400 carb
#1
12-05-2002, 09:28 PM
400 carb
Modquad,bubba or someone,
What gains will i get if i put a Scrammy 400 carb on my modded Trailblazer? Will i have to rejet the 400 carb? What else if anything will i have to do to the carb or is it a direct fit? Is it even worth the hassle to do it? I am running a 160 main jet on the stock 30mm carb. I dont know what the pilot jet is. I think the main jet on the 400 is 230. Not sure! Is that to big?
What gains will i get if i put a Scrammy 400 carb on my modded Trailblazer? Will i have to rejet the 400 carb? What else if anything will i have to do to the carb or is it a direct fit? Is it even worth the hassle to do it? I am running a 160 main jet on the stock 30mm carb. I dont know what the pilot jet is. I think the main jet on the 400 is 230. Not sure! Is that to big?
#2
12-05-2002, 10:15 PM
400 carb
Odds are, you'll have to rejet. The carb HPD sells for the mod 250 is a 35mm, the stock 400 is a 34mm. You won't have quite the throttle response as you would if you stepped up to the flatslide 35mm, but you should see more power. You can always install a UFO, on the bottom of the roundslide, they do help. I think Hot Seat still sells them. If not, I have a bored out 34mm with a UFO already installed I'd sell. Read those plugs.
Ken
Ken
#5
12-06-2002, 08:25 AM
400 carb
2manytoys,
Start with a 200 main jet on your 34mm carb. If you want to go to a UFO you will have to go to a 210. For pilot jets, start at a 40 without a UFO and 20 with a UFO. Use the 0-4 needle jet from your 30mm carb (the brass thing that the needle goes in) and the jet needle from the 34mm carb. This should get you close.
If you choose to go with the UFO, remember to half the pilot jet size and go up one on the main as a starting point.
Like Ken said, The UFO (Ultimate Flow Optimizer) is a little piece of plastic that fits into the bottom of a round slide carburator. It is designed to smooth out the airflow in much the same manner as a flat (Mikuni) or "D" (Keihin) slide carb does. Because it smoothes the airflow so much, you have to use a half sized pilot jet because it would siphon up too much fuel and choke the motor out if you used a regular sized one. Hey, in my opinion it's worth the $35 bucks you spend for it.
Before the UFO/ 34mm carb conversion the Trailblazer could never lift the front wheels off the ground (even with the RCR pipe, silencer and spring) Now it will with a little coaxing. I think you'll find it a worthwhile improvement.
Start with a 200 main jet on your 34mm carb. If you want to go to a UFO you will have to go to a 210. For pilot jets, start at a 40 without a UFO and 20 with a UFO. Use the 0-4 needle jet from your 30mm carb (the brass thing that the needle goes in) and the jet needle from the 34mm carb. This should get you close.
If you choose to go with the UFO, remember to half the pilot jet size and go up one on the main as a starting point.
Like Ken said, The UFO (Ultimate Flow Optimizer) is a little piece of plastic that fits into the bottom of a round slide carburator. It is designed to smooth out the airflow in much the same manner as a flat (Mikuni) or "D" (Keihin) slide carb does. Because it smoothes the airflow so much, you have to use a half sized pilot jet because it would siphon up too much fuel and choke the motor out if you used a regular sized one. Hey, in my opinion it's worth the $35 bucks you spend for it.
Before the UFO/ 34mm carb conversion the Trailblazer could never lift the front wheels off the ground (even with the RCR pipe, silencer and spring) Now it will with a little coaxing. I think you'll find it a worthwhile improvement.
#6
12-06-2002, 11:43 AM
400 carb
Hey 2manytoys,
I was just about ready to UPS the carb and saw this post of yours.
Well, I thought I would check it out before I
shipped it. Let me tell you, its a very tight fit into the 250's rubber
intake manifold. I had to heat it up before I could get the 34mm carb
to fit. So, with all of the jetting changes, checking and rechecking of the
plug and jets, might this cause some tearing to the rubber intake boot?
For you guys who have done this before. Is this the way to go or is there
another boot that will work better?
I was just about ready to UPS the carb and saw this post of yours.
is it a direct fit?
shipped it. Let me tell you, its a very tight fit into the 250's rubber
intake manifold. I had to heat it up before I could get the 34mm carb
to fit. So, with all of the jetting changes, checking and rechecking of the
plug and jets, might this cause some tearing to the rubber intake boot?
For you guys who have done this before. Is this the way to go or is there
another boot that will work better?
#7
12-06-2002, 06:24 PM
400 carb
talonhawk,
It really isn't that much of a stretch. If you have some problems getting it on, use the old rubber lubricant standby, dish soap. It works like a charm. I had mine on and off many times and never had a cracked boot. Also mine is an older model (1997). The only problem that MIGHT present itself is the brass fitting that mounts the choke plunger to the carb. For some reason it is different sized from the 30mm carb to the 34mm carb. Make sure you send that brass fitting with the carb. I re threaded mine with a 1/8" NPT but it is best to use the original if you can find it.
It really isn't that much of a stretch. If you have some problems getting it on, use the old rubber lubricant standby, dish soap. It works like a charm. I had mine on and off many times and never had a cracked boot. Also mine is an older model (1997). The only problem that MIGHT present itself is the brass fitting that mounts the choke plunger to the carb. For some reason it is different sized from the 30mm carb to the 34mm carb. Make sure you send that brass fitting with the carb. I re threaded mine with a 1/8" NPT but it is best to use the original if you can find it.
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#8
12-06-2002, 06:53 PM
#9
12-06-2002, 10:15 PM
#10
12-07-2002, 07:28 AM
400 carb
2manytoys,
You should experience an all around power increase. Those wheelies weren't accomplished by using the top end power, but mostly low end power. We all should know that larger carbs will give you a bigger top end boost, but I was surprised how much low end it has.
BTW, cold weather starting hasn't suffered in the least. My fiancee's Trailblazer had sat for several months without running. Then when I sold my Sport, I had to move it to get to the Sport out of the trailer. It started up quite nicely. I've been running the Trailblazer for two years with this set up and I'm still on the stock bore.
You should experience an all around power increase. Those wheelies weren't accomplished by using the top end power, but mostly low end power. We all should know that larger carbs will give you a bigger top end boost, but I was surprised how much low end it has.
BTW, cold weather starting hasn't suffered in the least. My fiancee's Trailblazer had sat for several months without running. Then when I sold my Sport, I had to move it to get to the Sport out of the trailer. It started up quite nicely. I've been running the Trailblazer for two years with this set up and I'm still on the stock bore.