Help needed with 78E - At wit's end and don't know what else to try...

[CK]

Guys,

First, thanks in advance for your help - I have a situation on my 78E where cylinders 3 & 4 aren't firing or aren't firing much. Problem started last fall when I worked on my gauge cluster to fix an annoying vibration. During that fix, the bike sat idle for about three months. This spring, when the current problem became apparent, I deduced from from reading posts that I probably had a clogged "low-end" jet and decided to clean the carbs. Since then all of the following has been done - but not necessarily in the order shown:

• Carbs cleaned by me with Pine Sol and reassembled - problem persisted
• Carbs cleaned again by experienced motorcycle restorer with Yamaha brand cleaner and reassembled - problem persisted.
• Petcocks removed and cleaned - fuel flows out freely in "prime" and freely in "on" with slight vacuum applied
• Gas cap disassembled, cleaned, and reassembled - problem persisted
• New fuel lines installed - old had some substantial kinks - problem persisted
• Carbs removed and air blown into tee that flows fuel to Carbs 3 & 4 - No problems noted and identical to same result on Carb 1 & 2. Vacuum tees to airbox tested and same results between 3 & 4 and 1 & 2.
• New carb boots installed - no obstruction observed between them and intake valves
• Idle mixing jets checked for broken tips and re-set to original setting
• Regulator/rectifier replaced - problem persisted
• Ignition coil's primary and secondary resistances checked and right on spec
• Spark plug wires resistance checked and connections to caps checked
• Spark plugs caps resistance verified at 5 ohms
• Good spark verified on #4 with plug removed and grounded to cylinder
• New spark plugs, bought, gapped to.030 and installed
• Spare ignition coil installed on cylinders 3 & 4 - no change
• Spare TCI unit installed - no change
• Swapped plug wires 1 & 4 - Cylinder #1 continues to run fine and #4 doesn't
• Generator has good magnetic field when key is turned on
• Visually inspected pick-ups for bad/broken wire and none noted
• Battery has been fully charged in each test
• Compressions - testing order/PSI: 1/121, 4/120, 2/112, 3/111

I'm convinced with the recent swapping of the 1 & 4 plug wires that it's got to be fuel related and not electrical - but maybe not. Cylinder 4 gradually heats up, 3 doesn't. # 4 heats up slightly after 1 - 2 minutes, but never enough that you can't keep your hand on its exhaust header.

Also, new problem from last night - either carb 3 or 4 has a stuck float as I left its petcock in prime and gas was leaking from the airbox - what's the best way to determine which carb has the stuck float and best way to fix. Bike was on its centerstand for about 10 minutes with this happening - should I change the oil?

June's here and I'm still not riding and starting to get the itch really bad - any help would be greatly appreciated. On the road next week but will be checking your posts.

Thanks,

Chris

[Cuda 69]

Chris,visually inspecting the pickup coil wires will not tell you if there is a broken wire,you need to pull on each wire individually and if there is any stretch to the wires,you need to do the pickup wire repair as stated on here. I had two wires broke internally and you could not tell they were broken by visually looking at them.My SG was doing the same thing.Search on here for the pick up coil repair on here and go back and check the wires again, Hopefully you find the problem before you replace anymore parts.

[Cuda 69]

Also,if your getting weak spark on 3 and 4,it's gotta be electrical not fuel. Carbs don't make spark. I will be the first to admit,i'm no expert on there machines so somebody will chime in to give more idea's.

[crazy steve]

You're correct in thinking that this is a carb problem, not an electrical issue. The cylinders are paired 1/4 and 2/3 electrically, but 1/2 and 3/4 for fuel. So looking over your list of things done, several things pop out....

Carb cleaning. These carbs have proven time and again that anything less than a very thorough job won't cut the mustard. Removing all the jets and being positive that every passage is spotlessly clean is the only path to carb happiness. You also don't mention re-syncing/adjusting the carbs after cleaning; this is mandatory after disassembly, 'resetting' them to the way you found them won't do it...

For rebuilding directions, look here: http://www.xs11.com/forum/showthread.php?t=36017

Carbs removed and air blown into tee that flows fuel to Carbs 3 & 4 - No problems noted and identical to same result on Carb 1 & 2. Vacuum tees to airbox tested and same results between 3 & 4 and 1 & 2.

This is not good either; if you did this with the carbs assembled, there's a good chance you collapsed one or more of the floats, assuming you still have the OEM brass floats. Damaged floats will likely have to be replaced, although a few have had success fixing them.

You need to go back into the carbs....

[natemoen]

The only thing that 3 & 4 share in common is the fuel supply, same petcock feeds both carbs, beyond that though it is all different.

Since 3 & 4 even act different, Did you ever swap 2 & 3 plug wires?

Have you checked your fuel vent on those carbs.

You say you blew air into the carbs, did you use an air compressor or just your mouth? Compressed air can often collapse the floats.

[Cuda 69]

AH,that's right,I had problems with spark on 1&4,see,I told you i didn't know much about these bikes.Always learning on here,just hard to keep all this in my brain.

[CK]

Hey thanks everyone for the quick replies - I'll try and catch-up now with everyone's post:

Cuda - about the pick-up coil wires, I've pulled on them gently, but was afraid I'd really mess something up if they weren't the culprit - Also, I don't really know if I have a weak spark. Wanted to ask you though, were you having the same symptoms, two cylinders not firing from different coils - the electrical stuff really trips me up so I wanted to ask. Thanks for your post.

Steve - You're post is building my belief in that talk I've read about "triple cleaning". I elected to do the Pine Sol because of the post I read that it wouldn't harm any elastomers in the carbs. On the second cleaning, the mechanic told me he felt confident that all jets checked out good. About syncing, I pre-synced with the bread wire method, then another way I read about the butterfly's edge over the ports. I know they'll need to be synced once I square everything, but I think they're pretty well pre-synced now. The mechanic is used also said the same.

Natemoen - I did not swap 2 & 3 but that's a good idea and will try that later in the week. You got me on the fuel vent - where do I check that? About blowing air into the carbs, I just attached a new hose to the tee where the fuel splits into the carbs and blew gently with my mouth. Fuel weeped out some of the ports, no different than when I checked 1 & 2.


For all - were my compressions ok for a bike with 24K miles. I think 2 & 3 would have been higher, but I think the battery was starting to tire with those last two cylinders.

Would it help to open up the idle-mixture jets - the manuals say to leave them alone.

What do you make of it that #4 starts to heat a little but #3 doesn't. Is the consensus to just re-clean the carbs with a full tear down?

Could the floats in 3 & 4 be the cause - A week or so ago, upon starting, 3 & 4 started heating up normally, then within a minute stopped heating up. I thought perhaps that upon starting, the fuel in the bowls was used up and no more fuel got in. Any thoughts here?

Thanks all for your input.

Chris

[natemoen]

What do your plugs look like? 3&4 could be fouling out.

[CK]

Nathan,

3 & 4 are just black & oily with no combustion seeming to be taking place. I really believe they're just not getting fuel, but it's hard to believe also that only 3 month of inactive use would lead to such a severe clog that two cleanings wouldn't get it. I know E85 is prone to gunk-up, but not that bad I would think in such a short time.

Chris

[CK]

Hey Nathan,

What fuel vent were you asking if I checked?

Chris

[BA80]

JAT..... have you tried a new set of plugs?

BTW.... The vent mentioned is the T on the carbs right above the fuel inlets. It looks just like the fuel inlet. Clogged vents can cause some wierd problems

[CK]

BA80,

Yeah, did get a set of new plugs and I actually thought that solved the problem, but that was short lived.

The vents, I did check them the same way as I did the fuel, with blowing gently into them, nothing seemed any different than the carbs on cylinder 1 & 2 though. Is there another way to check them? Thanks for your post.

Chris

[natemoen]

The black wet sooty plugs means either you are getting too much fuel OR it can't.burn.the fuel well. So when you put new plugs in and it ran well but only till the new plugs fouled up and quit firing.

So you need to pull the carbs and figure out why you have a fuel delivery problem.

The vent I was talking about was the upper T on the carbs.

[CK]

Nathan,

Good point - I'll clean them up and post my finding later in the week.

Chris

[CK]

78E Update

All,

With the exception of cleaning the carbs again, I did clean 3 & 4's plugs up and switched the plug wire from #2 to number #3 as Nathan suggested. With that swap, all plugs were reversed i.e. 1/4 & 2/3. I set the idle mixture screw on 3 & 4 to the factory recommended start point of 1 & 1/4 turns out. Also, before I started it, I double checked the air side from the airbox through the complete exhaust system and found everything normal.

I started the bike up and all four pipes heated up normally. I let it idle and placed a box fan blowing on it and left it for about 10 minutes. When I checked it again, pipes 3 & 4 were no longer hot.

I believe that initially on cylinders 2 & 3, the carbs are pulling gas from their full bowls and the cylinders fire normally until the fuel is depleted. The floats are apparently stuck in their high position not letting in more fuel and the carbs become starved for more fuel.

I checked the floats last weekend on all four carbs and the all seemed normal, but I think another inspection is due.

Any ideas out there on what specifically I should check on the floats except for free movement. Does everyone agree with my reasoning? All comments would be greatly appreciated.

Thanks,

Chris