more engine sputtering woes.. bad valve seats?

mhornfeck72205

mhornfeck72205

New Member
#1
#1
Not exactly sure what is the culprit here.

I recently changed my custom ground cam profile to close the intake at the bottom of the intake stroke where it had previously been closing half way up the compression stroke(ack!) so now I know the reason why I could run on regular, and why I now need to use premium.

I also have a slight leak in my exhaust valve seat which might also be a problem at these higher compression ratios.

I have no idea what would be causing these problems so I'm hoping someone can help me out. Seems to die around 3000 to 4000rpm or so. I'm rather short on money at the moment having just bought a new camera for my job(5DMKII) so I'm looking for some way to fix this and make it ride-able for little to no money. Heck, If anyone can do a cheap valve job for me(if that turns out to be what the problem may be), I'd owe you one. :)

Anyway, heres a few videos of the engine running. The sputtering while I was accelerating up the road was held at a constant throttle until the sound completely goes out.. It just stopped revving... The engine also dies if I leave the throttle open while this is happening, or when the engine is revving back down if it ever is able to rev higher.

YouTube - gx200 problems.
 
Oldsalt

Oldsalt

Well-Known Member
#4
#4
Stops revving? Engine falls on it face if throttle held open? These can be symptoms of very lean mixture on the upper end. You modded the engine and I can say for certain that will make it run very lean on the top end if not corrected. What kinkd of carb?
 
The Restore Kid

The Restore Kid

New Member
#5
#5
Oldsalt said:
Stops revving? Engine falls on it face if throttle held open? These can be symptoms of very lean mixture on the upper end. You modded the engine and I can say for certain that will make it run very lean on the top end if not corrected. What kinkd of carb?
Click to expand...
X2 :thumbsup: That is without a doubt %100 of your problem.. :thumbsup: Your engine was set up to run right(ish) before........ AFTER making the slight change in the valve train created a HUGE amount of compresion, so the engine is actually pulling or USING more air in it's mixture, and NOW the high speed end of the fuel mixture is way too lean.....

That stumble is you giving the the engine throttle which is dumping air to the motor, only the carburetor is not feeding enough fuel to match the air flow so it's basically trying to run on air.....

You need to adjust the high speed AND probably low speed fuel mixture as well to sync up with the air the engine is gobbling up. :xomunch: Thats why the high octane fuel is helping out just ever so slightly.. A tiny bit more bang for the buck with the exact same amount of fuel.. For that Mikuni you will need to purchase different jets with bigger orifice to increase the fuel flow.. Might as well buy two or three of them whilst you are at it... That was a pretty huge stumble, pretty well dies right out, so you will need at LEAST one size bigger and maybe even two or three.. I think I'd get the next three bigger jets and try installing one after another until it's right.. But ten and keep going until it's too RICH and flooding out on the high end, then go back down one size and you'll be all kinds of good. :thumbsup: i think I would go two jets bigger though..
 
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mhornfeck72205

mhornfeck72205

New Member
#6
#6
It isnt using the stock jet, I have the one that comes with it from nr-racing.com. I believe its the 130 or 135 jet.

It also bogs down and runs even worse when I open the current jet too much. Won't even idle. Should I try toying with the c-clip?
 
minidragbike

minidragbike

Supporting Speed Nut!
#9
#9
Oldsalt said:
Stops revving? Engine falls on it face if throttle held open? These can be symptoms of very lean mixture on the upper end. You modded the engine and I can say for certain that will make it run very lean on the top end if not corrected. What kinkd of carb?
Click to expand...
That sound like the problem to me.
It takes many jets to get it figured out. Every motor combo is different. Just because someone says to try this one out doesn't mean it will work perfect wit your motor.

One of the main reasons I don't run those carbs. I prefer riding more than getting my hands wet with gas or alky.
 
mhornfeck72205

mhornfeck72205

New Member
#11
#11
worked! Going to post the video in a few mins. It'll take a while to render and upload(its saying 2 hrs to render..). trying to figure out how to upload in 1080p
 
mhornfeck72205

mhornfeck72205

New Member
#12
#12
ok heres the video. took forever to upload on youtube. should improve quality in a little while.

YouTube - Mhornfeck72205's Channel

going to try tuning it a bit better tomorrow because it isn't the best it can be..

if people like these videos i'll keep going with it and when my friend comes over to work on his 250cc 5 speed, i'll vid that too.
 
minidragbike

minidragbike

Supporting Speed Nut!
#13
#13
mhornfeck72205 said:
ok heres the video. took forever to upload on youtube. should improve quality in a little while.

YouTube - Mhornfeck72205's Channel

going to try tuning it a bit better tomorrow because it isn't the best it can be..

if people like these videos i'll keep going with it and when my friend comes over to work on his 250cc 5 speed, i'll vid that too.
Click to expand...
That made a real big difference.
Nice video, it's good you got it to where you want it. You should try making a mount for the camera on your bike. Then that way you can take us all for a ride.
 
mhornfeck72205

mhornfeck72205

New Member
#15
#15
So... turns out that my jet is a 95 jet instead of a 135. I'll be buying a new one and hopefully that will fix things.

Does anyone know what drill size a 135 jet is? I'd like to give it a shot drilling it out to see if it will work for the time being.
 
minidragbike

minidragbike

Supporting Speed Nut!
#16
#16
mhornfeck72205 said:
So... turns out that my jet is a 95 jet instead of a 135. I'll be buying a new one and hopefully that will fix things.

Does anyone know what drill size a 135 jet is? I'd like to give it a shot drilling it out to see if it will work for the time being.
Click to expand...
Way back when I use to play with mikuni's I knew that at the top of my head. Been 10 years ago, and I don't like to even look at those carbs. But doing a search on google and you should find something.
 
mhornfeck72205

mhornfeck72205

New Member
#17
#17
found the proper drill bit and went with it.. now I cant even get off of a stand still. it just bogs and dies. Something odd is going on.. Tuned it all over the place and no luck.. :-( going to buy a proper 135 and hope that helps.
 
Oldschool

Oldschool

New Member
#19
#19
Starting from the beginning again....

"I recently changed my custom ground cam profile to close the intake at the bottom of the intake stroke where it had previously been closing half way up the compression stroke(ack!) so now I know the reason why I could run on regular, and why I now need to use premium."

Why would you do this?
You have shortened you intake valve durration significantly. You have decreased the amount of charge you can draw into your cylinder and weakend the motor. There may be a little more torque in the bottom end but Honda designed this to have somewhere around 220 deg of lift for a reason. Newton's first law bodies in motion and the intake charge at BDC has enough mass to continue cylinder filling at 3600 rpm and higher.

Second thought drilling a jet you need a drill press.
Put the jet in the chuck and spin it not the bit.
Put the bit in a small vice and square everything up before you try and drill. Spining the work and not the tool keeps you drill on center for a cleaner hole. Doing this by hand is much more difficult and its possible you drilled ata slight angle or moved making the hole larger than you wanted.

When you mess around with huge changes in your cam profile like you did your jetting requirements will change. For this reason a lot of people like the Tillotson carbs ( myself included )


Me I want more intake durration not less I want the cylinder filled at high RPM and not weazing for breath and falling off a cliff at 5000 rpm
 
mhornfeck72205

mhornfeck72205

New Member
#20
#20
"Why would you do this?
You have shortened you intake valve durration significantly. You have decreased the amount of charge you can draw into your cylinder and weakend the motor."

This is a homebrew custom welded cam.. Not some $100 performance cam. Never even degreed it right. After watching the piston and where the valve closed, it would have been ridiculous to leave it closing where it had been closing. I dont know why you would opt for more flow when it flows the fuel in and out before it is able to even compress. Half of the charge had been blowing right back out of the intake in a small puff of a gas cloud. I ran a flat top piston and 14cc head .010" gasket on regular gas. I'll be buying a proper cam from NR soon anyway.. Just being a bit experimental to keep myself busy in the mean time.

After getting as much fuel out of the 95 main jet that was in the engine to begin with, I'd say the butt dyno says I improved power. :biggrin: Another thing that I haven't discussed, the plug reading is also indicating that it is too lean.

No worries on the jet.. Was just trying to see if it'd work in the mean time while the correct jet is in transit in the mail.
 
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