mikuni round slide alky conversion question

mattf76

Member
I recently converted a knock off mikuni round slide for alky for an open animal. my first time using a poor mans method found online. the engine idles great and runs great at throttle but has a dead bog at part throttle 1/2-3/4. I turned the idle screw in to 1 turn from seated and moved the needle all the way up and it is better but still there. it is stock needle. What kind of mod is required on the needle as far as taper or size in general when changing to alky. Just a fun project any help appreciated. below is the steps I took to start. pm or answer here if any direction. Thanks!
Matt



***There is a "poor mans" way of doing it. I wrote this back awhile ago on planetsand. It will get you in the ballpark.

For four strokes--For the way your bike is at the moment, this is what you need to do..Get a good number drill bit set...remove the jet you are currently running and slide in the drill bit that fitss the best...snuggly not loose...now mic the drill bit...(example)-if it measures .050" then you need to drill it out to .100"....
Get all the shavings out...now take your needle out of the carb. and mic it's largest diameter just below the clip grooves at top...whatever it mics then you need to drill your needle jet (brass tube in carb) .022" larger...This is a must!!!! Now put your clip in the highest position (lowering the needle all the way down)....Check your specs for float height and make sure they are correct before you reassemble your carb...If too low you will suck your carb bowl dry...no need to mess with pilot at this time...drain gas. No need to flush out. Put in your methonal/alcohol...start engine...if it will idle, then no need for pilot to be drilled...if it wont idle at all even after idle screw adjustment, then you need to take back off and remove your pilot and drill out about .008"-.012" over stock. Dont go over .012 if it still wont idle then remove the pilot again and drill the carb body .008"...This should idle now...Now rev full throttle for a second..if it sounds like it ran out of fuel then comes back in again then good...its not running out of fuel...it is actually washing the spark out...
Now you need to start going smaller with you main jets. Go in .005 increments...When it revs and keeps climbing with no signs of cutting out then you are now very close to final jetting.

Take it out and run it...

Alcohol spark plug readings is exactly opposite than gas.

Tan to brown is lean condition...
White to gray is perfect...
It should look like a brand new plug...

Porcelain should be white/gray.

2-Strokers---All the same as above...Drilling the brass tube is a must!!!!Dont forget this step...Because it will run...Run away that is even with the ignition off!!!
If you dont do this eng. damage will occur...When you let off the throttle, your needle slams shut immediately, when it does the tube doesn't have enough fuel in it to stabilize engine rpm. Needle will force out all fuel then it will lean out...Engine will start to race very high...Shutting off switches will not stop the motor...it will keep on running and rpm will keep climbing until something comes apart...If you feel yours starts to do this immediately put in gear and hold the rear brake and dump the clutch...This will also happen if you run your fuel tank out..or forget to turn the petcock on..it will run off compression and no spark...if you dont believe me then go ahead and try it...(not adviseable though)....
 
Having same issue but have been running alcohol on the stand motor will go full throttle but once on a load it has a complete bog 3/4 to full throttle. Did you ever fix the problem?
 
I recently converted a knock off mikuni round slide for alky for an open animal. my first time using a poor mans method found online. the engine idles great and runs great at throttle but has a dead bog at part throttle 1/2-3/4. I turned the idle screw in to 1 turn from seated and moved the needle all the way up and it is better but still there. it is stock needle. What kind of mod is required on the needle as far as taper or size in general when changing to alky. Just a fun project any help appreciated. below is the steps I took to start. pm or answer here if any direction. Thanks!
Matt



***There is a "poor mans" way of doing it. I wrote this back awhile ago on planetsand. It will get you in the ballpark.

For four strokes--For the way your bike is at the moment, this is what you need to do..Get a good number drill bit set...remove the jet you are currently running and slide in the drill bit that fitss the best...snuggly not loose...now mic the drill bit...(example)-if it measures .050" then you need to drill it out to .100"....
Get all the shavings out...now take your needle out of the carb. and mic it's largest diameter just below the clip grooves at top...whatever it mics then you need to drill your needle jet (brass tube in carb) .022" larger...This is a must!!!! Now put your clip in the highest position (lowering the needle all the way down)....Check your specs for float height and make sure they are correct before you reassemble your carb...If too low you will suck your carb bowl dry...no need to mess with pilot at this time...drain gas. No need to flush out. Put in your methonal/alcohol...start engine...if it will idle, then no need for pilot to be drilled...if it wont idle at all even after idle screw adjustment, then you need to take back off and remove your pilot and drill out about .008"-.012" over stock. Dont go over .012 if it still wont idle then remove the pilot again and drill the carb body .008"...This should idle now...Now rev full throttle for a second..if it sounds like it ran out of fuel then comes back in again then good...its not running out of fuel...it is actually washing the spark out...
Now you need to start going smaller with you main jets. Go in .005 increments...When it revs and keeps climbing with no signs of cutting out then you are now very close to final jetting.

Take it out and run it...

Alcohol spark plug readings is exactly opposite than gas.

Tan to brown is lean condition...
White to gray is perfect...
It should look like a brand new plug...

Porcelain should be white/gray.

2-Strokers---All the same as above...Drilling the brass tube is a must!!!!Dont forget this step...Because it will run...Run away that is even with the ignition off!!!
If you dont do this eng. damage will occur...When you let off the throttle, your needle slams shut immediately, when it does the tube doesn't have enough fuel in it to stabilize engine rpm. Needle will force out all fuel then it will lean out...Engine will start to race very high...Shutting off switches will not stop the motor...it will keep on running and rpm will keep climbing until something comes apart...If you feel yours starts to do this immediately put in gear and hold the rear brake and dump the clutch...This will also happen if you run your fuel tank out..or forget to turn the petcock on..it will run off compression and no spark...if you dont believe me then go ahead and try it...(not adviseable though)....
 
Did I miss the part about jetting? My 2 cycles would not idle with alcohol if the jetting was right in for racing. It takes about 2 1/3 more alcohol versus gasoline. That includes low-speed and high-speed. I have a graphic, might not do you much good, but it shows the percentages needed.
 

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i found it interesting . that this person drilled the emulsion tube too a dimension .022 larger then the needle .
something most probably do not do .
 
Did you open the pilot a touch,for alky,you want to be on the rich side. on the needle, get some emery cloth and sand the taper down thinner,do a little at a time until the bog is gone. Also,if you can get a hold of some different slides,they make 4 different cutoff,s. Round slides are finicky on alky,flat slides not so much
 
The cutaway is what the angle on the slide is called .
I can't remember which is which .
More or Less taper affect off idle .
Less is richer , is my thinking .
 
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