Engine started running badly and died - can't find the problem

[Fabman]

Riding home on my FJ Thurs the engine started running rough then died..I parked it at the credit union and came back to pick it up later that night. It would only fire at full choke, sounding like it is only running on 2 for the 4 cylinders. It dies if you close the choke and won't restart.
This is a naturally aspirated in-line four bike that has run well for years.

Things I've done,
1. Changed the plus hoping it was a fouled plug issue. No change. Still runs rought on start and can't get bouve 1K RPM, then dies.
2. Checked to spark to the plug. All have spark.
3. Checked tank venting in case of a vacuum, Vent works fine.
4. Checked the fuel line for kinks, none even when tank is mounted.

Any suggestions where to go form here?

[andyb]

What year is it (fuel pump or no pump version)?

What did the plugs look like when you pulled them?

Check the exhaust for someone jamming shit into it to be funny, look for obvious issues like the carbs falling off or massive blockages of airflow. 

Dumb question.... does it have fuel in it? 

[FJmonkey]

Welcome Fabman, is this a daily rider or does it get stored for periods?

[ribbert]

Dumb question.... does it have fuel in it?  

That's NEVER a dumb question, I'd like a dollar for every time...............(not me)

[movenon]

Welcome Fabman   Sorry about the trouble. As noted above what year is your bike so we don't talk about useless things to look at. If you can, tell us where you are located. Sometimes there are other members close by that can assit or at least drink a beer while you work  

Hang in there, it is fixable. More info please.
George

[Fabman]

It is an '87 with 49K miles. Daily driver.(Put 267 day on it last year)
6 tank of fuel
tank of good fuel
Gravity fed
It died when it was hot, but still ran rough when cold (after just installing new plugs).
Everyone else suggest pulling the bowls I know nothing got in the carbs from the tank unless it would be water. I cleaned the tank a while back (found no debris or filter screen clog) and installed a new filter/petcock when I fouled a plug but had thought I had debris in my tank.
Have a new closed cell battery that works great. Though I check the spark by just laying the plugs on the head, is there a way to confirm if the coil spark is too weak. I have no multimeter and don't know what the spark should be.  I have other coils, I guess I could just swap them and see what happens.
Friend suggeste hose breakdown. I have a new tank hose, but should check the carb splitter hoses for deterioration. Wouldn't have thought of that. .Question: when pulling the bowls, do I need new gaskets/seals?

[FJmonkey]

An easier test would be to put the bike on the center stand, put a clear hose on one bowl drain at a time, bend the tube up so the other end is higher than the carb bowl, open the drain screw and see how high the fuel level is. Check each of the 4 bowls and note the fuel level of each. They should all be about the same. If the levels look low then you have a delivery problem. It is also very important to understand what work was done just before any problem happens. If you just changed the plugs you need to consider that as part of your problem solving process. Did the bike run well after the plug change? Are the plugs correct? Are they gaped properly? Did the plug wires get put back in the correct order?

[markmartin]

No such thing as a stupid question, but lets test the theory of a stupid suggestion? Have you assured that there isn't a mouse nest in your airbox?   Air, gas, fire,  compression.  Are you getting enough air?

[Dads_FJ]

An easier test would be to put the bike on the center stand, put a clear hose on one bowl drain at a time, bend the tube up so the other end is higher than the carb bowl, open the drain screw and see how high the fuel level is. Check each of the 4 bowls and note the fuel level of each. They should all be about the same. If the levels look low then you have a delivery problem. It is also very important to understand what work was done just before any problem happens. If you just changed the plugs you need to consider that as part of your problem solving process. Did the bike run well after the plug change? Are the plugs correct? Are they gaped properly? Did the plug wires get put back in the correct order?

^^ What Monkey said.  Here are the drain screw locations on the bottom of the carbs.  This seems fuel related...  Checking the temperature of each exhaust pipe may indicate which cylinder(s) are having an issue.

[movenon]

This probably will not help but here is some pictures of the correct fuel line routing for reference. It is a thread so just scroll down a bit.
http://www.fjowners.com/index.php?action=profile;u=3248;sa=showPosts;start=30
George

[FJ_Hooligan]

Sounds like a fuel flow issue.  On full choke, the carb is drawing fuel from the lowest point in the fuel bowl.  Did you have the tank off recently or install any new fuel lines?  Have you done any recent work on anything?  You mention cleaning the tank.  Have you ridden much since that maintenance? 

Another possibility is the vacuum diaphragm in the petcock has gone bad.

[movenon]

Another possibility is the vacuum diaphragm in the petcock has gone bad.

+1
If that diaphragm is bad (or no vacuum) it will not allow full fuel flow... Suck test ? They have been known to fail.
George

[FJmonkey]

How to perform the Suck Test.

http://www.fjowners.com/index.php?topic=9787.msg95549#msg95549

[Pat Conlon]

I cleaned the tank a while back (found no debris or filter screen clog) and installed a new filter/petcock....

Tell us about your filter you installed...just a new screen on the new petcock...or?

If you have installed a new petcock don't bother sucking on it....(bad monkey)

[Fabman]

I doubt it is the petcock, but checking the diaphragm never hurts. Been riding for over a year since I last checked the tank, and about 8 months since I changed a fouled plug. About a month ago is struts red for 4-5 secs at highway speed then cleared up. I will do the float check mentioned. Sadly I have a 4into 1 pipe to feeling the exhaust is useless.