Jetmaniac 735 Carb Question

[Dorny119]

Hi all,

I used the idle drop method of tuning my low speed screws on my 735 (in an Aquabot). With the ski on the trailer, I turned the low speed screws in until I found the smoothest and highest idle. It ended up being 3/4 turns out. I hopped on the ski and it was falling flat on it's face when I hit the throttle. I played around with the low speed, going to and from shore with 1/8 turns in between. Eventually I found that 1.25 turns out to make it rideable.

My question is, why am I getting a lean condition from my low speed screws being set at the proper point for idle? Is this normal? Why do I have to set my low speed so rich? Pop off?

 

[Rushford_Ripper]

Did you rejet the carbs? You probably need larger pilot jets.

 

[Blue]

Our motors typically end up at 3/4 turn on low screw and 1 to 1 &1/4 on the high with a 40 psi popoff in dual 38s.
Thats using 75 pilot jet. Are you using stock filter box or aftermarket filters? What pipe and what reeds? Is it a topend kit or a complete motor with ported case?

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[Dorny119]

I bought the ski used, and wasn't able to get a ton of info. Dual 38's, Aftermarket filters, MSD enhancer, zero lightened flywheel, B pipe, JM Ported Cylinder (not ported cases), 175psi. I believe it has stock reeds. I have not done anything to this motor except turn the carb screws. I don't know what the jet sizes are.

 

[maxboost]

I’d go off what blue says for settings, double check pop off! Especially if n/s and springs aren’t brand new. I’ve never run the jet maniac setup but I’m guessing my setup isn’t terribly far off and I’ve found if I was lean on pop off OR LS jet I would get lean hesitation so you really need to play with both settings to know what works best. Like I said tho blue knows these engines

 

[Blue]

I will pm you my number if you want to give me a call. Its easier to discuss it over the phone.

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[SXIPro]

I will pm you my number if you want to give me a call. Its easier to discuss it over the phone.

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One more reason I bought my last motor from JM with Blue's port work.......

 

[Blue]

Thanks Guys. Thank You for your support.

I dont care how old your motor is. If its one of mine i want it ripping for you no matter if you bought it new from us or used off the X. It doesnt matter to me.

Anyway
After our talk I think we have a high popoff issue. He will be checking the jet sizes and testing popoff soon.

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[Dorny119]

Have been talking with Blue. What great support from him!!

My pop off was at 42-44psi. I have aftermarket air filters, so I lowered the pop off to 35-36psi. After testing, I noticed a slightly smoother throttle response, but it still isn't snappy. I still have to turn low speed screws out to 1.25 to make the ski rideable. I will try to lower pop off to 30 and see what happens.

Jets are 75, 137.5

 

[Dorny119]

I will tune pop off and update soon. In the meantime, does anybody ever use purple Loctite on the adjustment screws? My rear highspeed keeps backing all the way out.

 

[Mattyboy45]

I will tune pop off and update soon. In the meantime, does anybody ever use purple Loctite on the adjustment screws? My rear highspeed keeps backing all the way out.

Did you replace the gasket on the idle screws when rebuilding the carbs?


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[Dorny119]

I have never rebuilt the carbs. Although I did not notice any gasket after it backed out. So I suppose the previous owner must have misplaced it. I have never taken screws all he way out until now so I wasn't aware there should be a gasket!

EDIT: Ok I see it's an O-Ring when I look at pics. Does anybody know who sells the O-Ring? I could just pull the other high speed out, get the dimensions, and order one from McMaster.

 

[Mattyboy45]

Well they’re o rings but it might be stuck in the carb side. Pull up a carb diagram microfiche. Does the high speed needle have the spring in there( for tension)? Anyways sorry was just reading, may not be the issue at all lol.


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[Mattyboy45]

I have never rebuilt the carbs. Although I did not notice any gasket after it backed out. So I suppose the previous owner must have misplaced it. I have never taken screws all he way out until now so I wasn't aware there should be a gasket!

EDIT: Ok I see it's an O-Ring when I look at pics. Does anybody know who sells the O-Ring? I could just pull the other high speed out, get the dimensions, and order one from McMaster.

They come with carb rebuild kits. might want to check all the needles on both carbs


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[Dorny119]

They come with carb rebuild kits. might want to check all the needles on both carbs

Yea I pulled out the screw on the front carb and it has the O-ring. I can find the same Oring somewhere I'm sure. Also, the rear screw DOES have the spring and washer, just no O-Ring.

 

[Dorny119]

Alright so I'm getting a pop off of 31psi now, didn't make a difference in any of the symptoms. Pulse line is in tact. I guess I'll check the diaphragm for rips or tears next. I might just ride it like this for the rest of the season. It runs alright, just not super responsive. I don't think I'm hurting anything by compensating with rich low speed screw setting.

 

[Blue]

I would open the other side of the carbs up and check the internal filters and condition of the internal parts. It may be time for a couple of rebuild kits.

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[nightrider05]

What was your recommended jetting start point?

 

[Blue]

He has it correct at
75 pilot
137.5 main
He was at around 40 to 42 psi popoff which is fine for stock FA box but not open filters. At 31 psi now.
I think somethings either old, dirty or clogged on the fuel pump side. Maybe time for carb rebuild possibly the fuel pumps weak or the internal filters are clogged.

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[nightrider05]

He has it correct at
75 pilot
137.5 main
He was at around 40 to 42 psi popoff which is fine for stock FA box but not open filters. At 31 psi now.
I think somethings either old, dirty or clogged on the fuel pump side. Maybe time for carb rebuild possibly the fuel pumps weak or the internal filters are clogged.

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Thank you sir. I have a similar setup and was looking for some base numbers.