Running like trash when hot - Honda RC51 Forum : RC51 Motorcycle Forums
 
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post #1 of 6 (permalink) Old 07-14-2019, 10:44 AM Thread Starter
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Running like trash when hot

So before everyone tells me to look at old posts. I have been reading post on issues relating to my issue for months. I've tried everything. Nothing is working. Once the bike gets to temp it refuses to idle. It jumps all around and dies. No codes are coming up. After replacing the FPR for a second time yesterday I took it for a spin. Was fine for about 1/4 of a mile then started running like I only had one cylinder. I turned around and headed back to the house. It died in the driveway. Went inside and let it cool down. Bike was at 160 when I came back out. Fired right up. Idle wad perfect took it for a ride and it was fine. Once the temp got up to 218 same thing happened again. I'm stumped. Any ideas before I lose my mind and rip it apart again.
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post #2 of 6 (permalink) Old 07-28-2019, 01:16 AM
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Pop the gas cap next time it does this.. see is there is suction in the tank or vacum. See if it smooths out after .. What gas cap stock or aftermarket? If not that, i would swap out one ignition coil at a time. Road test..

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post #3 of 6 (permalink) Old 07-28-2019, 03:42 PM
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You might also check the Fuel Pressure Regulator for evidence of any seepage of gasoline through the vacuum side. A tiny amount of gas making its way to the intake manifold might not be enough to interfere with operation when cold but would become more noticeable as normal operating temperature is reached.

<edit> Sorry I see you already tried the FPR, my bad.

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post #4 of 6 (permalink) Old 07-28-2019, 07:15 PM
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Doing some more thinking about it (and this time actually carefully considering what you mentioned you'd tried before) the order I'd do things is:

* What rgv250f3 suggested with checking for possible vapor lock or over-pressurization in the fuel tank. Easy peasy and if it solves the problem you're mostly done.

* (Long shot) listen for vacuum leaks, which is really hard with an RC51 because of the whine and they tend to run a bit louder than a Gold Wing.

* Make sure the plug on the snout of the ram air intake is solidly plugged in and making good contact. Perhaps even disconnect it and use dielectric grease to freshen the contacts. That *might* throw a code though, so it may be moot.

* Check the air filter.

* rgv250f3's suggestion to try replacing the ignition coils one at a time is excellent but it's more work and expense than these other steps so I'd try them first.

If you're ever on a ride and you fall down, I'll be there. - The Ground
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post #5 of 6 (permalink) Old 07-28-2019, 08:06 PM
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I was goind to say for the fk of it throw a new fuel pressure regulator in also. Mine took a crap, went bad, and was dumping fuel, it was a crank/no start situation after sitting for years. But like gixxernut said, it could be the F.P. reg. diaphram leaking high engine temps...

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post #6 of 6 (permalink) Old 08-04-2019, 06:01 AM
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It occurs to me that this sounds like an oddball problem I experienced on a (fuel injected) Gold Wing maybe 20 or so years ago. I was riding through Nebraska where I noticed that "Premium" fuel was about $.10 cheaper than "Regular." I thought, "Call me crazy, but I'm buying the premium."

I might add that this was in the hottest part of summer.

So I filled up with premium and off we went. About 30 or so minutes after my bike got up to full operating temperature it started misfiring and the problem would continue to get worse until I had to stop. Since the problem started right after I'd gotten the cheap premium I assumed I'd gotten some water in the tank. So the next town we got to I went into a parts house and picked up a bottle of "water remover." I think it was Heet brand, not sure. Since the Gold Wing only had a 5.3 gallon tank I figured 1/3 the bottle would be plenty since it was enough to treat a full size tank.

But this made the problem even worse. It didn't take long at all until I couldn't maintain interstate highway speed. I pulled off at the next exit ramp (my wife was following on her BMW) and we noticed an abandoned convenience store nearby where two riders had pulled off in the shade to take a break. We pulled over and began chatting while I let my bike cool back down. As soon as I told these guys what was happening they told me what my problem was. And they were right.

Premium gasoline in Nebraska has much higher alcohol content than regular. Don't know if it's still that way or not. Alcohol has a much lower boiling point than no-ethanol gasoline. We opened the fuel tank, looked inside, and sure enough the gas in there was stirring around on its own.

When the fuel pump picks up air bubbles and sends them through the fuel line the injectors inject less (or no) fuel into the cylinders. Boiling alcohol hardly effects carbureted vehicles at all, but it can cripple an injected system. Turns out that the primary ingredient in "Fuel Tank Water Remover" is ... you guessed it ... alcohol.

Their recommendation was to stop often and top off with regular (less alcohol). Each top-off would put some cold gasoline in the tank to stop the boiling for awhile and dilute the alcohol.

We kept doing so until we were out of Nebraska and where I could I filled up with no-ethanol gasoline for that bike. It was particularly sensitive to the issue and would sometimes exhibit the problem with 'normal' levels of alcohol commonly found.

If you're ever on a ride and you fall down, I'll be there. - The Ground
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