Lost power over 3,500 RPM...but only when hot. That's weird.

[SA14]

Ok, so today I was invited to the nearest racetrack (129km away - 75 miles) to celebrate a friend's birthday with a few kart laps. Can't fit a rhino into a kart so I went to say happy birthday and take the bike for a long ride. Didn't go quite as planned.

First off today was a really hot and windy day. I live near a desert and the winds were coming directly off the desert and blowing hot air across Adelaide. It got to about 36c (98F). The ride to the raceway is almost entirely along the freeway and so was at top legal speed of 110kp/h for most of the way. Started out - all went well. Then at about the 80 mile mark I gave it a bit of a hand full at about 3,500 rpm for an over taking maneuver and it almost totally died then coughed back to life but had no extra power above 3,500 rpm. In fact it wouldn't even spin to over 4,000 rpm. I thought "that's weird". So I tested it and sure enough in no gear at all no matter if I gave it a full twist or opened her up gently there was no way it was going over 3,700-3,800 rpm. Cough, dive bomb, backfiring all over the place but no dice.

Luckily enough I can sit on 110 at about 3,200 rpm ish so I was able to make it to the race track. Luckily there was a practice day on for bikes so there was bikes everywhere but I wasn't about to start walking into pits and making a pest of myself but luckily a guy waved me down. Ends up he's a 14 owner and wanted to check out my front suspension because he said he was getting speed wobbles at 100kmh. We spoke about that a bit and I asked him if he knew if there any mechanics around and he said "the track has a few putting tyres on in the first bay".

I patiently waited around and found my opportunity to ask and he said "man we're under the pump today, short staffed and bikes are lining up for tyres. No can help, sorry. So I went into reception and they pointed me back out to the tyre shed or suggested I call the local motorbike shop who asked me if I wanted to book it in for March. Blank stare. They did suggest I let it cool off a bit and see if that would help which I'm guessing is the bike equivalent of the I.T. "switch it off then back on again". By that time it had cooled off a bit. I was able to place my hand onto the engine and keep it there so I started it and head to the karting track on the other side of the course.

Of course I had to try and see how it would rev and low and behold it was working fine again and I was able to rev it to 7,000 rpm ish in 2nd gear so I thought "that's weird".

Anyway, I proceeded to watch my mate do a few laps and then it was over (great) and they left. So I zipped up and started to head home again riding gently but with curiosity. Curiosity got the better of me and when I got back onto the freeway I made sure there were no cars within site in either direction and let it rev to 8,500 in second gear then quickly changed it up to top thinking "that's weird".

Didn't last long, for the first 10 miles it revved and performed as normal but then it burped at 3,500rpm and I had to nurse it home the remaining 60 miles changing gears at 3,000 no matter what. It never recovered and I even gave it a few free revs at the lights when I got back into town and no way would it even free rev over 3,500. I thought..."that's weird" so it's not a load thing and yet it behaves exactly like a load thing. Free revving test proves it's not a load thing.

Under 3,000 rpm - fine. Over 3,500 coughs and splutters and cuts power.

Got home but now the tear down begins. Where would you start? I'll remove the tank and check the plugs. I was able to check the leads on the outer two cylinders but without proper tools wasn't in a position (or mood) to remove the tank on the side of the road (or at the track) but I would've if I was stranded as I have the standard pressed metal tool set and a Leatherman Wave which I always bring with me.

I'm thinking fuel pump, filter...etc but why only when hot? Wouldn't that prohibit it from revving when cold or just warmed up? I consulted @Throttle and he suggests start at plugs, maybe leads, maybe coil packs. But there's a lot of maybes. The thing is I'm going to have to get it pretty hot to replicate it again (I'm guessing) so what fails that badly when hot?

Weird.

[SA14]

P.S. Saw a BMW 1,000(?) RR. $53,000 worth of bike according to the father who's son had just bought it (cash). Father was the 14 owner who approached me and flagged me down. Very intimidating looking bike. Those who know it (I didn't) will know what I mean.

[steve porter]

Fuel pump or filter wouldn't generally be such a definite specific cut off at the same revs, sounds electrical to me.

[Irish in Oz]

Check your battery is getting full charge from the alternator.

[Del]

Possibly camshaft position sensor - mine did something the same and coughed farted wouldnt rev but wasnt as bad as yours as mine cleared almost straight away

[SA14]

Fuel pump or filter wouldn't generally be such a definite specific cut off at the same revs, sounds electrical to me.

That's what I thought but only high tension stuff or maybe deeper into the magneto or timing side? Plus if it was the fuel pump or filter I'm guessing I probably wouldn't get it to ever rev to 8,500 under load hot or cold or might the pump also be affected by heat?

Check your battery is getting full charge from the alternator.

It's a brand new AGM battery done less than 1,000km and less than 6 months. Not familiar with checking charge; is that multi meter and see if it's getting 12v at revs? I'd have to replicate it by riding around until it does it then quickly whip out the multi meter I guess.

I forgot to mention, I put BP91 in this time (and last time) and last time I added some Wynns fuel injector cleaner (appropriate amount for 20 litres but no, not the good stuff, just the retail version). I'm guessing this tank would have had very little left as I filled this morning with just one bar on the gauge.

Also forgot to mention by the time I got home it was ticking pretty loudly. No imagination this time, definitely extra tappety. Could be shims but could also be something else.

[SA14]

Possibly camshaft position sensor - mine did something the same and coughed farted wouldnt rev but wasnt as bad as yours as mine cleared almost straight away

Mine definitely stayed bad. I should go out for a ride again to make sure it's gone when cooled down but I'll check the easy stuff, loose spark plugs or leads come off. Check all my vacuum hoses and have a general feel around.

[SA14]

Oh and I just remembered, I did a test from a lower rev range and gave it a hand full from 2,500 - same thing, no go. So it's not entirely rev dependent. It's also load dependent from lower revs. So below 3,500 any heavy throttle and it chokes. I can ride it normally at normal acceleration up to 3,000 ish but after that, heavy or light load and it chokes.

I also stopped and flipped the petrol filler open in case the breather was blocked and creating a vacuum but nope. Didn't change and didn't hear an pssss when I opened it.

[steve porter]

Worth checking the filter then, my teabag was blocked and it wouldn't take  handful, but I could gently get the revs up

[SA14]

Worth checking the filter then, my teabag was blocked and it wouldn't take  handful, but I could gently get the revs up

Would heat affect it like this though? My first thought was fuel filter and teabag but when it revved nicely when cooler I was perplexed. Figured it would never let it rev if it was blocked, hot or cold. Could be wrong. Do you think it's worth draining the fuel and filling with 98 again? I'm guessing nah but I'm still a noob at this (despite your caliper victory...lol).

[Hooli]

Oh and I just remembered, I did a test from a lower rev range and gave it a hand full from 2,500 - same thing, no go. So it's not entirely rev dependent. It's also load dependent from lower revs. So below 3,500 any heavy throttle and it chokes. I can ride it normally at normal acceleration up to 3,000 ish but after that, heavy or light load and it chokes.

I also stopped and flipped the petrol filler open in case the breather was blocked and creating a vacuum but nope. Didn't change and didn't hear an pssss when I opened it.

That does sound like blocked fuel filters to me.

Maybe the crap in there isn't solidly stuck to the filter material & takes a few miles to block up, then falls off when you stop. Which would match you 'only does it when warm'.

[Del]

Had a thought (it hurt slightly) have you checked rectifier/regulator and I know you have changed the battery but have you checked teh charging to see if it is over charging and this my be causing issues with the rectifier/regulator

I know you did a bit of titivation on the bike did you disturb any earths

[SA14]

Had a thought (it hurt slightly) have you checked rectifier/regulator and I know you have changed the battery but have you checked teh charging to see if it is over charging and this my be causing issues with the rectifier/regulator

I know you did a bit of titivation on the bike did you disturb any earths

I did replace the side covers. Reckon that might have disturbed something that's eventually come loose? I'll head in there if I don;t find anything obvious or find my fuel filters are dirty. Not sure how or what I'd check but I'll cross that bridge when I cross it. Something's been making a whining/whirring/spinning/humming sound for a long while lately after a ride when I get home. It sounded like a noisy radiator fan but that's never come on even on the hottest of days (like today). I think this is all related but only some sherlocknessness will reveal it's true identity.

Oh and I just remembered, I did a test from a lower rev range and gave it a hand full from 2,500 - same thing, no go. So it's not entirely rev dependent. It's also load dependent from lower revs. So below 3,500 any heavy throttle and it chokes. I can ride it normally at normal acceleration up to 3,000 ish but after that, heavy or light load and it chokes.

I also stopped and flipped the petrol filler open in case the breather was blocked and creating a vacuum but nope. Didn't change and didn't hear an pssss when I opened it.

That does sound like blocked fuel filters to me.

Maybe the crap in there isn't solidly stuck to the filter material & takes a few miles to block up, then falls off when you stop. Which would match your 'only does it when warm'.

Makes some sense, If nothing obvious comes after checking all the plugs and leads (how do I check the coils?) I'll be delving into the tank which is something I've been meaning to do since buying the bike as you know it sat for a very long time and I think we'd all be really surprised if they were clean.

Keep the suggestions or things to check off coming. In the meantime I'll suss out the plugs and leads. How do I check them at home? What tools do I need? I'm guessing a multi meter will be able to check for lead continuity but how does one stress test these items? Trial and error? Or is there a better way?

[Hooli]

That loud humming is also typical of blocked fuel filters as the pump is working harder.

[Big Phil]

Hi Baz,
           First thing I would personally look at are the spark plugs themselves. If you have fuel starvation, an ignition fault or overheating the colour of the electrode and insulator will look burnt. Check the back of your Haynes manual and it describes what to look for. It could just be as simple as the plugs need changing or cleaning.

Good Luck
Phil