PDA

View Full Version : Fl350 tuning



Buggy guy
04-12-2015, 05:06 PM
Hello all.
I have a fl350 that I cant get to idle, I can set the idle screw all the way in, and it still dies. Only way I can keep running is by giving it a little throttle. I've cleaned carbs. Please help.

nutz4sand
04-12-2015, 06:00 PM
Welcome to the site.

You have a two stroke and these need a regular test or you can just run it and gamble

You need to do a crank case pressure test. If the seals are leaking in the crank it will never idle very good and its the start of it wearing out the bottom end and you could melt the piston down if you have a seal leaking and it gets bad enough. Also gaskets and vacum hoses should be checked or replaced if any dryrot on hose to fuel pump.

Also of note the screw should not be all the way in. It should be out 1-1/4 to 2 turns and then adjusted in or out a little.

Do not crank it in to tight or you can cause irrepairable damage.

Buggy guy
04-12-2015, 10:33 PM
It's not that it won't idle very good, it won't idle at all. Reeds look good, no air leak in boot, fuel filter is good. I'm stumped.

LIDUNO
04-12-2015, 10:58 PM
I'm gonna ask the obvious questions, forgive me if they're too obvious.

Did you try turning the idle screw all the way in or are you talking about the A/F screw?

Have you tried a new plug?

Ever done a compression test?

nutz4sand
04-12-2015, 11:10 PM
It's not that it won't idle very good, it won't idle at all. Reeds look good, no air leak in boot, fuel filter is good. I'm stumped.


If you think the rubber boot around the carb is the only place air can leak you either need to start learning a lot or paying a good shop to fix it.

Not being rude just truthful.

Buggy guy
04-12-2015, 11:40 PM
A/For is 1 1/2 turns out, idle screw is all the way in. I do know about air leaks, did a test with staying fluid. I've had air leak issues with sleds, and I could still get them to idle.

Bullnerd
04-13-2015, 01:52 AM
Did it idle before you cleaned the carbs? Or ever?

I'm not familiar with the 350 carb, is the idle screw built into the choke knob like on a bike? If it is, your probably way out of the range of the idle.

Buggy guy
04-13-2015, 02:06 AM
The machine was in pieces, got it back together and running, but never able to get it to idle. I have carb off again, going to check jets. Idle screw is separate. It just hold plunger up. Have I feeling my jets are wrong.

nutz4sand
04-13-2015, 02:25 AM
You NEED to do a crankcase pressure check.....

Its a two stroke.

Buggy guy
04-13-2015, 02:26 AM
K, explain how.

nutz4sand
04-13-2015, 08:47 AM
You can buy them but they are not always cheap. Nor do they often contain all what you need for the motor you got.

So you put one together yourself.

Go to you favorite automotive store and buy a good vacuum pump. Its also a good thing while there to buy a manifold vacuum guage with a fuel pump pressure tester like older cars would use ( NOT a FUEL INJECTION pressure guage. WAY to high of a pressure!)

A good hand held vacuum pump will already have a vacuum guage on it. which is good for the negative pressure test of the crankcase. But for the positive you want a guage that also goes positive so you need the manifold/fuel pump pressure guage (it goes both positive and negative pressure. But only a few psi in each!)

You then need to hit the local hardware store. You are looking for PVC pipe end cpas and or copper end caps to match the rubber manifold your carb fits in. Measure the intake side of the boot and find one thats a good tight fit.

Then measure the exhaust side port. You will need to be able to seal this side too. In the same hardware store you should be able to find rubber pipe caps right near the other stuff. Again measure and find one that will fit tight.

Once the carb port and exhaust port have these caps on or in them put hose clamps to hold them good and sealed. You also need to seal the fuel pump port on many two strokes.

Once you can seal all the ports you need a way to get the pressure in the motor. If its a single cylinder with a fuel pump vacuum port on it thats a good way. If it does not have this then you will need to make a port in one of your caps you stuck in the exhaust or intake so you can add vacuum or a few pounds of pressure. (NEVER EVER EVER more than 6-10 psi and not over 6 if you have not glued the crank seals in!!!!!!!!!!!!)

Do not use an air hose!!!! You will blow the seals out. Fill a portable tank to about ten PSI then bleed it down to about 6 PSI.


So basically you need a vacum and pressure guage and a way to make vacuum and low PSI and anything you can to seal the motors intake and exhaust. As well as good quality hose and fittings to make sure they do not leak.

While at the harware store buy two spray bottles too. One for soapy water and one for clean pure water. The soapy water making bubbles one the 6 PSI pressure test is the easiest way to find a tiny leak that will likely grow.

LIDUNO
04-13-2015, 11:14 AM
All great advice as long as you've checked the basics first.

bazz
04-13-2015, 12:07 PM
Yes agree...have you checked your throttle cable for CORRECT adjustment clearance? You could be more off than a sun cooked prawn!:eek:

Buggy guy
04-13-2015, 12:07 PM
That's what I was hoping to do. What else could it be. Carb is out of whack I think.

bazz
04-13-2015, 12:12 PM
Wow,your quicker than Quick Draw McGraw!(and what I can beertype):D

LIDUNO
04-13-2015, 12:28 PM
That's what I was hoping to do. What else could it be. Carb is out of whack I think.I would consider the basics things like vacuum lines installed in the correct spots and not cracked or so hard they don't seal, good spark plug, good spark plug wire, good electrical connections, good compression, good fuel supply.

It sounds like a clogged jet but you mentioned that you already cleaned the carb.

Bullnerd
04-13-2015, 03:45 PM
Oh ok..so round slide carb?

DMoneyAllstar
04-21-2015, 03:54 PM
Did you ever get around to pressure testing the crankcase??

nutz4sand
04-21-2015, 04:11 PM
I will add that if you have a bad crankcase seal nothing else matters.

Crankcase seals ARE the basics on a two stroke.

Its not that hard to check. The parts you buy can be reused again and again.

Above it was aslo mentioned the carb slide might be closed to far. Do you know how to check that?

Buggy guy
05-02-2015, 02:35 PM
Ok, i got it to idle fine, ordered sigma racing jet kit. Now I bog over 1/4 throttle? Smaller main? I have a 145 in it now. :confused:

nutz4sand
05-02-2015, 04:29 PM
And the crank case pressure test went how??????

You "MAY" have compensated for an air leak down low. It will cause the leak to only leak more IF you have one. possibly ruining the piston and cylinder. Not to mention a big weekend of planned riding?

You are dealing with a machine thats quite old. You likely do not know when it was rebuilt or that it was done right.

I pressure test an engine before I tear it down to see what it tells me and after I rebuild it before I start it to make sure I got it right.

Anything less is a gamble and parts for these are not as common as they once were so it only makes sense to be careful with the ones you have.

Crankcase pressure testing should be a common regular part of any two stroke engines life.

If you do not KNOW the bottom end is sealed you could be chasing snipe.

Buggy guy
05-02-2015, 05:31 PM
Hehe, don't matter now, blew it up, rotax on its way :mad:

Buggy guy
05-02-2015, 08:25 PM
Plug fouled solid, exhaust side of piston had ring fused to it. Connecting rod looks good, maybe just a top end rebuild.

LIDUNO
05-02-2015, 10:05 PM
Exhaust side of piston failure usually means a lean condition.

You may have jetted it up enough for it to run rich while in low rpm but it looks like it leaned out in the high rpm. You probably have either a fuel dlivery issue or a vacuum leak.

Buggy guy
05-02-2015, 10:45 PM
I'm thinking I had a compression issue all along

nutz4sand
05-03-2015, 06:36 AM
I'm thinking I had a compression issue all along


Or...... wait for it................................................ . A lower end vacuum leak!

If you rebuild the top end and its still got a lower end leak the new top ends life will be measured in minutes.

Its YOUR money and you can do what you want but if you would like to save some of it the tests are cheap cheap cheap and easy easy easy to do to tell you what you NEED to know with a two stroke.

Did you ever even do a compression check? what was the PSI?
How do you think it was a compression issue all along???

Running cheap local gas with ethanol in it? If so you need to jet a two stroke rich to avoid a lean out as ethanol will make an angine run leaner than a pure gasoline fuel engine.

DMoneyAllstar
05-29-2015, 01:13 PM
Or...... wait for it................................................ . A lower end vacuum leak!

If you rebuild the top end and its still got a lower end leak the new top ends life will be measured in minutes.

Its YOUR money and you can do what you want but if you would like to save some of it the tests are cheap cheap cheap and easy easy easy to do to tell you what you NEED to know with a two stroke.

Did you ever even do a compression check? what was the PSI?
How do you think it was a compression issue all along???

Running cheap local gas with ethanol in it? If so you need to jet a two stroke rich to avoid a lean out as ethanol will make an engine run leaner than a pure gasoline fuel engine.


YEP -- agreed! 2-strokes are sooooooo darn simple, but you have to be diligent with setup.

And if switching to a 2-up 2-stroke 470 Rotax, that's TWICE the potential to spring a crank case leak. YOU MUST DO A LEAKDOWN TEST ON A 2-STROKE ENGINE.


2-stroke 101 here...

In order to confirm there are no crank case leaks, you NEED to do a leakdown test with 7-10psi air. Some praise positive pressure tests, some vacuum, some both. Cheap cheap cheap cheap cheap tool that will save your wallet and weekends.

In order to determine fuel octane needed to avoid detonation, you need to check compression. If running north of 150psi, I'd consider 100-110 octane and preferably something non-ethanol. Not like you're running 1,000mi a week in these things, so buy the best fuel and best oil anyways. Plus the "good stuff" has a great scent.

In order to confirm jetting, YOU MUST DO A SEPARATE PLUG CHOP (or at least a PLUG-LOOK) at idle, then at mid-throttle, and then at WOT. Once you are seeing good results, then you'll have a good baseline for condition/jetting changes, detecting snowballing issues, and comparing tweaks/upgrades. And once you have a baseline, you can monitor exhaust temps with an EGT gage.


My weed-trimmer, chainsaws, FL350R's, LT500R's, and all the random SkiDoo's I've owned have always lived nice long healthy lives by following those simple guidelines. I've never blown-up a top-end -- EVER.

[smilie=blowkiss.gi: