Carb Problems

[Blackzer0]

I picked up a 81 CB750 custom with keihin vb-34sc carbs. after about 30 min. of riding the idle jumped to 6k. After some tinkering we noticed that one of the lock bolts on a sync adjustment screw was stripped (I hope the phrasing is correct). We took the carbs out and replaced it. Once we got it all back we hooked up the tank just to get some gas back in the carbs, we then took the tank off so we could make sure everything was working properly. While running we synced the carbs up and by the time we got them synced the carbs about ran out of gas (engine sputtered). So we hooked the tank back up thinking everything was good and then the #1 carb poured gas out of the overflow. Thinking that the float was stuck up we tapped and no change, so we took the bowl off, took the float off, cleaned the pen, reassembled and still it is overflowing. As of right now I am completely stumped on why this thing is dumping gas. Any Ideas would be great. Thanks.

 

[Stabler]

If you didn't touch anything else on your carbs while synching them, and it after you put your tank back on the bike, a carb started over flowing, to me it sounds like you stired up some crud/filth in your tank while moving it about and it worked it's way into that carb, causing that float needle not to seal..

I'd clean that tank, maybe put an fresh inline filter on it justto be sure, and thouroghly clean the carbs again - and go from there..

 

[Blackzer0]

Yeah I think I need to try and clean them again. I already cleaned the float needle but maybe I just need to do it again, may of had a gas high at the time. Ha. thanks thats a little reassuring that it isnt something bigger and more expensive.

 

[Stabler]

I'd say you'd need to clean all of the carbs and every part of them. You'd be amazed about how little crud or dirt it takes for these not to work properly..

 

[Blackzer0]

If u have an Instagram or can look it up I'm @jared0425 I posted a video. Tried cleaning them (maybe not good enough) but getting frustrated. Thanks for all the help

 

[Blackzer0]

http://youtu.be/IIiteDsLMaM here's a link

 

[Stabler]

I saw the video. How did you clean your carbs? Carb dip? Ultra sonic wash? Did you fully remove all jets, screws, needles, o-rings and so on when you cleaned them? I'm only asking since I thought I'd cleaned mine enough with CRC Carb Cleaner, diesel, brake cleaner, tooth brushes and compressed air. None of that helped - I chased carb issues for a month before I got them fully disembled and ultra sonic washed. Then I found a ruined slow jet and that was it.

If you have had the carbs properly washed/cleaned and you KNOW to a 100% that they are clean, then I suggest that you get a new float needle and that needle jet to make sure they seal as they should. I'd also check the float levels to make sure they're within specs. The bowl drain screw seal as it should, right?

What lead you to the conclusion that you needed to synch the carbs?

 

[Blackzer0]

Well I cleaned the crap out of those things and we are back to the original Problem of the high idle. Looking at the pipes my two right cyclinders are running super lean. What I'm thinking is my carbs aren't sync'd probably caused by the uni's, now contumplating going back to an airbox. Any idea's or thoughts???

 

[dirtdigger]

Need to check into cracked or leaking intake boots and also look into the leaking air cut valves on the sides of the carbs. Your high idle can also be the result of the ignition advance mech sticking advanced or weak springs. Uni's wouldn't cause two carbs to be lean and not the others. Are the idle mixture screw o-rings in good shape? Are they even in the carbs? Float levels correct? Throttle shafts tight in the carbs with little to no clearance? More than likely if the carbs were very dirty with bad gas you still have a plugged or partially plug passage, these carbs are extremely touchy.

 

[Stabler]

I had my carbs soaked in diesel for over a week and then cleaned with a tooth brush, brake cleaner and compressed air. That didn't help! Not until I got them into an ultra sonic bath with chemicals did I get them clean enough to find what was really wrong with them.
Now you seem to describe an air leak on those two carbs, at least by my book. But it can be any of the things described by DD. Or a combination of more than one thing.
Rule of thumb is to check and double check everything BUT the carbs first. A faulty timing, ignition advance and what not can mask as a carb issue. When you KNOW all else is 100% up to specs, then Trouble shoot your carbs.