First Start Highs and Low!

[Neilw]

Well, I've finally arrived at the point where I can attempt a first start, having fixed the start button issue and the timing plate. The neutral switch is a little project to resolve, but I've managed a first start, which I'm elated about and the bike just about runs.

But i could do with some wise heads/advice, please.

The carbs, I cleaned thoroughly and reused all the original brass wear. The only thing I didn't check was the position of the circlip on the needles. I did a bench sync and set the float height at 22mm (it's a 069A set of carbs). The air/mixture screw is set at 1.5 turns.

I've been through lots of starts; most of the time, when I start with choke, it races to 5-6000 rpm immediately. I can temper the choke back and hold it just on so the bike idles at 2000rpm, but when i release the choke fully, it cuts out. I've adjusted the throttle stop to keep the throttle open, and that works to a point, but it eventually dies. I'm getting black smoke from the exhaust and the plugs are black and sooty.
I've tried adjusting the mixture both in and out half a turn; not much difference.

I can't see anything holding the throttle open, everything moves as it should. I've taken the tops off each carb to see if the sliders are stuck, and they are not.

I'm at a loss as to where to go now. At one point the bike was idling and i didn't have black smoke, so something si changing to cause the issue. Also, the racing to 6000rpm disappeared for a while, which makes me think something is getting stuck open/close, idk.

I've had the plugs out a few times to clean them while going through this process. The neighbours love me when i start it lol.

Any help, ideas or wisdom is greatly appreciated.

Cheers
Neil

[Bryanj]

You may have your bench sync wrong, its easily done

[Neilw]

You may have your bench sync wrong, its easily done

Can i check them while the carbs are still on the bike - i assume you mean the slider height and float height.?

[McCabe-Thiele (Ted)]

You state you have set the float heights, that's fine.

A bench sync is where you set the sliders with the carbs  off the bike, it's pretty much impossible to do it accurately on the bike.
You need to set the gaps so all four are exactly the same.
I have only bench synced my 400 & 500 with good results.
You can later fine tune the bench sync with a vacuum guage if you have one.

Done correctly ensures the engine (when warm) only idles on the idle circuit not by drawing fuel from the main jet, the air screw on each carb  should respond to the air screw adjustment.

Did you clean all the airways when cleaning the carbs?
If you are using the original air filter it makes sense to check the needle height position, it may have been altered by a PO especially if its had pods fitted in the past. You also need to check the needles are the correct ones.

[Neilw]

You state you have set the float heights, that's fine.

A bench sync is where you set the sliders with the carbs  off the bike, it's pretty much impossible to do it accurately on the bike.
You need to set the gaps so all four are exactly the same.
I have only bench synced my 400 & 500 with good results.
You can later fine tune the bench sync with a vacuum guage if you have one.

Done correctly ensures the engine (when warm) only idles on the idle circuit not by drawing fuel from the main jet, the air screw on each carb  should respond to the air screw adjustment.

Did you clean all the airways when cleaning the carbs?
If you are using the original air filter it makes sense to check the needle height position, it may have been altered by a PO especially if its had pods fitted in the past. You also need to check the needles are the correct ones.

I did the bench sync using a 1/8th drill bit as shown on a couple of youtube videos. I followed the rebuilds to the letter, cleaning all the paths with wire/brushes, sonic cleaner, carb cleaner, and compressed air; I did everything. Some of the brass bits were corroded, but cleaned up with a bit of fine wire wool.

I have a vacuum gauge, which i'll use when i can get the bike to idle. The airbox is the original, with a new filter fitted. I've replaced all the rubber, so there are no air leaks.

I guess i can check the needles while the carbs are on the bike, that way i'll know if the circlip is in the correct position and the sliders are functioning correctly.

[deltarider]

Black smoke usually indicates a (partially) blocked air intake. Could be a forgotten cloth, an airfilter element gone wet or choke flaps stuck closed.
I'd first temporarily remove the airfilter element, see if you can peek at the carbs mouths to see if the choke flaps are up. Are you sure the tiny O-rings around the main jets are Ok and seal well?

[McCabe-Thiele (Ted)]

I don't know if it's possible to check the needle clip position without removing the sliders.

What did you clean with  wire wool, was it just cosmetic cleaning of none metering parts.

Personally I think 1/8" is too big a gap as it does not leave room for a lower adjustment of the idle screw.
On my 400 iirc I used 3/32, on my 500 I used the point when the slider just started to move from the fully closed position effectively zero. Snag I hit was the adjuster screw was was so undone the spring was not compressed, I built a raised stop to fix this.

[Neilw]

Black smoke usually indicates a (partially) blocked air intake. Could be a forgotten cloth, an airfilter element gone wet or choke flaps stuck closed.
I'd first temporarily remove the airfilter element, see if you can peek at the carbs mouths to see if the choke flaps are up. Are you sure the tiny O-rings around the main jets are Ok and seal well?

I installed new O-rings, and the flaps were operating correctly before i re-installed the carbs, but I will check. No other blockages.

[Bryanj]

1/8 is too big you need a bew 1/16 or smaller, unscrew the tickover screw all the way and make sure ALL the slides bottom out, adjust the tickover screw untill the snank of the new drill(if its new its smooth!) Just slides under the engine side of the first slde that moves then adjust other 3 to same.
Unscrew the tickove screw again to check that all the slides still bottom out, adjust tickover again till slides only just open and try to start, hopefully this gets you good enough to run

[Neilw]

1/8 is too big you need a bew 1/16 or smaller, unscrew the tickover screw all the way and make sure ALL the slides bottom out, adjust the tickover screw untill the snank of the new drill(if its new its smooth!) Just slides under the engine side of the first slde that moves then adjust other 3 to same.
Unscrew the tickove screw again to check that all the slides still bottom out, adjust tickover again till slides only just open and try to start, hopefully this gets you good enough to run

I've followed the above, and checked and rechecked. I didn't manage to get the slider needles out as the screws were in very tight, and i didn't want to force anything and strip them. From what I could see, there was only a small amount of the needle sticking above the circlip, so it would suggest position 2.

I put the carbs back on and double-checked all seals and, frankly, everything. I set the air screws at 1.5 turns to begin with.

Bike started on choke, but still raced to 5000 rpm. With choke off, I had to hold the throttle open to keep it running, or it died. Lots of black smoke.

I adjusted the air screws to 2 turns and then 2.25 turns and retried. Each time, something similar.  I then left it for 10 mins went back and tried again, and it seemed to run ok, with no smoke, i even got it to idle for a while off choke using the throttle screw. Then the bike died; I realised I had left the inline fuel switch off!. Turned it back on tried again with similar results as before.

I've taken a break to write this, have some lunch and go back and try again.

It feels like there is too much fuel getting through or not enough air or both lol.

Just got back from lunch, tried a restart, ran out of fuel lol. Put more in the external tank i'm using and now i have an over flow leak on bowl 2, that no amount of tapping seems to stem the flow!.

I sorted the leak, i removed the bowl, blew in some carb cleaner and compressed air, jiggled the float about and put it all back.

Bike starts on choke, races to 5-6000rpm with some black smoke, take choke off, have to hold throttle open to keep it running, and then it stalls on own accord after about a 30 sec - a minute.

[deltarider]

[...] Put more in the external tank i'm using and now i have an over flow leak on bowl 2, that no amount of tapping seems to stem the flow!.[...]

In general: do not position an external tank higher than the original tank. The higher the more pressure in fuel feed. As a consequence float valves will not close causing overflow.

[taysidedragon]

You need to keep some choke on for a couple of minutes until the engine warms up enough to run without it. It will stall without any choke when cold. Gradually reduce the choke to keep the revs from rising as the engine warms.

[Neilw]

[...] Put more in the external tank i'm using and now i have an over flow leak on bowl 2, that no amount of tapping seems to stem the flow!.[...]

In general: do not position an external tank higher than the original tank. The higher the more pressure in fuel feed. As a consequence float valves will not close causing overflow.

Thank you. It's suspended from the ceiling joist, so well above the bike, so will try that.

[Neilw]

You need to keep some choke on for a couple of minutes until the engine warms up enough to run without it. It will stall without any choke when cold. Gradually reduce the choke to keep the revs from rising as the engine warms.

I'll try that too, with the improved fuel tank location.

[McCabe-Thiele (Ted)]

Ensuring the needle is in the correct position is pretty much a basic essential as is checking you have the correct needles, with the circlips all in the same position.

Assuming you are using the right size JIS screwdriver those screws should come out, as long as you have the strength to push into the screw head it should turn after soaking them in releasing/penetrating oil.