FZ750 Cuts Out When Idling & Trouble Starting

[Motorhate]

My FZ750 has a problem when idling in traffic, its runs fine when moving but standing still I have to keep a slight rev on to prevent it from cutting out. It also has problems starting at times. I always need to pull the manual choke out and sometimes it seems to flood. Its had a custom Quil exhaust stuck on it and I'm wondering whether the carbs have been jetted properly or whether its just a case of changing the air/petrol mix. I'm not that mechanically minded so any help would be appreciated.
____________________
Current - Harley Davidson FXDB Street Bob | Harley Davidson FLTR Road Glide | Harley Davidson Road King
GONE - Honda CB500 Ratbike | Yamaha FZ750 | Yamaha XVS1100 | Kawasaki VN2000 | Kawasaki ER-6 F | Harley Davidson XL883L Sportster

[Kickstart]

Hi

How many miles has it done? I would suggest checking the carbs thoroughly, partly for punctured diaphragms but also for wear in the nozzles in the carbs, especially if it has had a jet kit fitted. The down draft carbs were known to wear the nozzles oval.

However this would cause it to be rich, which might explain the flooding but odd that you sometimes need the choke to start it.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Motorhate]

Thanks Keith, I'm actually not sure of the mileage as its got the clocks from another bike, but I'd imagine its quite high. It always needs the choke out fully to start and after a while I take it down a couple of notches. Even after an 70-odd mile thunder down the M11 as soon as I was stuck in traffic it was struggling.

Its really responsive when riding and has some real poke in it, just makes me sound like a boy-racer when stuck at the lights and trying to stop the engine from dying.

I'll get the carbs checked as you mention. Thanks for the input.
____________________
Current - Harley Davidson FXDB Street Bob | Harley Davidson FLTR Road Glide | Harley Davidson Road King
GONE - Honda CB500 Ratbike | Yamaha FZ750 | Yamaha XVS1100 | Kawasaki VN2000 | Kawasaki ER-6 F | Harley Davidson XL883L Sportster

[Kickstart]

Hi

It is worth a check, but it does seem a bit inconsistent as to whether it is rich or lean.

They are good bikes.

Always worth wondering if the valve need adjusting. But they normally close up with wear, and with mine it was OK when starting from cold but became a real bugger when warm.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[jjdugen]

One of these gave me a long run-around. Same thing, ran fine at revs, tick-over splutter and running on three.
The main jet block is a screw in affair with a detachable block to hold the jets. There is a fine rubber gasket between block and carb body. This can shrink or be damaged. It leads to all sorts of odd slow speed running.
Agree that the engine is surprisingly sprightly, pity about the chassis.
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[davebike]

Yes one of those Yamaha with the Jet blocks
Carb rebuild time the weird O ring for the jet block is expensive but really needs replacing every few years now ethanol in common inn fuel

If a careful rebuild doesn't sort it off down the dyno to re jet

Dave
____________________
Dave
NC750Xdct + others at work !
[email protected]

[temeluchus]

Make sure the airbox is properly fitted and not leaking. Mine was an utter bastard unless the airbox was perfect.

Also check the carbs are clean and non leaky whilst you are loking at the airbox-one advantage of the downdraught engine is access to the carbs is very easy.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[Nobby the Bastard]

You definately have a problem. Mine starts (hot or cold) without choke and doesn't cut out or splutter ever....

This doesn't sound like valves, that'll show up as difficulty starting when cold, and no ability to rev until warm, regardless of what you do with the choke.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Motorhate]

Thanks for the replies fellas. Rode to to work this morning and the same thing. Stalled on Marylebone Road at the lights and caused a bit of a tailback before it started

Will get this seen to next week. As mentioned, there's obviously something not right at all with the carbs.
____________________
Current - Harley Davidson FXDB Street Bob | Harley Davidson FLTR Road Glide | Harley Davidson Road King
GONE - Honda CB500 Ratbike | Yamaha FZ750 | Yamaha XVS1100 | Kawasaki VN2000 | Kawasaki ER-6 F | Harley Davidson XL883L Sportster

[Robby]

I've had similar trouble recently with my XJ650. The XJ uses evil Hitachi carbs, I assume the FZ750 uses something more conventional.

Before pulling the carbs apart, check over the electrics. My problem was partially down to carbs (clogged mixture/idle system, unusual float heights, corrosion around the slides) but also down to corrosion on the earth points. Look where the coils are mounted on the frame and at the main earthing strap on the battery, take the connections apart and clean off any corrosion.

Mine would idle after that.

[Nobby the Bastard]

[temeluchus]

[Nobby the Bastard]

Your best bet to diagnose is to find someone with an FZ local to you and swap over the carbs. If that sorts your issue, then your carbs are at fault.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Motorhate]

Quick update on the bike. Took it to a garage who had a good look at the carbs etc. For starters they said one inlet rubber is letting air in so that is contributing but not the only problem. Air / petrol mix was completely wrong so they rectified that.

Basic upshot was that without dismantling the carbs it was difficult to say what the problem was. Questioned whether it was worth spending money on a bike that was so old and advised that any parts would be second-hand and without finding out the mileage on the original bike, was difficult to say how long they'd last. Also told me the wiring on the bike was a real hatchet job too. Said it would be an ideal project bike for someone with a lot of time and a garage, neither of which I have.

They got it running so as it will run on choke and start again if it cuts out. Still doesn't idle correctly when stationary but nowhere near as bad as before.
____________________
Current - Harley Davidson FXDB Street Bob | Harley Davidson FLTR Road Glide | Harley Davidson Road King
GONE - Honda CB500 Ratbike | Yamaha FZ750 | Yamaha XVS1100 | Kawasaki VN2000 | Kawasaki ER-6 F | Harley Davidson XL883L Sportster

[Fizzer Thou]

I had a Yamaha R1 4XV in the workshop the other year with exactly the same problem as the OP.The carbs checked out okay but the inlet rubbers had definitely seen better times

https://i666.photobucket.com/albums/vv23/WiNot_Rhencullen/Workshop/Picture352.jpg

I sourced new ones direct from Fowlers of Bristol at £13 each (wemoto are charging £34 each for the same part) and the owner was amazed at the difference

As for the carb jet holder seals,this link

https://www.wemoto.com/bikes/yamaha/fzr_1000_ex_up_3le/89-90/picture/carburettor_gasket_and_float_valve_kit/

shows the seal that shrinks with todays 10% ethanol unleaded petrol.This is another reason why I now run super unleaded in all of my bikes as it contains no ethanol.
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'

[Nobby the Bastard]

To check if the rubbers are the issue, wrap them in cling film. if the problem goes away, it's the rubbers...

By the way, Fowlers waited a week and a half to let me know that the throttle cable for my FZ is no longer available and they only told me becuase I rang them to ask where the fuck it was....
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050