Okay I'm stumped. Driving me crazy!

[chopit25]

I have got to be missing something. The timing is dead on. Starts first kick everytime. I cleaned the advance rod and lubed it all up proper. New springs on the advance weights. Everything assembled correct. Carbs are clean as new. New points gapped correct. Valves adjusted. Idle mix screws set at 3/4 turns out per 73 bs38s. It idles really high and I can't figure it out. The advance was sticking open but it seems better now that is cleaned and lubed with new springs. I cannot back the idle off to where the motor will sputter or die because the butterflies are almost closed. I can back the idle screws off so far that they don't even touch the mechanism that moves the butterflies. I don't know if the advance is the problem? I did have the advance weights pinned closed and the idle was low like it should be, or close. But that is still with the butterflies closed. I've read thru the carb guide. I took them back apart twice to make sure they were assembled right. Sorry for the rambling post but I have to be missing something that is probably obvious. Lol
Anyways I am not sure if the advance is causing problems or if its a carb issue or if I'm chasing the same problem in a circle caused by both. Any suggestions?

 

[hotdog]

check for air leaks around your intakes.

 

[pamcopete]

Sync the carbs.

 

[gggGary]

Make sure you have slack in the throttle cable at idle.

 

[jd750ace]

If you pulled the carb butterfly plates off and did not get them back in centered they can leave a big gap at closing because they bind on the throat wall, but usually if that's the case you can feel them dragging.

 

[chopit25]

I will check all of those things. I know it is not the cables hanging up. I am leaning towards carb boots and syncing them. The carb boots are really old and about the only thing I haven't changed yet so it would be likely they are bad. On the syncing I have no barbs on these and can't afford the expensive guages. I know I could bench sync them but I have read the process and for some reason I didn't understand it. I will read up on it again. Are you just syncing the height of the butterflies when bench syncing?
On the butterflies not being centered I do have one carb that is super smooth but the other seems like it doesn't return quite as smooth. I will check that too.

 

[jd750ace]

On bench sync, what works decent for me is to use a 1/8" or #30 drill bit. I put it under the left butterfly as close to bottom center as I can eyeball, then run the adjuster until I can get it under the one on the right with just a slight drag, not enough to make the left one shift. This places both of the plates at .128-.130 off the bottom of the carb throat. There are variances on this. I used to try to eyeball them, but have better luck with the drill bit method. YMMV.

 

[chopit25]

Cool I will do that. My carbs aren't linked together so I'm guessing that I will just do the same on each one individually and take my time.

 

[retiredgentleman]

I recommend you replace the needle jet O-ring on each carb, if you have not done so. If they are bad, they can allow extra fuel to be drawn and cause a high idle.

 

[chopit25]

I just rebuilt the carbs and I don't remember seeing or replacing any oring. Maybe I overlooked that. Where is that located? Sorry I have the carbs off and on a table but I'm busy this morning fixing my broken truck. It seems everything breaks at once around here. Lol

 

[TwoManyXS1Bs]

Hey Chopit25, one final trick after you've checked all the above posts, is to set your idle timing at the most retarded mark, 13°, or even less to 10°. This will force you to open up the idle stops a little to get idle. Then check full advance, and bend the weight stops as necessary to get 38-40°.

 

[retiredgentleman]

I just rebuilt the carbs and I don't remember seeing or replacing any oring. Maybe I overlooked that. Where is that located? Sorry I have the carbs off and on a table but I'm busy this morning fixing my broken truck. It seems everything breaks at once around here. Lol

Easily overlooked. The 70 to 79 years have a groove where the O-ring fits.

 

[chopit25]

Hey retired, yup the o-rings were toast! Looked just like black smears. Anyways I tried to replace with an assortment kit I have but that was a no go. Does mikesxs sell these? Ordering new boots today.
What size is that o-ring? I was going to look local also. Of course they didn't come in the rebuild kits. It looks like a real tight fit. Any ideas?

 

[hobodictator]

that oring is 4mm i.d. x 1 mm thick

 

[chopit25]

Thanks hobo. I tried a few automotive places but they were all too thick. Now I have an idea of where to go.

 

[jkocr2]

Also check the throttle shaft seals. I couldn't get the left cylinder to die while trying to dead sync but if I put my finger over the return spring on the throttle shaft end I could. I have seals on the way, hopefully that fixes it. My right side isn't as bad but it's still leaking.

 

[retiredgentleman]

Thanks hobo. I tried a few automotive places but they were all too thick. Now I have an idea of where to go.

You can get them from McMaster Carr. 1 mm thick X 4 mm ID Viton.

 

[hard_y_rd]

Easily overlooked. The 70 to 79 years have a groove where the O-ring fits.

Sorry to hijack, I went through my 73 bs38's. Didn't replace the o-rings. How do you remove the needle jet to replace the o-rings?

 

[chopit25]

Grabbed the base and wiggled left to right a little with needle nose pliers and it pops out. I was real careful though not to damage the tube.

 

[hard_y_rd]

I soaked mine with the tubes still intact. Wasn't sure if they came out or not. Thought they might be a pressed fit. Didn't want to break anything. I guess my o-rings are toast as well.