing the throttle plates a bit to get back to the correct idle speed. And I've noticed that on many bikes the carb sync becomes uneven as the throttles begin to open, probably due to slight misalignment in the linkages. So, I would want to tweak the syncing again if needed.

Then this refining of sync will likely lead to smoother idling and allow you to refine the mixture adjustments further by making it easier to zero in on the 50 rpm drop point. So I would run through just the last stage of individual mixture screw adjustments, not the all at once first steps. Confused yet? Grin

Last but not least is to confirm with the old "butt dyno" that the bike idles well and responds smoothly to initial throttle opening. If it seems to stumble a bit when the throttle is cracked slightly, try backing out each mixture screw a half turn to richen slightly. On my bike, after blipping the throttle the engine would often die when dropping back to idle. Turning each screw back in 1/2 turn corrected the problem, so my bike likes a "final setting" of 1/2 turn, not one turn. Your mileage may vary.

12  General Category / Tech Corner / Syncing carbs & adjusting idle mixture on: March 17, 2018, 07:49:19 PM
I thought I would share my take on synchronizing throttle plates and adjusting idle mixture screws. I described Honda's "idle drop" method for adjusting mixture screws in a previous post here:,5607.msg27986.html#msg27986. But the two adjustments, syncing and mixture, affect one another so they really need to be done in sequence. And I find it best to make multiple passes of sync/ adj. pilots/sync/ adj. pilots for best results since errors in one can affect your perception of the other.

First, to have decent access and visibility of the adjusting screws you need either a remote fuel tank or to set the gas tank off to one side. I find it easiest to just add an extra short length of fuel line and set the bike's tank on a table off to one side. Yeah you can turn the tank around backwards and set it on the tail of the bike but for me that gets in the way of my head when looking for the syncing screws.

Then the sub-air filter/wiring plugs bracket along with hoses need to be pulled out of the way for best access to the syncing adjusters as well as the mixture screws.

Also, an accurate tachometer that can detect small changes in rpm is not necessary for syncing but is essential to be able to adjust mixture screws individually. There are lots of cheap tach/hour meters on ebay that do the job just fine. This one reads in 10 rpm increments and gets its signal from a wire wrapped around any spark plug wire.

Next you need a decent vacuum gauge setup. I use the Motion Pro Sync-Pro tool which works well but has one quirk you need to be aware of, namely that it's calibration changes depending upon vacuum level. It is a four part manometer, and the first step in using it is to connect all four tubes to a single vacuum source, then turn calibration screws so each column reads the same. OK fine, but for whatever reason the gauge columns will read differently at higher or lower vacuum levels than where they were calibrated. So I like to first connect each gauge hose to its own cylinder, start the engine and see where the readings are on the gauge. Here they are about 1/4th of the way up.

Knowing about where the gauge level is going to be, I connect all four gauge hoses to a single manifold port so they receive the same vacuum, temporarily plug the other manifold ports, and adjust the calibration screws on the gauge to equalize the readings. Now it will be totally accurate, right? If only it were so. It will be accurate at this vacuum level so I'm good to go for an initial synchronizing but will need to re-calibrate if gauge level changes. So for now I connect each gauge hose back to its own manifold and start the engine. The readings below are actually plenty close enough since I had done this when I first got the bike. But I will go ahead and get them as perfect as possibly.

Before adjusting sync screws you really need to know what each screw does, and Honda's manual is completely unhelpful in this regard. Sure you can eventually get the carbs synced going from one screw to the other until all four cylinders are either well synchronized or you run out of patience. But it saves a lot of trial and error to understand the following: On the CB-1 (and most Hondas with throttle plates instead of slides with individual adjusters) one screw equalizes vacuum between cylinders 1 & 2, another equalizes 3 & 4. Once those pairs have been synced, a third screw equalizes the 1&2 cylinder pair to the 3&4 pair. A change in any screw changes rpm and so changes all four readings, which can lead a person to jump from screw to screw in a whack-a-mole fashion, wasting time and getting frustrated. And truthfully carb syncing can be fussy work, but understanding what each screw does lets you take the most direct route to success.

So here I have turned the left screw slightly clockwise to equalize 1 & 2. While I make the adjustment I pay no attention to columns 3 & 4.

With 1 & 2 synced, I tweak the right screw clockwise to equalize 3 & 4. I pay no attention to the fact that 1/2 are different than 3/4 because that adjustment is last.

With 1&2 equalized and 3&4 equalized, I can now adjust the center screw to match right pair to left.

At this point I go through the idle mixture screw adjustment as described in the link above. I like to leave both vacuum gauges and tachometer connected and cycle through both sync and mixture adjustment twice or more to best refine the tuning. As mixture gets closer to optimum the idle speed keeps changing and so the idle speed screw needs changing which affects throttle plate position which affects - guess what - both idle mixture and throttle sync. So after setting sync and mixture, the vacuum level is now higher than it was when I did the initial gauge calibration. So now it is time to re-calibrate the vacuum gauge before the second go-around. I find it easiest to use a brake bleeder pump to apply vacuum to the carb sync tool, pumping it up to the current level at idle and recalibrating the gauge for the final run through for both sync and mixture adjustments.

13  General Category / Tech Corner / Re: Rear shock bouncy on: March 16, 2018, 04:40:14 PM
The stock shock is not rebuildable, but if you do a search of this forum for "shock" there are many posts with much discussion about pros and cons of various replacements. A CBR1100xx Blackbird shock is an easy swap and can be found used on ebay. There are other CBR model shocks that can also be used. My bike had a bad shock when I got it and I went with the Blackbird which for me seems to work pretty well.

14  General Category / Photo Gallery / Re: Some carb work and a road test on: March 15, 2018, 10:57:54 AM
Hah! I had the pleasure back in the late '70's while wrenching at a Honda shop. That was enough....

15  General Category / Photo Gallery / Re: Some carb work and a road test on: March 12, 2018, 07:44:18 PM
....The slight wandering idle may be do to typical emission lean-ness. I found 3 turns out to be the sweet spot for a nice steady beat and off idle throttle response but with factory exhaust you may find 2-1/2 to 2-3/4 to be better.  If you didn't grind off the stop tabs from your float bowl covers while you had them off you're limited on how far you can turn the idle screws in or out.

Thanks, yes the idle is much more steady after tweaking the pilot screws. Not perfect, but much improved. And defeating the pilot screw limiters is standard practice any time I work on carbs so equipped.  Wink

To adjust the screws I like the "idle drop method" described in Honda's Common Service Manual, at least as a starting point. For those not familiar, below are screen shots of the manual describing the procedure. First off, it requires a tachometer sensitive enough to detect a 50 rpm difference. I use a cheapo hour/tachometer meter from ebay. This one reads in 10 rpm increments so is plenty sensitive enough. Since the ignition coils are shared by two cylinders, every plug fires once per revolution so step 1 is to set the meter to one spark per revolution-

In the case of the CB-1 the "initial opening" of the pilot screws referred to above is 2-1/2 turns out (2-1/4 for CA models). The "final opening" is one turn out, which means after step 8, turn the screws 1 turn further CCW. Of course it might be that some other final adjustment amount might give a better transition from idle to off idle, but what I like about this system is that it customizes the adjustment for each carb which helps to account for minor differences between carbs. And in fact the final positions of all my screws ended up being slightly different. If I had set them all to the same number of turns the mixtures would not have been as consistent for each cylinder. Before doing this procedure my idle wandered over a range of about 70-80 rpm and now it wanders just slightly at 10-20 rpm. 


Pages: [1] 2 3 ... 6
Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!