poor running below 4000 rpm

[Z1B Alan]

After changing the carbs for the correct one's for the bike a Z1B I have cleaned the carbs checked the fuel height. The needles were set on the 3rd position from the top which acording to the Clymer manual was wrong so I have put them back to the 2nd position,I have balanced the carbs but still this problem is there.
I must say that with the needle set at the lower position the problem was much better I alterd the needle as that was what the manual said was the correct position.
The bike is standard in all aspects with new Dyna s new coils/leads/plugs/air filter.
My questions are:
1 What is the correct needle jet position.
2 The manual claims a height of 22cm of mercury should be achieved when balancing the carbs but at what revs is this at
3 What else could cause the problem as the bike runs well above these revs
4 The pilot air screws are set at 1,1/2 turns 1/4 turn out more than standard would this make a huge differance.
Any ideas would be helpfull as this is spoiling a good bike.

[kev edwards]

Hi Alan are you running standard air filters , a general rule of thumb is to have the needle on groove 3 , also are the needle jets themselves the right ones , as these may have been swapped at some time for different perfomance , with vac gauges it does not really matter if you are pulling 22 14 16 or whatever as long as the vac is the same across the bank of four , pilot srews normally 1 1/4 , also check for air leaks on the inlet stubs
do you also have the correct pilot jets in the carbs , i always check my vac at about a 1000rpm , you have fitted a dyna is it timed up properly i rushed when i put mine on and it ran like poo.

[Z1B Alan]

Kev, dyna timed up perfect, all mains and jets and pilots and needles are all of correct type. Any further suggestions?

[kev edwards]

what about needle valves are they sticking , i'll have a think about this one.

[Steve R]

22mg of mercury is at idle when balancing the carbs.

[debben1]

Hello Z1B Alan, check the springs on the auto advance unit, when these become tired and saggy the ignition bob weight flick out too early advancing the ignition too soon, often shows as poor running below 4000 rpm (after 4000 rpm the ignition should be on full advance anyway) Hope this helps, Regards, Steve

[PAULJAC47]

Hi Alan try to get a Gunson colortune (halfords)this is invaluable for setting correct mixture as you can see ignition flame in engine,sound like you have probs with pilot settiings to me! you would see this straight away with a colortune and any other jetting mix problems as you increase revs,have sotred out loads of probs on bikes and cars with mine!! Cheers Paul j...

[Al]

Hi Alan try to get a Gunson colortune (halfords)this is invaluable for setting correct mixture as you can see ignition flame in engine

Agree entirely with one additional observation.

I borrowed one and found it to be fantastic. It allow you to set a baseline datum and balance the mixture strength for all four carbs which i have noted in the manual. Something you cant do with a gas analyser with a four into one exhaust.

My issues started at that point because setting with a colourtune necessarily means a hot engine.
Believing i had it spot on i used the bike and then went hunting (and spending) for the reason why it would only start on two cylinders from this time foward when the engine was cold.

Bottom line is; when yellow turns to blue or blue turns to yellow is correct for the majority of engines i imagine. However it doesn't work for my bike with its CV carbs, big head, big bore, big valves, straight through exhaust etc etc

It should be 1 1/4turns out and will only run perfectly at about three turns out. The reason i believe it that these motors need an abnormally rich mix in the low throttle range. Mine in particular because of its updated arrangements.

Pilot jets provide 'trim' for the whole throttle range. Progressively less the higher you go in the rev range.
Up to 4 thou they are still in play albeit marginally.


AL

[Pigford]

Al: Pilot jets provide 'trim' for the whole throttle range. Progressively less the higher you go in the rev range.
Up to 4 thou they are still in play albeit marginally.

Actually, concensus of opinion says that its the slide position (amount of throttle opening) that dictates the fuel system in operation

In other words - if the throttle is open a bit (approx 0 - 1/4) the pilot system will be in operation, regardless of revs.
Likewise, if the throttle is wide open at 300rpm, the main jet will take presidence

[Al]

Likewise, if the throttle is wide open at 300rpm,

I agree Piggy ive seen you racing


AL

[Pigford]

300 - 3000