ccw dual carb conversion

stinger440 · Post by **stinger440** » Mon Jan 29, 2007 3:00 pm

Hey everyone. New to the site. Even though I don't own any JD sleds my friends do and I end up being the wrench for them so I have been reading a lot of the posts.

Now I have a couple questions for the group. Has anyone tried to put dual miks on a CCW reed valve motor? Did the mod make any improvements or just look cool? Where should I start with the jetting?

I have a 400/21 with a 76 liquifire intake. The carbs I have are 34mm. I think they came from a 340 liquifire. They have 40 pilots and 180 mains. Stock can exhaust, no tuned pipes. No air cleaner/box.

I have had the sled running. It doesn't idle very good but the plugs are not oily and black. I have not gone on any WOT runs yet due to lack of lake ice.

Is my jetting in the ball park? will I burn it down with this combination?

Thanks in advance and I look fwd to talking sleds on this site.

grasscutter97 · Post by **grasscutter97** » Mon Jan 29, 2007 4:39 pm

When I do a custom carb conversion, I always check similar jetting spes from an engine with same cc's. Example: switching to a mikuni on a JD300. I compared specs from other 300-340cc (piston port) engines that ran a mikuni. Start on the rich side and work your way down.

Its never just about main jets. All things need to match up. Needle, jet needle, pilot, cutaway, etc. Its a blast to do a conversion and have it work like a rocket!

Have fun.

stinger440 · Post by **stinger440** » Mon Jan 29, 2007 5:48 pm

I was planning on taking the specs from the 440 cyclone and splitting it in half to start with. I figured going from 440cc down to 400cc I should be on the rich side to start.

I am hoping someone has done it already and has it all dialed in.

Rodimus Prime · Post by **Rodimus Prime** » Mon Jan 29, 2007 7:38 pm

the 440 liquifire motor 76-78 ccw is the same motor except its liquid cooled so that would be your start place.

stinger440 · Post by **stinger440** » Tue Jan 30, 2007 11:48 pm

So I went through my carbs again and they did come from a 76 440 liquifire. So I have everything the same as stock except for the 180 mains. Tonight I was able to get it to idle well. It was 13 degrees outside and I put fresh 93 octane in her. It now starts easy and idles at 2000rpm.

Questions...

What will it do at 35 degrees? Will it run even richer? I want to have this as a set it and forget it .

Also when I check my plugs I always look at the ground electrode, should I be looking at the porcelin below it instead?

This is my first time jetting miks, so I will have quite a few questions

Thanks

Rodimus Prime · Post by **Rodimus Prime** » Wed Jan 31, 2007 12:37 am

short runs you look at the electrode for color long runs the porcelain or whole overall plug color. mikunis unfortuantly are not that easy to change from temp to temp.. althougha difference of 10 degrees is no biggie..

a rule of thumb for tuning them is to start at 1/4 throttle open on warm engine run at 1/4 for 1/4 mile kill engine without letting go of throttle check plug color.. change plugs do the same for 1/2 throttle... 3/4 and wot

for those who have it there is a little device for changing the wot.. you remove the cable from handle and insert it into the box insert box cable to handle.. adjust box for 1/4 /12 3/4 and wot. its handy.. some sleds have a cable adjustment further up that will allow this.. this way you hold throttle to bar for all checks and hitting kill switch is much easier..

another way is to use taped blocks on grips.

if your serious about getting into mikunis get a small tackle box has trays for jets needles needle jets washers inlet needles throttle valves gaskets orings.. i keep universal brake cable as well in mine.. jets should be seperated from used and new.. also mikinu sells foam pad for putting them in or use rubber block from those 1001 screwdriver bit thingys. pilots should be kept in a ziplock bag otherwise youll be hunting them alot. also individual spark plug boxes clearly marked for 1/4 1/2 3/4 wot. also 1/8 5/8 if your doing powerjets. it has advantage of being able to carry in field with spark plug wrench when testing.

stinger440 · Post by **stinger440** » Fri Feb 02, 2007 10:51 am

A quick update on my project. Engine (CCW 400/21) starts up very easy cold and will sit and idle at 2000 rpm. I took it out for a couple slow laps around the yard and got it warmed up. Goosed it to 1/4 throttle or so and it was completely flat. Took another lap and tried it again. Flat again. Then it didn't want to run at lower rpm at all. Got it into the garage and it would not idle so I shut it off. I didn't let it die. Plugs were pretty black.

So here are my thoughts. I never really got into the main circuit at all so I am thinking the 40 pilots are too rich thats why it starts so easy without the choke and idles nice when cold. With that in mind I am going to try 30 pilots and see if there is any improvements.

Any thoughts?

stinger440 · Post by **stinger440** » Sun Feb 18, 2007 3:17 pm

Another update on the dual carb set up. first it helps if the motor is nice and warm before you try to adjust the idle. I put in 30 pilot jets. It originally had 40's and I could not get it to hold an idle. it always wanted to die. Put in the 30's, warmed it up well and I increased the idle up to 2800 rpm. Now after I run it and stop it will keep idleing and not die. Oh and I am out 2 1/2 turns on the mixture screw. Plugs are darker brown so I am happy with that.

Now I need some open range/lake to check the rest of the system out.