400ex Poping

[a1965gt]

I did a seach but some posts say if your quad is popping is too rich others say its too lean. So which is it?
I just removed the choke, ground the welds on the headpipe, and put in a Sparks 6 deg. advance key. It already had a FMF Mega Max II slip on, and K&N filter it ran fine before with the stock jetting (38pilot and 148 main, maybe a little rich since the plug was black) After I put in these new mods I has been running really hot and would lose power after it would heat up. I have tried 158, and 162 main jets but it still gets a little too hot and looses power. I checked the plug and it is spotless, no carbon at all. I droped the needle clip one position and went to a 170 main and it seems to be running better but is poping at full throttle/high RPM. Still no carbon on the plug.
Can anyone help????
PS: im using Kiehen jets and AVgas (100 octane)
Thanks :confused:

[a1965gt]

Any help would be greatly appreciated.

[jb400exxx]

get a dyno-jet stage 2 jet kit, and use a 165 or a 170 main jet, and go up to a 42 pilot.

[a1965gt]

Do i have to buy a kit or does someone sell the jets individually? Who sells the jets/kits? Are the dynojets bigger than the kehin's?

First I think I keep reading how the AV gas is not good for these things, but for the purpose at hand here I just dont think many members have any experience jetting with it.

Dont confuse breaking up or hitting the rev limiter with lean popping. Most times the popping is on deceleration.

Dyno and Keihin jets are just diff. dyno uses a adaptor to mount there jets on the keihin. I recomend just buying the few keihin jets you need from a local dealer or who ever has them.

I think/hope you mean you raised the needle or dropped the clip cause the other way like you describe would lean it out more.

I would think that @ 170 main you should be good there but I am not experienced with you local elevation etc.

If you think you are lean try applying the choke and if it runs a little better you will have your answer cause the choke will richen it up and if it gets worse you would be too rich.

Could also fool with the air box lid to help determine whats happening too.

[VegasEx'r]

a1965gt, I'm gonna second what 440ex said, the lean pop thing usually happens when you let off the throttle to decelerate. It can also pop if the header & silencer aren't sealed together good.
I had my quad dynoed by dynojet a couple weeks ago, and was WAY fat on the main & needle, so I dropped the needle to the 2nd clip (from the top) & went to a 160 main (from 170). I am using the stock pilot & the air screw is 3.5 turns out. I have had it pop on me a couple of times now, so I might be a little lean, but I plan to leave it like that through the winter, then try a 165 in the summer.

What kind of 65 gt do you have?

[a1965gt]

It is poping while I am accelerating, I dont think its the rev limiter because the RPM's arnt that high when it starts, and it continues to accelerate after poping. As for the needle/clip position it is now in the 4th grove from the top of the needle. I have removed the choke so I cant use that to richen it up. I do have a stock airbox lid (without holes) that I have been using to richen it up. I will also double check the exhaust to make sure it is tight.
Vegas,
It a black 65 mustang fastback. I restored/modified it about 10yrs ago so its in need of a little TLC since it was my dayly driver for about 7 of thoes yrs but its still pretty nice.

[stock400]

Maybe you should put tripple pipe on your quad and see what happens. You removed your choke??? Sounds like you'll have to spend a little more $$ to get it dialed in, god thing you only paid $60 for that helmet!


2001 400 ex
$80 helmet
DMC pipe
1/2 unl 1/2 av
stock mtr
good running

[stock400]

WOW, this sounds so familiar......

Seems like I remember my uncle saying that my cousins husbands 400 ran hot, (he could smell it) and slowed down all the time.

Didn't you disagree and say no way, it's a four stroke. You can't smell a hot engine and why would it slow down?

[ill_lil_romey]

My 400 popping and sputtering from removing the choke was such a pain in the *** with trying to jet it that I put the damn thing back on!

[VegasEx'r]

How does it run if you put premium pump gas in it?

[a1965gt]

Didnt you say your brothers cousins uncles sisters mothers 400 was stock? I guess I was wrong, just didnt think a stock 400 would have thoes problems.
PS: why dont you list your 440 kit as part of your mods (Stock 400?)

[a1965gt]

Vegas,
I was thinking of going back to pump gas, do you think the AV gas could be affecting my plug readings?

[stock400]

I think you adjusted your valves too tight and now you've flattened your cam. Didn't you say you adjusted them to .001 clearance to get maximun lift and duration? I'm running 1/2 unL and 1/2 av and only experience backpressure popping durring deceleration.

and only experience backpressure popping durring deceleration. :confused: :huh

[a1965gt]

Lay off the pipe dude.
.004 intake and .005 exhaust
Now go bother someone on the sea-poo board, your getting to be as bad as Rob.

[stock400]

Sorry, thought you might be trying to squeez out an extra .00037 hp. Nobody on the seapoo site, I'd rather stay here and hear about your hoptie. Tons of great info. here!

[VegasEx'r]

Originally posted by a1965gt
Vegas,
I was thinking of going back to pump gas, do you think the AV gas could be affecting my plug readings?

Could be. I don't know a lot about the stuff, but I thought it was made for engines that run at extremely high altitudes, where the air is thin & cold.

I'd bet that if you switch to pump gas, you will be extremely rich.

[stock400]

1965 gt
Maybe it's because you got a quad nobody else would pay money for? didn't you trade a ski for that quad, it had two or three cracks in the frame didnt it? And the axel housing had to be replaced because the old one was shot? Had about 300 hrs on it. What do you expect? Sell it and buy a new one.

[DantheEXman]

YES!!! There was a whole thing on here on how AV gas effected the plug readings... Try some 93 pump gas... Then look at your plug... And By the way, If you were wondering, AV gas has additives in it to keep longer or burn cleaner or something.. Someone correct me if im wrong.

[stock400]

You should try a new quad or you'll end up doing the same thing to this quad that you did with that ski. Sink tons of money into it and still have it breaking down when we all go somewhere like your yamaha gpr.
You should have never traded for a pos.
You dont need to run higher octain unless you have a need. If it keeps detonating you need to find out why before you blow it up. Maybe its time for a rebuild, doesnt it have like 300+ hours on it.

[stock400]

aviation gas should be used for aircraft.

[a1965gt]

Thanks to everyone for the comments (except Stock400). I look forward to getting it running right and smoking Stock400's piped 440 as he barely has the brain power to turn a screwdriver.:blah

[stock400]

Hey now.... Im just trying to help. You used to not even know what a cam was for in a car and know it's me without the brainpower to turn a screwdriver? whatever man! You get what you pay for or in your case trade for.
Maybe fercho can help you with your quad too.

[stock400]

Put more money in it, make it faster... I know you will.