choke problems with restrictive pods

[beaverbeliever]

I've got a 79 xs 750 and I started the thread seeing more people on the XS11 site with issues with adding pod filters than I did on the 750/850 site. I haven't found anyone on either site that has had the problem I'm having with no high idle available with the choke.

The spec float height is 25.7mm. I'm at about 26.5mm and will likely try increasing it 1mm more and see what happens.

I appreciate the help and ideas as I run out of things to try.

[dbeardslee]

Beaver - while you've got the carbs apart you should probably check the condition of the bowl gaskets and make sure they're not plugging any of the holes around the bowl flange. If you've got filters in the rubber vent lines, try removing them first. Might save you a carb tear-down. That's what was screwing up my enricher circuit and keeping the choke from working properly. Of course that's for an 11, and I'm assuming the 750 has a similar setup.

[beaverbeliever]

I don't think we have the vent hoses on the 750s but I've lowered the fuel level down to the lowest spec and no improvement in the choke operation. At idle without the choke it is obviously lean and struggling to run. There has to be something in the vacuum operation of the choke that isn't drawing in air. There is a very small hole in the pickup tube at the gasket level and then the backside of the choke opening opens into and below the diaphragm area. This air is fed through the curved intake opening area. Its seems quite simple and I don't see where there could be any obstruction unless the diaphragm could some how be pulled against this opening which is unlikely.

[tarzan]

beaverbeliever,
Did you make sure the orifice in the bowl itself is clear?The air(vacuum)you talk about is in the venturi and automatically draws on the enricher circuit if the circuit is not restricted.So air is not your problem there.
Also this thread should be in the other bike discussion forum.This one is for XS11/XJ11 only.Just to let you know.

[dbeardslee]

Beaver - I checked the yamaha fiche on the '79 750, and sure enough there's no vent tube. The 1100's also have the hole in the pickup tube, but the bowl is also vented to the outside. Tarzan's suggestion of cleaning the small jet in the bowl seems prudent. A wire bread tie with the paper stripped off works well. Anything larger may not go through the orifice. When I clean mine I always check to see how much wire is going in just to make sure I'm getting it all the way through the jet.

You can generally tell if they're plugged by inserting the red plastic tube on a can of brake cleaner or carb cleaner into the hole at the bottom of the bowl and giving it a squirt. You should get an energetic and pretty-well atomized stream coming from one of the holes on the bowl flange. Make sure the flange is pointed away from you when you squirt (man does brake cleaner in the eye sting ). Your statement about it not wanting to idle would point to this as a possibility.

[beaverbeliever]

Thanks guys for the input. We do have a small vent hole in the pickup tube and I've wired and blown air through those so they are clear. THe valve/jet in the bowl is also clear as I can spray cleaner through it and get a nice mist out the top.

Its weird in that full choke when cold (its 35 today) and it won't start on full choke. Its starts quickly with no choke but needs full choke to keep running for about 10-15 seconds and then it bogs down. Move it over to half choke and over 2-3 minutes it very slowly comes up to idle and then it will idle fine on no choke. Still seems like too much fuel under full choke.

[tarzan]

So will it start and run on half choke?That is how I start mine, until it gets pretty cold out then I use full to get it started then go to half till it warms.It sounds like when you get past 2-3 min it runs fine.Is that right?Or do you have low speed bog or stumble,or will it just die?

[beaverbeliever]

tarzan,
It won't actually fire with any choke so I have to have my hand on the choke ready to switch it to either half or full as soon as I hear the first fire. It will usually need the full choke to stay running for 20 seconds or so when it is cold and then back to half. If I crank it for too long with half or full choke and it doesn't fire and I move it back to no choke it will usually have a loud exhaust backfire.

I put new coils, plugs, wires and caps on this fall but I suppose there is a potential that it has a weak spark? I had the battery charger on it yesterday to make sure the battery is fully charged (new battery last spring) and even turned the charger to "start" to see if it would take full choke at start...no change.

[beaverbeliever]

I had a thought this morning and wanted to see what you guys thought. What little I can find on this situation has led to people saying that my choke or pilot circuit is partially plugged. I've felt confident that my cleanings have made sure everything was open but I suppose its possible that I can get carb cleaner through the circuits under pressure but they may still be partially blocked and not able to pull enough fuel under vacuum. Here's the question..
AT full choke is it possible that I'm getting enough fuel to make the plugs black but it's pulling too much air and not enough fuel to fire? Continuing this theory it is able to fire with no choke because the mixture is closer to what it needs to fire and at half choke it runs a bit better because there isn't as much air being pulled in. This would mean its a very incomplete combustion and the plugs are black because its a higher volume of gas that isn't being burned well because there is too much air.

This would mean its really lean under choke with dark plugs?

[dbeardslee]

Beaver - I doubt it. The black stuff comes from unburned fuel in the combustion chamber (rich), so I doubt whether too much air (lean) is the problem. A lean condition results in a white residue on the plugs, and possible burned electrodes.

How did you adjust the mixture on your carbs? Could just be that the mixture or jetting isn't right. Although you will get conflicting opinions, I personally like to use a colortune plug. It allows you to see into the combustion chamber and 'read' the color of the explosion so you can more accurately adjust. It can also tell you if the jetting is correct. If it isn't you won't be able to adjust through the whole range of color (bluish white flame = lean, bunson blue = complete combustion, yellow = rich) using the mixture screw.

Have you modified the exhaust or intake or is it still stock?

Also, when I start mine cold using the choke I can't give it any throttle or it won't start. I just hit the starter and let it run a few minutes and then I can give it throttle.

My $.02

[beaverbeliever]

I'm running an aftermarket free flowing 3>1 exhaust along with open air pod filters. I have been tried larger pilot jets, playing with the mixture screws which are back at the stock 2 1/4 setting adjusted the float level to both sides of the range and have changed the needle jet from stock to one step richer and back to see if there were any noticeable changes. None of these seem to make a difference including taking off the pods and trying it without an air filter in place.

Compression is good at 140-150. Valves are good. Two intakes need one size smaller shims which are on order but shouldn't be enough to make a difference.

I took a hard look at the diaphragms over the weekend and can see that they are stretched a little near the inlet side of the choke opening. I'm wondering if the rubber has stretched enough over time to partially block the choke air intake? I suppose I could try taking the slides out and give it a shot. The air for the choke circuit comes in from the curved intake port and runs under the diaphragm into a hole for the choke plunger.

[dbeardslee]

There's a post under tech tips for jetting recommendations. It's for the 11's but I suppose it should work for the 750's too. Might serve as a point of reference with what you have - http://www.xs11.com/forum/showthread.php?t=382. According to that you should be four jet sizes bigger on the mains (from stock) and one jet size higher on the pilots. Don't know about the diaphrams. Maybe someone else will chime in.

[tarzan]

I dont think you need bigger jets.
My bike runs well with pilot screws out about 1 1/2 turns out.You might want to try turning yours in some.While it is idling and at operating temp. turn the screw in slowly until it starts to drop off(the idle) then back out about a quarter turn to get it to run good again.Then go to the next one.
So did you change those plugs?

[beaverbeliever]

It's about 20 degrees out right now and I thought I'd experiment a bit more with the bike in the garage. I cranked for quite a while with full choke and some half choke and it wouldn't even hint at firing in this cold. I got a slight hint of a fire moving to no choke but no go. I cranked a while longer with full choke and then pulled the plugs expecting to see wet plugs. The interesting thing was that they weren't wet at all. This was probably with a combined 30 seconds of cranking. This is starting to lead me to believe that it isn't getting enough fuel under choke and at half choke it's cutting back the air supply and can run a bit better. I'm wondering if I may still have a partial plug in the choke circuit that I can't quite notice while cleaning because I can see spray coming out when I shoot carb cleaner through the choke pickup tube and through the valve in the carb bowl.

[Rasputin]

Jat

I had something of a similar problem when trying to start my newest addition. It had not been running for about ten years. I just wanted to hear it run before I invested a lot of time and money into it. I could not get the choke cicuit to do much of anything and I wanted to see fuel in the carbs, as I already had spark. I added some good old Seafoam then I put it on full choke and cranked away. While cranking I held my hand over each individual carb until the vacuum from the motor pulled fuel thru. It did not take long before I had fuel all over my hands. You have to be careful doing this as the fire extinguisher best not be to far away. To make a long story short the damn thing fired right up. I did that a few more times to see if it cleared out any more gunk. Now it will start with the choke on like it was supposed to. I know I have to go thru the carbs and clean em all really good yet but hey it was running in no time at all. Now that I know I have a runner I can take my time and make it right.