problem with number 4 cyl - with pics

[Wipa70]

#4 cylinder

I just bought my 81 1100 Midnight Special. It was minutes away from reaching boat anchor status. Ive gone through the bike lubing and freeing up every moving part and changing all the fluids. I was having a problem with #4 cylinder being dead, actually still do. I found the rings were stuck and I was losing compression when it got hot. I fixed that with a few doses of seafoam. I went through the carbs and when i put them back and went to check the air/fuel mixture screw setting, i found #4 was stuck and ended up stripping the head. I believe this is common because of the screw being on top of the carb and the tilt of the bike exposes #4 to run off from the tank when the caps are missing or leaking.

I am waiting for a new part to come in this week. The bike runs a little rough at idle and through 5000 rpm but comes alive from 1/4 throttle up through to redline. At idle, I can pull the #4 plug wire with no change and i can pull the vacuum cap off with now change.When I pull the sprak plug out it looks wet. If I spray any cumbustible fluid in the vacuum port, the idle smoothes out. From what Ive read the mixture screw controls the air that goes in at idle because its on the back side of the carb. Something just doesnt make sense. Does anyone see anything Wrong with what Ive said so far?

[randy]

Something just doesnt make sense. Does anyone see anything Wrong with what Ive said so far?

Yes,

You write that the plug is wet, but when you give that cylinder some sort of fuel it fires. Doesn't make sense. Also, the mixture screw on the engine side of the carb controls fuel, not air, you go that backwards, or maybe what you read got that backwards.

[fredintoon]

Same mileage as the Buick

- - - hopefully i start getting better than 17mpg
anyone know what mpg a healthy 11 gets in the city? - - -

Hi Kev,
and that's full-size Imperial gallons, not the teensy US ones, eh?
Gawd, I thought my rig was thirsty at 28mpg but 17?
The only time my rig dropped to 17mpg was when it's #4 carb was plugged up and it was trying to maintain highway speed when only running on 3 cylinders.
Sounds familiar, don't it?

[tarzan]

You said you have good spark,so I woulod consider removing the carbs.
It isnt that difficult to do.You should be able to get them off the first time in less than an hour.I can get mine off in about fifteen minutes.
Then just remove the bowl on #4 to see the problem.
Just because a mechanic worked on ity does not mean he did it right.Or you wouldnt have this problem.
If all the other cylinders run good then there is no sense taking them apart.So just four screws hold on the bowl of the carb.Then you remove the float pin.Under that float is the float valve.That is probably where your problem is.Either a bad float valve or wrong float height adjustment or dirt in the float valve.
Rick

[kevxs]

update

dbeard - tested the ohms on the plug wires 1 - 4 got around 30 - 40k, couldn't get a reading on 2-3 but i'll try again when i have an extra set of hands. haven't done the water test yet . . .

its looks like i'll need to do get some mikexs coils on there, which i wanted to do eventually anyway. but the puddle is returning on the tailpipe and on the exhaust under the airbox, so a float issue looks likely as well.

tarzan - if i take carb #4 off and check the bowl, will i need the sync tool to get everything synced up again?

also #1 is runing rich, 2&3 are a little lean, what way do i turn what screws?

fredintoon - yep 17 imperial mpg, and i thought my grand prix was a pig!

thanks again guys

[Ken Talbot]

tested the ohms on the plug wires 1 - 4 got around 30 - 40k, couldn't get a reading on 2-3

Pick-up coil wires for the 2-3 coil, or one of the connectors or grounds for that coil.

[dbeardslee]

Kev - That's way more resistance than it should have. Could just be worn out caps, but I wouldn't count on it. You could try replacing the caps - even if that doesn't solve the resistance problem, your not out anything as they're the same caps you use with the HO coils. There is a way to graft new high tension wires into old coils too, but then you've still got old coils that only put out something like 16k volts. It's outlined in the tech tips if you want to give that a shot. Mikes has some new coils that they're selling that put out 45k at $69 a throw. It's an easy swap, and you end up with coils that you can easily change high tension wires on - one of those things that should be done periodically anyway.

[kevxs]

yeah i know i can't go wrong with the new coils and wires but should I be taking carb 4 apart as well? will I need to build a sync tool to get it working correctly once I put it back on?

[dbeardslee]

Kev - I agree on the carb issue - just responding to your resistance readings. Just about anytime you do anything to the carbs you should resynch. Build one or buy one. I put together a set of gauges for about $50, and they've done the job. Still, I've got my eye on the Morgan Carbtune Pro. Costs about $90 but by all accounts it is a quality tool. If I had to do it again, I would just bite the bullet and get the Carbtune. The other tool I find indispensible in carb tuning is a colortune plug. Opinions vary - some people swear by them, others swear at them. I love mine, and I use it a LOT.

Here's a deal where you can get them both Carbtune/Colortune combo

[tarzan]

If the carbs are in sync before you work on carb 4,your sync should not change as long as you dont remove the carb from the rack.
You can remove the float bowl without seperating the carbs.Just remove the rack of carbs from the bike.Drain the fuel out of them and then flip them over.
Just unscrew the bowl from #4 and remove it.Then you can check to see what condition its in.Then if you can fix it and put it back together it shouldnt disturb sync.
That being said I agree,any time I work on my carbs I check the sync.
Rick

[dbeardslee]

It may not change much, but it will change. When you adjust the synch your not so much setting how far openned butterflies are as you are adjusting the volume of the flow. That means when that piston starts firing correctly the flow is going to change on that carb. You can adjust the mixtures on carbs and it will change the synch. A lot of other things will change it to. That's why they always tell you the synch is the last thing you should do in a tune-up.

[kevxs]

carbs off

took the carbs off and checked the float height in number 4, its seems right at 25.7 when the carbs are upside down, compared it too number 1 and they look the same.

i took the valve out of the seat assembly and have it soaking in carb cleaner.

i think the problem must the carb related because i am finding gas untop off the exhaust on the right side. (see picture in previous post)

what else should i check while i have the carb off?

[dbeardslee]

Kev - Make sure the vent lines are clear, and make sure the orifice inside the carb isn't obstructed. Also make sure the little stop tab on the pin side of the float is set correctly. The float should allow the needle to unseat but shouldn't have too much travel. Maybe 1/16" clearance between the top of the pin on the needle and the bottom of the float tab (not the same as the stop tab).