URGENT TECHIE HELP NEEDED guys..It's driving us nuts!!

[Anotherbikerbabe]

right, first off, Sorry if this has been asked before, I have scoured through the 'fuel starvation' posts of old..Dave bought a VTR last Sept when he was working away in Africa,wasn't bothered too much as wasn't here until after October full time. It hasn't ran right from day 1 but the main problem is: It runs fine under normal speeds up to 65mph, then anything over 65 for more than 15 seconds, the engine cuts out.Sometimes, just before it cuts out, it feels as if it drops to one cylinder..Throttle off,leave it to drop down to below 60 again, engine starts up after a few seconds.
We have tried:
1) Carbs done..
2) Tank emptied,cleaned etc
3) Changed ICU
4) Replaced float needles
plus few bits more, he's thinking now it could be something to do with the diaphragm in the fuel tap or valve springs????

THIS is doing our heads in so if anyone out there has had a similar problem, please speak up and help as it is now fast becoming the biggest pain in butt! (NOT my bike pictured) If anyone wants to speak to Dave direct, please pm for his number. Mucho thanks .....
P.S Thinking the vacuum isn't strong enough to pull the diaphragm open for the increased fuel needed at prolonged periods above 65mph so it's just using what is in the float chamber and cutting out because it's empty,then after a few seconds, there's enough fuel back in the carbs to start the engine again!!! ??? proper head shed!!

[Wicky]

Coils?

[Anotherbikerbabe]

It's running normally up to 65mph without a blip so he doubts it is the coils wicky...

[turbo_billy]

Just a thought but could be the fuel tank breather being blocked. Try running the bike up to speed with the fuel cap open (obviously not with a full tank) and see if the problem remains. Or ride normally, wait for the bike to cut out and open the fuel cap and see if you get a rush of air in. Worth a shot

[Anotherbikerbabe]

Just a thought but could be the fuel tank breather being blocked. Try running the bike up to speed with the fuel cap open (obviously not with a full tank) and see if the problem remains. Or ride normally, wait for the bike to cut out and open the fuel cap and see if you get a rush of air in. Worth a shot

Thanks TB but,yep, we've also tried that, he rode down the dual carriageway with the fuel tap open......It's not that either...

[Wicky]

It's running normally up to 65mph without a blip so he doubts it is the coils wicky...

http://www.ehow.co.uk/list_7247427_prob ... coils.html

Coil Wires and Intermittent Miss
One symptom of a faulty coil will show itself with an engine that misfires occasionally, bogs down and starts up again, or cuts out altogether.

Failing that check that the carb rubbers into the block haven't perished and are leaky as that can cause odd running.

[Anotherbikerbabe]

It's running normally up to 65mph without a blip so he doubts it is the coils wicky...

http://www.ehow.co.uk/list_7247427_prob ... coils.html

Coil Wires and Intermittent Miss
One symptom of a faulty coil will show itself with an engine that misfires occasionally, bogs down and starts up again, or cuts out altogether.

Failing that check that the carb rubbers into the block haven't perished and are leaky as that can cause odd running.

Thanks Wicky, he'll take a look at the link and he said he's looked at the carb rubbers and they aren't perished..It's a real pain as a process of elimination and VERY frustrating! Cheers for the advice

[Kev L]

What revs are you hitting at the speed it misfires? It couldn't be the timing being set 180 degrees out, could it?

[lloydie]

Has it had the air tray removed ?
It's the black plastic tray that fits behind the head stock under the carbs.

[Anotherbikerbabe]

What revs are you hitting at the speed it misfires? It couldn't be the timing being set 180 degrees out, could it?

Thanks Kev, its 4000rpm n above and he's had covers off, checked timing the lot,that's all good, Dave knows all about the timing etc it aint that!! Short burst of 80-90mph it's ok, it is more than the 10 seconds and it's goes!!

[lloydie]

Air filter blocked enough to stop prolonged high revs

[Anotherbikerbabe]

Air filter blocked enough to stop prolonged high revs

...nope, air filer is fine too!! Thanks

[mattycoops43]

I am new to VTR's but ridden for years,

Got to be honest, starting to sound electrical to me, I think I would try swapping a set of coils to eliminate that. The behaviour is exactly what you get when battery is not charging and the voltage drops down, it can't provide enough current to supply the coils over a certain rpm.

can you swap coils with someone else to try it? if it's not that, I would check your charging voltage.

[sirch345]

Tracy, I would definitely check out the tap diaphragm as you said about. What about the diaphragms in the carbs? have they been checked for a split, also have the jets in the carbs been blown out when the carbs were done?

Chris.

[the exile]

Firstly, the bike looks bloody lovely. Like the white on the belly pan.
Any-hoo, my wifes Ducati Monster S4 (sorry) started to run like a sack o' poop, particularly at higher revs and after many fears it turned out to be the regulator/rectifier heating too much and not giving the correct voltage to everything; engine, lights, dash etc. It's a real simple check, plug your optimate type thing or a volt meter and run the engine on your drive until it gets hot ( 10 mins should do it ) and if the voltage drops or is lower than 12.5 ish then it's not doing its job.
Just an idea anyway and costs nothing to check.
Good luck
Ged