7000 rpm rev limit, bad coils the culprit?

[vladimirmartin23]

So i got my 1985 dohc kinda sorted out on the low end, and when i tried to do a 0-100 to test it, i realized it cannot rev past 7000. It hits 7500, then it skips back down to 7k like a really slow rev limiter. Tested the secondary coil resistance (plug lead to plug lead like the diagram in the manual says) and got some 36 Komhs, far from the specified 8 or so. Can anyone confirm or disprove that bad ignition coils can do that?

 

[kebabs]

So i got my 1985 dohc kinda sorted out on the low end, and when i tried to do a 0-100 to test it, i realized it cannot rev past 7000. It hits 7500, then it skips back down to 7k like a really slow rev limiter. Tested the secondary coil resistance (plug lead to plug lead like the diagram in the manual says) and got some 36 Komhs, far from the specified 8 or so. Can anyone confirm or disprove that bad ignition coils can do that?

hi. not sure about the coils .I would try a larger main jet.or raise the throttle needles by one notch.going by my previous experiences.

 

[vladimirmartin23]

hi. not sure about the coils .I would try a larger main jet.or raise the throttle needles by one notch.going by my previous experiences.

I Leaned it one step with the needle thinking it was rich, "limiter" stayed right there, but it did seem to have a bit more power at high rpm, and bang harder against that 7500rpm line". Plus, if i measured the coil resistances correctly, i dont know if the bike should even start...

 

[kebabs]

I Leaned it one step with the needle thinking it was rich, "limiter" stayed right there, but it did seem to have a bit more power at high rpm, and bang harder against that 7500rpm line". Plus, if i measured the coil resistances correctly, i dont know if the bike should even start...

put the needle back one notch and try a larger jet.i recently changed my coils.the reason I changed them because the bike would cut out when engine was hot at idle.it dosnt cut out now.in my carbs there is a small spring where you adjust the needle heights. the springs on each carb were fitted incorrectly by the previous owner ,the symptoms I had then were a splutter at 5000 revs and reluctant to go above 7500 revs .maybe your carbs dosnt have these springs. since putting the springs in the right location. the bike goes like shit off a shovel

 

[kebabs]

put the needle back one notch and try a larger jet.i recently changed my coils.the reason I changed them because the bike would cut out when engine was hot at idle.it dosnt cut out now.in my carbs there is a small spring where you adjust the needle heights. the springs on each carb were fitted incorrectly by the previous owner ,the symptoms I had then were a splutter at 5000 revs and reluctant to go above 7500 revs .maybe your carbs dosnt have these springs. since putting the springs in the right location. the bike goes like shit off a shovel

my carbs are bs34

 

[vladimirmartin23]

put the needle back one notch and try a larger jet.i recently changed my coils.the reason I changed them because the bike would cut out when engine was hot at idle.it dosnt cut out now.in my carbs there is a small spring where you adjust the needle heights. the springs on each carb were fitted incorrectly by the previous owner ,the symptoms I had then were a splutter at 5000 revs and reluctant to go above 7500 revs .maybe your carbs dosnt have these springs. since putting the springs in the right location. the bike goes like shit off a shovel

the springs go above the washer above needle clip, below the plate that screws into the slider, right? those are on. maybe i could try pulling the needle up 2 notches and seeing how it reacts. still highly doubt the 132.5 jets are too small...
also, what do you mean cut out? like a gap in firing when at idle?

 

[kebabs]

the springs go above the washer above needle clip, below the plate that screws into the slider, right? those are on. maybe i could try pulling the needle up 2 notches and seeing how it reacts. still highly doubt the 132.5 jets are too small...
also, what do you mean cut out? like a gap in firing when at idle?

yes thats correct how you have described the springs. so there ok.
if it were me I'd put the needles back to where you had them.install a larger jet.
make one change at a time.
CaptChrome is on this website. he is the man you want to get answers from .helped me loads.
before you do any changes. here's what I do .take the bike out and heat up the engine. take the plugs out and clean them.
find a good hill.put the bike in first gear and open up the throttle as far as you can take it.hit the engine kill button and pull the clutch lever at the same time.
take the plugs out and check the colour. if there black and sooty ,your too rich,if white its too lean.
this will tell you if you need to go up or down on jet sizes.
what I mean by cut out is the engine would stop when idling ,I had to keep it going by revving it .but the new coils cured the idling problem. the voltage must have been dropping when the old coils got hot.

 

[vladimirmartin23]

im gonna try that if i can get the soot off my plugs

 

[kebabs]

im gonna try that if i can get the soot off my plugs

thats maybe your problem .Trust me it's a good test.also for testing mid range throttle.heat the engine up .take plugs out ,clean them.run the bike for about 5 miles.dont exceed 5000rpm on each gear.check the plugs .If sooty your too rich lower the needles. ,if white its too lean raise the needles.that will let you know if you need to raise or lower the needles.one test at a time.been there done it .carbs on carbs off

 

[kebabs]

thats maybe your problem .Trust me it's a good test.also for testing mid range throttle.heat the engine up .take plugs out ,clean them.run the bike for about 5 miles.dont exceed 5000rpm on each gear.check the plugs .If sooty your too rich lower the needles. ,if white its too lean raise the needles.that will let you know if you need to raise or lower the needles.one test at a time.been there done it .carbs on carbs off

Once you have it fine tuned. try iridium plugs.not cheap but good

 

[CaptChrome]

I agree with @kebabs here (happy that your bike is running strong also!).
This sounds like a fuel issue. However, it also could be timing related and I would eliminate that first as it is easy to check.

1. Put a timing light on the bike and check the timing at idle and then check that the timing advances to the 35 degrees or so above 3-4K revs that the book specifies for your model. Retarded timing at high revs can hold the bike back.
2. Check that the petcock fully flows fuel
3. Check that the net screen attached to the float valve seat in the carbs is not full of stuff.
4. Verify the float bowl level in your carbs
5. Check carb synch
6. Finally, if all of the stuff above is correct, only then address the main jet. At >7K revs, you are most likely at the transition point from the needle jet to the main jet. If performance from 2K to 7K is pretty linear, then the needle setting is probably pretty good (verify that using plug color as above). Make sure you get the needle jet set before messing with the main.

 

[vladimirmartin23]

I agree with @kebabs here (happy that your bike is running strong also!).
This sounds like a fuel issue. However, it also could be timing related and I would eliminate that first as it is easy to check.

1. Put a timing light on the bike and check the timing at idle and then check that the timing advances to the 35 degrees or so above 3-4K revs that the book specifies for your model. Retarded timing at high revs can hold the bike back.
2. Check that the petcock fully flows fuel
3. Check that the net screen attached to the float valve seat in the carbs is not full of stuff.
4. Verify the float bowl level in your carbs
5. Check carb synch
6. Finally, if all of the stuff above is correct, only then address the main jet. At >7K revs, you are most likely at the transition point from the needle jet to the main jet. If performance from 2K to 7K is pretty linear, then the needle setting is probably pretty good (verify that using plug color as above). Make sure you get the needle jet set before messing with the main.

The petcock should be doing a full stream, right? Because mine just kinda pisses the fuel also, the timing is the last thing i would check, as if my tci is fried im in deep shit.