Carburators

[Brianmouton1987]

Good afternoon. I have a question hopefully someone can shed some light on. I have been tinkering here and there on a 99 1200 I picked up a while back that is in pretty rough shape from sitting for 5+ years. I got it started and have eased it up and down the road a few times to see if it felt like everything is functioning as it should mechanically and it appears to be sound at least from my great wealth of motorcycle knowledge (about 2 weeks). I have the air boxes off of it and as I was tinkering I put my hand over the carbs just to see if It was going to choke down and was a bit puzzled because the left carb had almost no suction on it and took about 3 or 4 seconds to build any vacuum (and that was very little) with my hand sealed over it and didnt effect the engine running at all only a bit of popping a 2 or 3 seconds after removing my hand. (My hand was full of gas and I am getting good spark on that cylinder) and pretty close to the same thing on the left inside carb. The 2 on the right however generated a lot of suction like I would expect them to and instantly choked the engine down. Can anyone shed some light on this issue? Thank in advance for any help on this issue

[MonsterMash479]

Does it have good throttle response or does it bog? I recently rebuilt the carbs on my 96 due to a fuel leak in the 2nd and 3rd carb fuel T. I wonder if it could be a bad diaphragm? Maybe? Do you see them move equally when you blip the throttle? I also bought a cheapo ebay carb synchronizer that seemed to work enough to get the bike running pretty good. Hopefully someone with more experience chimes in cause im only about 2 months in for wealth of experience haha. Rebuilt my 96 and now rebuilding my wifes 84 honda magna v30 (the v4 carbs are way more annoying)

[Brianmouton1987]

It has good throttle response up to about half throttle. After that it bogs pretty bad.

[GrandpaDenny]

After sitting for five years chances are really good that the carbs are in need of rebuilding. You can try running SeaFoam through it for a while - that stuff's amazing. Gertrude wouldn't do over 2800 rpm when I got her, SeaFoam made a huge difference. Still, it took replacing the carbs to get her really right. Old carbs were well and thoroughly hosed. Only took me four years and 50,000 miles to get around to replacing the carbs.

[triton28]

The first thing is to check the rubber mounting of the carbs to the cylinder head and make sure there is a solid mounting of the carbs to the head with no air leaks.
Is the engine operating on the cylinders you suspect have no vacuum? Are the exhaust pipes just as hot as the other cylinders? I use an infra red thermometer to check that.
I hope i am wrong but it sounds to me by what you describe that there is NO vacuum in the cylinder/s when the piston is going down on the intake stroke. In order to determine this one should do a compression test on your #1 and #2 cylinder for sure: no vacuum equals no/very little compression and vice versa.
Should you find little or no compression I don't think it would be stuck/poorly seated/burnt valve related as there would be reverse flow through the carburetor on the compression stroke and that would be obviously noticeable.
There are no good reasons for lack of vacuum and that is why I hope I am wrong and it is something simple rather than stuck rings or a scored cylinder wall.
But please do let us know what you find.
Dave

[Brianmouton1987]

Thank yall for the info. I will do a compression test and get back with my findings.