CB450 with lazy left cylinder. Need help!

[motopros473]

Got a 71 cb450 that I've been building for a few years. Been trying to get the motor running but my left side doesnt want to run. Here's a list of things already done:
New piston, rings, 125lbs compression on left, 135lbs on right...
Valve clearance at .012
Carbs are super clean, slides move like a champ, and they seemed to be set evenly
160 mains, stock leak jet, pilot jet drilled to 40 from 38
Using K&N Pods on the stock carbs
Points set at .014, and I've used a timing light to adjust and check the ignition timing.
Dyna 5OHM coils with new plugs, wires, and caps, I even swapped coils to see if there was a change and still nothing.
The bike starts first kick and runs and idles but you can pull the left plug cap right off and theres no change. But, while idling, if you spray a bit of carb cleaner in the intake it will run for about 30 seconds. I've ridden it up the street to see if it gets better and it feels like once your on the gas a bit it will run for a second, then just goes out. Plug comes out a bit wet but not burned at all...seems wierd, as the right side looks about normal, rich but you can see it is burning.
Any ideas would be greatly appreciated, expecting my first kid in the next few weeks so my garage time is about to be minimal i fear.

[Guest]

Hmm, this is a tricky one I've ran across the same thing before myself...

There's a couple of suspects that can cause this issue... but when you say it gets better and runs when spraying into the throat. Makes me think is a fuel/fueling issue, now for the sticky part... this could be from the carb or the timing.

If you swap the coil leads, and the problem changes sides... then timing or ignition system is faulting somewhere.

If the problem doesn't change sides then it's a carb issue... fuel delivery/vacuum/float level/shitty gas.

Problem is this is where a cross over occurs... it ceases to be a carb problem when it's in the head to explode the gas, then it crosses over to an ignition problem in the chain of events.

So I'm going to let that sit with you for a minute so you can determine which of the two it is coming from. After that determination... I'll be happy to help take it up from there; I'm going to be in and out a bit because I'm working on a build today myself but I'll try to get back to reply as soon as I can, but other members may decide to help in the mean time.

[rottenrod]

I would check your compression numbers again if those are correct that could be a problem as these bikes do not like to run with less than 150psi or there about. Next check your charging. Voltage. Your will not get ignition on both cylinders with less than about 12.5v

[motopros473]

Jetblack, Thanks a lot man, Yea I've swapped leads for coils and the left side still won't work. I'm going to go through the carb again today hopefully but thats where fingers seem to point...I've basically been chasing stuff around the carbs because, I rebuilt them and obviously theres NO WAY I could make a mistake....hahaha.

Rottenrod, thanks for the info, I've heard that 115psi is fine for these things. As for charging, the system seems to be charging great and I'm getting good voltage to the coils and plugs.

[Guest]

Have you pulled the plug on that side; held it against the head and fired it over? I'm curious if spark is present and the color and strength if present before you tear back into the carbs.

If it is present but weak and not a bright white; might want to check your condenser.

If it is bright then I'm still thinking the carb on that side... either it's pilot circuit is clogged or it needs a sync or the diaphragm if applicable is torn perforated or crimped causing an internal vacuum issue. If it is just starving a bit, perhaps T-ing the petcock feed to the same lengths in the middle of the carbs will balance the fuel between them? If that's the issue.

[CoyoteUSP]

Make sure the plug cap is firmly connected to the plug wire. Had a similar problem on a CL350.

[thermo1976]

I have a 74 cb450 and from my past research fresh compression #s can be as high as 180 psi. 160-170 are usual. Check hondatwins.net.

[MixtureMotorCo]

Have run into this and found that it was a carb issue. check air fuel screws and make sure they are not bent or incorrectly sealed. I know itd be a pain with the cable and the choke but id swap card sides and test to see if this is the issue. hope you get it worked out.

[motopros473]

Sweet thanks ya'll, been dealin with the doctor, dentist, and dmv so hopfully give you an update in a couple days!

[Guest]

The CM I picked up not long ago; just started doing this shit on my left cylinder today... guess it was meant to be to help with more solutions? Murphy is a bastard... Haha well anyway it's issue? It was either a bad plug or boot; I didn't take time to figure out which. But the spark was sometimes firing sometimes not, sometimes new plugs are bad right out of the box... so you may have won the new bad plug lottery?

I put new plugs and ngk boots on it trimming back a tiny bit of the plug wire.. before twisting the new boots on, and it now fires like it should on both. Might wanna try untwisting the wire from the boot some people pull on the wire, not the boot which can separate contact... or they shove them on in a wiggle instead of twist them on... I'd do that before dropping cash on more parts; take a look at the end of the plug wire if you don't see wire in the end you've found the gremlin nest. Take note of how much wire you have to reach the plug if you have enough to spare trim about a 1/4 inch off then screw the boot on clockwise don't push it will screw itself in you just twist. Then see what's up with it...

[thebiker45]

I had a problem like this on a kawi 750 twin I was workin on. Was lookin all over and couldn't figure out why 1 cylinder wouldn't run. Turned out that one of the screws for the drain on the carrb bowl was to long and it was plugging the jet that was behind it. Don't know if the carbs are similar, but this one had me baffled for a while. Usually ends up bein something simple that gets over looked

[motopros473]

So switched carbs and the problem switched sides so it was obviously the carb. Took it apart and when i pulled out the imulsion tube a bit of crap came out, i'm think some junk came loose that i didn't quite get when I went through them. Anyway fires right up and runs pretty good, thinking i need to play with jetting. Now it seems like at a cruising speed or wide open it does some sputtering but I'm not sure if its starving for fuel or just mis firing. Running 160 mains but it does have a big bore...

Thanks everyone for all the help!

[motopros473]

The CM I picked up not long ago; just started doing this shit on my left cylinder today... guess it was meant to be to help with more solutions? Murphy is a bastard... Haha well anyway it's issue? It was either a bad plug or boot; I didn't take time to figure out which. But the spark was sometimes firing sometimes not, sometimes new plugs are bad right out of the box... so you may have won the new bad plug lottery?

I put new plugs and ngk boots on it trimming back a tiny bit of the plug wire.. before twisting the new boots on, and it now fires like it should on both. Might wanna try untwisting the wire from the boot some people pull on the wire, not the boot which can separate contact... or they shove them on in a wiggle instead of twist them on... I'd do that before dropping cash on more parts; take a look at the end of the plug wire if you don't see wire in the end you've found the gremlin nest. Take note of how much wire you have to reach the plug if you have enough to spare trim about a 1/4 inch off then screw the boot on clockwise don't push it will screw itself in you just twist. Then see what's up with it...

Yea I put new NGK boots, wires, and DYNA coils on it so I was pretty sure I was good there, now that the carbs good this thing fires up so easy! Thanks for the advice!!!