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Discussion Starter #1
I was ridin my 86 vn750 into work today, I got on the freeway and it felt as if it lost power. I couldn't get it to go above 60 mph. I tried downshifting into fourth but that didnt help much. I had this problem a few times last year. When it happens I can pull in the clutch and hit high rpms but under a load it won't exceed 60 and if I hit an incline it won't maintain 60. At slower speeds it accelerates fine and sometimes I have no problem getting up to 90. It puzzles me, last year I replaced the plugs, wires stator and r&r. Just changed the oil. Also when it happened today the temp gauge climbed to almost red then started to come back down, I have no idea where to start. Please and thank you guys, this site has never let me down :)
 

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Prowling Tiger
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Engines do struggle to maintain power when they get hot. Might check the water thermostat and see if it is opening at the proper temp. IF not, it may not be cycling the water, thus, leading to a too hot condition resulting in power loss. Also check the fan switch and associated wires.

Does the power return when the temp drops to normal range?
 

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..have a vulcan good day!
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I was ridin my 86 vn750 into work today, I got on the freeway and it felt as if it lost power. I couldn't get it to go above 60 mph. I tried downshifting into fourth but that didnt help much. I had this problem a few times last year. When it happens I can pull in the clutch and hit high rpms but under a load it won't exceed 60 and if I hit an incline it won't maintain 60. At slower speeds it accelerates fine and sometimes I have no problem getting up to 90. It puzzles me, last year I replaced the plugs, wires stator and r&r. Just changed the oil. Also when it happened today the temp gauge climbed to almost red then started to come back down, I have no idea where to start. Please and thank you guys, this site has never let me down :)

With no load, .... RPM's rise no problem.
My first thought, one of your cylinders (spark) is dropping out (occasionally).

I would first Check / Clean ALL electrical connections/connectors partially @ Ignitor and @ coils.
And Grounds...Grounds....grounds...clean em' !

hope this helps

:smiley_th +1
 

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Discussion Starter #5
Engines do struggle to maintain power when they get hot. Might check the water thermostat and see if it is opening at the proper temp. IF not, it may not be cycling the water, thus, leading to a too hot condition resulting in power loss. Also check the fan switch and associated wires.

Does the power return when the temp drops to normal range?
I replaced the thermostat a couple of weeks ago, although maybe I got a faulty one, I think I'm going to pull it and test, also when I pulled the sensor from the radiator it has some crud build up, so maybe ill flush the radiator while I'm at it. Is there any suggestions on a good way to flush the whole system?
 

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Prowling Tiger
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I replaced the thermostat a couple of weeks ago, although maybe I got a faulty one, I think I'm going to pull it and test, also when I pulled the sensor from the radiator it has some crud build up, so maybe ill flush the radiator while I'm at it. Is there any suggestions on a good way to flush the whole system?
I'm certain here is; however, I'm not familiar with working on that part of the bike. Sorry.
 

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Jack of all trades
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I've flushed the whole system with a garden hose before. I opened the drain plug and flushed the radiator out off the bike. For the water jackets I hooked the radiator back up and ran water til it came out.clear. next I ran coolant and flushed 3 times. Seems overkill but I haven't had a cooling problem ever.
 

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Prowling Tiger
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I've flushed the whole system with a garden hose before. I opened the drain plug and flushed the radiator out off the bike. For the water jackets I hooked the radiator back up and ran water til it came out.clear. next I ran coolant and flushed 3 times. Seems overkill but I haven't had a cooling problem ever.
I wouldn't have an issue doing this; however, how does one dispose of the coolant? It's not exactly bio-friendly.
 

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Discussion Starter #10
Last night I flushed my cooling system real good. Also tested the thermostat and it is functioning good. So I rode to work today no problems. On the way home same thing, low power under load. Fine with no load. But I was quicker to observe the overheat this time. It didnt begin to overheat till it was experiencing the power problem. It is frustrating me
 

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have you looked at your plugs to see if it is running lean?

To me it almost sounds like the start of POOGS. Do you get a whistling from your gas cap by chance? was your tank about half full?

POOGS (Phantom Out Of Gas Syndrome) happens when the venting system in the gas tank is clogged and won't allow air into the tank to displace the fuel being used. around a half tank full it becomes a vacuum and prevents fuel from flowing to the carbs. It starves the engine of fuel and will run lean until it just quits.

The overheating may be a symptom and not the cause.....hard to say until you identify the exact problem.

I would suggest that you ensure the fuel cap is venting and that the vent at the bottom of the tank located under the front of the seat is clear and open. there should be a small vent hose attached to the nipple at the base of the tank that runs down under the bike. The hose should be open for proper venting.


read this LINK

You can take apart the gas cap and clean it.

You will see a nipple on the bottom of the cap that fits into an opening on the tank near the cap hinge. You can blow into that opening (or spray carb cleaner into it) to see if anything comes out the hose under the bike.
 

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Discussion Starter #13
Im wondering if that might be the case. I did have over a half tank but I have been noticing a noise coming from the front of the bike, not so much whistling but like a loud humming. I kept thinking it was the fan making a weird noise. Im definatley going to check that out.
 

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Discussion Starter #14
I dont believe my bike has the gas tank vent, in that link you sent it says 88 and on mine is an 86. Also I have had the tank off numerous times and the only think connected is the fuel valve and the fuel level gauge wires....
 

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..have a vulcan good day!
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I dont believe my bike has the gas tank vent, in that link you sent it says 88 and on mine is an 86. Also I have had the tank off numerous times and the only thing connected is the fuel valve and the fuel level gauge wires....
...my '86 tank has the same as yours. (non Calif.)

:smiley_th +1
 

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ok... older models did not have the tank vent, but they do vent through the cap as far as I understand it.
Couldn't hurt to clean out the cap.

The noise you heard might be the cooling fan. I would start it and let it idle till the fan kicks on (about half way up on the temp gauge) and take a good listen to it. It could be possible that the fan is loose or worn and making a noise (possibly slipping on the shaft). If the fan is defective it would definately explain the spike in temperature.

I still think you may have a fuel delivery issue and possibly the overheating is a byproduct. It could be that your jets are clogged.

What color are your plugs? we need to determine if it is lean or rich.
 
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