Third exhaust not getting hot

[Glynnrg]

 why cb550f1 the third exhaust not getting hot I presume this cylinder isn't running properly  plug seems to be getting wet when I pull plug cap of engine dies slightly tho sparks on all plugs don't seem that bright but not knowing what they should look like don't if this is normal Anyone got any ideas
Thanks

[mike the bike]

Try swapping plug 3 with one of the other ones to see if the problem migrates.

[Glynnrg]

Swaped plugs still third exhaust not getting hot
Cheers

[hairygit]

Next off I would do a compression test to rule out burnt/bent or otherwise damaged valves/seats or head gasket leak. If that checks out, it's onto looking at the carbs. I assume the plug cap is not cracked or otherwise damaged? Also, try cutting 5mm or so off the HT lead and refitting the cap.

[Glynnrg]

The plug electrode seems to be the right colour
How do you do a compression test
Thanks

[hairygit]

You need to beg, borrow or steal a compression tester, take all the spark plugs out, put the tester in each plug hole in turn, wind the engine over with the throttle wide open, and make a note of the reading for each cylinder. They should be within 10% of each other. If one is significantly lower than the others, do the test again, if the same one reads low again, it's time to take the head off to check/lap the valves and check the bores/pistons/rings, as any of those can cause low compression, which results in poor starting/running.

[Glynnrg]

Thanks

[Johnwebley]

can you use a set of vacumn gauges to set the carbs up?

 the cylinder may just be not open enough to run at slow speed

[K2-K6]

You need to swap the plug leads of cylinders 2 and 3 to see if the problem transfers with it. It's the same coil and fires at the same time so if you see the problem go over with the lead you know it's that which is doing it.

Also check the valve clearances on the defective cylinder to make sure you've not got a valve held partially open inadvertently.

[Glynnrg]

thanks for your advice I did try to swap the leads over but one wasn't long enough

[mike the bike]

Try unbolting the coil from the frame temporarily to swap 2 and 3 HT leads.

[Ashdowner]

I'm with K2-K6. Check the valve clearances to make sure one hasn't tightened up which can happen if you haven't used the bike for a while.

[K2-K6]

The bit that puzzles me is you've got a wet plug on that cylinder which would, all things being equal, fire at some point if the spark was ok.

I still think you need to verify the plug lead and swapping over as Mike has described would help you with a yes or no answer to the plug supply.

If you can't verify that both plugs are sparking under load you may be on a wild goose chase through other stuff, while staring the real problem in the face.

As ashdowner says, it's easy also to check tappets in about five minutes to see if there's anything untoward.

[Glynnrg]

thanks all for your advise
although the the plug was wet initially the float in the carb was stuck so not letting enough fuel through
all working ok now

[K2-K6]

At least you've got them all firing and that's the main thing.

Some nice weather also to try it out.