My bike for some reason fires up ok and will idle normal but when I try and rev uo the throttle she bogs down and sometimes stalls. With a higher idle set she seems to rev better without the power loss. Also when coming down off the throttle the bike backfires. My suspicions lead me to the carbs but I cleaned them out and checked all vacuum lines. Maybe its jetting or a timing issue? If anyone has any ideas it would be greatly appreciated. Thanks.

 

The backfiring when decelerating is an indication that your pilot jet is a lean. I would turn out all four pilot jets 1/2 a turn to fatten up the mixture.
You could have a jet in your carbs that is too big when you hit the throttle, but you won't know until you get into the carbs. I would run some sea foam first before tearing into the carbs. It's going to foul the plugs, so have a new set on hand. You can get this at Auto Zone or Advance Auto. Be sure not to put any of it into the engine oil because it'll cause the clutch to slip. If the sea doesn't improve the performance, then it's time to work on the carbs.
When working on the carbs, you'll most likely have to replace some o-rings in the carbs. Being how they're almost 13 years old, they're probably cracking. Once inside, look at the jet sizes, carbs 1 & 4 should be a #135 and carbs 2 & 3 should be a #138.
Even if you don't tear down the carbs, you should sync the carbs. You'll need a tool called a carb sync. I use the Motion Pro one because it doesn't use mercury. Follow the directions from Motion Pro for calibrating the sync tool and then follow the directions from Honda for syncing the carbs.

 

Thanks. I looked up the tool you suggested. Do you know which adapters you use with it? It says many Hondas use a 5mm. Just want to make sure before I spend any unnessecary money. It appears that the sync tool is just a vacuum guage though. Couldnt the same thing be accomplished with one of those? I have a vacuum guage already on hand and would be much easier.

 

what kind of pipe does it have?

 

Two Brothers Racing pipe with factory header

 

k so just a slipon, which causes more issues with our carb'd bikes more so than with the newer FI bikes.

A sync gauge is basically just a vac gauge, just more to it . If you know what your are doing you can use a reg vac gauge, but its gonna be more involved than with the sync gauge.

 

Alright cuz what I've read in the past is saying that all syncing a carb is doing is adjusting all 4 to provide the same amount of fuel based on the vacuum pressure to each one. The whole concept seems straight forward. I am an experinced mechanic, I'm just pretty new to streetbikes so alot of this is foreign to me yet.

 

okay, i am going to throw out a little bit into this conversation... as for the gentleman that recommended sea foam. i have a few problems with the statements that you were making. first is the claim that the pilot jets are suspect. there would be no way to know for sure which fueling circuit in the carbs was at play here without first asking what throttle/rpm range the backfiring is occurring at. also, even if your pilot jets are running lean, the only way to fix that is to change the jet. playing with the pilot (or Air/fuel screw) will only accomplish a change in the total amount of air/fuel at idle. once off idle, you will no longer be on that circuit. so as for the decel backfiring, it would be a lean condition, but most likely in the jet needle range. as for the issue with the bogging on accel, you will probably find that something is causing you to run extremely rich. i have seen everything from wrong main jets, to main jets fell off inside the float bowls (true story!). as far as main jet selections, you will want to run all the same size jets across the board. the practice of running the two middle jets a little richer stems back to the days when these engines were air cooled and the two middle cylinders would run hotter. they found that if you richened up the mix in the two, it helped them run at temperature. generally a lean motor is going to run hotter. rule of thumb. these bikes run a little on the rich side from the factory for EPA reasons. when you added the exhaust what you did was lean it out just a tad, probably the cause of your backfiring on decel. i wouldnt worry a whole lot about it, unless it is overbearing. i would venture to guess that if you took the carbs apart for a cleaning, you would find something dumping fuel into your cylinders, causing your bogging and stalling.... look for anything out of the ordinary. if all you have is a slip on, you would be able to get away without re jetting the bike. it actually increases your power on the top end when you run a little lean. hope this helps. plus, NEVER RUN SEA FOAM OR ANY OTHER MECHANIC IN A CAN PRODUCTS IN ANY VEHICLE!!!!!! if it is not running right, there is a reason. that sh*t will more often than not cause more problems.

 

I had this problem when I got my bike. it came from Cali (LA to be exact) and the jets were 140 and 142.5 I dropped them down to 138 and 135 (because im at high altitude) and cleaned the carbs while I had them out. This helped with the free rev and a little with the decel popping. I also removed all of my cali emissions stuff and dropped my needle position one notch to lean out the top end. I now have zero decel popping and a strong pull all the way to redline.

I have a k&N filter, ignition advancer, Dynojet jet kit and a Two brothers carbon M2 slip-on.

I would want to think you are running rich if it falls on its face when revving, does it do better if you slowly rev the bike up? I would start with Pulling the plugs and check the color. They will tell you all you need to know. white= lean, brownish/gray= normal, black= rich.

 

I think espelade seems to have it the closest. The bike will rev out but the throttle has to be brought on somewhat slowly or the bike just bogs and stalls. When I set the idle higher I eliminated this problem a little but the bike still feels a bit sluggish. I did check the pilots when I had the carbs out and I'm pretty sure that they were 140's and 142.5's. The decel popping is considerably loud though. If it was timid then I wouldnt have been concerned. It happens just about everytime you open the throttle up wide no matter what rpm. Maybe leaning the bike out slightly will help out with the excess fuel burning off in the exhaust and the problem will remedy itself.