1982 Honda CB900F Barn Find Restoration - Episode 8 - Getting it to run & Idle OK

Well, After cleaning the carbs and shimming the valves, She still didn't run great. However I finally got her sorted out to the point I can move on and actually start the main tear down of the bike now.

[@goldenboy5626]

I loosen the booths and turned them to finally get the carbs to fit properly. Mine was rock solid to. It is a struggle whit the old bikes but when they run good its rewarding 😊

[@true-moto-resto]

Yes, I usually soak the boots in wintergreen oil and alcohol for a couple of days,, softens them right up and they stay soft. Will do that again if I can’t find brand new ones

[@HorsepowerHouse]

I find it interesting how people recommend things (to you) that are likely not an issue on a bike that "ran fine" prior to removing the carbs: Ignition timing, compression, valve clearance, etc. (like these things just flaked out all of the sudden??) Come on, y'all. Making people do hours of unnecessary checks etc. BEEN THERE. Stick with what is the mostly likely issue. Logical things. Not ALL issues under the sun. We all know things like this are likely air leaks, lean jetting, wrong spark plugs, incorrect floats, (these are not adjustable,) clogs in small fuel passages. Been like this since the beginning of time. Glad you finally got it sorted. My 1981 CB650 has very similar Keihin VB carbs. Very sensitive little boogers, they are.

[@TonyCBX6]

Great work Dave! When synching carbs, No. 2 is the base to which all others are set. You first set carb no 1 to be the same as carb no. 2, then 3 to 2 and 4 to 3, then finally some minor tweaking to get 3 & 4 to match no. 2. When adjusting them, changes made on one carb will slight affect the neighbouring carb. It will start better and idle much smoother when done. New carb mounting boots will also improve things. IMHO only, I think the carbs always look better with the clamp screws pointing down and out of sight. Enjoy the process Dave!

[@true-moto-resto]

Cheers Tony, I’m gonna strip the bike to bare frame now for resto. Once I re assemble with new boots etc I’ll be sure to do the Sync etc and adjust mix screws too. Thanks again

[@grebermuncie3904]

Ex Honda Service mgr. here.... of course make sure the carbs are seated in the rubber boots but then, put your gauges on it and sync the carbs! Anytime you disassemble the carbs, they are going to be WAY out of sync. There is NO substitute for proper vacuum gauges on the bike. When you get the carbs synced, then you do a idle drop procedure to adjust the idle mixture screws. The book specs for turns out is just a starting point and you'll usually need to open them more. While adjusting the mixture screws, you're watching the vacuum gauges and re-syncing as necessary.

[@true-moto-resto]

Cheers, yea I have year to sync the carbs. Will definitely get to that

[@grize9999]

I have an 82 and my slow jets are removable.

[@true-moto-resto]

Yea, I suspect the carbs are off an earlier model, unfortunately for me.

[@owen368]

Think to much fuel going into exhaust is cause of pop/bang in exhaust which I would have thought was a carb issue if sparks ok which as far as we can tell is working.

[@true-moto-resto]

I think it’s carb#2 pilot is clogged. They’re not removable so I have to drill and tap the pilot jet to extract it. Bike is almost done now. Popping goes away when I squirt gas in carb 2

[@rodofsteel6662]

I’ve had a 81 900 custom I did the carbs and all, once hot the bike revs 5,000 rpm when I stop and pull the clutch in. I let it out and it’s ok but the bike is all hot and stalling.

[@true-moto-resto]

Sounds like Carbs problem or an intake manifold leak. When U say that you did the carbs, were they de-racked and fully disassembled ? and ultrasonically cleaned ? The carbs on the 81 require some very tricky removal of slow speed jets (I have a video of that, not for the uninitiated) Did you replace all the gaskets and orings? Did you rebuild the accelerator pump? New gaskets in the air check units? These are Some of the trickiest carbs I have ever done. If you’re not comfortable with some of what’s required to rebuild them, best to take them somewhere to be done.

[@rodofsteel6662]

@@true-moto-resto yes they are no doubt complicated. i just had to fallow a video and diagrams but I did the whole rebuild kit and tried to balance them with a drill bit holding one open. I’ve never done this but thank you. It runs good until it’s warm then that clutch thing happens.

[@goldenboy5626]

If you dont find any obvious fault then try to adjust the mixture screws. The high idle suggest air leak or is it just not turned down? On my bike the choke made it idle high so I adjusted it to get the idle down. Good work mate 👍

[@true-moto-resto]

Idle turns down ok with the adjuster underneath. The popping was an air leak. Seems to be fine now. Thanks for the reply

[@chrisraven-bb4jc]

In regards to the Air-Cut Valve. This unit only comes into play when you decelerate, and in all probability Honda did it to meet air pollution standards of the day. Personally I find it more trouble than enough, so I usually just plug the hole with a small piece of rubber and forget about it. I am not a fan of running my engine on the lean side, have had problems in the past. Thanks

[@true-moto-resto]

thanks, bike was sorted a long time ago, all good now. Thanks for commenting

[@JPmixet]

I got an 82 900F, K&N Airpods, Dynajet kit, and the cylinder 2 & 3 are super lean and 1 & 4 are super rich. Any thoughts?

[@true-moto-resto]

I’d look at the carbs (clean and check floats jetting etc. and check valve clearances. Follows by a Carb sync. I can’t think of anything else effecting rich can lean

[@JPmixet]

@@true-moto-resto Carbs were cleaned and rebuilt last year with the Dynajet, reshimmed a few exhuast valves today. even checked timing and advance.

[@true-moto-resto]

@@JPmixethmmm, well, I think I’d still be checking this carbs again. There really isn’t a thing else that would cause that issue I think. Have you checked for air leaks around the carb boots ? Are you running a stock air box or pods?

[@JPmixet]

@@true-moto-resto new boots last year when carbs were rebuilt, K&N airpods...going to try the airbox next

[@true-moto-resto]

I’d still check for air leaks if I were you, just to be sure

[@rodofsteel6662]

Just found the Bolt on my valve cover that holds the tachometer cable is stripped out and loose maybe that’s my vacuum leak 🤞

[@true-moto-resto]

not sure that would cause a vacuum leak

[@rodofsteel6662]

@@true-moto-resto me either I assume it hold the cable in but I’ll have to tap it or something, I’ll take the valve cover off might as well replace everything while it’s off lol

[@true-moto-resto]

@@rodofsteel6662nothing to replace in there except the cover gasket unless your going to check the valve clearances and re shim those. You need a special too to depress the rockers to extract the shims if you go that route.

[@rodofsteel6662]

@@true-moto-resto yes somebody had some glue all around the head gasket doesn’t look good and my cam chain I can check I guess a new gasket will be needed thanks.

[@karlvanboxel561]

Compression check?

[@true-moto-resto]

Yep, thanks, did that previously , all good. I only did it cold and dry (no oil in the cyl) and I got 158 -160 across all 4