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Discussion Starter · #1 ·
Sort of a followup up on my previous thread
Another Battery Question

The AGM I bought last spring seems to be doing pretty well, as does the new MOFSET. Voltage is stable and adequate, though oddly doesn't seem quite as robust as with my previous wet cell. Of course, there could be different factors at play too; things I've tweaked over the same time period.

I am also having trouble with hot starts. I'm aware this may have no bearing on the battery.

It never had this problem before though so I'm scratching my head as to why it's begun doing this. It happens about half of the time on a hot start (after the bike's at full temp and been ridden a while). The cranking speed is essentially the same (meaning adequate) but it won't fire. No throttle, no choke. If I just kept the button on, I have no idea how long it would crank away like that, but my intuition tells me to toggle it instead. It either fires right up when hot or will get into this non-starting funk.
Anyway, so I crank for a few seconds then pause and repeat. Usually on the 4th rep, it will backfire like a shotgun. After that, it usually starts within another press or two.
Any idea what's causing this?
 

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Sort of a followup up on my previous thread
Another Battery Question

The AGM I bought last spring seems to be doing pretty well, as does the new MOFSET. Voltage is stable and adequate, though oddly doesn't seem quite as robust as with my previous wet cell. Of course, there could be different factors at play too; things I've tweaked over the same time period.

I am also having trouble with hot starts. I'm aware this may have no bearing on the battery.

It never had this problem before though so I'm scratching my head as to why it's begun doing this. It happens about half of the time on a hot start (after the bike's at full temp and been ridden a while). The cranking speed is essentially the same (meaning adequate) but it won't fire. No throttle, no choke. If I just kept the button on, I have no idea how long it would crank away like that, but my intuition tells me to toggle it instead. It either fires right up when hot or will get into this non-starting funk.
Anyway, so I crank for a few seconds then pause and repeat. Usually on the 4th rep, it will backfire like a shotgun. After that, it usually starts within another press or two.
Any idea what's causing this?
Mine will do the same thing when I stop for gas. Using full choke makes it fire right up.

It's been so consistent on this, I just automatically choke it to avoid the backfire at the gas station.

I'm thinking the pickup coil mod might cure this.

On my race cars, hot starts were always a problem. I found that pumping the gas pedal about 5-6 times and holding it to the floor would make them fire right up. Always ran a lot of ignition timing, with the mechanical advance locked out, and that makes hot starts a problem.
 

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Sort of a followup up on my previous thread
Another Battery Question

The AGM I bought last spring seems to be doing pretty well, as does the new MOFSET. Voltage is stable and adequate, though oddly doesn't seem quite as robust as with my previous wet cell. Of course, there could be different factors at play too; things I've tweaked over the same time period.

I am also having trouble with hot starts. I'm aware this may have no bearing on the battery.

It never had this problem before though so I'm scratching my head as to why it's begun doing this. It happens about half of the time on a hot start (after the bike's at full temp and been ridden a while). The cranking speed is essentially the same (meaning adequate) but it won't fire. No throttle, no choke. If I just kept the button on, I have no idea how long it would crank away like that, but my intuition tells me to toggle it instead. It either fires right up when hot or will get into this non-starting funk.
Anyway, so I crank for a few seconds then pause and repeat. Usually on the 4th rep, it will backfire like a shotgun. After that, it usually starts within another press or two.
Any idea what's causing this?
When that four post battery first came out you could buy one line for $65 shipped I bought two of them one lasted about four years one died after a year and a half they replaced it there was no prorating on the replacement he just paid for shipping I liked it because I have so many accessories on my bike I like the idea of the four posts I’ve since then headwhen that Ford post battery first came out you could buy one line for $65 shipped I bought two of them one lasted about four years one died after a year and a half they replaced it there was no prorating on the replacement we just paid for shipping I liked it because I have so many accessories on my bike I like the idea of the four posts I have since then tried lithuim iron batt by Shoria and they upgraded me to the 18 amp size cause the 14 amp size could not get the job done . I installed it sideways and it’s in service 10 years going on 11 . In 2017 I won a contest in lake George got a free Usasa battery AGM . That went in the blue bike that last for 4 years . I am now 77 years young still ride but not as far or as long but I do ride.
 
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I had luck with using the choke when hot but there’d still be times when I made a gas station full of people duck. I’ve said it before in other posts that the pick up coil mod was the single biggest improvement I made to this bike.
 

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My technique for hot starts was to slightly crack open the throttle AFTER I hit the starter button. Like a 1/4 or less turn. Caught and started 99%of the time.
I have seen AGM batteries go bad, so you might also want to have yours checked.

Buddy….what you said bares repeating…😂
 

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Discussion Starter · #7 ·
No I haven't done the pickup coil mod. Just spent the last hour looking over the procedure. Seems simple enough and worth a shot. I should be able to tackle that this week or next at the latest. Does it matter that my bike starts perfectly cold - like I don't think it even turns over twice and BOOM, it's running (with choke of course).

Meanwhile, I will also try the various throttle/choke methods you mentioned. I think I may have tried giving it some choke once under those circumstance and it didn't work, but chances are, I applied the choke AFTER it failed to start, not proactively.

I don't even want to think about the possibility of getting a bum battery, but I will in light of what you added Buddy.

The only other things I've tweaked or changed since getting that new battery is replacing the RR with MOFSET, tightening the MCCTs a tad, Two wire and Blue Wire mods, and adjusting the idle ("air") screws to factory spec (leaner). That latter tweak incidentally (somehow) seems to have fixed another problem I'd noticed sometimes of a stumble under load around 4200 RPM.
 

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No I haven't done the pickup coil mod. Just spent the last hour looking over the procedure. Seems simple enough and worth a shot. I should be able to tackle that this week or next at the latest. Does it matter that my bike starts perfectly cold - like I don't think it even turns over twice and BOOM, it's running (with choke of course).

Meanwhile, I will also try the various throttle/choke methods you mentioned. I think I may have tried giving it some choke once under those circumstance and it didn't work, but chances are, I applied the choke AFTER it failed to start, not proactively.

I don't even want to think about the possibility of getting a bum battery, but I will in light of what you added Buddy.

The only other things I've tweaked or changed since getting that new battery is replacing the RR with MOFSET, tightening the MCCTs a tad, Two wire and Blue Wire mods, and adjusting the idle ("air") screws to factory spec (leaner). That latter tweak incidentally (somehow) seems to have fixed another problem I'd noticed sometimes of a stumble under load around 4200 RPM.
The choke may not work for you then. Sometimes I would forget, get the backfire and no-start, then use the choke and it would fire right up.

I've tried part throttle, full throttle, etc, but it always makes it worse. I've many bikes that wanted some throttle for hot starts.
 

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My bike always started fine when completely cold after I went with the AGM battery, but that did not help the hot start problem. Here's a little clip of the fun I used to have. This clip was taken after riding a little over a mile from home.

 

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It's funny, sometimes I can do it with no choke and blipping the throttle (we're talking gas station scenario, fully warmed stopped for ~5 minutes) and it starts right up. Other times, seemingly same situation: nothing 3 times, little choke, backfire, nothing, nothing, finally starts with the choke in some voodoo position. I don't know, it usually starts. Once I cranked it enough without luck to drain the battery but was at home, fortunately.
 

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Discussion Starter · #11 ·
It's funny, sometimes I can do it with no choke and blipping the throttle (we're talking gas station scenario, fully warmed stopped for ~5 minutes) and it starts right up. Other times, seemingly same situation: nothing 3 times, little choke, backfire, nothing, nothing, finally starts with the choke in some voodoo position. I don't know, it usually starts. Once I cranked it enough without luck to drain the battery but was at home, fortunately.
Yep, that's the same deal with mine; sometimes it works, sometimes it doesn't. The good news is that eventually (usually after the backfire) it always does start. It's never left me stranded or even afraid of being stranded.
 

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Discussion Starter · #12 ·
My bike always started fine when completely cold after I went with the AGM battery, but that did not help the hot start problem. Here's a little clip of the fun I used to have. This clip was taken after riding a little over a mile from home.
Thanks for the video mmart. It makes me realize that I am certainly not alone in having this problem and indeed, that others such as yourself have it even worse. I think if my bike ever took that long to start, I probably would start to get a bit worried!
 
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Thanks for the video mmart. It makes me realize that I am certainly not alone in having this problem and indeed, that others such as yourself have it even worse. I think if my bike ever took that long to start, I probably would start to get a bit worried!
That was one of the “easier” starts, the only reason I have it on video is because I wanted to try and mess with my GoPro that day. It got frustrating, so as soon as the weather cooperated I did the mod. Haven’t had a hard start since.
 

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I put a different ignition system on mine and it fixed the problem. I know that's not a solution for everyone, but I think I learned the cause of the problem in the process. Sorry, this will get a bit technical:

The stock ignition coil primaries are rate 1.8-2.2 ohms. That means they will "charge" up to 5.7-7 amps at a typical idle voltage of 12.5V. My own measurements showed about 7 amps at idle.
In my measurements I found that the factory system charges the coils for 14-15mS before they fire.
They really only need about 8mS, as the current doesn't increase much after that, at least at idle speeds.

Hot starts have two compounding issues.
First, when the coils are hot, their resistance rises. This results in lower current to the coils as it both takes larger to charge and the final charge current is reduced.
Second, when starting the system voltage is lowered. This too results in a slower charge and lower total current to the coils.
The end result is insufficient current to generate a strong spark.

There was some debate on if the issue was related to spark or fuel.
I did some temperature measurements using an IR camera and found nothing to suggest vapor lock.
Nevertheless, I put as much insulation and reflective tape between the engine and the carb and fuel lines as I could manage and there was no affect.
The backfire also implies raw fuel is getting into the exhaust and finally burning off.
This suggests no issues with fuel flow.

The last piece of the puzzle from my own experience was when I had a corroded stator connector. The result was low system voltage.
The symptoms were whenever I would accelerate hard from idle, it would misfire tremendously, but mild acceleration was fine.
From 3k-6k it ran perfectly.
Above 7k it would misfire again, getting worse with more throttle and more RPM.
According to the third graph on this page, it takes more power to spark with more load.
At idle, the voltage was so low that heavy acceleration resulted in insufficient spark, but it was enough to spark at mild acceleration.
At 3k-6k, the voltage was high enough to spark at all throttle positions.
At high RPM, the voltage came down again because the coils were drawing more power and the symptoms would return.
Changing out the stator connector fixed all problems.
Thus, I experienced the connection between system voltage and misfires.
The stock ignition system is barely adequate, so it doesn't take much to upset it.

The proposed fixes are:
1. AGM battery. This seems to help because the voltage doesn't drop as far during cranking, giving enough current to generate a strong spark.
2. Pick-up coil mod (moving the coils to 0.020" gap). This seems to help because moving the pick-up coil closer causes the coil charging to start sooner, giving the coil more time to charge up.
3. Direct coil wiring (using thick gauge wire through a relay to power the coils). This reduces the resistance between the battery and the coil, countering the higher resistance in the coils when hot.
4. Using choke. All else being equal, a rich mixture is easier to ignite. (See second to last "graph" on this page).
5. Iridium plugs (or new plugs). A sharper point on a spark plug requires less power to spark. Conversely, a warn plug requires more power.
6. Part/full throttle when starting. This probably won't help as this increases the load on the engine which is both harder to ignite, and it robs even more of the system voltage.

I tried all the above. While I never had it as bad as @mmart, there were a few times I started to get worried.
With my programmable ignition, I increased my coil charge time out to 20mS.
This had more benefit than all 5 listed above. In fact, I widened my plug gaps beyond stock and it still fires right up, hot or cold.
In my mind, this conclusively proved the cause of the issue.

But again, this isn't a solution for everyone. I write this to share what I've learned and hopefully the list of 5 above will get you reliably on the road.

I briefly considered adding a large super capacitor through a diode that would power the ignition coils during startup.
I never pursued this as the controller fixed the issue.
This should in theory work, and I'd be interested in hearing the results!

My documentation and measurements of the new ignition system can be found here.
 

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My technique for hot starts was to slightly crack open the throttle AFTER I hit the starter button. Like a 1/4 or less turn. Caught and started 99%of the time.
I have seen AGM batteries go bad, so you might also want to have yours checked.

Buddy….what you said bares repeating…😂
Yeah, I don’t know how that happened. I guess I cut and paste it without knowing it bears repeating.
 

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I put a different ignition system on mine and it fixed the problem. I know that's not a solution for everyone, but I think I learned the cause of the problem in the process. Sorry, this will get a bit technical:

The stock ignition coil primaries are rate 1.8-2.2 ohms. That means they will "charge" up to 5.7-7 amps at a typical idle voltage of 12.5V. My own measurements showed about 7 amps at idle.
In my measurements I found that the factory system charges the coils for 14-15mS before they fire.
They really only need about 8mS, as the current doesn't increase much after that, at least at idle speeds.

Hot starts have two compounding issues.
First, when the coils are hot, their resistance rises. This results in lower current to the coils as it both takes larger to charge and the final charge current is reduced.
Second, when starting the system voltage is lowered. This too results in a slower charge and lower total current to the coils.
The end result is insufficient current to generate a strong spark.

There was some debate on if the issue was related to spark or fuel.
I did some temperature measurements using an IR camera and found nothing to suggest vapor lock.
Nevertheless, I put as much insulation and reflective tape between the engine and the carb and fuel lines as I could manage and there was no affect.
The backfire also implies raw fuel is getting into the exhaust and finally burning off.
This suggests no issues with fuel flow.

The last piece of the puzzle from my own experience was when I had a corroded stator connector. The result was low system voltage.
The symptoms were whenever I would accelerate hard from idle, it would misfire tremendously, but mild acceleration was fine.
From 3k-6k it ran perfectly.
Above 7k it would misfire again, getting worse with more throttle and more RPM.
According to the third graph on this page, it takes more power to spark with more load.
At idle, the voltage was so low that heavy acceleration resulted in insufficient spark, but it was enough to spark at mild acceleration.
At 3k-6k, the voltage was high enough to spark at all throttle positions.
At high RPM, the voltage came down again because the coils were drawing more power and the symptoms would return.
Changing out the stator connector fixed all problems.
Thus, I experienced the connection between system voltage and misfires.
The stock ignition system is barely adequate, so it doesn't take much to upset it.

The proposed fixes are:
1. AGM battery. This seems to help because the voltage doesn't drop as far during cranking, giving enough current to generate a strong spark.
2. Pick-up coil mod (moving the coils to 0.020" gap). This seems to help because moving the pick-up coil closer causes the coil charging to start sooner, giving the coil more time to charge up.
3. Direct coil wiring (using thick gauge wire through a relay to power the coils). This reduces the resistance between the battery and the coil, countering the higher resistance in the coils when hot.
4. Using choke. All else being equal, a rich mixture is easier to ignite. (See second to last "graph" on this page).
5. Iridium plugs (or new plugs). A sharper point on a spark plug requires less power to spark. Conversely, a warn plug requires more power.
6. Part/full throttle when starting. This probably won't help as this increases the load on the engine which is both harder to ignite, and it robs even more of the system voltage.

I tried all the above. While I never had it as bad as @mmart, there were a few times I started to get worried.
With my programmable ignition, I increased my coil charge time out to 20mS.
This had more benefit than all 5 listed above. In fact, I widened my plug gaps beyond stock and it still fires right up, hot or cold.
In my mind, this conclusively proved the cause of the issue.

But again, this isn't a solution for everyone. I write this to share what I've learned and hopefully the list of 5 above will get you reliably on the road.

I briefly considered adding a large super capacitor through a diode that would power the ignition coils during startup.
I never pursued this as the controller fixed the issue.
This should in theory work, and I'd be interested in hearing the results!

My documentation and measurements of the new ignition system can be found here.
Ah it’s always a treat when you do a knowledge dump. (y)
So my personal experience with some of the 5 options:
The AGM did not improve the hot starts, it DID improve cold starts. This offered improvement but the much better AGM also masked my slowly failing stator at the time. In fact, when my stator did eventually blow, I was able to ride home (about 18 miles) on battery alone, as long as I kept the RPMs up around 1.5 -2K the bike stayed alive. Once I replaced the stator I also put in a new battery because I basically fried it. So from an observational perspective, I don’t think I can honestly say the battery did or did not help because having another failed electrical component taints the “control” scenario of having a fully functional electrical system.
I dealt with the issue for a while after that because after that debacle, I had no desire to spend any more time and money. Ultimately the frustration continued, so I decided to take the shotgun approach and I did the pick-up mod and put in the Iridium plugs at the same time.
From what little electrical theory I retained from my component level schooling many moons ago, it just made sense that the shorter distance in the coil gap in combination with a hotter burning spark plug would do the trick. And I’m happy to say it did. I’ll admit I did not put in the level of engineering rigor as Mr Pittenger, but I had a hunch that the electrical vs fuel debate would at some point in the future yield a compilation of detailed findings as displayed in this thread ;)
 

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I've always felt the location of the coils is a poor choice due to the amount of heat they absorb from the exhaust. I might relocate this winter and upgrade to higher output coils. I've got a 1985 I'll be playing with.
 

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Discussion Starter · #18 ·
Looks like I won't get to do the pickup coil mod this week after all - or this season. The prediction for snow here today prompted me to put the bike into hibernation yesterday. I did however have the chance to replace my fork oil and check my steering bearings (in reference to another thread). Nice to get that done.

Fascinating write-up Jason!
 
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