Updated - Still running rich

[LynnLegend]

Hello team,

I've had running rich issues for a while and gave my carb to a family friend to have an "ultrasonic bath" (sounds like a spa treatment) - it has been subsequently tuned to the correct specifications (as defined by DW Munro). I've faffed about with the air screw (unscrewed it quite a lot), put the needle on its lowest setting, but she's still running rich as buggery.

Would welcome any suggestions.

Thanks,

Sam.

[bsa-bill]

Short answer would be - modern fuel
as for the air screw if you can find a spot somewhere where the engine runs fine but either side of that spot the engine falters or slows then it doesn't really matter where that spot is.
If the screw needs to be right in or right out then you need the change the pilot jet to another size up or down
After that then your into needle position/slide cutaway
Others will correct me but I think main jet comes into it more at 75% throttle and over

[chaterlea25]

Hi Sam,
What bike, what carb' what setttings 
The first thing to get right with any carb is the fuel/float height

John

[edboy]

i ve had a similar problem and a 15 pilot jet cured it on one a10. throttle cut away 3 1/2. another runs perfectly on a 25 pilot jet. throttle cut away 4. i played around with the float level but as long as the level is fairly close it was not the cause. both carbs run bellmouths and the 15 pilot bike likes to rev not lug.

[JulianS]

Sometimes the float level is wrong due to a mistake in reassembling the carb.

The gasket sets come with a fibre washer which fits under the float needle seat on the "new" monoblics which take the thin o ring, the body having a machined recess to accept it.

The original monoblocs dont have this washer fitted, the joint is metal to metal and there is no machuned recess.

Put it in the old type and the float can stop on the tickler plunger before the float needle seats to shut off the petrol causing flooding.

Worth checking that the float is the right way around and that the little spacer is in place.

[LynnLegend]

Update on this one - I've got her so she's not spoiling the plugs at tickover, largely by faffing around with (what I believe to be) the pilot mixture screw (big one on the bottom) and the throttle position (or maybe air screw), which was the one closest to the "engine block" (for lack of the proper language to describe it.

One thing I am struggling with is the choke - I don't see where it makes any difference at all? Also, I don't know which position is open and which is closed, currently I have it patallel with the handlebars. Would welcome your help on this.

Thanks,

Sam.

[Greybeard]

Could you stick a finger into the carb while operating the choke lever?

[LynnLegend]

Could you stick a finger into the carb while operating the choke lever?

That is an experiment I can do. Presumably you want me to take the carb off the engine and air filter, then play with the choke and see what happens when it is in th various positions?

Alternatively, I can tell which position is pulling the cable tighter and which position slackens the cable?

[duTch]

 

........ largely by faffing around with (what I believe to be) the pilot mixture screw (big one on the bottom) and the throttle position (or maybe air screw), which was the one closest to the "engine block" (for lack of the proper language to describe it......

 In case I misinterpreted that , the Air Mixture screw is horizontal on the head side, and the Idle speed screw is bigger and pushes the slide up from the bottom at an angle...

 Can't help much with choke as I've never had or seen one, but imagine as GB suggests, if you hold the throttle wide open (engine off), you should be able to feel the choke open and close....should be open/up for riding I guess....

[LynnLegend]

 

........

 In case I misinterpreted that , the Air Mixture screw is horizontal on the head side, and the Idle speed screw is bigger and pushes the slide up from the bottom at an angle...

They're the ones 

[bikerbob]

The choke is important assuming the choke lever is on the right side of the handlebars then pulling the lever towards you will tighten the cable this should be pulled all the way thus opening up the air intake to the carb leaving it in any other position will result in a very rich mixture. it should only be closed partially to help with cold starting and then it may not even be needed in the summer it depends on the bike some need choke others do not but when running it should always be open.

[KiwiGF]

The choke makes little difference on my a10. The choke is off when pulled up eg it’s off choke when the cable is tight. I’ve heard the choke does help in very cold conditions.....which w3 don’t often get in nz.

To see what’s going on with the float on a monobloc you can remove the float bowl side cover and replace it with cling film and a rubber band.

When I did this piece of diagnosis I found the float level was very low but petrol was flowing down the inlet. The cause was a blocked float vent (this vent is a small hole in the tickler button). The blocked vent caused the float chamber to be slightly pressurised, and petrol seemed to be then forced throgh the needle jet. In my case the engine kept stalling and fouling plugs due to the excess petrol it was getting.

[ellis]

Hi LynnLegend,
 Easy Peasy, slack cable choke on-Tight cable choke off.   

ELLIS

[RogerSB]

I've always found when starting from scratch turn the air screw 1 1/2 turns out (anti-clockwise) from being screwed fully in and the throttle stop screw 1-1/2 to 2 turns in (clockwise) from the point at which you feel the slide (or throttle valve) start to be moved up by it in the chamber.
Then you should only need to to fine tune the air screw about a 1/4 turn each way to obtain the fastest tickover with the throttle closed and with free play in the cable. Then fine tune the throttle stop screw to get the best idling speed. Finally adjust the throttle cable so you have just a little free play.

My choke is mounted on the frame (see pic). In this position with the lever pointing forward the cable is being pulled tight and the air valve (choke slide) is pulled up out of the way and therefore it's off.

I had my A10 running this morning in temp about 8 C (so about 46 F). I used the choke but I only ever need to pull my lever back about 1/4 way to lower the air valve slightly when I need choke to start and keep the engine running until its warmed up. After a minute or so I can usually move the lever fully forward for the choke to be fully off.

[Greybeard]

It's funny how these engines differ in needing the choke. Mine only needs choke if it's really cold weather. I have an air filter; I guess bikes without one may need more mixture enrichment to get going.