I have a Saito 90 twin that I bought off of here - it is the older version with twin carbs. I have two problems - the engine isn't getting fuel, and one of the cylinders won't even fire.

The fuel delivery problem I think I can fix. The fuel tank center is about 1.5" below the carb, and I can't fix that. I may have to get a pump, but the pressure line comes from the cylinder that won't fire, so that may fix it if I can get it running.

This engine was crashed about 5-6 years ago, and one of the cylinders was broken off. It was replaced with a new cylinder, but hasn't been run since. The old cylinder fires and runs fine, but the other one won't. The timing is right, the valves are ajusted, the glow plug works, and I know it was getting fuel when I primed it. There is almost no compression, but I think that is because it is a new cylinder. There is no hint of it firing. I have also taken the engine apart, and everything looked good.

What can I do to try to get it to fire?

Thanks - NJD

I know someone has an idea out there - mabye the valves aren't seated correctly?

Thanks - NJD

Remove one plug and check the compression, now do the other side. Is there a lot of difference between them? If "Everything" is adjusted right, the compression should not be that far off. Who did the repair? Try downloading the manual from Horizon and check the timing yourself (if you haven't already). Are the carbs clear of dirt/debris? Open both needles about 2 turns and try starting it. BTW, how are the plugs? If in doubt, install 2 new OS "F" plugs.

Yes, the new cylider has almost no compression, but again I think that is because it is new - unless it could have somthing to do with the last paragraph.

The person that I bought the engine from did the repair, and like I said I took the engine completley apart and everything looked good. The only thing I didn't take apart was the valve assembly, but it appears to be working correctly. Also the timing is correct, I set it as stated in the manual - line up the two dots. Had to take out the front bearing to do accuratley.

The carbs are clear, fuel was coming out of the exhaust, although that might have been from the vent line.

The plugs are brand new "F" plugs, and I have checked them.

One thing I do notice is that the cylinder in question, when on the power stroke, is almost like it is creating a vacuum in the cylinder. The moment the exhaust valve opens, there is a pop, like the pressure was equalized - you can feel it as you turn the prop. And yes, the intake valve is opening.

NJD

Did the new cylinder come with new valves installed or did the previous owner install the old ones? It really sounds like the timing is off (maybe the cam is 180deg out of time to crankshaft). I know you said you checked it, but unless someone else has another idea, it's the only thing I can think of. When turning the engine over in the correct direction, bring it to TDC (compression stroke) for the bad cylinder, then use a pen and make 2 reference marks on the engine (1 on the hub, 1 on the block). Take the rocker covers off and watch the rocker movement. Compare the 2 sides, do the valves seem to open in similar positions and in the correct order? You could also take the cylinder off, install a glow plug and blow into the bottom, any air coming out through the valves? Short of sending it to Horizon, I'm out of ideas at the moment!

I did the timing the way they told me to - do one cylinder first, the rotate the crankshaft 180 deg. a certain way, and do the other, but maybe I screwed it up somehow.

The valves are the old ones, I have the old cylinder too.

I will try as you suggested, and take it apart again to redo the timing and check the valves - hopefully I will find the problem.

Thanks alot for your help, bdtsr!

NJD

Not a problem!

I have found the problem: The engine is a single throw crank, and I have the valves going like a double throw crank engine. The exhaust valve is opening on the intake stroke, and the intake valve is opening on the compression stroke! I followed the timing istructions exactly, but apparently they were wrong (the person I bought the engine frome had it timed the same way as me, too.) Hopefully this will fix the problem.

Thanks again for your help, bdtsr! Probably would have taken it apart and put it togeter again with the same problem had you not mentioned the valve sequence.

NJD

Glad you got it figured out! These are sweet little engines when setup right. Just wish I had one instead of working on one.
Brian

Yeah, they are great. I also have the new 60T, runs like a charm. Idles at 1200 RPM, and swings an APC 13x7 at 9400.
When you say you wish you had one instead of working on one, do you mean you have one with a problem?

NJD

No, just redid one for a friend. I have his 270 twin on the bench now. Someone turned it (270) over after it sat for several years and broke two rocker arm mounts. The lifters were stuck nice and tight too. Lucky they didn't bend any valves by hitting the piston while they were stuck open!

Ah, well they are sweet engines. Hope you get one soon.

NJD