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Discussion Starter #1
Does anyone know how to check the cdi's and ignition timing on an 83 vt750? I have looked online and in the manual but no dice. I have done all the tests in the manual on the coils and such and it all passes.
 

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You are right, Honda has no test for the CDI. Will your bike even start?

The only advice is to search ebay for a used one. I got rid of my Nighthawk because the CDIs are hard to find.
 

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Discussion Starter #3
It starts and runs fine but when you put it under load it quits. Carbs are good and I just rebuilt the top end because it needed a valve job. I did all the tests in the manual and it passes. I am about to tape my timing gun to the bars and watch that when it quits to see if it is spark that quits.
 

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It starts and runs fine but when you put it under load it quits. Carbs are good and I just rebuilt the top end because it needed a valve job. I did all the tests in the manual and it passes. I am about to tape my timing gun to the bars and watch that when it quits to see if it is spark that quits.
That is actually not a bad idea.

The timing is not adjustable, it is electronically controlled by the CDI boxes, if it fires right up when you start it the initial timing is fine.

You could be running too lean, or have a vacuum leak somewhere that is causing this, are all of your vacuum hoses hooked up correctly?
 

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Discussion Starter #5
everything is connected properly and no vacuum leaks. Charging system is good,batt is good,carbs are synched and I have upped the jetting a couple sizes and get the same problem. choke makes no diffence. It will do it in any gear but the higher the gear the less throttle I can give it before it craps out.
 

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Does this bike have a fuel pump? Reminds me of a problem I had in a different ride a long time ago... Guess I could go look in my own manual for that answer, but still ;)
 

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Here's how to check the timing:
Connect a timing light to the cable to either cylinder
Open the timing access port on the right crankase cover (put something on that nice floor, you're going to be spewing oil)
The crankshaft is marked to indicate the timing range. The timing should advance as you run the rpm up to 3500 or so. Once you've checked one cylinder, check the other. If the timing is wrong, or doesn't advance, you've got a bad cdi. If the timing looks good on both cylinders you can start looking for carburetor/fuel system problems.
Let us know if the problem turns out to be the CDI -- you can tell from the responses you've gotten that most of us would be surprised.
 

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Discussion Starter #8
I will try testing the pump flow today,which mark am I looking at? It has ft,rt,f,r for marks. I was thinking about this whole problem yesterday and remembered one time when jumpering the fuel pump relay (I have bypassed this for testing) I put the blue and black together and got a big arc and blew the main fuse. I believe that the blue wire goes to the cdi boxes to trigger the relay. Could it have hurt the boxes?
 

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Did the arc happen when the bike was running or turning over? The wire to the CDI is a ground only when the engine is turning over. A dead short through the CDI is probably why you are having problems. Here is a simplified diagram of this part of the wiring.

 

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Discussion Starter #10
not running, but with power on. I did some research on using vt700 cdi's and all I would need to do is add a wire from the starter button to the cdi. The more I think about it, seems the trouble started after I did that.
 

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Discussion Starter #11
Well I taped my timing light to the bars and took it for a spin and the light kept flashing, so I guess it's fuel related. now I just need to test the pump flow and go from there.
 
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