Right side not firing

[Whitbread]

Hello, I'm new here and this is my first post and any help will be greatly appreciated. I'm a fully certified automotive technician and work for General Motors on their proving grounds in Milford, MI. I have a 1998 banshee that has baffled myself and every automotive and motorcycle/atv guru I've talked and showed it to. I've run through all the standard fixes and checks and am losing my hair over this (what little is left anyway). Starting a year ago, the right cylinder started to not fire correctly. Yet the left cylinder runs perfectly and has enough power to pull a wheelie without trying. I'm also running a single carb intake manifold that i made with a 34 mm pj carb. Both cylinders are getting good, fat, blue sparks (advanced 2 degrees), both cylinders have exactly 125 psi compression, are definitely getting fuel (plug is wet and unburnt fuel is dripping from the silencer). The motor was due for a freshening up anyway so i put new rings in, new gaskets, new crank seals, new reeds, and lightly surfaced the head. After i was done, i both pressure and vacuum tested the crankcase and cylinders; they held pressure and vacuum for well over an hour. The rebuild made absolutely no difference in the running condition. Knowing the problem must be electrical now, i tried new coil, nothing, new stator and ignition module and checked clearance to the hall effect sensor, nothing, pulled wiring harness apart to check for bad connections or wires, nothing. The only thing i haven't replaced is the CDI box for lack of funds and from everything i've read about the banshee cdi boxes is that when they go bad, it just wont run, not run halfway. Using an infrared temperature gauge, the highest i've been able to get the right cylinder up to is about 140 degrees on exhaust pipe just ahead of the cylinder, where the left cylinder will be well over 300 so i know its definitely not firing right. Observing the exhaust smoke, the left cylinder will shoot out puffs with pressure that is able to be felt from 3 feet away, however on the right, the smoke just "pours" out in a stream out with no pressure at all. My best guess is that the right cylinder is somehow firing way too late in the stroke somehow. Could it possibly be a messed up CDI box? If anyone here has any ideas or experience with a bizzare problem like this, i would be greatly appreciative. Thanks in advance, Matt.

[moneybags]

If you can, Swap out your Flywheel with a different one. I have been pulling my hair out trying to get my Banshee running for the last month aswell. It turned out that it was my flywheel was the problem.

 

You can read the post if you want. It is under PROBLEM WITH MY CUB. Maby read the one tilted NO SPARK aswell. Good luck and Welcome to the HQ

[mpbanshee]

Sounds like you have covered your bases on this, but sometimes it can be the little things you don't think about. Have you checked your reeds on the right side?

[Handyman]

reading your post I saw that you never mentioned anything about the carbs. I had the very same problem but it was on the left side. Come to find out the needle was bent and causing a disruption in the air flow so whe the spark plug sparked the fuel and air mixture was all fucked up not causing a good explosion when the plug sparked causing it to not fire right.. it would idle fine with both cylinders firing correctly then when I accelerated, it was like a light switch and the left cylinder would not fire but then right before red line of every gear the the cylinder would come back to life and the shee would scream, until you shifted and dropped the RPM's and the cylinder would shut off. I would also try to accelerate slowly and the cylinder would fire intermittantly until very close to red line and then it came to life and I had to hold on so I wouldn't get dumped on my ass. It was in the shop for 3 weeks and they fucked with it every day. The owner even got involved and so did just about every mechanic that got a call about the issues I was having with my shee. They tore the engine down all the way to look at the base gasket thinking it was an air leak. The owner called a buddy of his from San diego who came up during the weekend to look at my shee and after about an hour of fucking with it the guy was playing with my slide and noticed the needle was bent just a little. they put it in the carb and slid it up and doen and it was hittind inside the carb. They put the engine back together with all new gaskets, plugs,crossover tube and with a new needle and the bit ran perfectly...They dialed in the jettign for me and I paid just for the diagnostic to see what was wrong and the needle I think I paid like $100 for 3 weeks in the shop, engine tear down,a new needle, and some extra stuff that I bought.

 

Clean the cabs real good and check your jetting and needle.

[Whitbread]

I have my banshee running on a single carburetor setup so i know its not a carb problem. The 34mm pj is a known good carb that came off my friends dirt bike. It ran the same after i went from dual carbs to the single setup thats on it currently. The reeds are new boyesen carbon techs, and i fully inspected the reed cages, they're in perfect condition. I even switched them from side to side, no difference. Do any of you guys have a spare flywheel or CDI box that i could potentially swap out to test real quick? The banshee is in Lima OH, but i live in South eastern MI.

[Satsol67]

Have you tried switching the plug wires to see if its the coil? just an idea

[Whitbread]

Thanks for the suggestion but unfortunately that was the very first thing i did, new BR8ES plugs and switch the wires, then i picked up a new coil and plug ends. ::

[bansheesmoke]

Hmm before buying all of that stuff being a certified mechanic you should have tested the coil and startor and pickup coil with and ohmmeter or multi tester. When you put the new stator on you didnt bend it by chance did you? Usually a cdi box does or doesnt work. It could be the cdi though.

Edited March 5, 2007 by bansheesmoke

[DieselTech]

Ok, it sounds like it's not an intermittent problem - it's all the time, right? Sounds like you've pretty much covered everything that's probable, so with compression being ok, and the reeds being ok, and a single carb, I'd suggest the following:

 

1. Crankshaft not in phase, causing late piston timing. After all, it is a 2-piece crank, it can happen, though unlikely.

2. Late ignition timing on that side. Too bad you couldn't throw a vacuum gauge on just the right bank to compare to the left (unless you have the original carbs & intakes) - you could tap in where the crossover tube goes into the factory intake manifolds. Or, you could mark the crank 180 degrees apart & use a timing light to verify ignition timing. I think the vacuum test would also identify a late piston timing issue, as the pumping efficiency of the engine should be lower.

 

Just my thoughts........good luck!

[Whitbread]

I purchased a new stator and ignition coil because i did test them with and ohm meter and they both were on the very edges of the allowable specifications and did not look to be in the best of shape (the bike was raced by the previous owner). And on the original stator it did have a couple of crushed coils. I didn't replace them just as tossing on parts. DieselTech, thanks for the suggestion about the crank being out of phase, that is something i completely overlooked. I can see how it would happen but could a stock bore, stroke, and compression motor just running an aggressive port, bigger carbs, and pipes actually do it? And yes, it is all the time now. It started with the cylinder coming and going but shortly there after, stopped firing correctly and ceased to blow the exhaust out with any pressure. Under load it will randomly feel like its trying to fire, but not for more than just a couple strokes. Unfortunately i no longer have the carbs and stock manifolds that were on it to do a vacuum test using the stock manifolds as a test point. Maybe i'll make a set of reed spacers and drill+tap a small hole for a barb on them the next time i have a free sunday.