Bike will not start with Choke on, will with Choke off

[fmcandrew]

Fella's...read all the choke related threads but didn't find anything that addressed my new issue. My bike will fire up and run fine (need a little throttle help to warm it up) without the choke. If I use the choke, it will not start. Now...I think this choke issue happened immediately after I drilled out my deflectors on my stock exhaust...I think...I'm getting old so not 100% sure. Anyway...bike always needed 1/4 choke to start previously. Is this coinsidence, or are they related? Haven't yanked the plugs yet so don't know if running rich/lean after the mod...plugs looked good before the mod. Currently running Seafoam in the tank. No spitting/stumbling/hesitation or anything like that...just will not start with the choke on...

Thanks a bunch,

Frank

 

[mavgrab302]

Drilling the deflectors in my opinion wouldn't make that much of a difference.. Maybe something else.. Crank it as usual check plugs and then use choke and recheck plugs, see if you getting too much fuel..etc. opening up exhaust will lean you but not enough to affect what your talking about.

 

[mavgrab302]

Also heck, you don't have to use the choke, if it cranks fires up and give it a couple throttle twists to stay running sounds good to me, that's what I do......

 

[jfeagins]

Sounds like your carbs are plenty rich.

 

[ninjaneer]

...opening up exhaust will lean you but not enough to affect what your talking about.

actually, on the max, opening up the exhaust will "rich" not "lean".

 

[midmoraider]

+1 on rich with open exhaust


Sent from my PG06100 using Tapatalk 2

 

[mr.maxx]

actually, on the max, opening up the exhaust will "rich" not "lean".

Mr Morley corrected me the other day with that same statement.
i allways thought the latter. :biglaugh:

i would be interested to know the exact technical aspect of that phenomenon:biglaugh:

 

[ninjaneer]

Mr Morley corrected me the other day with that same statement.
i allways thought the latter. :biglaugh:

i would be interested to know the exact technical aspect of that phenomenon:biglaugh:

i'll search for it. it's somewhere in the forum. i believe it was the guru himself who explained it.

 

[ninjaneer]

Mr Morley corrected me the other day with that same statement.
i allways thought the latter.

from what i understand, your initial thought isn't "wrong"--it just doesn't apply to the max whereas it does apply to other bikes.

i'll search for it. it's somewhere in the forum. i believe it was the guru himself who explained it.

Here you go

Drilling the exhaust will make the bike run rich. The way you have to think of this is that you have allowed the outlet of the engine to flow better. This increases the amount of exhaust gas that escapes the combustion chamber. The intake side has a limited intake size (limited by the airbox inlet and carb throat diameter) so you will have a greater intake velocity and will have a lower intake pressure. Your fuel system operates at a higher pressure than the intake pressure (atmospheric in the bowls through the vent tubes) so when the intake pressure drops it in effect pulls the fuel into the carb throat. The pressure differential partially dictates how much is drawn in. By lowering the intake pressure you increase the differential and more fuel is drawn into the carb throat. Thus the bike goes rich.

This is why jet kits such as Sean's need you to put in larger main jets when installed on the bike as they raise the intake "pressure", and allow the engine to take in more air, thus applying the same princples as above you will have less fuel flow into the carb throat. Putting in a larger main jet allows more fuel to flow and corrects the situation.

Remember, if you change the flow at either end of the engine you will have to check your jetting.

If you increase the ability to pull air in then you can start talking about leaning it out. By just adding a better flowing exhaust you are able to make the engine a better vacuum. So, now it's pulling harder on the carbs which means it pulls in more fuel. But, the same amount of air.

Numerous dyno's don't lie. Go ahead and do some dyno testing for yourself if you don't believe what they are telling you.

I've got lots of dyno pulls available if you want to download the reader.

You need to look up a phenomenon on called exhaust gas reversion and scavenging. The harder the pull on the exhaust side of the valve the clearer the cylinder is on it's next intake stroke. This allows for more fuel/air to be taken in since there is lest left over burnt gasses from the previous cycle.

In many engines what you are saying is correct that you will lean out with better exhaust. But most of the time you aren't working with a vacuum slide carb and restricted (as much) air intake flow.

Richening up the mixture by opening up the vboost can simply mask other problems at the cost of potential power and economy.

 

[fmcandrew]

Well, i'm running lean, pulled the plugs and they are a little too white for my liking. Wasnt that way before the mod/seafoam. Not going to say that exhaust mod is to blame, seafoam may have dislodged something, however all carbs are running lean (all plugs are whitish) so not overly comfy with calling seafoam the culprit either. Checked the mechanics of the choke, appears to be working, however #2 carb "pop" is far less audiable than the others, still would not account for all carbs running lean. I am running a K&N, so maybe the combo has leaned me out enough to create a "too lean" condition when the choke is used as it stumbles and dies. Looked for other air leak possibilities, none obvious...

 

[mr.maxx]

from what i understand, your initial thought isn't "wrong"--it just doesn't apply to the max whereas it does apply to other bikes.


Here you go

thanks for the info!!! i was VERY curious:biglaugh: i dont mind being wrong...lol
imma pretty good wrencher...but i shure as hell dont consider myself an expert.:rofl_200:

as for the issue at hand.....id check the pilot AF screws and see where those are set...and adj if needed. then id do a carb sync.

i have seen on bikes b4 when the pilot circuits were totally plugged....the owner would bump up the idle screw to get it to idle ....then the bike would feed off the main jets to compensate.

 

[fmcandrew]

So...it is true that I am running lean...but not on all cylinders...only the front 2, the rears are rich as everyone figured (and rightfully so as my a/f screws were 3 turns out and my needles had 2 washer shims)...however, I've discoverd small holes in the front carb diaphrams...would those cause the lean condition...I'm guessing yes...but would appreciate your thoughts,

Frank

 

[[email protected]]

I've discoverd small holes in the front carb diaphrams...would those cause the lean condition...I'm guessing yes...but would appreciate your thoughts,

Frank

Shouldn't make a difference at idle since the slides are not moving but, anything above idle, when the slides are opening, it could make a difference if the holes are large enough to prevent a proper vacuum and is making the slides open slower than they should. If the slides open slow, this means the needle is not coming out of the main jet and blocking fuel flow. You could check this by removing the top of the airbox and looking in while hitting the throttle.