blowit

I think your problems likely still lie with carburetion or simply plugs. If you are spitting fuel, usually one side is not firing is not getting the right air/fuel mix. Make VERY sure your carbs are balanced or sync'd properly. Brandon Mull Engineering

Guess I feel compelled to offer my input. The first thing I might question is the mechanic. We may not have the full story but it sounds like the bike has a starting problem but otherwise runs good. A comp value of 60psi, unless you are on Mt Everest, would be pretty much not running at all. I would first question that value. Seen this tooooo many times where guys end up doing a total rebuild over a poor compression test. The adapter that screws into the head is just as important as the gauge. Personally, I would pull the pipes and/or the reed blocks to get a good look at the rings. At 60psi and those hours, either your rings are welded into the pistons, or you have no problem at all. If the ports were so sharp that they destroyed the rings in a couple hours, that usually leaves some evidence in the bore, or a quick feel will tell you. Yes, it is normal for the pistons to look a little "loose" from the top. The top timing edge of the piston is designed smaller due to how it expands when hot. A sharp mechanic can simply move the piston around at TDC and determine if the rings are welded or not. To me this sounds like a choke problem. Not pulling it all the way out to the second click, cross tube is missing, etc, etc. Something simple Brandon Mull Engineering

I just thought I would add some food for thought. There are several variables that dictate how reed valves perform on an engine. Max flow at various pressures, and stiffness of reed pedals dictated by their tuned length, material, etc. I hardly know of anyone these days that actually adjusts their pedals but it is a paramount parameter for optimal performance! Let me offer this example. Test brand X and brand Y on a flow bench, both at 20"HG, then at 10"HG. You will find that as you lengthen the pedals, you increase flow but you have to keep allowable pedal deflections in check to protect the reeds. What I am saying is this might come down to less emphasis on the actual reed blocks, and more about the pedals themselves. You may actually find that brand X flows more at 20", while brand Y flows more at 10". Then this becomes a function of pulse activity in the intake. Porting, engine size, rpm, all dictate that vacuum pressure. IE, tune the pedals to the engine. Maybe that is just opening a can of worms?

That is entirely possible! The trigger circuit can be done several ways looking for 'A' voltage or looking for positive voltage. Maybe someone will test their bike to confirm. We have a test rig on the bench but our scope is out on a job or I would just test it. I have deleted my prev post so as not to mislead until that can be confirmed. Somewhere I have a snap shot from the scope. Will look. When I think about this more, I believe you see a sharp rise, then an opposite decay voltage and if it triggers off the opposite voltage, timing could be affected, causing a few degrees retarded timing.

Just a couple things from machine shop guy. 1. Heli coils are much preferred for this application because every time you run a bolt into an Aluminum thread, you are causing wear on those threads. 2. I would personally shy away from any drain plug with a cut tap tip on it. Every time you run that thing back it, it will try to trim those threads a little more. Cutting the threads with the proper tap and installing a normal drain plug is much more ideal for thread protection. From our experience in tapping thousands of Aluminum thread you MUST get your predrill size RIGHT and it is a sure bet that if you drill a hole with your Dewalt, it will be oversized when you are done. Lots of care must be taken to do this right. I highly recommend a reamer to take the hole to size when doing this manually. You can likely ream to your target size without ever touch a twist drill. Tapping is a science and there is all sorts of data about % of thread vs thread capacity. If you drill oversize, your tap will run in just fine, but you won't have the right amount of thread for good holding power. If you drill undersize, your tap takes too much torque and will break. If you chose to tap it, do NOT use a cheap tap!!!!! Tapping is tricky business and once a junk tap breaks, you have even more fun getting that back out. There are also something called a Time Sert which is a fully threaded barrel, not just a spring. They are more durable and most have a locking feature so once you get them installed, you drive the tines in, which mechanically locks them in place so they cannot come out. Just FYI and probably TMI as well, we use CNC to make threads whenever possible because we have much more control. Just about every time we try to even adjust a threaded hole manually, it won't pass inspection with go/no-go gauges, typically coming out too loose. If you pull even a little on one side of the tap, this will cause the tap to oversize the hole. I guess I get all worked up about threads because it can just get down right tricky even with the best tools available and not trying to scare you, just trying to alert you to the care that 'should' be taken when doing it. If you are even 1* angled going into that drain hole, it might all look great but will never seal without a goober of sealant because the washer is not getting uniform sealing pressure.

I think at this point I would go ahead and get the stator out and test it out of the bike. If it still reads low, clip the wires close to the stator so you can eliminate the wiring as the problem. If it still tests the same, shit can it and snag another.

Never do any low ohms testing without putting the meter probes together to see what that reads and that it is stable. If the value is all over the place, you need to rectify that first. If you truly have 3.2ohms, you have 2 options, pull use a needle to depress the small lock tab on the pin in the white plug and remove it for better testing, or open the side cover so you can do more testing. 3.2ohms is not going to work and indicates a partially shorted coil. In some cases, I have recommended to just cut the red/green wires so you can eliminate the plug as the culprit. Obviously if it is bad, you will replace all that anyway. If you find it good after cutting, then test backwards and fix the plug and resolder the connection with shrink and ride. We never replace a stator until we test right inside the stator because most problems we have found were just the solder connections in the stator, but they certainly do fail.

How did you clean the stator? Wire brush? That would be a no-no. When above member mentioned cleaning, he was referring to the contacts where you probed the wire and such. Cleaning the outside of the coils will not affect the reading but you could have damaged the lacquer coating on the wires, which will show up as shorted. Make certain of your meter settings. At a reading of 27ohms, that is nearly a guarantee that the stator is fine. You likely just had a minor contact issue or internal resistance in the meter. You may also have caused an electrical bridge somewhere when you cleaned it, like at the plug possibly?

Please PM with specifics and price and I will check with the customer. Thanks!

Customer sent us a head that is not repairable and he has a ride planned this month. Looking for a good used head with no damage or machine work, or possibly just a light mill on it. PM me if you have one and can drop ship to us asap. If you have more than one, we might take them. Mull Engineering

make sure carb balance (sync) is close by looking through windows on sides of carbs or checking visually AND your damn idle screws are set close side to side. If you look in the back of the carbs at 0% throttle and see one slide much higher than the other, you will have problems. turn air screws IN to richen. I would say go all the way to 1/4 turn right now and see what it does. No, 27.5 is just fine for right now for idle and should idle fine on them. If not, they are plugged. PS, I am making the assumption you have the TORS system unplugged? That most certainly can allow the bike to run everywhere else but idle. However, you mention it will idle with choke so I assume about the TORS because the bike would not care and would just shut off under about 1/8 throttle.

You would be well served to install an inline fuel filter and ignore that you even have one in the tank. I lost count of how many we worked on with sand in the tank. Guys would just keep repeating carb cleans until they went insane. Only when a fuel sample was pulled, did the real culprit show up. Also, If I remember correct, the Banshee has an Oring on the seat of the needle/seat valve. You can clean her till the cows come home and it will never stop fuel if that Oring is toast. As to your idle issue, adjust the air screws. It sounds lean at idle which can either be blocked pilots or air screw setting. If you cannot find an air screw setting that will work, you likely have partially blocked pilots. Brandon Mull Engineering

Grant, you are right, the clutch is certainly something that should be inspected and usually over looked for shifting problems. If the clutch basket is grooved up, this will cause the friction plates to want to stay partially engaged when you pull the clutch and it never fully unloads the transmission. You might do some testing and if your bike has a tendency to creep forward when in gear, this is a strong indicator of clutch basket issues. Brandon Mull Engineering

The single carb sort of isolates where your problems can be. I will offer a few tips to help. 1. Swap the plug wires L and R. If the problems still exist on the R cylinder, the electronics are not your problem, move on. Assuming you have fresh plugs. 2. the leak down test should be performed and should easily show the culprit if this is air leak related. 3. PORTING! I have seen this before. If those cylinders are ported, you may very well have ports that do not match, thus one side wants different jetting than the other. This becomes a port correction job. 4. REEDS!!! This is probably one of the very first things I would have looked at. If the pedals are damaged or not seating, when the piston goes down, proper crankcase compression cannot be built up, thus depriving the top side of fuel/air. Though most people do not follow proper practice, fiber reed pedals should be flipped periodically to ensure they seal correctly. Above all, I would NOT be chasing jetting at this point with a single carb. If you have one cylinder running good, and the other one not, that is not jetting. There is something different between the two sides. Only once you find that culprit will you be able to properly jet it. Brandon Mull Engineering

i hate to ding the new guy, as I am not into hazing but i have seen this before and the next thing you know, the OP is out there ripping his engine and installing crank seals. Though it is possible, a compression test would never show that. This is sounding more carb related but stay tuned. Who know where we are going.

I highly recommend our post. It could be improved but gets the point across. the gauge itself likely is not the issue, it is the end of the hose that will lie to you. If you have Lucas full synth, that might be a little 'slobbery' of a ratio. Might report back with more intel on that. Here is a few quick tips. When you say 'overheat' I read that to mean total engine overheat, which certain can cause the hole. However, I think you are suffering a more acute condition. detonation is rapid rise in compression after spark and usually on the exhaust side of the piston. IE, erosion on the exhaust side of the crown. A central hole technically 'is' detonation but actually caused by pre ignition. Pre ignition will be caused by extremely high compression, carbon build up, damaged spots holding carbon, super lean jetting, hot plug, etc. Basically with pre ign, something is acting like a glow plug. However, pre ignition means "ignition before we ask it to", it does NOT mean violent combustion. Ignitions just means "lighting the fire", the word detonation has more to do with burn speed. There comes a burn rate that I cannot remember that it is no longer 'burning' at a certain rate, it just rips ass and explodes. What I am getting at is the detonation caused by the high heat and pressure of preignition is what causes the hole. So........ Very likely a lean condition caused the hole..... Or something else...

OP, a couple things. I would first verify your comp tester works right. I might recommend you read a post we still have on our site about compression testing. I suspect you might have a setup issue there. If that is accurate, you have a real concern. What you describe certainly sounds carb related but from what I read, it might be wise to network with a local expert and learn a few things here as you might burn a few engines trying to figure some things out. It sounds like you could have some plugged jets, and a carb sync issue. Probably need to start at the top and work your way down. Mull Engineering

This is just not correct but no disrespect for trying to help.

The very first thing to do is test the resistance in the ignition coil. This will be the Red and Green wires. If you read OL or very high resistance, probe inside the stator directly where the magnet wire is soldered to the leads. Remember also, always put your meter leads together and see what the internal resistance is first and add that to your test figure. Once we know if the coil is open or not, we can figure more things out.

I will jump in and offer advice here. I will need to know if you are losing the lighting output or spark? Also, what is your skill level and what sort of test meters do you have available? Mull Engineering

Let me ask this, did you determine your target port heights by using your timing wheel on your current engine and adding marks in the cylinders where you want to be?

What kind of durations are you looking for? I think you might want to reassess your math on this build. There are a few concerns here. However, trying is learning. Mull Engineering

Yes, powder coat requires the parts be heated in an oven so anything rubber or plastic needs removed. As well, I would recommend you have a good chat with the coating company or someone competent to ensure no gasket surfaces are coated. I have seen this before and getting powder back off is not fun, especially when trying to salvage the surface. Mull Engineering

Advancing timing does not require rejetting, however, if jetting is borderline lean, this can lead to detonation issues. Make sure your jetting is dialed in, and as recommended, check plugs after timing change, especially the ground strap for indications of heat. However, 4* is a pretty standard and safe value for pump fuel engines and usually works without issue. Brandon Mull Engineering

Just curious, have you measured the ports and piston before making that statement?