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Help needed carbs ?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

Guest
Greetings and felicitations, alas, alack and woe is me, I'm in need of succour and advise

I bought the bike as a project, it came in a lot of boxes that had been stored outside for about 4 years,
it was in a pretty sad state, GS1000 engine, a GS750 frame, wheels and forks and very little else. After
a great deal of work and even more money I finally got a running machine (sort of) good enough to get
through the MOT anyway. But I still have a couple of problems (possibly related) that have me perplexed.
I have trained as a mechanic and have had bikes before but that was 40 years ago so Ive forgotten a hell
of a lot since then and they were a lot simpler (single carbs etc) anyway the areas I need help are:

1) The bike is running pretty rich, dry black sooty plugs, I've got a 4in 1 exhaust and K&M filters, I believe
its been jetted for the filters (have no history or info on bike) the main jet is a 115, after having the carbs on
and off about 50 times and trying almost all conceivable combinations of fuel levels and needle settings, the
combination the moment gives the best "on road" performance but something is not right.all other combo's
have made it worse.the float level is at a midrange setting of 24mm the needle is at centre setting, couldn't
get hold of any gaskets so made my own out of a piece of leather (tried cork and gasket paper but they
didn't work too well)

2) When I tried a vaccuum gauge on the carbs the needle was bouncing about like a demented yoyo and not
a stable reading as would be expected, The suction at the carb intakes is incredible you can really hear the air
sucking into the filters, I'm pretty certain (after a couple of attempts) that the valve timing and the gaps are correct
(unfortunately1/2 the plastic bit on the exhast camshaft was missing - the bit with the timing mark of course) valves
have been cleaned and ground in and the sims are gapped well within spec.

Anyway apart from these two problems the bike isn't running too badly apart from a top speed of around 65mph
and no power on acceleration (slow) no missing, no backfiring through exhaust or carbs so I 'm pretty sure the valve
timing is correct, static ignition timing is spot on, I've tested all the transistors and chips in the electronic electronic
ignition (Newtronic system) I added a couple of LED's to assist in setting up the timing, and I rewired the opto sensors,
the plugs are gapped correctly there is a reasonable spark though I think it could be stronger (little too white and
not enough blue for my liking)

So its either fuel too rich or not burning properly (weak spark ?) I know about the mixture adjustment (side of carb
to the back slightly angled from top) this is set about 1 1/2 turns out at present, But there is another screw underneath
at the front (pilot adjustment ?) it was originally set at 2 turns out is this about right ???? (I need to know about this setting
before I start lashing out a fortune on new jets or whatever) any help would be reeeeally appreciated.

Congrats on a great site but could you use a few 'carriage returns' now and then, so we don't have to scroll sideways
half dozen times (just a suggestion no offence meant)

Cheers and happy biking to all.
 
Sounds like you have VM26 slide type carbs so it would be 78-79 motor. Stock spec for GS1000 are
float height 23-25 Air screw 1.0 Pilot air jet 1.2 Pilot jet #15
cutaway 1.5 needle jet O-4 jet needle 5DL36-3 main air jet 1.5
Main jet #95. As far as the cam timing RECHECK IT
The arrow 1 on the ex cam should point flush with the joint surface of the cyl head, the mark #2 should be pointed straigth up Count the chain roller pins towards the intake camshaft starting from the roller pin directly above the #2 mark exhaust and ending with the 20th pin directly above the #3 on the intake cam
 
I had a similar problem last week (in fact still have it, just have not fixed yet!). I think it is the rubber o rings giving up on the pilot screws and possibly the choke circuit. It was running ok, then started runing richer down low, intermittent problem, now it runs terribly. Complex devices those carbs whne they play up, unappreciated when they work....

Also check out the basics as suggested above.
 
been tampering with pilot adjustment last night took it down to 1 turn out plugs a lot better dark but not sooty performance still sluggish but somewhat better just a case of getting all the settings working together
going to try raising needle today see what happens.

Pretty sure got the valve timing correct as I say the timing marks have broken off so its been a bit of extrapolation to determine where they should have been.

It is an early 79 engine as far as I can tell
 
Broken off? They are usually stamped into the Cam, near the edge of the chain sprocket. Like it was said above, from the right side of the bike, Ex. Cam-1 is even with the surface, 2 is straight up, 20 pins to #3, which is on the intake cam.
 
Do you have mechanical advance weights, and are they advancing the spark?
 
Interesting problem,

what kind of exhaust are you running and are you sure the main jets aren't bored out more than their original size?

Do all 4 downpipes get hot when running?

The 1000 should be good for about 130 mp/h top speed not 65 :!: The mechanical advance sounds like something to check indeed like Nert said.
 
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