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Fueling

  • Thread starter Thread starter wesleyweazel
  • Start date Start date
W

wesleyweazel

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I have a question that no one has been able to answer so far. Must there be an air cleaner filter on the carbs for them to perform properly? It's a 1981 GSX400F with Mikuni BS26SS carbs. The airbox sits under the seat. The carbs are variable venturi.

I have been reading about white smoke coming from the exhausts. My bike did the same only when it warmed up. Runs like crazy when cold ,but boggs down when it gets warm. I've stripped the head off and from what I can tell the valve stem seals and valve guides are gone. The bike had been standing for 15 years before I bought it. The valve stem seals are brittle and I can wiggle the valves in the guides quite badly.

How do you remove valve stem seals? How should I check the valve guides properly? How do you remove the valve guides from the head without damaging the head? Are the valve guides made from oilite?

The barrel still has honing marks in it and I can't find any blow by marks. The pistons look like their almost new. The bike only has 9000km on it. Thats 5625miles. How would I check the wear on the rings and the sleeves? I know that I am asking a lot of questions, but if no one has told you or shown you then how must you learn. I only have a normal feeler guage. O and it had a habit of dumping fuel into the sump. I only got something like 6km to a litre and according to some stats that I found it should be about 16km/l.

Any help with my engineering troubles will be greatly appreciated.
 
Do youself a favor and get a shop manual. Many of your questions will be answered in the manual with greater detail and accuracy than anyone can give you. Start with the manual and when you have questions come back here.
 
workshop manual

workshop manual

Am trying to buy one from Ebay in the UK. It's a cd of the original manual. Suzuki are the only ones who made a manual for that bike originally printed in 1981. This model bike only seemed popular in the UK, Germany and The Netherlands. There are no Haynes or Clymer manuals that I've seen for this model.
 
Most likely the motor is okay mechanically considering the low miles. To check valve guide wear you need a dial indicator; the wobble test is not adequate. I'd focus on cleaning everything up and looking for age issues - wear from use is not likely again considering the mileage. New valve stem seals and gaskets is most likely going to handle it.
 
Air filter is required

Air filter is required

When the bike was engineered the carb was selected and jetted based on the air flow the engine got through the stock box and air filter. If you remove either or both it will cause the engine to run leaner. If the original jetting was a little rich it might run OK. It also might run too lean at higher or lower RPM's causing over heating. I'd recommend getting some kind of filter in it and checking the plugs to make sure its not too lean.
 
You need the airfilter to cause enough vacuum to get the proper draw of fuel. Otherwise it will run lean and hot and that is not good for air cooled motors. The guides are not exactly a tight fit, the valve will be sloppy in it. If you want to replace the guides they will need to be pressedout and the new ones pressed in. Replace the seals, that will be good enough. Considering the miles on the engine, the bores probably still have the honing marks. The rings are probably not worn in completely. So they will be good too, the only thing that would have killed the rings with that distance would have been if the engine was overheated. Now, if the pistons look clean then I wouldn't worry about them.
Replace the valve seals, put a new head gasket and valve cover gasket on, then start it up.
 
Thanks

Thanks

Thanks a lot guys. I purchased a manual this morning on Ebay, now I have to wait for the shipping. So I should get away with just the seals? Thats good news cause its a 16v which makes everything more expensive. When I get the manual I should be able to find the correct wear limits for the guides. Perhaps I should just take it to an engineering shop to be checked.

I forgot to mention that no 2 cylinder has a hole in the one exhaust valve. Could this be caused by running lean? How much smoke could bad valve seals create ( out exhaust )? How do you seat a valve? I know it has something to do with grinding paste. Once again thank you for all the help. The answers that I get here are much better than the local mechanic's.
 
Exhaust

Exhaust

I forgot to mention that the exhaust isn't standard. The original headers are on, but I had the exhaust made up. It's got a canister for each side, similar to the original system. Would this also affect the way in which the carburretor operates? Thanks for answering my airfilter question. At least I am more informed now.
 
:shock: THERE'S A HOLE IN THE VALVE????
I've seen burned valves, but usually the seat and the edge of the valve are cooked. Is only one valve damaged, or are all the valves really cooked on the edges? Are the seats black and pitted? Are the tops of the pistons clean and smooth or are they pitted? If the engine was running that lean, you may need to do the rings and the head as well.
:-k
Smoking, now, what do you mean by smoking? Just when you start it up, or continuously?
If it is blowing smoke just sitting there at idle, you got problems, if it smokes only at startup, it is valve seals, if you get a lot of smoke when you engine brake, that is rings, if you get a lot of blowby out the crankcase breather, that is also rings.
:-k
Why were you running it without the airfilter?
And for how long did you run it without?
Lapping involves using grinding compound and a lapping tool, but if the valves are badly damaged, you will probably find it easier to have a rebuilder do it.
 
The hole in No2 exhaust valve and the fuel in the sump are from the same problem.

You have a bad fuel tap. The tap is controlled by a vacuum hose running into the carb manifold of No2 cylinder. When there is vacuum the tap opens, when there is no vacuum the tap closes.

That vacuum hose is sucking air when running, causing No2 cylinder to run lean and hot. And it is leaking fuel when stopped, which ends up in the sump.

You need a diaphragm kit or a complete fuel tap.

Kim
 
The white smoke on startup is from worn valve guides/seals. They are leaking oil from the cam area into the cylinder when stopped. When it is burned away the smoke stops.

The air box *needs* a filter in there. You can make one up from open cell foam with a light dose of oil squeezed through it, the thicker the oil the better.

Another consideration about the jetting is whether somebody has fooled around with needle settings. Fuel flow is controlled in three stages. Low rev running is controlled by the air/fuel screw. Mid range running is controlled by needle valve profile and height setting, high range running is controlled by main jet.

The air/fuel screw is the easiest to get at, therefore easiest to tamper with and get wrong. The needle setting is the next easiest to tamper with (and get wrong). Needle profile and main jets means replacing parts so they are not so easy to fool about with.

Your arriving manual should have info on the general rev range of each setting.

Kim
 
Fuel tap

Fuel tap

Thanks doc. Now that you mention it the tap is connected to cylinder no 2.

The reason that I've been running without a filter is because the bike is so old that the parts are insanely expensive and the dealers have to order them into the country. R 150 for an airfilter?!!!?? In dollars thats about 25.
 
wesleyweazel said:
In dollars thats about 25.
Click to expand...


Gee...thats pretty cheap...here's mine :shock:

Part# 13780-15500Desc FILTER,AIR CLEAPrice 65.37
 
wesleyweazel said:
Thanks doc. Now that you mention it the tap is connected to cylinder no 2.

The reason that I've been running without a filter is because the bike is so old that the parts are insanely expensive and the dealers have to order them into the country. R 150 for an airfilter?!!!?? In dollars thats about 25.
Click to expand...

Here in Australia mine was going to cost me about $60, that is why I made my own out of foam. I don't know how the 400 filter looks, but my GS1000 has a metal mesh box and the foam covers it on four sides and bottom. I just got quarter inch foam, double layer all around, glued the corners with hot melt glue, oiled it with super sticky filter oil, and that was it. $2 worth of foam and a bit of time.

Kim
 
So for saving 150 rand you will spend how much to fix the damage caused by the lean condition?
Up keep is essential, the filters need changing or cleaning, the oil must be replaced, yadayada......
A little maintenance saves you in the long run.
 
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