[Mark Kaplan]

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?

 

[Mark Kaplan]

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.

 

[Mark Kaplan]

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.

 

[Mark Kaplan]

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?

 

[Mark Kaplan]

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..

 

[Mark Kaplan]

I have receieved my replacement side cover from eBay. Luckily someone in South Carolina had one in decent condition. Ultimaely I bought a more angled crowbar from Harbor Ferieght and gingerly edged the carb out. I have now cleaned it, replaced the diaphram in both sides of the carb, replaced the cylinder head gaskets, and the cylinder head breather gasket. I cleaned lots of rubbery black and rust-colored gunk from the cylinder heads. The rear one was a pain, and filthy - probably the cause of all the backfires. Naturally, two of the cylinder head breather bolts are stripped (ordering replacements). To do this I had to drain the coolant so I will flush the radiator while I am at it. I have teaken the bike into the shop for most of its life, and it's really disappoinnting to find so many stripped bolts (including the coolant drain plug, which was also missing the copper crush washer). At this point, I am freaking out about all of the vaccuum hoses, and find myself with a tiny vaccuum hose that needs to find its home and another larger hose (that has a clamp on the end) that goes to nowhere...

Too bad I live in California, or I could toss the whole vaccuum system and cap the carb where needed. Big learning curve on this job.

 

[Mark Kaplan]

The problem is fixed! The bike runs and there is no more sporadic revving when I give it gas. The only problem is that now there is a new oil leak. It looks like it is coming from the cylinder head gasket, which, according to a couple guys I spoke with, would require me to remove the entire engine. I'm thinking (hoping) that there is leak from the cylinder head cover gaskets I replaced, and that I quick review of everything will solve the problem. Otherwise, the learing curve goes even higher as I figure out how to take the entire engine out to replace the cylinder head gaskets.