Jump to content

86 VFR 700cc


RayRay
 Share

Recommended Posts

Hello gentleman. I have an 86 VFR 700cc. It recently started acting up. It would start run for 30 min and just shut off(no spark) then it won't start. I would let it set 20 min or so and it would fire right up. The problem has only progressed and the run times has shortened. Now I get no fire. So I changed the coils new battery new plugs the bike started I rode it about 2 blocked and it died again wouldnt start. I let it sit a good 30min and it fired right up I road the same 2 blocks home and it died pulling in the drive way wouldn't start. I sure could use some help. I love the bike but driving me crazy. Thanks

Link to comment
Share on other sites

  • Member Contributer

HI Ray & welcome!

 

Let's gather some data:

1. Measure battery-voltage with bike off

2. Measure battery-voltage during cranking

3. Measure battery-voltage at idle

4. Measure battery-voltage at 4000-rpms

 

Those numbers would help narrow down areas to examine.

 

Also unplug 4p red plug going into starter-solenoid and let's look at contacts on both sides. Hopefully it doesn't look this bad:
IMG_2980.jpeg

Link to comment
Share on other sites

classic signs of bad pulse generator coils that work fine when cool but fail when the engine heats up.  same thing happened on one of my 700's too.

 

2061461410_Picture1-12-2020215.thumb.jpg.62d93534f5551fe74f25c15821916d7d.jpg

 

danno ^^is correct that the red plug can fail and interrupt power, and it's an all-too-common failure.

 

 

  • Like 1
Link to comment
Share on other sites

  • Member Contributer

Figured it can be some heat-related issue. Scope those pickup-coils and let's take look at their waveforms, cold and when failing.

 

There was recent case where trigger-teeth on flywheel was damaged and threw off signals. Although that prevented bike from starting at all.

Link to comment
Share on other sites

as a check, measure the resistance of both pulsers at the plug. the manual indicates the proper ohms @ 450-550 cold.

Link to comment
Share on other sites

  • Member Contributer

Further to the above.

According to my drawing for the US version 1986 VFR 700F. You also have a Cam Sensor that feeds the Spark Unit, White/Black and Yellow/Black wires. If you are loosing spark to ALL cylinders then the Cam Sensor would certainly need checking, it should measure 405 - 495 ohms. Check its continuity back to the Spark Unit. Make sure the Pulse Gens also measure correctly back to the Spark Unit.

Also make sure with Ignition to On, you have a solid 12v at the Spark Unit on the Black/White wire. This comes from your Stop Switch back to the Start/Ignition 10amp Fuse. See if this voltage at the Spark Unit disappears in the fault situation.

Also make sure you have a solid Ground on the Green wire of the Spark Unit, make sure this measures 0 ohms back to the Battery negative terminal.

By checking everything around the Spark Unit and its wiring, then by the process of elimination will most likley point to a faulty/intermittent/heat sensitive Spark Unit.

Something else you can try, as it does sound like a heat sensitive issue. If you can start the bike from cold, try blowing some warm air from a hairdryer over the Spark Unit, see if this suddenly kills the bike, before the engine heats up.

 

Good luck, keep us posted.

Link to comment
Share on other sites

  • Member Contributer

Went down this rabbit hole with mine a few months ago. One of the pair of pulser coils would fail hot, replacing it solved the problem. They’re only available in pairs, used(eBay?), so you’re gambling the replacements won’t have the same flaw. Took me weeks to track & solve, hopefully squirrel man & myself can save you some stress!

  • Like 1
Link to comment
Share on other sites

  • Member Contributer

Non-interference way to test for spark is to attach 'noid light to ignition-coil. This will at least quickly tell you if all coils or only some are not getting trigger signal.

https://www.amazon.com/dp/B004FEN84M/

 

also good for testing injector signals on EFI systems

Link to comment
Share on other sites

Never had, or heard of, a bad cam sensor.  But the pulse coils under the right crankcase cover...   highly likely the issue when it's heat related.

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy.