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Discussion Starter #1
Still struggling with not able to start hot engine. I need some help!

Initial tread is here: Engine not starting when hot till cooled down

Things done/checked:
  • Replaced coils, wires, spark plugs
  • cleaned carbs,
  • adjusted valves,
  • no cracks in rubber between carb and cylinder,
  • yes - there is nice spark,
  • yes - gas cap is fine,
  • yes - petcock is fine (take off the pipe after petcock, carb is not taking more fuel),
  • put E98 (E5) fuel.
Nothing helps. As soon as it is hot - no way to start.

I found that if I take out sparkplugs, put a teaspoon gasoline directly in cylinder - it is possible to start it right away. If I manage to start this way it is running OK.

Anyone have idea what is wrong here? Is it really vapor lock because of ethanol in the fuel? How to solve this issue? This is driving me mad. There is no more fuel without ethanol... In case of this a lot of people should have the same problem.
 

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Run through this cold - and then hot when the bike won't start.

201721


Looking at the other thread it seems fuel should be covered, though a high float level is possible. This can be checked on bike with some 4 mm clear hose.
 

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Discussion Starter #3
Do not understand, what do you mean 9 to yellow wires? In picture there is just 8-9 and 5-9
Could you point out which is "the other tread"?
 

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When you go to do the test you'll find the two plugs in the picture under your seat. next to them there is the third stator plug - the battery charging. This has the three yellow wires. Sometimes the insulation fails on the windings and the CDI windings short to the battery charging windings. That's why test yellow to 9. You don't want continuity here. {infinite resistance}

Just run the test as shown at 2000 ohms on your meter.
 

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Discussion Starter #5
When you go to do the test you'll find the two plugs in the picture under your seat. next to them there is the third stator plug - the battery charging. This has the three yellow wires. Sometimes the insulation fails on the windings and the CDI windings short to the battery charging windings. That's why test yellow to 9. You don't want continuity here. {infinite resistance}

Just run the test as shown at 2000 ohms on your meter.
OK, I can try this as I do not have any other options. I just cannot see how it could be linked. If I put gasoline directly in cylinder bike starts. So I assumed there is no problem with ignition.
 

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Have you tried removing the filler cap?

Get that 4 mm tube and check your fuel level.

Do it cold and when the bike won't start.

But I suspect you may have a thermal fault in the ignition windings.

I guess explore the last fuel items.

By other thread I meant your other thread that you linked in the first post.
 

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Discussion Starter #7
Have you tried removing the filler cap?

Get that 4 mm tube and check your fuel level.

Do it cold and when the bike won't start.
How it is done? Do you mean attaching clear tube to the overflow in the bottom and rise it along carburetor and open overflow screw?

Additionally it is suspicious that spark plugs are not wet ever after several minutes of drilling starter. After direct gasoline input it starts. It led me to some conclusion about fuel starving not overflow.
 

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Yes, hold up the side open drain with the petcock 'on'.

The level should be a couple of mm below the joint between carb body and float bowl.

It's worth a check, both hot and cold but I think if it were the issue you would suffer from fuel starvation while running.
 

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Discussion Starter #9
Yes, hold up the side open drain with the petcock 'on'.

The level should be a couple of mm below the joint between carb body and float bowl.

It's worth a check, both hot and cold but I think if it were the issue you would suffer from fuel starvation while running.
Just tried. The same behavior. Cold starts perfect, after riding 30KMs, shutting off engine, it did not start again
Checked fuel level in carbs as you wrote. Both levels are OK. Both are the same level cold and hot.

I checked resistance cold and hot. 9 to yellow wires - no continuity. All other oms are in the range except 5-9 = 270 (range is 387-473). On hot resistance increases for all about 20-30 ohms (I think it is OK).

One more observation - on hot engine, after some time and very intense starting I manage to start the engine. If it starts it runs smooth without problems. If I shut it down again, I could start it many times very easy on a single starter rev.

Spark plugs are never wet, they are dry even after very intense starting. No smell of gasoline around while drilling starter. Spark was fine as well.

Any other Ideas?
 

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I checked resistance cold and hot. 9 to yellow wires - no continuity. All other oms are in the range except 5-9 = 270 (range is 387-473). On hot resistance increases for all about 20-30 ohms (I think it is OK).
Pin 9 is your low speed ignition power, and as you noted, that reading is low. It may be that the rich condition caused by directly injecting fuel is able to overcome the weak spark.

Randall
 

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Discussion Starter #11
Pin 9 is your low speed ignition power, and as you noted, that reading is low. It may be that the rich condition caused by directly injecting fuel is able to overcome the weak spark.

Randall
But still, cold starts perfect with 270. Hot has 300 ohms but not starting. After getting it work, it is still hot and 300 and after this start I can shut it off and start again without a problem.

DO you have any idea what part is faulty for this 5-9 measurement?
 

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Just tried. The same behavior. Cold starts perfect, after riding 30KMs, shutting off engine, it did not start again
Checked fuel level in carbs as you wrote. Both levels are OK. Both are the same level cold and hot.
[snip]
One more observation - on hot engine, after some time and very intense starting I manage to start the engine. If it starts it runs smooth without problems. If I shut it down again, I could start it many times very easy on a single starter rev.
Do I read you correctly that if the engine is hot and you switch it off then try a restart right away you are successful but if it sits after a shut off while it is hot it then refuses to start?
When trying to restart the hot engine have you held throttle wide open and or given the throttle a couple of cranks before starting?
 

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Discussion Starter #13
Do I read you correctly that if the engine is hot and you switch it off then try a restart right away you are successful but if it sits after a shut off while it is hot it then refuses to start?
When trying to restart the hot engine have you held throttle wide open and or given the throttle a couple of cranks before starting?
Not exactly. If it is cold it starts without problem. When I ride for some time e.g. 30 KMs it becomes hot. In case I shut it off, it is not possible to start. Not even right after shut off.
Then I have an option
1. Wait while it cols down (time depend on weather. Now it is 30C so it is not so soon)
2. Torture the starter and hoping it will start after 5-10mins before battery is flat
3. Put some gasoline directly in cylinder

In case of 2 and 3 it is started it runs fine. In case I switch it off (even hot) I can start it again as it was cold (no throttle, just gentle start, take just a single rev of starter to start the engine). This seem weird to me. This leads me to some vapor lock in the carb, but where? There is gasoline in carb, I checked level it is the same as it is for cold carb.
 

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Have you tried cranking the throttle a couple of times before doing a hot restart? That operates the accelerator pump, assuming that your bike has one.
 

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Have you tried cranking the throttle a couple of times before doing a hot restart? That operates the accelerator pump, assuming that your bike has one.
He might not have an accelerator pump on a Latvian CX. That was a US (California) emissions thing, starting with the 1980 models.
Has anyone experienced temperature sensitivity in the vacuum petcock? (Though, he might not have one of those, either.)

Randall
 

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Yes, I suspect that there may be no accelerator pump. In that case using the choke may help to draw in fuel. I don't recall the OP mentioning use of the choke on hot restart.
IIRC he had an in-line fuel filter but removed it. Could possibly be a fuel line routing issue.
 

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Okay so just throwing my 2 cents in here...

My '79 CX would do that. Start great in the mornings, but once hot it'd never start. Couldn't even push start the bike. It'd drown the battery after a few cranks...even a new battery. Couldn't jump start it, either. I went through so much trying to sort it out and ultimately I just stopped turning the bike off unless I was REALLY sure I was done riding for a while. I dealt with it like that for over a year.

Then one day while riding I got a nasty puff out the back and no power. White "smoke", oil everywhere, chocolate milk in the oil, just generally nasty. Temp gauge never showed I was overheated. I went to change head gaskets only to find my headgaskets were both fine and unphased. Flushed the engine and she started right up and ran as good as she ever had. No exhaust gas in the coolant. Just real peachy. Except once hot...still...no starty. Totally miffed by this I dropped the engine back out and went snooping around. Someone here suggested that a bad seal in the water pump could be a potential source of coolant in the oil so I popped that cover off...and the impeller fell out. Splines were completely stripped, the inside of it was a mix of polished and tarnished and the hole was rather elongated. It had been that way for a very long time. After replacing a few seals and swapping a water pump over from another bike she ran perfectly...even started right up when hot.

The engine was getting too hot, causing things to start getting sticky. Coolant wasn't flowing so my gauge never really showed the temp spike in the cylinders and head.
 

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Discussion Starter #19
He might not have an accelerator pump on a Latvian CX. That was a US (California) emissions thing, starting with the 1980 models.
Has anyone experienced temperature sensitivity in the vacuum petcock? (Though, he might one of those, either.)

Randall
Petcock is not in charge. I even have transparent fuel tubes. I see the flow. If I remove fuel line tube after petcock, it is not flowing down, it remains in the tube This means carb is full. And it is as I measured level in float chamber yesterday.
 

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Discussion Starter #20
Yes, I suspect that there may be no accelerator pump. In that case using the choke may help to draw in fuel. I don't recall the OP mentioning use of the choke on hot restart.
IIRC he had an in-line fuel filter but removed it. Could possibly be a fuel line routing issue.
I have German version of cx500c. There is no fuel pump. When it finally starts there is no black smoke, so this means it is not too rich or cylinders pumped full of gasoline.
 
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