81 550L dies after 15 min. running

[Guest]

I am new to this site and have learned alot from all of your replies to
different situations with bike problems. What a site, you guys are to be
commended for time shared to help others in need and to give advise and
inscentive to perform the task at hand!
Question , I received 2 bikes this spring, they had not ran for 20 yrs.
GS 750 T with 6500 miles and a GS 550 L with 7500 miles. I was able to get the 750 to run after many long hours of off and on again carb
cleaning and adjusting, tank relining and general top to bottom cleaning and brought this bike back to life, what a challege and a great reward for the end result.
GS 550 L was the same, New carb boots and seals, carb o rings and cleaning, tank reline, plugs and air and oil change,rear master cyl. and a good cleaning.
The question the 550 runs after starting will die after 20 mins. running, and is very hard to start afterward. Will crank, has spark ,plugs
don't seem to be fouled unless choke is used to try to start, but still on restart very difficult. Seems to restart after 20 min. of ignoring it.
I have mastered taking the carbs off, 15 mins. because I have
been into them many times and really not proud of it!

Send regrets or replies anything is appreciated, bmac

[semerm]

Are you sure the cylinders are getting gas after the 15 minutes? Are the plugs wet? Do you have a in-line filter in the gas line?

[bmac]

Thanks for the reply, had a small inline filter on it, I took that off because I had the tank relined and read pros and cons about a filter, still the same results. Plugs are dry and tan, #4 is black and kinda sooty but I have spent alot of time idleing and really can't get a good adj. on #4 so that might explain that.

[bmac]

I have another question, can you idle these bikes to stall after a period of time?

[semerm]

Have you tried this with the fuel petcock on "pri" as well? When runnig, can you ride it and will it rev fine as well for the 15 minutes? Does it do the same thing? It sounds to me like it may be a petcock issue? To answer you rlast question, they should run without stalling.

[bmac]

thanks for the reply, it happens in all facets. I cleaned the petcock and did tests on it to see if it worked properly and it was fine. It fills on prime and does not drain gas until vaccum is applied. Also by chance looking for a carb to purchase for my 81 gs 750 t, it is #2 carb with vaccum port, I feel I might of messed up the idle jet tower for the idle needle. Not satisfied with the way it seats compared to the other 3.


bmac

[ddaum]

Maybe your gas tank isn't venting. Try running the bike with the gas cap off. If it fixes the problem, take the gas cap apart and clean the innards.

[Planecrazy]

BINGO! That was going to be my suggestion. If the tank isn't venting then you are slowly building up a vacuum in the tank, which eventually starves the engine. After twenty minutes the pressure equalizes and you get another twenty minutes. To test, run the bike until it dies and then open the gas cap ... if you here the telltale "whoosh" of air rushing in you've found your problem.

I have also heard (if the gas cap vent turns out NOT to be the problem) that there is a vent tube coming off the carbs on the '80 model (like mine) that can sometime cause problems, and that people have solved the problem by simply removing it.

Good luck!

[bmac]

Bingo, As we speak gas cap off and she has been running for about half an hour. Took cap apart not much in there to clean?

Thanks Gentlemen bmac

[ddaum]

Bingo, As we speak gas cap off and she has been running for about half an hour. Took cap apart not much in there to clean?

Thanks Gentlemen bmac

Glad we could help. My gas cap had some very small parts, air passages, and ball bearings. I just took it all apart and cleaned with carb cleaner.

[jimcor]

Quitit, quitit, quitit!!!

These little air cooled engines were never meant to sit and idle for 1/2 an hour! They've got to have cooling air blowing on the fins. Don't do this anymore. Your engine thanks you very much!

[bmac]

Thanks for the warning Jim, I have just took the bike out of 20yr. coma and needed to get all the bugs,critters and you name it out of it.
I'm 51yrs old and never had a bike , I got two bikes for a buck that weren't ran and worked on them. With the help from this site and clymeres got them to run well. Not sure what I am going to next but
they cleaned up real nice.

Thanks again Jim, I'll follow your advise,

bmac

[bmac]

Gentlemen, I also forgot to mention Bikebandit.com, spent alot of time
researching parts and found that they definitely were the way to go for parts, what a tool to have at your fingertips.


bmac

[Planecrazy]

If you have a box fan or a large oscillating fan you can use that to "create wind" on the engine while it's sitting and running...

Regards,

[jimcor]

"create wind" on the engine while it's sitting and running...

Regards,

:shock: :shock: :shock: sometimes the advice around here just stinks!

Just kiddin', the fan is a great way to help keep the engine cool.