My What Am I Getting Myself Into Combat Build Thread

TomU said:
With the wideband i can log the AFR. Don't have a dyno or tach input so it won't be very accurate IRT AFR vs load, but it's probably better than guessing.

Nobody's won the prize yet on what's wrong with the picture
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I'll just say you get do it again......:D
 
Won't be able to get your wideband sensors on with the bungs pointed to the frame?

You are sort of wasting your time without a dyno readout. The Sudco jetting is close enough.

I get the desire to try stuff. I am very guilty of it.
 
Ding ding. Greg wins the prize The exhaust nut is on the wrong side of the bung. Arrggghh :mad:. I was stoked when i got home until i noticed that little problem. I probably should have taken it back, but the shop is like an hour away and i really didn't feel like investing another couple of hours and probably another $80 for them to fix it. My alternate plan is to grind down the bung so the nut fits over it. Will need to take off about 1/16" on the top and another 1/16" on the sides.

And yes Greg, you put a spell on me ;)
 
TomU said:
Ding ding. Greg wins the prize The exhaust nut is on the wrong side of the bung. Arrggghh :mad:. I was stoked when i got home until i noticed that little problem. I probably should have taken it back, but the shop is like an hour away and i really didn't feel like investing another couple of hours and probably another $80 for them to fix it. My alternate plan is to grind down the bung so the nut fits over it. Will need to take off about 1/16" on the top and another 1/16" on the sides.

And yes Greg, you put a spell on me ;)
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That was too obvious and estuaryboy said the roses had fallen, which is the same thing as an exhaust nuts being in the wrong location. :)
 
You're right (i was reading his post wrong). Sorry Greg

And it's my opinion the Sudco jetting sucks. Their main jets are too big and their air jet is way too big (2.0). Of course, can't confirm that without AFR readings ;)
 
That's fricken hilarious. It'd be even funnier if the grinder wasn't in arms reach.

But no, he doesn't work with motorcycle exhausts and didn't know any better and i didn't think to tell him, so my fault
 
TomU said:
You're right (i was reading his post wrong). Sorry Greg

And it's my opinion the Sudco jetting sucks. Their main jets are too big and their air jet is way too big (2.0). Of course, can't confirm that without AFR readings ;)
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OK then

Does your wideband whatever you have setup chart AFR readings along with RPM so you have a reasonable idea about what jetting needs changing? Without the RPM info you are just relying on your seat of the pants dyno. That's all I use myself.

Have you ridden a Combat (2S) cammed 750 Norton with a 34mm twin Mikuni carburetion setup on it? I have and Sudco jetting is close enough unless always riding around in town short shifting between stop lights. The kits are for race use, so to get the most out of them on the street one does have to ride over 50mph in 4th, and hold gears a little longer. Otherwise the plugs will show rich, and I would imagine a wideband would as well. Now if the goal is to tune for slower short shift riding, then it is probably true that the jetting is wrong.

When you get done with the AFR numbers chase and change jets only to discover that the top end is weak, you might want to put the 230 mains back in.

This is the MAP kit I took off when I installed the 35mm FCR pumpers. My MAP Mikuni kit intake manifolds are modified for spigot mount on an Atlas oriented 750 engine, so they look different. I had a 2S cam in the motor, shaved head, Commando flat top pistons, and 2 into 1 exhaust. Head has 31mm intake openings and is ported. Jetting is as the carburetors came. I never did try a smaller air jet. I did try a bigger one and that was a bad idea. So the 2.0 may have also been on the big side. It did work though. I did try a bunch of main jet sizes, but the 230 was the best on my seat of pants dyno. Reason for trying different main jets was the 2 into 1 exhaust was terrible until I made it longer gutted it and put a SuperTrapp setup on the end. I have since removed the SuperTrapp disc setup and made my own full length baffle for the megaphone and I'm making more power sooner. Also quieter.

Sorry about the side track. Just trying to pass some experience with those carburetors on a Combat type engine.

My What Am I Getting Myself Into Combat Build Thread
 
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I have twin 32s not 34s and they came with 250 main jets, 35 pilot jets, 2.0 air jets and a P0 needle jet with the needle set at the P4 position. With no real experience with these settings, I changed to 230 mains, 30 pilots, 1.2 air, P2 needles and set the needle clip at P3 (in the middle).

Measuring AFRs is a lot different with carbs than fuel injection. The carbs are tuned with all the different jets which are affected by different throttle positions more so than RPM. FI is basically mapped to RPM. I am really only looking for abnormal readings more so than "dialing in" the carbs. Am i overly rich or lean at any give throttle position.

And i appreciate any help i can get
 
TomU said:
I have twin 32s not 34s and they came with 250 main jets, 35 pilot jets, 2.0 air jets and a P0 needle jet with the needle set at the P4 position. With no real experience with these settings, I changed to 230 mains, 30 pilots, 1.2 air, P2 needles and set the needle clip at P3 (in the middle).

Measuring AFRs is a lot different with carbs than fuel injection. The carbs are tuned with all the different jets which are affected by different throttle positions more so than RPM. FI is basically mapped to RPM. I am really only looking for abnormal readings more so than "dialing in" the carbs. Am i overly rich or lean at any give throttle position.

And i appreciate any help i can get
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My bad. I thought you had the same parts in your carburetor set that are in mine. Those jets that came with the carburetor set you have would be rich for 32mm. Good catch. The changes you made should get you in the ballpark, or be on the money. I had the 2.0 air and P0 needle jet with the 6DH3 needles in mine. The rest is the same as the changes you made. My needle jets are numbered differently, but somebody hand scribed P0 on the pair of needle jets I do have in the carburetors. Always thought that was odd.

I don't think you need help, or my unsolicited advice. You are doing the job right. Keeping it clean like you have done all along is going to pay off in the end.
 
Shelby-Right said:
You mig welded straight onto the chrome , and there is barely any heat affected zone . :)
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Yeah, i didn't weld it. If i did, the exhaust nut would be on the right side of the bung ;). The guy i took it too mostly does TIG welded custom car exhausts and intakes.
 
Schwany said:
I don't think you need help, or my unsolicited advice. You are doing the job right. Keeping it clean like you have done all along is going to pay off in the end.
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I can use all the help i can get. Thankfully Greg Marsh is only 7 miles away :)
 
TomU said:
...and the headsteady. Want to go with a CNW headsteady, but Matt's been out of stock for like the last 18 months :(
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Holland Norton Works have them in stock. by the looks
Your build and cycle have come together nicely 👍
HNW are great to deal with ...
 

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