Loud backfire, engine quits.

[Starquest]

Hello, everybody. After some months of maintenance and recovering from my leg, I run the bike last weekend. Nice weather here in Fl, in the 50s. I had encountered a few problems. The speedometer bounced a little bit above 65mph. I did put a new cable and greased up good. The tachometer started bouncing above 5000 rpm as well as the fuel gauge. Under this speed everything is rock solid. On the way back I stopped at the restroom . I felt a little miss for 1 sec. Next backfire and a miss. Five seconds later another backfire and engine quit running. Took the seat off to check for loose connections, nothing wrong I could seen. Push the star button, fired up and went home. The only thing I did electricaly was put another earth cable from battery to a bolt in the subframe behind the resistors. Carbs are rebuilt, new plugs, checked coils, cleaned coil ground and main ground and some connectors including the kill switch. Thanks to everybody here. I did a lot of reading and I learned a lot. Thanks Robert RPM. The bike runs very good with the rebuilt carbs.

[Starquest]

Update: I took the bike this morning for a ride. I rode it for ten min on the highway at 4000 rpm. All the gauges were fine. I took it past 5000 rpm and the tach, fuel gauge started bouncing. Then a miss. The bike started to cutting off. I managed to take it home at lower speeds. Took the tank off, checked spark plugs, wires, coils 3.6 ohms both. The Haynes manual says 2.7 ohms. My fault. I routed the fuel line above the other two and after riding a little bit and high speeds ,pinched the line. I will try next weekend.

[balky1]

Before I reached the end of your post I wanted to say to you to check the fuel line routing. Sounds like fuel starvation problem.

[Starquest]

Ok. Thanks. I'm busy this week. I will check Saturday. I'm going to take the fairing off and check all connections at the gauge cluster and run the line under the other two. I can't believe I made that mistake. Last year I run it under the fuel lines and I didn't have any problems.

[Starquest]

I went for a ride this morning. I routed the fuel lines correctly, clean the ground coils,lube the speedometer cable,check the coil pick up resistance (162 ohms, orange to black and grey to black) year 1986. I have done the fuel cap mod last year, safety wire the petcock. When I did put the line today,the fitting moved a little bit. Need to order a new one. So I took it to the highway for a short ride.I went to 80 mph. The speedometer was not bouncing,the tach was good and the fuel gauge was not bouncing. The bike run awesome for 5 mins until I went off the highway. Started cutting off and 5 mins later died. I started with not problems and went home. I checked again the pick up coil and went to 205 ohms. It's normal?

[Pat Conlon]

Pick up coils: 149 to 182 is the proper ohm range when the coils are heated up to 68*F
If you took your ohm reading right after your ride, your coils should be toasty warm...

205 ohms is definitely out of spec.  You have 2 pick up coils on your '86.
Are both coils reading 205 ohms or just one?
If one coil reads within spec, and the other coil reads 205, then you have a bad pick up coil.

If both coils read 205, then, I would be suspicious....the chances of both coils going bad, at the same time, are slim.

[Starquest]

Before I took a ride today, both coils read 162 ohms. After the ride both coils read 205 ohms. The bike run very good for the first 5 min, then started cutting off even at low speeds.

[Pat Conlon]

Hmmmmmmm...We know as the temperature increases, so does the coil resistance, but by how much?

Those coils are much hotter than 68*F (ohm test temp.spec.) after your ride, so when the pick up coils are toasty hot, is a resistance of 205 ohms acceptable?

I *suspect* your coils are ok...because both coils have the same reading when hot.

Let's ask the group....

Something is interrupting your ignition, hence the backfire.
Use a jumper wire to bypass your side stand switch (close the circuit) go for a ride, see if the problem goes away.
Clean your stop/run switch on your handlebar.....you might have a dodgy switch interrupting power to the ignition box.
Perhaps your keyed ignition lock is acting up? Hot wire it....go for a ride, see what happens.

Do not do these all at once. Do this step by step, ruling out each component as they pass the test.

Intermittent electrical gremlins are a bitch.

[aviationfred]

I had a similar fueling issue with my 95 awhile back. I would ride a mile or so and then it would act as if it was running out of fuel. The problem ended up being the Main Control Relay and the fuel pump power contact in the relay. I know your 86 does not have a fuel pump, but the issue could still be your main control relay. Unfortunately Yamaha no longer has any new ones. I did a quick ebay search and there is a NOS one from Germany.

Fred

[Starquest]

Thanks for the input guys. I took another reading 20 mins ago at the connector for the pick up coils. 75 degrees, bike is cool. 168,170 ohms. That relay control is located at the left side on the front fairing? I did disconnect and clean some connector over there. Replaced ignition switch connector, was melted and alternator connector. Now you mention the kill switch. I did notice something today. Bike in neutral,sidekick up. Hit starter button,nothing. Hit it again and started. I broke a little tab on the red connector on the kill switch few months ago before I started to ride the bike this year. I don't see anything out of place but I'll try bypass the side stand switch.

[Starquest]

Update: I was busy this week. Yesterday I took the tank off after I tried to run the bike early. The bike was sputtering,cutting and quit running. So, I found out that the fuel line was pinched at the curve section on top of carb 3. The line I put it 3 months ago was too soft.I replaced with a 3/8 fuel injection hose. The ones that came in 2-3 foot in hard plastic case. The end of the line is curved so I did put it on the t connection and under the 2 lines. I rebuilt the peacock just in case even it was no leaching. Took a 100 mile trip today. Bike was perfect. No even a hiss. Pat, Fred: I tried the sidekick bypass and the control unit that I bought but make no difference. Thanks for the suggestions. I think I'm going to buy the unipods so I can have more room for the lines.

[Starquest]

I rode the bike last weekend. It ran good for 20 minutes. After filling the tank,I took a ride and the bike cut it off. Wait for 1 min and the bike started and run for the rest of the trip. I was hearing a noise from the tank. I was surprised because I took the little 2 rubber grommets last year from the gas cap. I took it appart and I found out I did put it backwards.The next day I rode it for 2 hours. No problem. Today something weird happened. I was ridding at a constant 5000 rpm and the needle started bouncing 500 rpm down every 5 or 6 seconds,sometimes up. May be a coil or ignition box. I rev the engine pass 7000 rpm and it no make power. Too much fuel?. The bike has 4 to 1 exhaust, unifilter on ope stock airbox, 5 degree advance. 117.5 mains,40 pilots, needle on middle groove.

[FJ_Hooligan]

Check the main ignition connector and the coil connectors under the the front of the fuel tank.  Clean any corrosion and apply dielectric grease

[Starquest]

I replaced the connector and pins last year on the main switch. I cleaned the coil connectors too.Where did you get the rpm signal from?

[Carson City Paul]

Take note... dielectric grease is an insulator and should never be applied to metal connectors.