1997 SE Bogs down below 1800 rpm after Carb Rebuild


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AndyFromWI
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Motorcycle: 1997 GL1500SE

1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by AndyFromWI » Thu Apr 12, 2018 7:21 am



Hey I'm hoping someone can suggest some diagnostic tests to help me solve this issue.
My 1997 SE had a fuel smell issue for the past 9 months, rebuilt the auto fuel valve last year.
Besides the fuel smell, the bike was hard to start, I would have to crank three or for times for a few seconds each, then it would start.

A few weeks ago i pulled the carbs, got the randakks carb kit rebuilt the carbs, replace a bad pressure boost hose, put it all back together:
The bike starts great!, press the starter button it starts right up. No gas leak, I have put 150 miles on it, no smell what so ever.

Here is the issue:
1: It sounds different. I will take a video, but it sounds a bit louder... The bike idles fine, and will idle down to about 450 rpm.
2: Now power below 1800 rpm. I can hear the engine bog down, kind of a Blaaaaaaaa sound, then around 1800 to 2000 the power kicks in. Above 2000 the power feels stronger than before the rebuild.

I did check to ensure the accelerator pump is working, it is squirting gas.
When I did the rebuild, I did remove and replace the o rings and washers on the two PILOT SCREWS, then I reset them to the factory spec of 2 rotations open (I'm thinking the pilot screw on one of the carbs might be the issue).

I have tried running with partial choke, it is hard to tell if that is helping or not because the rpm is raised up to near 1800 with 1/3 choke, less air is helping or just that I'm at a higher RPM.

Any suggestions would be appreciated.

Thanks
-andy



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virgilmobile
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by virgilmobile » Thu Apr 12, 2018 9:09 am

It may be air starved.Remove the air cleaner,rap the throttle and see if both slides move.

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ct1500
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by ct1500 » Thu Apr 12, 2018 7:22 pm

How did you set the float levels?
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AndyFromWI
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by AndyFromWI » Thu Apr 12, 2018 10:21 pm

I measured the float levels, they were both at 8 mm per the manual, so I did not adjust them.
Hopefully tomorrow I will make the time to do some more digging.

-andy

DaveO430
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by DaveO430 » Fri Apr 13, 2018 6:04 am

Sounds to me like the mid range jets are plugged or something else is making it too lean off idle, the mixture screws would not effect that. Since the choke isn't really a choke it probably wouldn't make any difference. Possible too is you got the air jet controller hoses reversed, don't really know what that would do to it but maybe you found out.

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Mh434
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by Mh434 » Fri Apr 13, 2018 2:50 pm

I'd be suspicious that there's a leak in one of the vacuum hoses still...

AndyFromWI
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by AndyFromWI » Fri Apr 13, 2018 3:09 pm

I appreciate all the suggestions, and I have some more data:
High suction Left carb at idle.
Low suction Right carb at idle.

I pulled off the air filter to access the carbs, warmed up the bike, took some videos of the engine running (videos to be attached in a bit)

What I noticed is that at idle the LEFT carb had a lot of suction, where not as much on the right carb. I don't have a suction meter, but by just putting my hand over the carbs I could feel the difference.

Manually moving the Vacuum Chamber piston (the black cylinder/piston above the butterfly valves):
Idling around 1,100 RPM:
Slide the LEFT vacuum chamber fully open: The engine would die.
Slide the RIGHT vacuum chamber fully open: Almost no change in RPM.

At higher RPM about 2000 I do feel strong suction on both left and right sides.
I did not see a vacuum leak, but I will look closer later this evening.

The accelerator pump is squirting the same amount of fuel into both carbs.

I will attach some videos after they upload.

Thanks again for any suggestions.
-andy

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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by DaveO430 » Fri Apr 13, 2018 3:13 pm

AndyFromWI wrote:
Fri Apr 13, 2018 3:09 pm


What I noticed is that at idle the LEFT carb had a lot of suction, where not as much on the right carb. I don't have a suction meter, but by just putting my hand over the carbs I could feel the difference.

That indicates they need to be synched.

AndyFromWI
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by AndyFromWI » Fri Apr 13, 2018 4:41 pm

DaveO you are a Kung Fu Genius. It was balancing the carbs!
Perhaps they were previously balanced with the vacuum leak and a worn carburetor, and when I fixed the issues, the balance when way out of wack...

I did not have any of the proper tools to do the balance, so I figured I would try to do it by feel/ear.

I got the bike running, dropped the idle down to 800 per the manual, then proceeded to adjust the right carb adjuster screw (there is no adjuster for the left carb). I ended up turning it counter clockwise about 2 turns, then reset the idle back down to 800 rpm.

Since I did not have a vacuum gauge, I just used my hand to feel the difference between the left and right carb. A little testing, then adjusting and they boot feel about the same. 2000% better than when I started.

Now I can manually move the each carburetor vacuum chamber all the way open and the engine will not die.
Also the sound of the engine is much better. Before the adjustment the big black tube that connect to the Air Filter box, was very loud while sucking in air, if I plugged it with my finger the sound would go away. Now after the adjustment the bike sounds like it should, and there is such a big difference when the big black tube is plugged.

I took a short test ride in my driveway, wow I can go into first gear with out having to rev up to 3000. The bike feels normal. I would have liked to try a bit more testing, but wouldn't you know... It is snowing, that's April Wisconsin weather for you.

I will post some videos later when I have a chance. I know I should do a proper carburetor balance, but at least this has narrowed down the issue.

Thanks again for all the suggestions.
-andy

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kane67
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by kane67 » Sat Apr 14, 2018 1:30 am

Make a diy manometer, works perfect.
I use car steering oil (if I remember right)

Example pic from web...





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ct1500
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by ct1500 » Sat Apr 14, 2018 7:10 am

If you end up getting around 38MPG or more highway that was the problem, if not then turning the sync screw simply cancelled out the weak running bank of cylinders.
Last edited by ct1500 on Sat Apr 14, 2018 8:02 am, edited 2 times in total.
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AndyFromWI
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Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by AndyFromWI » Sat Apr 14, 2018 7:48 am

It will be interesting to see the MPG (once the snow clears).

Here are the videos.
The first three are the before, and the forth the after.

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-andy

AndyFromWI
Posts: 36
Joined: Fri Oct 02, 2015 6:32 am
Location: Cumberland, WI
Motorcycle: 1997 GL1500SE

Re: 1997 SE Bogs down below 1800 rpm after Carb Rebuild

Post by AndyFromWI » Fri Apr 20, 2018 7:04 am

Update: 4/20/2018
Now that the snow had cleared the roads I could test drive the bike.
It runs great! Starts right up instantly, idles great, I can idle at 800 rpm, slowly let out the clutch while in first and not kill the engine. Great power at all RPM.
I'm curious to see my fuel mileage. I used to average 35-38 MPG. I was down to 25 mpg when I was getting the bad gas smell. I will post an update next week after I can get a few hundred miles on the bike.

Summary:
Before doing any work on the bike: Strong Gas smell, 25 mpg
Rebuilt carbs, replaced pressure boost tube, it had a hole.
Manually re-synced carbs by feeling suction in the air intake of each carburetor.

The bike now runs great.
-andy



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