Topic: Thoughts about points

[AirCanuck]

.....when this thread have all facts, ideas, thoughts and experiences about points and also other ignition systems for a CB....
..... time for an oil thread to enlighten ourselves about what to feed our CB animals with....

It's up to the reader to extrapolate the facts, opinions, and suggestions while sifting through our silliness.

Definitely a challenge for the uninitiated lol

[HondaMan]

Do I smell beer?

[Don R]

 Well, since I contributed to the silliness, I'll add something usefull.
  Today I used a dwell meter for the first time on a 750 with success. It's an old sears almost new in the box tach dwell meter. I checked my previously set points on an evil running big bore K2 750. The numbers were 27-28* so I dialed back to 23* on both sets and re-set the timing. It did idle better although leaving a lot to be desired.

   I gave her a dose of fresh no alcohol gas with some techron carb cleaner in it, drained the carbs, changed to a set of used -7 plugs on a whim, changed out the two center plug caps since the outers already had new ones. At idle now, it does heat up all four pipes, that's a nice change. Tomorrow I'll see if I make it more than a block or two running on all four.

[Don R]

 As far as the points vs electronic debate,
  I'm an old drag racer that remembers using a different set of plugs driving to the lanes, then put in the race plugs and run, go to the end of the track and swap back to the pit plugs and repeat. Since we've gone to MSD, I've run the same ngk's for two seasons and will change them this winter just because it seems right to do it rather than risk a failure.
  I run a way better carb (1150 holley) now and it was jetted on a dyno so that may be a big part of the difference.

[PeWe]

This thread is a good thread with much experiences and thoughts. Fun with some ironic posts. Too boring without funny comments and facts only.

[Terry in Australia]

As far as the points vs electronic debate,
  I'm an old drag racer that remembers using a different set of plugs driving to the lanes, then put in the race plugs and run, go to the end of the track and swap back to the pit plugs and repeat. Since we've gone to MSD, I've run the same ngk's for two seasons and will change them this winter just because it seems right to do it rather than risk a failure.
  I run a way better carb (1150 holley) now and it was jetted on a dyno so that may be a big part of the difference.

Yeah, it's probably just a coincidence Don, but Ron (MCRider) and I were chatting via PM about our Yamaha FJR1300's on the weekend, both bikes were fitted with pretty basic electronic ignitions and non-iridium spark plugs from the factory, anyway, I told him that my bike (which has done 146000 miles without so much as a clutch replacement, gotta love modern-ish bikes for build quality) has done just over 35000 miles on it's current set of spark plugs, and Ron told me that up until his crashing his bike and writing it off, he'd done 22,000 miles without doing a plug change. I bought a new set of plugs for mine in 2016, but haven't gotten around to changing them yet, it starts at first press of the button and returns better than 50 MPG (imperial) so I haven't seen a need as yet? Cheers, Terry.  

[PeWe]

Those bikes have Fuel injection right?
The Air/fuel ratio can be perfecty mapped for all throttle openings, rpms, no need of too rich pilot to be able to react on a sudden WOT without hesitation as a carburetor.

Last time I did a Dyno with my K6 the dyno guy showed me an A/F chart from a modern fuel injection bike, more or less a straight line within the perfect area.

[Terry in Australia]

Yeah mate, EFI is fantastic, my VFR750 is similar though, it's still on it's original plugs (according to the 72 year old PO) and it's done 40,000 miles, with 4 CV carbs. Not sure if they're iridium or not, I've never looked at them.

[Geeto67]

As far as the points vs electronic debate,
  I'm an old drag racer that remembers using a different set of plugs driving to the lanes, then put in the race plugs and run, go to the end of the track and swap back to the pit plugs and repeat.

It's funny but with the GTO I used to do this too, and re-timing the distributor after each run. I'd drive the car to the track, see what fuel is available, retime the distributor, change the plugs out for the specially gap-ed "race plugs", check it after every run, then at the end of the day I'd put the street plugs back in and usually retard the timing for the crappy jersey pump gas I would have to fill up with on the way home. If I couldn't get 101 octane at the track and had to make passes on 92 it was a completely different timing setup than if I could get the good stuff (most of the time I was advancing it because street fuels in the 90's were crap - just by different amounts). Checking after each run was a necessity because pontiac distributors like to walk under WOT, sometimes as much as 5 degrees during a run.

[HondaMan]

One of the cool things about EFI is the ability to run lean, which makes the engines and plugs last longer. It goes richer for Start cycle on all EFI units, then switches to  match throttle requirements. I did something similar with my carb'd Fairmont Ford when I rebuilt it in 1995 (1 bbl Holley) with a re-cal, have now received over 375k miles from it. When a freeze plug cracked last winter and I pulled the head (thought it was a blown head gasket!) I was astonished to see NO ring ridge in the engine, whatsoever. Amazing how running it at 16:1 can do that...the valves are in perfect condition, too, and the temperature gauge runs half of what it did when at factory calibration. And the MPG went up from the factory 14 to 18 in town, and from 16 to 20+ on hiway, at the same time (and of course it climbs high mountains easier). I'm about to try this with my 750 this winter, switching to a leaner-burn setup to see how it does next season. I'm going to try for 16:1 above 2500 RPM (it needs more like 12:1 to start and idle well, though).

[Geeto67]

One of the cool things about EFI is the ability to run lean, which makes the engines and plugs last longer. It goes richer for Start cycle on all EFI units, then switches to  match throttle requirements. I did something similar with my carb'd Fairmont Ford when I rebuilt it in 1995 (1 bbl Holley) with a re-cal, have now received over 375k miles from it. When a freeze plug cracked last winter and I pulled the head (thought it was a blown head gasket!) I was astonished to see NO ring ridge in the engine, whatsoever. Amazing how running it at 16:1 can do that...the valves are in perfect condition, too, and the temperature gauge runs half of what it did when at factory calibration. And the MPG went up from the factory 14 to 18 in town, and from 16 to 20+ on hiway, at the same time (and of course it climbs high mountains easier). I'm about to try this with my 750 this winter, switching to a leaner-burn setup to see how it does next season. I'm going to try for 16:1 above 2500 RPM (it needs more like 12:1 to start and idle well, though).

you aren't worried about the barrier layer and burning a hole in the piston?

EFI's consistency is what made running leaner possible. Carbs are really crude as measuring and metering devices when you really think about them. Bringing this back to our points vs electronic spark that's the benefit - consistency over life of component that contributes to longevity.

My GTO ate through 2 packs of plugs a year, my EFI jeep has had the same plugs in it since 2005. My Dyna S CB750 has had the same plugs in it since 2009. I'd change them but why? they still work fine.

[AirCanuck]

Here I was laughing to myself this week thinking this thread had gasped its last...

[HondaMan]

One of the cool things about EFI is the ability to run lean, which makes the engines and plugs last longer. It goes richer for Start cycle on all EFI units, then switches to  match throttle requirements. I did something similar with my carb'd Fairmont Ford when I rebuilt it in 1995 (1 bbl Holley) with a re-cal, have now received over 375k miles from it. When a freeze plug cracked last winter and I pulled the head (thought it was a blown head gasket!) I was astonished to see NO ring ridge in the engine, whatsoever. Amazing how running it at 16:1 can do that...the valves are in perfect condition, too, and the temperature gauge runs half of what it did when at factory calibration. And the MPG went up from the factory 14 to 18 in town, and from 16 to 20+ on hiway, at the same time (and of course it climbs high mountains easier). I'm about to try this with my 750 this winter, switching to a leaner-burn setup to see how it does next season. I'm going to try for 16:1 above 2500 RPM (it needs more like 12:1 to start and idle well, though).

you aren't worried about the barrier layer and burning a hole in the piston?

EFI's consistency is what made running leaner possible. Carbs are really crude as measuring and metering devices when you really think about them. Bringing this back to our points vs electronic spark that's the benefit - consistency over life of component that contributes to longevity.

My GTO ate through 2 packs of plugs a year, my EFI jeep has had the same plugs in it since 2005. My Dyna S CB750 has had the same plugs in it since 2009. I'd change them but why? they still work fine.

No, I'm not concerned about that, at least not like Honda Warranty was in the 1970s. The gas today is far more consistent than it was back then. We used to see stuff like bromide and lead accumulating on the plugs when rich, shorting the plugs entirely. Now, it is just the occasional overly rich mixture that collects carbon on them, to short the spark out. This stuff cleans off easily with a sandblast o even wire brush, in most cases. But, the slow burn speed of ethanol-laced and ethanol-accepting fuel mixes today acts as if it is higher octane when it is not, and if the carbs are set to normal 1970s mix rates (like 12:1 A/F below 2000 RPM), the plugs get wet during heavy traffic idling. If you don't then get a change to immediately blow them clean with a high RPM blast, they slowly foul with the carbon. It doesn't much matter which kind of ignition the bike has then: the wetness and carbon stay on the plug and foul the tips. A good example is my own commuting: if I stay on the freeways I can ride all summer on the same set of plugs (I change them at every season, clean them, and put the old set in the tail trunk for the next year), but if I get stuck on the surface streets in typical Denver traffic, it can idle 20 minutes on a 30-minute commute, and the plugs will foul after a few weeks of this riding. The idle circuit is easily adjusted to stop this with the air screw, set to 3/4 turn instead of 1 turn to lean it out, but the off-idle-to-2500 RPM range is too wet (5-to-20 MPH in 1st gear stuff) and this slowly loads the plugs up wet. Dropping the needle or lowering the float levels can help here, but then the mainjet must go up a bit for the midrange comp, and then you're pulling the carbs to do it. Painful stuff then! So, it becomes an off-season project, lest the nice days get away.

These engines can run at 20:1 A/F mixture with today's fuels, as they are knock-resistant in order to cope with auto EFI systems, which can be slow to respond to sudden driver's foot requests. This was not the case when they were first designed, so the carbs were set conservatively rich to prevent warranty claims: sparkplug replacements were cheap as compared to pistons. And yes, you can get more torque with richer mixtures, a racer's favorite carb tweak - but racers go to the track with boxes of sparkplugs handy!

[Deltarider]

The idle circuit is easily adjusted to stop this with the air screw, set to 3/4 turn instead of 1 turn to lean it out...

Here I'm lost. What bike are you referring to? I have airscrews on my carbs, but setting them to 3/4 turn instead of 1 turn would certainly enrichen the mixture and not lean it out.

[Gene]

The idle circuit is easily adjusted to stop this with the air screw, set to 3/4 turn instead of 1 turn to lean it out...

Here I'm lost. What bike are you referring to? I have airscrews on my carbs, but setting them to 3/4 turn instead of 1 turn would certainly enrichen the mixture and not lean it out.

Depends on the carb and which side the screw is on (air or engine)

[PeWe]

About air screws...like a paint gun, less air will bring less paint to the nossle and spray. I finally understood it when Hondaman explained it. The pilot circuit will work like a paint gun, more airflow, more fuel will flow here.

I got it verified on my carbs with fuel screws. I got similar bangs on throttle decelerations as my old Honda stock carbs with air screws wich I thought was too lean back in the days and closed the air screws.
I finally understood that the bangs I heard was too rich mixture, closed the fuel screws a little and fixed it. Rich smelling idle was another thing.

[Deltarider]

This is an airscrew and I know what it does ...

[Deltarider]

... and this is a pilot screw (found engine side) which meters the already mixed air/fuel. That's why I asked which bike Hondaman referred to,

[Deltarider]

About air screws...like a paint gun, less air will bring less paint to the nossle and spray. I finally understood it when Hondaman explained it. The pilot circuit will work like a paint gun, more airflow, more fuel will flow here.

Not on my bike...

[BomberMann650]

About air screws...like a paint gun, less air will bring less paint to the nossle and spray. I finally understood it when Hondaman explained it. The pilot circuit will work like a paint gun, more airflow, more fuel will flow here.

Not on my bike...

Doesn’t the idle air screw INCREASE vacuum pressure in the circuit by closing the hole in the idle circuit?  Forcing the circuit to pull MORE from the jet than the throat?  That would be opposite of the paint sprayer function.

[AirCanuck]

About air screws...like a paint gun, less air will bring less paint to the nossle and spray. I finally understood it when Hondaman explained it. The pilot circuit will work like a paint gun, more airflow, more fuel will flow here.

Not on my bike...

Doesn’t the idle air screw INCREASE vacuum pressure in the circuit by closing the hole in the idle circuit?  Forcing the circuit to pull MORE from the jet than the throat?  That would be opposite of the paint sprayer function.

Uh, are we talking about idle screws or what? I’m totally lost

[TwoTired]

Hondaman and I have a difference of opinion regarding the idle screws on the earlier, non PD carbs.

I did exhaust analyzer testing of a 74 CB550, that clearly indicated that the air screws on those carbs made the mixture richer when turned inward.  Further, when I turned those air screws outward for leanest exhaust gas readings (ended up being 6 to 8 turns), the off idle engine response was dismal to  non-existent, even though it idled beautifully.  Certainly un-rideable as I just couldn't get the engine to rev up with the bike in any gear.
Gradually and incrementally turning the air screws inward eventually restored the throttle twist problem until it was street acceptable.  The Exhaust gas analyzer once again indicated it was rather rich during idle operation.  And, surprise surprise, my stock configured bike exhaust and intake ran best at Honda recommended air screw setting.  Who'da?

Hondaman explained the exhaust gas analyzer was being fooled, and the bike was getting too rich to accelerate.  My tuning experience just doesn't support this.

Too rich bikes blubber going in and out of too-rich-to-support-combustion mixtures.  Too lean mixtures have a fine border edge of tune where they either fire or don't.  Nothing to "clean up" when going in an out of combustion range, no blubber/no burble.  The Cb550 example had a throttle that acted more like a switch.  On idle it ran fine, off idle under load it didn't, like the coils were turned on and off and on.  No blubber, no burble to me means not a too rich indication.  I simply can't believe my exhaust gas analyser was being fooled, as engine behavior matched indications.

Finally, Honda's own tech article explains, inward rich and outward leaner for air screws...  Which Hondaman also says is wrong.

Therefore, as a result of my findings, I have to disagree with Hondaman's assertion, and maintain that turning air screws outward leans the idle mix and turning them inward makes the idle mix richer.  Of course the Idle Mixture Screws (IMS) found on PD carbs work the opposite way.

I can infer that since the CB750 Carbs have the same physical pilot/idle circuit arrangement as those found on the CB550, they would function in the same way as the Cb550 early carbs.  But, I have no early model 750 carbs to characterize.  If there is some subtlety about 750 carbs I'm unaware of, well believe what you wish.  But, I don't see any sort of venturi in the pilot circuit, the air screws meter the amount of air available to mix with pilot jet output, and regulate the pressure presented to the pilot jet output.  Opening the screw reduces the pressure in the pilot circuit, making it closer to outside atmospheric pressure, which equates to less fuel draw from the jet orifice while simultaneously providing more air.  This makes for leaner pilot circuit delivery.  Closing off the air screw, allows less air availability for mixing with the jet output, while simultaneously allowing the low pressure source (the carb throat) to exert more draw on the pilot jet exit. E.G. the mixture gets richer.

Pity there is controversy about this.

Cheers,

[BomberMann650]

The inverse can be true on other carb designs.  Relative to position of the screw in the circuit.  Right?

[TwoTired]

The inverse can be true on other carb designs.  Relative to position of the screw in the circuit.  Right?

I hesitate to generalize for all carbs in existence.  But, for the SOHC4, it follows that the air screw is on the inlet side, and the IMS is on the engine side.

The engine side screw regulates the combined air fuel mixture to the engine. It both allows more engine vacuum to effect delivery and allows the passage of more mixture to flow past the needle.  Open for more rich, close for more lean, all the way to completely shut off. PD carbs have this feature.

The air screws on the early carbs operate in the reverse, in my experience, and directly control the air entering the pilot circuit, along with providing the higher pressure of near atmospheric from the filter box at the inlet to the carb.

Cheers,

[Deltarider]

The picture TT shows is from the Honda Motorcycle Carburetor Instruction Manual. If only all of us would read the comprehensive and easy to follow explanation there, it would save a lot of confusion. https://www.4shared.com/office/jC4Zzkqhce/Honda_Motorcycle_Carburetor_In.html