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Discussion Starter #1
Hi,

Looking for some feedback on the weak spark issue.

Bike was lying up for 7 years. Done a full service, new plugs, new battery, flushed the tank, replacing fuel lines and carb strip and clean. Lots of other work completed below.

The spark is orange instead of the nice blue colour. Tried different plugs: no change.
Bike sometimes backfires and refuses to start. Also think I’ve killed the battery with all the charging cycles.

Was getting high resistance on electrical connections, including earths. All connections cleaned and WD40’d. Now resistance 0.2 to 1 Ohm’s. Even added extra earths.
Rectifier/Regulator is good. All readings match the Haynes manual. (ordered new R/R anyway).
Stator is ~0.4 Ohm’s between yellow wires and nothing to ground.
Voltage on B/W wires at coils is reading what the battery voltage is.

Coil resistance:
Coil (1+4) 3 Ohm’s and HT side 25.1 K Ohms with spark plug caps on.
Coil (2+3) 2.9 Ohm’s and HT side 26.2 k Ohm’s.
Nonetheless I took the caps off and cleaned them and WD40’d them. The caps have around 5k Ohm's.
Pulse Generator: 440 Ohm’s
Plugs are CR9EH-9
Reading ~0.2 Ohms between the other coil wires to ICM.
Good ground to ICU.

Exhausted manifold on cylinder 2+3 had holes in them. Removed them and got repaired I tuned the engine over (Ign off) and watched a fine petrol mist come out of each exhaust port. So happy with the carbs….somewhat. The choke was stuck when I stripped the carbs. I didn’t strip the choke on the rebuild, so I think I may have missed something.

Thanks,

Declan.
 

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Hi,

Looking for some feedback on the weak spark issue.

Bike was lying up for 7 years. Done a full service, new plugs, new battery, flushed the tank, replacing fuel lines and carb strip and clean. Lots of other work completed below.

The spark is orange instead of the nice blue colour. Tried different plugs: no change.
Bike sometimes backfires and refuses to start. Also think I’ve killed the battery with all the charging cycles.

Was getting high resistance on electrical connections, including earths. All connections cleaned and WD40’d. Now resistance 0.2 to 1 Ohm’s. Even added extra earths.
Rectifier/Regulator is good. All readings match the Haynes manual. (ordered new R/R anyway).
Stator is ~0.4 Ohm’s between yellow wires and nothing to ground.
Voltage on B/W wires at coils is reading what the battery voltage is.

Coil resistance:
Coil (1+4) 3 Ohm’s and HT side 25.1 K Ohms with spark plug caps on.
Coil (2+3) 2.9 Ohm’s and HT side 26.2 k Ohm’s.
Nonetheless I took the caps off and cleaned them and WD40’d them. The caps have around 5k Ohm's.
Pulse Generator: 440 Ohm’s
Plugs are CR9EH-9
Reading ~0.2 Ohms between the other coil wires to ICM.
Good ground to ICU.

Exhausted manifold on cylinder 2+3 had holes in them. Removed them and got repaired I tuned the engine over (Ign off) and watched a fine petrol mist come out of each exhaust port. So happy with the carbs….somewhat. The choke was stuck when I stripped the carbs. I didn’t strip the choke on the rebuild, so I think I may have missed something.

Thanks,

Declan.

Turn off the fuel, drain the float bowls, try starter fluid. If she fires and runs then the problem is fuel supply.
 

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Discussion Starter #3
Thanks bladeracer. The carb bowls are full. Waiting on a new rectifier and will stick in a new battery. Will update when I get them.
Would the ICM cause a weak spark?

Dec.
 

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Discussion Starter #4
Hello,

Just to update: Issue was the carbs. I used a "inert" vacuum grease on the rubber seals on my last carb rebuild. Turn out the "inert" grease turned into gel when mixed with petrol. So stripped and cleaned the carbs again and made a cheap ultrasonic bath with cheap cola, plastic tub and sander to clean the carbs in.

Upon rebuild the bike fired into life on all cylinders. Balanced the carbs and now is running sweet.

Moral of the story: Don't use fancy grease.
 

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Hello,

Just to update: Issue was the carbs. I used a "inert" vacuum grease on the rubber seals on my last carb rebuild. Turn out the "inert" grease turned into gel when mixed with petrol. So stripped and cleaned the carbs again and made a cheap ultrasonic bath with cheap cola, plastic tub and sander to clean the carbs in.

Upon rebuild the bike fired into life on all cylinders. Balanced the carbs and now is running sweet.

Moral of the story: Don't use fancy grease.

Thanks for the update! Coils going bad on these models is pretty few and far between. In fact a friend of mine just used my spare 1993 RRP coils to get his 96 YZEDF750 back to life after a few years. Anyway thanks for coming back with the results!:thumb:
 
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