running on three cylinders until 2500 rpm

[crazy410]

Hey guys I am new here and this is my second vmax now, I have been reading on here for a few years now and found multiple fixes but now I am stumped.

The other day I left my new to me 1990 vmax outside for the night after riding it for a few weeks without a problem, then it rained. Now when i start my bike the tachometer doesn't work, the back light is on, and it doesn't start to work until right around 2500rpm. Along with the tach not working until then, it runs on three cylinders until 2500rpm then it comes alive. It is always the front left cylinder that doesn't fire. I have taken apart most of the connections I can access easily and they all seemed clean, sprayed a little WD-40 into them and plugged them all back in. This has done nothing for me, any ideas you guys might have for a direction to look would be great.

 

[SpecOps13]

You need to eliminate the carbs on that cylinder as the cause... Drain the float bowls into a white paper cup and look for any black trash coming out. Screw on the right side, half way or so up and down or so, of each carb needs to be backed out a few turns, The drain hose is under each carb. All the crap collects on the left side as the bike is normally on the side stand....Harbor Freight has a laser temp indicator if that's an option, you can check the exhaust temp with it and it goes on sale at times for $30.00. Let us know your progress or further questions.

Good Luck and Welcome to the forum...
Dave

 

[crazy410]

I drained the bowls, only a few small particles came out of them, not enough to make me wonder too much, probably just some junk that was in the lines. I took temps of the exhaust and all were around 200* except the front left with was around 130. Where does the tachometer get its signal from... could the gauge cluster getting wet could it have burned out a resistor or something inside there?

 

[Rollie]

Have you pulled the plugs and looked for corrosion on and around the hole / wires / connections / plugs themselves ?

 

[crazy410]

About three weeks ago I put in brand new plugs, gapped them, removed the wires and cut a little off the end and reinstalled them and the bike ran great for about a month riding it on the weekends. The only thing that changed was it sat out in the ran just one night.

After a long morning of trolling at work around the forum and I am leaning towards the TCI being the culprit, also found out that my bike is an 89 with the yellow labeled box. When I was leaving for work this morning I fired it up and got it up to around 2500 to 3000 rpm when the front left cylinder would fire and when it does run on all cylinders it misfires. I have been looking around for a used one or refurbished and they pretty hard to track down. From reading I need to get a hold of Sean Morley and see if he might have one or know where I can get one.

 

[johnpclynch]

With the dampness, could the culprit be a cracked coil? But then, the front coils are notourisly hard to get at
The COP mod will bypass your coils ... or if you're really good at electronics you can swap the feed to each coil and also the plug caps to see if the problem switches from the left side to the right?

I had a misfiring cylinder, the cause was corrosion inside the wire but this shouldn't affect the tachometer

I found the reason for an intermittent dead cylinder, usually when it was raining or after washing the bike.
For some unknown reason, most of the wire had corroded at the connector, only the insulation was holding it together
View attachment 21664

 

[sdt354]

+1 to the coil swap. A Spark checker is a tool for every owner. They're cheap at HF. And very helpfull. Switch the coil, wire, then plug, and see if the problem follows to a different cylinder. If it doesn't, I'd look at the TCI. That's, after checking/cleaning connections, doing a pick-up resistance check. Nothing like having a known good TCI, to just plug in and see if it was the problem. It may or may not be. One step at a time.
Steve-o

 

[sdt354]

Hey guys I am new here and this is my second vmax now, I have been reading on here for a few years now and found multiple fixes but now I am stumped.

The other day I left my new to me 1990 vmax outside for the night after riding it for a few weeks without a problem, then it rained. Now when i start my bike the tachometer doesn't work, the back light is on, and it doesn't start to work until right around 2500rpm. Along with the tach not working until then, it runs on three cylinders until 2500rpm then it comes alive. It is always the front left cylinder that doesn't fire. I have taken apart most of the connections I can access easily and they all seemed clean, sprayed a little WD-40 into them and plugged them all back in. This has done nothing for me, any ideas you guys might have for a direction to look would be great.

Is this a stock, cable driven tach?

 

[Rhoy Carter]

Stands to reason that your problem dtsrted after leaving the bike out in the rain, the problem is most likely a bad connection. I would clean all the connections and use dielectric grease in the connectors including the connectors into the tci unit.

 

[crazy410]

The tach has three wires on the back of it, grey, black, and brown I believe. When you say the pickup resistance test, do you mean testing the three white wires coming from the stator? If so I have tested the resistance of those going to the rectifier and they are all 0.9 ohms... When I get home from work today I am going to tear into it some more.

 

[DMAN999]

I believe he's talking about testing the Ignition Coils (part #25G-82310-10-00).
The Left Front Coil connects to the Right Front Cylinder and the Right Front Coil connects to the Left Front Cylinder.
I just did the Cops Mod because my Right Front Coil was cracked and was only firing intermttently when it got hot.
I left the Coils on the Bike and just removed the Wires and Boots, it was easier than trying to get those Front Coils off the Bike.

 

[sdt354]

The tach has three wires on the back of it, grey, black, and brown I believe. When you say the pickup resistance test, do you mean testing the three white wires coming from the stator? If so I have tested the resistance of those going to the rectifier and they are all 0.9 ohms... When I get home from work today I am going to tear into it some more.

Ignition pick ups I meant. Prolly ok, but free to check. And now that I think about it, effecting just one cylinder? Not likely to be the cause of just one cylinder.

 

[crazy410]

thanks for all the input guys, when I have made some progress. when I got home from work today I took the TCI off the bike and opened it up and turned the oven onto warm in the kitchen and placed it in there for 20 minutes or so. Plugged the connectors back in after a little WD and fired it up. All cylinders firing, tach working, test ride goes good down the road just a slight misfire while cruising under light load. So now the hunt is on for a new / refurbished TCI. Somehow some moisture had to have gotten in to cause some weird stuff to happen.

 

[deekjx]

thanks for all the input guys, when I have made some progress. when I got home from work today I took the TCI off the bike and opened it up and turned the oven onto warm in the kitchen and placed it in there for 20 minutes or so. Plugged the connectors back in after a little WD and fired it up. All cylinders firing, tach working, test ride goes good down the road just a slight misfire while cruising under light load. So now the hunt is on for a new / refurbished TCI. Somehow some moisture had to have gotten in to cause some weird stuff to happen.

Awesome, thanks for keeping us posted. I just now read through the thread. The Tach gets its signal from the firing of the second cylinder in on an older vmax and from the 3 third cylinder on the newer ones if I recall correctly.