Carb queries

[Bess]

Hi Phil,

The hole nearest the engine is the pilot the other is the pilot bypass. The pilot hole supplies fuel for idling, as the throttle is opened the pilot bypass supplies the fuel.

Best wishes...

[Phil C]

I was at my local motorbike repair shop this morning. The (very experienced) mechanic had a look at my carb, took it into his workshop, came back and assured me both the tiny holes in the bore were clear. Back home, I squirt carb-cleaner into the fuel gallery and it shoots out of one tiny hole (like before) but little if any seems to come from the other. Any thoughts please?  Phil

[Phil C]

Obviously the mechanic will be right. I'll put the carb back together, stick it back on the bike, put some fresh fuel in the tank, and see what happens.  Phil

[royblackburn1@btinternet.]

May be when the engine is running the fuel is drawn in through the other hole when the slide is lifted, just a thought 

[Greenfield]

Hi Phil
The fuel will take the path of least resistance. Put your finger over the hole where the cleaner sprays out and squirt cleaner through the pilot jet. Hopefully you'll now see cleaner coming out of the other hole.
Fingers crossed.

[Phil C]

Hi Paul, I did try putting my finger over the other hole, but still wasn't sure it was coming out of the suspect one. It's a bit difficult to fully block the hole with a finger, so I'm a bit unsure. I'll give it another go before I put it back together. What I was hoping for was the same as the "good" hole, ie like a tiny fountain of liquid coming up out of the hole.  Phil

[Phil C]

Tried again, same result. Frustrating and confusing. Phil

[DAVE BRADY]

Hi Phil,

It sounds like a lack of fuel.  Assuming that all the settings are as per the book the bike should start and run.  Perhaps a bit erratically until it is warm.
 
Will it run if you keep the throttle open wider so that the slide and needle/needle jet are in play?
As soon as it fires keep the ticker down to keep the fuel level high in the carb so creating an over rich mixture and keep the throttle open - does it keep running?
Try raising the slide with the throttle stop to give a very fast tick over - does it keep running?
It is possible that there is still bit of an obstruction in the pilot jet system and getting the engine running at higher revs may help to clean it by making more of a vacuum.
Also if it will run at faster revs, remove the air filter and whilst the engine running quite fast almost completely block the cab intake making sure the pilot air holes are clear.  This will cause all of the suction of the engine to pull through the pilot system and may pull through any bits remaining after cleaning.

Dave.

[Phil C]

If there is a blockage, its whereabouts is a mystery to me. When I squirt down the pilot fuel route little if any comes from the tiny hole nearest the engine but a good little fountain comes from the other one. But when I squirt down the pilot air passage a good fountain comes from both. As I see it, if the jet/bush had a blockage then fuel would reach neither of the tiny holes. If there were a blockage at the pilot mixing chamber or at the tiny hole itself, then I wouldn't get a nice healthy fountain from both when I squirt down the air passage. Am I getting this right? I'm using the Bushman's sketch to analyse this. I'd like to understand exactly why this is happening.  Phil

[Pete A10]

Have you tried blasting the holes from the other side I.e. the engine side of the carburettor. If there is some minor debris partially blocking one or both of the holes it may come out if you essentially back-flush it

[Phil C]

You mean blowing down the two tiny holes?

[Pete A10]

Yes. Carb cleaner sprayed through the pilot air inlet should spurt from BOTH holes. If it isn't then one of them is blocked. The two holes are the narrowest part of the system and would therefore be expected to catch any detritus coming through. Back blasting it would push the detritus through the wider parts of the system. You will need a narrow flexible tube (like you get on a WD40 can) which can be held tight over the small holes while attached to a carb cleaner nozzle. If necessary you could do it with WD40.
Another alternative to clean the pilot ways is to leave the carb body soaking in paraffin for 24 hours, then try blasting it out with carb cleaner.

[Phil C]

Carb cleaner sprayed through the pilot air inlet DOES spurt from both holes. But when I spray it through the fuel inlet it only spurts through one. It might come through the other - not sure - but it doesn't spurt.  Phil

[Pete Gill]

Hi Phil

I'm not sure it should come through both holes EQUALLY as they serve different purposes.
If you spray down the air screw hole and block off each of the exits in turn then i think you'll find a good jet should emerge from each hole in turn?

Pete

[Phil C]

When I spray down the air hole I get a good jet from both holes. It's only when I spray down the fuel hole that I get a good jet from one hole but not the other. I think I'll assume it's okay and put it back together. Thanks very much everyone.  Phil