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Discussion Starter · #1 ·
Hey guys, in need of some suggestions on what might be causing my bike to not run properly.
I have a 1971 CB450 with 14,000 miles. Rebuilt except the motor.
Pamco ignition
New single unit reg/rect
Rebuilt and ultrasonically cleaned carbs with factory jetting
Rebuilt the air cleaner with form and oiled
Baffled aftermarket exhaust
Adjusted valves
Coated gas tank with new petcock and lines
New battery last year
Idles when hot at about 1600RPM

This bike has been in and out of the shop for various things and I had it running well for about 3 weeks but noticed it was blowing a lot of smoke and my plugs were getting pretty sooty. Also when cold starting the bike it would take about 5 cranks on the button to get it running. It will idle fine but when I kick it into gear and ride it it's definitely only running on 1 cylinder, but when I rev the motor up high and struggle around the block a few times the other cylinder frees up and it runs good.
I'll get it to the pub go have a beer, come back out and it'll fire back up, but then embarrassingly as i ride away its again running on only 1 cylinder. It takes me revving the crap out of it and ridding it for a couple minutes to get both cylinder going.

After this I determined it was running too rich so i turned in both mixture screws 1/8 turn and changed the plugs, now its not burning so much out the pipes but the other issues still persist, and the other night it was stalling at red lights.

Any help appreciated.
-Mike
 

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1-weak battery 2-check float levels/make sure your turning petcock off.3-check timing with a strobe.4-balance and sync carbs:)
 

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And if you haven't yet, check the compression - since you mention that the engine has not been rebuilt, you might have a weak cylinder
 

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Don't take this the wrong way, but it sounds like you're long on enthusiasm, maybe a little short on tuning experience. No biggie, but you'll need to do some trouble shooting and tuning to get it running right. It probably just needs a little tweaking, but most tuners start with the basics and move forward.

Compression test, to make sure both cylinders are about equal, not grossly worn out.
Re-check ignition setting (point gap if you got 'em) then timing.
Condition of plug wire to boot connection
Start it up, figure out which cylinder is the 'dead one' by either pulling the shark plug lead, or touching the head pipe (or using an infrared temp gun). Cold one is the dead one. You can also feel the exhaust gasses coming out the pipes.
Sync the carbs, follow a manual. Read and re-read how to do that. Get an exploded view of your carbs and study it, know the difference between the idle speed screw, and idle mixture screw, idle and main jet. First sync for idle mixture and speed, then, sync for part open throttle. (I've never seen a youtube vid on synchronizing Honda twin carbs that was worth a darn. If you find one, let me know).
1600rpm idle, or stalling you say? sounds to me like it's just running on one cylinder at idle. Work on the dead cylinder's idle circuit. If it's been sitting since the carbs were rebuilt, remove the idle jet and blow out with compressed air. Modern gas goes bad in a few months in small quantities, like in an old motorcycle's float bowl. The idle jet openings on our bikes are almost microscopic!
Check for vacuum leaks using spray carb cleaner, brake kleen, wd40. Barely push the button, aim the straw near the intake manifold joints. If the idle jumps up a few hundred rpm, you've got an air leak that needs addressing before you can sync the carbs.

Stick with it, you'll get it. It's just a machine!
 

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Discussion Starter · #6 ·
Thanks for all the great tips.
Starting from the first few suggestions;
-I tested my battery and its fully charged.
-My float levels are good.
-I religiously shut on my petcocks after every ride.
-I have a pretty ancient compression tester thats showing 125 on the right and 115 on the left. From reading on these forums I'd want to see it at 150. For the month that it was running well this summer it pulled hard on the highway and never stalled at lights, is it plausible that in that short amount of time its worn the rings and cylinder walls down enough to drop the compression to the point where its running like crap?
-Brand new plug boots, tested them and they are good.
-When i rebuilt the carbs I went through them pretty thoroughly and even had them ultrasonically cleaned.
-Felt the exhaust tips at idle and they both feel equally strong. If running on 1 cylinder should't the dead side be significantly weaker?
-Don't have any vacuum ports to vacuum synch the carbs but I followed this video
-The bike sat in a garage for 25 years before i got to it, all of the upgrades and carb work has been in the last year, riding it, tweeking it and riding it so more, hasn't had a chance to sit for long periods of time since I've worked on it
-I will confirm tomorrow if there are any vacuum leaks and double check which is the dead cylinder, and maybe buy a new compression tester

Thanks again, hoping to stop lining the pockets of my local shop.
 

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Discussion Starter · #7 ·
Update-
Fired it up this morning to check which cylinder is the dead one. Let it idle for about 5mins, unplugged the left plug lead and immediately stalled, did the same to the right and it also immediately stalled.
So that tells me its not a dead cylinder issue.
I put it in gear and rode it around my parkade and it sputters almost like it begging for fuel and little to no power. From my experience running too lean it will pop and backfire which it is not doing. When I back out my idle mixture screw 1/8 it doesn't correct the problem, although it probably shouldn't because correct me if I'm wrong but the idle mixture screw is simply for the idle circuit, it doesn't effect the fuel delivery at speed. Is this correct?
I'm guessing my next step is to pull off the carbs and go through them again.
 

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but the idle mixture screw is simply for the idle circuit, it doesn't effect the fuel delivery at speed. Is this correct?
Yes... and bravo on you no longer lining the pockets of the local shop. Have you re-checked the other aspects of the overall tune-up? Valves, cam chain and Pamco timing? Retarded timing can cause flat feeling performance at low speeds as well
 

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Discussion Starter · #9 ·
Checked valves, timing all good.
Did notice today that the Nuetral light is actually flashing and mimicking the way the engine is sputtering and staggerying when I rev up the rpm and hold it above 2500. So I'm thinking there's a bad ground or something shorting on that neutral light circuit. It does go to my kill switch. Could that be my issue, the kill switch?
 

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Discussion Starter · #10 ·
So it turns out that the issues were being caused by electrical faults.
Fixed some bad grounds that were messing with my ignition, I also bypassed the kill switch and it's running like a top.
Going to order a new kill switch assembly from the web and replace that soon.
?
 
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