Carb Sync Issue?

[Anonymous]

Hi all,

I have bone stock 1100ex with an annoying carb problem. The carbs are completely standard, all jets are as factory recommended but number 3 cylinder carbon fouls at low revs. This is not a new problem it is one that has be going since I've had the bike.

Synchronisation (according to my gauges and two other mechanics one of whom has a mercury setup) is fine, float operation and height are perfect. Bike seems to have no loss of performance and does not seem particulary thirsty for fuel (average some 15-16km/l @ 120km/h on a trip).

What I have found is that when all four pilot screws are 3 1/2 turns out plugs 1,2,4 are perfect and 3 fouls. Changing the number of turns on #3 to 2 turns makes #2 run lean while 1 and 4 stay at 3 1/2 turns out and remain perfect. At this setting #3 still fouls. Currently I have #3 at 1/2 turn out, #2 at 5 1/2 and 1 and 4 at 3 1/2. At this setting 1,2, and 4 the plugs look pretty damn good but #3 is rather dark and I think starting to foul as I have noticed a little bogging down whne taking off from traffic lights. What is happening here is that for every turn in on #3 I am having make the same adjustment out on #2. Also I have few vibes coming through the tank now. Just doesn't make sense. Every time I changed the pilot settings I have checked and adjusted carb synchronisation.

To me it seems like a synchronisation problem but my gauges say otherwise. I don't want to keep the current settings as they are just plain wrong. Changing pilot jets doesn't seem right.

All suggestions welcome.

[redliner1973]

Swap coils and see if the problem goes to the outboard cylinders...sounds like a weak coil problem.

[Jethro]

Maybe hotter plugs would solve the problem?

[Anonymous]

Have swapped coils several times. Have new leads, caps, plugs. All swapped at some point as weel. Should also mention that the valves have all bee checked in the 800km, compression on four cylinders is 135 or better, and uses very little oil. Carbs are absolutely spotless, guaranteed.

Tried hotter plugs (standard plug being D8EA) D7EA, DP8EA, DP7EA, very little benefit. I also very relunctant to try it even - its just comenstating for something else.

[redliner1973]

OK, stupid question time: I am NOT trying or implying to Insult your intelligence, just trying to rule everything out possible.....When you are making your carb adjustments, do you have the tank off? if so, is the Vacuum line for the petcock plugged off? is it pliable and not cracked/torn? If all there is well, only other thing I can think of right off is float needle/seat worn, sticking, or otherwise not shutting fuel off on the #3.

[Anonymous]

Thanks for your time Tim, vacuum line is plugged but have not checked its condition. I thought of needle valve not seating properly but that theory was blown out of the water when I swapped all of the internals of #3 with the others.

[nert]

I have a similar issue with my 82' 1100gl, except all (4) are rich and thats with mix screws out 1/8 to 1/4 turn. Doesn't foul plugs, just plug read is rich. All jets are stock, stock exhaust, stock filter, etc. float level is dead nuts on. (i made a float bowl with a window and set them on the bench, talk about anal.) thats another story. BUT!! maybe YOU have a bad choke valve on that carburetor. Try inspecting for obvoius failure to the seat. Then, swap it with one of the others.

[nert]

I have a similar issue with my 82' 1100gl, except all (4) are rich and thats with mix screws out 1/8 to 1/4 turn. Doesn't foul plugs, just plug read is rich. All jets are stock, stock exhaust, stock filter, etc. float level is dead nuts on. (i made a float bowl with a window and set them on the bench, talk about anal.) thats another story. BUT!! maybe YOU have a bad choke valve on that carburetor. Try inspecting for obvoius failure to the seat. Then, swap it with one of the others.

[Anonymous]

Re: Carb Sync Issue?

You have eliminated, ignition, ignition timing, valve clearances, float heights, debris in the carbs, compression, vacuum synchronization, jetting and plug heat range. If only cylinder #3 was in question, I would suggest that the vacuum line on the petcock was faulty and weeping excess fuel into the #3 intake. However, leaning out #3 results in having to richen #2. This should not happen if the problem is the petcock weeping fuel into #3. The most probable cause of the problem is a minor oil leak of the head gasket allowing #3 intake stroke to draw a slight amount of oil into the combustion chamber. Try retorquing the headbolts. Loosen them all, then turn them down incrementally using the criss cross sequence for each increment so that the head is seated uniformly.

Bandit12

[quote="AC"]Hi all,

I have bone stock 1100ex with an annoying carb problem. The carbs are completely standard, all jets are as factory recommended but number 3 cylinder carbon fouls at low revs. This is not a new problem it is one that has be going since I've had the bike.

[Anonymous]

Thanks for all the replies. Nert thanks for your idea on the choke but it has been swapped with another (#4 if I remember correctly). Bandit12 the fuel line goes to #2 not #3 and have already dealt with that particular issue last year. Your oil leak idea is interesting but I had the head off some 5000km ago; problem was there beforehand.

Cheers all,
Ron.

[Anonymous]

Like bandit 12 said, check the valves. My bike had a similar problem, #3 (the non-adjustable one) was rich and the others were perfect, I syncronized and that didn't help, then I adjusted the valves and that made the plugs all good.

[Scud]

I thought I had purchased all the same size pilot jets and came to find out that one was the wrong size and this made one cyliinder run rich and fouled plugs similar to what you are experiencing. Just a thought, never hurts to check although a pain to remove carbs

Scud

[AOD]

Something that worked for me, by chance, was I used B8ERS plugs (Resistors) instead of my B8ES plug once, and the plugs which would normally foul after sitting 2 weeks or so, did not foul.

Just a quick suggestion, might be worth a shot.

[Anonymous]

Vaves were last checked 1000km ago, 5000km before that, etc so I'm not particulary sure on that option. Thanks for the reply though. As for the jets - they are same across all four carbs and have been swapped around. Plugs idea sounds interesting however this bike is used daily and clock up some 1000-1200km per month (on average). One thing that is interesting is that the temperature on #3 is the same as all the others - they were all pretty much the same.

Thanks

[nert]

You adjust #3 and #2 changes? They are next to each other. Something going on with the air box/air filter? Perhaps one of the carb vent, vent hoses, or something like that is playing with our heads.