'85 VF1000R won't restart hot; fuel or spark?

Looking for some mechanical advice or sharing your own tales of the workshop wonder.

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kx250rider
Member
Posts: 5
Joined: Mon Apr 22, 2013 4:04 pm


It's been awhile since I've been on the forum, and I think I had posted about this issue a year or so back. My bike starts right up easily in any weather, and runs fine, and will restart fine if in a minute or so from when I shut it off.... But if I stop for lunch, etc., it will not restart for several hours (or until stone-cold). I can't tell if it's a fuel problem (suspected vapor lock), or loss of spark. I notice that the tach doesn't "dance" when cranking when the bike refuses to restart, and that's a clue, I guess, that it might be an electrical issue. I don't remember anyone having had this issue with the same details, so hopefully someone might have some clues since then? What I've done so far: Checked all ignition wiring and replaced the plug and socket to the pickup coils (was corroded & frayed). Cleaned and adjusted carbs, then later swapped the whole carb rack with a known good one from my other bike. Replaced the CDI box, and verified all connections are good at those plugs. I even jumped a second battery in place to test to see if it was a battery failure under heat, but that made no difference either. This problem has been this way now for at least 2 or 3 years, and hasn't gotten worse or better. The fuel pump is bypassed, but again, the bike runs great at all speeds, so I don't think I have a fuel delivery problem unless it's vapor lock; which might be the case if the fuel pump needs to pressurize the lines to prevent vapor lock.

Anyway, please excuse the long post, and I really appreciate any input :wink:

Thanks, Charles
kx250rider
Member
Posts: 5
Joined: Mon Apr 22, 2013 4:04 pm


2 1/2 year followup here... I still have not really resolved this no-start when hot issue, but I may be close. The biggest factor seems to be the ethanol gas, which is all you can buy now in most states, has a boiling point lower than old gas. That would mean it will vaporlock much easier than it would have with old gas, and if the floats are set slightly low, it would make it even harder to get gas into the pilot jets to start hot. Also, my fuel pump wasn't starting when the starter motor runs, and that's a wiring harness problem evidently. So I have rewired the pump with a separate fused pushbutton circuit, so I can pressurize the fuel system before starting. I haven't ridden enough to be sure this fixed it, but it looks promising so far!

I also just did a meticulous carb rebuild, using a Keyster complete kit, and had the bare carbs ultrasonic tanked at the dealer. I also set the floats to 7.5mm, which should keep the pilot jets fed even with the gas vaporizing. I'll post when some results are known ;-)

Charles
kx250rider
Member
Posts: 5
Joined: Mon Apr 22, 2013 4:04 pm


Time goes by!!! Just another update as of yesterday: The problem had not happened in over a year, and I had all but forgotten about it 'til I went to ride it last week... I pulled it out, checked it over, and went to start it, and it just cranked with no hint of firing, and no movement of tach, and the engine was cold (first time this happened when not fully warmed up). So I pulled it back inside, and started checking voltages, and I think I FINALLY found it!!! Although I had checked the kill switch and handlebar wiring very carefully in the past, I think the kill switch has been the problem all along. I had my meter on the 12v line feeding the coils, and I flicked the kill switch off, then back on, and I had 6v... Then again I had 0v, and several more clicks and 12v. I took the switch all apart, and the contacts are flattened out, and burnt. So I sourced another switch ass'y for a good price with a bad starter button, and I swapped the kill switch into my handlebar switch, and now I have a very stable 12v, and the kill switch acts like it should.

I'll repost after enough time has passed to be sure, but I'm fairly confident this time. Hopefully this could help somebody later on, as I was befuddled by the problem for several years.... And I'm a certified electronics tech and electrician, and felt that I had excused the kill switch with usual testing methods. So it was a tricky one...

Charles
86FANINPHILLY
Member
Posts: 27
Joined: Sat Nov 15, 2014 7:43 pm


Thanks for the heads up and the perseverance to track down that intermittent electrical gremlin. I know people that never touch that kill switch and only use the key for that reason. I've never had a problem myself on any of my four Hondas though. Good for you for tracking it down. Now you can have peace of mind and enjoy the ride.
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