Topic: Misfire after Rain

[SOHC]

First Off let me start by saying i searched the forums and couldnt find a similar problem with a cb650. So this may have been covered b4, but i couldnt find the topic.

About a week and a half ago i got caught in a major down pour, so heavy i had to pull over, and while stopped the bike idled just fine, and the bike also ran great the rest of the way home.

The next day it started and ran great, until i got it into 4th gear & also 5th gear. It was popping and misfiring etc.
The Bike has brand new OE coils, and they are not split, plus it will pull hard or gently all the way thru third, then and soon as i shift to fourth it starts to spit and sputter.

The few things i have done so far are.. Replaced Plugs, Cleaned Carbs (not rebuilt), drained tank to check petcock filter (its non-existant) so i installed a new filter to no avail.
I am not sure if the igniters are wrecked, i found some of the black acrylic or whatever they use to seal them on the bottom one.

I am baffled as to why it would run great all the way thru third, then fall on its face in fourth (no matter the throttle position).
The bike ran awesome until that day, im not to upset since its so close to winter here in MN, but i wouldnt mind riding it a few more times before i tear it down this winter.

Btw its a 1979 CB650 /w stock PD carbs, with stock air box (yes i even tried removing the filter to see if it was wet)

[HondaMan]

First Off let me start by saying i searched the forums and couldnt find a similar problem with a cb650. So this may have been covered b4, but i couldnt find the topic.

About a week and a half ago i got caught in a major down pour, so heavy i had to pull over, and while stopped the bike idled just fine, and the bike also ran great the rest of the way home.

The next day it started and ran great, until i got it into 4th gear & also 5th gear. It was popping and misfiring etc.
The Bike has brand new OE coils, and they are not split, plus it will pull hard or gently all the way thru third, then and soon as i shift to fourth it starts to spit and sputter.

The few things i have done so far are.. Replaced Plugs, Cleaned Carbs (not rebuilt), drained tank to check petcock filter (its non-existant) so i installed a new filter to no avail.
I am not sure if the igniters are wrecked, i found some of the black acrylic or whatever they use to seal them on the bottom one.

I am baffled as to why it would run great all the way thru third, then fall on its face in fourth (no matter the throttle position).
The bike ran awesome until that day, im not to upset since its so close to winter here in MN, but i wouldnt mind riding it a few more times before i tear it down this winter.

Btw its a 1979 CB650 /w stock PD carbs, with stock air box (yes i even tried removing the filter to see if it was wet)

In the taller gears, it pulls harder. So, if it has weak spark or a slightly lean fuel mix, then the misfire is more apparent. Things to check:
1. Did you also install new sparkplug caps?
2. Look into trying to tighten up the connections between carbs and head. There may be some well-cooked rubber hoses holding those carbs to the head: at about 1/2 throttle this can make things start to lean out abruptly. A symptom of this is: once past that RPM range, it may get better again, if you can get there. The hose clamps might be stretched out, or just loose, or the rubber so hard it leaks vacuum.
3. Fuel feed: disconnect the hose at the tank and drain into a quart jar: it should fill up in less than 2 minutes. There might just be some accumulating crud in the screen, needing some attention?

[Retro Rocket]

1. Did you also install new sparkplug caps?

That was my first thought too....

[SOHC]

Do you mean Plug boots? No.
I only replaced the plugs, because i thought i might have fouled one, but they all were light tan, so i replaced them anyways, and it still ran the same, as it did before i replaced them.

I pulled the boots and checked they were screwed in properly, and the wires didnt feel wet.

After the rain I rode the bike for atleast an hour on dry roads before i got home. And it ran mint like it always did before the rain, i dont think its plug boots, but i wouldnt doubt anything on a 35 year old bike, and i will put it on the parts list.

[Deltarider]

This problem is common on our bikes with HTleads exposed to spray. I had it more than once. Rainwater (or mist) on HTleads can leave a film of particles that can conduct. HTleads often are not clean. Sometimes when dry the problem goes away, sometimes it remains intermittently. Clean HTleads well and make sure there's no arcing between HTleads and ground (enginehead).

[Phoenix]

I was just about to start a new thread when I read this.  Since I am now going on multi-day trips, I am concerned about rain and it's effect on the bike.  In the old days, there was a spray I put on the wiring of my sports cars to "waterproof" the system.  How do you guys deal with prevention-if any_ and getting the bike running again.  It's raining today and I leave for the Dragon next week.

[SOHC]

Well, since i am purchasing a Motorcycle lift from harbor freight, i have decided that i will not ride the bike again this year, and i will be beginning the tear down for its hard tail conversion.
So if i decide to go with dyna coils (3ohm) whats the better option, the wires with boots already molded in or the screw on style boots and wires? (i love the red NGK boots davidsilverspares.com has)

[SOHC]

2. Look into trying to tighten up the connections between carbs and head. There may be some well-cooked rubber hoses holding those carbs to the head: at about 1/2 throttle this can make things start to lean out abruptly. A symptom of this is: once past that RPM range, it may get better again, if you can get there. The hose clamps might be stretched out, or just loose, or the rubber so hard it leaks vacuum.

BTW Hondaman
Yes the boots are dried out and cracked, they never affected the bike before, but they surely need to be replaced. Like i stated the plugs didnt show signs of running lean. But when i rebuild this winter, they surely will get replaced

Hondaman, have u ever heard of someone adapting cyclex's cb750 duel carb setup to a cb650? The head intakes arent angled like the 750, just wondering if it might even be possible.

[Retro Rocket]

Do you mean Plug boots? No.
I only replaced the plugs, because i thought i might have fouled one, but they all were light tan, so i replaced them anyways, and it still ran the same, as it did before i replaced them.

I pulled the boots and checked they were screwed in properly, and the wires didnt feel wet.

After the rain I rode the bike for atleast an hour on dry roads before i got home. And it ran mint like it always did before the rain, i dont think its plug boots, but i wouldnt doubt anything on a 35 year old bike, and i will put it on the parts list.

The plug caps are the part cap that pushes over the plugs, I have seen these with minute cracks in them, almost unseen with the naked eye, but once wet it creates a short, sometimes if you run the bike on the side stand and have a close look at the plug caps you can either hear a jumping spark or even see it, this may not be the case here but its worth checking...

[DH]

Do you mean Plug boots? No.
I only replaced the plugs, because i thought i might have fouled one, but they all were light tan, so i replaced them anyways, and it still ran the same, as it did before i replaced them.

I pulled the boots and checked they were screwed in properly, and the wires didnt feel wet.

After the rain I rode the bike for atleast an hour on dry roads before i got home. And it ran mint like it always did before the rain, i dont think its plug boots, but i wouldnt doubt anything on a 35 year old bike, and i will put it on the parts list.

The plug caps are the part cap that pushes over the plugs, I have seen these with minute cracks in them, almost unseen with the naked eye, but once wet it creates a short, sometimes if you run the bike on the side stand and have a close look at the plug caps you can either hear a jumping spark or even see it, this may not be the case here but its worth checking...

Along retro's suggestions, if you have an adjustable spray bottle with water, lightly mist the wires/components, one part at a time, while engine is running and listen for changes in engine performance. If its a moisture issue, that will often times bring it out. Mist LIGHTLY and be as precise as possible.

[SOHC]

Do you mean Plug boots? No.
I only replaced the plugs, because i thought i might have fouled one, but they all were light tan, so i replaced them anyways, and it still ran the same, as it did before i replaced them.

I pulled the boots and checked they were screwed in properly, and the wires didnt feel wet.

After the rain I rode the bike for atleast an hour on dry roads before i got home. And it ran mint like it always did before the rain, i dont think its plug boots, but i wouldnt doubt anything on a 35 year old bike, and i will put it on the parts list.

The plug caps are the part cap that pushes over the plugs, I have seen these with minute cracks in them, almost unseen with the naked eye, but once wet it creates a short, sometimes if you run the bike on the side stand and have a close look at the plug caps you can either hear a jumping spark or even see it, this may not be the case here but its worth checking...

Along retro's suggestions, if you have an adjustable spray bottle with water, lightly mist the wires/components, one part at a time, while engine is running and listen for changes in engine performance. If its a moisture issue, that will often times bring it out. Mist LIGHTLY and be as precise as possible.

I like that idea i might just try it before i do my teardown.

[calj737]

And did you happen to check beneath the points cover? There's a gasket there for a reason. If the rain was that heavy, may well have saturated your points, or whacked a condenser.

[MiGhost]

And did you happen to check beneath the points cover? There's a gasket there for a reason. If the rain was that heavy, may well have saturated your points, or whacked a condenser.

650 = Electronic Ignition. No points, condenser, or cover gasket.

[Don R]

I'd want it running right before I changed anything major, you might end up chasing a problem later and it will be harder to find. I don't think the cycle x 2 carb set fits a stock frame. if you're cutting and welding and they have manifolds for a 650, maybe.Call cycle X.

[calj737]

And did you happen to check beneath the points cover? There's a gasket there for a reason. If the rain was that heavy, may well have saturated your points, or whacked a condenser.

650 = Electronic Ignition. No points, condenser, or cover gasket.

Oh go ahead and read the whole dang thing, MiGhost!  Sorry, missed the earlier posting. 

 Don't know whether it's this bug-y upgrade on my tablet or the forum re-boot but having a hell of a time with certain threads...

[HondaMan]

2. Look into trying to tighten up the connections between carbs and head. There may be some well-cooked rubber hoses holding those carbs to the head: at about 1/2 throttle this can make things start to lean out abruptly. A symptom of this is: once past that RPM range, it may get better again, if you can get there. The hose clamps might be stretched out, or just loose, or the rubber so hard it leaks vacuum.

BTW Hondaman
Yes the boots are dried out and cracked, they never affected the bike before, but they surely need to be replaced. Like i stated the plugs didnt show signs of running lean. But when i rebuild this winter, they surely will get replaced

Hondaman, have u ever heard of someone adapting cyclex's cb750 duel carb setup to a cb650? The head intakes arent angled like the 750, just wondering if it might even be possible.

If your sparkplug caps are OEM, they ARE done for. The copper-to-carbon contacts in the caps are chromate-plated, which flakes off after about 10 years (like the fusebox clips). They are toast, bet on it. This corrosion raises the resistance: you can measure them with an ohmmeter. OEM ones were around 7500 ohms (10,000 ohms on the 1980) and are considered used up at 8500 ohms, or if one of them is more than 500 ohms different from the other, on one coil.

The carbs: if you don't change the intake valve on the head, bigger carbs won't do much but introduce nasty flat spots at low RPM when it disturbs the low-speed volumetrics. A better thing: do a port job when you have it apart. When I do this to the Mid-Fours, it really wakes them up: the valve guides are gigantic, so there is quite some restriction in and around the intake valves.

[SOHC]

And did you happen to check beneath the points cover? There's a gasket there for a reason. If the rain was that heavy, may well have saturated your points, or whacked a condenser.

Don't worry i do that all the time too, i usually get excited to write a reply and forget to read the rest of the post LOL, so no worries!

I'd want it running right before I changed anything major, you might end up chasing a problem later and it will be harder to find. I don't think the cycle x 2 carb set fits a stock frame. if you're cutting and welding and they have manifolds for a 650, maybe.Call cycle X.

I will be installing a hardtail from Voodoo Vintage this winter, and i had planned on upgrading coils, wires, boots, R/R, (igniters with dynas?) and many other parts, not because she needs it, but because i want them new, then i will have spares on hand as well.
Everytime i emailed him, his answers were short, and didnt seem even interested in making an exhaust he has for a 750 to adapt to a cb650, I might just have to drive over and bother him this winter LOL.

2. Look into trying to tighten up the connections between carbs and head. There may be some well-cooked rubber hoses holding those carbs to the head: at about 1/2 throttle this can make things start to lean out abruptly. A symptom of this is: once past that RPM range, it may get better again, if you can get there. The hose clamps might be stretched out, or just loose, or the rubber so hard it leaks vacuum.

BTW Hondaman
Yes the boots are dried out and cracked, they never affected the bike before, but they surely need to be replaced. Like i stated the plugs didnt show signs of running lean. But when i rebuild this winter, they surely will get replaced

Hondaman, have u ever heard of someone adapting cyclex's cb750 duel carb setup to a cb650? The head intakes arent angled like the 750, just wondering if it might even be possible.

If your sparkplug caps are OEM, they ARE done for. The copper-to-carbon contacts in the caps are chromate-plated, which flakes off after about 10 years (like the fusebox clips). They are toast, bet on it. This dorrosion raises the resistance: you can measure them with an ohmmeter. OEM ones were around 7500 ohms (10,000 ohms on the 1980) and are considered used up at 8500 ohms, or if one of them is more than 500 ohms different from the other, on one coil.

The carbs: if you don't change the intake valve on the head, bigger carbs won't do much but introduce nasty flat spots at low RPM when it disturbs the low-speed volumetrics. A better thing: do a port job when you have it apart. When I do this to the Mid-Fours, it really wakes them up: the valve guides are gigantic, so there is quite some restriction in and around the intake valves.

Thanks for the coil info, good to know.

I wasnt really interested in bigger carbs as much as i want less carbs, and a cooler looking setup LOL. I would have of course rejetted them as need be, but i was also considering a breadbox from these guys www.steeldragonperformance.com since they are from MY State Minnesota, and the PD Carbs on my 650 are the same as the 77-78 750.

I was honestly debating, porting and polishing the heads, because to be honest, im not real concerned about more power, yet on the other hand i will have time to do it this winter, and breathing better never hurts.

Hondaman, I am by nature one of those guys that, if a motorcycle will go 180mph, I WILL GO 180mph, not that the honda is close (105 at the moment), i just dont, need any more speed, i bought it to cruise on the weekends with my buddies.

[my79650]

I just carry a can of ignition spray in my saddlebag. Spray it on the wires and caps; spray up underneath to the coils as well. When i turns a light white it is working but says to use on a cold engine. Has saved me from missing on those rainy days and nights when leaving work. Just a suggestion for you.