John Deere LT 170 misses under load?!?!?!?!?!

Hi Guys / Gals,

I though I would see if anyone had any suggestions for me before I start replacing ( more) parts.

I have an LT 170 with a briggs 16 horse V twin. Just recently (past two months) started missing under load going up hills and is getting worse. What I have done:

1) Use Stabil - no change
2) Change airfilters - no change
3) Change fuel filter - no change
4) Change and gap plugs ( new) - noticeable improvement old plugs were .005 out of tolerance.

Most of the missing had greatly diminished...almost all gone...but the next use seemed to take a step back with performance degrading again under load again. Adding choke under load seemed to make a slight improvement in performance, but it is imperceptable at times and is hard to say how much improvement if any.....

5) Changed fuel pump - no change

I would entertain looking into the carb first, but have considered coil / wires which appear to come as part of the armature assembly......realy want to nail this down a bit further before I throw more at it.

Any one care to share his / her thoughts? It would be greatly appreciated!!

Best,

Steve

Hello Steve... & WELCOME to LMF....

There is no reason to double post, all it will do is spread any replies you may get, all over ...
The fact that it has any improvement when using the choke, that will move me away from ignition and toward the carburetor....

Are you saying this only seems to be happening when going up a hill. And not necessarily when subjected to a heavier load???
If that is the case, I'm right back at the carburetor... The float is not at the right level OR there is water in the bottom of the float bowl... it will accumulate there over time... :smile:KennyV

Thanks for the reply Kenny.

Typically I do not double post, but my thoughts were along the lines that certain people look in certain sections and do not look through the entire site. Just figured I'd take a chance with replies in multiple areas to increase my exposure.

As far as your reply is concerned would you mind explaining your load comment to me?

Perhaps I did not give enough detail..... It is a very steep hill, full throttle, pedal is 99% depressed. I would normally think an engine would be under load on an incline, at least to a greater degree than over a level surface. When ascending my hill with the mower deck engaged, the engine is probably under the highest load I encounter. I did notice the load imparted by the mower deck seems to push it over the edge to start missing.

I guess my thoughts were also to look at the carb, but I would be suprised to see water. Who knows, I'll take a look and see what I find.

Thanks again for your input!!

Much appreciated!!

You should be able to load the engine with the mower deck... heavy green thick grass at a goo speed should load it, if your problem is not there during that kind of load, on level ground....
But is there when on a hill, That would be a strong indication that the float is not adjusted right OR that the fuel is setting on a layer of water in the float bowl ... :smile:KennyV

Thanks Kenny!

I will take a peek and check back soon to report my findings.

Thanks very much for your response!!

Steve

You said you put new plugs in, how are the plug wires.

You might also want to check the condition of your battery. Under load, if you have a bad cell or low voltage, it will miss. Does it run OK without the mower deck engaged? If it does, then I would take a long look at the battery.

Thanks everyone for the input.....have not gotten to check anything else yet, but will say the original 9 year old batter was just replaced with a new one in May....I'll check the voltage when running and under load just to see...you never know.

I will say though, my original battery was on its last leg and I got only 2 -3 starts every event before it died, but if she was running I did not have the miss issue.

The new battery is from Walmart, so maybe its crappy.....I will see.

I also suspected the wires but without taking anything apart yet, it looks as though (from the IPC) the wires are integral with the armature / coil assy. It was hard to tell from the drawing, but they did not list the wires separately.....figures. I think the armature / coil is like $ 40 a piece (x2)

Thanks again

Hi Everyone,

Pulled the carb, looked good with no water in it. Completely cleaned out and reinstalled with no improvement. At least I was able to clean up the carb area and change the rotted fuel line!

I will be going after the coil armature assemblies now. The have the spark plug wires attached and integral to these units. I am thinking it must be ignition related as it seems I have ruled out the fuel system.

Let me know if anyone has any good places to order part online as my local store is closed for the week.

Thanks in advance for everyones help!!

Have you been able to resolve your issue with new coil(s)? I have a John Deere 425 with a 20hp V-Twin, and am having the same problem - it will miss sometimes under the load of the mower deck. I've also tried all the things you mentioned, including replacement of the ignition relay module. It comes and goes, and sometimes I'll get engine backfire when I shut it down. Without load, it runs fine.