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Need help, 5.5 hp suzuki is knocking

4613 Views 40 Replies 18 Participants Last post by  O P M
I have a 21" toro with a 5.5 suzuki. My problem is, after about 10 minutes of mowing, my mower starts to knock, ping, rattle, I am not quit sure. It does'nt seem to affect the cutting at all, but I am unfamiliar with 2 cycles and don't know if it is normal or not. The sound does seem more pronounced when it is on grass instead of concrete. If anyone can help I would appreciate it.
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Lonnie i have a 21 proline 4yrs old with 4-1/2hp suzuki it does make a ratteling sound but never knocks, id take it back to your dealer and let him hear the machine, good dealer will take care of you.....Marks Mowing Service
Mine is doing the same thing. So I called my dealer this morning he said it could be a detonation problem or it could something with the blade? Hopefully they can get it figured out. :confused:
Mine too!

Ten minutes of hard work and it starts to knock and rattle. The mower is less than a month old. I only run about 1 to 2 tanks of gas through it per week, so you can imagine it's not worn out.

My a$$hole dealer tells me it is normal. I had a customer ask me if I hit something and hurt my mower, because it was rattling. I told her no, and she said it sounds like you need a new mower. Yup, 983 dollars and less than a month old, and that's what I get.

Dealer had it for three days and gave it back telling me it is fine and dont worry about it. He's losing a ZTR sale over this issue. I'll never buy from him again.

I thought the 2 stroke Proline was the best there is. Now, I wonder. Sorry to vent, but I thought I was the only one who had a noisy Suzuki.:cry: :cry: :cry:
Hey guys, Mine also started knocking soon after I got my mower which was in April, but it quit and I haven't heard it since, until this week. My dealer also said that it could be the blade hub that is under the mower could be loose,but it sure doesn't sound like I would expect $985.00 mower to sound. I also told him that other people were having the same problem. I'm supposed to take it monday, if I find out anything I'll let you know. Have a good weekend. :cool:
Oh great, I just ordered mine (due in next week) and I can just see my wife now yelling at me for going overboard on a Proline and then having it knock. She wanted the kawaski and I said no, the Suzuki is the better engine. Hopefully it is just a loose part and not the engine!
Is everyone running the same oil who has knocking???
I use only Stihl oil. I use the gas station's digital pump to assure that I get the exact amount of gas needed in each can.

My dealer checked compression on my machine and said it was good, so he knows I didn't run straight gas through it or anything (it would have hurt the piston and cylinder running it without pre-mix).

They also took off the blade hub and stuff underneath and spent hours scratching their heads trying to figure it out, They said that the noise is in the engine for sure, not external.

He told me to run it till it scatters. I'm gonna be hard to get along with when it finally breaks and I have to use my back up Snapper (POS). Nothing I can say will make him warranty it till it blows up. I'm definitely not buying my ZTR from him. I bought my Scag walk behind there, I hope it doesn't ever need warranty work.:angry:
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I'm running stihl oil thats all I have in my two cycles. I don't think it is a major problem,as there are too many of them out there. It is just annoying as heck to hear this clanging sound. It is more of a rattle than a knock. As for the two cycle vs. the kaw I ask the dealer and they told me the two cycle hands down for the commercial work. So I hope they're right. :)
I just Switched my order for 3 of the Kaw Prolines to Suzuki's because of the biGGer gas tank & Much Better Air Filter. From what I understand Both models will be replaced with the Gutless Honda neXt year.

Do You people with the Knocking Problem Have the BBC?
Not to get to far off topic, but what made the 5.5 Suz two stroke more attractive than the 6.5 Kaw. Test drove one at my local shop could not believe the ground speed, and how quite the thing was. Not really too seriously looking for a trim mower so did not cut any grass with it The proline was 850 out the door.
The Kaw has a sMMall gas Tank & I don't Like the Filter set-up compared to the Suzuki's because of the open Mouth.

The Suzuki is also alMost Maint. Free.
:) Only oil i use in mine is lawnboy 2cycle, it don't rattle all the time just under a load, Like Ultimate said the Suzukie's are almost maint-free, funny why the 5/5hp is knocking, good thing is there new and under the warranty........Marks Mowing Service
The knock is caused by carbon buildup in the cylinder. The piston is hitting the carbon. It it louder after running 10 min. due to expansion in the engine. The engine needs taken apart and de-carboned. After you get engine de-carboned switch to Amsoil 100:1 premix oil and you'll never have that problem again.
I've heard about these things carboning up, so, I asked the dealer when I took it in, if it was going to be carboned up already, bieng so new (6-8 tankfulls) and he said, no, mine's not been used enough to have that much carbon already.

I understand it take more usage than I've done to accumulate the carbon.
Sorry to hear about your problem. If it is any consolation, we have a 96 Proline 2 Cycle which knocks and rattles on and off. It has been doing it for years and is still running strong. However, it is the best purchase we have ever made.

Now, in my case, I believe the cause is carbon.

I looked in the Toro 2002 LCE Service School Notes and they have listed the following under Tech Tips. This was never issued as a service bulletin though so your dealer might not be aware of it.

Direct Quote:

"Suzuki Engine Knock

We have had reports that some 1999 and 2000 21" Heavy Duty mowers, with Suzuki engines, experienced excessive engine knock when hot and under load. After investigating we found that some engines had the high altitude jet (p/n 81-2340) installed, causing a lean condition in normal altitude operation. If you encounter this situation with any of the above mentioned models, install main jet, (p/n 81-1060). "

Iwould also write the Toro tech line under the Toro Web Site under "" I have found them to be helpful.

I hope this is help to you and good luck with resolving the problem with your mower.

Craig Jones for Tim's Lawn Service
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That is exactly what I was going to suggest...going to a bigger main jet in the carb. After years of racing 2 stroke motorcycles, that definitely sounds like you are running lean. I would first try at least 93 octane pump gas, or even better, find a station that has some 100+ octane race gas and try it. If you are running too lean though, that's a quick way to tear up a perfectly good motor.
Ok, so I ordered mine from, which is in Colorado. I had not thought of Toro making different set-ups for different markets, but it makes sense.

So, how does one know if they have the "high altitude" jet versus the "standard jet". If I bought it "elsewhere", will a local dealer do this substitution free of charge?
I wouldn't count on your dealer changing it for free. I am sure they would be happy to check/change it for a fee. I am not sure how the carburetor is on that engine, but most likely all you need to do is take the bowl off the bottom of the carb, and the main jet will need to be unscrewed from the carb. It will most likely be brass. It should have the jet size stamped in it. See if your dealer will give you a diagram of the carb. This should get you the info to do it yourself if you are mechanically inclined.
You can check the Toro website under "Parts Lookup" You would need the model number and the serial number. They have an excellent diagram of the carburetor.

This should be quicker than getting it from the dealer.
I checked with and they said that all of the two-cycles come set for sealevel operation. Since they are in Denver, the ones they sell locally they switch the jets to the high altitude jet.

If this is true, then I am not sure why some people clearly not in a high altitude areas would have the wrong jets unless they were purchased used from these areas. Maybe there is another issue??
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