Keihin carbs on my LTD 750 issue

Hello,Everyone.Been lurking for a bit as I keep working on my '81 750 4 holer.My question is my new K&L carb kits came in last week and my pilot mixture screws don't seem to want to go into the carb body deep enough.Same size as the ones I removed.Shop manual shows oring,washer,spring,mixture screw.I can only screw these in about 2 full turns before they bottom out.Wired George and the manual says 11/2 turns out from seated.This barely holds and vibration loosens them right up.What gives? I took the old ones out(plugs were already removed)and they were definnetly screwed in deeper.This thing runs like a big bear once the revs get past the pilot circuit and get on the main jets. Hope someone can help tonight.Thanks for the excellent and informative site.

Anyone??

Hey Ferrous,

WG is just around the corner.

If he hasn't done it, you'll have to plough new ground and tell us about it.

It's how we all learn.

kzcsi

I know exactly what you mean but am not sure what to suggest.
I had one once which would not seem to go back in the way it should. Gently took it in an out repeatedly and eventually it settled in right.
I would check out the hole. Maybe run a Q tip soaked in carb cleaner around the inside. If you look in the hole can you see light at the bottom through that tiny hole? Is it possible the old ones were screwed in to far and a screw tip broke in that tiny hole. Maybe a bit of old O ring down there. ?

All I can suggest is to put on the spring, washer and o ring on the screw - and make sure the O ring is not rolled up along the screw or that could jam it and try again. I seem to remember once holding the carbs upside down and putting in the assembled screw, spring etc upwards.

It's late and I'm tired and rambling. Sorry not much help. I can sympathise. They are little bu**ers.
Persevere but whatever you do dont force them.

Yeah I gotta' be missing somethin'. Old pilot screws or my new screws just don't seem to be going in deep enough:unsure: The old mixture screws I took out were definetly deeper.As it is now the heads are barely flush with the tops of the carb body.All the old orings and washers came out.Tommorrow morning I'll have a look.This is a nice running bike for the most part-best $250.00 bucks I've spent in a long time.

Ramble on my brother..I'm thinking a little lube on each screw..anti-seize or some such.All 4 screws are doing this.PITA.I'm hoping this is why it's boggin' and burnin' rich down low-screws are leakin',right?

Put a little anti-sieze and screwed them in and backed them out,in,out,in,out.they seated:) Still bogs a bit at low rpm.idle doesn't come down as it should.I may yank em' off later this week and check choke butterflies and make sure they are fully open.I gotta' re-sync and do some other minor things.PeaceB)

If the rpms dont come down when you let off the throttle then maybe an air leak around rubber boot connectors to the cylinders ? ...or missing or badly fitting vacuum caps on the carbs? Have heard that spraying WD 40 around the boots and watching for a change in idle speed is a sign.

If it stumbles at low rpm as you increase the throttle then check those little plastic or neoprene or whatever they are little white plugs which cover the pilot jets. One of the o rings in your rebuild kit was for those plugs. They should be sitting tight. Maybe check the pilot jet for clean while you are at it. Another thing which can cause stumble at 2 - 3000rpm is blocked transition holes. Three tiny holes in the throat of the carb just where the throttle flap closes. Just behind the hole where the tip of that air mix screw you were having bother with would point.

Yeah, synch would probably help

good luck

Post edited by: JR, at: 2007/11/17 18:45

Yeah,JR I've put them back on for now.Really runs great when warmed up-it's about 40 degrees out today-takes a bit to get heated up.I've got the idle set a bit high and just have to slip the clutch a bit.I've sprayed my intake boots to check leaks and have new hose clamps on airbox and intakes.Vac caps are new and tight.This bike led a hard life-scraped crash bars,tank with bondo and rattle can black,suzuki gs turn signals up front,ripped seat,non working kill switch,tach with missing needle,no center stand,etc..Lights work,brakes are fine,charges at 13.6 volts,does nice burnouts in my driveway.( Gotta' rile up the neighbors.) I haven't ridden a road bike in 20 years anyway so I can't compare it to anything but my WR Yamaha....Nice bike for 200 bucks or whatever I paid for it:) I don't mind throwing a few more into it.Brake flush and pad inspection on tap for Sunday.Stay cool

Yeah,JR I've put them back on for now.Really runs great when warmed up-it's about 40 degrees out today-takes a bit to get heated up.I've got the idle set a bit high and just have to slip the clutch a bit.I've sprayed my intake boots to check leaks and have new hose clamps on airbox and intakes.Vac caps are new and tight.This bike led a hard life-scraped crash bars,tank with bondo and rattle can black,suzuki gs turn signals up front,ripped seat,non working kill switch,tach with missing needle,no center stand,etc..Lights work,brakes are fine,charges at 13.6 volts,does nice burnouts in my driveway.( Gotta' rile up the neighbors.) I haven't ridden a road bike in 20 years anyway so I can't compare it to anything but my WR Yamaha....Nice bike for 200 bucks or whatever I paid for it:) I don't mind throwing a few more into it.Brake flush and pad inspection on tap for Sunday.Stay cool