J-Madd

What are the specs on the carbs? Are they sync'd? Maybe one carb isn't opening up all the way, which would lean that cylinder out. YOu have powerjets, right? If so, make sure one isn't vibrating closed. I have seen that also.

Good info, except that he's running alcohol. Surely you mean the primary gear keyway, not the clutch basket??? Usually a bad seal on that side will draw in tranny fluid and leave deposits on the plug. It will burn the fluid but not usually burn down a cylinder. While swapping carbs left to right will rule out certain issues, I'd hate to ruin the other cylinder just to rule out an air leak on one side. Try a different set altogether if you want to rule out a carb issue. There has to be an air leak somewhere, or a bowl is running dry, or something. Maybe its the base gasket?? I had a bad base gasket keep burning plugs. It didn't run erratic like you think it would. Are you running a new gasket every time you put it together? I ALWAYS pressure test any motor after it has been apart, regardless of the condition it was in before. What kinda shape are the bearings in on the bad side? 3 melt downs can't be good on the crank.

Have you read the Gordon Jennings and A.G. Bell books? I respectfully disagree with your statement. Port duration, dome shape, ignition timing, pipe design, carburator design, intake design, etc and how each will affect power output is mentioned in those books.

The guy (358Banshee, or something like that)building the fuel injected Banshee has a wideband 02 sensor. Check that thread out.

All of that is over my head, but I have a hard time grasping the blow down "area." I thought you were trying to cut the piston to match the existing exhaust port so that it opens the whole top of the port at exactly the same time.

The klotz is good, but $$$$, so is the Bel-Ray gearsaver. You can also use 10w-30 or 30w motor oil. Just make sure it doesn't have detergents in it. I don't know what oil has detergents; I've never seen one. You can use Castrol, Pennzoil, Valvoline, etc. In drag racing we use ATF type F a lot, but you have to change that a lot, and it likes to find any imperfections in the clutch cover gasket and leak, whereas the other oils are thick enough to not leak as bad, or even at all.

Cutting the piston is great to experiment with different durations (and maybe port shapes?? as your trying to to). That way you don't ruin the CYLINDERS you're experimenting with. When you find the duration (or shape?) that works on the piston; you can then alter the exhaust port and use an uncut piston. I know of a stock stroke Cub that picked up 10 hp on the dyno by cutting the piston. As far as I know he is still running the cut pistons and has yet to raise the ports (as he originally planned.) Do you have a dyno to test this on?

There's not a lot of power to by found out of a 421 Cub with porting. You can probablly get more peak hp out of one, but it won't necessarily be faster at the track unless you have a super light rider/chassis. I dynoed one of my 421s and got 100 hp with a cleanup port with little tuning. Lots of tuning and with it drag ported (port timings probably not changed) and got 103 hp. Maybe could have got the 103 hp on the cleanup port with more tuning, but I was satisfied with it. The guy who ported it said it would take waaaaaaaayyyyyyy too much time/work to get the max hp out if it. I wanted it reliable, and lasting as well.It may have 5 hp left on the table, but it's not cost/time efficient, and would lose some reliability. You know the saying - the first 80% takes 20% of the time, the last 20% takes 80% of the time. JMO.

Just about any 4 mil Cub can run with or beat any other one, ported or not. HP to weight ratio, tires, gearing, chassis setup, wheelie bar length - that's what makes one faster than the other on the track. The fastest 4 mil Cub (397cc )in the country is owned and built by Jason Menz. He built the motor and chassis. I'm talking about 300 ft track racing - you may be talking about dunes, hill shooting, etc.

The only way to lower the ports is to deck the bottom of the cylinders or run without a gasket, that's all. I was just wondering how you knew the ports were lowered, but that is the answer.

The CPIs I was referring to are the non stamped version. I'd almost call them hand coned - the have many more seams than the stamped pipes.

I don't think the 10 hp gains are typical. Also, it was most likely a gain in peak or high rpm hp; which you're not looking for. You could just as easily gain some peak hp by raising the ports, which you also probably don't want to do. Was the bottom decked? Are you running without a base gasket?

With the lower exhaust duration, you will be better with the Shearers. CPIs are great pipes,just depends on the porting. I have a 10 mil Cub that picked up hp at all rpms with BB CPIS vs RDZs. The exhaust port duration is 200*+. I have another 10 Mil that likes Shearers due to much lower exhaust duration (THough I admit I haven't dynoed it with anything other than SB and BB Shearers). You may also look into getting some Sniper Pipes.

I have a similar setup as the OP on my trail Banshee. Head milled 0.020", +4 or 5 timing, T5s, K&N in box/no lid, 350 mains, but only 25 pilots, 300 ft elevation. That Banshee hasn't been beat by any other non-ported stock cylinder Banshee. It could use bigger pilots, and runs a little rich on top, but revs out clean and pulls good. It runs on pump gas.

SAme sprockets, but these people are great to deal with, and probably quicker shipping unless your on the west coast. http://www.rebelgears.com/orderhere.html

Exactly. If you're 90 mph, theres gonna be even more distance between the 2 in a tenth. It's worth a few grand to get a tenth; or a shot of spray.

Due to variances in the casting of the stock head, it's hard to estimate. Definitely check to be sure. Be sure and check compression also.

Did it just start doing this? Didn't watch the video, but if this just started out of the blue, I'd suspect the stator.

I'm gonna say you can knock 10% of that dyno number. I'd also like to see a comparison on another dyno. (Not knocking your motor - it will still be a good runner; my 10 Mil Cub only makes 103-105 hp and it runs like a champ at the track.)

Sounds like the slides are in the wrong carbs and backwards, assuming stock carbs.

Anywhere in the intake flange.

If you choose not to port it at least degree it or take some measurements to make sure it was cast to spec. http://www.cpindinc.com/pub/view_product/43?lm=3&name=CPI-6864

Move the clip on the needle richer and see if it gets better or worse. If worse, then move it leaner until it stops bogging.

Never hurts to test the ignition coil and check the plug caps.