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Hot starting issues

elteeron

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First question, can a bad solenoid still crank? If bad and still able to crank, will it reduce the battery to starter voltage?
Second question, drove today for about 2 hours, stopped, and it wouldn't crank until it sat for a while. The battery is a Gel type, not a year old, and was charged. The bike ran fine while riding.
All charging tests come back fine.
81 CB 750C Bought new in 81.
 
What exactly is fine? On that particular alternator the demands are much tighter than most, the alts will commonly pass testing to still be bad. I've been in your exact same issue before and it was alt, the rotor and what most of them do. The rotors can test well in the good range and still be bad.

The problem being the field is rotating on that one and the windings then break loose inside to short the field out in varying amounts that are often even speed related. Say 3500 rpm and charging fine, go over 4500 and it quits, or only half charging. Then you test rotor just sitting and it says good. Centrifugal force moves the windings around.

The rotors there get changed by the thousands and even the rebuilders have the same fits with theirs doing the same. 'New' ones too. Besides the early DOHC, the CBX and SOHC 650 use the same alt and the same issues on them too. Why you see so many rotor sellers.

Can be other things of course but 90% the rotors, however, driven long enough the missing charge then makes the regulator ramp up the field trying to get it back and then the reg fails too from overheating.
 
I understand what you are saying, but it seems like it is a hot issue, since it cranks very slowly after running for a while, and when cold, it is better, but still not like it being jumped or fresh charge.
 
Hot engines need more battery amp to start, all engines do that. As well, the starter itself gets hot from the cylinder airflow over it, then the amp requirement to turn it goes way up for that too.

I sold batteries for years in car parts, the conventional wisdom always says batteries go bad in the dead of winter, it's bullsh-t. I often changed far more in the dead of summer when the heat kills them by the thousands. BOTH extremes kill batteries.

The alt being just marginal and not failed 100% yet can easily make that show up. BTDT. The alt can fail depending on the short location and be at say 75%. It may do fine at 90% and not show issues for a couple months in that case. Depends on how much of the field coil gets cut out of the circuit by the short.

I've driven mine at 55 mph and no issue but go at 70 and then after an hour you got a starting issue. The faster speed then activates the short. Just the headlight on all the time can strand you too, why on mine I made up a switch to kill headlight in case the alt ever failed to get further down the road.
 
I suppose somebody could figure out a way to patch in an amp gauge there. 750s don't strain the starters though, it's the 1100 that does that, using same starter. Highly unlikely the starter is the issue unless it had a thousand starts on it, a 750 should whirl away all day long. You should be ohming out your starter leads first. High mileage solenoid will do it too when the contacts get pitted enough to not relay 100% start current.

Myself have never had the need, the issue commonly being the alt if it showed up. Rotor fixed it the 3 times it happened to me.

The service manual makes no mention of it other than if slow turning look at excessive resistance in the starting circuit.

I wouldn't be too proud of that AGM battery either, I've seen plenty of those fail and way ahead of time. I used to sell the 'best of the best' (snicker) Optima car line and those batteries failed left and right. Many times under 2 years, that kind of battery does not like long term sitting at ALL but no way do they tell you that when they tell you how wonderful they are. The ONLY thing a gel battery does better is to defy vibration yet the conventional wisdom thinks they can cure cancer. What a farce! Look at the warranties, they commonly are way less than many liquid acid batteries.
 
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Well, I agree it probably is the battery, since it sat for a few months, then started giving me trouble. Even after 3 days of a trickle charge, it only responded well one time. Then it started acting up again. I'll get another one.
 
Maybe this one needs resurrecting since I seem to be having a similar issue. Curious to know what the fix turned out to be. In my case the problem starting a hot CB750 has been going on since I bought the bike years ago, I just kick it over or try not to turn it off. means keeping it running while I fuel up sometimes but going out in a fireball has a certain romance.

Kidding aside (I don't want to burn), mine now has gotten a bit worse and I'm wondering what to try and in what order. BTW, I put a Dyna S on it a couple years ago. When it's hot the starter just really struggles (the headlight dims way down), and even kicking it over is sometimes impossible if I've been on a ride in the summer and it's really hot. That makes it seem like it's not a electrical thing to me, but I'm not great with electricity beyond using a multi-meter. I'm going to look in the forum for how to test things I know to test, like the solenoid and battery, but wondering what else or if folks here have suggestions.
 
Well, it sounds electrical to me if the headlight is dimming. Use your meter and read battery voltage directly off the battery while cranking. If it sags below ~9.5 volts it is suspect. If it stays up, go through connections from the battery out and clean the contact surfaces. Start with battery terminals, then both solenoid terminals. Then do the cranking while checking voltage on the starter connection of the solenoid. Include the ground connections in the cleaning. Use Scotchbrite, wire brushes, sandpaper, etc. to remove oxidation from connectors. The green on copper terminals is verdigris - not a good conductor and poisonous if ingested in high enough quantities. Clean it off.
Maybe this one needs resurrecting since I seem to be having a similar issue. Curious to know what the fix turned out to be. In my case the problem starting a hot CB750 has been going on since I bought the bike years ago, I just kick it over or try not to turn it off. means keeping it running while I fuel up sometimes but going out in a fireball has a certain romance.

Kidding aside (I don't want to burn), mine now has gotten a bit worse and I'm wondering what to try and in what order. BTW, I put a Dyna S on it a couple years ago. When it's hot the starter just really struggles (the headlight dims way down), and even kicking it over is sometimes impossible if I've been on a ride in the summer and it's really hot. That makes it seem like it's not a electrical thing to me, but I'm not great with electricity beyond using a multi-meter. I'm going to look in the forum for how to test things I know to test, like the solenoid and battery, but wondering what else or if folks here have suggestions.
 
Hot starting

Well, it sounds electrical to me if the headlight is dimming. Use your meter and read battery voltage directly off the battery while cranking. If it sags below ~9.5 volts it is suspect. If it stays up, go through connections from the battery out and clean the contact surfaces. Start with battery terminals, then both solenoid terminals. Then do the cranking while checking voltage on the starter connection of the solenoid. Include the ground connections in the cleaning. Use Scotchbrite, wire brushes, sandpaper, etc. to remove oxidation from connectors. The green on copper terminals is verdigris - not a good conductor and poisonous if ingested in high enough quantities. Clean it off.



Mine turned out to be a melted connector between the Stator and the voltage regulator/rectifier. Problem solved. The connector is under the seat.
 
Battery is toast now, that's for certain, so I guess that's the thing. But I still wonder because even when the battery was new the starter would struggle when hot. Something tells me there's more to it. Did I mention it's even hard to kick start it hot? Sometimes impossible until it's cooled down. How the mechanics of turning it over with the starter vs just kick starting works is a bit unclear to me. I guess I need to do some youtubing.
 
When you kick-start, you aren't dragging down battery power through the biggest load on the bike - that starter. Therefore, more power available to the coils and a hotter spark.

Starters are generally easy to clean up if you take your time and return them back the way they belong. Often packed with carbon dust, worn brushes, or corroded and arced commutators. I had to chuck my GL1000 starter armature in the lathe and clean up some bad arc pitting (do-able by hand, but spinning in the lathe with fine silicone carbide paper is easier if you have one). Also replacing grease that is long-past hardened up.

Starters don't spend a lot of time under power, but when they do run, they work hard. You really should check the voltage at the starter while cranking, too. The solenoid contacts get arc damage over time, eventually becoming intermitent or failing alltogether.
 
Battery is toast now, that's for certain, so I guess that's the thing. But I still wonder because even when the battery was new the starter would struggle when hot. Something tells me there's more to it. Did I mention it's even hard to kick start it hot? Sometimes impossible until it's cooled down. How the mechanics of turning it over with the starter vs just kick starting works is a bit unclear to me. I guess I need to do some youtubing.
 
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