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I have an SP-1 with about 10,000 miles that I bought used in 2005. I hadn't ridden it much in recent years, so I went through and freshened everything up. I had never had an issue with it running. Now after it heats up (10-15 minutes of riding) the idle drops and eventually stalls. When this occurs I have to pull the choke and open the throttle 1/4 to 1/2 turn while thumbing the stater to get it going.

The other day I checked and replaced coolant. Coolant is circulating fine. Then a day later figured I'd start it and make sure the fan is kicking on when supposed to. Got it up to just under 220F and the rpms slowed and eventually stalled. I pulled the choke and stated it. Just past 220F the fan kicked on and the temp dropped to 190 pretty quickly, but the bike still wasn't idling properly. So I guess coolant temp isn't the issue.

Anyone have any ideas?
 

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Discussion Starter #3
LDH, thanks for the response.

I have not replaced the fuel Pressure Regulator.

I don't know that 190° is the magic number or if it is time thing, but after running for 10 minutes or so RPMS gradually drop from 1,000 at idle to stall.
 

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Maybe you have your idle set too low. From your description of dropping off from 1000 rpm and dying.
At 180 or above, set your idle to 1300.

Check your fpr for a leak at the vacuum line, it sounds highly suspicious to me. I'd probably install a new one.
But it's weird that you give it some choke to restart. A bad fpr usually dumps extra gas into both throttle bodies which causes a mild flood and stall at idle.
Check the vacuum line to the fpr is not leaking.
 

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I have just restored an Sp1 to full running condition and have posted on anther thread recently. Replacing the Fpr was the final successful step. Easy to test and replace as per Jondog’s post. Thanks to all on this forum for sharing,it has been a fund of information for me.
 

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Just past 220F the fan kicked on and the temp dropped to 190 pretty quickly ...
I agree with the others, it is most likely your FPR. However, I would like to comment on your temperatures. Unlike the SP2, the SP1 uses a Fan Motor Switch to activate the radiator cooling fan. Over time, the internal resistance of the switch changes altering the temperatures at which the switch opens and closes. Per the shop manual, the switch should close between 208 - 216 F (fan turns on) and reopen between 199-207 F (fan turns off). If your fan is not turning on until past 220 F and doesn't turn off until 190 F you should replace the switch. It's fairly inexpensive and easy to change, especially since you will have everything apart to check/replace the FPR.

jondog9, with regards to the "choke;" given that the bike is fuel injected I don't believe the "choke" is actually a choke. Though I am not certain, I think it is actually a manual idle control. By pulling out the "choke" he is actually increasing the idle by opening the throttle body butterflies slightly. Thereby leaning out the fuel/air mixture, not enriching it as an actual choke would. This is equivalent to partially opening the throttle as he describes. And, yes, I know, even the owner's manual and the shop manual refer to it as a choke. There is even a small choke butterfly stenciled on the knob. Correct me if I am wrong, but to the best of my recollection there are no choke butterflies on the throttle body itself.
 

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They're enriching circuits , just like a carb , it opens a fuel passage..
So it is indeed a choke, despite the engine being fuel injected. I always assumed that the enrichment was done by the ECU via an extended pulse duration to the fuel injectors. But now I see how the enrichment is done in addition to the injectors via the mechanical enrichment circuit. Thank you for clarifying that, Joe XR.

jondog9, that goes back to your comment about the choke. The bike should indeed be easier to restart after being flooded by the faulty FPR with the choke fully closed.
 

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A choke has a plate to restrict the inlet of a carb to pull up more fuel , an enriching circuit opens a fuel passage and is NOT a choke.
 

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... an enriching circuit opens a fuel passage ...
So it simply enriches the fuel/air mixture by introducing additional fuel to the throttle body. That would explain why there is no choke butterfly.
 
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