off idle flat spot


Information and questions on GL1500 Goldwings (1988-2000)
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Georgecule1
Posts: 2
Joined: Thu Jul 17, 2014 12:53 pm
Location: St. Louis, MO
Motorcycle: 1995 GL1500 Interstate

off idle flat spot

Postby Georgecule1 » Thu Jul 17, 2014 1:21 pm



Hi, My name is George and I have a background in motorcycle mechanics. However, I am having a lot of difficulty resolving a specific problem. I obtained a motorcycle in the spring that had been sitting for three year. Carbs badly varnished. Pulled the carbs and meticulously cleaned, paying close attention to the circuits. The flat spot occurs after a good steady idle. I do not believe the problem is in the idle circuit itself but in the primary main between the idle circuit and the main jet with the needle. I am sure this is a leanness issue because when riding it out west and going up in altitude, the problem decreased and at sufficient altitude disappeared. Upon descending to lower altitude the problem presented again.
So far I have verified the location of the air bleeders and I believe they are correctly connected and are functioning properly. I did a short dunk in harsh carb cleaner and immediately washed out and went at all the circuits with compressed cleaner. I also ran a couple of cans of Seafoam through there and it had no effect. I traced all the circuits and all were clear, but I am thinking there must be something up in the carburetor body which is not accessible due to the pieces being pressed in. Again this problem is confined to off idle in the primary main fuel system. Anybody out there have ANY ideas!!

PS: I am going to try the carb bodies in an ultrasound cleaning and if it has any miraculous effect I will post the results.

PPS: There is an additional mystery in the slides. I think someone was in these carburetors prior to me. One of my slides had to be replaced because the varnish had destroyed the slide diaphragm. I got the new assembly from the local dealer. I didn't look at it that closely but upon tearing the carbs down a second time I noticed there is a difference between the new slide in the left carb and the old slide in the right. If you turn the slide upside down, and look at the bottom of the slide where the needle comes out, there are two slots. On the old carb, these slots are open. On the new slide from the dealer, there is a plastic piece that blocks off these slots. My question is this, am I looking at a superceded part and of no significance or is this missing piece possibly contributing to this off idle problem. Incidentally the new needle has a richening washer under the cap and old needle of the slide assembly on the right hand carb has no washer.???? What am I to think of this??
THANKS! GC



User avatar
virgilmobile
Posts: 7659
Joined: Sun Sep 19, 2010 5:39 pm
Location: Denham Springs,La.
Motorcycle: 1988 GL1500 I
Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: off idle flat spot

Postby virgilmobile » Thu Jul 17, 2014 2:10 pm

The different slide...Can it be made exactly like the original..???Air passage ports,needle size and distance are important and must be the same for both carbs...I do mean EXACT.
Each carb is ported to each side of the engine...eg..the left carb will not feed any air or fuel to the right side.
The rubber carb couplers..are they still good.??Mine hardened up and would not seal very well...
Scrutinize the vacuum lines for the same problem..especially where they make a sharp 90* bend..They tend to get soft there...Some leaking vacuum lines are found where they connect to the intake runners..I think there's 4 of them...2 on each side,rear intakes.
Another thing to consider....The accelerator pump...Replace the diaphragm and the 2 "O" rings on the connect (riser) tube...Test the check valve in the riser tube too and the accelerator pump function before you put the carbs back in...
I use a shop vac attached to the bottom of the carb...one at a time...to test the slide action...
I also pre-set the idle jet screws and pre-sync before install then a final sync on the bike followed by the idle mixture settings (idle down)...

User avatar
virgilmobile
Posts: 7659
Joined: Sun Sep 19, 2010 5:39 pm
Location: Denham Springs,La.
Motorcycle: 1988 GL1500 I
Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: off idle flat spot

Postby virgilmobile » Thu Jul 17, 2014 2:28 pm

Keep in mind..my 88 was the worse case scenario and I "heavily modified" mine to overcome it's OEM shortcomings...The end results were fine for me...almost a bit too much...Mine ended up being a bit touchy on the throttle..just a twitch sends it down the road quick...

Soooo... I do not suggest modifying yours in any way..they should be fine...in OEM condition.
You can and should take a mental wash and start like you never saw it before...
Diagnose the current problem fresh...assume nothing..
Pop the top and look down the carbs..Twist the throttle a few times and see what there doing...
Does the accelerator squirt right away???
Do the slides jump the same way,time and amount.???
Is the flow of fuel from the main jet look the same when you pop the throttle..???

Georgecule1
Posts: 2
Joined: Thu Jul 17, 2014 12:53 pm
Location: St. Louis, MO
Motorcycle: 1995 GL1500 Interstate

Re: off idle flat spot

Postby Georgecule1 » Thu Jul 17, 2014 3:46 pm

Thanks for the prompt response. Not sure if the om slides came with the insert and the washer on the needle. Threw it away (duh) when I got the new slide. Responding from a cell phone right now bit will print out and review your comments in detail when I get home. Just put around 10,000 miles on the bike driving to and from st. Louis/alaska. Bike was great except for this idle flat spot.
Gc




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