Need jetting vs running issues suggestions

[db]

I need a idea of which direction to go with this.

Supposed 380 with cut airbox lid, dual layer foam filter, DG pipe.

Under full throttle, I get a power on/off/on/off type bucking.

Under decel, I get a backfire.

It came with:

Main 155
Pilot 42.4

Thanks.

 

[Guest]

damn a 155 is a pretty big main...check your needle and it kinda sounds like it cud be an electrical prob but most likely not...rich the needle maube and see what that gwets ya...id do a plug chop first b4 anything plugs will tell you almost everything u need to know...

 

[jasonp]

I need a idea of which direction to go with this.

Supposed 380 with cut airbox lid, dual layer foam filter, DG pipe.

Under full throttle, I get a power on/off/on/off type bucking.

Under decel, I get a backfire.

It came with:

Main 155
Pilot 42.4

Thanks.

I would go leaner on the main and out on the fuel screw or bigger pilot, if all other things are in correct working order.

 

[ratchracing]

Did it bog out like this before you changed the timing as stated in your other thread?

 

[Guest]

try a 150 main maybe and play around with your fuel screw see what you get...plug chop will tell you if your lean or rich if your still stumped

 

[db]

Did it bog out like this before you changed the timing as stated in your other thread?

That I don't know. When I bought it, it had a really loud engine tick. I rode it about a mile (felt really down on power) then parked it to figure out the engine tick. Found the intake valve backed way out, and discovered the timing issue when doing that. So I fixed both at the same time.

At this point with the intake valve not fully opening it was running pig rich (per the solid black plug)

After I got it all put back together and started it, at first it wanted to die whenever I pushed the throttle and one I could push the throttle without it dieing, it would backfire alot. After letting it a minute or so that all cleared up. Then around 10 minutes later when I took it for a ride, it started and idled fine, but I had this issue.

I am guessing that I am lean on the top end as the plug is pretty light after taking this last quick run (the same mile run as before). It pulls really well through the gears until I hit wide open.

I am going to stop at the bike shop tomorrow and pick up a few jets.

 

[db]

Well, I stepped up to a 160 main and the plug is now on the slightly rich side instead of slightly lean side.

I did may attention a little more on this ride. It almost seems that I may be hitting a rev limiter?? I can run wide open for a couple seconds with it being fine, then it does it's stuttering.

 

[jasonp]

when I have my jetting spot on the plug doesn't really change color. Just what I've found with the way my setup works.
Yup your rich on the main jet. As the rpm's start to pickup when have the throttle pinned then you find that the richer you get the more the engine will studder or have that rev limiter effect at a lower rpm. Going lean you basically want to get to the point where you lean the engine down until that goes away. Each time you change the jet leaner you will feel a little more power and then finally you will feel a little more hit in the power band when you are right on.

 

[jasonp]

if you go down to much on the main then the engine will bog.

 

[db]

Thanks for the info.

What I am confused on though, is that the plug was on the leaner side with a 155, and on the richer side with a 160, but it's doing the same thing.

I did not check to see where the needle was clipped at. If that is incorrect, could that be a cause of this?

Since I plan to take it out this weekend, I'll leave it as is on the richer side, then next week pull the carb back off and go through everything and reset it to stock (I need to buy a stock jet for it) and see where it is at.

 

[griff]

Hmmm, I would seriously consider triple checking that cam timing.

If its off a tooth, it will still run, but you'll never get the jetting right.

On this engine, a tall-tale sign of cam timing being off is having to go richer and richer on the main to try and get it to run.

I cant remember for sure on this engine, but I think the timing chain can be off 1 tooth (half a tooth) off every other 360* to TDC. I've seen this on several Yamaha and Suzuki engines before, my old GSX-R and Bandit are exactly like that.

On some engines, for example - If you line up the TDC mark at the end of the crank, the chain and cam timing mark arent exactly lined up, VERY close though, theyre just slightly off (the infamous half-a-tooth mistake). Pull the cam, and rotate the crank one turn back to the TDC mark on the crank again, and the chain and cam timing mark are perfectly lined up.

I've seen this quite a few times - guys swear the cam timing is OK, only to find out it was off a tooth when it wouldnt jet worth ****. Hell, I've done that myself before on an engine I've torn apart a dozen times.