The batteries are off-the-shelf alkaline.

I did mention I did a continuity check. But my post was only a few minutes before yours. Perhaps they crossed in the ether.

If you are using the spring loaded battery boxes, those can be flaky.

I am, but as you can see from the photo, I am keeping the batteries from bouncing around, or vibrating out with the foam cover, held down under pressure by the dowel. Also, on this box, the springs are very tight. This morning, I removed the plug from the motor and stuffed it into shroud out where I can see it while it's sparking. most of the time, I hear that clicking from the ign box each time I pass a magnet by the sensor. Sometimes, I DON'T hear that from the box. When that happens, the plug fires. Otherwise, there is no spark from the plug.

Based on the above, I still think I ruined this ignition box by running it when the hot wire wasn't making contact with the plug. At this point, I'm pretty sure the clicking from the box is the coil arcing, bypassing the plug. Sometimes, for whatever reason, when the coil doesn't arc internally, it happens to deliver a spark to the plug. Statically, that happens about once in every 15 magnet passes. I'm calling CH for a new one.

OK. A new ignition should cure the problem. I fought my home made boot all summer before I figured out that's what it was. I swapped in another ignition and put a good amount of flight time on it in the fall.

Yep. Ok a new CH ign is on order, made up for 1/4-32. Hope it arrives in time for the 20 deg weather they promised for Saturday! Then continue tuning. I really think Paragon or RCEXL owes me a new ign because it was their boot that didn't work. I think that's a lost cause.

Ha ha ha Terry, you put two and two together. You should work for Homeland Security for doing a better job of connecting the dots than they do. Either that or there's only 10 very active people in this hobby! Anyway, thanks for the quick response!

Update on Saito glo-to-gas conversion: As you'll recall, this project stalled when I discovered I'd blown my ignition module because the RCEXL 1/4" spark plug adaptor was only intermittently connected to the plug. This led to all kinds of conflicting symptoms that threw me off for awhile, including hard starting, suddenly quitting at any rpm, and erratic rpm's when it did run. The module was not completely blown, but was arcing internally to the box. This was probably due to an insulation breakdown in the coil sometimes providing a more sympathetic pathway to the high voltage than the spark plug. A clicking could be heard inside the box at these times.

I ordered a CHEXL electronic ignition box and sensor from CH Electronics. It arrived, I intalled it. My first observation is the metal shroud is far more secure than the RCEXL boot was. It takes a lot more force to install and turn-to-lock. It also comes with contact grease pre-installed. Also, the shroud is not a full 90 degrees, but something less. This helps do the twist in engines where the cooling fins hide the plug area.

Primed the engine, hooked up the battery, and it runs VERY well. Excellent transitions with no stumbling. No overheating, good idle. I have no idle or WOT data yet because I can't get my tach to work with the 60hz lighting I'm stuck with. But the sound tells me it's already pretty good. We're expecting a January thaw by this weekend, so that's the time to take this outdoors for a good tach reading. Where would we be if the sun had 60 hz too??

The last issue to deal with is there is an imbalance at around 3k rpm. I suspect this is the new rod and needle bearing I installed. I'm going to rebalance the prop, and if that doesn't fix it I'll reinstall the original rod and do a test. If that fixes the imbalance, I'll leave it that way and perhaps reduce the fuel/oil ratio. I'm currently at 30:1. I'm told that I don't need to do this by some folks, others insist it's necessary. I'd hate to sieze the lower end bearing finding out. Maybe 20:1 is the answer.

My thanks to CH for having a quality IGN and especially the boot unit, and for their quick shipping.

If your balance problem is the rod weight, then try using an UNBALANCED prop. You added crank pin weight so with the engine at TDC set the prop so that the heavy blade is at the bottom. Just see if it helps, if it does then unbalance your prop hub.

Thanks for the prop idea. I'll run the engine in the offending rpm range and lightly tap it with a sharpie marker to ID the angle of worst displacement (or vibration). I'd hope this coincides with either TDC or BDC but due to the vararies of resonances, angular momentum, and phase shift I'm expecting almost anything.

Then I'll try the prop idea. I've researched (a little) engine balancing and come up with one factoid. Traditional engine balancing assigns one third of the rod's mass to the reciprocating component, and the other two thirds are assigned to the rotating crankshaft. I'm sure that doesn't include the heavy needle bearing though. Just the aluminum arm.

I'd invite anyone's balancing expertise. Maybe someone has a spreadsheet.

By the way, the engine runs great. Still not a lot of tuning and no rpm data due to the 3600rpm (60 hz) of the shop lights. This video shows my exhaust elimination system, that works pretty well. No danger of sparks because the vac has a brushless induction motor. Here's a link to youtube of this engine running: http://www.youtube.com/watch?v=2pie14LuV68

Thanks for everyone's help in this thread. I've learned a LOT.

I have just received a ZAMA C1Q P8 ( 6,5mm venturi) carb wich i want to mount on my Saito FA80.
This carburettor two external brass tubes. I suppose the thick one is the fuel line but i don't know what the other tube is used for.
This straight brass tube is located next to the low needle. Also this carb has small hole above the intake valve at the flange side. I suppose it is a pulse hole but i don't know wether it is a pulse from the carter or from the intake manifold.
Can someone help me with answering the Questions:
1. what is this brass tube used for
2. What is the small hole for?
3. do i have to use both connections and where should i connect them to

I think that the smaller fitting is for a fuel return line when the engine has a primer buld. If you don't have a primer bulb then solider the fitting closed. or use a short piece of fuel line that is plugged with something.

The small hole is the pulse hole.

The Zama cross references to a WT456-1. It's made to pump using the negative-only pulse from the intake. Check to make sure there is a 98-3226 spring inside the pump cover though. See the detailed photos earlier in this thread for what that looks like.

TKG and W8ye are both correct. In the WT-456 instruction book there's a little paper that says "If the carburetor you're replacing doesn't have a primer, the primer fitting[tube] on this carburetor MUST remain plugged". They supply a little red vinyl cap for this situation, and it only fits the brass tube right next to the L needle valve. I'd recommend plugging rather than soldering it in case you want an external primer in the future. It helps for starting, but it's not mandatory.

As for the other little hole on the carb mounting surface, it actually "LOOKS" like there's two, but one is blind. The one that shouldn't be blind is adjacent to the pump cover (that's the cover that has one screw). It must lead to the intake pipe somehow. My adapter routed the pulse path externally thru a tube, but usually in such carb's original product application this is taken care of via a molded plastic spacer between the engine head and the carb. The pulse pathway is molded into the spacer. Since you probably don't own a mold shop, try to find an intake tap for this tube a little away from the carb if you can.

On this Saito 150 gasser, it became hard to start. I introduced a bubble into the fuel feed line so I could see if that bubble travelled up the line and guess what? It was stationary. I took the carb apart and found the typical wrinkly curled pump diaphragm. The reed valves were really curled...they couldn't possibly function, they were lifted away from their respective holes. I wonder if there's a replacement that is made of that glass cloth stuff? Anyone know how to tell from Walbro's p/n's if the part is the "new" stuff or not? I've looked on Ebay and found that rebuild kits seem to have a black, or a tan(glass), or a blue pump diaphragm. Anyone know the difference between tan and blue in terms of material and application? I guess the black one is the old school material before the corn lobby and the greenies got together?

The black one is the used for ever original pump. There have lots of reports that it is unhappy with some of the stuff in smog gas. But it pumps the best. The tan one seems OK for new gas, and the pumping is only a little less. The blue one is almost bullet proof, but it has lousy pumping action.
One of the weedie runners here in the conversion forum has started using Coleman fuel with the correct oil ratio as a carb after run fuel. Seems to help with pump life.

Coleman fuel. Basically kerosene?

I put the old plain rod back in and changed the prop. Still has bad vibration. Beginning to suspect a bent crank tho it turns smoothly. I have no idea how that could have happened. I'll put a dial indicator on it to find out.

Colman fuel is mostly naptha

Some people use it instead of gasoline because the smell is more pleasant

It works well in the weedies but from a flame travel speed perspective I don't think you will like it in a four stroke for a complete gasoline substitute

Coleman fuel is 55 octane, small displacment (under 50cc) two strokes can use it, but if that engine has a decent CR it might not like the low octane.Flame speed has nothing to do with it, its all about knock resistance.

The brown diaphragm is for alcohol fuel it should with stand the low alky content in pump gas.

If the crank is not bent, then you just have to live the vibration. Sometimes low speed roughness can be traced to mixture issues.

Cannot let this slip by

Flame front travel speed of the fuel is directly related to engine knock if you care to read about knock resistance

Thanks to all for answering my questions about the different colored diaphragm materials. I do wonder if the brown stuff worked pretty well, why did they also come out with the blue one. Cost reduction? I'd love to get those engineers in a room and ask a bunch of questions about the tradeoffs they considered.

I knew the "flame speed travel has nothing to do with it" would elicit a comment from someone. But thanks for the answer: mostly naptha. I suppose it's available at Naptha Auto Parts???

Although it seems counter-intuitive, octane boost actually slows down combustion. This confuses people because higher octane fuels are always associated with higher performance engines. Well, high compression ratio is too. Only problem is that higher compression also causes the regular fuel to pre-ignite from compression and high cylinder wall temperatures. It's called pinging. So octane is added to SLOW DOWN the flame allowing the charge to fully compress, e.g. allowing the piston TIME to get close enough to TDC to deliver the power to the downstroke, not fighting the upstroke. It's a race between combustion speed and the piston. Also, octane smooths out combustion, delivering the power over a slightly longer time period. That's easier on the piston top and the main & rod bearings.

The other way to help knocking, pinging, or pre-ignition is to retard the spark. Your car does this by monitoring the knock sensors for preignition signature and computer-retarding the spark. This will only help to the extent the knocking isn't being caused by auto-ignition (high wall temps, etc.). Retarding the spark won't help if the fuel is igniting by itself. Like, lets say, you're just using the wrong fuel for your car. I have a Honda Civic SI with a 195 HP 4 cylinder high compression 1.9L engine. It's a pocket rocket, but you put regular gas in and you get less power because the timing gets retarded. It doesn't knock noticably though. A car that diesels when you shut it off is auto-igniting.

For the Saito, I indicated the crankshaft and the total indicator reading (TIR) is .001". So that's not the problem. Nosedragger, I'll experiment with different fuel mixes per your suggestion.

I also plan to put an APC prop on there and try it. I've been using wood props until now. At this point, one must cover all the bases. I have to admit I was astonished the vibration was still there after I removed my home made rod and bearing.

I got the Saito running again by making my own diaphragm. Yes, believe it or not I did it and it worked. Years ago I got a bunch of sample materials from a now defunct flex circuit company called Adflex. They were spun off by Rogers, in Chandler Az. I don't know if they're still in business (Rogers) but I have many sheets of some kind of glass impregnated thin membrane material. The color is beige, too. Looks similar to pictures of the brown diaphragm I see online, though I've never seen one in person. So I traced the old wrinkly diaphragm and cut a new one carefully with an xacto knife, scissors, and a hole punch. I can supply photos of this material if anyone is curious. I put a swatch of this stuff in some gas and it's sitting there as a fuel resistance test. So far no wrinkling. Time will tell.

The difference in flame front is not that great between high octane and low octane.Flame speed is influenced more by combustion chamber shape than octane.
Suggested reading: Internal Combustion Engine Fundamentals - 1st edition. J.B.Heywood

Regarding the vibration, it's possibly the mounting. I suspect there is absolutely no side to side (and it's certainly not going to escape with that anvil and tree stump!); but if you grap the prop ends I bet there is some flex up/down.

Nosedragger wins this one. Good job Nosedragger! Octane rating measure the presense of fuel compounds specifically designed to interfere with a series of low temperature (relatively) reactions leading to "combustion" in advance of the main flame front from the spark. Once the flame front is initiated, the flame front runs at about the same speed. The problem is with preignition of these end gases, you get a double pressure wave. That is the pinging we've all heard.

HOWEVER, in practice, it's a distinction with little difference. The end result is the absense of the double pressure wave makes it seem as though combustion has been slowed down, and the engine runs better. So people just say it "slows down the combustion".

So, the big question is why are car manufacturers spending millions putting anti-knock sensors in cars when this can be solved by using the correct fuel? Perhaps the reason is pollution control, and the desire to precisely control and get complete combustion.

Saito update: Changed the prop to a 16-6 Master Airscrew nylon prop. There is a significant reduction in vibration. It's not perfect, but improved. Next stop....hobby shop to grab an APC which I consider a better prop. I will also move this test rig outdoors so I can finally get a true RPM reading.

A big part of the reason for the knock sensor is to control knock that can occur with sudden application of WOT at cruise or low speed when the EFI is running the engine lean. The computer dials in spark advance to ignite the lean part throttle mixture. Lean mixtures are harder to ignite and so use more spark advance.Full throttle application can not use as much advance so the knock sensor works with the computer to take out spark advance to keep the engine in one piece.
The old days a vacuum advance distributor would sense the drop in vacuum from sudden application of WOT and reduce spark advance accordingly, but the engine could still ping or worse detonate.The knock sensor prevents this so the spark advance can be optimized.

They don't like automotive discussions here so I'll leave it at that, I just want to help you get your conversion sorted out.