Bog/stall at high rpm followed by no start w/o choke

[thebigrooster]

History: 1999 blaster,
aftermarket cpw 28mm carb
came with 200 main jet, 35 pilot, 5j21 needle on 2nd from top
full fmf pc2 & fatty gold series pipe
Uni air filter

Current problems

I had a 260 main jet in it, clip on 2nd from top. Sputtered all through the throttle range. Popped off airbox cover, pulled like a raped ape. This is when it ran best. Knew I should be a little lean at that point.

Today I put in a 280 and drop the needle to middle clip, using this logic.

230 stock
+1 32:1
+2 air box lid off
+3 fmf full exhaust
+1 cold weather
300 should be what i use, but i only had 280.

280 ran bad. couldnt even get on pipe, sputtered.

pulled plug, had a little wet oil on it.

inserted 270

Ran good as long as i stayed on pipe. sputter/miss throughout most ranges except 3/4+ --

However, i probably close to being on the pipe for 2-3 minutes, then all of a sudden it dies like nothings there. I shift down to try and get it to rev back up, and it has nothing. incresing throttle only changes exhaust note.

try to start, nothing. push it to the garage, let it sit for 5 minutes, try again, fires up like nothing is wrong. take it out, as soon as i get on the pipe, it does the same thing 'boooooooogggg' even as i shifted down, no missing, backfiring, random fires. Just shuts down. No restart.

Any ideas?

 

[blasterdemon7]

You need to do a leak down test then a plug chop. Also check carb float and fuel flow from tank.

 

[Larry's Shee]

While leak testing push on carb boot. While carb is off, clean it well, not just quick douche with spray can. Take everything apart.

 

[thebigrooster]

I have gone through carb meticulously, and im buying the plug to leak down today. I just don't understand how I can be riding it around at wot on the pipe, running strong, then it goes down in revs a bit, then loses everything.

 

[thebigrooster]

Update:

Took off carb boot, checked reeds. Looked flat and in decent condition, no cracks or anything. Put it all back together, leak test. Holds 5 pounds for ~ 1 hour. Later realized It was supposed to be tested at 7psi so I tested there for the 5 minutes and it held fine.

Also tore down the carb, even choke assembly this time. Carb is very clean. Aside from the gas smell you could eat off it. I put a 250 mj in it. It ran noticeably better then the 270. Had someone else ride it and keep it on the pipe, and there was a light plume of smoke on the pipe. Dropped down to a 230, cloud dissapeared and it ran like a raped ape again (how it was when I first got it, and it was jetted at 200. O.O )

So I have premix 50:1 amsoil, it was 55 yesterday, full fmf, no airbox lid, and it stops rich smoke and stutter at wot at a 230 mj? This makes no sense. I am going to plug chop but I figure I can get in the realm before I start destroying plugs.

Anyone have any clue as to whats going on?

One question about plug chopping I have is that until my spark plug is snugged, it has a little play in the threads. I didnt see any leaking there, but it seems to me pulling out a plug while the engine is hot is a bad idea as far as the threads on the head are concerned.

 

[wwholden]

Sounds like a plugged fuel system or improper float level. Check the float level and then blow out the fuel line to the tank. Check the needle and seat to make sure theres nothing plugging the passage ways. Make sure its flwoing plenty of gas. Dont worry about the spark plug threads when you go to remove the plug while the engines hot. As long as your loosening and not tightening it up more youll be fine.

 

[Blaaster]

For your motor to be running a #230 main, the needle on the second from top clip, there must be a float problem, either maladjusted, sticking or heavy.

Is the O ring on the fuel enrichment plunger (choke) in good condition?

 

[Awk08]

hows the fuel flow to the carb ?

pull the petcock and check the screens

how's the vent in the fuel cap ??
it has a one way valve in there that if sticking will cause the fuel tank to vapor lock, the vent line must be open also

 

[thebigrooster]

I think i worded the last portion of my last post badly.

I put in the 230 main jet yesterday. Second clip from top on the needle. Air screw backed out waaaay to far (again, I'm just trying to get an idea of where it will run right at, i know pilot should be at least 32.5)

At those settings, it had some sputter in the mid range but on top was great. We rode it around for probably 30 minutes yesterday. It did bog on me once as it was getting on the pipe, i let the rpms drop and drove about 1000 feet and then it was fine all over again. At 250, it was smoking at wot. I know my pilot is rich, if I lean out the pilot would that require a richer main jet? It just seems to me the jump from 230-~290 is a huge jump for the pilot needing to go down to 32.5. I have seen fuel trickle out pretty steadily from the petcock on several occasions. I will dissassemble the petcock and double check the gas cap as well.

 

[Blaaster]

Pilot has no effect on the main.

All the symptoms point to an excess of fuel.

Make sure the float is set at the correct height and the carb is not in any way flooding.