Bucks or labours

[barnfind]

What would cause a bike to buck or labour at around 60-65 mph ?
Thanks

[icerigger]

Tell us about the bike. Year, model, any mods, recent changes etc. My SWAG is you're running pods 'cause that's right about where they screw things up.

[TOOLS1]

Many things can cause this. Most likely a fuel problem though.
TOOLS

[barnfind]

It's a 69 cb750, it sound like fuel to me too. This is the first time this year that this happened.
The tank was at 3/4 or so. I'm running one fuel line to one set of carbs and the other to the other set from the petcock. Filters look good same with lines. I'll take it for another run today and see what's going on.

[TOOLS1]

If it starts to act up again while on your ride, open your gas cap. If it cures the problem, your gas cap vent is plugged, it it does not, you have ruled that out, and we can move on to other causes.
TOOLS

[barnfind]

I'll try that.
Thanks

[Re-run]

Well, normally this would not affect your year, but in 74, Honda made the final gearing tall to lower rpm while cruising along and for better mpg. What actually happened was that the engine would lug once a person hit 5th gear and people ended up riding in 4th to maintain power till they could swap out the front sprocket for something with a lower tooth count. I think the 74 came with something like 18/45 for the sprockets. People would change to a 17 tooth front and that solved the problem. It only occurred in 5th.

Without knowing more, it is hard to say if this would be an issue but I thought I would throw it out as the gearing caused the engine to lug. I know you said it was first time this year, but if you had changed your chain and sprockets...

I would also check your timing and plugs if TOOLS suggestion doesn't help. Easier than pulling a carb bank.

[barnfind]

Thanks for the info re-run. I did change my sprockets at the beginning of the year to 18-46 and also my exhaust to a scorcher muffler from Carpy's. I was going to set my needle valve clip to the bottom setting and jet the main up to 140. What do you think ?
I'm also running a 16" rim in the rear which I'm going to change back to a 18".

[Re-run]

Well, usually an exhaust change doesn't affect things too much. I certainly would not jump to a 140 main, at least not just from an exhaust change. You can check your plugs and see what the insulator looks like. Use this as a guide. If your engine is stock and using the airbox, a 140 will make things really rich in upper rpm ranges.
The scorcher is a small muffler alright, and while it will lean things slightly, but I don't think it would be enough to need 140s.
I would stay with what you have and tune your air screw if needed, before tossing in larger jets.

Also, the ratio there with 18/46 is 2.55. My 78 750 with its stock ratio is 2.73. Now, that doesn't sound like much, but it can make a big difference. These bikes like rpm, so go out and leave it in 4th and see how it goes. I would almost bet that it will behave much better.

If you still have a little bogging, pull the choke and see if it comes back. If it does, then the carbs are adding to the issue.

[barnfind]

THanks a lot for the info re-run. I awoke the beast yesterday, I moved my needle jets to the bottom setting and took it for a ride and wow ! The bike is completely different. Throttle response is now, no hesitation and goes like hell.the labouring is gone so far didn't take it on the highway just in the city but still doing in some parts 60 mph or so for great amount of distance. I do notice my idle is up about 2000 rpm's im going to remove my tank and adjust my throttle cables hoping that helps.
Thanks for the help again.
Ray

[Re-run]

How is your idle knob set? Keep in mind that idle changes as the bike warms up. SO it will seem good when cold, and faster once warmed up. Set idle to be proper when warmed up and use the thumb screw under the throttle to hold the idle when cold.