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Unread 08-04-2014, 01:40 AM   #1
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Default 399 rotax in EZGO problems

So I have an old EZGO and I have put a 399 Rotax in it from a Ski-Doo sled and boy has this project sent me on an interesting ride. I have a few questions about the engine itself and about how to modify different parts to work better for me.

1) This engine is loud as all get out and I'm wondering what type of two stroke exhaust set up would be best for noise reduction. I know the nature of a two stroke is loud but I'm not exactly at a lack of power here with such a large engine so whatever option to quiet it down and compromise some power is not a worry of mine.

2) The Rotax carburetor is a Tilotson and I am having the toughest time tuning it. It seems that a temperature drop of only 10 degrees requires attention to the dang thing. Is there a fix to this or possibly a carburetor replacement?

3) The engine has a magneto that puts out AC which on the old snowmobile was supposed to run the lights, I would like to use it to either charge a battery or run the lights (whichever is easiest) but my research tells me I need a rectifier regulator in line in order to control voltage spikes and convert to DC. What is the usual procedure to do this?

4) Back to the tuning of the carb, when I'm test driving after a new tune or something it has a habit of bogging down and losing power then back firing and quitting on me. This sounds like the carb is flooding to me so I try to lean it out but it seems like nothing I do gets the desired effect! When the engine is cold and I take it for a drive it is common for me to see 30 mph on the gps speedometer but after the engine gets good and warm it becomes sluggish and sounds like it is only revving to about half of what is does when it is running correctly. Any tips on a better system to tune the carb?

Thanks in advance for any help
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Unread 08-04-2014, 06:21 AM   #2
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Default Re: 399 rotax in EZGO problems

Quote:
Originally Posted by buggynovice12 View Post
So I have an old EZGO and I have put a 399 Rotax in it from a Ski-Doo sled and boy has this project sent me on an interesting ride. I have a few questions about the engine itself and about how to modify different parts to work better for me.

1) This engine is loud as all get out and I'm wondering what type of two stroke exhaust set up would be best for noise reduction. I know the nature of a two stroke is loud but I'm not exactly at a lack of power here with such a large engine so whatever option to quiet it down and compromise some power is not a worry of mine.

2) The Rotax carburetor is a Tilotson and I am having the toughest time tuning it. It seems that a temperature drop of only 10 degrees requires attention to the dang thing. Is there a fix to this or possibly a carburetor replacement?

3) The engine has a magneto that puts out AC which on the old snowmobile was supposed to run the lights, I would like to use it to either charge a battery or run the lights (whichever is easiest) but my research tells me I need a rectifier regulator in line in order to control voltage spikes and convert to DC. What is the usual procedure to do this?

4) Back to the tuning of the carb, when I'm test driving after a new tune or something it has a habit of bogging down and losing power then back firing and quitting on me. This sounds like the carb is flooding to me so I try to lean it out but it seems like nothing I do gets the desired effect! When the engine is cold and I take it for a drive it is common for me to see 30 mph on the gps speedometer but after the engine gets good and warm it becomes sluggish and sounds like it is only revving to about half of what is does when it is running correctly. Any tips on a better system to tune the carb?

Thanks in advance for any help

I grew up on snowmobiles and 2 stroke bikes. I'm not an expert on them, but regarding the carb/fuel issue, you may check for any possible vacuum leaks around the intake manifold/carb. Tank height compared to carb can make a big difference. I'm assuming the engine when it was on the sled probably had a vac. operated fuel pump on it.(?) Happen to have a different carb you could try?

Sound...I don't imagine you have a lot of room for much of an exhaust. Might want to post some pics. Don't know if you have room for an old school hot rod "glasspack" on there do you? I can't remember what it was on, but I remember seeing some guy had used a glasspack I think on a sled that quieted it down more than I thought it would. Took that "crack" out of it.

A couple years ago I wanted to put some LED lights on my snowblower. Same situation the stator puts out ac and led lights need DC. I found a link on a snowblower web site that I hyperlinked in the quote.

Good Luck. Have any videos?
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Unread 08-04-2014, 09:37 AM   #3
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Default Re: 399 rotax in EZGO problems

The carb has a bladder pump on the bottom with like 3 or 4 different channels that have vinyl-like inserts, I have never seen one like it so I'm not sure how to describe it. Is this what you mean by vacuum pump? I tried to make a air intake that would suck air from outside of the engine compartment so that it would be sucking the same temperature air even after the engine got hot (trying to take out all variables and narrow down the tuning problem). I do think the carb pump system has a leak but would that be robbing the carb of gas enough to cause the twitching tuning?
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Unread 08-04-2014, 09:56 AM   #4
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Default Re: 399 rotax in EZGO problems

I am trying to figure out how to post the pics I took, lets see if it works. The pics show how I have the engine and intake set up and also a close up of the carb. The tank is in the rear floor board on the back. If it has a bladder system fuel pump then in theory the tank height won't matter right?

I am thinking I need to go ahead and order a Tilotson carb rebuild kit and start there. Do you have any pointers on how to prevent overheating? Im in Texas and I have heard these engines tend to overheat in our hot summers.

I believe I have enough room for really any type of exhaust. I have a buddy who is much better with a welder than I am so I plan to use his skills to make a custom fitted one to tuck behind the engine maybe above the rear axle. Is the glasspack as mentioned special for small engines or just like a car glasspack?
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Unread 08-04-2014, 05:09 PM   #5
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Default Re: 399 rotax in EZGO problems

On my cart I took the stock exhaust expansion chamber and welded on an exhaust from who knows what but I kinda stacked it up to make room. In regards to your carb I would scrap it and get a mikuni sled carb with a separate fuel pump. I had a old scorpion sled with a carb like that on it and no amount of tuning could get it to run right till I replaced it.
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Unread 08-04-2014, 07:27 PM   #6
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Default Re: 399 rotax in EZGO problems

Quote:
Originally Posted by buggynovice12 View Post
The carb has a bladder pump on the bottom with like 3 or 4 different channels that have vinyl-like inserts,
Yup. Some are external, but yours is built into the carb.

The sled that had a "glasspack" on it that I remember was about 30 years ago, and I can't remember if it was anything other than a "cherry bomb". That's what I thought it was. I could be wrong. That was many beers ago....

I like your cold air intake, but personally, I'd just put on a slip on air cleaner on the carb, and route that duct to the cooling fan intake if possible. As you mentioned....that thing is going to get pretty hot. I'd bump up the oil/gas ratio a little. Again, that's what I'd try. Not saying I'm right.

You get that thing geared right and it's going to fly!!
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Unread 08-04-2014, 08:15 PM   #7
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Default Re: 399 rotax in EZGO problems

Thanks cohocarl! The air filter can on the floorboard is actually a christmas cookie can and I screwed the lid to the engine compartment and the base of the can just pops on and off. It was a rough trial but that is a good idea to run the duct over to the cooling fan. Ill look into that. I also took your advice about a possible vacuum leak and just went ahead and ordered a Tillotson carb rebuild kit. It was only 25 bucks so I figured I might as well try it lol

joejoeguns, I have another muffler that I was planning to do that exact thing with! Did it help as much as you wanted? Also, did your carb swap convert over fairly easily? If the tilly rebuild kit doesn't solve my problem I plan to swap it, and I've heard the Mikuni is a safe bet.
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Unread 08-04-2014, 08:52 PM   #8
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Default Re: 399 rotax in EZGO problems

It was years ago but if I remember right I had to some fabbing the carb I had was a walboro but "worked" the same as your tilly. Your mounts with two studs and the mikuni mounts with a hose clamp type band.They do make adapters.
My muffler works great,still sounds like a sled but not crazy loud.
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Unread 08-04-2014, 10:06 PM   #9
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Default Re: 399 rotax in EZGO problems

Oh ok I see what you mean here about stacking the exhaust. That looks good man. What did you do for electric start?
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Unread 08-05-2014, 04:52 AM   #10
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Default Re: 399 rotax in EZGO problems

It was an electric start sled. The battery is on the other side, I lengthened the starter key switch and choke cable and have them mounted on the dash.
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