Hard to start when cold

[lrburke]

Hey Guys, I have a 1981 GS550 and just finished rebuilding the carbs. I also replaced the o-rings and the intake o-rings from Robert Barr. The fuel mixture screws are 2 turns out and I did sync the carbs with my carbtune pro. Once I actually get it running it runs perfect and idles better than any suzuki I have ever had. I can't figure out why it's so hard to start after sitting overnight. I know it's really hot during the day and pretty warm still at night. Is there a trick to starting these old GS's as far as using the choke. Do you guys still use full choke even on a really warm morning? What else might cause hard starting and the bike still run fine? Thanks for any suggestions

[tkent02]

Your valve clearances are probably too tight.

[lrburke]

hard starting when cold

If the valve clearances were tight then wouldn't it be hard to start after it's at normal operating temp and shutting it off and restarting it. It starts right up after that. The compression is right where it is supposed to be when cold if that matters.

[azr]

Your floats could be set incorrectly as well and it's funny how a small mixture change can effect starting from cold. I have to use choke every time I start the bike, even on the hot mornings, but only for 1/2 a minute or so.

[lrburke]

hard starting when cold

Should I try to back the mixture screws out a half turn each?

[azr]

Sure or you could do the fastest idle method to tune them each perfectly or close to it anyways. I saw that your bike should be 3.5 turns back according to the factory OEM specs, but I also saw you adjusted your main jets so I'm sure that would effect your pilot screw adjustments. Try the fastest idle method and it should get things pretty close with the set up you have. At least she's idling well when warm. Any other symptoms? popping on decel? funny colored plugs?

[tom203]

I have a 81 gs 650; even in 70 degree temp, I have to pull up ( hold ) "choke" . Bike will then start instantly. If I don't use full choke, I might have to crank for a minute. Once it catches, I drop choke almost all the way- it runs rough for a while but quickly stabilizes. Make sure all your carbs are responding to "choke" cable correctly.

[Steve]

I can't figure out why it's so hard to start after sitting overnight. I know it's really hot during the day and pretty warm still at night.

Your valve clearances are probably too tight.

I will second the suggestion on valve clearance checks.

If the valve clearances were tight then wouldn't it be hard to start after it's at normal operating temp and shutting it off and restarting it.

No. Because the valve clearance changes with temperature (due to differing expansion rates of the various components), it will work just fine when it's warm. Changes in clearance will also affect valve timing, and that is what causes the hard starting. This is also why it is specified that valve clearance is checked when the engine is "cold" (meaning room temperature). It is far easier to duplicate the 60 or 70 degree environment than it is to heat the engine to any other specific temperature and keep it there for the duration of the clearance check.

Should I try to back the mixture screws out a half turn each?

Many of us will start with the screws out three full turns after rebuilding the carbs, but will then adjust them for the "highest idle speed", which means that the engine is getting the best possible mixture. You may find that 2 turns is optimum for your bike, but there is no way to tell unless you experiment and adjust.

I have a 81 gs 650; even in 70 degree temp, I have to pull up ( hold ) "choke" . Bike will then start instantly. If I don't use full choke, I might have to crank for a minute. Once it catches, I drop choke almost all the way- it runs rough for a while but quickly stabilizes. Make sure all your carbs are responding to "choke" cable correctly.

Thanks for putting "choke" in quotes.

There is no flap that covers the intake to "choke" it, like older cars. The system is actually an "enrichment system" that works by opening different passages for air and fuel that bypass the normal routes, as long as you leave the throttle CLOSED. Opening the throttle AT ALL renders the enrichment system ("choke") useless.

.

[BassCliff]

Hi,

Check the valve clearances. They should be checked every 4000 miles. This is not optional. If you don't check/adjust your valves they will burn. Maladjusted valves are the number one cause of hard cold starting.

It all has to be right; float height, idle mixture screws, valve clearances, etc.


Thank you for your indulgence,

BassCliff

[SqDancerLynn1]

A weak battery can cause problems too.

[lrburke]

thanks for all the replies! I will check a few things out for sure!