Power drops/cuts after engine warms up 10 minutes 1994

When were the valve clearances checked, if tight when it gets hot the valves that are tight won't close causing power loss and burnt valves.

 

Here's some pics of my 2006 GS500F I bought cheap after the guy cooked a rod bearing going uphill low on oil. All valves were tight never checked with 27k miles, the rt clyinder ex valve had zero lash cold so when hot the rt cyl had no power the left did all the work till the rod bearing failed. I rode it before tearing it down cold it was ok, hot power loss and knocking from 4k rpms up.

 

If no other problem is found a compression test hot might reveal a tight valve (no clearance hot) and compression loss.

 

you said that you had done major electrical work due to issue of rodents liking insulation......some circuits are temp controlled. If it is a heat thing, like water temp getting to say 170F (this is wrong and will be different, it is a "for if" idea) where the fan is supposed to come on, it may be shorting to the frame or adding power (like on the pulse generator line) where is shouldnt be.

I agree that crap in the petcock, filter, carbs, lines could be the culprit, but I would be leary of the electrical. The fuel stuffs is easy and quick to check, so after a hot compression test(to make sure your not leaking) id start there. but then again, there are way more qualified ppl here

 

yes dont rule out the fuel pump. it is electric yes?? not familar with the older ones.
I had the same problem as you discribe for 4 months on my 87 FZ700, I tested the fuel pump many times and it always ckd out fine... untill that is 4 months later when it died for good.
In the mean time I went nuts try'n to figure out what was wrong and it only did it when it was hot.
I would try to simulate the problem while staying close to home and your tools. once the bike dies pop off the fuel line between the pump and the carbs and see if it is pumping, this is the only way to rule out the pump 100%
good luck and keep us posted.

 

Ok,
Drove the bike around for a while, 30 minutes in first through third gear without incident....though the throttle felt a little "off". Took choke to start.
Nothing wrong at all but it is 30 degrees cooler today than thursday.

Took it apart to change the rear coil bank and look for anything obvious.

When I went to pull the right rear plug, it literally came off in my hand with feather pressure. The crappy mechanic before the last one had fitted a "used" plug wire that looked ok but was hanging by a thread.
I have not road tested yet but started it first turn without the choke. The idle has settled about 300 lower where it is supposed to be as well.

If all goes well on the road tomorrow - - - - - - YOU ELECTRICAL GUYS WIN.

If not, compression test hot!

Thank you all for your help. I will post back after the real test-drive.

 

oh.....I cleaned my Petcock and hoses too. So you Petcock guys could be right too. There I said it,,,

 

The symptom you describes are those I had on a 84. When hot it was loosing what looks as half it power. In fact it was running on 2 cylinders. Problem was one of the pickup coil. They are in the engine, with heat an expansion, the circuit opens, no longer providing its pulse. On the vf1000f one of the pulse, after the going through CDI boxes) also feed the tacho, the other feeds the fuel pump. In my case, the tacho going to 0 while the engine was still running helped diagnose the problem. This being said, I am not sure of the design or wiring of your model.

 

Exactly what I was getting at in my earlier post. In cases where the ignition subsystem that controls the fuel pump fails, first the bike begins to run on two cylinders...then it begins to run out of gas and just plain dies. This scenario isn't that rare. It's very easy to misdiagnose this as a fuel problem, and have seen many people do so and spend 'megabucks' on parts that aren't needed.

Anybody that's spent much time working on Honda's knows that pulse generators are the most common ignition component failure (besides fouled plugs). Often they fail when the bike gets hot, then five minutes later they start to work again. You can see this in a resistance test...but you only have that five minutes to diagnose. Matter of fact when this happens, you can watch the resistance coming back with an ohmmeter (you'll probably be sitting by the side of the road) and know exactly when you can restart the bike.

 

I am going later today for the road test....

Take and ohm meter with me and check resistance over what connection? Yellow/black wires coming through the V and to the right side of the bike?

BTW, these wires were rodent damaged and had to be soldered.

Mark

 

Refering to manual now for Ignition system inspection p256.

I am going to try to make it have symptoms, then limp home and check the system right away. The Ignitoin pulse generator spec. is at 68deg F.... They are refering to ambient I assume, not enging.

 

UPDATE-

No longer have the symptoms of losing power - Ran for 30 minutes at highway speed and it runs great.

NEW PROBLEM-
Now I have completely lost idle. It will not idle at all.

SOLUTIONS? -
1. Adjust idle, as it was probably adjusted with a bad spark on that cylinder?



What problems does this new update rule out?

Thanks guys, almost there just in time for a great riding day tomorrow... 61deg and sunny all day.

 

Adjust idle with black knob.

make sure your throttle cable is loose enough to have some freeplay at grip.

 

Black nob wasnt doin it. Gave it a try several times but it was a no go?

 

Regarding idle...possibly slow jets clogged from remnants of matter in fuel system? Feather the throttle and slowly apply choke, if it seems to run better this is likely. Also try to trace idle speed knob to the throttle valve pulley (throttle cables hooked to it) turning the idle knob should allow the pulley to turn slightly. Careful with the knob turning counterclockwise, it can become unscrewed from the 'boss' that it's threaded into, in which case it would be useless, without rethreading into the 'boss'. This can be difficult sometimes.

Regarding pulse generator testing...find the small harness coming out of the right engine cover, follow it to its connector. It should be a 4 pin with (usually) yellow, yellow/white for one PG. , blue, blue/white for the other. Unplug it and test the two similar color wires for resistance (engine side of connector,total of two tests)...probably gonna be somewhere between 100 and 400 ohms. If your bike fails again, quickly make the same test. What you're looking for is a VAST difference in one or the other test...like mega ohms. If you see this that pulse generator has certainly failed. Since it's unlikely both would fail at the same time, you can compare readings from one PG to the other. You could also just do a quick spark test with a spare plug to help narrow the problem to ignition or fuel...or other unlikely cause.

Hopefully whatever you did before fixed your bike already...what's with that idle though?