Running Problems

[rekievit]

I recently purchased an '80 midnight special. It was running well, but now not so much. I have problems coming to a stop (it will stall when I apply the clutch and the RPMs drop). First gear is also tough, I have to keep pretty high RPMs (about 5) to keep from stalling when moving from a stop. Also when I am running the bike feels like is is only half in gear. Every second or so I get a little lurch or bump in speed like it caught for a second. While traveling above 30 mph when I twist the throttle, which has no response, RPMs don't rise but eventually (over about 30 sec) the bike will gain in speed.
By no means does the bike run smooth when traveling in higher speeds and this lurching really has me worried.
This all started when I stopped of the side of the road to meet some buddies and turned my petcocks off (The vacuum system was removed by the PO of the bike so they will leak if not shut off). Of course I got sidetracked and did not remember to turn them on again, the bike stalled and afterwords runs like this.

It feels like the clutch/transmission does not work properly (like i am half in gear half not), but I have a feeling it may all have to do with the carbs.

Not sure what to do and would appreciate all help I can get, I don't really have the money to take the bike to a mechanic.
Any thoughts?
Thanks
Rob

[Pat Kelly]

Possibly when the carbs ran dry it caused a float(s) to stick. I'd do a good carb cleaning.
See this section Carb Cleaning
and this thread Thread

[TopCatGr58]

Hey Rob,

Welcome, congrats on your acquisition, a rare find MNS!!

Okay, PO removed Octy, no big deal. BUT did he rebuild the petcocks?? There is a rubber disc valve inside it that can eventually break down. ALso, how old are the fuel lines? They, too can break down, particles can flow into the carbs,blocking the fuel paths, etc.!!

Pull the fuel hoses from the petcocks and make sure fuel flows when you turn it to ON. Also, make sure that they DON'T Flow when set to OFF! IF they trickle when in OFF, then there's a possibility of it overflowing the carbs...IF the carb float valves are not sealing properly, then you can get fuel into the OIL!

Also, you can pull the plugs to inspect them for signs of fouling, should look nice a tan/gray around the white center insulator, but if wet/black/sooty/oily then it's fouled!

While you've pulled the plugs, you can take a good PAIR and plug them back into the #1 and 4 plug wires, lay them on the engine and turn the engine over with the starter to check for SPARK. Then to the same with #2-3, the spark plugs are PAIRED like this, and BOTH are needed to be plugged in for the spark to travel from 1 plug, thru engine back thru other paired plug/wire!

IF you have same amount/color of spark on both pairs, then you can concentrate on the carbs....most likely the problem! You don't need to be a mechanic to work on them, just fair with common tools, observant as you take 1 carb apart at a time to clean, put it back together, and then do the next one. You don't need to remove them from the bracket they are attached to, and do NOT soak them in a bucket of cleaner, just use carb spray on the body, and soak only the metal parts you remove. READ ALL of the tech tips you can find about the carbs, maintenence, repairs, etc., so you'll learn about some of the pitfalls. If you have a dig camera, take photos as you remove the bowls, so you can keep track of what they should look like inside when you are reassembling!

When done, use occasional doses of SEA FOAM to help keep them clean during use!
T.C.

[Ivan]

any other clues like black or blue smoke from exhaust? odd sounds etc?

I am not grasping the half in gear half out. You mean it feels like the clutch is slipping? or just lacking power?

I'll second the stuck float idea. You could try tapping the carbs with a soft face hammer a bit to see if it knocks it loose. If that works, it is definitely time for a carb redo.

I also wonder if you don't have an intake obstruction, or plugged air filter.

[Ken Talbot]

I'm going to put my bet on pick-up coil wires. Your engine is basically running on only two cylinders most of the time. Then once in a while, the broken wires makes contact, you get a brief shot of life, then it's back to two again. Unless you know better from experience, you could run on two cylinders for a long time and think the engine was working okay. Once you know what it can feel like, there is no mistaking the problem.

[rekievit]

THANK YOU for all the help and suggestions. Please keep them coming if there are more.

(@ Ivan
There is somewhat of a puttering sound, like little backfires, when i am at a stop, its harder to tell if there are any when i am moving. Also it feels like a great lack of power.)

I'm going to try and replace the plugs, check the air for blockage, and test the pick-up coil wires as suggested. Should I replace the coils too?
If none of that works I will take the carbs and clean them.
Ideally I would like to clean up the carbs anyways but I am afraid of getting them out of sync or messing something up. Is it hard to sync carbs (special tools required)? I have never worked on carbs before but am mechanically inclined.

[bikerphil]

coils & carb

I would test the coils with an ohm meter as prescribed in the service manual. They don't go bad very often, but you never know. After cleaning carbs, you can do a "bench sync" to get them close. This should get the engine running but then you will need to do a vacuum sync to smooth it out nicely. You will need a set of gauges or mercury sticks. Not very difficult.

[Ivan]

Carb synchronizing

I made something like this.

I put ATF in it, and had to make a couple vacuum restrictors. I just used a couple old pilot jets with all but the very end hole soldered shut, so very little air will pass through. Put one in each end of the tubing about an inch in.

I couldn't synch all four at once, but there is a way.

Synch carbs 1 & 2 to each other. Then synch carbs 3 & 4 to each other. Then synch carbs 2 & 3 to each other.

FWIW, just the pressure of the screwdriver on the synch screw will show up as a change of an inch or so. You need to let it stabilize, then tweak, then let stabilize and repeat ad nauseaum.

Also, I had to run through them a couple times, partly because I am a a perfectionist and partly because it took me a couple shots to figure out which ones to synch first second and third.

With out the vaccuum restrictors, the fluid will suck up into your engine before the engine fully starts. ATF makes a heck of a cloud of smoke, but other than that shouldn't hurt anything. They also help the fluid not bounce back and forth so much.

[rekievit]

Thanks again,
I will clean the carbs soon I think, but in the meantime I went to take the airbox apart to look for blockages and check the wires and such and there was a pretty decent amount of fuel that had leaked. I took a closer look and it seemed to be dripping from the bottom of the airbox. Also on the #4 carb there was some leakage where the carb connects to the airbox (the rubber boot?).
I am thinking that the petcocks are leaking and need to be fixed or replaced. Does that sound like the problem?
Thanks for your help
Rob

[bikerphil]

leaks

That's part of the problem, the leaking petcocks. The main problem is the float valve (needle & seat). Your's is an '80 so fuel is probably leaking past the o-ring. Might want to replace the float valves & o-rings. The leaking petcocks will only flood the carbs when you forget to turn them off (engine off).

[Korr]

Carb boots

Oh make sure the little tubes that stick out of the carb boots are plugged up also. When i got my bike the PO said i have to keep them plugged up or it will run like crap. Here's the link

http://cgi.ebay.com/82-Yamaha-XJ1100...3286.m20.l1116

[rekievit]

Its all good now, thanks for your help.
Two of the pickup coil wires were broken, i patched them up and everything seems to run great.
I put some seafoam in and will be going through the carbs this winter because I am sure they need a good cleaning and at least one of the floats is not sealing well.
I did a quick fix on the leaking petcocks by adding inline shutoff valves after replacing the fuel lines.
I did have another quick question though, what range (RPMs) do your guys run your bikes at? I was told the older bikes like to run at higher ranges but what do you think?

[Ken Talbot]

Originally posted by rekievit
Two of the pickup coil wires were broken,

Bingo!

[rekievit]

Yes, thanks Ken, you were right on and
"Once you know what it can feel like, there is no mistaking the problem"

[DiverRay]

RPM range is a personal thing. TC likes to run his at 6 to 8K, and I try to run mine around 2.5 to 4.5K. These bikes don't really care, they just RUN. Ride the way YOU want, and run REGULAR GAS to keep the carbon down. IF you run up long hills, or HOT weather, you may need to go up to mid-grade.