Archived

This topic is now archived and is closed to further replies.

jailerman

Carburetor Help!!!

12 posts in this topic

I hope someone can help me. I have a 674 gas with a Marvel-Schebler model TSX carb on it. It always runs really rich. It operates this way from idle to wide open, looks like a diesel pulling a load! I've had the carb apart twice with a new kit. This model is of the fixed jet style so there is no adjustment needle on the main jet. It just has the idle adjustment needle and can't get it to lean out even on idle, you can screw that one in until engine quits and will smoke til it shuts off. I've adjusted the float so I know that the bowl is not overfilling. If you unplug the the anti-dieseling solenoid the engine will clear up and sound good right before it quits. Any ideas before I say the heck with it and get a different carb?

Share this post


Link to post
Share on other sites

Well I was really hoping someone would have some ideas for me. I went to the CIH dealer today and talked to a couple of mechanics and the best answer they could give me was to bring the tractor in so they could look at it. I think at the current shop rate it would be cheaper buying a new carb if indeed that is the problem. Does anyone have any other ideas? Could it be something else like fuel pump putting out to much presure and blowing the needle off the seat? Vaccum leaks should cause it to run lean and not smoke or fowl plugs out right? Someone has to have an idea that I haven't tried yet I hope. I do know of a 574 that i'm sure I can borrow the carb off of to see if it is the carb for sure as long as thats the same one as my 674 uses.

Thanks

Share this post


Link to post
Share on other sites

Figured somebody would have chimed in by now, here is my two bits.

Leaks are certainly just what you think. Burnt parts usually follow.

If it consistently runs fat, then it generally isn't a pressure problem. Going from low consumption idle to full load will generally change the symptoms if it is a pressure related. A stuck piece of dirt in the needle usually causes the same thing if it makes the needle not seat.

It sure sounds a lot like an internal leak. Does the smoke factor change with load?

Share this post


Link to post
Share on other sites

Have you tried operating this tractor with the air cleaner pipe disconnected? Once upon a time we had a John Deere 2 cylinder tractor that ran rich all the time. Turned out that the air cleaner piping was plugged up with mouse nest crap.

Share this post


Link to post
Share on other sites

Are you sure that this is the correct carb for the rig? Being a fixed jet it could be from a different engine, or set for a different altitude than your currently at. Being rich you can make a quick tweek to the jet by inserting a small peice of wire in the jet, efffectly reducing the orfice size. Remove the jet and insert the wire bending it so that it catches both sides of the jet and will not fall out. Consider ordering the correct jet from CIH, or go to the local carb or hotrod shop and see if a Holley or Carter jet will fit.

I assume that you have checked for a sinking float. Stampmaint also has a very good suggestion in making sure that your getting good air to the carb inlet and take it a step further and check the that the choke plate is opening correctly.

Have you owned this rig long or is it new to you? Have you ever seen it run correctly or has it been wonky since you've had it. If ran good at one time and then changed, while you've owned it, then we can assume that the jet is correct. If you've never seen it run correctly then you have to figure out what the PO may have done or changed to get it to run rich. It could have been the PO wanted more HP and figured the easy way to get it was to drill the jet.

lg

no neat sig line

Share this post


Link to post
Share on other sites
I hope someone can help me. I have a 674 gas with a Marvel-Schebler model TSX carb on it. It always runs really rich. It operates this way from idle to wide open, looks like a diesel pulling a load! I've had the carb apart twice with a new kit. This model is of the fixed jet style so there is no adjustment needle on the main jet. It just has the idle adjustment needle and can't get it to lean out even on idle, you can screw that one in until engine quits and will smoke til it shuts off. I've adjusted the float so I know that the bowl is not overfilling. If you unplug the the anti-dieseling solenoid the engine will clear up and sound good right before it quits. Any ideas before I say the heck with it and get a different carb?

Check that metering orifice is in solenoid end. Is the plastic venturi distorted\melted?

Share this post


Link to post
Share on other sites

Ok here is a little more about this one. Dad bought it brand new and about 8 years ago had a major overhaul done on it. It has the orginal carb yet. I got it when dad retired from farming the second time about 4 years ago. The first 2 years it ran great then it started this running rich thing. The first time I had the carb apart i had it and all the parts cleaned. I also checked the float for leaks and make sure it wasn't sinking. The second time I took it apart was to reajust the float to make sure it wasn't over filling the bowl. Both times I ran it with out hooking up the air intake pipe so I know for sure it isn't restrickting the flow and can see that the choke is wide open. I brought up the fact about the fuel pump because sometime after puting on a new one is when this all seems to of started.

As far as the metering orfice it all matches what the book shows is should look like but everything is brass not plastic?

Oh yea as far as changing underload or at different rpms idle to around 1500 is the worst but pulling a load or running down the road wide open it still smokes quite a bit. Its black smoke too not the blue like if it were burning oil. Been checking that too and have to dump oil often as you can smell gas in it after a while.

Share this post


Link to post
Share on other sites

Yes it could be your fuel pump is putting out more pressure than the needle and seat can hold back. One thing you can try is to rig up a temperary gravity feed fuel tank to the carb. I think I would try this first.

Share this post


Link to post
Share on other sites
The first 2 years it ran great then it started this running rich thing.

I brought up the fact about the fuel pump because sometime after puting on a new one is when this all seems to of started.

The first two years... was this the first two years since new or since you owned it? And when was the fuel pump put on?

Lets assume that you have properly diagonsed that the fuel pump is the culperit. Can you easily take the pump out of the system and run it on gravity flow? On the few old tractors that I've worked on these all have run on gravity flow from the tank to the carb. If you can rubber hose around the pump as a test it would give you a data point to go with. If that proves good then you can can do what ever is necessary to keep the fuel pump from pushing fuel past the needle valve, which is what I suspect. Or you didn't fail to put a gasket under the needle seat before installing it or have developed a crack in the casting. Lets assume that you've not left the gasket out. Then it comes down to knowing what the fuel pressure is to the carb, what it is supposed to be.

I'm going to leap out here with a wild guess... you didn't get a diesel pump per chance. I think that they are quite a bit higher in pressure than a gas rig. I would guess that the gas rig would be in the 3-5 psi range and diesel in the 20-35 psi range.

I'm basing my opinions on years of hotrodding and some tractor repairs around the farm. I'm not familier with your rig but have been into a few of these carbs in the past.

lg

no neat sig line

Share this post


Link to post
Share on other sites

You may want to try a new float. I have seen dimples worn in the old float by the old needle valve. When you put in a new needle and seat, it hits in a slighlty different position, tries to fall into the worn hole, and binds the needle. It wont' seal and runs over. I know Binder is proud of their floats but we have seen that a needle/seat change sometimes requires the float also. Look for a divot worn in your old float arm, this may be the culprit.

Make it run without the air cleaner pipe attached. When it runs as it should, then reattach it. This will take that potential air cleaner problem out of the loop. The guys are right, there have been a lot of wierd stuff found in air cleaners.

The diesel lift pumps are generally identical in pressure. All either has to do is get a full flow of fuel to the carb or diesel pump.

Keep us in the loop.

Share this post


Link to post
Share on other sites

Thanks for the additional input guys. When I say it ran great the first 2 years that would be of the 4 that I have owned it since dad moved to town. Nothing was done with the tractor other than use it and change oil, the only thing that did change since i owned it was 2 years ago I replace the fuel pump. About that time is when I started having the problem but it has continualy gotten worse. I don't have a way to check the fuel pressure and as far as hooking up a gravity flow tank I think I can rig something like that up. Yes I have the air intake pipe unhooked right now so I know its not a restriction in there and can also see the choke blade so I know it is fully open. I haven't tried a float yet so that is another possibility. What do you guys think about swapping a carb from a 574 on to it just to see if it is indeed a carb problem?

Scott

P.S. fighting with this tractor is starting to make law inforcement a lot more fun!

Share this post


Link to post
Share on other sites

If it looks like it will bolt up (haven't a clue there but odds are good) and is easy to swap, I would do it just to prove it to myself. The circumstances are suspicious, but are probably just that. A new pump can expose old weaknesses. You would think a float problem would have gas running out the carb, but sometimes it takes vibration to make the magic happen. :lol:

Share this post


Link to post
Share on other sites