[pampadori]

i've had the bike about a year or so. Has always been reliable and the throttle has never stuck like it is now.

i put on an old fiberglass tank about 2 months ago.
Today was really nice, so i got the bike out and was warming it up. i gave it a little gas, and the throttle didn't return. i had to pull it back (the push / pull cables are a blessing if an when your throttle sticks.)

removed tank, look at cables. they look fine. remove carbs and the still stick without the cables attached. so its for sure not the cables.

i have a suspicion that some contaminate might have went thru the tank and into the carbs, but not sure at all.

i take apart the carbs and clean them. i cleaned the main jet and the needle and the cyl that the slides go up and down in. i get the carbs to where they don't stickf anymore.

Reinstall on the bike, and feels fine. start it up and try to go warm it up again. after it starts to get a little heat, they start to stick again! arghh~!!!

I then decided to call it quits and stop working on it. and now i am here typing. is it common for these cb750 carbs to stick from anything in particular? What are some items i can check? i'm going to remove the tank and carbs again tomorrow and dismantle them one more time. so any advise, or if you have seen this before, what caused/fixed it.

i ended up riding my 1974 cb750 instead today, and that bike decided to start running on 3 cyl after 30 minutes. fucking bikes man. love hate relationship sometimes. i think the 74 is just plugs or something simple.

Shaun

'72 cb750
'75 cb750
'76cb750
'82 cx500 (but mine is cool, i swear. Why don't you believe me?)

 

[leo]

Pam,
You mentioned the bike has an old glass tank. When you cleaned the carbs, how did they look and feel? Any kind of sticky goo?

I first ran into this with a BSA with a glass tank (and never put 2 and 2 together). And later on a Norton with a glass tank, that after fitting a Mikuni, and thinking I was chasing a carb issue, had me stymied for days.

Not saying it's your problem, just an idea, but something the boat guys have been hip to for some time. Modern ethenol enhanced gasolines, which might be new to your area, will start to react and dissolve a glass tank and really gum up the works. Perhaps look into an epoxy sealant for the tank. I had good luck with a product from Caswell (check their site).

Just a thought. Hope you get it sorted.

Cheers- Leo

p.s.- Wonder if Bret @ Glass from the Past has any input on this issue

 

[pampadori]

i didn't notice any goo or anything sticky. but my gut is telling me its something about the tank. i'll check again tomorrow. i can't sleep with something broke. i'll have to drink the thought away i guess until i can work on it tomorrow.


'72 cb750
'75 cb750
'76cb750
'82 cx500 (but mine is cool, i swear. Why don't you believe me?)

 

[Fang]

Pam, this thread is getting old, but this is what I expect is your problem.

Those old fiberglass gas tanks (and many of the new ones too) cannot hold up to modern gas. Gas has changed a lot over the last three decades, mostly for the worse, and now it eats these fiberglass tanks. I think that the thing that is gooping up your carbs is the innards of your tank dissolving.

You probably need to pull the tank and get it lined. Many radiator shops can do this for you. The fuel lines and filter should be replaced, and you need to clean out your carbs again to get the old goo out of your system. You might even need to replace the spark plugs.

Good luck!

Peace and grease
-fang

 

[joe c]

im guessing its the tank actually binding the cable some how.

jc

 

[parks61]

yeah
i heard fiberglass tanks can bind up cables from across the room too.
-parks

 

[pampadori]

they stuck even with the tank off and cables off. hell, they stuck on my work bench.
ended up feeling the bores for the slides again and they felt sticky (like leo said).
I took the petcock off the tank and the screen was starting to gather a gum in the area the fuel flowed thru. I ordered Caswell tank sealer about a week ago. should be here soon so i can coat the tank.
Leo wins a cookie!