Suzuki LT80 20mm carb

[phatlt250r]

Ok I need some help. I just put a new FMF Fatty Gold Series Pipe and FMF Powercore II silencer on my sons LT as well as the DG 20mm carb and intake since then my sons quad will die out after a short time of riding. I havent pulled the plug after it dies to see what the plug looks like. There are no other mods done to his LT80. I was wondering if anyone has had the same problems with this carb. I think I need smaller jets for this carb. My friend thought it was starving for fuel.And it very well could be, I have a hard time believing that since this carb is much larger then the stock. Any help would be greatful.

My Son on his quad before mods:http://mysite.verizon.net/4littleflowers/LT80.htm:confused:

[400exdad]

We've got a pretty hot little LT80 ourselves, however, I have yet to install an aftermarket carb. However, if the carb is too fat or rich, it should feel really sluggish as it warms up.... like it did with the stock carb and the choke on.... I'm thinking that this is not the problem though. I would guess that the kit might be relatively close for the LT with a pipe, so I would think that it would run... maybe not perfect, but shouldn't die after a few minutes. What I am thinking it the vaccuum hose that runs the fuel petcock. You may know this, but the LT uses an automatic fuel cutoff. When the motor is off, the gas is cut off and when the motor is running, the petcock is "opened" by engine vaccuum. Does the aftermarket carb have the same hose installation? My guess is that it may not be the same and the petcock is not truly open in the automatic "on" position. Another thing and maybe the real problem, if the carb does have a vaccuum hose attachment, is the fact that with the bigger carb, the motor has less vaccuum to actuate the automatic petcock. I have experienced this once or twice on really long uphills with ours. The fix is to turn the petcock over over to "prime". This is the same as "manual on". Make sense? If you knew all this, sorry for the long message. :eek: Welcome to the forum. :D

[400exdad]

I just finished looking at the pics and see that you do still have the stock petcock.... the springy line is actually the fuel line... anyway, try turning it over to "prime". That will probably do the trick.

[phatlt250r]

Thank you for the response. I did however change it over to the primer position. And it still died out, I also replaced the fuel pitcock in January. Do you know if they make a race fuel pitcock? That might be needed with this carb.
I was hopping this carb would be fun for my son. But now I am wondering if I should go back to the stock carb and up the jets to meet the pipe. Dont know what size jets i will need to buy. I also thought maybe I need to replace the reads to for some race reads, or even look into replace the jets in the new carb with smaller ones. Any light you can shed on my problem is truely be Appreciated..:(

[400exdad]

I don't thing that they make a race petcock for those. I think it should flow plenty of fuel for 80. Some folks block off the vaccuum part on the carb and petcock to eliminate probs. Mine works great though. Tell me, when it quits, does it start back up? Also, do you need the choke to crank the LT when it is cold and with the new carb? Also, when it quits, are you gassing on it? If not, the pilot could be way too big and you could start there, or at least with the air screw. My guess is the jetting is way off for your motor... especially if the motor is stock. The reed cage and factory porting is really restrictive. Before I had my motor ported, I think I was running a 95 or 98 main jet, and the stock pilot.... with an aftermarket pipe. When I ported it, I went to a 105 MJ. I'm still running the stock carb and I have a CT pipe (modded), modded reed cage with Boyesen reeds, mid range port job and most of the clutch mods. If you are stuck on the big carb... it prolly helps with some more mods, you could call Hetrick or Tony Doukas Racing and get some recommendations on jetting with your set up. Good Luck.

[phatlt250r]

Ok you are right they do not make a race fuel petcock. I did speak with midwestminis at: http://www.midwestmini.com/lt80_hop-ups.htm
Who did tell me just about everything you wrote,fuel switch needs to be in the primer position when running. And he did say to block off all other lines minus the gas line to the carb. They also mentioned that some people were converting petcocks over to the standard on and off and not wit the vac attament. (All though they didnt say what kind)I havent tried to block off the vac line yet. He did say that it sounded like it was running out of fuel. Problem discription 1 more time: Runs fine at full throttle for about 100 yards once you let off the gas and then try to give it gass quad reaves high then dies. Turn choke on and wait awhile then starts back up. Yes I am giving gass when it quites.
And yes since I put the new carb on the bike takes awhile to start with the chock on. Suggestion should I hold off on this carb until after porting and replacing reeds?
When speaking to the midwestminis I told them I had the FMF gold series pipe and power core II and wanted to know if I should replace the jets in the old carb from 92.5 to 95, they told me that the old jets are fine. Are they?
Jet sizing on stock carb:92.5 idle 20
Jet sizing on 20mm carb:98 idle 58
I will be taking some pictures of the old carb and new carb, just show people the size increase on the air horn. Also I notice that the new carb seats at an angle. Crazy...

Help me OB1 conoby you are my only hope..

[400exdad]

OB1, I'm not, but thanks for the vote of confidence. :D I like the performance of the stock carb. It seems to give us plenty of power, but I have wondered about the top end improvement from a 20mm carb. I also like my air box. Because we ride mainly in the woods, we need the airbox due to water crossings and puddles. LT80, here at Exriders, is very knowledgable about the stock carbs and stock exhaust too. You may want to PM him or check out MacDizzy.com for info on MacDizzy's LT80. Look for a link on the bottom of the page.... but he runs a 19 or 20mm also. If we could compare our LT to someones that has a 20mm carb, it may make me think differently. ;) Anyway, the stock reed cage has a ton of room for improvement. It's not difficult to do and MacDizzy has pics of his and how he opened it up to work with his LT. I didn't quite open mine up as much as his, mainly because I still have the stock carb and when I did it, I hadn't bored and ported it yet. FYI, the clutch mods make huge difference. Also, I have never messed with the pilot in ours.

Anyway, the bottom line is that the carb should be able to be made to run with your motor, but it may sacrifice some bottom end in doing so. I would try running it with the choke on, or partially on and see if that makes it stay running. If it does, you know you are lean. Also, you could temporary some sort of fuel line or tank (bottle) to eliminate any possibility of fuel starvation to the float bowl. One more thing..... and maybe this is the biggie... is the hose you have connected to the petcock really a bowl vent? If so, this wouldn't allow the fuel to flow into the bowl. :D I'm thinking that this is it, because I highly doubt the aftermarket carb would have a vaccuum port. Let me know if it works.

[phatlt250r]

Ok you were right it was bowl vent, once I discunected it and left it open on another hose, and blocked the vac port from the gas tank I took it for a spin around the block and it responded nicely. I will have to take it out on a good dirt surface and let my son ride it and see how it feels for him. I have posted some pics of the carbs at http://mysite.verizon.net/4littleflowers/LT80Carb.htm
I am sure after reading your responses that i would of caught on to bowl vent, sorry my missunderstanding. I must of inhalled to much smoke throught out my years.( 2 strock smoke) I was missunderstanding a vent hole and vac hole. :confused:
I also added the spacer back in between the carb and the reed plat. don't know if it was to stay on or off. but its not hurting anything. Have you done a clutch job on your LT80? I found this artical that was really full of good information its a three part (page) on how to respring your clutch.With a good diagram of the clutch. (worth keeping) I have been reading up on this and I am considering removing three of the weights. Here is the artical: http://www.off-road.com/atv/kidskorner/clutching1.html
If you have time give me your thoughts on this.
Once again thank you for the advice on this carb issue.....:D

[400exdad]

Check your PM's. I sent you some info on the clutch.