86 VT500C pulse generator check/verify

[heybiker]

I have seen many posts here about the pulse generators. My situatution is the bike ran but hesitated like no spark then run again. We replaced the plugs and battery (fouled plugs and dying battery). I tried to do the pulse generator test but not sure which wires to check, or if I am at the correct connection. The book says a 4 pin connection, and there is one above the coils and the wiring harness seems to go down to the right side of engine. Should I be measuring this connection and which two pins measure the generators? Also the tach is going in and out, intermittent failure. Is this symptoms of a failing pulse generator, loose wiring, or the generator loose in the housing? I think the part side (toward the engine) has yellow mark on white wire. I also now have no spark to the rear cylinder, but it had spark before. Where would I find a replacement pulse generator?

[tubes_rock]

Welcome to the madhouse!

Your cylinder spark failure and intermittent tach seems to point in the same direction. Your tach gets its pulses from the ignition coils, so if they aren't getting pulses from the pulse generators, you're sunk.

Pulse generators have a habit of being intermittent when they fail, so this aligns.

You will want to test them hot and cold.

I don't have the wiring diagram for your particular model, so i don't know what the wire colors will be. Since the pulse generators are inside the engine, a small-gauge 4-wire harness that goes into the engine is a great place to look.

Your bike has 2 generators, one for each cylinder. Since each generator has two wires, that's all 4. Set your meter to ohms x 1 and just try to combinations until you find the two pair that make the meter move. If you can't get the meter to move for two pairs of wires, you certainly have a bad pulse generator (or two!) The book will tell you that you should have something like 430 ohms +- 10%. Don't sweat the numbers too much. As long as you have more than 100, and less than 1000, and they are within 20% of each other, you're fine.

--Justin

[trumpeteer]

With the tack going in and out that would point to a bad transisorized spark box. The pulse generators output goes to the spark boxes where it gets amplified and then to the coils. Being an 86 bike, over time sometimes the wire solder connections fatigue and you might get away with resoldering the connections inside the box. They can be a bitch to get apart because the circuit board is glued in there but it can be done even if you have to cut it apart and silicone it back together. Done it many times. Good luck

[rocksolid]

First thing to check is the ground connection on the frame from the battery. If it's loose or corroded, the bike won't run right.

Diagnose the charging system
Technical Resources - ElectroSport Industries
Print out the diagnostic chart and tech article on CDI's
this will help you understand what you are working with and also diagnoses the charging system. Be sure to check the connector with three yellow wires from the stator. It should be cut out and the wires soldered, or substituted with another connector(s). It corrodes and can cause a fire.

Get a genuine Honda service manual. You need specs and procedures for your tests. You will use it a lot. Here is one on Ebay.
Honda VT500C, VT500FT Service Manual. Excellent Cond. - eBay (item 260756771139 end time Mar-28-11 19:00:00 PDT)
I don't like working with computer cd's or files

Any glitch in the ignition system can cause intermittent failure. Go thru it with the volt meter and see what shows up. Check the coils, pulse gen., look over the wiring. Even a bad ignition switch can do this. Swap the CDI's to see if the non-firing cylinder changes.
The pulse gen test (detailed in the manual) is on the wire bundle running into the right case. It may require you to pull the cover off the right side. Keep some gasket material handy. You can make a new gasket by tapping the gasket sheet on the case with a ball peen hammer so that it cuts the paper.
I looked and didn't find any new pulse generators for this bike. Used ones show up on Ebay. If needs be, Dyna makes coils that can be used if you can't get OEM.
The tach problem is probably related to the intermittent firing. It may , however be bad in addition to something else. The tachs from this era had a lot of cold solder joints in the circuit boards. There is a test for the tach in the manual. They can be pulled apart and the joints resoldered.
This is the best advise I have untill you do some tests. "Tubes" is a smart guy, especially with electronics and older bikes. I listen to what he says.
Good Luck!