problems after exhaust install

[95katman]

Whats up everybody? I am new to this site and I am having some issues tuning my bike. I have a 95 katana 750. I bought a set of remanufactured carburetors off ebay that had a dynojet kit installed supposed to be for a stock setup with 116 main jets. They ran good with the stock exhaust and air box other than a very noticeable flat spot between 5,000-7,000 rpm. I lowered the needles one groove and that helped. I live about 2,200 feet above sea level which seems to make everything run a little richer. My problem is I installed a full vance and hines exhaust and the flat spot became a bad stumble in the higher gears. In lower gears I can blast through it and it runs great. I tried putting 120 main jets in and it made the problems worse. I tried 118, 116, 114, 110, and acutally have 106 DJ main jets in right now (didn't have 108). I know this is much leaner than stock, but it did get rid of my stumble, Although power seems to be down considerably everywhere else. Pilots are 3.5 turns out. Any ideas what is going on? I was considering putting a K&N replacement filter in my stock air box. I am very confused, because I know I should have to richen it up after an exhaust install. Can anyone help?

[Kreylyn]

Whats up everybody? I am new to this site and I am having some issues tuning my bike. I have a 95 katana 750. I bought a set of remanufactured carburetors off ebay that had a dynojet kit installed supposed to be for a stock setup with 116 main jets. They ran good with the stock exhaust and air box other than a very noticeable flat spot between 5,000-7,000 rpm. I lowered the needles one groove and that helped. I live about 2,200 feet above sea level which seems to make everything run a little richer. My problem is I installed a full vance and hines exhaust and the flat spot became a bad stumble in the higher gears. In lower gears I can blast through it and it runs great. I tried putting 120 main jets in and it made the problems worse. I tried 118, 116, 114, 110, and acutally have 106 DJ main jets in right now (didn't have 108). I know this is much leaner than stock, but it did get rid of my stumble, Although power seems to be down considerably everywhere else. Pilots are 3.5 turns out. Any ideas what is going on? I was considering putting a K&N replacement filter in my stock air box. I am very confused, because I know I should have to richen it up after an exhaust install. Can anyone help?

First thing I would check would be the needle jets for wear. If those things are egg shaped, your gonna have issues in those RPM ranges.

Krey

[95katman]

Thanks for the input, I have adjusted the needles a few times now. Currently they are in the 3rd slot from the top. They show signs of age, but other than that they look ok. Is it normal for these carbs to go rich in this rpm range? Do you think an aftermarket filter would help? Has anyone else ever had similiar issues with dynojet kits? Why does it mostly happen in higher gears, any other ideas?

[Kreylyn]

Thanks for the input, I have adjusted the needles a few times now. Currently they are in the 3rd slot from the top. They show signs of age, but other than that they look ok. Is it normal for these carbs to go rich in this rpm range? Do you think an aftermarket filter would help? Has anyone else ever had similiar issues with dynojet kits? Why does it mostly happen in higher gears, any other ideas?

From this response, I'm not sure you understood what I posted.

Needle jets are the top portion of the emulsion tube that surrounds the needle as it's inserts in. If this area is worn, you end up with significantly larger dropletts of fuel flowing into the engine and this causes problems.

How to check for wear... http://www.factorypro.com/tech/needle_jet_wear.html

Krey

[95katman]

Yeh, I did misunderstand you. These carbs were supposed to be remanufactured, is it normal to replace the tubes when this is done? I will look into it, how do you replace them if needed? I know a little about carbs, but I am no expert. thanks for your help.

[Kreylyn]

Yeh, I did misunderstand you. These carbs were supposed to be remanufactured, is it normal to replace the tubes when this is done? I will look into it, how do you replace them if needed? I know a little about carbs, but I am no expert. thanks for your help.

I would check them for wear, but no... not normal to replace them. Most carbs do not have the milage to warrant the wear and replacement.

If they are worn, then... yes, they will need to be replaced. The newer nickel plated ones sold today last alot longer though.

Krey

[scottynoface]

Ftr, I always had a small flat spot in the midrange with my dj kit.

[arsenic]

Who'd you buy them from? arsenic1016? Cause that's me. It's not common to replace them, but I check them on every set I do. If it was from me, trust me, they wouldn't be egg shaped.

[95katman]

I can deal with a small flat spot, but when on the interstate in top gear my rpm is right around the 5,500 rpm range and if I want to accelerate it stumbles real bad. The only way I can accelerate is to change down, very aggravating! How do you remove the needle jets? Could it be a mismatch of a free flowing exhaust with a restrictive intake?

[arsenic]

Take one of the float bowl screws, screw it in where the main jet was. Take that out by the way. Than hit the head of the screw with a hammer. That will knock the plastic slide guide loose and you can pull that and the needle jet out.

[95katman]

Who'd you buy them from? arsenic1016? Cause that's me. It's not common to replace them, but I check them on every set I do. If it was from me, trust me, they wouldn't be egg shaped.

Hey arsenic. I did buy these carbs from you. They look great and I had them running pretty good with the stock air box and exhaust, but that stock exhaust sound was terrible. When I installed the vance and hines it developed the stumble. I was able to smooth it out, but I had to put 106 dynojets in them, but I lost power everywhere else. What are your thoughts? thanks

[arsenic]

I really don't know why it would run good with the stock exhaust and not a full exhaust. I would have just done what the directions said, shouldn't you be using like DJ120 mains? Why are the DJ106 mains in?

[scottynoface]

I really don't know why it would run good with the stock exhaust and not a full exhaust. I would have just done what the directions said, shouldn't you be using like DJ120 mains? Why are the DJ106 mains in?

IIRC the dj instructions had us putting in DJ116 mains.

93 600 full yoshi and uni filter.

[95katman]

I really don't know why it would run good with the stock exhaust and not a full exhaust. I would have just done what the directions said, shouldn't you be using like DJ120 mains? Why are the DJ106 mains in?

I tried the 120's and it made it much worse. I tried several different jet sizes and the 106;s were the best as far as smoothing it out. With the bigger jets it ran great once it hit 7000 rpm, but would stumble from 5,000-7,000 in higher gears. In the lower gears I could gas straight through it. I guess that would work at the dragstrip, but not so great around town.

[arsenic]

Yeah, he's got a 750, the mains jets are different.