79 XS400 - Hard starting and poor idle.

[grusvag]

Ok gang, I'm trying to get my 1979 XS400SG running again and here's one of the things I need to sort out:

I recently installed a new battery and cleaned the carbs out. I need to check / reset the basic idle but that being said, the bike is very hard to start when cold. So far, the only way I can get it started is to squirt copius amounts of starting fluid in the carbs with the air cleaners removed. Once the engine fires I have to keep the revs up fairly high or it will stall. After letting it warm up for a while I can very gradually drop the revs down, by a combination of putting the choke back in and turning in the throttle adjuster near the hand control. Even then it's somewhat erratic and won't hold a steady idle too well. Part of my problem seems to be with the cable itself but this is not the cause of the problem, only something else I have to solve.

Tank has fresh 93 octane fuel in it and new spark plugs.

Can anyone recommend a troubleshooting checklist for me to work through to try to figure this out? I wonder if the carbs need to be cleaned better or more thoroughly. I'm not too familiar with the inner workings of carburetors and had a friend help me partially disassemble mine. He thought the insides looked pretty clean but I'm sure we took out all of the jets.

-John.

[drewpy]

its def your carbs mate, especially if you left fuel in them when parked up. the best way to clean is strip and ultrasonic clean them, get someone professionallly to do that, or buy a unit and do it yourself it will be cheaper and will learn something.

[grusvag]

its def your carbs mate, especially if you left fuel in them when parked up. the best way to clean is strip and ultrasonic clean them, get someone professionallly to do that, or buy a unit and do it yourself it will be cheaper and will learn something.

Yea, I was afraid someone was going to say that. Oh well, I actually just picked up a pair of spare carbs so guess I'll buy a rebuild kit and have a go at it! Might use a can of dip-and-dunk carb cleaner instead of the ultrasonic method.

[drewpy]

Yea, I was afraid someone was going to say that. Oh well, I actually just picked up a pair of spare carbs so guess I'll buy a rebuild kit and have a go at it! Might use a can of dip-and-dunk carb cleaner instead of the ultrasonic method.

get an air line then

[grusvag]

Progress Report:

-checked and cleaned petcock filter (a few flakes of tank paint on it but otherwise clean)

-adjusted valves. One makes noise now so I need to recheck them but it seems to run smoother now.

-reset electronic ignition timing. Definitely runs more smoothly and dare I say, even starts easier?!

Still won't start without taking the air filters off and shooting some starting fluid in there but on the whole it does seem to start more easily. Idles better too. Once it was warmed up I pulled the choke in and out and didn't notice a difference which leads me to suspect they're not working or doing what they're supposed to. So a carb rebuild is definitely needed.

Drewpy, I have a compressor. Are you simply suggesting I use compressed air to blow out and clean various parts of the carburetor? Maybe I'll look into having the parts cleaned ultrasonically though I'm not really familiar with who would do something like that. A machine shop?

Next will be trying to diagnose the electric starter and get that working too. After watching "The Long Way Round" my wife now wants to go for her license!

[drewpy]

Progress Report:

-checked and cleaned petcock filter (a few flakes of tank paint on it but otherwise clean)

-adjusted valves. One makes noise now so I need to recheck them but it seems to run smoother now.

-reset electronic ignition timing. Definitely runs more smoothly and dare I say, even starts easier?!

Still won't start without taking the air filters off and shooting some starting fluid in there but on the whole it does seem to start more easily. Idles better too. Once it was warmed up I pulled the choke in and out and didn't notice a difference which leads me to suspect they're not working or doing what they're supposed to. So a carb rebuild is definitely needed.

Drewpy, I have a compressor. Are you simply suggesting I use compressed air to blow out and clean various parts of the carburetor? Maybe I'll look into having the parts cleaned ultrasonically though I'm not really familiar with who would do something like that. A machine shop?

Next will be trying to diagnose the electric starter and get that working too. After watching "The Long Way Round" my wife now wants to go for her license!

yep, use compressed air that way you can also check if the drillings are blocked. ultra sonic cleaning may be done by a machine shop, but I use JRS in england, ther is sirrus online who are based in canada, they do it too. you need to google for your area I suppose.

does sound like your cold start device is not working, sorry I mean choke!

[grusvag]

yep, use compressed air that way you can also check if the drillings are blocked. ultra sonic cleaning may be done by a machine shop, but I use JRS in england, ther is sirrus online who are based in canada, they do it too. you need to google for your area I suppose.

does sound like your cold start device is not working, sorry I mean choke!

I'm going to clean the bits using carburetor cleaner. Probably the same stuff over there, but here it comes in a gallon can with a strainer. Cheap. Put the parts in the basket and let them soak. Has always done a great job for me in the past!

Since I've never completely disassembled carburetors before I'll have to go slowly, take good notes and maybe even photograph the process so I can put the thing back together the same way they came apart!

Thanks drewpy.

[stanman44012]

the xs400 has 2 jets on it one the small one is the one that is blocked up that is your idle jet try pulling it and pushing compressed air through it if it is still blocked you can but be very careful not to ream it out take a single bristle from a wire brush and poke it threugh there. That should solve your problem.

[stanman44012]

Also be careful there are some parts you do not want to soak

[grusvag]

Thanks everyone. Will let you all know how it goes when I get this done. Will probably be a few weeks and I might have a few questions once I get into it. Wish me luck!

[grusvag]

Progress Report:

Bike now starts on first kick! (electric starter needs to be replaced) and idles not horribly. Here's what I did:

1. New battery

2. New plugs

3. Fresh 93 octane fuel

4. Rudimentary cleaning of carburetor (not sure this was really necessary)

5. Set electronic ignition timing

6. Adjusted valves (I think this was the real key and I noticed a big improvement after I did this)

So now it starts, dare I say, easily and idles without fear of stalling around 1,500 (I know that's still a little high but I'm still a little gun shy). Still feels like it has no power (it is, after all only a 400cc and I'm a big guy) which I'm attributing to the carburetors. It hesitates at certain throttle openings and just feels "flat". Still planning on rebuilding the carbs but I also suspect that they might not be perfectly balanced. Not sure that's ever been done since I've had it.

So there you go. Lessons learned:

1. A fresh battery is a great thing.

2. Set timing.

3. Adjust valves.

All for now.

[Cy Welch]

Progress Report:

Bike now starts on first kick! (electric starter needs to be replaced) and idles not horribly. Here's what I did:

1. New battery

2. New plugs

3. Fresh 93 octane fuel

4. Rudimentary cleaning of carburetor (not sure this was really necessary)

5. Set electronic ignition timing

6. Adjusted valves (I think this was the real key and I noticed a big improvement after I did this)

So now it starts, dare I say, easily and idles without fear of stalling around 1,500 (I know that's still a little high but I'm still a little gun shy). Still feels like it has no power (it is, after all only a 400cc and I'm a big guy) which I'm attributing to the carburetors. It hesitates at certain throttle openings and just feels "flat". Still planning on rebuilding the carbs but I also suspect that they might not be perfectly balanced. Not sure that's ever been done since I've had it.

So there you go. Lessons learned:

1. A fresh battery is a great thing.

2. Set timing.

3. Adjust valves.

All for now.

Make sure that the float level is correct. If their too high or too low it won't run well. Also when adjusting the idle mix I found that adjusting it out until the idle speed started to go back down and then leaning back out for max idle speed worked well for me. Mine starts on the first tap of the starting button now and if cold I use full choke for about 30 seconds and half choke for about 2 minutes. No high idle even with the choke on any more (which is used to do always). One thing I found wrong as well was that one float didn't have the float chambers at the same height (apparently I bent it slightly at one point) so I made sure that then were both at the same height and adjusted according to the manual and I was rather surprised at how much better is was. Very careful attention to detail making sure things are correct and it should work fine.

[grusvag]

After riding it a bit these past few days I've come to believe that one of the jets (main?) is clogged for the following reasons:

1. Still needed to spray starting fluid in the carbs to get it started this morning.

2. Simply feels "flat", and although the engine runs ok, it just doesn't have the power it should. I can barely go up hills full throttle.

3. It sometimes backfires when it's shut off leading me to believe it's running lean.

4. It sometimes surges like the blockage temporarily clears but only very briefly.

I may remove the carbs on the bike and try to figure out exactly where all the jets are and try to blow or clean them out and then just put it back on the bike to see if that makes a difference. I still want to completely clean and rebuild the spare carbs but want to see if cleaning the jets out is what the problem is.

Thanks for the advice about the floats, I'll make sure they're as they're supposed to be.

[joecool85]

After riding it a bit these past few days I've come to believe that one of the jets (main?) is clogged for the following reasons:

1. Still needed to spray starting fluid in the carbs to get it started this morning.

2. Simply feels "flat", and although the engine runs ok, it just doesn't have the power it should. I can barely go up hills full throttle.

3. It sometimes backfires when it's shut off leading me to believe it's running lean.

4. It sometimes surges like the blockage temporarily clears but only very briefly.

I may remove the carbs on the bike and try to figure out exactly where all the jets are and try to blow or clean them out and then just put it back on the bike to see if that makes a difference. I still want to completely clean and rebuild the spare carbs but want to see if cleaning the jets out is what the problem is.

Thanks for the advice about the floats, I'll make sure they're as they're supposed to be.

Wrongly adjusted floats will cause the problems you are having, I think if you do that and give some air through the jets you might find yourself riding a nice running bike. I use a small 12v air pump for cleaning out carbs, I attach a basketball needle to the end and use that to clean out any orifices in the carb - works real well.

[drewpy]

Wrongly adjusted floats will cause the problems you are having, I think if you do that and give some air through the jets you might find yourself riding a nice running bike. I use a small 12v air pump for cleaning out carbs, I attach a basketball needle to the end and use that to clean out any orifices in the carb - works real well.

that's a good tip Joe, no basket ball needles but plenty of football ones

[grusvag]

I've got a shop compressor and can dial in a specific pressure. Can I use that instead of a bicycle pump? Sounds like I shouldn't use high pressure.

[drewpy]

I've got a shop compressor and can dial in a specific pressure. Can I use that instead of a bicycle pump? Sounds like I shouldn't use high pressure.

i'd say high pressure is best to shift the crud. just be careful

[joecool85]

i'd say high pressure is best to shift the crud. just be careful

Wrong, high pressure can damage things on certain carbs (not sure on this one). You only need ~20psi or so, you could probably use a lot less even.

[drewpy]

Wrong, high pressure can damage things on certain carbs (not sure on this one). You only need ~20psi or so, you could probably use a lot less even.

what certain things?

[joecool85]

what certain things?

I'm actually not sure, but I figure I'd rather be safe than sorry. Someone once told me I could damage my carb with high pressure compressed air. And since 10+ psi will normall blow out any passage on a carb, what's the point in using 100 or more?