Bikedecided not to start

[jstubb]

Hey folks how are all of you? Thanks for reading this, I am a bit confused. My bike has run without a hitch since I bought it four years ago, until this spring. I rode it a couple of times and no problems and the other day I took it out of the garage and it wouldn't start. The fuel pump was working fine and I was in a hurry to get to my destination so I left the bike out in the sun. When I got back it had warmed greatly from being in the garage and it started right up and ran great! I rode it a minute and tried starting it again and it worked fine. I parked it in the garage and the next day I tried starting it again in the cool garage and it wouldn't start. I started testing and I had no spark at the plugs. I talked to a small engine mechanic friend of mine and he suggested warming it up with a heater and seeing if it started and low and behold as soon as it warmed up quite a bit it had spark and started again. Is there anyone out there that might know the cause of this and where to get the parts to fix it? Thanks for your help. And BTW, this is a '90 VR.

[RedRider]

Crack in the coils is my guess. Try starting it in the dark and see if there are some sparks around the coils.

 

RR

[Marcarl]

When was the last time you put new plugs in it.

[cowpuc]

and Plug Caps - (c - vid)!!

 

I do the dark room testing too.. Night time is a good time to be looking for electrical leakage, especially anything to do with the high voltage, secondary side of the ignition coils!!

 

[cowpuc]

By the way Stubbs,,

[7 lakes]

An electric problem that comes and goes with temp changes is quite likely to be a poor connection somewhere. Things contract when cold and expand when warm so something may be shrinking away from contact and expanding back to it, usually its a circuit board of some kind but a poor connection anywhere can do the same thing and act as a temperature sensitive switch, like a temp sensor for an idiot light. The cracked coil suggestion is a good one, it would be a good place to start because it should be easy to see one if it's there. Look for obvious cracks / breaks in things and then check harness plugs, a bad connection inside the plug where you can't see it can do the same thing. A thin film of corrosion between plug pins and sockets can do the same thing, I've seen poor connections in plugs when they didn't even look corroded, just dull. If it is a wire or plug connection, the connection when warm should still be sensitive enough that you can break it by wiggling the harness. If it is in a circuit board, warming it up with a hair dryer can sometimes help find it.

 

I would first do a complete visual check, then check each component with a meter for correct specs. If specs are bad or open circuit is found, warm the component and see if it works. If so, cool it and do it again to verify.

 

We had issues with our internet and cable relating to temp changes, after weeks of in and out service I was finally able to talk to a senior line tech and told him I thought they had a cracked circuit board in the splitter at the end of our street that feeds me and my neighbors. When I described what was going on and suggested that was the problem, he sent a crew to check it out and called me back later to tell me I was right. He was pretty surprised. The early days of electronics in cars were plagued by this same issue, boards of the day weren't really up to the vibration and temp extremes at first. I replaced a lot of early GM modules with this issue.

 

Tim

[Flyinfool]

A cracked coil does not sound like the culprit, the odds of all 4 coils going in and out at the same time and temps is really high. These bikes run pretty good on 3 cylinders. I would believe more along the lines of a bad connector or a bad solder joint on a PC board, like maybe the TCI.

 

You will need to do some testing while it is not working to track the culprit down. All the testing in the world while it is running will not tell you why it sometimes does not run.

[jstubb]

Hi all,

Thanks for the replies and taking the time to try and help me figure out my issue. My shop is dark and I tried starting it cold and there are no sparks or glowing anywhere. I have all the covers and fairing off so it is easy to see. I put the heater on it and warmed it up to between 75 and 80 degrees, (temp determined with a laser thermometer) and it started right up. I checked all the engine compartment again while it was running for any sparks or glowing and none showed. I checked the resistance of the plug wires and all were within tolerance, the plugs were all good and properly gapped and work well when there is spark and the boots are in good shape. I had one suggestion that it might be the TCI (transister controlled ignition) unit, something in there is either loose or broken and the heat makes it expand enough to make contact again. I was hoping someone out there may have experienced the same issue and had a good fix. Is anyone aware of a good source for electrical parts for these bikes? I also found a great download site for a factory service manual that had some fun information and it was totally free and I would be happy to share it with anyone interested. Again, thanks for the time you all have given me and thanks for the welcome to the site. Hopefully some day I can repay the kindness.

[Flyinfool]

This site has the service and owners manuals in the technical library.

 

When you say the bike will not start, is it cranking but not firing, or is it not cranking at all?

[jstubb]

The bike turns over all the time without a problem, it looses spark when it cools down. I have been doing comparison testing since my shop is cool and I can easily warm up the engine compartment. So far I haven't been able to find any differences between warm and running and cold and no spark. I think my next step is to remove the TCM and see if I can find out anything with it unless someone has a better suggestions.

[Flyinfool]

Do some testing first

See if there is power going to the TCI on the red/white wire while there is no spark.

Also check the black/white wire at the TCI to be sure it is not connected to ground.

 

There are a number of safety circuits on the bike that could turn off the ignition via these 2 wires. The TCI could be fine and something else could be the problem. The only way to test a TCI is to swap with a known good one.

[Prairiehammer]

Your 1990 Venture (and the 1991, '92, '93) has a single pick-up coil. A faulty (corroded/loose) connection from the pick-up coil to the TCI will result in no fire for any of the cylinders. Pull the left side cover and trace the cabling (containing an orange and a black wire) from the stator cover to the white connector and on to the TCI. Inspector the connector.