Topic: First start attempt - Fail

[Mark K]

'73 CB750, bored .50 over stock, new pistons, rings, engine rebuilt, stock airbox with freshly cleaned, oiled K&N air filter. New coils, wires and spark plugs.
Attempted start yesterday, unsuccessful. Using test fuel tank feeding into a tee fitting to carb fuel lines. Used jumper cables from car battery. Cylinder 1 fired in a previous video, sounded like one of our Kawasaki 140s, single firing, too long to post here, had some smoke out of Delkelvic 4-1 exhaust. Cylinder 1 header only pipe that got warm, 2, 3, & 4 pipes cold. Gas running out of overflow tubes (wetness on cement under bike). Although I could not tell which carbs were leaking out of overflow tubes, forgot to tag the tubes before start attempt.

Trouble shooting after failed start attempt - Pulled all sparkplugs - 1 & 4 good spark, 2 & 3 sparkplugs no spark. Cylinder 1 only sparkplug with carbon on electrodes. 2, 3, & 4 sparkplugs clean like just out of the box. No fuel smell on 2, 3, or 4 sparkplugs. When I set the points a month or so ago, I had a difficult time setting the points for 2 & 3, but finally got them set per the FSM procedure. I think 2 & 3 points might be the cause of no spark on plugs 2 & 3. I have not installed HondaMan's ignition yet, wanted to see if we could get it run before installing it.  I do not have a clue on the fuel running out of the fuel overflow tubes. I adjusted the floats per the FSM, making sure I did not compress the small plunger piece. I know the carbs are getting fuel, it's running out of the overflow tubes.

Any and all advice, suggestions, recommendations welcome, thanks in advance.

[ekpent]

There was a guy on here once who had the fuel lines hooked up to the wrong nipples (vent tube spot) and not on the fuel tee's where they belong. If you don't have a good spark on both 1& 4 and 2 & 3 then its fruitless so get that sorted at least first.
  Be really careful with sparks and those jumper cables if you have raw gas and vapors collecting around you.
  Is your slave tank a homemade job or store bought and does it vent ? 

[bryanj]

Check the yellow and blue wire connections in the boot where the rear brake light wires go, have had them pull out more than once, you can also turn ignition on and ground those wires from loom with points disconnected to see if when you disconnect loom wire from ground you get a spark, if so problem at points if not power to coil or wiring down to boot

[Mark K]

There was a guy on here once who had the fuel lines hooked up to the wrong nipples (vent tube spot) and not on the fuel tee's where they belong. If you don't have a good spark on both 1& 4 and 2 & 3 then its fruitless so get that sorted at least first.
  Be really careful with sparks and those jumper cables if you have raw gas and vapors collecting around you.
  Is your slave tank a homemade job or store bought and does it vent ? 

The inlet fuel lines are connected to the two tee-type fuel tubes (has an o-ring on each side and connects two carbs together for fuel intake). I have strong spark on 1 & 4 and plan to trouble shoot ignition problem first. Good point about the jumper cables, spark and gas vapor, something I didn't think about. Also forgot a fire extinguisher, going to buy one tomorrow to have on hand. Slave tank is the one pictured from Bike Master, it's vented. Thanks for your advice!

[Mark K]

Check the yellow and blue wire connections in the boot where the rear brake light wires go, have had them pull out more than once, you can also turn ignition on and ground those wires from loom with points disconnected to see if when you disconnect loom wire from ground you get a spark, if so problem at points if not power to coil or wiring down to boot

I will double check the yellow and blue wires. Sorry, but not sure what the loom is?

[PeWe]

Main harness

[grcamna2]

subscribed

[bryanj]

Yup, im in UK and we call it a wiring loom, i think you call it a harness

[Don R]

  It's easy to ground the yellow or blue wire at the points by accident, check where they attach to the points.
  You may need to clean the float valves. I like to remove the bowls one at a time, pull that float and needle then turn on the petcock to flush the inlet. I catch the gas in a cut down oil bottle.  I've also seen floats hang up on the bowl gaskets at the sides. You may also hold the float manually and observe the fuel turn on and off while raising and lowering the float. Be sure to get lots of ventilation and catch the gas in a container.

[Stev-o]

What condensers are you running?

[TwoTired]

Point contacts can get a film on the surface which insulates an electrical connection, even if new.  So, hit the contacts with contact cleaner or a point file ( not sandpaper) to insure they can function.  You can also test for function with a voltmeter.  With ignition on and points physically closed there should be no voltage across the contacts.  When open there should be.
 You can also do a rudimentary condenser check with an ohmmeter (key off) if it has a needle display. On lowest scale place probes on case and lead contact.  The needle should jump and then return to zero. Reverse probe polarity and look for needle jump and return.  It is harder to to see this with a digital meter.  But, what you are doing is charging the plates of the condenser.  It takes current to do this until that condenser absorbs all it can.  That’s the meter jump.  Reversing polarity creates opposite charge on the plates = meter jump until current absorption stops.

While you are in there. Be sure the posts on the points don’t have bits that hit the main plate and short the points to the plate.  This bypasses the points and prevents the coil from charging up.  It is point opening  and the condenser function that creates the spark.

[TwoTired]

It might help to know that the coil output is the two ends of a single insulated wire wrapped around a metal core.  For spark to occur, the two ends have make an electrical connection.  That path is the ignition leads, cap resistors, spark plug and spark gap, and the head metal connecting the two spark plug bases.  Both plugs fire when the voltage is high enough to make a spark conductor channel in the electrode gap of both of the spark plugs in pairs.  The total gap in the path between the two coil outputs Cannot exceed what peak voltage the coil is capable of making.  The stock gaps are .025 in. at each plug.  More total gap than this makes the coil work harder (until they can’t).  When the resistors in the caps get loose, extra gaps can form, adding to the total gap in the circuit.    When the gaps are small, the coil overcomes the needed increase in voltage.  But, the resistors erode with time, the accumulated gaps can eventually get too large to fire reliably.

[TwoTired]

Each of the four carbs keeps a small reservoir of fuel in each carb in a float bowl.  The level in each is controlled by a float system.  When the level raises the float a connected valve moves to shut off fuel entering the reservoir. The reservoir has a stand pipe incorporated so if the fuel level gets too high, the excess fuel gets dumped out the overflow tubes connected to the internal stand pipes.  This is preferable to allowing the engine cylinders to fill with incompressible liquid and diluting the oil supply with gasoline.

Overflow occurs with improper float setting, float valve seal issues, or cracks in the stand pipe.  Sometimes the float can hit internal bits or bulging gaskets, preventing their free movement to properly close the valve.  Sometimes the float pivots can bind and prevent float valve seal.  Remove, inspect, correct .

[grcamna2]

Point contacts can get a film on the surface which insulates an electrical connection, even if new.  So, hit the contacts with contact cleaner or a point file ( not sandpaper) to insure they can function.  You can also test for function with a voltmeter.  With ignition on and points physically closed there should be no voltage across the contacts.  When open there should be.
 You can also do a rudimentary condenser check with an ohmmeter (key off) if it has a needle display. On lowest scale place probes on case and lead contact.  The needle should jump and then return to zero. Reverse probe polarity and look for needle jump and return.  It is harder to to see this with a digital meter.  But, what you are doing is charging the plates of the condenser.  It takes current to do this until that condenser absorbs all it can.  That’s the meter jump.  Reversing polarity creates opposite charge on the plates = meter jump until current absorption stops.

While you are in there. Be sure the posts on the points don’t have bits that hit the main plate and short the points to the plate.  This bypasses the points and prevents the coil from charging up.  It is point opening  and the condenser function that creates the spark.

Very good info 

[Mark K]

Main harness

Got it, thanks!

[Mark K]

Yup, im in UK and we call it a wiring loom, i think you call it a harness

Thank you!

  It's easy to ground the yellow or blue wire at the points by accident, check where they attach to the points.
  You may need to clean the float valves. I like to remove the bowls one at a time, pull that float and needle then turn on the petcock to flush the inlet. I catch the gas in a cut down oil bottle.  I've also seen floats hang up on the bowl gaskets at the sides. You may also hold the float manually and observe the fuel turn on and off while raising and lowering the float. Be sure to get lots of ventilation and catch the gas in a container.

I'll double check the yellow/blue wires attachment area at the points.  I had removed the carbs during teardown, completely disassembled and cleaned using a homemade ultrasonic cleaner w/CLR. I'll try your method and make sure I do it outside to avoid fume buildup.

What condensers are you running?

Not really sure, Ill attach a picture of the points/condensers.

Point contacts can get a film on the surface which insulates an electrical connection, even if new.  So, hit the contacts with contact cleaner or a point file ( not sandpaper) to insure they can function.  You can also test for function with a voltmeter.  With ignition on and points physically closed there should be no voltage across the contacts.  When open there should be.
 You can also do a rudimentary condenser check with an ohmmeter (key off) if it has a needle display. On lowest scale place probes on case and lead contact.  The needle should jump and then return to zero. Reverse probe polarity and look for needle jump and return.  It is harder to to see this with a digital meter.  But, what you are doing is charging the plates of the condenser.  It takes current to do this until that condenser absorbs all it can.  That’s the meter jump.  Reversing polarity creates opposite charge on the plates = meter jump until current absorption stops.

While you are in there. Be sure the posts on the points don’t have bits that hit the main plate and short the points to the plate.  This bypasses the points and prevents the coil from charging up.  It is point opening  and the condenser function that creates the spark.

I cleaned the points (they were not new - see the picture). I will attempt the checks you suggest, I have both types of multimeters.

It might help to know that the coil output is the two ends of a single insulated wire wrapped around a metal core.  For spark to occur, the two ends have make an electrical connection.  That path is the ignition leads, cap resistors, spark plug and spark gap, and the head metal connecting the two spark plug bases.  Both plugs fire when the voltage is high enough to make a spark conductor channel in the electrode gap of both of the spark plugs in pairs.  The total gap in the path between the two coil outputs Cannot exceed what peak voltage the coil is capable of making.  The stock gaps are .025 in. at each plug.  More total gap than this makes the coil work harder (until they can’t).  When the resistors in the caps get loose, extra gaps can form, adding to the total gap in the circuit.    When the gaps are small, the coil overcomes the needed increase in voltage.  But, the resistors erode with time, the accumulated gaps can eventually get too large to fire reliably.

That is very helpful information. I did double check the spark plug gap, as I had removed plugs to put a little oil in the cylinders before start attempt.

Each of the four carbs keeps a small reservoir of fuel in each carb in a float bowl.  The level in each is controlled by a float system.  When the level raises the float a connected valve moves to shut off fuel entering the reservoir. The reservoir has a stand pipe incorporated so if the fuel level gets too high, the excess fuel gets dumped out the overflow tubes connected to the internal stand pipes.  This is preferable to allowing the engine cylinders to fill with incompressible liquid and diluting the oil supply with gasoline.

Overflow occurs with improper float setting, float valve seal issues, or cracks in the stand pipe.  Sometimes the float can hit internal bits or bulging gaskets, preventing their free movement to properly close the valve.  Sometimes the float pivots can bind and prevent float valve seal.  Remove, inspect, correct .

Removing the carb bowls is on the list and will check the items you suggest.

Thanks to everyone for the advice, recommendations and suggestions. I probably will not be able to get back on the problem until this weekend.

One other question, could the fuel overflowing out the drain tubes be caused by lack of compression, the cylinders not 'pulling' the fuel forward? Someone suggested that could be the cause of no fuel smell on the plugs - low compression = not getting fuel into cylinder? Thought I'd ask the experts here.

[MauiK3]

The overflowing fuel is due to a float problem, when the bowl is full the float valve should shut the flow off, like a toilet bowl valve.
I like to verify my float level with a clear tube connected to the drain, it really tells the story.

[ekpent]

Make sure your float needles aren't in upside down or something weird like that.  When you have spark on all 4 again make sure you know how to use the choke lever and its a very primitive system. No fast idle and you have to feather it back and forth a little to keep it going well. They do not like having the choke left full on for long to run well at the start- up.

[HondaMan]

Your points plate is the best one we have today, made by TEC. It should be OK as far as having good condensors (which is a big problem right now with other brands of condensors). Like as mentioned above, their might be some cosmolene-like goo on those points to protect them from corroding/rusting in storage, so cleaning their contact faces is always a good step. DON'T hook up the Transistor Ignition until you have at least 50 miles on those points: they have not finished settling themselves yet. This is a new issue that showed up somewhere around 2008 or so: the contacts are now tungsten-plated copper instead of pure tungsten, which they originally all were in all points. The modern CFL and LED lightbulbs have killed the old tungsten market (filament-style lightbulbs have tungsten filaments inside) so it has become very expensive with most mines shut down these days. So, these points are now made from tungsten-plated copper pads instead. The idea here is that the 2 metals will arc-weld themselves together with use to become a normal tunsten-pad system, but this arc-welding requires that the points be run with their condensors as per normal for a time. Then the Transistor Ignition can be hooked up and all will be fine, and the usual wear will stop.

[Ellz10]

Your points plate is the best one we have today, made by TEC. It should be OK as far as having good condensors (which is a big problem right now with other brands of condensors). Like as mentioned above, their might be some cosmolene-like goo on those points to protect them from corroding/rusting in storage, so cleaning their contact faces is always a good step. DON'T hook up the Transistor Ignition until you have at least 50 miles on those points: they have not finished settling themselves yet. This is a new issue that showed up somewhere around 2008 or so: the contacts are now tungsten-plated copper instead of pure tungsten, which they originally all were in all points. The modern CFL and LED lightbulbs have killed the old tungsten market (filament-style lightbulbs have tungsten filaments inside) so it has become very expensive with most mines shut down these days. So, these points are now made from tungsten-plated copper pads instead. The idea here is that the 2 metals will arc-weld themselves together with use to become a normal tunsten-pad system, but this arc-welding requires that the points be run with their condensors as per normal for a time. Then the Transistor Ignition can be hooked up and all will be fine, and the usual wear will stop.

I'm glad i read this as I was shortly going to be running my ignition from you as well right off the batt.

[Mark K]

Point contacts can get a film on the surface which insulates an electrical connection, even if new.  So, hit the contacts with contact cleaner or a point file ( not sandpaper) to insure they can function.  You can also test for function with a voltmeter.  With ignition on and points physically closed there should be no voltage across the contacts.  When open there should be.
 You can also do a rudimentary condenser check with an ohmmeter (key off) if it has a needle display. On lowest scale place probes on case and lead contact.  The needle should jump and then return to zero. Reverse probe polarity and look for needle jump and return.  It is harder to to see this with a digital meter.  But, what you are doing is charging the plates of the condenser.  It takes current to do this until that condenser absorbs all it can.  That’s the meter jump.  Reversing polarity creates opposite charge on the plates = meter jump until current absorption stops.

While you are in there. Be sure the posts on the points don’t have bits that hit the main plate and short the points to the plate.  This bypasses the points and prevents the coil from charging up.  It is point opening  and the condenser function that creates the spark.

TwoTired, I checked for voltage across the points, open and closed. 1/4 points tested correctly, 2/3 points had voltage both open and close the first couple of times I checked them. I was rotating the engine w/ratchet and socket on the timing nut. After a few rotations, 2/3 tested correctly. I don't know what would cause points 2/3 to act that way, but I've ordered new points and condensers and should have in about a week. That is how 2/3 points 'acted' when I was setting them a month or so ago. I think 2/3 points are defective.

My multimeter (with the needle display) battery contacts were extremely corroded from me leaving the battery in meter for a really long time, broke the tiny wire, to small to solder for me, so I'll see about getting another one.

[Mark K]

New points / condensers received, installed yesterday, set to .014 static setting per the FSM. Checked for voltage across the points open and closed. 1/4 and 2/3 points tested correctly, voltage only when points open. I noted the voltage on multimeter while doing this. 1/4 points had 12.02v, while 2/3 points had 10.7v  I don't know if this makes a difference or not? I did switch the yellow and blue coil wires to see if the 10.7v followed the switch, it did not. 2/3 points read 10.7v when it was connected to either of the coils.

Moved on to check for spark at spark plugs. Pulled all plugs, rechecked gap - all still set to .025, re-installed.  Hooked up jumper cables to my truck battery, turned key to position 1.  Clutch in, press starter button, starter turns, get strong spark 1 & 4 spark plugs, NO spark at 2 & 3 spark plugs.  Switch the yellow and blue wires at the coils and try again. Now I have strong spark at 2 & 3 spark plugs, NO spark at 1 & 4 spark plugs. The coils, wires, caps and spark plugs are all brand new.  Some of you may remember the issue I had awhile back with the old coils that were on the bike (http://forums.sohc4.net/index.php/topic,190541.0.html) . I bench tested those coils, 2/3 coil was suspect. I remounted old coils on bike and tried them - no spark on 2/3 even after switching yellow and blue coil wires. At that point I ordered new coils. Received new coils, installed and had the same problem, NO spark on 2/3. So I figured it was the 2/3 points, ordered and installed new points. I'm back to where I started, with NO spark on 2/3.

Today I tested the new coils for resistance on the bike. I had not tested them when I received them as they were brand new. Unscrewed plug caps, measured resistance on each secondary coil with multimeter set to 20K (no auto ranging on my meter).

Resistance measurements between spark plug leads.
1 & 4 - 16.41 ohms
2 & 3 - 15.85 ohms

Measured the NGK plug caps.
1 - 5.24 ohms
2 - 4.83 ohms
3 - 5.21 ohms
4 - 5.46 ohms

Measured the black/yellow and black/blue, using 200, lowest resistance scale. Meter resistance was .5 ohms
Black / Yellow wires = 4.7 - .5 = 4.2 ohms
Black / Blue wires   = 4.7 - .5 = 4.2 ohms
(Old coils tested at 5.1 - .6 = 4 .5ohms)

Also checked for continuity and resistance on yellow / blue wires from points to first connection by rear brake light switch. Also checked the yellow / blue wires in from the rear brake light switch area to where the blue / yellow exits harness at the points.

I am at a total loss on how to correct the lack of spark on 2/3.  By switching the yellow & blue coil wires, the spark follows, which makes me think it's the points, especially since 2/3 is only getting 10.7v when closed. But the points are brand new. Is there something else that could be causing the issue?

What am I missing here? Any help is greatly appreciated.

[TwoTired]

Swap the condensers and see if the problem follows.  If you have old condensers try swapping that in.

A leaky condenser can become resistive and bleed off voltage as well as prevent spark at  the plugs.

[grcamna2]

Swap the condensers and see if the problem follows.  If you have old condensers try swapping that in.

A leaky condenser can become resistive and bleed off voltage as well as prevent spark at  the plugs.

Would new/'fresh' condensers still be available ?
Where can I buy fresh condensers with a manufacturers date stamp ?
I remember HondaMan/Mark describing that if an NOS condenser has been on the shelf longer than 5 yrs,it's already 'on it's way out'.

[Don R]

  My goodness you've done your due diligence, sorry we haven't helped yet.