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Discussion Starter #1
Have been working on a 81 CX500 Custom;

So Far -
  • The carbs have been cleaned/rebuilt using Larry's Book with an ultra sonic
  • Sealed Air/Vaccum Leaks
  • Replaced Air Filter
  • New Spark Plugs

When checking the spark plugs, I pulled them and found they were NKG DCPR7E and I could not find this plug on a compatable list for the cx500 custom. Went with NGK DR8EIX and did the brass rod mod, installed them and ran the bike this morning. Everything appeared to be going fine, 5 miles with stop and start traffic and getting up to about 55 MPH at one spot. On the way back, while slowing at a stop light the bike died, and I coasted towards a parking lot and refired and it died almost right away. Got the bike home and it died at almost every stop.

Here are the symptoms I was experiencing
  • Dieing at Low RPM
  • Hesitation when accelerating from stop

Could this be caused by the new plugs or some other gremlin?

Thank you.
 

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I don't recall if the 81 had vacuum petcocks but check if there are two or three hoses (can't remember) and see if there are air leaks. I do know 79 and 80 models were gravity feed and there are air passages under the filler cap.
 

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Discussion Starter #4
Mine does have a vaccum petcock, I will be sure to check for a leak there.

Thank you both for the suggestions, I will update this thread if I find a solution. I have an idea of what caused the initial problem and its possibly an embarrassingly easy fix that I should have checked before adjusting some of the other parts of the bike.
 

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Discussion Starter #5
*Update*

Checked that there was no problem with the petcock and that the bike was getting fuel; I thought I had it back and running and went out for a test drive. Everything ran great until around the time the bike got to operating temperature, the temp gauge started to creep past the second zone into the third zone about halfway to the red indicator by the H. This is when the bike started to behave just as it had the day before, it didn't die right out at stops but there was a clear loss of power. This loss of power is only when the bike temp was in zone 3, and the bike was at low RPM.

If it were only overheating I would think it would either be a thermostat, fan, pump, or coolant problem. The loss of power sounds like its possibly a head gasket? A quick search seems that a compression test is possibly in order. Anything I might be missing here?

Thanks
 

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If the bike gets hot enough at lows speeds could be boiling the fuel in the carbs.
 

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the temp gauge . . . halfway to the red indicator by the H. This is when the bike started to behave just as it had the day before . . . The loss of power sounds like its possibly a head gasket? A quick search seems that a compression test is possibly in order. Anything I might be missing here?
Not saying I think this is your problem, but . . .

When an engine overheats, the pistons will expand in the cylinders and can bind up. I've driven cars that behave just as you describe, stalling at low rpm, due to overheating. Sometimes they're ok after a cool down. Sometimes after cool down they're left with excessive piston to cylinder clearance. I don't think you would get this hot as long as you still have coolant, circulating or not.

If your coolant looks ok, I like Murray's electrical theory.
 

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Discussion Starter #9
I will check the coolant condition/levels tonight and test the 7v Node as well as verify my stator values.

Thank you for the suggestions.
 

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Discussion Starter #11
Did a reading of the stator;

1/5: 115
2/5: 97
3/5: 212
4/5: 112
6/5: 98
7/5: 212
9/5: 315 <- Uhoh
9/8: 85

So, I take this to mean my source coil low speed is bad.
 

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OK, 81 500C... PCO1E 2206820... Your number is higher than the cutoff point. Resistance for numbers higher than PCO1E 2114151 is 315 - 385 ohms so at 315 yours is just in spec.

I wonder if you have pulled rust through into your idle jets. Have you recently been on reserve and do you run an inline filter?
 

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Discussion Starter #16 (Edited)
OK, 81 500C... PCO1E 2206820... Your number is higher than the cutoff point. Resistance for numbers higher than PCO1E 2114151 is 315 - 385 ohms so at 315 yours is just in spec.

I wonder if you have pulled rust through into your idle jets. Have you recently been on reserve and do you run an inline filter?
I have had to switch to reserve this week, and while I did do an inspection of the filter, I think that is possible debris might have been in there. I think I will be taking off the carbs again to double check everything and see whats what.

Randall-in-Mpls said:
Did you take those readings with the engine cold?

Heat her up and do the tests again. Since the symptom appears after it gets up to operating temp, I suspect you'll find different resistances.


R
Those readings are cold. I will get a ride in tonight or tomorrow morning and see if the readings on those pins change with temp. Thanks.

Adding an edit to this post:

The bike is back out on the road today.
The following are things I fixed/adjusted
-Cleaned Radiator and cooling system
-Pulled Carbs to check jets for debris
-Bench Balanced Carbs
-Verified absence of air/vacuum leaks

I am looking into getting an inigtech at this point as well.

Thanks everyone for the help.
Cheers,
S.
 
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