Bike will not run smooth on idle.

[Cass]

I bought this FJ1200 1993 just over a year ago as a project to rebuild. The bike had been sat for 10 years as the previous owner had ridden the bike home, parked it up and died of a heart attack over night. So I knew it had been running but having sat for so long it was a bit rusty around the edges and tired looking so I stripped it right down and rebuilt it. During this process the engine was not touched as it only had 23k on the clock and with some oil down the plug holes turned over easily. The carbs were stripped down as they were full of varnish/old fuel deposits and thoroughly cleaned. All new jets and valves were fitted. On the day of firing it up I could only get two of the cylinders to fire. 3 and 4. 1 and 2 had cold headers so I knew which were not firing. It seemed as though they were not getting fuel so the carbs were stripped out and the floats re-adjusted. All four have fuel and by adjusting the idle valve I can get 1 and 2 to fire but with a lot of back firing as if they are now over fuelled. The idle jets on 3 and 4 are out 3 turns but on 1 and 2 I have got them out to 4 and a half before they will start to fire but loads of back firing on idle. Wind them back down and the pots stop firing. If I take it out on the road it goes like a train with the throttle half to full open all four pots are firing and humming away but shut it off and it's back firing again but just out of the right hand side which is 1 and 2 pots again. It can't be the coils as the work on 1 and 4 and 2 and 3. The carbs are clean, fuel in all four float chambers and throttle butterflies balanced with a vacuum gauge. Compression is even across all four pots with new plugs which have been swapped around to eliminate a faulty plug. It runs great on half to full throttle but is a bitch on idle on these two pots.
Can anyone suggest what the problem might be?

[Motofun]

Air leakage past the carb boots?  At idle too lean but when you give it a lot of gas it overcomes the leakage?

[FJ1100mjk]

Even though you stated that you had thoroughly cleaned the carbs, my guess is that you still have blockage in their passageways.

When you cleaned them, did you verify that they were cleared with the method below, and that there was also flow through the little group of holes, as shown below?

Pics are not from an FJ, but the method and holes shown, are relative.

[balky1]

Idle circuit is blocked somewhere in the carb body. Do the above. And try ultrasonic bath.

[Cass]

Even though you stated that you had thoroughly cleaned the carbs, my guess is that you still have blockage in their passageways.

When you cleaned them, did you verify that they were cleared with the method below, and that there was also flow through the little group of holes, as shown below?

Pics are not from an FJ, but the method and holes shown, are relative.

Thanks for the advice and photos. The carbs were stripped and cleaned. Carb cleaner was sprayed in and then blown out with an air hose. I did nt stick my fingers in any of the holes though to increase the pressure in the other places so I will look again for the micro holes you have indicated. On another forum for Kawasakis someone suggested the problem could be with the ignitors referring to the ECU. Could this be a cause of my symptoms on the FJ and would it be worth while swapping out the ECU. I can pick up a spare second hand unit for £30?
Frustrated from Torquay.

[Motofun]

Take some very fine sandpaper and taper the end of the red plastic straw that comes with the carb cleaner.  The objective is to be able to wedge the straw into the tiny orifices to make a better seal.

[FJ_Hooligan]

The symptoms you describe scream obstructed idle circuit(s).

[balky1]

I had a similar problem. It was a cracked rubber manifold holding the carb, sucking air where it shouldn't.

[FJ1100mjk]

Could this be a cause of my symptoms on the FJ and would it be worth while swapping out the ECU. I can pick up a spare second hand unit for £30?
Frustrated from Torquay.

I doubt it. You mentioned in your first post, that the bike was running when it was parked by the departed previous owner. The OEM ignition systems are pretty robust, as evidenced by the number of FJ still on the roads without any OEM ignition failures. If you haven't done so, you can also remove (even ohm them out to verify where they stand) the spark plugs' caps, trim the ends of the leads off 12-13mm, and reinstall the caps.

I could be wrong, but my money is still on clogged passageways in the carbs causing your problems. Many owners here, have had to take their carbs off, and work on them multiple times before all was well with fueling. If not done so, the aforementioned ultrasonic cleaning of them, and the verification of flow through all passageways afterwards, is probably in order for you. Sometimes, the deposits in the passageways can be a real bear to get cleaned out. You may find one, that defies all cleaning methods, and the carb body will need to be replaced with a known good one.

Another source of issues with starting, and initially running on all four cylinders, is the clogged orifice in the float bowls where the enrichment circuit's fuel pick up tube goes into. That orifice in particular will defy cleaning at times.

I have had good luck boiling carb bodies (completely disassembled) in distilled water for around 45 minutes, to remove deposits. But the real tool for cleaning is the ultrasonic cleaner. If you don't want to buy one, break the carbs down (and re-assemble them) yourself to save money, and then pay someone else to ultrasonically clean them with theirs.

Good luck!

[scotiafj]

I'm having problems too on my FJ1200 3xw .. when you go to start it .. full choke out ,it fires up but revs dont go above 1800/2000 rpm after a couple of mins knock the choke off n switch it off ,full choke on again fires up and revs go well up above 2000/3000 rpm ..it seems to rev higher on choke once there is some heat in the engine .. choke off and it ticks over about 1300/1400 rpm n revs up cleanly  ..on the road it revs up good n no misfires tho could do with the fuel consumption being a bit lower ,prolly having a 40t rear with the gixxer 750 rear wheel n a 70 profile tyre thats upset the gearing a bit ,just under 4500 rpm @70mph where as with the standard 16'' rear it was just under 4000 rpm @ 70mph ..

[balky1]

I'm having problems too on my FJ1200 3xw .. when you go to start it .. full choke out ,it fires up but revs dont go above 1800/2000 rpm after a couple of mins knock the choke off n switch it off ,full choke on again fires up and revs go well up above 2000/3000 rpm ..it seems to rev higher on choke once there is some heat in the engine .. choke off and it ticks over about 1300/1400 rpm n revs up cleanly  ..on the road it revs up good n no misfires tho could do with the fuel consumption being a bit lower ,prolly having a 40t rear with the gixxer 750 rear wheel n a 70 profile tyre thats upset the gearing a bit ,just under 4500 rpm @70mph where as with the standard 16'' rear it was just under 4000 rpm @ 70mph ..

I didn't find anything wrong with the bike in your post. Higher revs on choke when warm are normal. Check the balance and valves. Valve job and balancing improved greatly how the bike acts on choke in my case.

[Cass]

First chance I have had since getting the replies to take the carbs off and try to clean them again. Stripped them down and found the micro holes. Sprayed the good part of a can of carb cleaner in to every hole imaginable and had the stuff coming out of every other hole including the micro holes. Reassembled and put them back on to have exactly the same problem. With all four pilot jets set at 3 turns the bike starts but only on 3 and 4 cylinders. 1 and 2 down pipes are stone cold. Wind the pilot jets out on 1 and 2 to four and a half turns and all four start to fire. Still not running smoothly and the weather was not conjusive to taking the bike out for a ride to see if it was still back firing.
I have a friend with an ultra sonic cleaner so I think the next step is to strip them out again and hand them over for an ultrasonic bath. Its easy enough taking the carbs off as I have left the air filter off this time but the hard bit is reconnecting the throttle cables to the carbs each time. Never mind it has to be done unless someone comes up with another reason why the carbs are not running correctly. 

[FJ_Hooligan]

If you're certain the carbs are clean, then another option is cylinders 1 and 2 are getting more air than 3 and 4. 

Sources of unmetered air in the intake stream include bad O-rings between the intake manifold and the head, cracks in the intake manifolds, or the choke plungers not sealing well and letting air sneak past them.  Have you tried the "diaphragm slide blow test?"  That's where you look at the carb intake from the air filter side and blow into the oval shaped port at the top of the carb intake.  This should lift the slide and hold it suspended without leaking down.  If it doesn't hold pressure then the choke plungers are not sealing or the diaphragms have holes in them.

I'm assuming you've got all the sync ports capped off?

A remote possibility is the idle mixture screws were tightened too much and have deformed the opening in the carb body.  Never having experienced this, I do not know how this would affect the mixture settings.

I say wind the idle mixture screws out and see if you can get acceptable running. 

[ZOA NOM]

Try Sea Foam.

[Cass]

A Dry day today abit windy but able to get the bike out for a run. Bike ran fine, no back firing and idled ok but I now think its the choke which is the problem. On starting the bike with the choke out it is only firing on two cylinders (3 and 4). When you knock the choke off it fires on all four. I am assuming from this that when you look down the barrel of the carb at the micro holes there appears to be one by itself which is the idle and then a group of three which I assume are the choke. When I stripped and cleaned the carbs I was not sure if these holes were clear or not. I had spray coming out of the idle hole and I stripped the choke plungers out and sprayed inside thinking I had cleaned out the muck. Am I right in saying that fuel is drawn up from the float chamber via the long brass tube and goes through a channel to get to the end of the choke plunger so when the plunger is pulled out (choke on) the fuel goes through these three micro holes into the barrel of the carb??
I think the carbs need to come off again to be ultrasonically cleaned. A job for next week.