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73 Tnt 400FA primary coil


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#1 MickW

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Posted 18 June 2017 - 01:34 PM

How would the TNT 400FA act if the resistance was off a little from spec? Manual says 325-365 ohms and I have 311 ohms. The engine seems to run fine up until a little past 5000 rpm then power goes away and I haven't been able to find anything else wrong.



#2 396F/A

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Posted 18 June 2017 - 10:04 PM

To me that 311 is likely OK, could easily be that variation in the meter ??

Do you know if you have a original 73 to 75 stator or is it possible you have a newer 76 to 78 stator ???

The timing advance stops in that system at ~ 5,000 RPM, many boxes fall on their face at the end of the advance. Or....If you have a newer stator and the original CD box or a Asian box it will do exactlly as you describe ( even if both components are in good condition )



#3 MickW

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Posted 19 June 2017 - 12:03 AM

I don't know if the stator is original or not. I have a new cdi box from here. 

 

https://cdibox.com/p...-cdi-for-rotax/

 

The original cdi has most insulation gone from the wires so I decided I should replace it. I think I better contact

them and ask about how they set the boxes up. After your input I would bet that is my problem. I think I will try the old

box and see what happens.



#4 396F/A

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Posted 19 June 2017 - 09:44 AM

The box from cdibox.com should work OK, they are not a asian box. Many fellows have had great luck with them.

I believe they did have some issues a few years ago with their boxes with certain stators but think they got it rectified.



#5 396F/A

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Posted 19 June 2017 - 09:59 AM

StatorCDIs005.jpg

 

Do you know if your stator looks like the one on left or on right ??



#6 MickW

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Posted 20 June 2017 - 03:33 AM

Yes, it's the one on the right.



#7 396F/A

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Posted 20 June 2017 - 10:17 AM

Yes, it's the one on the right.

You have a original stator in place.  The cdibox.com unit should work fine with that stator.

Its likely a long shot, but......Have you tried to unplug the wiring at the junction right at the engine then run it ??? This will eliminate any external wiring issues that may be causing a problem.



#8 MickW

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Posted 20 June 2017 - 11:05 PM

Yes I did. I tried it with both the original cdi and the fireplug unit. My thought was current might be getting through

that old wiring and grounding out. But it wasn't the problem. I don't want to confuse things more but this machine 

had no problems hitting 8500 to a tad over 9000 rpm when I last ran it. Now with either cdi unit its like the rpms hit 

a wall at 5100 or 5200 rpms. I have checked for air leaks, checked fuel pump, cleaned carbs twice, put kits in carbs,

tried two new carbs, tried the new cdi, tried retarding timing with the new unit like they recommended. That caused

popping and ran worse, so then I went the other way and advanced timing and that was best it has ran during all this.

Truthfully I am at a loss for Ideas. In my 35 plus years turning wrenches I haven't had this kind of trouble finding the cause

to a engine not running correctly. I have a feeling it going be something so simple. I just wish I could find it.






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