Topic: Pop on decel

[Sticky Gerbil]

I knocked my bike off of some jack stands when I was replacing the tires. Nothing was physically damaged (dents, etc.), but  the tank had a ton of crap come loose inside. This crap entered the fuel filter, blew it apart internally, and then the crap entered the carbs and clogged them.

I have a 650 engine, but the carbs are the slide type common to early-mid-70s 750s, you know the ones, the Keihin slide type. I took them all apart and off of the holder thingy, and cleaned them thoroughly using carb cleaner and compressed air. I replaced all the jets (previously 105s) with 110s and replaced the needles with matching needles. I put the clip in the center position on all of them. Slow jets are a 21.

I measured the float heights correctly and put the carbs back together after making sure the slides were even. Did not touch the mixture screws.

Next, I started the bike up after putting the carbs back on and cleaning/regapping the plugs. Bike ran great, but had an ever so slight pop out of the 3/4 bank. I have 4->2 exhaust so this would be the RH exhaust pipe when standing behind the bike.

I busted out my carb sync gauge and put it on the bike after it was nice and warm. I put a fan in front of the bike. I had adjusted the valves before replacing the tires, so I figured I was good to go. I set all the carbs to about 11" vacuum.

The bike runs great, has plenty of power through the gears, etc. But when i decelerate, it pops like a mafk through the RH pipe. It also has a very slight pop like nanananapopnanananapoppopnananana  while idling.

How do I get rid of this? Should I fiddle with the mixture screws?

[triple]

try rechecking your valve clearance on these cylinders first up.

you may also need to richen the slow speed mixture a bit

[evanphi]

Slightly more rich on the air screws will take away the popping. 1/8 turn at a time.

HOWEVER

You should make sure your mixture is correct first, anyway. Some popping can be expected if the mixture is LEAN... normal mufflers would have masked the sound.

You're not hurting your bike by having this bit of popping.

[Deltarider]

Has the bike been sitting for some time? Any water in the fuel system?

[Sticky Gerbil]

I've tried fussing with the screws a bit; think I'll try some more. Gonna pull the plugs.

Bike never sits except for rain or snow- I ride it even in single digits.

Forgot to mention (please don't kill me) the bike has straight pipes and stupid pod filters. This popping never happened before though- it's had both for a while.

I will check valve clearance when I can (wife calls my bike the other woman)

[BobbyR]

Mine suddenly started doing that. It turned put to low level in one float bowl, I used the clear tube method to find the low one.

[Sticky Gerbil]

I would love to try the clear tube method; unfortunately my float bowl screws are seized and one is missing.

[Tews19]

Mine suddenly started doing that. It turned put to low level in one float bowl, I used the clear tube method to find the low one.

Can you explain how to do the clear tube method?

[flybox1]

Mine suddenly started doing that. It turned put to low level in one float bowl, I used the clear tube method to find the low one.

Can you explain how to do the clear tube method?

Depending on your model of carbs, the 'tube' will either come out of your drain screw hole, or off your overflow pipe.

[Tews19]

Awesome flybox! What do I attach to the screw to attach the clear tube? I have the 069a carbs for a 550F.

[flybox1]

Awesome flybox! What do I attach to the screw to attach the clear tube? I have the 069a carbs for a 550F.

for my 350F, i had to heat and stretch a section of tube to 'taper' it small enough to turn it into the drain screw hole
kinda like this...



(for PD carbs, the tube is attached to the overflow pipe)

[Tews19]

Ah I got it. Just stick it in where the screw was. Now how long do I cut the tube and what size should I get? Thank you and appreciate you for taking the time to help me out!

[flybox1]

Ah I got it. Just stick it in where the screw was. Now how long do I cut the tube and what size should I get? Thank you and appreciate you for taking the time to help me out!

take a drain screw to the hardware store, and get any cheap clear tubing with an OD slightly bigger    1/4", 3/16"   i dont know...   you could probably taper the ends with a blade, too....8" should be enough for each carb.   
be sure to secure each section of tubing well, and close to the bowl for ease of reading...

[Muckinfuss]

Plan B if you're anal about this sort of thing like I am, find a carb for parts (should anyway!) at a swap meet, take the drain screw from it and drill it out so you can insert some brass tube from a model supply (used with glow plug fuel airplane/car engines) and solder to fuse the two.  Then attach your appropriate size fuel line to make your gauge.  This tool will last longer than you.  The downside is it's a $20 solution to a $5 problem.

[Tews19]

When it comes to  ride quality I'm anal as can be. When it comes to looks of a bike that is mine, not so much. Well I checked the plugs again and wow they are dark! Dry soot but dark. 1-3 while 4 looks lean.... first pic is from left to right 1 and 2. Second pic is 3 and 4. Looks like I need to check the float level first.

I'm not trying to high jack the thread but it's a motogp pipe and hopefully it will help others.

[flybox1]

Once you know your fuel level is correct, you can move on to making carb adjustments to correct your mixture issues.
What were the of your plug chop test?  new plugs? what throttle position? etc.

[flybox1]

tews...i just posted your next plug chop test on the other thread 

[Tews19]

I will look. If you saw my other chop that was with 2.5 out. But everything else is the same. That's why I'm wondering about the float lwvel. I didn't putz with once I had them at stock level. I'm going to keep posting on that thread and not on this one.