Topic: '77 750K Intermittent Power Issues While Riding

[skatedad]

Background: I have a 77 750K I bought last spring as my first bike. Known modifications are the 836cc kit, 4 into 1 exhaust with a baffle, electronic ignition, and oil pressure gauge. Original airbox, no pods or anything. Only issues last summer were replacing the battery and the ignition switch assembly. Other than that it ran fine last year. For winterizing, the previous owner just put stabilizer in the tank and kept it in his attached garage. That's pretty much what i did this year too, stabil in the tank and let it run through the system then turned off the petcock and let it run until it died and parked it. I recall the previous owner saying that he'd never cleaned the carbs and I haven't yet either but I'm running a fuel additive with carb cleaner in it right now though i know i need to tear them out and clean them good soon.

Problem: This spring an intermittent running issue has appeared. What happens is that while I'm riding all the sudden my engine will cut to what feels like half the power and sound really low and grumbly. While it's doing this I have to give it a ton of gas to get moving from a full stop and things like that. Then after a while it does this thing where it kind of pops and I'm back to full power. there doesn't seem to be any certain action on my part that causes it to occur or to clear. One thing I noticed yesterday is that when idling during the problem the oil pressure gauge reads 0 but when it clears the gauge jumps back up to a reading. Not sure what that means.

My question to the forum is where you would start trouble shooting? I've had some people say maybe I have a coil problem and that when it happens that not all cylinders are firing. Others say that it could be a carb issue. I'm a mechanical novice with a handful of tools and a Clymer manual but I do have some more experienced friends that can help me once I decide what to start doing.

[flybox1]

I recall the previous owner saying that he'd never cleaned the carbs and I haven't yet either but I'm running a fuel additive with carb cleaner in it right now though i know i need to tear them out and clean them good soon.
YES!
Complete the items listed in the 3000mi periodic maintenance.
Clean your carbs.  Do it once. Do it well.
Clean/check/dielectric grease all of your electrical connections.
Check your plug caps resistance, cut back old wire 1/4" (+/-) to get to good clean copper, and re-install
You should be good to go.


a .pdf of your HONDA shop manual is located here...
http://www.honda4fun.com/materiale-documentazione-tecnica/shop-manual

[Rgconner]

One thing I noticed yesterday is that when idling during the problem the oil pressure gauge reads 0 but when it clears the gauge jumps back up to a reading.

is that gauge electric?

If so, it is an indication you have a wiring issue. Probably cutting power to one side of the ignition.

[skatedad]

is that gauge electric?

I don't think so. This is what it looks like.

[BobbyR]

This is probably very simple. I will guess you have a Dyna electronic ignition. This is the tip off:

This spring an intermittent running issue has appeared. What happens is that while I'm riding all the sudden my engine will cut to what feels like half the power and sound really low and grumbly. While it's doing this I have to give it a ton of gas to get moving from a full stop and things like that. Then after a while it does this thing where it kind of pops and I'm back to full power. there doesn't seem to be any certain action on my part that causes it to occur or to clear.

Dynas made in the past were bullet proof. Something either changed in the design, manufacturing, or parts supplier. You are dropping two cylinders when the bike heats up. It starts to happen slowly like a blip in power, Then it progresses to a point you drop two cylinders which stay dropped until the bike sits and it cools down.

I had it happen to me and I bought a PAMCO. You can reinstall the points. Better yet is points with a with a Hondaman ignition. i have been trough this and you need no further troubleshooting.

[scottly]

Thanks Bobby, I was getting tired of being the Dyna s Grinch....

[BobbyR]

If you can reproduce the problem while idling, test the heat of the exhaust pipes to ascertain which cylinders are being affected. If it is a pair, and that pair is served by the same coil, then Bobby may well be onto the root cause.

However, if you find its only a single cylinder, or cylinders not sharing the same coil, then I would absolutely start looking at fuel delivery issues. (Wouldn't hurt to check this anyway).

Scottly, my pleasure.

I have a really simple low tech and simple test that I did on the side of the road. When the power craps out, you reach down and pull the wire off number 1 or 4 wire. If the motor is still acting up the 1-4 Dyna pickup has failed. If it stalls, the 2-3 pickup has failed.

It is really simple to diagnose this problem. Your Dyna is crapping out. On flat ground you can do about 40mph on two cylinders. If you are moderate distance from home. Take off the points cover, let the Dyna cool and run with the cover off it may keep the temp low enough to keep the unit cool enough to operate. When you get home decide what you are going to replace it with.   

 

[Stev-o]

Only 1 thing to add: coils are often mistakenly diagnosed as the electrical issue. They rarely go bad. 

[skatedad]

thank you everyone for the suggestions. No one I had talked to before mentioned anything about the ignition possibly failing. I'm off work here in about an hour and I'm going to be spending the afternoon attempting to troubleshoot based on what you guys have said.

[BobbyR]

thank you everyone for the suggestions. No one I had talked to before mentioned anything about the ignition possibly failing. I'm off work here in about an hour and I'm going to be spending the afternoon attempting to troubleshoot based on what you guys have said.

I went through the same thing. It was a Google search which gave me the lead. Forums like this were filled with stories of Dynas crapping out.  Guys with older Harleys  use Dynas and they identified the problem first.

[skatedad]

just for the sake of closure and in case anyone ever comes up on this in a search for something similar, I put in a PAMCO ultimate kit with the ignition, coils, wires, and caps and changed the spark plugs to iridium while I was at it and that took care of the issue. The previous owner didn't upgrade the coils with the dyna ignition (it did end up being a dyna s) and since I wasn't 100% sure which part the problem was I figured I'd just replace it all and know I was good for a while.