Newbie to the site, not new to 2 wheels, slight TEAPOT woes

[Stevep]

Greetings All, and thanks for having me on the site.

I've read the rules and fully agree with them, and hope not to get too much of a r(B)ollocking from admin if I screw up.

I'm stuck in Birmingham UK, been into 2 wheels since I was 9 years old, had loads, come off more times than i'd like to admit, even fell off standing still outside the garage once or twice.

All I do these days is buy, restore and sell on bikes, of all makes and persuasions, one I'm quite proud of is an old 1971 Suzuki F50 Cutlass. Given to me by a friend of my fathers, it looked like it had been sat at the bottom of the ocean for decades and took the best part of 2 years to finish it.

Here's a quick pic of before and after:

 

 

 

However, that's not the reason for this post.

I have a GSXF750, 2000/2001 model, another that I bought because somehow I liked the look of it even though it was the wrong colour in my eyes.

I've done all the work on it, valves gapped properly, cams/chain inspected, carbs ultrasonic cleaned, upjetted from 117.5 to 122.5, fitted alarm/imobiliser, calipers completely overhauled, new fluids etc etc, stripped all the body/swing arm etc and re-painted the lot with new decals.

It's all good apart from one thing. Goes well enough for a 750 but when it gets to 8000rpm.........it's like the rev limiter cuts in. Which I know it shouldn't.

First time the bike just cut stone dead, I thought that maybe the timing chain had gone or it had shot a rod or something else catastrophic, but no, after a couple of prods at the starter button off we go again. Strange me thinks.

Up the road again, 8000rpm, uh-uh, this time I managed to keep it going, until........died.

It's completely normal if I keep it below the 8000rpm mark, no mis-fires, stutters, nothing.

Side stand switch has been bypassed, new plugs and caps, coils are within testing spec across the windings.

I'm wondering if maybe the cdi/ignitor could be failing at higher rpm's?

Any pointers would be most welcome.

 

 

[clivegto]

Petrol starvation maybe, try running it with fuel tap in the prime position. 

[Jaydee]

1 hour ago, Stevep said:

It's completely normal if I keep it below the 8000rpm mark, no mis-fires, stutters, nothing.

Could be your float heights set to low. Not enough fuel being feed to the bowls at higher revs.

Edited March 1, 2020 by Jaydee

[Blubber]

Hi and welcome 

[Stevep]

Thanks for the replies.

I did think about the float heights last night in the pub actually..................I'll check the pdf for the level heights, thanks

Just checked the cdi number in case it had been swapped out somewhere along the lines, it is the correct one for the bike.

For the hell of it here's a couple of before and after pics:

 

[Stevep]

A thought just occured to me.

I remember setting the float heights when I stripped and ultrasonic cleaned the carbs. I remembered when I read the specs on them. 13mm on the 36mm carbs.

And to quote Clivegto "Petrol starvation maybe, try running it with fuel tap in the prime position."

Although having the tap in the prime position allows free flow of fuel to the carbs, theoretically the float needle should shut off the fuel flow when the bowls are full.

I know from previous bikes like the xtz super tenere that if the taps were left open it could cause a hydrolock due to fuel getting past the carbs and sitting on top of the pistons, wondering if it could do the same on this..........

[Dezza]

Nice ped but it needs black and silver plates. Is it registered as a historic vehicle?

[Stevep]

OK, this is definately something electrical.

In the garage on the main stand, let it warm up, slowly raise the revs to 8000, cut out, (single little misfire)

Won't re-start unless I turn the key off and on again.

Raised and held the revs at 7000, through to 8000, needle bounced through to 9500, died.............

Just to clarify Clivegto's thought with the tap on prime, same result.

[Stevep]

3 minutes ago, Dezza said:

Nice ped but it needs black and silver plates. Is it registered as a historic vehicle?

The rear is black and silver; as you can see from the first pic the front was black and white so I kept it like that.

I had to have it dated by the club, cost me £75 I think, for dvla's satisfaction....................robbing gits

It's a nice little 2 stroke 3 speed........now at least............

[Stevep]

PROBLEM SOLVED

IT WAS THE IMMOBILIZER RELAY.

 

Let me explain.

On some alarms it is necessary to fit a normally closed relay into the circuit for the immoblisation to be active. This is one of those alarms.

If the alarm is triggered the normally closed relay opens and cuts the ignition circuit. Then you have to switch the bike off and back on to reset the alarm.

With this, where I had mounted the relay on the frame, it was sideways; i.e. pins facing left instead of straight up or down.

With the bike coming up to 8000rpm it was producing enough vibration or resonance through the metalwork to make the relay contact open just enough to cut the ignition circuit.

How did I prove it?

I took the relay off it's holder so it wasn't touching any part of the bike, started it, revved it to 10000 rpm and it stayed there, no misfires, no cutting out.

Now I have to find a way to insulate it from any vibrations because the wiring is too short for it to go anywhere else except where I originally put it.

[Captain Chaos]

6 minutes ago, Stevep said:

Now I have to find a way to insulate it from any vibrations because the wiring is too short for it to go anywhere else except where I originally put it.

Put it in the bin.

Aftermarket alarm systems are all shit, sooner or later they stop operating in the prescribed manner. Rip it out and connect the bikes wires as original.

[Stevep]

1 minute ago, Captain Chaos said:

Put it in the bin.

Aftermarket alarm systems are all shit, sooner or later they stop operating in the prescribed manner. Rip it out and connect the bikes wires as original.

But then I would have no immoblizer on the bike, which kind of defeats the object don't you think.....

 

[Captain Chaos]

6 hours ago, Stevep said:

fitted alarm/imobiliser,

sorry, I missed this bit. I assumed you bought the bike with the immobiliser fitted.

Anyway good that you found the malfunction.

[Stevep]

Oh hell no, been down that road on other bikes and I agree, utter nightmare trying to undo somebody else's work with alarms and immobilizers.

This one I fitted, just never in a million would I have thought that this could happen with a simple relay picking up vibrations through the frame.

It's not fitted direct to the frame, it's on one of those relay "tangs" so it may well have been that allowing it to vibrate enough to trip the contact, which is something I'll try actually, fix it direct instead of on the tang........hmmmm