Carb Czar out there?

[Guest]

Guys, I have a strange one that needs some help. I have a very hard to start GS650G.

When it's cold as you first press the starter is fires right up and rev to a few thousand RPM then dies. For the next few minutes the starter will crank the engine but it just won't light off. As the starter is engaged it puffs and stutters but not enough to start. Eventually by a combination of choke on/choke off/add throttle, throttle closed it may fire up.

One sure way to get it to fire up is to blow on the carb vent tubes. This seems to work every time. But it usually results in a small puddle of gas out the air filter box drain. .

I have remove them, totally cleaned them in dip, changed all o-rings and the boot o-rings. They have been sync'd and timing checked. The worst thing I found was on the brass tube that goes from the choke to the float bowl. #4 was slightly crushed and the flow restrictor (the tinly pin hole at the bottom of the tube) was missing. I got one from another carb and tapped it into the hole...it's not perfect but could be close to the original vent diameter. Even if it was totally wrong it seems like that would only affect one cylinder and only while on choke.

It's a stock 650...the only thing affecting airflow is some rust holes in the muffler. Screws were set to 1 1/2 per factory spec. then out to 2 1/2 to see if it would help. Best RPM was at about 2 turns out. That's where they are now.

When running if I pull the choke out it does rev up some as I would expect. Immediately after strating, as it's warming up it is very sensitive to throttle and will die if you twist the grip much. Once it warms up some this problem goes away and it runs like a scalded cat.

Once it starts it runs great and will not give any trouble starting after it's been running that day.

anyone have any ideas?

Larry

[Steve]

First of all, when using the starter button, LEAVE THE THROTTLE ALONE.

Using the throttle at all will defeat the enrichment ability of the 'choke' system.

When is the last time the valves were adjusted. If your answer is either:
a) I don't know
or
b) More than 4,000 miles ago

then you need to adjust your valves because the intake valves are too tight.

When the valves are adjusted, turn your mixture screws out another half a turn, set your 'choke' lever (or knob) to about half, pull the clutch (unless you have disabled that function), turn the key to ON and push the starter button. Be prepared to modulate engine speed with the 'choke' ONLY, do not use the throttle. After it warms up, check your carb sync again then enjoy your 'new' bike. It will surely seem like a new bike because it runs so much better.

.

[TheCafeKid]

First of all, when using the starter button, LEAVE THE THROTTLE ALONE.

Using the throttle at all will defeat the enrichment ability of the 'choke' system.

When is the last time the valves were adjusted. If your answer is either:
a) I don't know
or
b) More than 4,000 miles ago

then you need to adjust your valves because the intake valves are too tight.

When the valves are adjusted, turn your mixture screws out another half a turn, set your 'choke' lever (or knob) to about half, pull the clutch (unless you have disabled that function), turn the key to ON and push the starter button. Be prepared to modulate engine speed with the 'choke' ONLY, do not use the throttle. After it warms up, check your carb sync again then enjoy your 'new' bike. It will surely seem like a new bike because it runs so much better.

.

To clarify, because its a bit confusing to think about if you're just learning: When he says your valves are too "tight" he means the the necessary clearance between the cam lobe and the shim on the bucket which depresses the valve (opens it) is below minimum threshold. The cam lobe is now constantly pressing on the shim, which in turn pushes down on the valve, opening it. The valve never closes, and the compression in the cylinder(s) is low, making the bike hesitant to start. If they arent TOO bad out of whack, eventually the cylinder will heat up from the constant attempts to fire, things expand, and the compression levels come up to a point where the bike will start. However, if left uncorrected long enough, eventually the bike simply wont start. And if you've gotten to that point, you may be looking at replacing a few burnt valves as well. The adjustment is a necessary maintanence proceedure because as the valves wear, the guides wear down, the valve heads start to "tulip" a bit, recessing a bit farther into the head, but leaving it unsealed. The correction (on the 8v bikes) is to simply replace the current shim with a slightly thinner shim, thereby increasing the distance between the cam lobe and the shim.

Wow, that sounded like i read it out of the manual...Im a nerd.

[focus frenzy]

can be a combination of the things already listed or even the choke cable is not adjusted right or as it was in my case, the low speed jetting was to lean. plus 1 size on the pilot jets made a huge difference in my case.

PS: I am in the "neighborhood"

[almarconi]

Guys, I have a strange one that needs some help. I have a very hard to start GS650G.

When it's cold as you first press the starter is fires right up and rev to a few thousand RPM then dies. For the next few minutes the starter will crank the engine but it just won't light off. As the starter is engaged it puffs and stutters but not enough to start. Eventually by a combination of choke on/choke off/add throttle, throttle closed it may fire up.

One sure way to get it to fire up is to blow on the carb vent tubes. This seems to work every time.

I've got a similar problem I've been chasing on my 750L. I pulled the carbs and guess what.. 3 out of 4 pilot jets are clogged. There was also some trash in the #1 float needle seat and the main jets were clogged on 2 of the carbs. I suspect that when I changed the petcock on the bike some crud got dislodged and went in the carbs. I'm going to install a filter before I reinstall the carbs. The valves have been adjusted, ignition timing checked, coil replaced, plug wires, plugs, air filter..etc didn't seem to cure the problem. I'd be willing to bet that your problem lies in those carburetors.

[bmac]

hard starting

I agree with the replys noted and have experienced same situations on different model bikes, my response to this is that the pilot jets are in need of cleaning, but what Steve said and the Cafekid explained about valve adjustment is a must as a maintanence item. A partially open valve during combustion will create a very hard start condition also. Just for grins take a compression check and see where you are at with cylinders and compare them. If there is a considerable difference in the 4, there is the place to start. bmac

[tkent02]

Ok, guys you are going down the wrong track here. I've been working on this bike with him for a while. It's getting to be a pretty decent bike, needs a little more work.

The valves are adjusted recently, the compression is high and even.
Choke cable is adjusted correctly, the choke moves all the way in and out.
Carbs are VERY clean, there are no clogged jets, it has new spark plugs, strong sparks, timing is perfect.

When it is running it is running very well indeed, smooth and powerful, throttle response is great. Very quick bike.

It's just that it needs a little puff on the bowl vents to get it going, or nurse it to life for about five minutes.

Larry has restored a lot of GSes, and so have I. We know how to clean carbs, adjust valves, and how to start engines.

Just don't quite know why we need to puff on the bowl vents.

I'm thinking one size bigger pilot jet may help, but it seems we should be able to get it to work by adjusting the screws.

[TheCafeKid]

Ok, guys you are going down the wrong track here. I've been working on this bike with him for a while. It's getting to be a pretty decent bike, needs a little more work.

The valves are adjusted recently, the compression is high and even.
Choke cable is adjusted correctly, the choke moves all the way in and out.
Carbs are VERY clean, there are no clogged jets, it has new spark plugs, strong sparks, timing is perfect.

When it is running it is running very well indeed, smooth and powerful, throttle response is great. Very quick bike.

It's just that it needs a little puff on the bowl vents to get it going, or nurse it to life for about five minutes.

Larry has restored a lot of GSes, and so have I. We know how to clean carbs, adjust valves, and how to start engines.

Just don't quite know why we need to puff on the bowl vents.

I'm thinking one size bigger pilot jet may help, but it seems we should be able to get it to work by adjusting the screws.

Id check the petcock, fuel hose routing, etc, before i messed with screws. If that doesnt help, 2-2.5 turns out on the screws has been a perfect starting point from my experience. Generally, the bikes will start right up at or around that setting, and tune to taste.

[waterman]

It almost sounds like bad gasoline. My dual sport is rather moody like this, hard to start, runs poorly for a while and then runs great after a brief warm up. In this case, I think the volatile gasoline components have evaporated leaving behind the garbage that turns to varnish. I ended up getting into a routine of opening the drain bowl and dumping the urine colored gas.

My gs650 will fire up to an even staccato and be driveable within 30 seconds. I have noticed that it is rather sensitive to how I have the choke set, it doesn't need more than half. If I forget and pull it too far out, it may not fire up at all. Then I go into flooded bike mode and try to start without any choke.

Secondly, my suzuki will practically run on any excuse for gasoline. The dual sport only gets premium to keep from pinging, the suzuki loves the cheap stuff.

Next time you start it, open a float bowl and drain some of the gas out, put it on prime and set choke to whatever will make it fire up. Maybe just a shot in the dark. Good luck.

[Suzuki_Don]

I think it would be worth going one size larger on the pilots. To see if that improves things.

[LarryA_Texas]

can be a combination of the things already listed or even the choke cable is not adjusted right or as it was in my case, the low speed jetting was to lean. plus 1 size on the pilot jets made a huge difference in my case.

PS: I am in the "neighborhood"

Howdy, Neighbor.

By plus 1 size I assume you mean 42.5 stock up to 45...next size up. Since it starts out pretty lean I'll give that a try. Bike Bandit wants $12.15 each for the little suckers, so I'm still looking for a source.

Valves have been checked. Compression is great.

It's just stubborn getting out of bed in the morning. I have teenage boys in the house...so it's more or less an epidemic here.

[Steve]

MR Cycles has stock jets for 6.84

MotoGrid has them for 5.81

Full Throttle has them for 6.09

many other places besides Bike Bandit.

Of course, the ones listed were stock jets, might have to some serious searching to find one a different size.

.

[chef1366]

Check the volts at the coils.

[Big T]

Try here

http://www.jetsrus.com/main_page.htm

[focus frenzy]

Howdy, Neighbor.

By plus 1 size I assume you mean 42.5 stock up to 45...next size up. Since it starts out pretty lean I'll give that a try. Bike Bandit wants $12.15 each for the little suckers, so I'm still looking for a source.

Valves have been checked. Compression is great.

It's just stubborn getting out of bed in the morning. I have teenage boys in the house...so it's more or less an epidemic here.

yep, next size up. especialy factoring in the reformulated gas we have around here, these bike were pretty lean to start with with the gas of the time (80's)toss the alky in and they are even more lean, the fuel enrichner only adds so much, so you and up being to lean to start reliably when semi cold.

my 80 1000G was very tempermental and it took several sputter coughs when it was in the lower 40's to get it going.
the change to the next size bigger pilot jets cured it and the addition of the coil power relay mod took it to the next level.

PS: on the teen start problem, keep cups of marbles in the freezer, when they grumble and fail to start in the morning, toss a cup of frozen marbles under the covers with them! that will get them out of their beds!!