Need jetting help w/heavy mods

[superevil]

86 motor/aggressive port job/cool head/ported reed cage/38mm air stryker/K and N filter/curtis sparks mx pipe/no airbox lid.

Got a 170 main and 50 pilot in right now,air screw 1/2 turn out. It runs ok,just seems to hesitate to rev out a little bit. It doesnt want to idle very long,even with the idle screw all the way in. I tried turning the air screw out to 2 turns,wich helped the bottom but then it hesitates to rev out worse.


It runs ok now like i was saying,just wants to hesitate a little before it revs out and doesnt seem very snappy off the bottom,any help would be awesome

[kiesta00]

What needle are you running? What cylinder/bore? May want to move the clip in the needle 1 notch up (Leaner = higher clip position) at a time until revving it becomes crisp. Then do some plug chops with a fresh plug to get that main jet dialed in. May want to get a smaller pilot jet to make it idle too.

Let the pros give their advice first before trying this!

[superevil]

I have no idea what needle is in it i never checked but it is in the center position

[86 Quad R]

first off........... is the carb completely clean(been flushed with carb cleaner and blown out with compressed air)? have ya made certain that the float is adjusted correctly and is shutting fuel off?

if so then i suggest ya start out with about a 45 pilot, needle in the center and a 170 main.

get the pilot cicuit adjusted out and then work on the mid range (needle) and then do wot (plug chop) on the main.

attached is some helpful information


Jetting (http://www.duncanracing.com/techfaq/Tech_keihin-carburetion-jetting.phtml)

[superevil]

The carb is clean,but im going to make sure tonight.
I have a new electrical system im putting on as well.

[LT250RMan]

Check your spark plug, If the end of the plug looks black or a really dark brown then your running it to rich and if the plug looks white or a bright yellow color then its jetted to lean. The color of the plug should be a nice chocolate brown color when you have it jetted right. The needle and pilot jet and main jet will all change the air fuel mixture, so make sure you check your plug everytime you change anything on the carb. If its kinda bogging out around idle to quarter throttle I bet you plug is black or a dark brown color.

The pilot jet works the most from idle to quarter throttle. Make sure you only change one size at a time when jetting or you could jet it to lean and blow up your engine. It matters on your altitude and the tempature of your location for jetting.

[bluetrx]

im not a jetting pro and cant offer any advice based on your symptoms, but i can tell you what im running in mine with a similar build at sea level. mine was tuned with fuel mapping on a dyno so i know its good.

60 pilot
185 main
DCQ needle clip in 2nd notch up from the bottom

'86 motor, aggressive port job, 4mil stroke, cool head, fmf fatty pipe, open element air filter no air box, 38mm pj.

i dont know if this will tell you anything but i hope it helps.

[bushwesl]

Originally posted by bluetrx
mine was tuned with fuel mapping on a dyno

Can you explain this please.

[bluetrx]

fuel mapping is when a probe is inserted into the pipe, it draws out the exhaust gasses and passes them by a heated o2 sensor. the air fuel ratio is displayed on a line graph with rpm. since rich/lean is determined by throttle position not rpm it is very important that the throttle is open smoothly from closed to wide open as rpm increases for this pull. it shows where in the throttle youre rich or lean. ive attached a map that shows a lean pilot a lean needle that gets progressively leaner, and a rich main jet. the fix for this is a step larger pilot, and move clip down one notch on a needle with a steeper angle. leave the rich main in it and run it again to see where your at, anyway thats how my tuning went. this service cost me $60 at crazy deals (stupid name but great service) in coos bay or.

[kiesta00]

Originally posted by bluetrx
im not a jetting pro and cant offer any advice based on your symptoms, but i can tell you what im running in mine with a similar build at sea level. mine was tuned with fuel mapping on a dyno so i know its good.

60 pilot
185 main
DCQ needle clip in 2nd notch up from the bottom

'86 motor, aggressive port job, 4mil stroke, cool head, fmf fatty pipe, open element air filter no air box, 38mm pj.

i dont know if this will tell you anything but i hope it helps.

I had the same setup as you except with a 38 a/s pwk and my jetting was:

170 main
52 pilot
dgk needle in the middle clip