I am starting to think that I should have just left my 300 stock, and bought a bigger bike that already had more power.I started out getting it quite cheap so I figured a few mods and it would have enough power to satisfy me.Anyway when I bought it, it was bone stock. First I removed the cylinder and rebored it to .010 over to freshen it up. I figured while it was apart I should clean the ports up a bit too.I cleaned up the intake and transfers and then I widened the ex. by about 3mm.Basically I just radiused the sidewalls of the ex. port. Then I polished the ex. too.While the head was off I figured I might as well shave it .035 too to up the comp. a bit. I put it all back together and it seemed to work a little better.I was happy for about a week. I needed more.I then did the airbox mod of cutting the downpipe and getting a Uni-filter too.It seemed to give it better throttle response.Then I started reading how going to a bigger carb will give it more power too.I got a new 34mm scram.carb off a firend of mine who took it off his bike the day he bought it.I put it on my bike.It seemed to give it more mid and top end at the expense of a little bit of bottom end.Then I figured I could get some of the bottom end back by adding a UFO to the carb.I added the UFO and after a frustrating week or so I finally got it jetted where it seemed to run quite well.It really helped the throttle response and lowend power too.I have run them on 2 different snowmobiles in the past so they weren't that hard for me to get dialed in. I still needed more.By the way I tried various clutch springs during this whole process and I like the white with a 1/4 shim under it the best.( Can't afford any more calls to Rick for clutching advice)

Then I figured I would do the big jump and order a pipe from RCR.Well My first impressions were quite good but the more I try to tune it the worse it seems to get.The bike kinda runs like it has an on-off switch for a throtthe now.It is either all or nothing.I am having an almost impossible time getting it to stop detonating at 1/8 throttle too. I have tried ign. timing, richening up the jetting and It still will detonate at 1/8 but not all the time.My egt guage shows it is not running lean but the detonation can't be jetted out. I even doubled up an the headgasket thinking I shaved too much off the head.It helped a bit but not anough to eliminate it.The bike is so fussy to jet now I have to run the needle in the 2nd groove with a .020 shim onder it .If I take the shim out it is way too lean but if I raise the clip too the 3rd notch it is way too rich.
I have tired different float heigts too.The bike is getting harder to trailride because it is either lazy or "on the pipe"all the time now.
Also sometimes when it starts to detonate if I let off the throttle the bike seems to keep going like its leaning out cause its running out of gas.I even tried a new fuel filter too.Also replaced the crank seals too.

I am getting real tired of working on it more then my butt sits on it.I think it might be time to put all the stock parts back on it and sell the whole mess separetly. Bike included!!!

P.S. I am a licensed mechanic with my own small engine repair shop and I do this kind of stuff all day long for a living too.

 

sparkys,

Wow man, you are beginning to worry me. I just got my 34mmTMX carb today. My RCR pipe should be here by the end of the week. My frame is painted and started to put everything together. So far I have my front suspension on, motor is in place, tranny is in place and steering system is about ready to be installed.

I'm still wondering how to hook the new carb up. It is way to big to use the stock intake boot, besides it measures 30mm inside anyway. That would defeat the whole purpose of the bigger carb. I'm sure I'll get it figured out but still kind of clueless.

I sure hope mine don't turn out to be as finicky as yours.

I wouldn't give up on it thou. It could be a combination of everything to something really simple. From what you say you do for a living, you should be able to figure it out. That kind of stuff is a learning experience that I crave. I can't give up on something until I figure out what is going on. You strike me as being the same way.

 

Well Elroy, I do enjoy working on my bike but it is getting very frustrating.I think a lot of myproblems are from the carb. It is not designed for a 300 it is for a 400. I think the only way I might get it to run the way I want and eliminate all the detonation is to try some different needles in it.It needs more gas at 1/8 throtthe but not more anywhere else.The only way to change this is to change the needle.I know the UFO throws all the stock jetting right out the window too. But i don't think it is giving me the lean 1/8 throtthe thing.Also it is strange the way the bike will run on sometimes like its running out og gas. I've checked everything from carb vents to the tank vent to the crank seals too.I'm getting tired of thinking its working great and the next time I go out on it its either "rattling " at 1/8 throttle or its too rich and blubbers when I am crusing along.As I said before it seems like the more mods I do to this engine, the more finicky it gets. It ran perfect before I started to try to mod it. Might be time to try to stuff a twin in it. I always wanted a 500 indy sled motor in a bike.Theyre about 85hp stock!!!

 

Just a thought, Xplor was having a LOT of trouble with the jetting in his scrambler, It turned out the carb was vibrating and causing the fuel to foam. He has a raptor now, so he hangs out in the Yamaha forum now, but bend his ear, he may offer some help.

Also, I have heard that the UFO's can make tuning a real headache, I went to a 39 PWK on mine, rather than fool with the 35 Mikuni on my scrambler.
Elroy, I chamfered the inside on the stock slightly with a sharp knife, and use silicone grease ( It won't destroy the rubber like a petroleum grease will ) to get it to slide into the boot.

 

Well Elroy I think I might have cured it. I went out tonight and went all over it. I put a new vent line on the gas tank vent and ran it down the steering stem the way its supposed to be.The old one broke off and was sitting under the plastic that covers the tank.I also put new vent lines on the carb and made sure they weren't getting blocked off in anyway. I also raised the float heigth about 2mm.Also I put a new highflow fuel filter on it. I took it for a short ride because its raining. It seems alright now.No detonation that I could hear.I think it was running lean for some reason. Thats why the bike would want to run on sometimes when I would let off the throttle.Its strange though because if it was running lean the EGT guage should have been going out of sight. And it wasn't.

I'll know more after I can take it for a longer ride.