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Mystery (non) combustion event???

  • Thread starter Thread starter J Paster
  • Start date Start date
J

J Paster

Guest
Hi, I'm hoping someone else has experienced this and can point me in the right direction. I have a '78 GS550E, stock save for pipe and K&N filter. PO did the pipe and had been running pods. I got the bike after 8 years parked and went through the carbs, set valves, rebuilt petcock and replaced trashed intake o rings. Installed OEM air box w/K&N filter, lid off air box. Have ridden the bike for the eight months since, and it runs great. I had noticed during that time that if I didn't ride it for about three days, it took quite a bit of turn over to fire it. Even ran down the battery once, and turning the petcock to prime didn't really help. Well, now that I've pulled it apart to paint / polish everything, I can see why... The carbs are completely empty, and the fuel has all ended up in the cylinders! The float bowls are dry! The petcock doesn't leak. Duh, what causes the cylinders to suck all the gas out of the bowls?!?!
 
J Paster said:
Duh, what causes the cylinders to suck all the gas out of the bowls?!?!
Click to expand...
In another "Duh" moment, I would guess the normal, proper operation of the valves and pistons could do that. :-k

Of course, it would have to be accomanied by the LACK of proper operation of the petcock, not allowing it to supply fuel. :o

Check the petcock for proper fuel flow, might have a clogged filter screen on the inside of the tank.


.
 
I considered petcock issues. I initially rebuilt and cleaned it because it started messing up # 2 cylinder due to vacuum line taking on gas. Since, it runs great, idles great, and doesn't get crabby about starting if I start it every day. Reaching back to when I went through the carbs, I remembered that I used the (almost) new needles and seats from the VM26's not being used by my GS1000. I should also report that the carbs on this 550 were VERY gummed and corroded, so much so that even after Berryman's I had to use strands of copper wire to poke out jets, passages in the float bowls, etc. to finally get it to run well. I got new pilot jets for it and noticed when changing that the originals were still very clogged / narrowed when comparing under a light to the new ones. I guess I'm just stumped as to why the bike runs well all the way until I park it, then the bowls start draining into the cylinders. Could that happen if the bowl vents were clogged? I don't remember checking them...:o
 
J Paster said:
I considered petcock issues. I initially rebuilt and cleaned it because it started messing up # 2 cylinder due to vacuum line taking on gas. Since, it runs great, idles great, and doesn't get crabby about starting if I start it every day. I guess I'm just stumped as to why the bike runs well all the way until I park it, then the bowls start draining into the cylinders. Could that happen if the bowl vents were clogged? I don't remember checking them...:o
Click to expand...

It's uphill from the bowl to the cylinders, so it shouldn't happen unless the petcock is flowing gas into the bowls AND the overflow tubes are plugged. The VMs don't have the problem of filling the crankcase with fuel like the CVs, the overflow tubes prevent the fuel getting high enough. Unless they are not open, or they are routed upwards so fuel can't escape that way?

J Paster said:
I remembered that I used the (almost) new needles and seats from the VM26's not being used by my GS1000.
Click to expand...

Did you check that the needles are free in the seats? Sometimes people pull them out with pliers, the tube part of the seats get smashed, the needles can get stuck if they rotate to where the wide part of the needle is in the smashed part of the circle.
 
I will check petcock, needles / seats and float bowl drains tonight and report back. Thanks,
 
The gas can't "wick" up into the carb throats, or we all would have had trouble long ago. It must be evaporating, or leaking out.

The gas in the bowls is constantly evaporating, and removing the vent tubes will allow it to do so faster. You are in AZ? The warm dry climate could help too.

10-20 seconds on prime should fill the bowls if the fuel is flowing ok. I watch the fuel filter to make sure I have a good flow on Prime and turn it back to ON when the carbs are full.
 
Reporting back

Reporting back

My float bowls are nice, clean and clear. It was about two weeks idle as I started the restoration before I pulled the carbs to find them empty, so I guess the heat here could have dried them up. My petcock performs correctly - no gas unless vacuum is applied. Prime works correctly. But that won't start it without some starting fluid help. However, the vent tube blow trick works real nice. Heh, heh. Blowing my bike to fire it up.;) Heh, heh.

Thanks again, gentlemen!
 
J Paster said:
But that won't start it without some starting fluid help. However, the vent tube blow trick works real nice.
Click to expand...

It sounds like the fuel passages to the chokes are clogged, at least partially. Blowing on the vents pushes fuel up through the needle jet into the venturi, in effect doing the choke's job of enrichment.
 
That very well could be. As previously stated, these carbs were really crudded up, so much that it took three tries to get things poked out even after chemical dip / air cleaning. Maybe I should break them down and send out to one of those places that do the "ultrasonic" cleaning.
Or, I could pick up another set at the local yard and take my chances...
 
J Paster said:
That very well could be. As previously stated, these carbs were really crudded up, so much that it took three tries to get things poked out even after chemical dip / air cleaning. Maybe I should break them down and send out to one of those places that do the "ultrasonic" cleaning.
Or, I could pick up another set at the local yard and take my chances...
Click to expand...

Well, some of the guys on this forum will do a better job for you than those guys.
But it sounds like you almost have it, just make sure that the carb cleaner spray goes through all the choke intakes the same, and it sprays uniformly out of each tiny orifice. There are probably five tiny orifices on each choke pickup.
 
hard starting is a symptom of tight valves, even if they're still under the "check up period" you should check em out
 
Since I've got it in pieces for the resto, I'll go ahead and soak / poke the carbs some more. Would seem silly to take such a good running set and toss 'em just because of hard starting after sitting a couple days.
I've put about 3k miles on it over the summer, set all the valves to .005 before riding while sorting it out. Of course, I'll reset them again after I replace the stem seals, so that'll get done regardless.
If I get it back together and still experience the same symptom, guess I'll give those vent tubes a puff and see if that works.
Thanks,
John
 
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