Yes, these are pretty old and often neglected bikes. It's very rare to just buy one and be able to ride off into the sunset on it, lol. All the various systems, brakes, fuel, charging, etc., usually need to be checked and/or gone through. Everyone's telling you fuel related but there could be other factors at work too. Your ignition timing could be off, spark weak, charging not up to snuff. These bikes don't run well with a low battery, the ignition will start acting up. Eventually, when the battery gets too low, the bike will just die.
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First highway run; engine bogs at 60
- Thread starter tzimmerm
- Start date
This is the classic symptom of a lean mixture , usually caused by a tiny air leak somewhere on the inlet rubbers or carb bodies.
How many turns out do you have your idle mixture screws set to and what pilot jets are fitted?
As 5twins says these symptoms can also be caused by a battery that is not being charged correctly or is not holding a good charge......... although I generally find that an undervolt battery causes my engine to misfire spit and fart when I try to rev beyond 2-3000rpm .
This happened to me on a run yesterday for about 8-10 minutes until the battery received a charge from the alternator.
I have not touched the carbs at all since I bought the bike, so I don’t know. (With the exception of adjusting the idle screw) It ran well when the PO started it for me the night I bought it. Then he rode it to my place to deliver it the next week when it was nice out. Over the last 3-4 weeks I’ve taken it on little trips around town. Progressively faster and harder riding. Yesterday was the first highway speed ride, and today it totally sucks. It would make sense that after being woken up it’s developed an air leak at the intake or some issue with the carbs after I filled it with supreme gas and octane boost and rode it hard. I guess my first plan of action will be to replace the intakes and spray out the carbs while they’re off.
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I wouldn't discount the possibility that you might also have a sticky throttle cable (or part thereof) along with air leaks. Is there a nice crisp 'snap' at the carbs when you release the throttle?
Yes; I just replaced all the cables; clutch, throttle, front brake, speedo. The throttle snaps back every time like it should; it’s definitely not sticking. It feels like an air leak. Whatever the carbs were doing was independent of the throttle.
Premium grade gas AND additives ...? you spoilng that bike ! 
These bikes can be frustrating at times and its a steep learning curve but theres immense satisfaction when you finally get them running well .
I had the same issue with my bike when I first bought it. I must have removed, cleaned and refit my carbs at least 5x times before I finally solved the problems.
When you see how minute the air and fuel holes are in the idle or pilot jets you realise how even the tiniest air leak can cause issues
These bikes can be frustrating at times and its a steep learning curve but theres immense satisfaction when you finally get them running well .
I had the same issue with my bike when I first bought it. I must have removed, cleaned and refit my carbs at least 5x times before I finally solved the problems.
When you see how minute the air and fuel holes are in the idle or pilot jets you realise how even the tiniest air leak can cause issues
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It's possible there was gunk built up in the carbs and all your riding, especially the hard riding, has broken it loose. I had that happen on a dirt bike I bought years ago. It ran fine when I gently test rode it around the side streets by the seller's house but when I got it home and went blasting across the open fields (took it off-road), that broke loose dirt sitting in the bottom of the float bowl and the main jet plugged up solid, lol. It would start, idle, and run at lower RPMs but wouldn't rev out past 2500 or so.
That’s why I mentioned and took that pic of the yellowish stuff on the bottom of the carbs. I know you can’t tell much from looking at it on my finger in the pic, but I didnt see it anywhere else; it was just on the bottom of the fuel
Bowls. I wondered if it was old varnish from the bowls that the nice gas and octane Booster melted. I am a bit worried about getting home. And damnit my girlfriend is getting righter every day, which is NOT a good thing in this particular case.
Bowls. I wondered if it was old varnish from the bowls that the nice gas and octane Booster melted. I am a bit worried about getting home. And damnit my girlfriend is getting righter every day, which is NOT a good thing in this particular case.
Does the varnish smell like old fuel? I got a $50 on it being nothing more than dirty carbs and as there's really no cost involved, assuming the gaskets are salvageable, it's where I'd start. Plus, you got an old bike so you could learn to work on it, right?
I did try to smell it, but it didnt really have a distinct smell. It was just really yellowish. So to be clear, if I take my carbs off to clean them, do I necessarily need to take them apart, or could I possibly get away with draining the bowls, spraying carb cleaner through them, and putting the new intakes/gaskets on? Shouldnt I buy a carb kit for things like O rings and jets as well? 5Twins, you havent berated me for buying new rubber intakes from Mike’s yet. You okay?
A lot of hassle taking carbs off. Best to do a thorough cleaning job when they are off to save having to do them again.
I had this before, cause by less than tight rear sprocket. I've found the way to get it to stay put is use new locking tabs, bend up three sides, and don't hammer them up hard enough to thin them. If you have a gas problem, it might be the whole bottle of additive. It isn't needed.
The binding sound is coming from the front sprocket. Apparently the new brake shoes I ordered from amazon were delivered yesterday, so I’ll have the rear wheel off again this weekend. I’m planning on picking up some feeler gauges, carb cleaner and anti-seize after work to tackle the brakes, head retorque and valve check. I’ll have to remove the carbs to replace the manifolds, so I will at least try to clean them up a bit and try running it that way before taking them completely apart. I don’t want to have the bike sitting outside without carbs for very long. I don’t think it’s wise to attempt dissassembling them until I have every tool/part that I’ll need to properly reassemble them again. That is how old bikes become basket cases. I wondered about the additive, too. Could under diluted cheap octane boost cause these problems? I mixed one bottle “suitable for a tank of gas” in 5 gallons of premium gas.
Wad up two or three plastic grocery bags and stick them into the intakes to plug them.
I wouldn't use any at all. Especially before I had the bike all lined out to a good reference point. I've never used it.
I know to cover them; I’m just saying since I don’t have a garage and live at an apartment complex, I don’t feel comfortable starting potentially long term projects that leave the bike debilitated.
I actually have Mike's intakes on mine, lol. But, they are from years back and have held up OK. There were reports a year or maybe 2 back that the ones they had now were failing from the ethanol. Hopefully they've addressed that issue. Guess you'll know soon enough, lol.
I see one of your pics shows a fair amount of oil leaking down the cylinders. What you found on the carb bottoms may just be blow-back from that. It may be oil mixed with the dirt and varnish on the carb bottom. Did it feel like oil?
Luckily, there aren't many rubber parts in your carb set. There is only one o-ring, on the needle jet. There are, however, a couple other rubber items, and they're important. You want to keep carb cleaner away from them so they don't get damaged or ruined. The biggie is the rubber diaphragm attached to the top of the slide. This is what makes the vacuum operation of the carb work. Hose it down with carb cleaner and it will shrivel up like a used condom, lol. It's best that you remove the carb tops, remove the slide/diaphragm assembly, and place it faaaaar away from the carb bodies before squirting any carb cleaner at them. There are also little rubber seals on each end of the butterfly shafts. Again, keep carb cleaner away from them. It may not be possible to keep it totally out of them but don't go spraying that area directly. Anywhere you do use the carb cleaner, flush and rinse afterwards with something mild like WD40. Oh, the tips of the choke plungers are also rubber, so don't be spraying them either.
Actually, I start the cleaning process with WD40. Using the straw on the can, I spray it through the passageways. If they're clear, I don't even use the carb cleaner.
I see one of your pics shows a fair amount of oil leaking down the cylinders. What you found on the carb bottoms may just be blow-back from that. It may be oil mixed with the dirt and varnish on the carb bottom. Did it feel like oil?
Luckily, there aren't many rubber parts in your carb set. There is only one o-ring, on the needle jet. There are, however, a couple other rubber items, and they're important. You want to keep carb cleaner away from them so they don't get damaged or ruined. The biggie is the rubber diaphragm attached to the top of the slide. This is what makes the vacuum operation of the carb work. Hose it down with carb cleaner and it will shrivel up like a used condom, lol. It's best that you remove the carb tops, remove the slide/diaphragm assembly, and place it faaaaar away from the carb bodies before squirting any carb cleaner at them. There are also little rubber seals on each end of the butterfly shafts. Again, keep carb cleaner away from them. It may not be possible to keep it totally out of them but don't go spraying that area directly. Anywhere you do use the carb cleaner, flush and rinse afterwards with something mild like WD40. Oh, the tips of the choke plungers are also rubber, so don't be spraying them either.
Actually, I start the cleaning process with WD40. Using the straw on the can, I spray it through the passageways. If they're clear, I don't even use the carb cleaner.
AAAAND one post changes the trajectory of my evening. Thanks for saving my carbs and my sanity. I was totally planning on taking the carbs off the bike when I got home and spraying the shit out of them with carb cleaner. So how exactly DO I clean the carbs without damging them? I have no experience with Carbs; I understand the fundamentals of how they work, but little details like using wd40 to clean them and to avoid hitting rubber with carb cleaner are important details that I didnt know. If I don’t need to buy a rebuild kit, what am I doing? Taking off the carbs, dissassembling them carefully, spraying the metal parts only, “rinsing” them with wd40 and carefully reassembling them to the specs listed in the carb guide here at the forum and pop it back in the new manifolds?
In reality, a carb "overhaul" or "rebuild" is 99% about the cleaning. Having compressed air available so you can blow the carb cleaner and/or WD40 through the passageways is a big help, but you can usually get by just spraying the stuff through with the straw on the can. If you have the carb cleaner in a spray can, you can spray some in a little plastic cup to soak some of the little parts in, stuff like the jets.
