carbs synced, still uneven engine load felt

[stilkus]

I have spent a lot of time troubleshooting my carbs, I had it lean/rich/not synced and a lot more until recently things are fine and the motorcycle is performing good. I still feel that my carbs have something wrong which I am unable to figure out. I am going to list the symptoms hoping someone would help me figure out what I did wrong on my carb treatment journey.

1 . backfires from carbs every now and then when I drive with a cold engine. I don't push it hard or anything, all sub 3k rpm driving. also when it backfires from the carb I feel loss of power at that instance.

2. whenever I remove the rubber cover of the rear right cylinder to attach my vacuum gauge the engine rpm drops badly (drops at least 400 rpm) until I plug my gauge or return the rubber cover. this never happens with any of the other 3 cylinders, instead a slight engine hesitation happens.

3. when I apply a high gear and pull full throttle I hear very loud carb (blops), it would make this sound ( blop, blop, blop, blop, ..... ) till I release for sure or till the engine rotates faster, also this (blop) sound is slightly felt between my legs. I just feel I am a harley and that makes me uncomfortable as I like the silent power of the vmax.

that's all

 

[naughtyG]

I think your 1. is normal - don't expect the motor to work smoothly until it's warmed up.

2. is also normal, if you create a big vacuum leak the engine should drop rpm as it becomes fuel-starved by the increase of air.

3. is hard to tell without actually hearing what you call 'blop'. Also, what kind of rpm are you talking about when you say 'apply high gear'?

 

[MaxMidnight]

Check for air leaks, particularly #3. Puff some Easy Start around the intakes and listen for a rise in revs.

What colour are the plugs?

If not doe so already do a plug chop at the revs you are having an issue.
The plugs are a good indication to what the mixture is doing.

 

[stilkus]

I think your 1. is normal - don't expect the motor to work smoothly until it's warmed up.

2. is also normal, if you create a big vacuum leak the engine should drop rpm as it becomes fuel-starved by the increase of air.

3. is hard to tell without actually hearing what you call 'blop'. Also, what kind of rpm are you talking about when you say 'apply high gear'?

2. I understand, but my problem is that it's only happening in right rear cylinder, it won't happen in any other one.

3. I'm talking 2500rpm fifth gear, full throttle. I hear the carburetors make a loud "blop" sound and feels that each one of those "blops" related to every intake stroke.

 

[stilkus]

Check for air leaks, particularly #3. Puff some Easy Start around the intakes and listen for a rise in revs.

What colour are the plugs?

If not doe so already do a plug chop at the revs you are having an issue.
The plugs are a good indication to what the mixture is doing.

I will check for air leaks, also I knew of this issue before installing the carbs so I made sure it fitted tight.

about the plugs colours, I didn't change my spark plugs for a long time, since before I've done my carb service, so the question here is, can this be an accurate reading to the current condition or am I going to get the pre-carb service readings ?

 

[dannymax]

Are your valve clearances in spec?

 

[sdt354]

How are the idle circuits on all the carbs? Is there a good response from the a/f needle adjustment on all? It can be hard to get them truly clean. I've had to use guitar wire on crud before getting the carbs really clean.
Steve-o

 

[alorio1]

Check your sync gauges for out of calibration and then re-sync carbs.

 

[customizedcreationz]

You should notice a slight drop in rpm on all carbs as you unplug them. If not I would check for vacuum leaks as mentioned. Vacuum leaks can cause crazy problems and until that is diagnosed out of the way, then you could be chasing your tail. A can of carb cleaner sprayed around all the joints and seals while the engine is running will tell you if you have leaks or not as it will seal them for a second while it is sucked in. Starting fluid works also. As it will make the motor rev up noticeably when its sucked in.

Todd

 

[stilkus]

Are your valve clearances in spec?

I checked them before summer started and they were fine, that was 800 miles ago

 

[stilkus]

You should notice a slight drop in rpm on all carbs as you unplug them. If not I would check for vacuum leaks as mentioned. Vacuum leaks can cause crazy problems and until that is diagnosed out of the way, then you could be chasing your tail. A can of carb cleaner sprayed around all the joints and seals while the engine is running will tell you if you have leaks or not as it will seal them for a second while it is sucked in. Starting fluid works also. As it will make the motor rev up noticeably when its sucked in.

Todd

I do have a slight drop in the engine rpm when unplugging the spark plug cords or when removing the rubber cover on the vacuum gauge ports. my concern is that the biggest drop in rpm would be related to the rear right cylinder, feels like it's doing most of the engine's job and I can't figure out why.

I also double checked the carb sync and it's synced.

The motorcycle is having a higher idle when warmed up, starts 500rpm when cold without choke, rises to 1000+-50 when warmed up, 1400 when around cooling fan operating temperature.

 

[tugla]

wide open cut for a plug read not idle. if they are old the plugs i'd change them start fresjh. also sounds like air leaks. use a spray or propane torch to test for air leaks around the carbs.

 

[Rhoy Carter]

Sounds to me like you need to drop a couple gears and quit lugging the motor, 2500 is ok for cruising but to accelerate drop it to third gear

 

[Diablotin]

Check for air leaks, particularly #3. Puff some Easy Start around the intakes and listen for a rise in revs.

What colour are the plugs?

If not doe so already do a plug chop at the revs you are having an issue.
The plugs are a good indication to what the mixture is doing.

+1 I had similar issue due to exhaust leak near the muffler.

Sent from my GT-I9100 using Tapatalk 2

 

[alorio1]

If you or the PO had the carbs apart and used an impact screw driver, the carb rack may be slightly distorted . If thats the case all 4 carbs will not be in sync when you are accelerating.

 

[Rusty McNeil]

Sounds to me like you need to drop a couple gears and quit lugging the motor, 2500 is ok for cruising but to accelerate drop it to third gear

+1 on this, the motors going to lug at 2500 rpm in 5th no matter what you do.

What kind of riding are you doing in 5th gear at 2500 rpm? Or are you just doing that as a test?

The constantly hunting for a set idle speed sounds e a vacuum leak.

The synch and alve lash would have to be absolutely perfect for all cylinders to respond to pulling the vacuum plugs or to respond equally to the a/f screws.
The throttle opening is so very slight at idle that it's very easy for one carb to not be doing any work if the synch is off even a little.

The following is Just my opinion but if it idles on all four cylinders it's ok. ( you can check this with an IR thermometer on the exhaust although it's tough with the stock system)
Once it's off idle the difference in throttle angles due to poor synch becomes a smaller and smaller percentage of overall opening that I find it very hard to attribute synch problems to any thing but idle and extremely slight throttle opening position symptoms you may be having. Or in short, at WOT synch doesn't matter. Poor synch can give you that annoying feeling off idle when one cylinder decides to wake up.