Craftsman 26 HP Pro V twin- Model #SV735S
The problem has gotten worse since the beginning of the season. The mower starts fine but at some point it loses RPM's, not much, but enough to slightly bog down the blades. It then smells like the exhaust is running rich. It' s random on when this happens and how long it lasts. Eventually, like someone hits a switch, it instantly revs back to full RPM. Now it runs with loss of RPM more than it runs at full RPM.
At the beginning of the season I changed the oil and filter, fuel filter, air filter, the plugs, and cleaned the deck.
The only thing I see is when I remove the air filter the carb has two holes about the same size, one looks like it has a nice finished edge and the others looks like it has a melted edge? Is there supposed to be two holes there?
Any help is greatly appreciated.
Thanks,
Mike
Thanks for the reply Rivets.
I'm a novice in small engines; where can I get more info on the carb for more details.
I would like to see if the other hole in the carb is normal.
Thanks, the manual is great, but it still doesn't show me the view I need to see if there is one hole or two in the top intake. I sprayed some carb cleaner in there with it running, a few short bursts. It seemed to run fine but that was only for about 15 minutes or so. The problem is random and I doubt that a simple dose of carb cleaner will solve my problem.
I'm going to cut the grass again soon so I'll see how it acts again and get specific about the symptoms.
Remember, I can't see what you are talking about with two holes. I can only assume that you mean the air vent and bypass openings when you are looking into the carb from the air cleaner side. Back to my original statement, time to clean the carb. If you don't feel comfortable doing it, you'll need to find someone who does.
AH-HA, so there are two openings (maybe). Anyway not important now. I'll see what I can do about cleaning the carb. I have cleaned a carb on an old Honda motorcross bike; I guess it will be similar. Do you have any tips or suggestions... products to use?
Thanks for the help!
Best way to do it is to take it to a shop which has an ultrasonic cleaner. Most of your top repair shops should have them. You will be able to get your rebuild kit there also. With limited experience, doing this yourself could end up costing you big bucks for a new carb.
Before I had read your last post I watched some you tube videos and decided to take apart my carb. It was very clean. The mower has about 200 hours on it. I got the float needle out, it was shiny and clean, rubber tip still looked brand new. The float seemed to be working fine, no gas in the float. The fuel bowl was shiny clean. I was spraying carb cleaner on everything and using compressed air to blow out the jets? or anything that looked like it moved gas or air. I unscrewed something from the bottom of two jets? just under the float, sprayed cleaner and air through those; put everything back together and within 30 seconds of starting the mower it lost RPM's all at once , like someone flipped a switch, not much RPM's but enough for the engine to change sounds and the exhaust to smell rich. The blades still turn, just slightly slower.
When the mower did this, I shut off the blades and pulled the lever to the slowest setting, idle, within 5 seconds you can hear the engine kick back up, I then would push the lever back to full and kick the blades on and it would run fine for about 10-15 minutes, then lose those RPM's again at some point. I was able, everytime, to get it come back up to full song by going to idle with the blades off until I hear it kick back in and then going back to full and turn the blades back on.
What else in the carb should I be looking for?
Do those symptoms tell anyone where else I should look?
Thanks for the help
I'll see if I can a place to do the ultrasonic cleaning, and compare that to the cost of a new one.
At this point, are we pretty sure it's the carb? Or is there anything else I might be able to check before I involve a professional?
Thanks
I got the carb back from the ultrasonic cleaning and rebuild, $102 total. I still have the same exact problem. It's not the carb, unless the cleaning missed something. The shop said I could bring it back to have it cleaned again, but it's so clean, only 200 hours, I don't think this is the problem.
I got a spark tester and when the engine started to show it's *** I caught it on about the third time; the right side spark plug wire had no spark. While I was watching the tester, in about 1 second the spark reappeared, and the engine was singing at full song.
Did I find the problem? And what next?
Any help is appreciated.
I took the ignition module off of the right side, the side with no spark, last night. The shop said they've got the ignition module for $56. I'll try to pick up the new one on Monday.
Oh yeah, that "other hole" I was talking about was on the plastic "breather" that sits on top of the carb and holds the air filter. I believe there is supposed to be two holes there.
I'll update after I get the new ignition module installed.
Am I heading in the right direction?
Before you pick up a new coil, try removing the kill wire on the coil, ignition module, set the air gap at .010 and see if you have consistent spray. You can do this with the should off. If the engine runs smooth, you may have a kill wire short. Don't run it to long will out the should, as it is a main part of the coll system.
Thanks for the reply, however I'm still a novice on engine work. I think I can figure out which wire is the kill wire, but I don't know what you mean by set the air gap at .010 and check for consistent spray. I'm guessing the air gap of the plug? and consistent spray somewhere in the carb?
What is a should and a coll system? I'm guessing the shroud maybe, the plastic around the engine. I don't see any way to take apart the ignition module. And coil system or cooling system?
I just found out the shop would need to order the ignition module and they are $101. I'd like to try your method first, but really sure what to look for.
If you look at the electrical diagram part (I) is the ignition module (coil). The air gap I am talking about is between the legs on this coil and the magnets on the flywheel. Read pages 67-68 of the manual I posted.
OK, I understand the magnet and coil part now. Thank You! The manual says the gap should be 0.30mm or 0.012in. between the magnet and the ignition module. I'll check the gap with some feelers or something. I'll will remove the kill wire on the coil, check the gap, and crank it up but I'm still not sure where to look for the consistent spray. I guess I would notice the by the engine sound.
Usually the mower doesn't have any problems until about a 10 minute warm up. I guess I should I should get it warm first of all, then do the other stuff?
I took the coil over to the shop; they said they tested it and said it was bad. This is the first time I've used this shop, not sure if I can trust them. I didn't buy a new one yet. Can you test a coil in a shop? it really wouldn't be the same as being in the mower's conditions, heat...
After looking at the mounts for the ignition modules, they look like they cannot be moved/adjusted like the manual says. I guess that is for a different model. There is no way for them to slide. It bolts solid to the cooling fins with two bolts. I see the magnet spins past both ignition modules but there is no way to adjust the modules. Does the magnet adjust?
The coil legs have slots, loosen the two bolts, 1/4" nut driver works best, pull the coil away from the flywheel and tighten the screws. There gap at this point is less than .050. Turn the flywheel until the magnets lineup with the coil legs.insert feeler Gage, I use .010" on all engines. Loosen screws and the leg should draw tight to the flywheel, you need to do both legs at the same time. Retighten the screws and you are done. Magnets on the flywheel cannot be changed or moved. Hope this makes sense. Today's coils can be tested with a specialized expense tester, which many shops do not have. I test them by setting the coil, removing the kill wire, and spinning the flywheel while looking for spark. No spark, bad coil. I do not have the bench tester to test off the engine. Hope this helps.
Thanks for the replies guys. I'll look at the module again, but I did not see any way for it to be adjusted. The manual shows the slide rails(model SV740) but my model (SV735-S) did not have any rails. I have the DSAI, which makes the price of the coil go way up.
I understand the process of testing the coil, but I just don't see how the module is supposed to move. It's 105 heat index here, at some point I'll try to get another look. Even if they don't adjust, I'll disconnect the kill wire and check for a spark.
But the problem has been random from the start. Even after I caught the right side not sparking, when it acted up I shut it off and put a spark tester on the wire, saw no spark, pulled the tester off, started it back up, it ran fine for the next hour. I got the grass cut and it was still running fine. The next day 5 minutes after start, it started acting up again, but random. It would come back up to full song, run that way for a while, then drop RPM's again, just sitting running in the driveway not moving.
While trying to cut the grass, I've caught the right side with no spark 3 different times, the left side always had a spark.
I'll update after I try again. Thanks for the help.
Problem solved!!
Thanks for the help guys, I would have gotten no where without Rivets.
I put the new ignition module (coil) on, $101. There is no way to adjust the coils, they are a fixed amount away from the magnet. It fired up and ran with no problems for 2 1/2 hours. I think we've fixed it.
