1976 RD 400 My right cylinder is running lean. I have done a leak down test that looks good. Swapped coils from side to side. It is stock except for UNI foam filter and boyeseen power reeds. I currently have 140 main in left carb with needle in middle position and a 145 Main in the right Carb with needle moved down one position. Compression test shows about 2-3 psi difference in cylinders. And temp check with IR gun shows about 25 degrees hotter on right cylinder also. Any ideas on something else to check for I am running out of ideas. Bike runs good just lean on right cylinder.
Thank.
Q: In the right side you have the "needle moved down" or is the clip moved down raising the needle?
At what throttle opening is the lean condition?
Have the carbs been completely disassembled and thoroughly cleaned?
Timing is the same both sides?
Yes the needle clip is moved down one position raising the needle. Carbs have been apart several times and soaked in cleaner. Seems to be lean at all throttle positions. I feel like it is an air leak but leak down test looks good. Timing is same both sides.
Quote from: Rhino363 on August 26, 2020, 09:09:19 PM
Yes the needle clip is moved down one position raising the needle. Carbs have been apart several times and soaked in cleaner. Seems to be lean at all throttle positions. I feel like it is an air leak but leak down test looks good. Timing is same both sides.
Post a picture of your plugs. Also, what PSI are you putting into the motor and how long does it take until the pressure drops? When pressure testing, are the pistons roughly in the middle of their travel? I.E. One piston isn't at TDC? Not saying it's the cause but a small air leak at the spark plug or head gasket can cause lean conditions too.
Check your timing?
Leak down start at 6 psi and loose about 1 psi in about 45 min
I have checked timing several times. Cleaning the left carb again now
Bring it to Eric Heyman and he can sort it out for you if you cant figure it out. He runs Oily Pipes in Blue Bell, PA. He is a wizard when it comes to fixing these things.
Quote from: Rhino363 on August 27, 2020, 05:52:01 PM
Leak down start at 6 psi and loose about 1 psi in about 45 min
I have checked timing several times. Cleaning the left carb again now
The problem is on the right side correct? Just checking because you said you're cleaning the left carb again.
How are you cleaning the carbs? Are you
completely disassembling them, pulling all the brass/jets out, then soaking them? Are you blowing out all passages with compressed air after?
Are the jets and other brass parts new? Are they authentic Mikuni parts or was a rebuild kit used in the past?
Have you double checked that that needles, needle jets and pilots are clean and free of any debris? Are they the same sizes on each side?
Have you verified that the float height is correct, and same both sides? Should be 23mm (+/-1)
Are the carbs properly synced?
Try switching carbs with a long hose between the chokes. Then you will know if it is the carb or electrical
Quote from: rodneya on August 28, 2020, 01:12:08 AM
Are the carbs properly synced?
Try switching carbs with a long hose between the chokes. Then you will know if it is the carb or electrical
:agree: A lot of "jetting" problems can be a result of electrical issues.
Yes I meant the right carb cleaned again. All new mikuni jets. Float height is set to spec. New points and condenser from economy cycle. Swapped coils side to side. Even when starting and letting it warm up the right cylinder runs about 25-30 degrees hotter than the left.Checking with IR gun. Anything I else to check electrically points are set at 2.0 mm
Thanks
check exhaust baffles for clogging. :twocents:
Yes had exhaust off and baffles out cleaned all the holes had new packing in and tried taking packing back out also with no difference
have you ridden it then checked on side of road? also, verify timing is equal on both sides.
did you clear your airjet, gets missed all the time on the 400's.
Rarely but it can happen that a pressure test will pass but a vacuum test will fail. Pulling oil past the right crank seal will lean you out. Vacuum at 5 or 6 psi should let you know if that is the problem. I've heard of but never experienced a base gasket allowing pressure to hold and vacuum to fail. Just as a side note when installing base gaskets don't allow the inside edges to overlap.
Yeah everything looks good that I have checked so far. Starting to think about looking more into the left side to see if something is making it rich.
swap carbs left to right. just cap the choke crossover. see if it follows the carb.
Yeah brass balls are drilled out and air jets cleaned and tapped and plugged off with 5mm set screw in a couple threads.
If one ring was stuck on a piston would it cause that side to run lean or rich?
Starting to think maybe something other than carb or air leak
beats me but i think you're reaching. however a top end inspection is never bad idea if just for peace of mind.
Yeah, I would see if your top end is fine. I opened up my bike and discovered a destroyed top end (and it still wanted to run). It sounds like you're going through all of the motions to figuring it out.
I swapped carbs side to side and it followed the carb. So definitely a carb issue not sure which carb now if one is lean or the other is rich. I have had them apart several times soaking in carb cleaner and new mikuni jets. Drilled the brass balls out and plugged with set screws a couple threads. Going to go back thru them again.
there you go. now you're on the right track. :cheerleader:
Hmmm, I wonder if its the carb body or the actual brass parts inside...You may have an airleak somewhere on the carb giving you extra air to your mixture.
if anything id suspect jet tube had an issue. did you get new jet tubes? rarely is the body the issue unless somebody modified something previously.
are you using genuine Mikuni Jets?
Some of the aftermarket jets are all 0ver the place with sizing
Quote from: Rhino363 on August 31, 2020, 03:31:13 PM
I swapped carbs side to side and it followed the carb. So definitely a carb issue not sure which carb now if one is lean or the other is rich. I have had them apart several times soaking in carb cleaner and new mikuni jets. Drilled the brass balls out and plugged with set screws a couple threads. Going to go back thru them again.
did you ream the airjet after you took the ball out? You should be able to see the end of the reamer/wire if you look up through the jet tube, that way you know you've cleared it.
And are the jest all new genuine Mikuni ? Try blasting wd40 through the jets and compare left to right and then repeat on all the drillings/passageways. Could be as simple as a blocked pilot bypass hole.
And did you set the fuel levels?
Everything has been cleaned and wire thru passages I can get to.all new mikuni jets. I didnt set fuel height just the float height but I have swapped floats between the carbs with no difference. Is it ever common to run larger jets in one carb? I didnt replace the main nozzle that the main jet threads into but they look to be ok.
Thanks
on a streetbike? no. somethings wrong w the carbs for sure.
Quote from: Rhino363 on September 01, 2020, 08:15:09 PM
Everything has been cleaned and wire thru passages I can get to.all new mikuni jets. I didnt set fuel height just the float height but I have swapped floats between the carbs with no difference. Is it ever common to run larger jets in one carb? I didnt replace the main nozzle that the main jet threads into but they look to be ok.
Thanks
Yes but never more than one size different side to side.
I think I may have found my issue i swapped the main nozzle jet over from carb to carb and it followed to the other side. I just ordered 2 new ones and am having them overnighted.
I had that once on an r5, good catch. thats a hard one to diagnose. :clap:
Awesome. It takes time to diagnose, but you'll figure things out.