question on my 420

Willyr · Post by **Willyr** » Mon Jul 04, 2011 6:19 am

Heck of a question.

Engine has smoke like too much fuel at idle (adjust screw turned all the way in), no smoke whatso ever in higher speeds.

Also no power. Hope its timing, have to find some one with a strobe, solid state ignition you cant check by gap on points. Tried to load tractor onto trailer yesterday and had to choke it to keep it running. Plenty of fuel, good quarter inch of fuel streams out the line.

JD440ICD2006 · Post by **JD440ICD2006** » Mon Jul 04, 2011 6:57 am

Spark plugs too cold, valves not adjusted (.015 cold), timing, air leak between carb and intake manifold, etc.
It can drive us crazy. I make a list and then begin to eliminate each possible cause.
Good luck and keep us posted.

Willyr · Post by **Willyr** » Mon Jul 04, 2011 3:11 pm

Valves are adjusted 3 months ago. Originally the exhaust valves were .040 and tapped like crazy.

manifold gasket checked by spraying wd40 around gaskets (no change in smoke or performance). when carb was put on I always use a thin film of black permatex.

Plugs were replaced with NGK's set at 20 thou. Solid state ignition is hotter and require special wires as the voltage will burn traditional wires. Carbon wire as opposed to copper.

I had previously fiddled with timing and set it to where it sounded best, as to why I believe timing my be suspect?

Willyr · Post by **Willyr** » Mon Aug 01, 2011 5:56 pm

Well a buddy of mine (Greg Ring) came over with his strobe light. The spark was so far off it wasnt even seen in the hole. After rotating the distributor some 20 degrees the spark mark is now where it is supposed to be.

Also she has a better bark to her too!

Post by **Lavoy** » Mon Aug 01, 2011 10:23 pm

Idle mixture screw on a Marvel Schebler TSX series is an air screw, not a fuel screw. All the way in is full rich, out is leaner.
Lavoy

Willyr · Post by **Willyr** » Tue Aug 02, 2011 12:02 am

Ok I will check that, thanx. All info is good to know.

Paul Buhler · Post by **Paul Buhler** » Tue Aug 02, 2011 12:35 pm

Idle mixture screw on a Marvel Schebler TSX series is an air screw, not a fuel screw. All the way in is full rich, out is leaner.
Lavoy

Lavoy: On my TSX688, I have to completely close the idle jet to get a smooth idle.
Any ideas as to why?

I've disassembled the carb, cleaned all the ports and galleries with compressed air and carb cleaner, and then reassembled it with Permatex on the gaskets to seal up any gasket air leaks - I also checked and tightened up the throttle shaft felt seal. The tapered idle pin looks good - no evidence over tightening. Thanks

JD440ICD2006 · Post by **JD440ICD2006** » Tue Aug 02, 2011 4:58 pm

There are idle circuits that many times need to be cleaned with a wire. Compressied air will not always get the crud, even if they have been soaked.
What is happening is similar to having to use choke to keep one running. Instead, you are having to close the air bleed all the way to full rich just for it get enough spray to run at idle.

Post by **Lavoy** » Tue Aug 02, 2011 5:49 pm

I have found more than not over the years on average I have had to run most of the ones I have done closer to closed no matter how clean the carb is.
Lavoy

Paul Buhler · Post by **Paul Buhler** » Tue Aug 02, 2011 7:04 pm

Thanks guys. I noticed that on a few carb sites, they sell long drills for cleaning the various galleries, yet the manual strongly recommends against using a wire. I was wondering if it was worth replacing the needles and jet orifices, but mine seem to be in pretty good shape. I know that one can get pretty obsessive about these things.

Since I've gotten the machine to start, run strongly and pretty reliably, I think I'll just work it as is and be happy. Maybe some day I'll spring for a professional carb rebuild. but until then, I can use the monies for some other more pressing need.

Thanks again, Paul

JD440ICD2006 · Post by **JD440ICD2006** » Tue Aug 02, 2011 7:35 pm

This is the basic design of the later TSX carbs. My other books are at the farm.

Believe it or not, sometimes they will clear up or run a little better after you put some hours on them.

As you can see by the diagram, there are a number of ways the idle can be fouled. P, Q, R, I, H, G, T, C, and D can each have some small crud, varnish, or rust particles in them and cause problems.
You never want to use anything but the drill bits that are specifically made for this carb, and use them with great care. These are small and precise passages. Any enlargement of any passage can create issues that can never be fixed correctly.
Also, the holes in the nozzle must be aligned properly, and the velocity stack must be in the correct direction.
This is part of the reason why so many carbs, after soaking and compressed air, etc., still do not function correctly.

Paul Buhler · Post by **Paul Buhler** » Wed Aug 03, 2011 11:52 am

Thanks again. Paul

H-D · Post by **H-D** » Wed Aug 03, 2011 11:53 am

Cleaning the passages with anything metallic used to be majorly frowned upon, but with the advent of ethanol 'enhanced' fuel that caveat is pretty much out the window. As a case in point, Honda now has metal ended tools in their inventory to clean their off-road power equipment's carbs. I'm fortunate enough to have a station near me that vends 0% ethanol content fuel, which I found through a site Pure-Gas.org. It's ~ $.50/gal. higher, but it does have more BTU/gal than the new stuff & I have way fewer carb hassles than my neighbors.

JDcrawlers Messageboard

question on my 420

question on my 420

Who is online