jetting help

[Dreamer]

Mods are fmf fatty expansion chamber, aftermarket silencer not sure of brand, open air box lid w/ uni air filter, stock 34mm carb, and v force 3 reeds. Engine is a stock rebuild with a re-sleeved stock jug and wiesco std bore piston. Compression is 185 and it only dropped from 9.5 to 9 lbs over 15 minutes in a leak down test. Current jets are 145 main and 38 pilot needle(what it came with) on second clip and air screw 1.5 turns out. It is having trouble idling as is and smoking pretty bad, fuel is fresh 93 with Lucas oil mixed 40:1.

[Jar350r]

What needle are you running? Elavation ?
Stock cylinder I say 50-45 pilot dgh needle 3rd clip 158-165 main

[Dreamer]

needle says R1471L S which is stock for the 88 correct? Where is the best place to buy jets these days. i havent bought them in probably 10 years.

[Jar350r]

Jets r us, or straight from keihin

[Dreamer]

SO i replaced the jets with a 52 pilot and 168 main needle second positon and air screw 1.75 turns out. Still bogs in every gear at every at every rpm and smoke pretty bad. However when i turned the gas off and was idling it to burn all the gas up in the bowl it ran perfect and had a real crisp throttle response and sounded great at idle until it was nearly out of fuel where it started to two stroke runaway. What would make it run good with the fuel off for a while but not with fuel on.?

[rk88r]

Check float for proper function.

[Jerry Hall]

SO i replaced the jets with a 48 pilot and 165 main needle second positon and air screw 1.75 turns out. Still bogs in every gear at every at every rpm and smoke pretty bad. However when i turned the gas off and was idling it to burn all the gas up in the bowl it ran perfect and had a real crisp throttle response and sounded great at idle until it was nearly out of fuel where it started to two stroke runaway. What would make it run good with the fuel off for a while but not with fuel on.?

A bad float valve may not be maintaining a constant fuel level.

 The needle jet may have ware and can make the carburetor rich at an idle up to about 1/2 throttle.  If this is the case the carburetor is a throw away or you are going to have to look for another needle with a larger initial diameter.


Measure this diameter at the straight portion of the 1471 needle with a micrometer that has the ability to measure in "tenths".  A pair of digital calipers are not precise enough for measuring needles.  Once you determine the diameter of the straight portion of your current needle, find another needle that has the same taper and reference length and increase the straight portion diameter to the next leaner increment.

This is one of the many negative design features of the Keihin series of dirt bike carburetors.  The needle you have is an OEM needle from something.  The after market keihin needles use a different numbering system.  

I think 1471 needle nomenclature is : 14 designates the taper and the 71 means the needle has a 2.71mm straight section diameter.

[Dreamer]

Well i adjusted the float to what i believe was correct using this link http://www.allthingsmoto.com/forums/f-15/how-set-your-motorcycle-carburetor-float-level-more-commentary-13608/. float height was right at 16 mm with the float assembly tang just touching the internal spring bumper. It seemed like it ran better for a little while then went back to doing the same thing, bogging and smoking horribly. When sitting still and going full throttle it falls on its face wont rev at all. Needle measured .1069 which is what it should have measure so i think the needle is still good.

[Bowtie316]

What elevation are you at? And are you sure it's a 38mm carb?

The 48/165 should be pretty close if everything is working correctly.

 What plug and gap are you running?

What clip position on the needle?

Sent from my SGH-T679 using Tapatalk 2

[Dreamer]

Im in st.louis, elevation is around 460. Carb is a stock  88 34 mm carb, original post had an error. Clip on second position, pilot 52, main 168. I didn't get around to gaping the plug so its running whatever it was new.

[The_Steve_Man]

I had that problem when I first put my motor together. I had a CT pipe , ported cylinder,  v force2 reeds and ran the stock 34 carb.  Could not get it lean enough.  I had a 39 pwk I put on it and the problems went away.  I am at about the same elevation as you.

[Bowtie316]

Im in st.louis, elevation is around 460. Carb is a stock  88 34 mm carb, original post had an error. Clip on second position, pilot 52, main 168. I didn't get around to gaping the plug so its running whatever it was new.

My 88 with very similar parts (800' el.) likes a 48 pilot, 165 main and DGK needle, clip in 3rd position.  Is the air cleaner dirty? that will cause it to run rich.  Also check for obstructions in the silencer. Close the spark plug up to about .018".

[Dreamer]

air cleaner is freshly cleaned with new oil and silencer freshly repacked. Im going to check the plug gap tonight and see if that changes anything although i don't see that fixing the over fueling issue.

[Jerry Hall]

Mods are fmf fatty expansion chamber, aftermarket silencer not sure of brand, open air box lid w/ uni air filter, stock 34mm carb, and v force 3 reeds. Engine is a stock rebuild with a re-sleeved stock jug and wiesco std bore piston. Compression is 185 and it only dropped from 9.5 to 9 lbs over 15 minutes in a leak down test. Current jets are 145 main and 38 pilot needle(what it came with) on second clip and air screw 1.5 turns out. It is having trouble idling as is and smoking pretty bad, fuel is fresh 93 with Lucas oil mixed 40:1.

 


    Originally Posted by Dreamer
Well i adjusted the float to what i believe was correct using this link http://www.allthingsmoto.com/forums/...mentary-13608/. float height was right at 16 mm with the float assembly tang just touching the internal spring bumper. It seemed like it ran better for a little while then went back to doing the same thing, bogging and smoking horribly. When sitting still and going full throttle it falls on its face wont rev at all. Needle measured .1069 which is what it should have measure so i think the needle is still good.



Your choke may be partially adding fuel all of the time. Do you have someone that has a bike and carb just like yours? If so borrow it and see if anything changes.

[Dreamer]

    Originally Posted by Dreamer
Well i adjusted the float to what i believe was correct using this link http://www.allthingsmoto.com/forums/...mentary-13608/. float height was right at 16 mm with the float assembly tang just touching the internal spring bumper. It seemed like it ran better for a little while then went back to doing the same thing, bogging and smoking horribly. When sitting still and going full throttle it falls on its face wont rev at all. Needle measured .1069 which is what it should have measure so i think the needle is still good.



Your choke may be partially adding fuel all of the time. Do you have someone that has a bike and carb just like yours? If so borrow it and see if anything changes.

Unfortunately no, currently none of my buddies even have quads. I jumped in with both feet hoping they would follow, having a bike that doesn't run isn't helping :02.47-tranquillity:. I found that the idle/choke knob had two o rings in it, pulled out the extra and it idled better but that's about it. Still smokes bad and has horrible throttle response. Checked the float again today and it again looked fine as best i can tell. I checked the plug and the one in the bike as well as the extras the guy gave me are all ngk bpr7es which from everything i can find is wrong, going to pick up some b8eg's hopefully by the end of the week. Here's a video of it idling and a picture of the plug after idling.