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D17 Carb? Compression Checked....results.


 
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Smith1000
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PostPosted: Thu Jun 14, 2007 3:49 pm    Post subject: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

I just checked the compression in the D17 that has not been started/run for many years. I have been able to start it, but can't keep it running very easily for very long and it smokes a lot. I have been thinking in terms of stuck rings and maybe lack of compression being the reason for no gas going into the engine.

I just checked the compression (non-running) and here is what I found: All 4 cylinders are about the same. The first stroke=92-95, second stroke=118 to 120, 3rd stroke=128-130 range. That's the max--about 128, maybe 130.

I have no idea what the compression should be, but this seems very good to me and should be enough to create pressure to suck the gas into the engine from the carb. Each of the cylinders did not hold the pressure. They all decreased in pressure very slowly--maybe because I could not get the gauge screwed in tight. It may have been leaking some around the threads. At any rate, the readings seem consistent.

I am back to thinking I have a bad carb. When trying to keep it running by taking my hand off the carb and putting it back on, I could see the governor/throttle rod working back and forth.

If the pressure is okay, I may just go for a new or rebuilt carb. I do not know this carb well enough to know if any parts are missing or if something is seriously out of whack. Just can't get it to idle/run though--high or low. The smoke today looked very black-somewhat blueish. I took out the mixture screw and it ran the same either way. Any thoughts on how I should proceed? Thanks.
 
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PostPosted: Thu Jun 14, 2007 4:12 pm    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

I'd say your compression is quite good. If it is over about 110, the engine should run great. The cylinders will leak down - that is normal. It is also normal to need a couple of strokes to get the maximum pressure. The compression indicates that both the cylinders and the valves are plenty good to run. What is left is ignition and the carb.

If the smoke you see is dark, the engine is getting too much fuel.

Before you buy a carb, check the spark. Pull each plug wire one at a time and hold the metal end (push back the boot so the metal is showing) about 1/16" from a good ground. You can obtain a good ground by cleaning the paint and rust off a space on the block or head. Turn the tractor over. If you see a consistent, bright blue spark on all wires, your ignition is probably ok. If it is inconsistent or weak, fix the ignition before proceeding with any changes to the carb.

The starting position on both carb screws should be 1 1/4 turns on the idle screw and 1 1/2 turns on the power screw. That is a good place to start.

If the tractor has not been run for a long time, a thorough cleaning of the carb and all passages is necessary and may solve all of your problems.
 
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PostPosted: Thu Jun 14, 2007 4:33 pm    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

Those numbers look good to me also. I would try what Texas says and see what happens. Weak spark can cause all sorts of problem in them self and as he said it the smoke is sort of black its not oil but the carb being set to rich
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Smith1000
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PostPosted: Thu Jun 14, 2007 6:19 pm    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

Thanks for the pointers. When I first started working on it last Sunday, it had no spark at all, so I went ahead and replaced the points, condenser and coil on Monday. That seemed to do the trick for the electrical. It then was/is getting spark at each plug. I replaced the plugs too, just yesterday. I do think I'll check for a blue spark though. I have been using a plug tester that lights up. It lights up yellowish, but I am fairly sure it is getting good spark now.

I am kind of back to the carb. I have good fuel flow to the carb. From there, the fuel does not seem to want to "atomize" to go into the engine. When I put my hand over the throat, I think it just finally sucks enough liquid gas into the engine, making it way too rich, but is does run until it burns up. It then just quits. The plugs look very black after.

Not sure I quite understand which tube the gas is to come through in the carb--I think the tube in the middle. Kind of a mystery to me as far as what is supposed to happen in there. This carb has a round, cone or barrrel that sits in the middle. It had to have problems last time it was run because the idle mixture screw was all of the way down when I started on it. Probably someone worked on it and couldn't get it right.

I guess a good soaking would help it. Could give that a try, but it does seem fairly clean and open currently. I can spray carb cleaner through each hole/opening. There is probably something fundamentally wrong with it that is right in front of me that I do not know to change/fix. I'll keep looking at it. I need to find a diagram for it. That might help. There might be a part missing for all I know. I sure appreciate the help.
 
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PostPosted: Thu Jun 14, 2007 6:24 pm    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

One thing I haven't checked is the intake manifold gasket. Maybe it is sucking air and it is loosing its pressure there.
 
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PostPosted: Thu Jun 14, 2007 6:44 pm    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

Cleaning a carb on an old tractor is not easy. I cleaned a carb on a Farmall M three times before it worked decently. It can look clean but still have one of those channels plugged or restricted.

The gas is introduced at load through the tube in the middle of the carb throat. At idle or even low rpm but no load, gas is provided through the idle circuit. It sounds like something is awry in the idle circuit. On some carbs, turning in the screw makes the mixture richer. Some others, turning in makes it leaner. Sorry, no idea which you have. If adjustment makes no difference (sounds like your issue), the idle circuit is clogged. Use some fine wire to run into those circuits along with a little carb cleaner. May take hours of probing to get them clean.

Since you say that you are getting black smoke, I'm wondering if the float is level and the needle and seat are working properly. Usually mis-adjustment of the idle screw will make it run worse. Black smoke says the adjustment is way off which usually doesn't happen at idle - hard to get way too much gas through the idle circuit - way too much is required for black smoke.
 
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PostPosted: Fri Jun 15, 2007 5:12 pm    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

The barrel thing is the venturi. Make sure you don't put it in upside down. Remove the main jet with a thin wall socket. Make sure holes in it are clean. Squirt carb cleaner in the hole where the main jet screws in. Should squirt out in the bottom of the bowl. Bet it is stopped up.
 
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PostPosted: Sat Jun 16, 2007 3:32 am    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

Thanks. I have looked a the venturi closely. Like you mentioned, I thought I may have put it in upside down. It is okay though. One end is smaller in diameter than the other and to countersink into place, it has to be in the right way.

I picked up a gallon can of carb cleaner yesterday. It has a basket inside to set the parts in. Will have it soaking shortly.

Also, I picked up the AC Shop Manual. It has the diagrams for the Marvel-Schebler TSX-773. I noticed that, in the diagram, the one in the book has a "high speed mixture needle" in the bowl. The carb I am working on does not have that. Instead, in that spot, it has a hex head plug only (kind of inset). Maybe some did not need the "high speed mixture needle" (not essential)?

I haven't quite figured out the "high speed mixutre needle" and the "main jet nozzle". The book looks different from what I have. I need to take the carb apart while looking at the book. The main jet in the carb appears to come out with a screwdriver. It is a very small jet. The main jet mixture nozzle does not appear to be removable with a socket--from what I recall. I need to take it off and look at it closer. Something is definitely different looking there.

The top part of the carb (throttle body) looks just the same as what I have-no differences at all.

Thanks again. I'll get this figured out--just need to keep looking at it. Hope it is just a good soaking/cleaning.
 
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PostPosted: Sat Jun 16, 2007 3:44 am    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

Just re-read you posting. I know for sure that (right now) if I squirt carb cleaner in the main jet nozzle or in the screw-in main jet, neither squirts out at the bottom of the bowl (currently).

They both squirt out, but not at the bottom of the bowl. The nozzle squirts out at the top of the bowl through 1 or 2 holes near the center. The main jet squirts out in the center or through the 2 holes-not for sure, but it is not coming out near the bottom of the bowl, so I bet you are right and it is clogged somewhere.

The bottom of the bowls has 2 little holes at the very bottom, one on each side of the center piece, in the middle. They open to a center opening/very small compartment at the bottom. The compartment or opening at the bottom has a plug screwed in from the bottom--presume this is a drain. I took it out and it appears this opening at bottom center is solid (inside-upper center). So, maybe it is plugged tight and I just missed where the hole is for the gas to go up to the jets. Hope that is the case. What you are saying makes sense to me though. Otherwise, how does the gas move from the bowl into the venturi? I am tracking with that and will look closer. Thanks.
 
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PostPosted: Sat Jun 16, 2007 4:48 am    Post subject: Re: D17 Carb? Compression Checked....results. Reply to specific post Reply with quote

Just took the carb apart again. Got it figured out, but it is not going to run for now. It is missing the "High speed mixture needle" and the screw in body/assembly. Someone must have taken it out--probably needed it for another tractor. It was replaced with a hex head plug to close-up the carb. The little orafice at the bottom of the bowl, for allowing fuel to go into the nozzle is completely blocked off by the substitued plug-so no gas into the nozzle or into the engine.

I am now wondering where or if I can order specific parts for the carb-the high speed mixuture needle and body. For this carb, the piece is really more of a valve than a needle. It just adjusts the flow into the nozzle. If I can't order it, I might be able to make something to fit in it to work for adjusting the flow. Maybe a plumbing piece-small valve from the hardware store would work. Looks to me like the needle is to adjust the flow into the nozzle that is about it.
 
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PostPosted: Sat Jun 16, 2007 6:15 pm    Post subject: Re: D17 ...Running Good.... Reply to specific post Reply with quote

I finally have it running and even mowed with it quite a bit today. I figured out something to work for the bowl valve. Picked up a 3/8 in. fine thread bolt at the hardware store and some other pieces, nut and rubber washer. I cut a groove with a dremel tool about 1/4 into the end of the bolt to let gas through. Bolted it in and ran down the nut, washer and rubber washer to seal the plug hole. It started right up and the new make-shift plug is even adjustable as far as fuel flow. I didn't cut the groove very deep, so I can tigten it down and acutally shut off the flow entirely. It ended up costing about 50 cents total for the parts.

It smoked quite a bit at first. I adjusted the carb and that helped. The longer I ran it today, the less it smoked. It had quite a bit of blue smoke. The rings are probably loosening up some. Seems okay now, but I think I need to pull the plugs and clean them up. Probably oil fouled somewhat.

I'll clean it up some more tomorrow and try to fine tune it some. The clutch doesn't seem that great. Not sure if it can be adjusted some. Kind of tricky getting used to not having live hydraulics. I have a 54 Super MTA with live hydraulics. I am used to it. I need to figure out what all of the levers are for on this D17.

Thanks for all of the help from everyone! I couldn't have figured this out on my own.
 
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