Three-day engine death (question)

[Lucien Harpress]

Alright, I've got a bit of a mystery on my hands. A while ago, I took the carbs off and apart, cleaning them in an attempt to fix a sluggish idle/acceleration issue. I got them back on the bike and (despite a bit of popping) it ran rather well- certainly better than before.

Next day I go to check the carb sync. I hook everything up (syncing with a vacuum gauge), and notice that it's running quite rough and will die on anything less than half-choke. A quick check of exhaust pipe temperatures told me that (somehow) I managed to drop the first two cylinders.

Fast-forward one day later and (after swapping the fuel lines to see if it was a fuel-flow issue) now I can't get it to start a all.

As far as I can tell the petcocks are both fine- work like they should, and they aren't gummed up with anything. I know I'm getting a spark out of at least one cylinder (No. 1), and I have a feeling that the other one works as well.

The only thing I did the last day was to switch the left fuel line (which normally goes to carbs 3 and 4) to carbs 1 and 2 and the right fuel line to carbs 3 and 4. I think I'm going to switch it back tomorrow to see if it makes any difference whatsoever.

As a final note, when I went though the carbs I took everything apart EXCEPT for the mixture screws. I don't know how much difference this makes when it comes to dropping cylinders, but it's best to give all the info I can in a situation like this.

Does anyone have ANY idea what could be going on with this?

[Crazcnuk]

Since the idle mixtures screws are everything when it comes to idle, that may be part of the problem.

The other problem, which got me, was when I switched the fuel lines side to side, they got kinked under the frame.

[Lucien Harpress]

Okay, fuel flow (at least INTO the carbs) is not an issue. I checked that today, and that's fine. There's something going on in the carbs, but I have no idea what it would be to explain the three-day death of the engine.

[tarzan]

You have to take the idle mixture screws out.If those are late model carbs they have o-rings on them.If those o-rings are 30 years old and you soaked them with cleaner then the rings break down and you can have a mess in there.
You can drill the plugs out very easy and get to the screw.
You will chase your tail forever.

[62xs]

what size bit do you use?

[tarzan]

look at the silver bit in this pic.it has a little center drill on one and a tapered extractor on the other end.Both ends are left handed.I just drill with the one end
till it just goes through.The plugs are only about 1/8 thick.Then just turn the bit around and slowly run the drill while pulling straight back.Theycome right out.

You could also just drill it with like a 1/16 drill bit,then use a wood screw to get a hold of it and pull it out.

[Lucien Harpress]

Where would one go about getting replacements for the mixture screws, O-rings, etc.? The carbs on the bike are the 1980 style, and I was told these were different for the earlier ones. I figure if I'm going to take them out, I might as well do it right.

[Crazcnuk]

You can buy kits from various sources that have anywhere from just the gasket and float needle set, to ones with main and pilot jets, mixture screws etc. all included.

Georgfix, or Carbkitcapitol, etc., I think are good sources.


http://cgi.ebay.com/ebaymotors/4-YAM...Q5fAccessories

MikesXS.com sells all the individual parts and the gasket/float needle kit.

On Mikes you're looking for 80-84 BS34 parts. The have all the screws, jets, needles, etc.

[crazy steve]

One other thing to look at is, how 'clean' did you get the carbs when you cleaned them? If they were gummed up and you didn't FULLY disassemble them, crap can escape from hiding places and re-infiltrate into places you don't want it. Compressed air to blow them out is a must.

My experience is, if they need cleaning, it has to be a very thorough job or you're pretty much wasting your time.

'78E original owner

[tarzan]

I have not ruined any screws on the newer carbs.And I've rebuilt 4 sets of those.However i ruined a pilot screw on an earlier set though.In fact I had to take that carb to work today and drill out the tip.
I would be pretty surprised if you mess one of those screws up.I'm not sayin it never happens,but I wouldn't replace them unless yours are bad.Unless of course you need kits anyway and the kits come with them.
And I agree with crazysteve,I would make sure thay are clean and you can blow air or carb cleaner through all the orifices.
Rick

[Lucien Harpress]

Last time I had the carbs apart, I took apart pretty much everything I could, minus the mixture screws and the whole top gasket/needle assembly. On each carb I soaked all the metal parts (jets and the needle housing- that long tube with the small holes in it). I didn't soak the carb bodies at all- I sprayed carb cleaner through all the holes I could find, then blew everything out with compressed air.

There's only a few things I can think of that I missed.

-Mixture screws (obviously)
-I wiped a bit of the oil off the gasket assemblies. I'm not sure if it was enough to impede the movement of each, which resulted in what I'm pretty sure is a lack of fuel flow to the cylinders.

All I know for sure is the only way to get it running now is to put on full choke- I get it running for about a half second- I'm assuming that it's using the small amount of fuel dumped into the cylinders from the choke, and nothing else. After that, nothing, even if I use the choke again.

If/when I take the mixture screws out, I'll get a photo of them to see if they need to be replaced. It's not the screws so much as the O-rings, as I have no clue what condition ANY of that is.

[crazy steve]

....I didn't soak the carb bodies at all- I sprayed carb cleaner through all the holes I could find, then blew everything out with compressed air.....

That is probably the problem. The carb body is what needs soaking the most; spraying cleaner into it and then blowing air through it likely just loosened up some stuff that has now broke loose with the addition of fresh fuel and clogged something. The only caution when soaking the body is keep the throttle shafts out of the cleaner; there's o-rings that will be damaged. Me, I removed even the shafts and o-rings then soaked the whole body several times until I was sure it was clean.

These carbs can be cantankerous. I had a XS650 that I had to remove the carbs every spring and clean them. Always looked clean when I pulled 'em, looked exactly the same when I put them back, but the bike would run crappy if I didn't do it.

'78E original owner

[SFerinTEXAS]

I took apart pretty much everything I could

You didnt specifically mention the pilot jets. If it wants to run with the enricher engaged seems to point to the pilot circuit , as the enricher
in effect bypasses that path. Pilot jets cleaned?

[Lucien Harpress]

The pilot jets I got out. They all seemed clear, but I soaked all of them anyway (and will be soaking them again this go-around as well). My initial problems centered on a low-RPM stumble, so I gave these special attention.

I got the No. 4 mixture screw out. The "good" news is that I found a bit of gunk on the end of the needle. Hopefully, this is what's causing my problem (because my engine is getting NO gas whatsoever). The bad news is that, when I was trying to "seat" the screw to see how far it was in, I could only manage a quarter turn. This either means it was gummed up too much to turn freely, or it was set ungodly lean. Either way, when it comes to putting them back it, I'm pretty much starting from scratch.

[Crazcnuk]

The actual position of the needles means nothing. My special has all 4 needles less than 1/2 turn off seated.

This doesn't mean that my bike is set lean, it just means this is where the engine wants them, lean or rich.

Due to dirt and/or wear, and other factors, the needles will end up where they need to be, not rich or lean.