'79 GS550E fires but won't start

[Catbus]

got the bike a couple days ago, was running and cold start was fine before I bought other than needing a few tries. Got 5 or 10 KMs before it lost power and wouldn't start. Noticed one of the fuses was popping out, but then after that, got maybe 10 more KM, died, a couple bump starts, kept getting 200 meters before cutting off again. Ultimately needed towing due to battery being dead.

Since it entered the backyard shop we've gotten a brand new quality battery, took out the carbs which appeared quite clean and adjusted the floats which only 1 was 2mm higher than the recommended 24mm , but did not remove any of the jets or remove parts further than that.
The sparkplug is clean and seems to run fine, the furthest we got it to run since rolling it into the shop was taking the air filter out and spraying starter fluid directly in. but it could not hold an idle whatsoever. The petcock strainer straw is in excellent shape and the carbs appear to be getting fuel as they had some inside when we took out the carbs.

at this point we're at a loss til we can get a proper new air filter and maybe replace all the hoses eventually.
Any ideas folks?

 

[Guest]

You might try and see if the bike will run with the petcock in the prime position. You may have a weak vacuum source for the operation of the petcock diaphram.

 

[hillsy]

Sounds like a few issues (not charging / fuel starvation).

However, if you are trying to start it with a fully charged battery, then the charging issues shouldn't be a problem for a hundred K's or so.

It sounds like the carbs aren't getting (enough) fuel. Just because they look clean doesn't mean they are OK.

Put the fuel tap to ON (or PRIME if it has this) and then unscrew the drain plugs on each of the carb bowls. You should get a good steady flow of fuel out of each.

 

[Catbus]

So my friend and I read up a bit more on vaccum hoses and went to check around the bike and while we were trying to rule out things, I suggested if maybe a hose of some sort got crimped or kinked after we wriggled the carbs back in, and lo and behold the fuel supply line had been kinked. We moved it around and then it fired right up via kickstart. Hend an idle after some tinkering. Now, every first kick it starts up, but likes a bit of Starter fluid too to help. now it holds an idle at about 1500rpm now nicely but was randomly rising up to 3000rpm or so which required adjusting. the idle adjustment screw falls below 1000rpm if fiddled with. This rules out a lot of stuff and is probably vacuum related most likely

 

[Catbus]

we checked and it runs with the petcock on ON position

Sounds like a few issues (not charging / fuel starvation).

However, if you are trying to start it with a fully charged battery, then the charging issues shouldn't be a problem for a hundred K's or so.

It sounds like the carbs aren't getting (enough) fuel. Just because they look clean doesn't mean they are OK.

Put the fuel tap to ON (or PRIME if it has this) and then unscrew the drain plugs on each of the carb bowls. You should get a good steady flow of fuel out of each.

 

[Steve]

It "fires but won't start"??? :-k Sorry, but in my book, "firing" is what happens when it starts.

Two major culprits for a bike not starting are valves that are too tight and carbs that are not clean.

A fuse popping out doesn't help, either. It appears that the fuse holer has lost tension. One of the biggest reasons for loss of tension is heat. Heat is caused by dirty connections.

Things that should be on your to-do list:
1. THROW AWAY THE STARTER FLUID.
2. Adjust the valves.
3. Clean the carbs.
4. Clean the fusebox connections.
5. When the bike is running, check the charging system.

.

 

[Catbus]

Now that it can kickstart from tank gas we shouldn't be needing to prime her with starter to get her going, we will probably take the carbs out again and thoroughly look at the jets, while it's off I'll take a look at the intake boot and clamps, will take the fusebox and bend the connectors to a more gripping position, might have to leave the valves for last if it still has issues as a last step due to it being a bit larger of a job but since I discovered the pinched fuel line it kickstarts on the first try and we got it to hold a steady idle at 1200rpm for a minute before we turned it off. Petcock should be fine now that it can feed fuel through since it was idling reasonably? Will read up more on vaccum lines though.
Thanks for the tips, will write em down and process of elimination here we go!

It "fires but won't start"??? :-k Sorry, but in my book, "firing" is what happens when it starts.

Two major culprits for a bike not starting are valves that are too tight and carbs that are not clean.

A fuse popping out doesn't help, either. It appears that the fuse holer has lost tension. One of the biggest reasons for loss of tension is heat. Heat is caused by dirty connections.

Things that should be on your to-do list:
1. THROW AWAY THE STARTER FLUID.
2. Adjust the valves.
3. Clean the carbs.
4. Clean the fusebox connections.
5. When the bike is running, check the charging system.

.

 

[Guest]

Now that it can kickstart from tank gas we shouldn't be needing to prime her with starter to get her going, we will probably take the carbs out again and thoroughly look at the jets, while it's off I'll take a look at the intake boot and clamps, will take the fusebox and bend the connectors to a more gripping position, might have to leave the valves for last if it still has issues as a last step due to it being a bit larger of a job but since I discovered the pinched fuel line it kickstarts on the first try and we got it to hold a steady idle at 1200rpm for a minute before we turned it off. Petcock should be fine now that it can feed fuel through since it was idling reasonably? Will read up more on vaccum lines though.
Thanks for the tips, will write em down and process of elimination here we go!

You should do it in the exact order Steve has outlined or you might start chasing your tail.

 

[Catbus]

We will check the valves. For what it's worth the bike has 33k KM it , starts first try kick and button now and with some throttle and choke babying it holds an idle. After a cold night it still idles at 1200. Bogs down with throttle increase.

You should do it in the exact order Steve has outlined or you might start chasing your tail.

 

[cowboyup3371]

CLEAN THE CARBS PROPERLY. Okay, I'm sorry for the yelling but please don't just look at the jets as they won't tell you the whole story. You need to properly separate and dip each carb overnight.


Follow the procedures listed on Basscliff's site for the VM Carbs - http://members.dslextreme.com/users/bikecliff

 

[Steve]

... , starts first try kick and button now and with some throttle and choke babying it holds an idle. After a cold night it still idles at 1200. Bogs down with throttle increase.

That sounds normal, if you don't understand how the "choke" works. :-k

You may have noticed that many of us put the word "choke" in quote marks when referring to the GS bikes. That is because the mechanism that richens the mixture for cold starting does not operate the same way as a car with a carburetor. On a car, there was a flap that covered the intake, literally CHOKING it. The extra vacuum caused by blocking the air intake would draw extra fuel through the normal passages, yielding a richer mixture for starting.

On our bikes (doesn't matter if you have VM or BS carbs), activating the "choke" mechanism actually opens separate air and fuel paths that bypass the throttle (either the VM slide or the BS butterfly). Those separate paths are the "enrichener circuit" and rely on the high vacuum of a CLOSED throttle to operate. If you open the throttle AT ALL while on the "choke" circuit, you will defeat them and will be trying to run off the normal (leaner) circuit. On a cold engine, of course it will 'bog down'.

Proper starting technique is to set the "choke" to whatever setting you have experimented with and found to be 'best', turn the key ON, pull the clutch (unless you have bypassed that), then push the starter button. If any speed change is necessary, use your "choke" control, do NOT touch the throttle.

If your mixtures are set correctly, after about 15-20 seconds, you will be able to blip the throttle to see if there is any response. When you get a somewhat crisp response, you are ready to head out. By the time you shift from second gear into third, you can turn the "choke" OFF and keep riding.

.

 

[Catbus]

UPDATE :

We took another good look and cleaned the hoses and found a vacuum leak and I think that combined with new sparkplugs , which when used the gapper on the old ones the gaps were off from what the manual said of 0.6mm. We gapped the new plugs and that combined with the exhaust leak and the vacuum fix, we adjusted 1 floater in 1 carb, it actually runs better than when driven off the property to travel home. Lots of tiny little fixes

 

[Catbus]

I am quite a layman and this info has been very helpful. Thanks again.

That sounds normal, if you don't understand how the "choke" works. :-k

You may have noticed that many of us put the word "choke" in quote marks when referring to the GS bikes. That is because the mechanism that richens the mixture for cold starting does not operate the same way as a car with a carburetor. On a car, there was a flap that covered the intake, literally CHOKING it. The extra vacuum caused by blocking the air intake would draw extra fuel through the normal passages, yielding a richer mixture for starting.

On our bikes (doesn't matter if you have VM or BS carbs), activating the "choke" mechanism actually opens separate air and fuel paths that bypass the throttle (either the VM slide or the BS butterfly). Those separate paths are the "enrichener circuit" and rely on the high vacuum of a CLOSED throttle to operate. If you open the throttle AT ALL while on the "choke" circuit, you will defeat them and will be trying to run off the normal (leaner) circuit. On a cold engine, of course it will 'bog down'.

Proper starting technique is to set the "choke" to whatever setting you have experimented with and found to be 'best', turn the key ON, pull the clutch (unless you have bypassed that), then push the starter button. If any speed change is necessary, use your "choke" control, do NOT touch the throttle.

If your mixtures are set correctly, after about 15-20 seconds, you will be able to blip the throttle to see if there is any response. When you get a somewhat crisp response, you are ready to head out. By the time you shift from second gear into third, you can turn the "choke" OFF and keep riding.

.