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For Royal Enfield owners and enthusiasts
- Sun Oct 07, 2018 3:28 am
#79490
Hey, guys. I need your help again here. I was able to swap all the jets from the Mikcarb into the Mikuni, with the exception of the incompatible needle jet, as was previous explained to me. I tried to use the 3.0 slide from the Mikcarb, and that's where I ran into problems-- it doesn't appear to be interchangeable either. The slide from the Mikuni is so tall it won't sit fully in the spigot, and so it will never retract fully at full throttle. I'm currently using the needle that came with the Mikcarb along with the 2.5 slide that came with the Mikuni, and I'm getting a bit of a bog when I open throttle quickly at idle. I can't seem to find the Mikuni size 3 slide anywhere-- and I do mean ANYWHERE. What's a guy to do?
- Sun Oct 07, 2018 3:28 am
#79491
Hey, guys. I need your help again here. I was able to swap all the jets from the Mikcarb into the Mikuni, with the exception of the incompatible needle jet, as was previous explained to me. I tried to use the 3.0 slide from the Mikcarb, and that's where I ran into problems-- it doesn't appear to be interchangeable either. The slide from the Mikuni is so tall it won't sit fully in the spigot, and so it will never retract fully at full throttle. I'm currently using the needle that came with the Mikcarb along with the 2.5 slide that came with the Mikuni, and I'm getting a bit of a bog when I open throttle quickly at idle. I can't seem to find the Mikuni size 3 slide anywhere-- and I do mean ANYWHERE. What's a guy to do?
- Sun Oct 07, 2018 7:40 am
#79493
You can turn easily the 2.5 slide into a 3 by increasing the height of the cutaway, or a 3 into a 2.5 by removing base material. But only once!!!!
- Mon Oct 08, 2018 7:58 am
#79499
TONUPBOY [Enfield owner?!] says: 'I'm getting a bit of a bog when I open throttle quickly at idle'
aA regular cause of carburetion flat spots and pinking is opening the throttle too suddenly, especially at low engine speed or when the engine is under load.
Sudden opening of the throttle may create a sudden weakening in mixture strength. A weak mixture may cause the engine to falter or ‘pink’, especially at low engine speeds or when the engine is under heavy load. In some circumstances the engine may stall.
The cause is the differential of inertia between fuel and air.
When the throttle is opened suddenly a partial vacuum is created in the carburettor venturi. Air rushes in to fill this vacuum. As fuel has greater inertia than air, the carburettor draws is a disproportionately greater weight of air than fuel. The result is a momentary weak mixture.
This temporary weakening of mixture may cause the engine to hesitate or ‘pink’ – the opposite effect what is normally expected when the throttle is opened.
These effects will be marginally more obvious with methanol than petrol, methanol having a higher specific gravity than petrol (791 for methanol, 737 for petrol).
Some carburettors incorporate an ‘accelerator jet’ to alleviate this problem. A mechanical pump is activated by sudden opening of the throttle. The pump injects neat fuel into the venturi compensating for the disproportionately too great supply of air.
aA regular cause of carburetion flat spots and pinking is opening the throttle too suddenly, especially at low engine speed or when the engine is under load.
Sudden opening of the throttle may create a sudden weakening in mixture strength. A weak mixture may cause the engine to falter or ‘pink’, especially at low engine speeds or when the engine is under heavy load. In some circumstances the engine may stall.
The cause is the differential of inertia between fuel and air.
When the throttle is opened suddenly a partial vacuum is created in the carburettor venturi. Air rushes in to fill this vacuum. As fuel has greater inertia than air, the carburettor draws is a disproportionately greater weight of air than fuel. The result is a momentary weak mixture.
This temporary weakening of mixture may cause the engine to hesitate or ‘pink’ – the opposite effect what is normally expected when the throttle is opened.
These effects will be marginally more obvious with methanol than petrol, methanol having a higher specific gravity than petrol (791 for methanol, 737 for petrol).
Some carburettors incorporate an ‘accelerator jet’ to alleviate this problem. A mechanical pump is activated by sudden opening of the throttle. The pump injects neat fuel into the venturi compensating for the disproportionately too great supply of air.
- Fri Oct 12, 2018 4:18 pm
#79565
further to my above posting (now back home with the info)
1.0 cutaway = 1/16"
2.0 cutaway = 2/16"
2.5 cutaway = 5/32"
3.0 cutaway = 3/16"
3.5 cutaway = 7/32"
You can go from a Mikuni No.3 to a 2.5 by lowering the cutaway. Remove material from the base not the cutaway itself until the cutaway height is correct. As mentioned you can only go down (richer) by 0.5 slide size, if going up by altering the cutaway to make it weaker the slide can be modified by a couple of sizes.
1.0 cutaway = 1/16"
2.0 cutaway = 2/16"
2.5 cutaway = 5/32"
3.0 cutaway = 3/16"
3.5 cutaway = 7/32"
You can go from a Mikuni No.3 to a 2.5 by lowering the cutaway. Remove material from the base not the cutaway itself until the cutaway height is correct. As mentioned you can only go down (richer) by 0.5 slide size, if going up by altering the cutaway to make it weaker the slide can be modified by a couple of sizes.
- Wed Oct 24, 2018 1:41 am
#79894
I've also recently replaced my Mycarb with the Mikuni VM28-49. The needle, needle jet and pilot jet will swap over to the Mikuni. The only thing to remember is that you need large hex jets versus the round jets. Also, the flow rate are different for the jet so you'll need to cross reference. I have had no issues with the 2.5 slide cutaway and it seems to improve the low end performance.
I'm my opinion, the Mikuni is superior in quality especially in the float system and overall construction it also moves the air bleed screw to the opposite side foe ease of adjustment.
I'm my opinion, the Mikuni is superior in quality especially in the float system and overall construction it also moves the air bleed screw to the opposite side foe ease of adjustment.
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