Carb Support for VM29 Smoothbores on a CB750

I made this support using some 3/8 aluminum round and a few screws. Its held in position by one of the top case screws. Well see if it works for the long haul.

The reason I need this support is because the aftermarket boots to asapt vm29s to a CB750 kind of suck. They are quite soft out of the package and get even softer as they go through a few heat cycles. They also have a tendency to leak, which is a potential cause of my continually shrinking main jet size. I've been chasing a rich conditio all the way down to 110s and on pulse type carbs, a leak at the intake boot will cause the engine to run rich. This counters the more common thought that a leak here woyld cause a lean condition. Something good to keep in mind.

Ill be doing a little leak checking in a bit.

Acid Sunrise - a 70's CB chop

Finished up the new chopper just in time for the World Honda Chopper Meet this year.  Tore the bike down in March, replaced just about everything, and ended up with just what I wanted.  Sorry there weren't any in-progress shots, I got busy and didn't take many pictures.  Bike rides great, time for the next project.  A big thanks to TurboGrimace for the wiring, motivation, and general assistance in getting this bike together so fast.

Rock Flute: Tuning Session 2, in the rain.

I spent some time going over a few things on the bike prior to continuing with the carb tune. Tune the drive, tune the clutch etc. etc.  Tunessss mannn.  All positive waves.

 

I installed a 17 tooth front sprocket and a longer chain. Originally 15/48 3.2:1 final drive, now 17/48 2.82:1 final drive. 3.2 is loads of fun but not realistic for anything other than stupid fast bar hopping and light racing. 2.82 is within the range of stock but still toward the upper range to take advantage of the engine mods. The cam kicks hard at 5000 rpm and above. With the new final drive, a shift to 4th at 65 mph puts the bike right under this 5000 rpm threshold and a shift to 3rd ignites the rockets.

I also adjusted the clutch and put on a new cable. John "jleather" spun up a cute brass barrel adapter to replace the one I lost when my cable broke. Unfortunately after a lot of adjusting, I have to settle with a neutral that is very hard to capture. The clutch lever does not have enough throw to allow a clean shift to neutral and full compression of the clutch plates. Ohh well. Later I will find another clutch lever with a longer throw.

So finally to the CARB tuning. Like I said before, I'd resume with the 115 mains, 15 pilots, air screws at 1.5 turns, and the needles now all the way down. Well... its darn near perfect. There's an occasional tiny stumble with a slight rotation of the throttle off of idle. Its right at the bottom of the throttle cruising range for low speeds. The plugs are gorgeous but I can still feel the hesitation. The rest of the throttle range feels spot on and provides a slightly rich color to the plug base ring. Below is a picture of the plug chop cruising just above the stumble. The remainder of the chops at varying throttle all look similar this. Always work from the bottom up. Otherwise your lower throttle ranges can screw up your readings.

I'm going to try and tweak the stumble out with the air screws, but it's certainly something I can live with for now.  The strap looks a tiny bit hot so I may benefit from a spark plug with more heat capacity.  I'm running a .026" gap and might close it up a bit to see if I can get a more complete burn.  The balance between the increased compression and the higher spark voltage should balance out a bit to where a .026" gap is nearly ideal.... Maybe?  

The final steps are to replace the rocker shafts and run a tool over every nut and bolt. HOME STRETCH!!!

Rock Flute: Tuning Session 1

I've done a little work on the VM29 smoothbores since the engine rebuild. I bench synced the carbs to a random .116" because I don't have vacuum ports to sync them on the bike. First few runs its been running rich on 120 mains and 20 pilots. Tuning from the bottom up, I swapped jets to 115 mains and 17.5 pilots, which is the spec for a stock cb with vm29s. The bottom end was still incredibly rich but a lot better with the air screws out over 2.5 turns.

I dropped the pilots to 15s and kept the mains at 115. Idle looked good with 1.5 turns on the air screw but off idle was rich enough to cause a stumble. Plugs showed a lot of soot. Not wanting to mess with the pilots anymore, my suspect now is the needle and main. WOT pulls well without hesitation which indicates the main is close. To alleviate the stumble in the transition from idle to 1/8 throttle I dropped the needle down. The stumble was a lot less noticeable but still their.

I went for a ride to pick up a starter switch for johns bike and was going to drop the needle to its lowest position when I got back. Unfortunately I didn't make it home under my own power due to this little gem:

Jeff Yarrington and the Scooby Van to the rescue!  My million year old, burnt, dry clutch cable finally gave up the ghost. I couldn't find a picture of Jeff's sweet van but I did find a picture of him sleeping in it. Thanks Jeff!  He got me back to John's place where I dropped the tuning for a while and resumed wiring John's black chopper.  So many things to do.

 

My fruitless quest for a starter switch was kindly remedied by Jeff. When he picked up my bike he brought two momentary switches. What a friend. Thanks AGAIN!

Ok sorry.  Back to the tuning.  With a broken cable, I was down for the night.  My next step will be to drop the needles all the way down and then refine the a/f ratio based on some plug chops. Hopefully I'm good with the 115 mains because I feel like 112.5 or 110s on a hopped up engine is a bit absurd.  Just one more week before we leave for the Roost.  TIME IS RUNNING OUT!!!

Rock Flute Dyna 2000 Ignition Install

Now that the engine is together and I've run it a bit with the stock points, I'm going to throw on the Dyna 2000 and minicoils.  Most of my electronics are under the gas tanks so any mods will be relatively hidden. 

Here's the coil placement.  I noticed that the suppression core wire kit I bought from Dyna does not come with the proper terminals for the minicoils, so I hacked the plug end of my old wires off and used them.

 

I love wiring.  It's very relaxing.  Unfortunately I dont like modifying an existing wiring harness as much as building a new one.  The area under my gas tank is already cramped and adding the 6 extra wires for the D2K is making things messy.  To alleviate some of the confusion that can arise from a mad cluster of wires I put some sexy labels under clear shrink tube.  Mmmmm,.  The goal is to keep visible wiring to an absolute minimum.

 

Below is my completed hot mess.  The coil wires will leave out the front of the gas tank under the backbone.  I added a stonger starter button as well.... It's in that mess to the right.

Next I had to find somewhere to hide the giant 3" by 5" by 1" ignition module.  It wasnt going to fit under the tank and there isnt really anywhere else to stuff it.  I didnt want some blue anodized piece of modern technology hanging off of a weird throwback bike so I made a little leather bag out of some scrap.  The back side of the ignition module has 4 small screws that I replaced with studs.  I used the studs to mount it to the battery box.  I can access the controls and plug in the curve maker harness through the bag.  After some weather, I think it will blend in nicely. 

50 cents of leather covering a $400 digital ignition module.  Tadaaaa!

Here's a finished Rock Flute.  You cant see any more wires than before.  The chianti box is reinforced with 1/8" plate 5051 aluminum and 304 SS tubing, top end is rebuilt, new ignition is hidden in plain sight.  The new air filters are a snug fit.  Just a few more things to do.  Engine break-in, carb tuning, brake adjustment, new kickstand tab, and more tuning.

Time to go for a spin.  WOOOOOOOOOOOOO!!!!!!!!

Rock Flute: Valve Train Assembly and Cam Timing

Time to wrap up the top end of the Flute.  I've already retorqued my head bolts and found true TDC.  Next I installed the cam tower pucks.  I've added some yamabond so that I can reduce the chance of developing a leak down the road.  These little pucks are what cause an old engine to weep oil from between the head fins.  Most notable on the left side of the bike since the oil will run across the fins toward the kickstand.  I also installed the guide dowels, four small orings and the oil injectors (not shown in the picture below).

I replaced my cam towers, rocker shafts, and rockers after noticing some damage.  The picture below shows damage to the cam race on one of my cam towers.  This probably happened while installing the old cam. When replacing cam towers, remember that the top shell and the main body of the tower that make the cam race are line bored and must be kept as a set.  These parts are labeled with two identical letters.  An example can be seen a few pictures below (for example, the cam race top shell is labeled FF and the right side of the cam tower is labeled FF, these parts should go together).

I went through quite a few towers to find ones that mic-ed close to the original specs.

Once the parts were cleaned, I installed them on top of the head.  Make sure that if you use a little sealant on the cam pucks that you wipe off the excess.  Any extra sealant can cause the cam tower to sit a little higher and cause more friction at the cam races.  And once you've installed the cam towers, do not lift them back up.  You will pull the pucks out of the seat and have to reinstall them.  Lay a little oil down on the races and inside the rocker shaft bores.  I'm using 30 weight since I have it on hand.

Slide the cam in from the left side, first through the chain and then through sprocket.  Be as gentle as possible with the cam and try not to rest it on the cam towers until all the races are lined up.

Next I installed my rockers with the tappets completely loose.  With a stock cam, you should be able to slide the cam in through the rockers with the tappets fully recessed into the rockers.  The lift on a stock cam is smaller than the travel of the tappets.  This is not the case on an aftermarket cam and you will need to do a bit more work to get the rockers installed.  I set my tappet clearances on cylinders 1 and 4 to .005".



Next I lined up the hash marks on the cam with the mating surface of the cam race.  The keyway faces up.  At this point, cylinder 1 should be in the overlap position between intake and exhaust.  This is a decent starting point for degreeing your cam.  Note the letters stamped on the end of the rocker tower assembly in the picture below.  These two pieces are best friends for life.

With everything bolted in place, apply oil to the small ports on top of the cam tower races, as well as the rocker oiling ports.  Give some oil on the lobes and all other areas where there is metal to metal contact.

I verified my lobe centers using the degree wheel and a dial indicator referencing the surface of the valve retainer.  I should see 105* int and 104.5* exh.  Below is my reading for the exhaust valve of cylinder 1.

Next I measured the lobe center of the intake valve on cylinder 1.  

My final readings of the lobe centers are 105* int and 105* exhaust.  I'm pleased with those results.  degreeing in your cam like this helps to eliminate the propagation of errors in machining tolerances.  It allows you to set up the cam as close to the manufacturers specifications by compensating for the modifications and characteristics of your engine.  Below is my intake reading.

 

With all of the tedious stuff out of the way, I installed the cam sprocket bolts, applied the cam chain tensioner, verified tension on the front side of the cam chain, and snugged the sprocket bolts down.  Torque to spec and use a little locktite.  It can't hurt to be thorough.

Finally, I set all my tappets at .005" clearance, installed the valve cover, and snugged the cam tower support bolts down.

She's almost complete.  Carbs, exhaust, plugs, oil, gas, and shes ready to fire.



Happy Memorial Day!

Making a Chopper King/Queen seat from scratch!

I wanted to take a minute and do an article on making a king queen seat for a chopper. This is incomplete as the seat isnt finished yet, but this is the first part of it anyway.

First I made the seat pan out of 16g steel. Rolled the center section to match the fender...about a 14.5" radius, then cut the front and rear sections and tacked them on.

then I cut the side panels and tacked one on..and added a 1/2" rod in the back for support.

next came the internal stash tube made of stainless to cut down on rust. There is a threaded rod inside for threading the cover on. I also welded in some 5/16-18 nuts in the bottom with holes drilled for mounting.

then I rolled the seat pan insert and tacked that in...

with the cover...and all welded up and sanded smooth..

..

test fit to the frame and sissy bar that I also made...(that's another blog entry later)

all good...now for foam. I first started with the 160lb foam at 1" for the main base of each seat..

added in some wedges for the transitions..

next comes the layer of 60lb foam for the back of each seat and over the 160lb for some cushion..this is for the passenger back...cut a relief out for the 1/2" rod so there isn't a bulge in the back rest.

60lb on the rest...

edges are trimmed with a knife and shaved with a die grinder..

ok guys...that's all I have at the moment til I get some more foam adhesive (ran out)...next will be the final layer of 35lb foam for that super soft feel...and then a whole 'nother entry on doing the upholstery for the seat...

Meal Time!

Pork rinds and hot sauce. Mmmm. Spent all day working on the bikes. This is a much deserved treat.

Finding True TDC

Finding top dead center can be done numerous ways.  You can use the stock markings on the engine block and the advance mechanism, you can use a dead stop, you can watch a screw driver move up and down, you can even yank the head and use a dial indicator on the piston.  All of these are valid methods... To a degree (or several).  But when you're setting things up, why not do it the best way possible?  Especially when this precise method doesnt take much longer than simply lining up the stock marks.

The stock marks on the CB750 can be off by a few degrees.  Ever notice that the little pin on the back side of the advance mechanism doesnt fit very snug into the detent on the end of the crankshaft?  This adds one error.  Another error is the size of the arrow casted into the top case that you line up the T-dash mark with.  That casting mark imay not be held true to the line boring of the crankshaft over the years.  Then there's the distance between the dash mark and the casted arrow versus the angle of your eye through the viewing window of the points plate.  Etc. etc.  Propagation of error.

The errors in using the stock timing system can add up.  Whether it's significant or not is up to you.  For me, and since the dead stop method is so simple, it is significant.  So heres how to get true top dead center using a degree wheel and a dead stop.

The above picture shows you all the tools you need to find true Top Dead Center (TDC) using a dead stop.  A degree wheel and a dead stop.  The dead stop I'm using is made from a gutted spark plug and an M8-1.00 fine thread bolt.  A dead stop is a tool that is placed into the spark plug bore and is used to stop the pistons travel in the cylinder.  The bolt can be adjusted until it is in the path of the piston.

First mount your degree wheel on top of the advance mechanism using the long M6 stud.  Remove the large nut and mount the plate against the teeth protruding from the tip of the advance mechanism.  You dont need to tighten it down very much, but make sure that it doesnt move easily and stays mounted solid to the advance assembly.  Next take a small piece of wire and secure it to somewhere on the engine.  Adjust it so that it acts as a pointer on the degree wheel.  Again, make sure that the pointer is very secure and will not move.  Set the degree wheel so that the pointer is at 0.

 

Next place the dead stop into cylinder 1 or 4 (shown above, between the fins).  I use cylinder 4 since it's on the side of the engine where I'm working.  Run the bolt down a bit and turn the engine by hand until it stops rotating (i.e. hits the dead stop).  DO NOT USE THE STARTER TO ROTATE THE ENGINE.  If the engine rotates without hitting the dead stop, adjust the bolt down further.  Again, rotate until the engine hits the dead stop.  Once you've hit the dead stop, look at the degree value on the wheel.  Mine is reading 51* ATDC in the picture below.  Since we've set the degree wheel to zero initially, we simply divide the number indicated by the pointer by 2.  51 divided by 2 is 25.5. 

 

Move the degree wheel so that the pointer is now at 25.5*.  Moving towards 0* of course.  Following along, my movement can be seen in the picture below.  Only move the degree wheel during this process, not the crank.

 

Now, rotate the engine in the opposite direction until you hit the dead stop from the other direction.  When the piston hits the dead stop, look at the value on the degree wheel.  It should be opposite of your other reading, but identical in value.  My reading, shown below, is now 25.5* BTDC.  If everything was done correctly, the value you adjusted the wheel to previously and this new value should be the same. 

Now we know where true TDC is.  Remove the dead stop and rotate the crank until the degree wheel is at 0*.  This is true TDC.  See the below picture... and my knee in the clutch cover.

Now, just to show you how much my plate was off, here is a picture of the alignment of the T-dash mark on my advance mechanism lined up at true TDC.  It's a little bit to the left, which means that if I used this to mark my TDC, I would have been a little retarded (~2*).  No pun intended.

 

Again, the significance of the difference between true TDC and the TDC determined using the stock marks is up to you.  When installing a new cam, making ignition adjustments, etc, etc.  precision is key.  Especially considering you're already working with a few degrees in either direction.