'89 DOHC running issues, bad starter

[willem]

I've got a slightly neglected '89 DOHC since a few weeks. So far it's been taken for a new set of tires, clutch cable and battery, and I've put in some new spark plugs.

Because there are some problems with it. First of all, it has trouble running. It starts (sometimes takes a few tries, sometimes on the first tap of the ignition), but often stalls and then refuses to start again. The startermotor does make the engine turn, but there is just no ignition. I've tried going to work on it twice this week, but both times I didn't even reach the end of the street (about 500 meters, nearly half a mile to you crazy imperialists). It has fresh gas, the battery is brand new (although by now probably somewhat empty) and new spark plugs. Sometimes when I turn the key the lights don't go on, I guess the wiring is a bit worn there. That could make it stall, but not prevent it from starting again right?

Anyone have similar problems? And where should I start looking?

My own idea would be to check (in this order):
- air filters
- electrics
- fuel lines/tubes
- carburetors (although that is a bit daunting for me, this is my first time trying to fix stuff on a motorcycle.

Hope you can help

 

[bentwrench]

Reverse your order. Carbs first. They're the most likely culprit. There's a ton of stuff on this site to help you through it, and just post pictures and questions as you go along. Also, use the XS650 carb guide (search google). Our carb bodies are the same, jets are different sized. Follow the instructions there (lots of pictures too) and you'll do fine.

 

[16VGTIDave]

Carbs, carbs, carbs!

Seriously, clean them repeatedly. Probe all passages with fine wire. Clean more. Save yourself a lot of grief and just do as we are suggesting. We've learned the hard way!

It also sounds like your ignition switch needs a good cleaning as well. So while you have your carbs in the cleaner, you can remove the ignition switch and clean it as well.

Once your carbs are clean, install an inline fuel filter just to make sure, though the float needle seats should have filters on them.

 

[willem]

OK will do. Think I can make some time for it this weekend. Battery charger is on its way, should be there tomorrow as well.

Thanks for the help! I'll post some pictures later, maybe even make a little step-by-step just for fun.

Oh yea, it says in the manual I need LOCTITE or something similar, I should buy some before I start, right? I also have some petroleum based solvent to clean with (dry-cleaning naphta, white spirit, refined petrol is the translation of what I have). Anything else you recommend I get before getting started on the carbs? I'll probably try to work on it on sunday and then I won't be able to get supplies.

 

[16VGTIDave]

Naptha should work well for removing oil and fuel residues. Just don't use it in your Optimus stove afterwards! I used a can of aerosol carburetor cleaner as my carbs were very nasty.

You will want to use a mild acid to remove corrosion from the carb bodies. I used a household cleaner that removes hard water stains. Lemon juice also works, as does white Vinegar. Heating or even boiling the parts in the cleaner will dramatically increase the effectiveness and reduce the time required. Make sure to rinse well with clean water, to prevent further corrosion.

Since you are going to have the carbs completely disassembled, now would be a good time to replace all the seals and gaskets, and even the diaphragms. I don't know if you can find a local shop that has these in stock.

Good luck!

 

[willem]

OK I'll definitely try that! but how about the LOCTITE?

Don't know if they'll have that stuff in stock but theres a local shop that has been dismanteling old bikes for 56 years, perhaps I'll have some luck there

It says in the manual that for cleaning you dont need to disassemble the entire things, but I guess I might as well to get everything cleaned properly right?

 

[willem]

Ah nevermind, that's only the separation of the carburetor bodies with the LOCTITE. Won't need to do that, so don't think I need to go buy some of that. Also I should be able to replace the seals and gaskets either way

thanks!

 

[bentwrench]

I wonder what you'll need loctite for?

Anyway, you're looking for a bolt adhesive - something that will go on the threads and hold them in place. For what it's worth, I've never used Loctite when cleaning carbs... I like to be able to get things apart again later...

 

[willem]

It says in the manual that you should use it when you separated the carbs and are putting them back together. But as I won't need to separate them in order to get them cleaned and to replace any gaskets or seals, I won't need it.

But if you're still wondering, it's in the carburation section in the DOHC manual!

 

[bentwrench]

I figured. Yeah, separation is not required, or advised.

 

[willem]

So I opened up the carbs yesterday, I think alot of junk came out. The gas that was in the float chambers was all orange-ish brown, so it was definitely good to clean this out. I did not manage to open up the tops of the carbs, so couldn't clean over there. I did probe through all the jets with some wire, and cleaned everything as far as I could.

After putting it back together, things hadnt improved.. The engine still runs, but after a little while it stalls and then refuses to fire up again. Maybe I should get the carbs cleaned professionally at a shop? Or do you have other suggestions that will definitely work? I feel that because I didnt take out the vacuum chamber cover I wasn't able to clean everything, but trying again might not help. The screws were impossible to get loose. Perhaps cleaning it in an ultrasonic bath at a shop would be good?

 

[JARichmond]

Did you stick a fuel filter in too? If there's junk in your carbs, it came from your tank. Stick a filter in there for good measure, and have a look at your idle settings. I know that I could get my bike to run for a good minute or two when I first got it but it would stall pretty darn fast. I fiddled with my Idle air screw settings (3-3.5 turns out from lightly seated) and it improved significantly. They should be located above the wet side of your carb body.

 

[willem]

I didn't put a fuel filter in yet, still looking where I can get one of those. I think I should definitely clean out my tank some time soon as well.

I'll try fiddling with my idle air screw later, haven't tried that yet so it might just do the trick.

 

[willem]

I'm curious, how does adjusting the idle screw differ from pulling out the starter choke? Does turning out the idle screw make the mixture contain less or more air? Or does it just make the mixture larger, so more mixture can reach the cilinders? And how does it differ from turning the gas handle a little?

 

[bcware]

You can get a fuel filter at any store that carries common lawn mower supplies; automotive stores, hardware stores, department stores, etc.

Opening the throttle or adjusting the idle will increase volumetric flow (the idle adjustment screw opens the throttle).

The "choke" lever opens an enrichment circuit which provides a lot more fuel to make starting easier. The mixture created when using the "choke" is too rich for normal use; it will cause fouling of the spark plugs after a while.

The idle mixture screws are how you tune the bike at idle and the first few thousand rpms. The bike should be fully warmed up before you try to tune it.

On my SOHC 1978 turning the idle mixture screws out causes the mixture to become richer. This could be different for your DOHC; I don't know! It's easy to test while the bike is running and warmed up: if the screws are making the mixture leaner the rpms will eventually start to jump and "hang" and there could be popping or backfiring. Conversely if the mixture is becoming too rich the engine will tend to "bog" down and rpms will fall and the engine won't want to rev up.

Carburetors have different stages of fueling. At idle the pilot jets are providing the fuel; the mixture screws control their flow and the idle adjustment controls the volume of air coming in. When you open the throttle more air rushes in because the engine is acting as a vacuum pump just like your lungs! The throttle butterfly valve serves to choke this vacuum and control the flow. The vacuum created causes the needle and diaphragm to rise; as the needle rises it unplugs the main jet. Eventually the needle will rise maximally and the main jet becomes fully unplugged. So, the needle position controls the mid range of rpms while the main jet size is most influential at wide open throttle (WOT).

Some carburetors have more or different features, but I think this will get you started.

 

[willem]

thats really helpful! nice clear story, thanks!

If only there was a way to keep my XS running long enough to warm it up now, then I could adjust the idle mixture screws maybe a better cleaning will help.

I'm gonna open up the carbs again this weekend, I'll get a fuel filter and some new screws for the vacuum chambers before I start. That way I can go at the stuck screws will pliers and such to open them.

How about synchronizing the carburators? Haven't done that yet, cause I would need a special sync tool for that which I don't have. I haven't separated the carbs, so they should still be fine. Would synching them help with my running issues?

 

[bcware]

The most common cause of running issues related to carburetors is being dirty or having incorrect settings. The later models also have o-rings under the idle mixture screws that deteriorate and cause problems. You should check to see if you have these o-rings and that they are intact.

Synching will certainly help, but the motorcycle must be warmed up and have a relatively stable idle. Do a search for "manometer" on here and you will find ample instruction on how to make your own for very little money and how to use one.

 

[willem]

OK thanks, I'll try to get it running and then I'll start on syncing.

Last night I took off the carbs again, attempting to take the vaccuum chamber cover off and screw out the pilot jets this time (last time I didnt have a screwdriver that fit)

But I'm afraid I messed up one of my pilot jets! I was trying to unscrew it but it was butter-like soft, I just took some gold colored metal pieces off and then that was the end of it. I highly suspect this jet to be the culprit of my running issues..

Also I still couldn't get the vaccuum chamber cover screws off.. Everything is now soaking in naphta since last night, hopefully taking off most of the grime. I think I should take the whole think to the shop tomorrow, see if they can help. Any ideas here on how to take out the pilot jet and how to unscrew those impossible vaccuum chamber cover screws?

 

[16VGTIDave]

I use a small impact driver (not an impact wrench!) to loosen stubborn screws. A smack with a 2 Oz. mallet and out they come.

If you are soaking the carbs in Naptha as they are, you are soaking the diaphragms as well. You should plan on replacing those. Old rubber and cleaners or solvents is not a good idea. You can buy just the diaphragms from http://jbmindustries.com/

 

[willem]

thanks for the help

Went to the shop with my carbs yesterday, the guy there took out the pilot fuel jet for me. The head was a bit messed up, but as long as I saw a new nook into it it should be fine.

Also he checked out the rest of the carbs, vacuum chamber seems to be working properly so he said not to take it apart. Those pesky bolts need not to come out, so I'm happy. The rubber o-rings around the float pins are also still in good condition.

Now cleaning out all the little fuel and air pathways and I hope my xs will run smoothly then! Can't wait to get it running properly so I can ride around