Won,t run off choke

[BFC]

Recently bought a wreck of a Z900A4. Starts ok but won't run at all off choke and cuts out altogether when the throttle is opened. I've checked the fuel supply and removed and cleaned the carbs. All appears ok. Having said that I didn't check the float heights. Would too much fuel in the carb bowls result in the above problem or should i be looking elsewhere? Any advice gratefully received.

[Steve S]

Sounds like lack of fuel to me,with choke on it gets lots of fuel,opening the throttle tends to cancel the effect of the choke and lets more air in.

[DogsbolloxofZ1B]

1. Has this bike ever run properly?
2. What's different now between when they last ran properly? i.e. Been laid
up for a while.
3. Have you done the basics?
i) Adjust the air-screws to basic settings.
ii) Adjusted the slide heights to basic settings.
iii) Float heights, as you say
iv) Insufficient airflow across the needle & its jet, this results in a low
vacuum and can't draw sufficient fuel into the airstream. Are the
needles set on the correct notch & main jet correct size?

Just a few pointers for starters.

Mike

[GEZ635]

I would check the pilot jets and make sure they are not blocked as well as air screw settings, needle settings etc. Might as well check your timing as well while your at it.

[Rich]

blocked pilot jets and emulsion tube holes?

[BFC]

Thanks for your help chaps. Apparently the bike was kept under a tarp in a garden for a couple of years.Running ok previous to that.

I've checked/adjusted and cleaned all jets. adjusted float levels. Checked slides. All appear to be in good condition and adjusted properly. I've also checked the fuel supply which is also good. Bike starts quickly with a couple of kicks. As much as touch the throttle and it cuts out immediately. Taking it off choke has the same affect.

Think i'm missing something blxxdy obvious.

[Russ]

Hello matey,
I think we discussed this at the meet a couple of sundays ago you may remember me. OK here goes; choke picks up fuel from the bottom of the float bowl through a drilling. Now if the float levels are too low the engine will flood with air when opening the throttle. So more likely the floats are set too low. The fuel level in the float chambers needs to be within 10mm of the joint face with the main body of the carb to work properly. That is the whole emulsifier tube assembly needs to be submerged in petrol to be effective. Now I have a special tool so that you can measure the level accurately in situ and I'm happy to lend it too you if you like. I'll bring it too the next meet if you want it. PM me..........Russ

[BFC]

Hello matey,
I think we discussed this at the meet a couple of sundays ago you may remember me. OK here goes; choke picks up fuel from the bottom of the float bowl through a drilling. Now if the float levels are too low the engine will flood with air when opening the throttle. So more likely the floats are set too low. The fuel level in the float chambers needs to be within 10mm of the joint face with the main body of the carb to work properly. That is the whole emulsifier tube assembly needs to be submerged in petrol to be effective. Now I have a special tool so that you can measure the level accurately in situ and I'm happy to lend it too you if you like. I'll bring it too the next meet if you want it. PM me..........Russ

Thanks Russ, i appreciate the help. I'll take you up on the lend of the fuel level tool if I may. Meantime i'm going to have another go at the carbs in the next couple of days. I've stripped them down so many times it only takes a few minutes. Bit frustrating but i'm determined to get this thing running before the end of summer if only to get it down to one of the berks meets to remind everyone wot rust looks like.

[BFC]

Just reset the floats and cleaned and checked the rest of the carbs. Fires up straight away now but the choke lever can be used to throttle the bike whilst the throttle itself still cuts it out. I'm off to drink heavily.

[chrisNI]

Take the tap out of the tank and make sure it's not about an inch deep in crap (I'm assuming you're running on reserve if you haven't had it out on the road) this can cause fuel starvation when you open the throttle and give it more air. Keeping the choke on can mae it rich enough to run and give these symptoms. You could still have some coming out the pipe when you check visually just not strong enough flow. The aforementioned crap (if it's there) coming down the pipes can also block pilot jets as fast as you clear them which compounds the problem.

[BFC]

Thanks for the info. I have cleaned the fuel tap and it was indeed fullof crap. The flow appears to be good. The throttle acts as an instant cut off switch at the moment.

Think it's worth sending the carbs away for professional cleaning. Anyone know of anywhere suitable in Berks? or west london? I intended to do it anyway when I start the bike refurb in Autumn. Now seems as good a time as any bearing in mind the probs i'm having.

[chrisNI]

I know we're still covering basics here but I assume your tank isn't vacuuming that's easy checked by opening the cap, but that usually causes problems when you've gone for a bit rather than just opening the throttle at a standstill. Either way air is killing it so it's fuel starvation, if it's coming down the pipe it's not going through the pilots. Sometimes a set of new pilot jets is the cheapest and quickest fix.

[sweptail]

i had these symptoms last week.turned out to be a kinked fuel pipe;fuel starvation. Tommy

[BFC]

Thanks for the advice chaps. I've taken the carbs off again and checked everything. Jets are all clean, floats set correctly. All seems ok. Fuel is running ok as well. I've attached a fuel line and rotated the throttle pully. Not really sure what the hell i'm doing (read it in a clymer manual as a way of testing fuel supply). Assume I should see fuel coming up into the carb throat. This happens when on choke but doesn't when choke is off. Anyone know what should be happening? am i right in saying that fuel should be flooding into the carb throat when the throttle is opened? If that's the case I might be a step closer to the solution.

My apologies if this is a stupid question. I'm on a serious learning curve at the moment.

[Al]

Hi BFC a few thoughts mostly clutching at straws;
Are the carbs the correct size for your bike?
In particular; body and choke diameter. Not Z650 ones for example.

Can you conn the bike into revving up using the butterfly spindle or the throttle cable at the carbs rather than at the handlebars. (possible electrical problem in switch gear)

Can you turn the throttle screws further open to increase tickover or shut to decrease?

What exactly does the engine sound like on the choke;
Is it either; a 'HEAVY' regularised beat or a hunting-surging intermittent chatter.
The former is too much choke ( over fueling ) the latter is short of fuel (blocked pilots subsidised by an excess amount of choke circuit to keep it going.

What do you see and smell coming from the exhaust when running on choke.
Black smoke; very rich
Blue smoke; oily
White smoke; ???
Steam; ???


Strong acrid smell or carbon monoxide or fragrant smell of unburnt hydrocarbons or excess fuel?

With the filters removed can you cup your hand and finally block off each carb inlet in turn to see the effect. What happens? Some or all will have an effect. Those that dont are suspect. It will probably stall each time but it matters little as the idea is to create a massive vacuum in each carb and pull through any debris.

Do all 4 chokes operate?
Are there similar very dark deposits on each spark plug after running on choke for a short time?

Use a piece or rubber tubing 1/4 inch diameter and a foot or more long to listen to each carb inlet with the other end just inside your ear.
You should hear a stuttering hiss but more importantly it needs to be the same on each carb.

Use a candle on the exhaust manifold studs after 30 seconds or more to determine what the temperature of each cylinder is.
Its easily removed later with a wire brush but should tell you whether one or more are running hotter or not firing at all.

How long are you running it on choke for before you attempt to operate the throttle?
Seconds~minutes?

Is it running points / condensers' or electronic ignition?
How strong are the sparks?
How old are the plugs?
Is the exhaust blocked?
Does it have equal compression?
Everything else equal and it may not have enough compression to run without excess fuel to bump it up!
If it has good compression and condensors then changing them may very well help, its not unknown for weak sparks to evaporate when under high compression scenarios: oiling, high comp pistons, carboned up in combustion chambers, etc

How old is the fuel?
Have you tried to spray anything into the inlets when it is running?

Does it have a PRIME (PRI) position on the fuel tap?


AL