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Discussion Starter · #1 ·
Bike starts fine (with choke), idles well.
When I give it gas, RPMs fluctuate - bike loses pwer, then regains it, then loses it, regains it, etc. all with steady throttle. Lots of backfire.
I replaced the air filter.
I replaced the fuel filter.
I replaced the spark plugs (which were filthy)
Tried to get the carb off, it's stuck fast. Actually broke a piece off the right front cylinder head cover trying to pry the carb up. (A whole other headache. Suffice it to say the carb remains on the bike, as I seek other solutions.)

Any ideas?
 

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1983 Honda vt750 Shadow
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Always tell us the year and model.
Is there 1 or 2 ounces of fuel in the fuel bowls? Loosen the drain screw on the bottom to see.
 

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Discussion Starter · #3 ·
Always tell us the year and model.
Is there 1 or 2 ounces of fuel in the fuel bowls? Loosen the drain screw on the bottom to see.
2001 750 ACE (picture in my profile). Yes, I drained the fuel bowls with the bike on its kickstand. Fuel came from both bowls, more from the left than the right side. I thought the right side was a little dry, but it still drained some even though it was higher than the left side.. I plan to spray some carb cleaner up through the drain holes tomorrow when I have time. Still cannot explain the consistency of the "wave" of RMP changes.
 

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1983 Honda vt750 Shadow
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What if you add choke when it does that?
What color are the spark plugs now?
I wonder if the carbs need sync?
 

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Discussion Starter · #5 ·
I haven't added choke. I've just been trying to "burn it off", but it hasn't gotten better. The spark plugs are new, and I am sure the carbs need syncing. But the bike ran fine, then sat for a week and this happened. Really strange. After I spray some carn cleaner in it and reattach the air box I will start it up and try this. Thanks for your suggestions.
 

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2003 VT1100C Spirit
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My '03 VT1100 Spirit had the same symptoms as what you describe a few years ago, but it had sat for a couple of months. I took it out riding, tried some fuel conditioner, let it sit overnight, tried riding again, etc. Results were minimal. Long story short...pulled the carbs, cleaned 'em. Ran great.

When I pulled the carbs I also cleaned out the tank which had a surprising amount of sludge built up in it. The petcock screen was dirty and brittle, so that got replaced. (I did not replace the "secret" inline fuel filter because it's hard to get to on the VT1100's...that's gonna be an upcoming project.)

I'm not sure, but I think the inline fuel filter on the VT750's is easily accessible. Also, 21 year old carbs and a 21 year old fuel tank could maybe use a good cleaning no matter what.

I cleaned the carbs on my '98 Valkyrie when they were 23 years old. The bike was running fine, but I was looking for projects during the covid shutdown. I replaced old vacuum hoses, cleaned the tank (lots of sludge), etc. Put her back together, synced the carbs and set the fuel mixture screws using the Idle drop procedure. Man, what a difference! I had not realized that the bike was not running anywhere near its potential.
 

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Discussion Starter · #7 ·
Here's a phtoo of the plugs I pulled. The dirtiest one came from the right front. TW, I tried pulling the carbs, removed the gas tank and air box, disconnected the throttle, loosened the clamps on the intake manifold and the choke cable, disconnected the air and fuel lines but couldn't budge the carb...Then, following a YouTuber, I tried to pop the carb off with a pry bar, and snapped a piece off the cylinder head cover. The carb remains stuck fast in place, no play whatsoever. Any ideas? Did I miss something?
Insect Food Wood Ingredient Cuisine
 

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Try a hair dryer to heat the boots, should help soften them a bit. also spray some penetrating oil./wd40 etc around the boots and carbs, let it soak a while.
 

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Other thought is to pull the air box and observe the slides in action. It will hesitate with the air box off but should still rev and run smooth, I'd suspect one of the slides is sticking a bit or fluttering from a bad diaphragm.
 

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Discussion Starter · #10 ·
Other thought is to pull the air box and observe the slides in action. It will hesitate with the air box off but should still rev and run smooth, I'd suspect one of the slides is sticking a bit or fluttering from a bad diaphragm.
Thank you.I will try both of your suggestions. Later today I will use the hair dryer. I put some penetrating oil on the bolts two days ago, but it did nothing. I will try that again, as well as seeing what I can see about the slides..
 
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