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Discussion Starter · #1 ·
Happy riding season everyone. I just pulled my 350 out of storage and had a great ride back to house. I fixed my top speed issue (wasn't going above 65mph) and my new exhaust sounds great. But as usual there is a new problem to deal with. Once at running temp, the engine stumbles below 2k rpm and cannot idle. It runs perfectly when I've just started it up. Always runs great above 3k rpm no matter the temp.

I'll try to give a picture of the state of the bike. The engine is pretty solid and was rebuilt 600 miles ago. Valves set, head bolts retorqued this winter, compression 180/180. I can't imagine running temperature is affecting the carbs significantly. Which leaves the electrical. I put a pamco on this winter, which I know is a major achilles heel, but I want to rule out everything else before I put points on again. My right plug is brown and left plug is a little black but nothing serious. I had to rejet to 110/70 for my slightly more open than stock exhaust.

What could cause an idling issue only at running temperature? Thanks in advance.
 

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My bike had bad rubber carb mounts. Did not leak cold, leaked hot. Vacuum leak caused high idle and stumbling. Got bad enough that it would not run at all after 20 minutes.

Sent from my SM-T830 using Tapatalk
 

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Discussion Starter · #3 ·
Thanks, I'll look at my mounts. They're new though and I dont have a high idle issue... it just wont idle and I have to keep it revved.
 

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Discussion Starter · #4 ·
The problem seems to be electrical. When i hooked a timing light up to my right cylinder, the light does not flash at the same time there is a stumble in the idle. The left cylinder is fine. Then when I took the bike for a test ride and it died at idle as it is now doing regularly, it would not start back up. Its almost as though the battery was straining to trip the solenoid--- it wasn't even turning over. All this reminds me of what happens simply when your battery isn't charged. But when I plugged my battery into a tender the tender seemed to believe that the battery was at greater than 80% charge. I'm starting to suspect the battery is bad and I just have weak spark at idle, even though it's a 1.5 year old AGM that hasnt given me any grief before. However, it would explain why I don't have issues above ~2500 rpm--- above that the charging system would pick up the slack of the battery.

I'm not sure why I would be having this issue only at running temp and not when cold. Is it easier for a weak battery to pass a spark across the plug gap when the engine is cold?
 

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Classic symptom of a bad coil which would once warmed up start to produce inconsistent sparks. Often times it will correct itself once it cools down.
 

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Also test your battery. Anything less than 12.5v at rest means it's on its way out.
 

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Discussion Starter · #7 ·
Thanks 76twin. I tested my battery and with the key off its 12.9v. Key on and it drops to 2.3v. Thats 2.3, not 12.3.

What on earth could be causing that big a power drain? It wont crank, none of my LED gauge lights come on. I think you might be onto something with the coil... when i was setting up my pamco my coils tested at 5.5 ohms. Im going to take my tank off and test them again.
 

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From your Voltage Tests you have a bad battery.

No Battery that is good and fully charged or even 1/2 Charged will drop from 12.9 to 2.3 volts by just powering the coils.

What you are seeing is it cannot handle a LOAD.

Take the battery out and to a Auto Shop they can do an "OFFICAL" Load Test on it to determine it's health.
 

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Discussion Starter · #9 ·
Got it, thx. I will look into load testing. Both my coils are also testing 3 ohms cold, which is below spec for the pamco. I dont know why its 2.5 ohms lower than when i tested them in the winter. Ill address that after the battery.

The bike wont even run when kickstarted... a few revs and it dies.

So i can avoid it in the future, what would cause a new-ish battery to fail like this?
 

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Discussion Starter · #10 ·
Yeah, im pretty sure you are right. Even with the coils off it cant even make the solenoid click.
 

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Discussion Starter · #11 ·
Figured it out. For one, the battery was bad and I think it may have been ruining various electronics around the bike. My charger I've had wired up for over a year went up in smoke a few days ago and the coils also turned out to be bad. I had a set of blue stock ones laying around and with them installed the difference is like night and day. I have all this low end power closer to idle that I'd never had before, which leads me to believe the coils were always bad. It makes sense though--- the kill switch was bad until I replaced it this winter and the PO had wired the coils to always be powered. That may have done them in.

It runs great now but there is a sound the clutch makes when it is engaged (plates engaged, clutch control released). It's not quite a whirring, and not quite a grinding. Sounds harmless but is new... since sitting over the winter the clutch has gotten stuck a few times, so maybe that has something to do with it.
 
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