OS 65 4s no fuel flow

[Den Moran]

Hi everyone. My summer venture into i/c is going farely well, but I have hit a snag with my OS.65 4stroke. I am doing the blow/flow test, but cannot get air pastthe barrel/inlet.The intake nipple is clear, and only when I unscrew the high speedle to within a 1/16th turn  of its max (then it falls out), does the air flow. Any suggestions, please?

[Cuban8]

A bit more info might be useful.....new or used engine? has it run OK previously? carb been stripped before?

Exact model of engine would be handy.

Edited July 12, 2023 by Cuban8

[john stones 1 - Moderator]

Maybe it's me not understanding, I thought the blow test was for low speed needle, what issue are you trying to resolve ?

 

[Jon H]

Slow run needle might be bottomed out. Did OS make a 65?...

[Cuban8]

W

9 minutes ago, Jon - Laser Engines said:

Slow run needle might be bottomed out. Did OS make a 65?...

Just what I was thinking.

Maybe realignment of the adjusting screw as explained in the OS instructions? Only 65 I'm aware of is the 65LA two stroke.

Edited July 12, 2023 by Cuban8

[Engine Doctor]

If its been run and stored its probzbly has gummed up jets incarb . OS as far as I am aware  made a 60 open rocker and pre surpass . A 62 and a 64 v but not a 65 . Carb issue will likely be the same remove carb and soak in a jar of fuel over night with neeedle out then re set all needles befor retrying . Air flow test is performed with throttle closed , main needle two turns open then adjust the slow running needle until you can just hear air passing. This is only a basic starting point for tuning the carb. If an overnight soak doesnf soften or clear the nlockage then it might need stripping and cleaning wit solvent like cellulose thinner to remove set castor.

 

Bear in mind that if castor has set in carb then its likely to have set inside the engine and could damage it if run without vleaning , especially a four stroke. Once running Never use castor based fuel in your engines . Ask forfuĺy synthetic oil based fuel.

Good luck and let us know how you get on .

[Den Moran]

My apologies - Its a ASP 65, I was told they are 'the same as' OS, and that stuck in my mind. 

I know the blow/flow test is used for low needle stuff, I'm just trying to get ANY fuel into the barrel (unfortunately, the quick route through the air intake is not easy, as the intake points downwards, and my test bench set up doesn't allow easy access, although I can block it with my finger!) Thanks everyone, your help is much appreciated. I need the engine for my old Astro Hog!

[Den Moran]

Cuban 8 - I'm not sure if the carb has been stripped before I did it last week.It's whistle clean, no gum etc. I don't know when it was last run,it's been on my shelf for about 5 yrs!

[Tom Gaskin 1]

Den,

Try the 'blow test' with the throttle wide open, plus both needles unscrewed. That will at least show that the carb body is not blocked. Then screw one needle in, test, then the other and test again. If they are successful have a go at ED's setup suggestion earlier.

 

Tom

[Den Moran]

Thanks, Tom - no flow until high speed needle is falling out! 

[Martin Harris - Moderator]

I assume you’re doing this test with the throttle open?

[RottenRow]

There must be a blockage in the spraybar tube. The air that you get flowing just before the needle drops out must be going past the needle’s thread and O ring.

 

If you remove the needle, and unclip the friction spring, you can use an 8mm socket to unscrew the tube that the needle goes in to. If you then look into the hole you will see the spraybar hole. This must be blocked with old fuel residue or something.

 

Clean it out using methylated spirit or clean fuel and a piece of copper wire or similar. Under no circumstances use a steel wire or anything like that. A paintbrush bristle is also good.

 

When the spraybar is clear, you should be able to blow into the hole, and with the throttle fully open and with a finger over the fuel inlet pipe, hear air hissing out of the carb. throat.

 

Hopefully you will just about be able to see the spraybar hole in the photo below.

 

 

That should clear the problem.
 

Brian.

[Jon H]

what happens if you take the slow run needle out completely? 

 

I know Tom suggested this but im not sure his meaning was understood fully. I would completely remove both needles and the throttle barrel as well (why not eh?). make sure you can see light through the hole in the spray bar and if not poke it with a bit of wire to clear it out. 

 

 

[Andy Stephenson]

I've seen some engines that won't run at all if the slow running needle is screwed too far in. No matter where the main needle is set.

 

Edited July 17, 2023 by Andy Stephenson

[Martin Harris - Moderator]

That’s quite understandable - although the main needle needs to be open a certain amount to admit fuel to the carburettor, the low end needle controls fuel flow to well over half throttle so if the low end needle is too far in, unless you start the engine at somewhere approaching full throttle it can’t fire. 
 

Glow engine carburettors are extremely basic metering devices and rely on a balance of setting the needles combined with design of the simultaneous opening of air and fuel controls. This is why setting main and idle needles is an iterative process as each adjustment affects the other. 

[Christopher Wolfe]

For cleaning a blocked spraybar safely and gently an 'Interdental Brush' works very well.

Normally used to clean between teeth and readily available.

 

 * Chris *

[Engine Doctor]

One other thing to consider if its a secondhand engine is that are all the parts the correct ones for the engine? 

A friend of mine now sadly passed away bought an OS 30 fourstroke S/H at Wings and Wheels a few years ago for £30 !! It looked in very good condition but had fuel issues0 in that the fuel came in too fast and  even with the neeedle wound right in it was still too rich. Yes somone had changed the threaded part that the needle screws into for a wrong part. Took a few mins to sort out but what a bargain . Obviously sold as a non runner . 

[Den Moran]

Thanks,everyone, for your help.

                                                     Recognising that this was above my pay level, I took it to my friend,Don, and, after an hour, he had it running like a watch, low idle 'nall! There wasn't anything specifically wrong, but a buildup of things like wrong felt washers and o rings (hardened), plus a super sensitive idle screw adjuster. It seemd to me that a 1/16 of a turn made all the difference between running smoothly at all throttle settings, and refusing point blank to start.

    Just a case of sod's law! Thanks once again,

Den,

Abertawe.