1982 Yamaha XS400 R Seca - Need Carb help

[ferchja]

Anyone know anything about older cycle carbs? Or know of a good forum like this for yamaha. With the 85 spree I got an 82 Yamaha, I have great spark. Now need to get the carb up to snuff. It has a mikuni twin carb.

I am taking it off again to check all of the jets again.

Thanks in advance!

[noiseguy]

What's wrong with them now, that you need to dig into them? They are a CV carb, I'm guessing, not a piston-slide carb, right?

[ferchja]

Yes.

Here is the issue. This cycle I am guessing has not been run in 5-8 years.

I pulled the carbs, and cleaned the enriching circuits, main jets, and idle jets. I can get the cycle to run for 10 seconds by putting fuel in the spark plug holes. It has the diaphram top for the fuel needle and large cylinder that moves up in the carb to open the main jet.

It obviously doesn't idle, and the enriching circuit is not enriching the fuel. Yes I have the choke on full. The air filter is off, but like I said the engine runs great with gas in the cylinder.

I am 100% sure it is the carb idle jet/enriching circuit/idle fuel-air mixture screw I need to find a site with the carb exploded to find the hidden cleaning area I need to get that I haven't. With it running I tried to hold 3/4 throttle and it still died.

Just trying to fish for some thoughts before I spend money to rebuild the carbs.

Thanks noise,

[noiseguy]

How do the carbs look? Are they really crusty inside? How does the rest of the bike look? (Abused, pristine, taken apart by monkeys, etc.) Was this left outside too?

I assume that the bike has gas in the carbs when you try to start it? Are the vacuum slides moving up and down freely?

The CV's like to have an air filter present when you use them. There are a lot of guys that try running pods on this type of carb (like on my CB900F), and have a lot of problems with flat spots, etc. Try reconnecting the airbox to see if this helps. Don't know why this would affect idle, but nothing surprizes me anymore.

There's also a idle air screw on most of these, but assuming it ran at one time, I wouldn't mess with this yet. If you have to pull it you'll need to resynch them, starting from factory settings.

I pulled my 900F out of an 8 year storage, and have yet to pull apart the carbs. The gas in the carbs had evaporated (or been dumped,) and the vacuum-petcock had kept gas out of them over storage. But it had been stored inside, and was in good shape.

If it's firing, it probably has workable compression and the valves are closing. When you get it running, recheck compression and the valve clearances. These clearances often get ignored and trash engines. Like oiling systems.

I have a feeling you'll end up buying at least a Chilton's manual for this bike. Check the library, you'd be surprized the books they keep on these subjects.

[ferchja]

The bike is in great shape, the left turn signal was broken from it falling over in storage, but everything else is near perfect (for a bike 23 years old)

The engine is tight, turns over perfectly. It was obvious that gas was left in the bowls, the left one had more slugde then the right from it leaning on the kick stand.

I will end up buying a Chilton. But before I do, I am trying to educate myself on what this type of carb costs in parts etc. If the pieces that typically fail are hundreds of dollars then there is no econmic reason to rebuild. But if the parts are usually long lasting and/or cheap to repair, then I can go ahead and start to dismantle and just do a thorough cleaning. My experience is that I end up replacing about 60% of the gaskets etc. and rebuild, not because the gasket/oring was bad, but I tried to pull the old rubber/gasket off and ended up destroying it when I didn't need to open that part of the engine/carb, cause the failure was somewhere else.

The carbs are mounted in tandem on a bracket. They come off as a pair and seem to be mounted together quite substantially. I agree that some minor differences could be had with the moving of the set, but if I keep them mounted together it should still be adequate to get it running to determine the rebuild needed? Only to balance properly when you know its worth spending the time on. I do not plan on driving it any distance unless I have things set to spec. The goal now is to get it to fire and idle.

[noiseguy]

No, those Keihin carbs are rebuildable for about $20-40/pc. I would not separate them; that's getting into a whole other can of worms with those carbs and probably not a running issue.

I'd start by removing the jets and bowl and soaking them in carb cleaner, and make sure that the idle jet is open in each. Check the slides are free, attach the aircleaner, and see if it will fire. Keep a fire extinguisher around in case it catches fire. No joke; it's happened to at least 2 guys I know.

[ferchja]

Make it 3, i tried to start the bike on Sunday and started the cycle on fire , it back fired into the air cleaner where I had just sprayed starter fluid into the intake plenums, I am guessing it pooled a bit. Fire jumped to a oily rag on the floor of the garage and I was busy trying to get the fire out in the air box, and the oil rag under the engine.

All was fine, but the wife nearly killed me when it was over, as the garage and half the neighborhood was lit up with white smoke.

30 minutes later, after run to store, extinguisher was installed in garage.

[vette76]

that will scare the * out of ya. i was welding a busted weld on the frame of the spree once and i guess a piece of loose slag jumped up under the seat and lit up my tank. good thing i had an extinguisher ready. now i can laugh. man, that was stupid of me.

[ferchja]

Took the carbs off and removed everything. After talking to some Yamaha repair guys locally on the phone. They suggested tearing down the entire carb, and cleaning everything with carb cleaner and an air gun. They pointed me to the air mixture screw which I missed in the earlier cleaning. I also found under the diaphrams on the top, there is a pilot channel to the bowl that was clogged like a mother. The repair guy says that all the old bikes that people try to start after sitting usually miss this. I think it provides the air vacuum to pull gas into the idle mixture screw from the idle jet.

From looking at the carb and cleaning it is amazing the tapping and angles/channels that are drilled to get fuel and air to mix. Its like looking at an ant hill. One tunnel hits another...etc. All plugged with what looks like brass ball bearings.

Anyways the last of the plugged holes is going to soak tonight with carb cleaner and then I will blow all clear tomorrow. Hopefully it will fire on the first pull.

The bowls were good and the float needles were working very well.

I will post the results. If this works this will be the cheapest repair to go from "no go to go" which in this case was no spark along with no fuel. Fuel filter, fuel line, 5 quarts of oil and numerous bolts and screws to replace after breaking them badly on removal. I think I am at a total of $35 for parts. The bike cost me $55. Spree rebuild was $20 for the scooter, and like $290 in parts and paint. One can go 100 mph and the other is a steady 25 mph. Can't wait to take it out and taste the victory like the Spree.

This site is a great wealth of knowledge, underestimated as spree web site but able to get you started with general motorcycle basic repairs. Would never have started the Yamaha without cutting my teeth on the Spree and everyones help here. Thanks again all!

[noiseguy]

Glad to help. Those CV carbs are a royal pain, they really illustrate how simple the Spree carb is.

[ferchja]

She's up and running. Sounds like it just rolled off the showroom floor. I think I may have the idle screws set out to far, but other than that it idled at startup perfectly. I will get the screws set tomorrow.

Thanks for the assist guys, other than needing specs to get the idle set the thing will ride another day.

[noiseguy]

Sounds like you're well on your way, congrats!