Author Topic: CB650 Surface Turbulence™ (Read 10155 times)

cb650 · « **Reply #25 on:** March 16, 2011, 05:50:35 PM »

I think 70 or 80 should be easy. I have gotten 67 and dad "the putter" always did.

Pinhead · « **Reply #26 on:** March 16, 2011, 07:25:09 PM »

Quote from: cb650 on March 16, 2011, 05:50:35 PM

I think 70 or 80 should be easy. I have gotten 67 and dad "the putter" always did.

What kind of driving?

cb650 · « **Reply #27 on:** March 17, 2011, 03:27:59 AM »

Puttin around slow. Last time i got 67 I was on old gravel roads doin 40 in 4th.

Pinhead · « **Reply #28 on:** March 17, 2011, 01:31:24 PM »

Quote from: cb650 on March 17, 2011, 03:27:59 AM

Puttin around slow. Last time i got 67 I was on old gravel roads doin 40 in 4th.

What sprocket sizes are you running? RPM at 40mph in 4th gear?

Pinhead · « **Reply #29 on:** March 17, 2011, 07:55:33 PM »

Idle! Before the rebuild the engine wouldn't idle any lower than 900 rpm, now it will idle much lower (can't tell exactly with the mechanical tach).

So I am curious if this is a function of the mods that I've done, or if it's simply due to being a freshly rebuilt motor.

VIDEO:
[EDIT] Video has been removed by my media hosting service. :/

It is able to idle slowly enough to count the power strokes.

cb650 · « **Reply #30 on:** March 18, 2011, 06:19:50 AM »

18/37 17" rear Think its about 3500 rpm. Dont remember exactly.

Pinhead · « **Reply #31 on:** March 19, 2011, 04:20:03 PM »

Crap. So much for getting accurate MPG figures out of the first tank... I left the petcock on over night and came to it today with about a gallon of gas on the ground.

Pinhead · « **Reply #32 on:** March 20, 2011, 09:45:17 AM »

I'm going to get new clutch plates soon but am wondering if stiffer springs will be needed to cope with the extra power. Does anyone know where I can get stronger clutch springs? I can't get the new power to the ground with the clutch slipping...

bwaller · « **Reply #33 on:** March 20, 2011, 10:31:22 AM »

Try shimming your existing springs.

cb650 · « **Reply #34 on:** March 20, 2011, 02:27:23 PM »

I bought a couple sets from DK years ago. I even thing they was barnet.

Pinhead · « **Reply #35 on:** March 31, 2011, 05:18:13 PM »

After some driving the head gasket has started to leak profusely. Badly enough that I can see bubbles coming from the gasket when the bike is idling. I guess I'll have to take it back apart and re-torque the head bolts and if that fails, find a new gasket. :/

Pinhead · « **Reply #36 on:** March 31, 2011, 07:35:14 PM »

Since it's supposed to rain tonight I'm not going to tear the top-end apart to figure out what's going on with my head gasket.

So instead I'm going to spend some time working with Pipemax to see how far off the stock exhaust system is.

My problem is, I'm missing a few specs. This is what I have from the factory manual:

Quote

Exhaust Opens 40° BBDC
Exhaust Closes 5° ATDC

Intake Opens 5° BTDC
Intake Closes 35° ABDC

These are at 1mm lift.

From these values I calculated duration, LSA, and overlap (again at 1mm):

Intake duration - 220°
Exhaust duraiton - 225°
Overlap - 10°
LSA - 106.25°

I still need these the Intake CenterLine the Camshaft was Degreed on (90 to 125 Degrees), and the Rod Length.

I installed the cam by the book. Can any of you camshaft gurus help explain how to calculate the Intake Centerline? If I understand this correctly, from the above given specs it should be 105 degrees??

Pinhead · « **Reply #37 on:** May 26, 2011, 06:57:28 PM »

It's been a long time since I've updated this thread so I figured I'd better get on it.

I haven't completely finished everything that I had planned for the bike unfortunately. I still need to get the Ignitech ignition installed (having trouble with the hardware) and tune my ignition advance curve. I also am running the same carb jets as before the rebuild. They could conceivably be replaced with smaller jets due to the stronger vacuum draw from the larger pistons and higher CR, in addition to the other more unconventional mods which should lower lean burn limits.

The ignition of the Constant Energy HEI type, driven by two GM 7-pin HEI modules firing 0.5 ohm Chevy Cavalier coils. Two-inch sparks are no big deal with this ignition. Unfortunately, however, without the Ignitech unit I don't have vacuum advance so my mileage is suffering. I changed to the cooler (and side-gapped) NGK D9EA plugs to stay in line with the higher CR.

With all of that in mind, the bike is running astonishingly well. On the trip from KC to Oakley and back (1032 miles round trip) in mostly 95°F weather, the 11:1 engine happily ran on 87 octane fuel with the factory timing curve and absolutely no audible detonation (and verified by reading the spark plugs). A few stretches at 80 mph fighting a strong headwind didn't bother the bike a bit.

Idle is beautiful, rivaling most fuel-injected inline four's (remember this is also without tuning/optimizing the carbs). Power is much greater throughout the entire rev range. Torque below 4000 rpm is astonishing, especially for a carb'd 650. I'll have to get some new clutch plates and probably stronger springs to cope with the added torque and especially the power above 7000 rpm where the clutch slips like mad.

I would definitely consider these engine experiments a success.

MPG is generally the same as it was before the rebuild (~50mpg) which is probably due to the unoptimized timing and fuel curves and much more spirited riding. When the clutch decides not to slip, 100 mph is absolutely effortless.

If anyone wants to try the port mods send me a PM and we can work something out.

Pinhead · « **Reply #38 on:** July 09, 2011, 10:55:08 PM »

Tuning has been underway. The last 9 tanks have been better than 55 mpg and each consecutive tank has been higher than the last. Tonight's tank was 60.49 mpg. Mostly 55-60 mph, though there were probably 5 sprints up to 95 mph or so while testing the ignition's capabilities. I've had to settle for 0.080 inch plug gap because my plug wires and boots aren't up to the task of holding the voltage of a much wider gap (aiming for 0.100" if it's possible). Each increase in plug gap from 60 to 80 thou (in 5 thou increments) has netted a slight improvement in MPG. Still some work to do.

willbird · « **Reply #39 on:** July 10, 2011, 06:20:42 AM »

As I recall your bike came with electronic ignition ? Reading the link in your other thread the HEI modules when used with those pickups shows some spark retard as RPM increases....this is compensated for apparently in automotive systems. Did they also compensate for it with the Honda advance system ? More or less my question is...does the advance system on the electronic ignition bikes do more advancing ? As I recall about 5 to 8 degrees more would be required.

Is the breaker plate and other parts on your bike a drop in for an earlier 70's CB750 ?

My 1972 CB750 would knock out 50mpg like clockwork with the stock airbox and an action fours header...adding K&N's and a Mac header dropped me to 45 mpg...but that was with 1996 gasoline...dunno yet what todays "gas" will do.

Pinhead · « **Reply #40 on:** July 10, 2011, 06:50:39 PM »

The modules themselves don't cause the spark retard - the factory reluctors do. It is this way with the stock Honda modules, as well.

Quote

http://home.comcast.net/~loudgpz/GPZweb/Ignition/CBstockIgnitionNotes.txt
Due to the nature of inductive pickups, there is a small delay from the time the rotor's tip passes the center of the pickup and when the spark fires. This delay can be seen with a timing light on the pickup. At 1300 RPM, the delay is about 3 degrees. At 8000 RPM, the delay has increased to about 8 degrees. At idle, this delay is compensated for by rotating the timing plate. This is a static compensation of 3 degrees. Therefore, at 8000 RPM there is a net delay of about 5 degrees. This reduces the amount of advance provided by the mechanical advancer, and is normal. Similar behavior can be found on most reluctor-triggered ignitions.

I don't see how there's any way around it without a programmable curve. I also don't see it as a true disadvantage, as the much more powerful spark will effectively advance the timing, since the flame front will be taking off more quickly.

As to trying to fit the 650's advancer plate onto the 750, I have no idea (never worked on a 750). I have seen Dyna S triggers designed for 750s grafted into 650s, though, so I doubt it's impossible. With a Dremel and some ingenuity, anything can be done.

Pinhead · « **Reply #41 on:** June 24, 2015, 07:21:17 AM »

Old topic bump because I may be doing similar mods to a '71 Ford 400 V8. Haven't been on here in ages. I moved twice, changed jobs thrice, and went through three vehicles since I posted here last. I haven't done much of anything to the bike, which has been sitting in my barn for three years. :/

I never got done tuning it because I burned up two Ignitech ignitions - which means I can't recommend using them with low resistance coils. I don't doubt they would work adequately with high resistance coils (3 ohms or more) though! The GEM HEI conversion is rock-solid and I can't recommend it enough. Definitely the hottest most reliable ignition I've ever worked with.

The bike still runs beautifully, and the MPG was pretty steady at ~65 mpg at 55 to 60 mph. I haven't done any carb tuning.

cb650 · « **Reply #42 on:** June 24, 2015, 12:07:30 PM »

Glad to hear from u again. You still in KS? I been pondering a trip to oakley again.

Pinhead · « **Reply #43 on:** July 23, 2015, 12:49:31 PM »

Sorry for not responding sooner; been working on other projects and the bike hasn't moved for way too long. Yep, though I'm in central KS now instead of the KC area.

cb650 · « **Reply #44 on:** July 24, 2015, 04:28:43 AM »

Nice maybe we can plan a meet sometime.

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Author Topic: CB650 Surface Turbulence™ (Read 10155 times)