#2 & #4 not firing below 2000 RPM

[venturesome]

I just bought a 1983 VR ($100), so I am surprised that it runs at all! It runs good at higher RPMs, but does not fire #2 and #4 plugs at idle. Also tach shows zero at idle, but comes alive at higher RPM's. I have ridden the bike "down the road" and the gears seem to be in good shape, so I am considering restoring it if I can get the kinks worked out.

Anyone else had this problem?

[Neil86]

Best place to start would be checking resistance of the pickup coils,

mounted in the stator cover.

 

Access the 5 wire plug, unhook and test resistance down to the pickup

coils testing each color vs black wire in harness, looking for consistency

in readings with engine warm.

 

If they test okay next checks would be at the TCI (igniter).

[KIC]

Also, just check the plug wires. There is a thread or two that explain how to check them resistance and corrosion. I would post the info but I am TDY in Maryland and do not have my "Venture Library" available to look through.

 

Here is a thread with some good info:

 

http://www.venturerider.org/forum/showthread.php?t=82832

[Condor]

Idle jets plugged??

[camos]

The important clue here is the tach does not work at idle. That is a known issue that I cannot remember the solution to at the moment. The problem is most likely caused by a poor electrical connection that is overcome once the RPMs get high enough to get full output from the stator.

[Flyinfool]

The important clue here is the tach does not work at idle. That is a known issue that I cannot remember the solution to at the moment. The problem is most likely caused by a poor electrical connection that is overcome once the RPMs get high enough to get full output from the stator.

 

:sign yeah that:

The tach is driven off of the primary side of the #2 coil. The fact that the tach is dropping to zero when the cylinder drops out means that the problem is on the primary side of the #2 coil. A carb or plug cap problem would not drop out the tach.

 

It is easy to slap a volt meter on to be sure that the charging system is putting out the full voltage. Low voltage on these bikes causes all sorts of weird things.

Clean all of the connectors in the primary side.

Clean all of the grounds.

[bongobobny]

The tach is fired by the TCI, number 2 cylinder if I remember. I would suspect the TCI or the vacuum advance being defective. The TCI is different for the '83 and can only be used on the '83. The vacuum sensor is under the battery under the coils next to the TCI.

 

I would highly recommend updating your TCI with an ignitech unit available from member Dingy if the TCI proves out to be the failure. Check the pickup coils and all electrical connections to it and the TCI as well as the vacuum line to the sensor...

[bongobobny]

Heh! Jeff and I were typing together!!

[venturesome]

Thanks for the suggestions. Next step is to pull the TCI out so I can see it and then clean and test all connections per Jeff. I had an old experienced aircraft mechanic tell me once that weird electrical problems were usually bad ground.

 

I will post results.

[Neil86]

You might test the pickup coils first....there are 4 but they are paired up so 2 share

a ground wire.....so losing 2 cylinders at same time can sometimes indicate a failing pair

of the coils.