Enriching a Carb?

[Seacat]

Okay how does one enrich the carbs on these bikes?

From where I'm sitting there seems to be two options. (Correct me if I'm wrong.)

The first seems to be the Pilot Screw. Screw it in and you enrich the idle by reducing the amount of air going through. (Good for idle but not a lot more.)

The other seems to be the Synchronisation Screw. This, from what I see is attached to the throttle body. From what it looks like if you screw it in you open the throttle on that carb but not the others. Screw it out and you cut down on the gas flow and add air to the equation which leans the carb out.

Am I right about this?

If I am, could this be the problem I am dealing with? Is my one cylinder not getting enough fuel to fire correctly? (Hence the cylinder not firing, but the backfires into the carb?)

Cat

[cbRider]

Back firing into the carb means it's lean. For whatever reason you're not getting enough gas in that carb or have an air leak.
Assuming you have compression and spark.

[gonebiking-2]

The synchronising screw that you mentioned, is that the screw under the carbs just above the starter motor cover ??? If so, that opens the butterflies on all four carbs as its attached to the throttle arms on all four carbs. A vacuum gauge connected to all four carbs should be used to synchronise all four carbs at the same time. That will also tell you which carb is running lean, particularly if its backfiring through the carb when you open the throttle. Playing around with the idle mixture screw will only iron out the roughness when its idling. The correct setting is to close the idle mixture screw and then turn them all out one and half turns. Thats as near as accurate as possible. Its then a matter of getting the motor up to normal running temperature and then playing around with each screw by making qaurter turns in or out until such time as the motor is idling at 1000 rpm and is nice and smooth. You may have an incorrect main jet in the carb thats backfiring. As I`m in Australia and 99% of all the post are frmo the USA, I`m just guessing from what you have written. I spent 30 + years in the motor industry tuning mutiple carbs and have tuned many of these Honda carbs over the years.

I hope you find the answer to your problem.

[gonebiking-2]

Have just been browsing through my workshop manual in the Fuel System and under the one of the headings of trouble shooting, "BACKFIRING" It lists three possible causes : 1) Ignition malfunction  2) Carburettor Malfunction  3) Faulty Air cut off valve or accelator pump. So take your pick and see where the problem lies . Hope thats some consolation

[Seacat]

Well I have just bought some Starter Fluid. (No I didn't have any around.) Tomorrow morning I'll be doing a bit of a field test. I'll pull the air filter and start the bike. When it's idling I'll spray some of the starter fluid into the intake end of the carb and see if the cylinder fires. This will tell me a little bit at least about what's going on.

I'll let you know what I find.

Cat

[woodsrider250-2]

Also ensure valves are adjusted correctly.

[Seacat]

Now this was my Birthday present to me. I removed the carbs and rebuilt number three. (The kit came in.) I then put the carbs back on the bike with a minimum of cursing. (Didn't want to scare the neighbors again you know.)

After everything was on and adjusted I fired the bike up.

No number three didn't fire this time either but I wasn't done yet.

I reached under the carb and started slowly screwing the Pilot Screw in. A quarter turn then listen, rev the engine a bit and check the pipe. After something like the third time doing this the cylinder started firing. (Yahoo.)

I've played with it a bit more and have it running as smooth as I can for right now. I reckon the next step is to synchronize the carbs.

Cat

[woodsrider250-2]

Indeed.

[gonebiking-2]

Well there you go. A malfunctiong carburettor. Now its running and you have the idle screws turned out one and a half turns +/- now all it needs is synchronising and it will be  purring lke a Rolls Royce. Perseverence and paitence is the name of the game with these carbs.