Author Topic: Carb help please (Read 8890 times)

Loctite77 · « **on:** August 09, 2015, 06:17:49 PM »

Forgive me, but i know little about jetting/tuning carbs. I ave searched but cant find what I am looking for. This is my first post here but ive been reading a lot.

So I got my 76 CB750f together last night after rebuilding the carbs. Happy that it cranked and ran, but not great. First of all I am running new KandN carbs and just installed a 12" reverse come muffler (open) from cone engineering. Before the carbs rebuild it ran well just maybe a bit lean with the stock pipe. I went up to 110 on the mains from 105.

Now I am getting some hesitation when I roll on the throttle quickly, like a bogging. And some popping from time to time. If I stay on the throttle it will pull through the bogging and really take off but there is a lag. Do you think I should go up to 115 on the mains?

Also I parked it for a bit and forgot to turn the fuel off and within a few minutes fuel started running out the drain tubes of the float bowls. I know duh turn the fuel off dummy, but I have left the fuel on many times before I rebuilt the carbs and never had that happen.

Yes I know just enough to be dangerous. looking for some help here.

DaveBarbier · « **Reply #1 on:** August 09, 2015, 07:01:23 PM »

Can't help with the jetting but regarding the fuel running out of the float bowls: Sometimes when the bowls are drained dry the floats get stuck in the down position. All that's required to unstick them is rapping on the bowls with the handle of a screw driver. Or it's possible that you introduced some debris into the carbs which are preventing the float needle from sealing which may just require a flushing out. Like draining the bowls and refilling. Maybe a couple times.

SOHC Digger · « **Reply #2 on:** August 09, 2015, 07:06:40 PM »

The mains don't come into play in the area you are talking about. You might need to go up one size on your slow jets. Also, did you sync your carbs to the engine after rebuilding them?

Loctite77 · « **Reply #3 on:** August 09, 2015, 07:19:32 PM »

Quote from: SOHC Digger on August 09, 2015, 07:06:40 PM

The mains don't come into play in the area you are talking about. You might need to go up one size on your slow jets. Also, did you sync your carbs to the engine after rebuilding them?

Let me clarify. I had a shop rebuild the carbs. I sent them to him and he redid them and sent them back. They have been bench synced according to him. And the bogging down happens at 1/2 throttle and above, usually in 3rd gear or higher. I thought the slow jets were more idle jets?

Yeah Son!

flybox1 · « **Reply #4 on:** August 09, 2015, 07:35:56 PM »

So...pods and an open exhaust on an 76F
What model carbs do you have? and what is your slow(pilot) jet size?

harisuluv · « **Reply #5 on:** August 09, 2015, 07:46:17 PM »

The adjustment of the needle is absolutely necessary with pods. This should have been discussed with your carb rebuilder. Did you inform them you would be using pods? If you are unsure about it, assume that you have stock needle position. If you didn't mention it or he didn't ask, there's no reason he would just change the setting. If you're unsure, you should get in touch with him as they are the most knowledgeable about what is going on.

Loctite77 · « **Reply #6 on:** August 09, 2015, 08:03:41 PM »

I'm embarrassed to say I'm not sure what model these are?

Slow jet is 40

Yeah Son!

Loctite77 · « **Reply #7 on:** August 10, 2015, 02:04:26 PM »

Anybody?

Yeah Son!

flybox1 · « **Reply #8 on:** August 10, 2015, 02:14:53 PM »

turn your air screws IN all the way, and then back them out .5 turns.
report back if it improves acceleration from a full stop.

harisuluv · « **Reply #9 on:** August 10, 2015, 02:16:26 PM »

Quote from: Loctite77 on August 10, 2015, 02:04:26 PM

Anybody?

Yeah Son!

What do you mean? We're waiting on more information from you. I asked about the needle.

Loctite77 · « **Reply #10 on:** August 10, 2015, 02:19:33 PM »

Oh sorry harisuluv. I missed that part. I did email the guy and he suggested starting by lowering the clip one notch on the needles. He did know I was running pods, but the open exhaust was an after the fact addition.

Yeah Son!

Loctite77 · « **Reply #11 on:** August 10, 2015, 02:21:33 PM »

Quote from: flybox1 on August 10, 2015, 02:14:53 PM

turn your air screws IN all the way, and then back them out .5 turns.
report back if it improves acceleration from a full stop.

Are the airscrews the ones on the air intake side right next to where the pod filter attaches? They are currently out 1.5 turns. Will turning them in to .5 make it richer?

Yeah Son!

harisuluv · « **Reply #12 on:** August 10, 2015, 02:30:46 PM »

Quote from: Loctite77 on August 10, 2015, 02:19:33 PM

Oh sorry harisuluv. I missed that part. I did email the guy and he suggested starting by lowering the clip one notch on the needles. He did know I was running pods, but the open exhaust was an after the fact addition.

Yeah Son!

What is the needle clip set at now? Turning your air screws IN will make it RICHER. Yes the air screw is closer to the pods in your picture.

Loctite77 · « **Reply #13 on:** August 10, 2015, 02:31:47 PM »

Quote from: harisuluv on August 10, 2015, 02:30:46 PM

Quote from: Loctite77 on August 10, 2015, 02:19:33 PM
Oh sorry harisuluv. I missed that part. I did email the guy and he suggested starting by lowering the clip one notch on the needles. He did know I was running pods, but the open exhaust was an after the fact addition.

Yeah Son!

What is the needle clip set at now?

I don't know and he didn't say, I guess ill just take it apart and look. ??!!

Yeah Son!

harisuluv · « **Reply #14 on:** August 10, 2015, 03:00:34 PM »

Quote from: Loctite77 on August 10, 2015, 02:31:47 PM

Quote from: harisuluv on August 10, 2015, 02:30:46 PM
Quote from: Loctite77 on August 10, 2015, 02:19:33 PM
Oh sorry harisuluv. I missed that part. I did email the guy and he suggested starting by lowering the clip one notch on the needles. He did know I was running pods, but the open exhaust was an after the fact addition.

Yeah Son!

What is the needle clip set at now?

I don't know and he didn't say, I guess ill just take it apart and look. ??!!

Yeah Son!

In order to get in there, you need to take them off the rack which can slightly throw off the sync and even the choke synchronization. Surely just calling and asking him would be easier to check. Also, there's no sense in dropping it if it is already dropped one or two notches, the problem would be something else.

Loctite77 · « **Reply #15 on:** August 10, 2015, 05:04:42 PM »

He says they are "2nd or 3rd from the bottom" i thought i have seen on youtube i can get to the needle without unracking them? No?

harisuluv · « **Reply #16 on:** August 10, 2015, 05:21:16 PM »

Well stock is 2nd from the bottom. Third would be LEANER. This means your carbs are at stock settings or leaner. He did not adjust your needle for pods.

You'll need to unscrew the carbs for the backplate to fix them. While you're in there check if you have real needles or you got aftermarket (garbage).

Loctite77 · « **Reply #17 on:** August 10, 2015, 05:27:58 PM »

Quote from: harisuluv on August 10, 2015, 05:21:16 PM

Well stock is 2nd from the bottom. Third would be LEANER. This means your carbs are at stock settings or leaner. He did not adjust your needle for pods.

You'll need to unscrew the carbs for the backplate to fix them. While you're in there check if you have real needles or you got aftermarket (garbage).

Okay so I should go 1 from the bottom then? Thanks for all your help sir.

harisuluv · « **Reply #18 on:** August 10, 2015, 05:34:11 PM »

1 from the bottom is stock. You need to be in the last position (5 from the top). Also, probably 115 or 120 mains. Make no mistake though, the needle position is more important.

Loctite77 · « **Reply #19 on:** August 10, 2015, 05:41:58 PM »

Quote from: harisuluv on August 10, 2015, 05:34:11 PM

1 from the bottom is stock. You need to be in the last position (5 from the top). Also, probably 115 or 120 mains. Make no mistake though, the needle position is more important.

Ill let you know how it goes, wished I had sent them to you to rebuild in the first place. Seems like you really know your stuff.

Thanks

Loctite77 · « **Reply #20 on:** August 10, 2015, 06:58:30 PM »

Well now i know why the jackass that "rebuilt" them for me didn't know if the needles were 2nd or 3rd from the bottom. Because he never touched those parts, inside the throttle slides were thick with corrosion and it was obvious that the two screws had not been touched in any of them. Good news is i do think i have the original Keihin needles. They are stamped K2720 or something like that, hard to see. Do you recommend Keihin brand main jets or would aftermarket be okay? Where is the best place to buy them? Thanks.

harisuluv · « **Reply #21 on:** August 10, 2015, 07:19:43 PM »

Kei hin are best of the best. Aftermarket can be ok, different manufacturers vary in quality and tolerances. Jetsrus.com has a lot of stuff that is mostly kei hin. I also keep stock of that size, I can give you a little better price and faster shipping probably.

Loctite77 · « **Reply #22 on:** August 10, 2015, 07:55:42 PM »

Nice. How should I order from you?

Yeah Son!

calj737 · « **Reply #23 on:** August 11, 2015, 03:47:06 AM »

Do yourself a favor, take your carbs off the bike, clean them externally, pack them very, very carefully into a box, address them to Harisuluv and ship them off. Upon return, they'll be as clean as a surgeons fingertips, properly jetted and bench synched. Then you just bolt them on and away you go. And if any tuning help is needed, at least you and Haris are working from the known good baseline.

Making you eat your words....

Quote from: Loctite77 on August 10, 2015, 05:41:58 PM

...wished I had sent them to you to rebuild in the first place. Seems like you really know your stuff.

dusterdude · « **Reply #24 on:** August 11, 2015, 05:20:28 AM »

What cal said

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Author Topic: Carb help please (Read 8890 times)