Help with First Restart After Carb Rebuild

Nessism wrote:

Coil resistance spec is something like 2.2 ohms.

Let's reset here.  First start had the engine reving out to a high rpm, right?  That can't happen if the plugs are not firing.  Boots replaced, airbox installed, then problems start.  Sounds like something carb related, not spark.  

Do the choke flaps move smoothly with the lever?  They often bind up, and hang open, thus choke doesn't work, which causes hard starting.  Some starter fluid, carefully used, will test that possibility.

Get what you are saying and it seems logical, I only suggested a basic spark check given that #2 & #3 dropped which are on the same coil - however if the posted readings are correct this has thrown up a couple of issues, the coils should be between 2 & 3 ohms on the primary side but have measured as 5 ohms which will give a weak spark and also there appears to be a significant volt drop in the coil feed which will also weaken the spark further. This could be carb related but could also be the result of disturbing wiring when re-fitting the airbox ??

Wookie58 wrote:

Nessism wrote:

Coil resistance spec is something like 2.2 ohms.

Let's reset here.  First start had the engine reving out to a high rpm, right?  That can't happen if the plugs are not firing.  Boots replaced, airbox installed, then problems start.  Sounds like something carb related, not spark.  

Do the choke flaps move smoothly with the lever?  They often bind up, and hang open, thus choke doesn't work, which causes hard starting.  Some starter fluid, carefully used, will test that possibility.

Get what you are saying and it seems logical, I only suggested a basic spark check given that #2 & #3 dropped which are on the same coil - however if the posted readings are correct this has thrown up a couple of issues, the coils should be between 2 & 3 ohms on the primary side but have measured as 5 ohms which will give a weak spark and also there appears to be a significant volt drop in the coil feed which will also weaken the spark further. This could be carb related but could also be the result of disturbing wiring when re-fitting the airbox ??

I tried a different multimeter. When I used my second meter and took the resistance readings again on the primaries I got EXACTLY 2.4 ohms on each coil.

SnyperX wrote:

Wookie58 wrote:

Nessism wrote:

Coil resistance spec is something like 2.2 ohms.

Let's reset here.  First start had the engine reving out to a high rpm, right?  That can't happen if the plugs are not firing.  Boots replaced, airbox installed, then problems start.  Sounds like something carb related, not spark.  

Do the choke flaps move smoothly with the lever?  They often bind up, and hang open, thus choke doesn't work, which causes hard starting.  Some starter fluid, carefully used, will test that possibility.

Get what you are saying and it seems logical, I only suggested a basic spark check given that #2 & #3 dropped which are on the same coil - however if the posted readings are correct this has thrown up a couple of issues, the coils should be between 2 & 3 ohms on the primary side but have measured as 5 ohms which will give a weak spark and also there appears to be a significant volt drop in the coil feed which will also weaken the spark further. This could be carb related but could also be the result of disturbing wiring when re-fitting the airbox ??

I tried a different multimeter. When I sued my second meter and took the resistance readings again on the primaries I got EXACTLY 2.4 ohms on each coil.

Your coils are likely good.

I'm not the sharpest knife in the drawer, so I try not to over think a situation. Instead I revert to the basics and go over my work again. 

Nessism wrote:

SnyperX wrote:

Wookie58 wrote:

Nessism wrote:

Coil resistance spec is something like 2.2 ohms.

Let's reset here.  First start had the engine reving out to a high rpm, right?  That can't happen if the plugs are not firing.  Boots replaced, airbox installed, then problems start.  Sounds like something carb related, not spark.  

Do the choke flaps move smoothly with the lever?  They often bind up, and hang open, thus choke doesn't work, which causes hard starting.  Some starter fluid, carefully used, will test that possibility.

Get what you are saying and it seems logical, I only suggested a basic spark check given that #2 & #3 dropped which are on the same coil - however if the posted readings are correct this has thrown up a couple of issues, the coils should be between 2 & 3 ohms on the primary side but have measured as 5 ohms which will give a weak spark and also there appears to be a significant volt drop in the coil feed which will also weaken the spark further. This could be carb related but could also be the result of disturbing wiring when re-fitting the airbox ??

I tried a different multimeter. When I sued my second meter and took the resistance readings again on the primaries I got EXACTLY 2.4 ohms on each coil.

Your coils are likely good.

So I attempted to start it again yesterday afternoon. I did get it running and idling at around 1k rpm, but it seemed to bog down at times when giving it throttle. Most of the time however it revved strong up to like 4k rpm. Now, after it had been running and I killed the engine I tried to start it again. This second attempt it didn't want to start and when it did it was missing a couple cylinders again. I had a high power shop fan blowing on the engine to keep temps decent as well. So I am wondering if my coils might have an issue once they has heat soaked from the engine?

That is easy enough to check. Warm the engine up a gain, shut it off and immediately check the coil resistance. If you have a heat gun, you may be able to warm the coils up enough that way.

Made a video of how it will bog down after idling well for awhile. 

When checking your coil resistance also check between the primary circuit and the mounting lug incase the coil is going to ground when hot (insulation breaking down)

That could also be a clogged fuel tank vent. If the vent is clogged, a vacuum will form in the tank, preventing the flow of gasoline to the carbs.

To test this theory, run the engine with the fuel tank cap open and see if it bogs down. Please save your cigar for later to avoid a major redecoration job.

TexasKZ wrote:

That could also be a clogged fuel tank vent. If the vent is clogged, a vacuum will form in the tank, preventing the flow of gasoline to the carbs.

To test this theory, run the engine with the fuel tank cap open and see if it bogs down. Please save your cigar for later to avoid a major redecoration job.

So the petcock on my KZ750 has two connection. The fuel line and a vacuum line, does that make a difference for the test you mention?

SnyperX wrote:

TexasKZ wrote:

That could also be a clogged fuel tank vent. If the vent is clogged, a vacuum will form in the tank, preventing the flow of gasoline to the carbs.

To test this theory, run the engine with the fuel tank cap open and see if it bogs down. Please save your cigar for later to avoid a major redecoration job.

So the petcock on my KZ750 has two connection. The fuel line and a vacuum line, does that make a difference for the test you mention?

leave it connected, it is not affected by the test. Also, if it is disconnected, the bike will  be running on three cylinders until the fuel bowls run dry, then it  will die.

Wookie58 wrote:

When checking your coil resistance also check between the primary circuit and the mounting lug in case the coil is going to ground when hot (insulation breaking down)

PS: forgot to mention (if you didn't already know) when measuring resistance disconnect the wires from the component being measured (otherwise you will get a false reading through the circuit) and you need to test "hot" when the fault is present