'81 Midnight Special carbs?

[FJ111200]

Hello there, long time no post.
I've tried searching but not found anything like. So anyway, I've bought this 4W1 '81 Midnight Special and it's come with these carbs that seem to have some of the jet orifices blocked by something.
Is this right or what? Also the main jets are 125 across all four.
Anybody shed any light on what's happened and what I need to do? Thanks in advance.

[bikerphil]

Those pilot jet towers should be completely open unless there is a crossover passage between the pilot jet tower and the main jet towers, in that case, they should be completely blocked off. Those metal plugs with holes in them are wrong, looks like an attempt to lean out the pilot circuit.

[FJ111200]

Thanks for the info.
I've just been and sprayed some carb cleaner into the holes in those plugs and it sprays out of the air pilot jets.
So there's no blockage there but is that what it should do?

[skids]

Hello there, long time no post.
I've tried searching but not found anything like. So anyway, I've bought this 4W1 '81 Midnight Special and it's come with these carbs that seem to have some of the jet orifices blocked by something.
Is this right or what? Also the main jets are 125 across all four.
Anybody shed any light on what's happened and what I need to do? Thanks in advance.

Are those float bowls correct for an 81? I would check, but I got rid of mine. PS, what is 4W1?

[3Phase]

Thanks for the info.
I've just been and sprayed some carb cleaner into the holes in those plugs and it sprays out of the air pilot jets.
So there's no blockage there but is that what it should do?

Yes.

That spray's going into the pilot circuit through the fuel jet part of the circuit, from there it can follow the path of least resistance back to the air jet in the intake bell or forward to the triple cluster for the transition ports and the idle port with the mixture screw.

Are those bodged plugs pressed, glued, screwed, or some nightmarish combination that will require drilling? They will have to come out so you can clean the pilot jets but I can't tell what was done from the picture.

Edit: Skids, 4W1 is the Model code, like 2H7, 2H9, 3H3, 3H5, etc.
1981 XS1100LH 4W1-000001 New Yamaha Black

Or it could be a Yamaha brake rebuild kit.

[FJ111200]

Are those float bowls correct for an 81? I would check, but I got rid of mine. PS, what is 4W1?

I'm pretty sure the float bowls are correct.
4W1 is the engine and frame number for the LH '81 Midnight Special.

[FJ111200]

Yes.


Are those bodged plugs pressed, glued, screwed, or some nightmarish combination that will require drilling?

Thanks for the info on that.

yes, your guess is as good as mine on that.
I'll try and use some sort of "pigs willy" or extractor on them. Don't really want to drill them and have bits of swarf blocking the job.

Looks like i'm getting there with you lads help. Thanks.

[3Phase]

Be careful when you remove the plugs, FJ.

As Phil said, there was a transition design for the late-model carburetors that had a crossover tunnel to pull Pilot circuit fuel through the Main jet like the '78/'79 carburetors. The Pilot jet well had to be plugged or the fuel would go up through the crossover and totally bypass the Main jet. That would be bad.

Or they could just be the wrong carburetors and went on some other bike that used the Mikuni BS34. Did you actually remove them yourself or did it come with the carbs in a box bungee'd to the seat along with some other obscure but interesting parts?

If someone tried and failed to remove those threaded plugs and passed them on to some other poor barsteward you could break the tower or tear the threads right out of it and since they're made out of the finest whatever-we-can-pour-into-the-mold metal they might be difficult to repair.

[FJ111200]

Thanks for the advice.

Yeah, I pulled them off the bike this morning. I've been renovating it, in a way, and took it for a run yesterday to see how it handled with new tyres and shocks. I'd run it a few weeks back but never took it over 40-ish but last week I put a K&N air filter in it and then yesterday it seemed to run like crap so decided i'd have a look at the carbs. One of the diaphragms is holed and the others are showing signs of wear so need replacing.
Here's a picture from yesterday. I think that exhaust system is a MAC 4 into 2.
I've nearly given up on the UK forum, it's dying a death, but I've sent a photo to TomB just waiting a reply. I'm no stranger to the old XS, this is my fourth one.

[3Phase]

That's a beautiful bike, FJ, and the 4-to-2 looks great! It might blatt a little compared to the stock exhaust but there aren't many options left any more except one of those custom rocking-horse SS exhausts extruded from Germany.

I thought I recognized your forum handle but you know what happens when you assume. Yes, I've noticed that the UK forum is a little quiet. There was a thread in their forum a while back along with another one on the Triples site about going to Facebook and almost like the Grandfather Clock, Brian's parts database seems to have stopped short — never to go again.

[skids]

Very nice looking seat. (That kind of comment could get Trump in trouble).

[FJ111200]

That's a beautiful bike,

Thanks.
I've also de-linked the brakes so the front m/c just operates the front brakes and the rear the rear only. Overhauled the calipers with new seals and pistons. Added Renthal gold 'bars instead of those weird looking pullback contraptions, if anyone can use 'bars like that they must be a contortionist. Front forks have been overhauled and I used some genuine internal lower bushes. Hagon shocks with 10 position rebound damping with heavy duty springs set for the combined weight of me and my mrs for two up riding.

[FJ111200]

Very nice looking seat.

Thanks, not too bad but needs recovering.

[FJ111200]

Ooops, missed the edit timeout, and should also have said that I had the forks re-chromed and painted the lowers, fitted new headstock bearings, re-greased the swingarm bearings and painted the swingarm.
Still needs a few things cosmetically but winter is about to arrive here so I've time do it.

[FJ111200]

OK then, got the offending plugs out using a "pigs willy" extractor. They seem to have been just pressed in and the pilot jets were still in place.
Looking in the Clymer manual it does state that there are some jet plugs and pictures show an early XS model. I can't understand it really, is it for US emissions because we don't have that here. These 34mm Mikuni carbs are basically the same as 36mm Mikunis fitted to FJ's which over here are not plugged.