81 GS650L, Choke doesn't do much/anything

[DaveP]

Not having too much trouble getting the bike started, but the choke doesn't have any effect. Bike will stumble along below 1,000 rpm on cold start and eventually I will be able to give it some throttle to get it warmed up and idling smoothly at 1,100 rpm. Carbs were dipped, all o-rings replaced, passages picked, and carb cleaner could flow through the enricher passage and pickup tube. Choke cable is also actuating the plungers, but idle is not impacted by the position of the choke. Original air cleaner too.

Operation has been the same independent of weather conditions and time between starts.

From other posts, it seems that the choke should have an impact on the idle rpm at start up to help the bike get warmed. Even mention of half choke so the engine doesn't over rev before oil is circulating.

Any direction on what I should take a look at?

Thanks,
Dave

 

[2BRacing]

The choke will have a definite effect on RPM at start up, if all passages are properly cleaned. Are the small holes in the bottom of the float bowls that feed the choke pickup tubes properly cleaned and open? Look at pages 50 and 51 of 77 of the CV carb rebuild tutorial. When you spray carb cleaner down the pickup's passage in the float bowl, it must "spray", not "flow", out of the little hole at the bottom of the float bowl (hold it away from your eyes!!).

When you set the choke to start the bike, you must NOT twist the throttle at all during the start-up, or else that enrichening circuit will be inoperative.

 

[tom203]

It seems unlikely that all four carbs have clogged enricher circuits. Did you leave the choke plungers out of the dip? (Hopefully yes)
my bike ain't interested in cold start unless "choke" is fully up. Then it goes crazy till choke is backed done abit. Drive away and fully off within two minutes- if I don't turn it off it will hesitate on accelerating. So yes, the choke should have a big effect.
Did you bench sync the carbs, so throttle plates appeared just about fully closed on idle stop screw?

 

[DaveP]

I did follow the carb rebuild tutorial and did make the mistake the first time of almost shooting myself in the eye with carb cleaner when the spray came flying through the passages. They were clogged before I started, but I had fluid spraying through all passages before putting things back together. Wouldn't think that they all clogged up again in a short period of time. Sta-bil is in the fuel that I have been using.

Choke plungers were not dipped due to the rubber end cap.

Bench sync was done and vacuum sync at about 1,500 RPM once the bike was running. Then idle set back to 1,100 RPM.

Throttle is not touched at start-up to stay on the enricher circuit. Once it has stumbled along for 5-10 seconds, then I try to start feeding it some throttle to get the idle up and smoothed out.

I can pretty much move the choke cable back and forth with not much noticeable difference.

 

[tom203]

What you describe says your enricher circuits aren't working- odd that all 4 appear to be doing nothing. I would think that just having two going would be enough to produce high idle at cold start.

 

[jbird7262]

Not to hog the thread, but a question about the choke operation, GS750E. It seems that my choke is always held in the down posisition by spring pressure, even if I pull the knob up, it won't stay in the up posisition. What holds the choke up verses chokes mounted on the side of carbs. verses knobs mounted on the triple tree?

 

[tom203]

?.........What holds the choke up verses chokes mounted on the side of carbs. verses knobs mounted on the triple tree?

On the triple tree mount, you can tighten the nut (black plastic doohickey just below knob)to add more friction to hold knob up

 

[jbird7262]

Thanks, I'll ck. into that.

 

[tom203]

Back to DaveP....... What I don't understand is how your bike can still run OK with choke plunger open- this is letting extra air pass behind throttle plates mucking up mixture . See attached pic (sorry about sizing ) for Keihin carb but mikuni uses same idea
http://faq.ninja250.org/images/e/e8/Jim_carb_10.jpg

 

[DaveP]

Choke is full closed once it is running and idling smoothly.

Starting procedure:
Fuel on prime or run.
Choke fully open.
Start.
Stumbles around below 1,000 rpm.
Play with choke knob, no changes.
Start closing choke.
Add throttle to improve idle (enricher circuit must be working somewhat because opening the throttle too soon will kill the engine)
Choke closed.
Hold throttle at about 1,500 rpm for a bit.
Ride away...

 

[tom203]

Since it rides/idles OK once warm (when you don't need the enricher circuits), indicates that no/little fuel is climbing up "choke" passages and reaching plunger area.

 

[DaveP]

Sounds like do over time.

 

[tom203]

Winter fun! I'd probably pull and separate carb rack, remove fuel bowls and choke plungers, stick gumout tube into each plunger fuel inlet and see if you get good spray flying out those little tubes.then blast thru bowl orifices.

 

[81GS850]

I just pulled my carbs apart on my bike... You didn't mention the condition of your tank? Rusty? Willing to be you have tiny rust particles getting in the orfices plugging stuff up. I'm about to coat my tank in red-cote tank sealer found at O'reillys. Also what are your float heights set at? How is your gas mileage? I was managing about 32-33mpg when my bike should be getting 40+.

 

[barnbiketom]

o-rings behind intakes and INTAKES good????? Does the bike run CORRECTLY after warm up? all the time? does the idle hold true ALWAYS after warm up?? I just wonder if the o-rings behind the intakes are allowing air leaks. all 4 on mine were BAD.. including the intakes.. bike would run but not perfect.
If your intakes are bad ( i can't believe they aren't if stock) and/or o-rings, then enriching would merely accommodate the already lean condition at startup.. and maybe NO HIGH IDLE...??

 

[DaveP]

I have been pretty lucky with the condition of this bike so far. It hadn't run for a few years before I got it, but it was kept in the garage all of the time. The tank is very clean, definitely no rust or debris coming from the tank to clog things up. Fuel petcock and hoses were replaced with OEM.

Float heights were checked while taking the carbs apart and also when putting them back together. The way the floats were set, there was more fuel in the bowl than there is now. Originally the floats were measuring correctly at the shoulder (step) of the float vs. the body of the float. I raised the float (lowered the fuel level) so that the measurement was at the proper location. Verified float heights with clear tubing from the float bowl drain before ganging the carbs back up and reinstalling to the bike. Clear tube measured fuel height at 5mm below bottom edge of carb body. When checking again this way, the fuel level was still high, so I raised the floats (lowered the fuel level) a bit more.

Not sure on fuel mileage yet and have been filling up from a portable gas can. I've only ridden this bike about 50 miles since it has been back together. I ride my fuel injected bike more since I can just get on and go.

Intake boots are original, but o-rings were replaced. One of four intake o-rings was cracked already when the boot was removed. All original o-rings were brittle and came out in pieces. Intake boots are supple, but I didn't pull on them the way that was shown in the video.

Idle does rise a bit during riding. 1,100 RPM pretty steady most of the time. Has hung up around 1,500 RPM as you disengage the clutch to come to a stop. Will then settle back towards 1,100 RPM.

Intake boots: http://twowheeljunkie.wordpress.com/2014/06/22/intake-boots/
Carb cleaning and float height: http://twowheeljunkie.wordpress.com/2014/06/15/carburetors-cleaned-and-float-tested/

 

[barnbiketom]

Nice work!! I had a gs400 and poor running. No effect while spraying ether..carb spray or propane. New boots still solved my hanging intermittent idle..and every bike since gets new ones. I will be following this with interest..tommie

 

[DaveP]

Did the carb cleaner spray test today to see if I could detect any vacuum leaks at the intake boots. No change in idle while spraying all around the intakes...

 

[DaveP]

Finally pulled out the spark plugs this weekend to see how they looked:

The appearance of the spark plugs would suggest that it is running rich instead of lean and not a clogged carburetor issue. They are all fairly consistent too.

Could it be that the air filter is not letting through enough air? Or just the idle mixture screw settings. I believe they are all three turns out.

 

[Guest]

Finally pulled out the spark plugs this weekend to see how they looked:

The appearance of the spark plugs would suggest that it is running rich instead of lean and not a clogged carburetor issue. They are all fairly consistent too.

Could it be that the air filter is not letting through enough air? Or just the idle mixture screw settings. I believe they are all three turns out.

Yeeeoow those are way rich. Check the air filter to see it is clogged. Don't think its the idle mixture screws unless you let it idle for long periods. Once you get on the throttle, the other circuits over ride the idle circuit. Here is one thing you can do is put in a fresh set of plugs and do a plug chop to get a better idea what maybe is going on. Ride the bike so it gets up to operating temps and find a long piece of hiway and run it up to about 70 for about 5-7 miles, pull in the clutch and kill the motor and coast to a stop.Pull the plugs and see what color it is then. Might need to let it cool down for a bit. So bring some refreshment with ya lol.