Author Topic: Missing carb piece 1977 CB 750 Keihin 41A (Read 4184 times)

anotherCB · « **on:** March 28, 2011, 11:22:46 AM »

Can someone tell me what the piece that is missing in the picture is for? There should be 2 but one is gone....This is off my carb #2 and that specific cylinder would run really bad when bike was cold. After warm-up it was fine. Thanks.

anotherCB · « **Reply #1 on:** March 28, 2011, 11:23:32 AM »

Meant to add this pic...

TwoTired · « **Reply #2 on:** March 28, 2011, 11:26:21 AM »

That would be your pilot circuit air jet.

anotherCB · « **Reply #3 on:** March 28, 2011, 11:58:00 AM »

That's the idle jet, right?

Is there a place where I can buy that part, does anyone know?

MasterChief750 · « **Reply #4 on:** March 28, 2011, 11:59:35 AM »

long story short no not really, unless theres a way to get them from keihin

TwoTired · « **Reply #5 on:** March 28, 2011, 12:38:17 PM »

Quote from: anotherCB on March 28, 2011, 11:58:00 AM

That's the idle jet, right?

No. It is not the idle fuel jet, it is the idle AIR jet that regulates the total air that the idle system can get.

It is more correctly called the pilot circuit. But, some call it an idle or slow circuit as well.

Quote from: anotherCB on March 28, 2011, 11:58:00 AM

Is there a place where I can buy that part, does anyone know?

I don't know where you can buy one, unless it includes a "parts carb"?

Cheers,

anotherCB · « **Reply #6 on:** March 28, 2011, 01:19:15 PM »

Could that be the reason that the cylinder barely runs when the bike is cold? That was one of the issues I had. After a while it used to "kick in".

TwoTired · « **Reply #7 on:** March 28, 2011, 01:27:40 PM »

Without that pilot air jet, the pilot circuit will run way lean, and may not allow the cylinder to fire at all. You should be able to tell that the head pipe for that cylinder was a lot cooler. A 4 cylinder bike running on only 3 cylinders, doesn't run well. A warmed up bike can probably stand a little leaner mixtures and still fire. As you open the throttle other carb circuits dominate fuel mixture. So, the pilot circuit has less effect at larger throttle openings. The way the engine uses fuel is different cold from hot, too.

I can't say it is THE reason. But, it wouldn't surprise me if that were at least part of the reason. Lot's of things can make the bike run poorly.

Cheers,

anotherCB · « **Reply #8 on:** March 28, 2011, 01:42:13 PM »

What you are describing is exactly what I observed. I was able to touch the headpipe for that cylinder for a minute or so after starting up. The other 3 headpipes at that time were way too hot to touch. After warming up the bike ran good. I say good and not great, since I only got it 10 days ago and rode home as it was, without going through anything.

Now where can i get that freakin piece without having to buy a set of 4 carbs???

cobra2411 · « **Reply #9 on:** March 28, 2011, 03:53:49 PM »

http://www.factorypro.com/products/jets,%20Mikuni,%20buy.htm

Don't know if anything here would work but maybe you could adapt something.

Otherwise parts carb.

bollingball · « **Reply #10 on:** March 28, 2011, 04:03:48 PM »

Start looking for a rack. You will allways have a need for parts.Even if someone here can help with a donation extra parts come in handy.

boatsdickson · « **Reply #11 on:** March 28, 2011, 04:47:03 PM »

CB.... when I make it home tonight Ill have a look-see. Think I have whatcha need from an old rack.....letcha know before I turn in.

TwoTired · « **Reply #12 on:** March 28, 2011, 04:50:53 PM »

I don't know your mechanical prowess. But, it is possible to adapt something. All you need is a calibrated hole for the air jet.

First find out what size you need. Another carb should be able to provide that. I don't have any accessible now. But, you can gently insert small drill bit shanks to determine go/no-go and then measure the shank that "goes". Then you just have to find a jet with the correct orifice size that you can fit into that opening in the carb body.

Cheers,

anotherCB · « **Reply #13 on:** March 28, 2011, 06:41:09 PM »

Thanks boatsdickson, that would be terrific!

@twotired: I don't have any carbs or pieces lying around, so i probably won't be able to go the route you suggest. But will definitely keep my eyes open and try to find a spare carb for the future...

TwoTired · « **Reply #14 on:** March 28, 2011, 06:47:07 PM »

Quote from: anotherCB on March 28, 2011, 06:41:09 PM

@twotired: I don't have any carbs or pieces lying around, so i probably won't be able to go the route you suggest. But will definitely keep my eyes open and try to find a spare carb for the future...

Wait a minute. Are you saying all four of your carbs are missing that part, or just one?
That jet should be the same size as what is found in the other three carbs.

I know that some of the Keihin carbs did not have a brass jet, but the jet hole was drilled into the carb body. However, all four carbs should have the same features.

Cheers,

boatsdickson · « **Reply #15 on:** March 28, 2011, 07:11:48 PM »

My apologies CB, my usual storage places for little carb parts didnt have what yu need. Ill check back with ya if it turns up though. Like others said though, it will b yur best idea and collect additional racks or partial racks as the years tick by. It will pay off. Boats

anotherCB · « **Reply #16 on:** March 28, 2011, 08:56:16 PM »

@twotired: 3 carbs have two of those pieces, this one carb has only one, so it's different than the other three.

@Boats: thanks for looking!

TwoTired · « **Reply #17 on:** March 28, 2011, 09:48:59 PM »

Quote from: anotherCB on March 28, 2011, 08:56:16 PM

@twotired: 3 carbs have two of those pieces, this one carb has only one, so it's different than the other three.

Ok, so it IS possible to use the other carbs' jet measurement to get the proper size for the missing one.

So, you *could* make one, in a post apocalyptic environment.

Much better/easier to rob one from a parts carb, I expect.

Cheers,

754 · « **Reply #18 on:** March 28, 2011, 09:55:31 PM »

I got parts carbs, I assume they in most cases just about fall out?

TwoTired · « **Reply #19 on:** March 28, 2011, 10:19:36 PM »

Quote from: 754 on March 28, 2011, 09:55:31 PM

I got parts carbs, I assume they in most cases just about fall out?

The one he needs is a press fit into the carb body. They should pull out in the same manner as yanking the pilot jet.

Cheers,

anotherCB · « **Reply #20 on:** March 29, 2011, 07:58:47 AM »

Yes, I "could" make one and yes it is that press in piece at the airbox side of the carb. Here again the photo from the beginning of the thread.

754 · « **Reply #21 on:** March 29, 2011, 08:03:03 AM »

I will try to pull one off today, takes around a week by mail to get there.

anotherCB · « **Reply #22 on:** March 29, 2011, 09:02:01 AM »

That would be awesome

Let me know how I can "pay you back"!

754 · « **Reply #23 on:** March 29, 2011, 08:16:27 PM »

Is gonna cost big time..
but.. I cant get it out.. will try to make a tool tomorrow..

anotherCB · « **Reply #24 on:** March 29, 2011, 09:05:19 PM »

I tried myself to pull on the other one, didn't get it out either....seems like a tight fit "press in".

News:

Author Topic: Missing carb piece 1977 CB 750 Keihin 41A (Read 4184 times)

bollingball