carburetor help on a fd620

[JohnF]

Thanks John
That's the info we should be giving to someone who admits he is not "mechanically inclined".

Oh. Well then ignore all of that other stuff I wrote.

[SixGunNick]

Ok I pulled the plugs and they r both white and dry as a bone so I'm runnin to lean then ok next question I need to richen it so I have to get the black plastic piece off of that screw and I'm afraid I'm gonna brake it should I try cut the black plastic off nobody was open to try and get the 112 jet today may have to order it anyway

[JohnF]

That adjustment, the air screw, is only for the idle circuit. Adjust it like you did earlier when you said the idle was great.
The surging is a lean condition in the main circuit which is controlled by the main jet. If you are sure that jet was clean then order the 112. There is no other adjustment.

[Bazooo guy]

Yes the exhaust is coughing soot the choke seems ok

doesnt sound like its running lean.

It can also surge when rich. This you could probably smell but it will also smoke a bit and cough soot. This could be fuel leakage in the carb; although in this carb I don't know where, unless the float valve doesn't work. Could also be a stuck/broken choke.

Totally agree with that.
And now

The surging is a lean condition in the main circuit which is controlled by the main jet. If you are sure that jet was clean then order the 112. There is no other adjustment.

Yes install the 112 it's the standard jet for that engine Someone has changed it.
If your engine is fd620D the valve cover gaskets are here:

http://tewarehouse.com/7-02498

[JohnF]

doesnt sound like its running lean.

There are two circuits in this carburetor. (with a third function that we haven't gotten into yet.) One can be running rich while the other lean.

The air screw adjusts one circuit and the main jet the other.

Yes install the 112 it's the standard jet for that engine Someone has changed it.

The 112 is a larger jet - to fix a lean condition. It is not necessarily the standard jet shipped as many went out with the 110. Do a search, I posted the jetting chart for the conquests and how they changed over model years.

SixGunNick, your engine doesn't know anything about your elevation, it really runs at something called "density altitude". I am betting that the place you test drove it was perhaps a bit higher, warmer, and dryer - all conspiring to give the engine an effectively higher density altitude. Now that it is (colder, lower, wetter???) it has bumped the bottom of the mixture ratio and won't run. At 500ft, you should have the 112 anyway.

If you think it is running both cylinders then just leave the valve covers alone for now.

[Bazooo guy]

Page 28 of the manual states the main jet 112 is standard 0 to 3000 ft.
Must be a misprint

[JohnF]

Page 28 of the manual states the main jet 112 is standard 0 to 3000 ft.
Must be a misprint

Depends on the engine version. I gleaned my info from the aggregate documentation. Here, I did the search for you. Yes, 112 is probably the jet for SixGunNick's machine in the conditions he is experiencing. Just like I said oh so many posts ago.

But, 112 is not "the standard jet" delivered in all machines. I venture to guess that 110 is. And no, not a misprint.

[SixGunNick]

ok if the plugs r white and dry it is lean tho right i ordered a 112 jet.I originally had black soot and coughing but i may have been using the choke too much to bring idle down to shift,so now i have the idle low enough to where i can shift easily and am using no choke if the jet dont do it ill take it in to get it fixed,i mean this could be a very easy fix that i am just not inclined enough to know that somethings wrong with it so i dont want to keep you guys on this goose chase i will post when i get the jet in if it helps change anything.I am also ordering new springs and links for the linkages.Also my buddy was over and said that the engine sounds way too smooth to have a rod out but he said the adjustment could be out especially if it was never done so we may tackle that tomorrow.Oh and yes when i bought the machine it was very hot out and now that it is cold here it seems that this issue with surging is more prominent to me.

[Bazooo guy]

If you are running with the choke even partially closed it will run rich,
That's probably why John said to check that the choke is working and open fully.
I would also test the fuel pump to confirm it is able to supply enough fuel at wot and the lines and filters are clear or it will run lean.
Make sure the linkage and springs are installed correct and install the 112 jet
If you decide to take it somewhere to have it fixed tell them the carb was just rebuilt.
I am curious to hear what they find,

[SixGunNick]

Ok thanks yea today I'm replacing all the fuel line and the rear filter and doing the pump test I hope that the jet doesn't take too long to come in.I just wanna ride I think I may eventually get a brand new pump anyway and carry this one for a spare cuz I primarily bought this machine for lake erie icefishing and u don't want to mess around out 5-8 miles out on the ice.I think I jinxed the ice here this year because we didn't even get a skim coat out there,but the machine was out of comission all ice season anyway

I also noticed I guess there is supposed to be a spring that goes over the actual throttle linkage next to the carb the manual says this must be in place to hold them to each other mine is just the link and its all bent up and looks to be a piece of coat hanger could this be my problem? My link is bent into an arch and kinda has play between the two arms the one in the manual looks sraight,could someone try to look at they're conquest and tell me if they're link is pretty straight or does it have about a 45 degree bend like mine and when I ordered my parts this so called over throttle link spring was unavailable so maybe ill try to put a different spring on it later

[Bazooo guy]

Yes the link rods and springs are very important for proper governor operation.
Wrong spring or bent rod can cause the engine to surge as soon as it comes off idle.

[Rock Doctor]

I also noticed I guess there is supposed to be a spring that goes over the actual throttle linkage next to the carb the manual says this must be in place to hold them to each other mine is just the link and its all bent up and looks to be a piece of coat hanger could this be my problem?

This could very well be your problem, those springs are actually pretty important and will cause problems if they are missing, incorrect, or stretched. That linkage is not supposed to be bent all over the map, but it's not straight either.
Without seeing your carb, just going on your description, I would suspect this as a cause of your problem

RD

[JohnF]

Hmm, I was going to say we should reference the manual that Bazoo Guy linked for us but the pic doesn't show these very well. I'm not anywhere near mine right now but the two link rods are not straight. If it's coat hanger then replace them. Ultimately if you fabricated a link rod of your own and you put curly Qs in it, it wouldn't matter if it operated linearly at the same distance as the real rods, and in fact that operation distance is uber important - this is how we adjust the high idle (when we get there.).

As for the springs, there are 3. I think the one you are talking about goes over the throttle link rod. It's job is to keep the throttle link rod from jiggling out. (and annoy you every time you remove/install the carb. ) If it is missing it won't cause surging. Another goes from the control tab that is connected to the throttle cable to the governor arm and opposes the third spring. The governor works just like a drive clutch and your action on the twist grip is sort of corollary to the driven clutch. If one of these is missing then the bugger won't have throttle control. If they are mismatched then the governor will operate at the wrong value. This is a positive feedback system and for this to cause surging means that at some part of the governor travel it goes negative. I can't imagine what that would be but weird twists and misaligned control points can do this.

Everything you say is adding up to running lean. Get that jet. If the throttle link rod spring is missing then replace that. If the link rods aren't OEM then I would personally replace them too. Since in your description you mention that things ran fine before then I bet your other springs are fine.

I hope the jet comes quick for you. It took a couple of weeks for me. Hopefully the Denver guys get them from NY.

[SixGunNick]

I would think so too and it does surge immediatly off of idle and there is quite a bit of play in the link so ill will tinker with that t,,,v onite.

[Bazooo guy]

Maybe you can disconnect the governor linkage temporarily and see if the surging goes away.
Don't over rev it and don't leave it disconnected...it protects the engine from too high of rpms
You will know as soon as it starts and you give it a bit of throttle if the surging is gone.
Just don't rev it or it could explode.