Wont idle when hot, cuts out on throttle, seems rich … any ideas? - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 11 (permalink) Old 10-31-2011, 06:39 PM Thread Starter
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Wont idle when hot, cuts out on throttle, seems rich … any ideas?

My UTV with RC51 SP2 motor is acting up after doing great once electrical bugs were worked out (I think!). It’s the beginning of the sand dune season and first ride started not doing so well. Ran perfectly for first part of ride of say 30 minutes. Then still seemed to be doing ok but it died on me shorly after putting clutch in to come to a stop. We rested 15 minutes or so and then still seemed to be doing ok power wise but when stopping continued to die and became difficult to start it and get going. Let it sit a good 30 minutes and then it was really having tough time starting, wont idle at all, and was cutting in and out a bit when on the throttle. It seems like a heat thing and it was a hot day in the 90’s but my temps seemed about where they have always been ~207-219.

I am stumped as again worked great last time a couple months ago and when first ran this time. Only thing different that I am curious about is I put new exhaust clamps to hopefully hold header to mufflers better but each does have a good amount of leakage bypassing the mufflers. I noticed when it is hard to start it does have some black smoke but only when starts up and perhaps because I have to give it throttle to start. Let it sit for a day and in cooler temps started it back up to get on/off trailer and it idled for a while but did eventually die. Any chance an exhaust leak has changed my Power Commander mapping it is just really rich and could perhaps be causing this or similar and jacked up the spark plugs? Either way need figure out something to stuff in clamp or similar to get a good seal as its really loud now (not that it was ever quite).

Maybe the fuel pressure regulator or my UTV fuel pump?

Will probably just take it in and get it back on dyno/to my mechanic to figure out as no clue where to start but got the feeling it is something fairly obvious. Any ideas?

Polaris RZR with an '04 SP2 transplanted in it. Chain driven through a gear box with axles and CVs. The only thing left stock on the RZR is the frame and plastics . But, the frame is beef'd up too .
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post #2 of 11 (permalink) Old 10-31-2011, 07:55 PM
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Pull the vacuum hose to the pressure regulator diaphragm and see if fuel drips out.
If so, it's the pressure regulator.
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post #3 of 11 (permalink) Old 11-06-2011, 01:54 PM Thread Starter
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Starting to narrow this down ...

1.Got some exhaust tape and have a good seal on headers to mufflers again.
2. Installed fuel pressure gauge and I do appear to be right about 50 PSI plus or minus a few PSI. I do see that the analog gauge pressure needle vibrates around a couple PSI at a high frequency. I assume this is just vibrations and/or since it is flowing rather than a static pressure or should I be concerned?
3. Checked my Power Commander and it did not loose its map and seems to be ok.
4. Ran the engine for a little while, shut it off, and pulled the vacuum line on the fuel pressure regulator. No fuel flowed out of it or the nipple but the line did look a little moist. The nipple then slowly started to drip fuel. So regulator is bad, correct ...should never see any hint of fuel? If so, just change it and am good or is there other cleanup to do as I see it T's into other vacuum connections? Does it seem there was just a bad run of these regulators and once replaced are good for life in most cases or is it something that genrally fails every few years, etc? I have easy access to change it ... any tips to changing it or very easy? Thanks ...

Polaris RZR with an '04 SP2 transplanted in it. Chain driven through a gear box with axles and CVs. The only thing left stock on the RZR is the frame and plastics . But, the frame is beef'd up too .

Last edited by twvette; 11-06-2011 at 03:01 PM.
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post #4 of 11 (permalink) Old 11-06-2011, 05:03 PM
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These fuel pressure regulators have come up in more threads than I can think of. It's just a thing with most FI Honda's. I've been through 2 of them. One on my VFR, on on my RC51.
From what I've read in your post, I'm pretty comfortable saying, just change the FPR and you'll be right back to normal.

Here's what I found when I pulled my vac hose the last time I suspected my FPR.

If you pull your vac hose, turn on the key for a moment while the fuel pump primes, then be ready to shut it off, a bad FPR should leak like this.
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John, 2000 RC51 #000100

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post #5 of 11 (permalink) Old 11-06-2011, 11:14 PM Thread Starter
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Yep, looks like mine. Got one on order and will keep a spare. Will change the spark plugs too just incase. Thanks.

Polaris RZR with an '04 SP2 transplanted in it. Chain driven through a gear box with axles and CVs. The only thing left stock on the RZR is the frame and plastics . But, the frame is beef'd up too .
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post #6 of 11 (permalink) Old 11-18-2011, 08:12 PM Thread Starter
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Changed the fuel pressure regulator and the spark plugs. It fired INSTANTLY and ran smoother than it it ever has especially since it has traditionally been cold blooded and needed to warm up until it would idle without the fast idle/choke pulled out ... not anymore ... it seems to be loving life but wont know for sure until can drive it this week but signs are very good.

My spark plugs were extremely black. It was dyno tuned last year when it was running ok but honestly not sure if the fuel pressure regulator was perfectly ok then either, but I should be as close as reasonably possible in theory with my Power Commander map. Does the fuel pressure regulator going bad explain why I might have gone so rich in any way? Just curious if maybe I didnt have two problems working against me at the same time and might want to get it on the dyno again if slightly bad fuel pressure regulator effect the map.

Polaris RZR with an '04 SP2 transplanted in it. Chain driven through a gear box with axles and CVs. The only thing left stock on the RZR is the frame and plastics . But, the frame is beef'd up too .
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post #7 of 11 (permalink) Old 11-18-2011, 10:07 PM
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There have been examples of fuel pressure regulator failures where raw fuel was dripping from the mid-pipe joint.
So the answer is yes, it's possible.
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post #8 of 11 (permalink) Old 12-03-2011, 11:54 AM
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Maybe unrelated to your issue but since you have plenty of space to do so have you thought of an oil temperature gauge? How is your oil cooling/capacity being handled for your type of use?
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post #9 of 11 (permalink) Old 12-03-2011, 12:52 PM Thread Starter
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Running good now with new fuel pressure regulator and plugs.

I think the stock oil cooler is being used. There was one with the bike correct? I see the builder installed a small radiator looking thing behind my stock stock RZR radiator for coolant so I assume that's an oil cooler. Gauge is not a bad idea but likely not add that.

Polaris RZR with an '04 SP2 transplanted in it. Chain driven through a gear box with axles and CVs. The only thing left stock on the RZR is the frame and plastics . But, the frame is beef'd up too .
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post #10 of 11 (permalink) Old 12-03-2011, 01:54 PM
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Quote:
Originally Posted by twvette View Post
Running good now with new fuel pressure regulator and plugs.

I think the stock oil cooler is being used. There was one with the bike correct? I see the builder installed a small radiator looking thing behind my stock stock RZR radiator for coolant so I assume that's an oil cooler. Gauge is not a bad idea but likely not add that.
Yes these bikes come with oil coolers.
The hose fittings are on the left side near the alternator.

If you want to use different oil coolers, you can buy fittings with AN-6 male fittings from TygaUSA.
http://www.tygausa.com/en/thermae-ra...-fittings.html
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