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GS650 Hard to Start

  • Thread starter Thread starter LarryA_Texas
  • Start date Start date
L

LarryA_Texas

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I've posted about this bike here before, and it's been discussed on other threads. I thought I would put the whole story on one posting and see if anyone has any other thoughts. It's long, so bear with me.

'81 GS650G. starting problem: especially when it's cold outside the starter turns and there are only the very occasional little puffs of a cylinder trying to fire. Eventually these little puffs become more frequent until it finally kicks over...if the battery lasts that long.

I have adjusted the valves and all are in spec.. Just to make sure I checked them again today and found all good. I checked compression; 140 on 1 and 4 and 135 on the other two. Timing is set.

Carbs have been removed and cleaned, dipped, twice. All o-rings are new, including the choke o-ring. The boots are ok soft and those o-rings have been changed. Stock airbox with a good seal and filter.

The spark plugs looked white, I mean paper white, and I've seen on here a message that Suzuki made it run very lean for EPA concerns, so it made sense to go up a step on the pilot jets. Since some lists here indicate that 42.5 is stock, I tried 45 and at one point put in a set of 47.5 pilot jets. It may run slightly better with the 45 set, but the 47.5s didn't help at all.

Screws were set at 1 turn (per spec) and then adjusted up to 2. When warm it runs great...but that didn't help the starting issue. They're back to 1 1/2 turns, where it ran best.

The only thing that seems to make a difference is if you blow on the vent tubes. I have no idea what this is doing, or why it helps, but it does. TKent suggested it, and it does work, but it's a band-aid to whatever is really wrong.

During these start attempts opening the throttle about 1/8 th of a turn seems to help it start, but more than that and the little puffs stop. Also pulling the choke doesn't help at all. The occasional little hits go away with any choke at all and it makes no attempt to start.

It has new plugs...re-gapped to spec.

Once running about 1/2" pull on the choke can help it run 'till it warms up, but more than that and it's just quits.

The plugs make me think way too lean. The choke issue makes me think way too rich. I still have not found a solution.

So...I'm at a loss. I have no idea what else to do. Does anyone here?
 
2 things come to mind.

First is weak spark, fixed by the coil relay mod. It's easy to check if this is the problem: Run a wire from the + battery terminal to the + coil wire junction. This will temporarily give you full voltage at the coils so you can see if starting is easier (do NOT leave that wire connected).

Second is the choke fuel access. 2 parts to this are the tubes that come down from the carb body and the crossover hole in the bowl. The holes in the end of the tubes need to be open (use a copper wire strand to check/open). The crossover hole in the bowl allows fuel to reach these tubes. Wear safety glasses, and spray gumout into the inside hole (not the top hole that goes through the gasket). The gumout should stream out the top hole. If not, clean the hole with fine twisted copper wire strands, and repeat until it is open.
 
Just to complete the fuel fault tree, I would also verify the carbs are getting fuel by checking that the petcock is operating properly. Does it make a difference how it starts when in the PRI position??

Then I would check the spark, as Don-lo suggested. The coils themselves may be weak (in which case the coil realy mod won't help), or the spark plug caps may need replacement. Remove them & cut the wire back a bit (1/4" - 1/2") and reattach them to "good" solid wire...

Good luck...
 
I still say the enrichner (choke) circuit is not working.

PS: Larry, would you happen to be a TWtex member and do you attend any of the friday night bikes and ice cream get togethers?
 
I spoke to another forum member that found 3 of 4 choke circuits effectively plugged, even after cleaning once before. It;s a choke circuit problem, not an ignition issue.
 
I had a similar problem with my bike. Hard to start, had to crank her over for 10 sec at a time to finally get it to catch. However, my bike was definitely running rich, based on the condition of the plugs and the smell of the exhaust. I fiddled with the carbs for months, must've had them off half a dozen times or more. What I did was replace the float needles (from Z1 enterprises). When I measured the difference between float height with the old needles and the new ones they were all off from 0.5 to 2 mm. Now I use full choke, hit the button and vroom, she starts right up.

Based on your white plugs, I would verify all your jets are stock, or appropriate for your mods. Good luck.
 
Sounds like a fuel supply issue; the business about not wanting to start with the choke pulled is a sign.

Next time the bike does this I'd stop after cranking a while and pull a plug - it should be wet if the bike is getting fuel. You also might want to remove a drain plug on the float bowl - a goodly amount of fuel should pour out, not just a dribble.

If the plugs are wet and there is fuel, only other thing is weak spark. Easy to check by laying a plug on the side of the engine and cranking the engine while watching for spark.

Fuel or spark, one or the other. My vote is fuel.

Good luck.
 
Couple of questions, how do you normally start bike, full choke no gas? Once started how long does it take to warm up so that you could drive it?

My 650s seem to be easy to start and warm quickly with stock carb setup, only change I have adjusted pilot screw for highest idle. I also have found both only require half choke to fire most of the time if weather is warmer than 50 degrees. This morning was a cool 30 and need full choke to start. Even still I could drive away within a minute.

I also have the coil mod and it makes this bike fire up immediately. Only costs around $10 if you have wire. I am not sure it is electric, tend to agree with Mr. Ness, wonder if your fuel level are correct.

Maybe try starting with less choke or after it puffs a couple times, try again with less choke. I think you may be too rich on the pilots if running a stock setup.
 
mine was ridiculously hard to start....gave a full carb clean and no problems since...
 
Fixed it!

Fixed it!

focus frenzy said:
I still say the enrichner (choke) circuit is not working.

PS: Larry, would you happen to be a TWtex member and do you attend any of the friday night bikes and ice cream get togethers?
Click to expand...


Just an update for this thread. Thanks to everyone for their contribution

I think I finally found the problem. I've been looking at the choke from the carb body side of things...not the float bowl.

Ok...so here goes. When you take the float bowl off there is a little brass tube that dips down into the fuel. That tube goes into a little hole in the bowl, but not the fuel bowl itself. In order to get fuel into that bowl you have to have a small opening at the bottom of the bowl. That opening was blocked completely in all 4 bowls. A little plug of dirt stopped the fuel from ever getting to the brass tube. Pulling the choke allowed air into the system, but not the fuel that necessary to enrichen the mixture for starting. They are clean now and it started very well and runs great. I'll know for sure tomorrow when I try to start it cold.

This passage is clearly described in the carb cleanup series. I just missed it.



Yea.
 
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