Tuning a rebuilt carb

[sphen]

As ive mentioned in previous threads, ive finally got the carbs rebuilt and the project bike wired up enough to get her started. Here's where i am right now: (GL1200)

pilot screws adjusted to manual spec - floats measured out and set to spec (at least to my novice reckoning)

Bench tuned best i can tell.

starts without much trouble, but idles around 800 rpm with the choke pulled. even after warmup, if i drop the choke it dies instantly. Any amount of throttle given is instant death.

I played around with the idle adj screw a bit - if i open it too much, the bike wont even start; or if i ease it open after starting, it dies. to a certain extent, if i close the idle adj, rpm goes up a little (like say from upper 600s to 800s). so theres a (low) sweet spot where it will start and run...sorta.

With that as a starting point, what should i look at next?

[Whiskerfish]

sounds like a significant air leak. Make sure you did not pinch the orings between the intake runners and the heads and that the clamps on the top of the intakes at the carb connection are tight.

[rcmatt007]

on a 1200, do you have a bad diaphragm?

[sphen]

on a 1200, do you have a bad diaphragm?

which diaphragm are you referring to?

[Rat]

Take the top off your 1200 carb .... there is a rubber diaphragm that can fail

Gord

[rcmatt007]

I had assumed you had rebuilt the carbs.... yes under the top flat plate is where the diaphragms are, if they crack, or not in the correct position they will leak air

[sphen]

oh yeh yeh the CV slide stuff. I will check. I do remember them seeming a little 'shrunk' and barely fit back in their grooves. may have slipped out during top install, or may need to be addressed (repaired or replaced?)

also, im running an airfilter but didnt put the airbox back on yet - might be an issue/might not. i dunno how sensitive this bike is to such things.

[rcmatt007]

having the box off would not make much of a difference

[robin1731]

CV carbs are sensitive to having an air box. Always have the airbox on and filter in with lid on.

.

[sphen]

Current status of the diaphragms:

RH:

D5E3906A-7874-4F7D-90EC-82D4EA50F875.jpeg

LH:

0DF14487-8D6A-462D-B19D-C549909619F4.jpeg

Honestly I’m not sure what they’re supppsed to be like, but they seem like they could be more pliable and stretchy

[rcmatt007]

it has been several years, but I do not recall them looking like that.... but I have slept since then

[sphen]

wondering if they can be refurbed, or if i need new ones (and if that is indeed my problemo)

[robin1731]

wondering if they can be refurbed, or if i need new ones (and if that is indeed my problemo)

Randakk used to sell new ones for the 1200 but too many people did not follow install instructions and blamed the part. I installed a set and they worked very well. Yours really don't look too bad going by the pics. The one on the right in the second pic does not look like it was seated at about the 11:00 position.

Been quite some time since I had any 1200 carbs but on other carbs with the rubber like that if you hold the slide up and put the rubber in the groove it fits much better. Then while holding it put the cap/top on.

.

[sphen]

I braced the slides up per the manual when i first installed them, but they seem to have some stiffness and "memory" - particularly the one you mentioned - and i had some trouble keeping them seated. will give it another go.

when done, i tested by lifting the slide and looking/listening for the seal and delay in the slide falling back down to its seat

is there a way to restore shape/pliability? controlled heat perhaps? warm water?

[pidjones]

Any chemical softening of the rubber will drastically shorten it life. You can however put it in hot water just prior to assembly to make it more pliable for that.