Huge pilot jet

[Martint93]

Hi, my 86 cr 500 engine with sem ignition and a wr 400 pipe wont idle properly unless I use a big pilot jet. It now has a 55 drilled from 35. It is the carb from my 87 wr 400.
I tried a 40 pilot but hang a bit high in the rpm scale before it drops down to 1800/2000 IF it does at all. No mater how I adjusted mixture and idle screw. This was with a 3.0 slide. Swapped back to the 2.5 slide and it got sligthly better. Then I put in the 55 pilot jet again and it got much better right away. Still hangs for about 2 seconds but nothing like before. Can't find any airleaks. Has used this pilot on all the engines been in this frame. The wr400 the 430 and now the 500. How come I need THAT big pilot jet to make it idle? Feels a bit rich puttering around from 1/8 to 1/4 throttle.

Current settings are:

Mikuni vm 38mm

Main 430
Pilot 35 drilled to 55
Needle 6DH20
Clip 2 from top
Needle jet R-0
Slide 2.5
Air jet 2.0
Float almost paralell with carb. It close maby 1 degree earlier
Air screw 1 turn out

Idles at 2000rpm now

Yes, main jet is big, but is on its way down. Just had a break down, so started fat this time..

Anyone? Though 40-45 should be fine..

 

[justintendo]

weird...maybe try adjusting the float so its level? do you have an air leak? crankseal? my 88 250 is running a 450 main

 

[Martint93]

The reason I adjusted the float to this setting is because before I did, it ran over and filled the crankhous up. Changed the float needle but didn't help..
About the main, I tink 350-370 will be where I will end up. This 430 is way to big.

 

[Martint93]

Crank seal should be fine. Lefthand is 30min old, the righthand seal is 3hours old..

 

[jo360]

check the cylinder and manifold for air leaks.

 

[ruwfo]

Part of the reason a large main jet is needed is you have 2.5 slide, which will make it run leaner then a 2.0, there all tied together.

 

[Martint93]

J

Part of the reason a large main jet is needed is you have 2.5 slide, which will make it run leaner then a 2.0, there all tied together.

Where did you get the idea that I need a big main jet? It is a big pilot we are talking about here. The main jet I find quite small compared with other huskies 500's with mikuni 38mm

 

[jo360]

i have been having simlar issues with my 430 after the rebuild thought it was a carb issue but turned out to be an air leak at the cylinder head, the problem only showed up when the engine was hot.i had simply not torqued the head down fully, went bigger on the pilot without any change.
now i have tracked down the air leak i will have to re jet the pilot down again.
500 equals higher vauum which should mean smaller jets.

 

[2premo]

Hi, my 86 cr 500 engine with sem ignition and a wr 400 pipe wont idle properly unless I use a big pilot jet. It now has a 55 drilled from 35. It is the carb from my 87 wr 400.
I tried a 40 pilot but hang a bit high in the rpm scale before it drops down to 1800/2000 IF it does at all. No mater how I adjusted mixture and idle screw. This was with a 3.0 slide. Swapped back to the 2.5 slide and it got sligthly better. Then I put in the 55 pilot jet again and it got much better right away. Still hangs for about 2 seconds but nothing like before. Can't find any airleaks. Has used this pilot on all the engines been in this frame. The wr400 the 430 and now the 500. How come I need THAT big pilot jet to make it idle? Feels a bit rich puttering around from 1/8 to 1/4 throttle.

Current settings are:

Mikuni vm 38mm

Main 430
Pilot 35 drilled to 55
Needle 6DH20
Clip 2 from top
Needle jet R-0
Slide 2.5
Air jet 2.0
Float almost paralell with carb. It close maby 1 degree earlier
Air screw 1 turn out

Idles at 2000rpm now

Yes, main jet is big, but is on its way down. Just had a break down, so started fat this time..

Anyone? Though 40-45 should be fine..

drilling a pilot does not always equal accurate flow numbers

 

[Martint93]

i have been having simlar issues with my 430 after the rebuild thought it was a carb issue but turned out to be an air leak at the cylinder head, the problem only showed up when the engine was hot.i had simply not torqued the head down fully, went bigger on the pilot without any change.
now i have tracked down the air leak i will have to re jet the pilot down again.
500 equals higher vauum which should mean smaller jets.

i have been having simlar issues with my 430 after the rebuild thought it was a carb issue but turned out to be an air leak at the cylinder head, the problem only showed up when the engine was hot.i had simply not torqued the head down fully, went bigger on the pilot without any change.
now i have tracked down the air leak i will have to re jet the pilot down again.
500 equals higher vauum which should mean smaller jets.

Hey, thats interesting. How did you see/detect the air leak? Was it on a ac or lc?

 

[jo360]

mines an ac just process of elimination after checking everything else.when i took the head off i could see soot around the two allen key bolts i forgot to tighten properly, the bike would surge when hot sort of idling from 1200 upto 2000 or more.