Carb Jet Question

[drfong]

Hello all, New to the forum. I searched around and couldn't find the answer so I figured I just ask. New to V-max bikes. Bike has been running poorly, needed a little choke to run. I figured gumed carbs and pulled them to clean. Float heights were all over the place and mixture screws also. They were a bit gumed up but not much. Every thing clean and set the floats using the bench method posted. As I was puting them back together I noticed the main jets were 170's. The bike has a stock airbox, air filter and I believe exhaust is stock.
First question: is there anyway it should have 170 mains? It seems like that is too much of a change from stock for what I believe is a stock bike.

Second the needles are set to the fourth clip position (from the point end) 3rd from the top. They look like they are probably stock needles but I can't find any markings on them.

Third, where would be a good place to set the mixture screws to start. They seemed to be about 2 1/4 turns out on average.

Fourth, the air jet under the diaphram looks like they are maybe 120's? very hard to read even with a magnifing glass.
Any insight appreciated

 

[veebooster]

Stock mains are 152.5 mikuni, paj2 under the diaphragm should be 170's. Unless you have a full header and stage 7 you shouldn't be near 170 on the mains.

Dale#2592

 

[MaxMidnight]

Have a butchers here

 

[Rhoy Carter]

The early model venture carbs were 34 mm carbs and all the vmax's has 35 mm carbs

 

[drfong]

I guess it's possible that whoever got into these before mixed up the main and paj2 jets but the numbers on the paj2 jets look like about 120, so I'm sure they would be way too small for mains.

I think the paj1 jet is on the venturi air box side. They are all 90's so I assume they are correct. I guess I'll pull all the 170's out of the mains and if they are the same jet as the paj2 jets I'll put them there and get stock main jets to start. Also the chart list 150 in 2 cyl and 152.5 in the other two. Should they be split or use all 4 152.5's?

Thanks again

 

[drfong]

Update, I pulled the main and paj2 jet out of one carb. Looking very closely trough a magnifing glass it looks like the PAJ2 jet is a 170. It is also larger than the 170 jet that was the main. A .069" pin gauge fits through the PAJ2 170 jet but does not go through the 170 Main jet. Also the PAJ2 jet has a small mark i can't identify and a small square inside a square mark. The main has no marking except the 170 number, maybe an aftermarket jet? Odd that they are both 170's yet different sizes. Do air jets and fuel jets have different sizes for the same number? Now I'm not sure what to do since it looks like the PAJ2 jets are 170's so I don't think they were just swaped.

I'm going to check all the PAJ2 jets and make sure they are the same size, if so I guess I'll leave then and order stck mains. If anyone has any thoughts I'd appreciate them.
Gary

 

[gamorg02]

i think paj2 is supposed to be a 170 stock. a 170 dynojet main might be closer to i believe a 160 mukini, so still not great but not that far off.. sorry i can't be more help. some pics with a high -res camera might not hurt?

 

[drfong]

Thanks, it may be a dynojet 170 main. All my PAJ2 are the same size with the same markings.

 

[drfong]

OK, I reinstalled the carbs and sync'd them and set the pilot screws as dirrected in the sticky thread. Test riding and it runs good down low but stumbled above 5000rpm. It pulls through but misses. I did the test from the carb tune sticky thread. Here are the results:
Test 1, 4k in 5th gear then WOT. Result Bike reacted quickly but sputters above 5k all the way to 9k rpm.
Test 2, didn't do because bike was already warmed up.
Test 3 3rd gear from 3K rpm. Result Bike pulls but starts sputtering about 5K through 9K
Test 4 Cruise at 5K rpm Result Bike holds 5K rpm easily

Based on these test I read this to mean it didn't have enough needle. I assumed it meant the needle needed to be raised. I raised the needles 2 clip positions (from fourth from the point to second from the point) The bike seems to run worse sputtering even more.
Obviously I need to atleast move the needle back if not the other direction, but I guess I need some clarification on what is meant by too much or too little needle.

Here also is everything I know about the bike.

K&N air filter, cobra exhaust (I didn't know what type of exhaust when I originally posted) 170 Main jets of unknow brand. They are smaller than the 170 Mikuni PAJ2 jets. The needles have no markings. The pilot screws are set at 2 turns out.

 

[maleko89]

I'm guessing they are DJ170's which is pig rich. Put Mikuni 145's in there and also stock needles.

 

[Kratos]

OK, I reinstalled the carbs and sync'd them and set the pilot screws as dirrected in the sticky thread. Test riding and it runs good down low but stumbled above 5000rpm. It pulls through but misses. I did the test from the carb tune sticky thread. Here are the results:
Test 1, 4k in 5th gear then WOT. Result Bike reacted quickly but sputters above 5k all the way to 9k rpm.
Test 2, didn't do because bike was already warmed up.
Test 3 3rd gear from 3K rpm. Result Bike pulls but starts sputtering about 5K through 9K
Test 4 Cruise at 5K rpm Result Bike holds 5K rpm easily

Based on these test I read this to mean it didn't have enough needle. I assumed it meant the needle needed to be raised. I raised the needles 2 clip positions (from fourth from the point to second from the point) The bike seems to run worse sputtering even more.
Obviously I need to atleast move the needle back if not the other direction, but I guess I need some clarification on what is meant by too much or too little needle.

Here also is everything I know about the bike.

K&N air filter, cobra exhaust (I didn't know what type of exhaust when I originally posted) 170 Main jets of unknow brand. They are smaller than the 170 Mikuni PAJ2 jets. The needles have no markings. The pilot screws are set at 2 turns out.

In my experience so far, it has been difficult to determine by sound/feel alone whether it is a lean or rich problem. I have noticed that a lean condition causes it to sound like a popping/cracking, while a rich condition makes it sputter and feel sluggish/boggy. So in your case, you probably should have lowered the needles as your test.

The rpm you are describing would point more to the main jets, I believe. As Maleko said, yours are way rich. There is probably a bit of overlap from the needles with what you are seeing, but you need to get your main jets dialed in before troubleshooting the rest of the circuits. I'm not sure where to tell you to start on main jet size as I have not dealt with the cobra slip-ons, but I think the are similar to the Supertrapps but don't flow quite as well. So you would probably be OK with trying the stock main jets, or maybe even one size smaller as a starting point.

If your needles are adjustable, then they are not stock, you need to determine if they are stage 1 or stage 7 needles. Since you just have the slip-ons, your best bet might be to get ahold of a set of stock needles and maybe some washers to shim if needed.

 

[drfong]

Thanks for the advice guys. I have been thinking the jets must be too large for it to run as it does at higher rpm where the needle should be "out of the way". I just want to carify that even with the K&N and exhaust it should be leaner than stock? Were these things really fat from the factory?

Looking at the needles vs pictures on needle stick, I would say that someone installed a DJ stage one kit on the bike. That being said, they probably drilled the slide and changed the springs. Do you think that will be a problem going back to stock. Maybe I should just change the mains first?

 

[Kratos]

Thanks for the advice guys. I have been thinking the jets must be too large for it to run as it does at higher rpm where the needle should be "out of the way". I just want to carify that even with the K&N and exhaust it should be leaner than stock? Were these things really fat from the factory?

Looking at the needles vs pictures on needle stick, I would say that someone installed a DJ stage one kit on the bike. That being said, they probably drilled the slide and changed the springs. Do you think that will be a problem going back to stock. Maybe I should just change the mains first?

You have basically what I had, except I had the Supertrapp slip-ons with 8 discs and open end caps. Not sure of the exact comparison between the Supertrapps and the cobras, but I was able to keep everything stock and just went down a size in main jets.

I'm not positive since I've haven't used a DJ stage 1 kit, but I believe the shorter springs and slide drilling is reserved for the stage 7 kit.

 

[drfong]

I looked up on Dynojets website and the instructions for both the stage 1 and stage 7 both include drilling the slide and changing the spring. There are several other steps that are stage 7 only. You have also confirmed going down on main size with the mods to your bike. I guess this just seems backwards to me. Better airfilter and flowing exhaust but smaller mains?
Also per the stage 1 instructions whoever installed the kit probably should have gone with DJ's 165 instead of the DJ170 Mains. Those would have been only slightly fatter than stock 152.5's. The 170's are just smaller than 160 mikuni's based on a comparison chart I found online. (I know the comparisons are estimates and not exact) But it sounds like less than stock is the way to go even with the mods.

Also if anyone has a set of stock needles laying around they aren't going to use, I'd be interested in them.

 

[maleko89]

The thing to keep in mind is that the K&N doesn't increase the air flow because the air box is so restrictive. You could completely remove the air filter and it would be the same as with it in place.

The general rule is increasing flow before the carbs (airbox, filter, etc) leans you out. Do the same to the carbs or after (vboost, valves, manifolds, exhaust) richens.

The problem is your Cobras are ultra restrictive which is why you are going way rich. Yeah, stock bikes are a bit rich from factory but only if you are 500 feet above sea level and above. Even with stock jetting your bike would be pretty damn rich. I would use Mikuni 147.5's at the most. 145's would be better. Larger PAJ2....say 175's or 177.5's would help your idle circuit too.

 

[Kratos]

I looked up on Dynojets website and the instructions for both the stage 1 and stage 7 both include drilling the slide and changing the spring. There are several other steps that are stage 7 only. You have also confirmed going down on main size with the mods to your bike. I guess this just seems backwards to me. Better airfilter and flowing exhaust but smaller mains?
Also per the stage 1 instructions whoever installed the kit probably should have gone with DJ's 165 instead of the DJ170 Mains. Those would have been only slightly fatter than stock 152.5's. The 170's are just smaller than 160 mikuni's based on a comparison chart I found online. (I know the comparisons are estimates and not exact) But it sounds like less than stock is the way to go even with the mods.

Also if anyone has a set of stock needles laying around they aren't going to use, I'd be interested in them.

I now have Mark's 4-2 headers with LOR 13" mufflers and Sean Morley's jet kit. I actually went down further to the 147.5 mains to get me where I needed to be at WOT above 6K rpm. So yes, it seems odd that you would need to decrease main jet size to increase performance. The thing to remember is that it is all about the proper air/fuel mixture, NOT bigger jets = more power. The best thing you can do is get it on a dyno, or get an air/fuel ratio meter so you can see exactly where you are with each change you make. Trying to diagnose carb issues by sound/feel can be very tricky unless you have a lot of experience. I finally broke down and bought an Innovate Motorsports A/F gauge kit because I was tired of spending so much time chasing issues without having any real data or the experience needed to make the correct adjustments.

In your case, if you plan to make any changes later on, it might be best to buy an A/F kit so you don't have to take it to a dyno to get tuned now, then take it back later if/when you make any changes.

 

[drfong]

Thanks guys, very informative.

 

[tugla]

I got a total stock set up in the carb and cobra's and big runs smooth, strong(for cobras) no issues anywhere in the power band. sounds like gotta chg carb set up or exhaust. a set of marks will really make you happy along with a morley kitunk:

 

[drfong]

I finally got back to the Vmax. I ordered some 145, 147.5 and 150 jets. I installed the 147.5's. I was too worried about going too lean to put the 145's in first. I reset the stage one needles to the fourth grove from the point, re-adjusted the pilot screws (they ended up at 1.5out) and re-synced the carbs. Took it out for a ride and man is it fast. It pulls hard all the way to redline with no hesitation or problems. I have not had time to run it much under multi conditions to see what fine tuning it may take, but man is it running pretty good as is. Thank you to everyone for the advice!

 

[gamorg02]

No surging @ cruise or accel or popping on decel? Then keep running it!

Glad its running great

I finally got back to the Vmax. I ordered some 145, 147.5 and 150 jets. I installed the 147.5's. I was too worried about going too lean to put the 145's in first. I reset the stage one needles to the fourth grove from the point, re-adjusted the pilot screws (they ended up at 1.5out) and re-synced the carbs. Took it out for a ride and man is it fast. It pulls hard all the way to redline with no hesitation or problems. I have not had time to run it much under multi conditions to see what fine tuning it may take, but man is it running pretty good as is. Thank you to everyone for the advice!