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Discussion Starter #1
My cousin got an 87 250R yesterday and I'm working on it for him. The engine is in great shape and has 182psi at 200' ASL, reeds are great, no leaks, etc. It also has a Pro Circuit exh., K&N with outerwear and no airbox lid, and what was supposed to be the stock carb.

The floats were so far off that it was pouring gas out of the needle slide (or whatever it is at the bottom of the inside of the carb), so we fixed that. Then, we cranked it up and it idled rough for a bit and died. Plug was wet, fixed that, cranked it and let it idle until it died. Got about 30 more seconds this time. Wet plug. Repeat. Got a good 3-4 minutes this time. So I get on it and drive it down the driveway and get about 100' and it dies. No response to different throttle positions, no ting ting, just sounded like I killed the ignition.

We push it back and the plug was dry, so we choked it and it fired it up after 5-6 kicks. Tried it again and got the same thing, so I double checked the floats and they were perfect. We ran out of sunlight and decided to call it a night, but I couldn't stand it and went back out and started working on it about 1100. I pulled the carb out and noticed that the carb boot had a bigger boot around it. I pulled it off and there was a smaller white tube (looks like it came off of a clorox bottle) inside that. I measured the carb and got 39.2mm. Then, I checked the main and it was 152, and the needle was in the second from the top ring.

Mother..... . well, I'm pretty sure that the pilot is Honda factory as well, so I'm going to have to rejet completely.

What do you recommend I start with? Again, my mods are:

-Pro circuit exhaust
-KN, no airbox lid
-Potentially a very mild port or port cleanup
-39mm carb:ChairBash:

Lastly, what RPM range will a PC exhaust make power in? Thanks in advance guys.
 

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Discussion Starter #2
Slight update.

Floats were set to 16.02mm per calipers and the float valve is perfectly surfaced. It seals off very, very well with the bowl off and the floats pushed up. I installed the carb back on the quad, but it still has a bit of trouble getting fuel to the engine after 1-2min of very light riding. After it sputters, it dies and gas pours out of the overflow tubes.

I consulted a lifelong friend/professional Honda mechanic and he's going to take control of the carb situation because the owner of the bike is a friend of his as well. He's called the 2-stroke wizard amongst his colleagues, so I'm glad that it isn't my problem anymore.

The pilot jet was completely clogged with some gunk that I couldn't dislodge with the flat end of a drill bit (not in the drill btw), so I soaked it in carb cleaner for 6-8 hours and it came out with a piece of wire. Good to go now.

Next, we need to fabricate the airbox lid.

After talking to him, we decided to start with 170 main, 52 pilot, and whatever needle that he says he has stashed away.

Thoughts?
 

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Discussion Starter #3
Update:

After cleaning the carb several times, I'd had enough. I fabricated a little cage out of some old chicken wire and put the carb in it. Then, I screwed the chicken wire into a drill (360rpm) and submerged the carb in gas and let it rip. after a few seconds, I flipped it in reverse and held it before switching it back to forward. I repeated this process for a good 5 minutes. I then let the carb sit in the gas overnight and then started at it again. That afternoon, I did it one more time and then cleaned it. I have no clue where all of the gunk came from, but holy shit did it appear. It looked like a tablespoon of garbage sitting in the bottom of the gas after I pulled the carb out. I gave it a final cleaning and set the float height again and set it to the side.

I received a call from a good friend/250R guru that recommended a 185 starting point for the jetting, but a 175 would probably be the final choice. I took the carb out and removed the 170. I put the carb on the table and leaned over to get the box of jets. While reaching for the jets, I slipped off of my seat and grabbed the table without thinking. Off comes a load of tools and other stuff, to include the carb. It hit the floor right on the floats, so I cleaned it AGAIN. Upon reassembly, I noticed that the float valve seat looked odd. Through the magnifying glass, it was very evident that someone had tried to "re-seat" the seat and had screwed it up. There were gouges that look like the drill just caught the material and dug in, but there looked like no repairs were attempted after that.

I attacked the 2 high spots with my carbides and leveled them. Then, I took the carb to my grandfather's shop. I mounted the carb to the drill press and went to work as slowly as possible. Then, added fine grade valve grinding compound to the seat and threw the drill in reverse. Down into the seat with the bit, 30 seconds later, bam. I re-assembled the carb and it held gas like a champ.

In the midst of all of this, my cousin was convinced that the carb was trash (which it was to start with), so he ordered a pre-jetted 36mm Keihin from Duncan Racing, along with a 22cc dome, UNI filter, 1mm head gasket, and a base gasket. When we received the carb, we installed it immediately. No float issues, instant snap with low throttle positions, great stuff. We drove down the driveway an it started to miss AGAIN. We tore the bike down and found that the stator wires were dangling by 2 strands on the hot side and 1 thread on the ground side. We fixed that and also went over every point on the quad. We removed paint, added new fittings, new bolts, replaced a few wires altogether, and reassembled the quad.

Down the driveway we go. It pulls like a monster and spins in 3rd without hesitation.

However, 4-6th now slip the clutch. When the owner gets off of his ass and orders new plates, discs, and springs, we can change the clutch. When the clutch is out, we'll also switch the head for the PT/DRI head and 22cc dome. At that time, we'll see if the engine is ported and what bore it's on.

*side note: we assumed a 67.5mm bore and port clean up when talking to Duncan. So far, their pilot, screw, and needle selections have been perfect. Definitely give Duncan a consideration if you're in the market for a new carb and want a very good starting point on jetting. We were only charged $240 for the carb even though the site lists $250. The carb normally goes for around $190-$210 everywhere else. Another $30-$50 isn't too bad of a price to get a carb that's jetted as accurately as ours was.*
 
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