Topic: Back from the dead HELP!!!

[vinny9744]

Ok, I have a 73 cb750 that I recently purchased and started working on. P.O said bike sat for 10 years. I cleaned and rebuilt the carbs. Changed the oil. Installed a new Dyna-s ignition. NHK plugs and wires. Adjusted valve tappets ( checked them three times) and ajduusted the cam chain tensioner. After all that it started right up. I took her to a local shop where I got hosed.. Two tires mounted. carbs synced and I guess he adjusted them.

The bike runs but not very well the left half of the motor seems to have a backfire under throttle. The right side is fine. I can hear this from 4 -2 exhaust.  It bogs a little in second and third gear.
I checked the timing. First staticly and then with a timing light. Seems to be good. Unsure about the way to adjust while at 2500 Rpms though...

What could be causing this any help would be greatly appreciated.

[greenjeans]

Sounds like it could be an Exhaust leak ?   happened to me last summer.  Had a leak at the head and it backfired a bunch.
Maybe try some new exhaust gaskets - they are cheap and readily available at your local Honda shop for about $2 bucks a pop.

If you haven't synchronized your carbs, that needs to be done.  You can get a Morgan Carbtune for $100 or less and have it forever.  If you can do all that
other work, carb sychronizing is easy.

I'll also add that since yours sat for 10 yrs (as did mine) the more you run it, the better it will run - rings become looser and seal better - basically your just burning off
all the gunk that's been there for the last 10 yrs.   

I'd start with some new exhaust gaskets and see where that takes you...cheap & easy

[Hush]

Could also be an air leak at the carb collars, check their tightness and if they look a bit old spray with silicone spray or CRC or whatever  while the bike is running and see if that helps, if so you have a leak there.

[vinny9744]

Thanks for the idea with the exhaust gaskets. I just ordered them.

The boots from the carbs to the airbox are good, they are brand new. I could have killed someone with the old ones. Could the other side from the carbs to the head be a problem?


When I said it back fires its more like a pop


Also it idles like hell. I have nothing to compare it to but is that the norm?

Thanks guys.
Vinny

[MCRider]

Yes the carb to the head boot is much more important. A lean pop could come from an air leak. Reconditioning is often possible. Soaking, rubbing silicone into the cracks after heating with a hair dryer, many such tricks. and the clamps. The stock clamps only pull so tight. If they are as tight as they'll go and they still turn on the rubber boot, because the boot has shrunk with age, a screw type hoseclamp may be in order to get them tighter.

[Johnie]

You said, "carbs synced and I guess he adjusted them."  Does not sound to convincing to me.  A bad sync by someone that does not know how to work with these older bikes could be the source of your problem.

[vinny9744]

Yeah I'm not completely convince he had the slightest clue either.. I am taking everyones advice. I ordered new exhaust gaskets and new carb boots (insulators). I should have them this week. The more I read about carbs it seems that my bike is running lean. When I change the boots I will probably also move the needle clip position to richen it up. 

Thanks for all the help and suggestions. I will post results and pics soon...