1 cylinder running.

[sam.arnold]

Hi All,

I've had a superten 750 for about 5 years and have found advice on this forum a few times so thank you for that. Unfortunately I can't solve the latest batch of issues so any advice would be greatly appreciated.....

This bike's first trip was 1500 miles in Europe. Known charging issues caused lots of problems, clutch cable pulled out of its end solder bit, and it ran on one cylinder for a day. Later found blocked idle (I think, the one held in by the brass fork) jet.

Chased the charging problem round the place and ended up new elextrex coils, new wiring, new rec/reg, new AGM battery.

Before lockdown it was running badly, always bogged with throttle application at low throttle. Had to park it for a few months. In frustration and stupidity I'd set the idle screw waaay too rich in November. Reset to 2.5 turns out, cleaned the plugs. It ran well last week. Nice weather yesterday so got geared up to go out, got 100m up the road running great at 1/2 throttle and then died at idle, wouldn't start. Waited 10 mins, started and just got me home but dying again.

This weekend I had the carbs off, sprayed cleaner through every orifice, all jets out. Diaphragms look perfect, slides move freely. Some limescale type build up on the needle which I wiped off. Checked float levels, a tad low but the same both sides. Changed the fuel lines so it has an in-line filter under each tap so it flows more easily. Pump has been replaced, and it has a full tank so the pressure head is enough to fill the carbs I would imagine.

Bright blue spark both sides with the plugs out (I forgot that it happily runs on 1, that gave me a fright). The plug that isn't firing always came out wet.... So maybe theres fuel? Or maybe it's the starter fluid I sent down to help it go....

Carbs are back off, am I going for a full rebuild with new jets and emulsion tubes? I've heard of them ovalling, but the symptoms seem wrong. Quite an essay, sorry! Any ideas?

[BMurr]

Could the white deposit be antifreeze? Gasket issue? A compression test might be interesting.

Scrap that, I thought you said deposit on plug, I see its needle you wrote

[Hawk]

Check your fuel and vacuum hoses - that would be my guess for causing the running problems.

Once you have eliminated fuel and spark as possible causes, you can dig deeper.

[sam.arnold]

Many thanks for the swift replies.
White/green residue, the usual old carb crud.

Compression test: 159 left (good side)
167 right (bad side)
Not sure what's normal but sounds good to me.

Fuel lines:
All lines to the pump are new, and after the pump are clear. Both bowls filling so don't think they're a problem.

Vacuum lines:
Pulse works, so I think that one's ok... Apart from the 2 chunky atmospheric lines, what other external vacuum lines are there?

I sprayed starter fluid at the boots when it was running and there are no leaks after the carb.

The only thing that worried me in the carb was the o ring round the main jet was pretty flat. Could it be leaking round that, running so rich it won't fire on that side?

Carb rebuild inbound.....

[sam.arnold]

Uh oh... That's crazy high compared the manual.



Brand new tester, out of the box. Not sure how to test the tester.

Could this be carbon build up?
These numbers make it 11.5 : 1 versus stock 9.5
Equivelent to 7cc carbon build up per cylinder, sound crazy

[sam.arnold]

Ran half a can of seafoam through the inlet. Confusing compression reading after that so I'm going to ignore it for now....

Went over the fuel system again, blocked vacuum line to the pump. I overlooked it because the pump was relatively new, and I really don't understand how that hasn't caused issues before. Anyway...

Managed a 40 mile ride and it's much better. Only issue is not perfect idle and bogging at low throttle when bringing on power. I'll put new plugs in and look at idle mixture first. If that fails it sound like 'ovalled' needle jets.
Any other thoughts?

Edit - wouldn't start tonight. What's the scrap value?

[Bowler]

Hi Sam Arnold,

what did you already do to your carbs? I would rebuild it, with new choke slides, needles and needle jets. These wear and cause rich running of the bike. I've heard stories about people having to do this every 20k km, so it's the first thing I would look at. I would also clean the carbs in an ultrasonic bath, as this tends to clean the passages in the carbs.

If the problem persists I would look at the idle mixture, but not before.

Cheers,

Timon

b.t.w. did you already check the clutchbasket springs? These tend to destroy themselves (on early S10's) and then destroy the engine.

[sam.arnold]

Hi Timon,
Thanks for the reply.

Disassembled the carb, sprayed cleaner through all orifices, all jets and metal bits spent an hour in 'ultrasonic' (a tupperware glued to a mouse sander) with carb cleaner, and overnight soak.
Replaced all gaskets and seals but not any jets or the needle. New diaphragms and slides.

The bike has done 35000 miles, and jets all look stock so might well be ovalling... They're all stock sizes and the exhaust is a slip on Laser.

I'll look at the springs. Is it worth replacing straight away? Something like this?
https://www.wemoto.com/bikes/yamaha/xtz ... heavy_duty

Anything else I should do while in there?

Many thanks,
Sam

[Bowler]

Hi Sam,

those are not the springs I mean. The clutch basket has springs on the back. This sites shows them:
https://sites.google.com/site/3ld16150/home

You don't need to change the jets, only the choke plunger, the needle and the brass part in which the needle moves up and down.

cheers,
Timon

[sam.arnold]

Sorted.
The needle jets were definitely worn, more noticeable on one side. The idle is now perfect, it pulls soooo much better. Thank you very much!