im almost sure it is gonna be a vapor lock problem,so how do i correct that?

Question

Could it be vapor lock?
it seem to run out of gas but is full i polished needle and seat and float is working. the filter goes empty and it will restart after a while if i shake the bike the filter fills back up, but it still takes a while to start. it only does it after a little while of hard running maybe 5 minutes. but if he rides slow on the street in front of the house it runs fine.im pretty sure it is not a carb problen as that is all working well,and has been cleaned a few times in the last week. i thought it was a dirty tank, it had lotsa rust, but we cleaned it out and lined it.any help would be great!!!! thanx!


Additional Details
i have tried that as well every thing in the fuel systen is as clean as if brand new, by the way it is a 1980 Kawasaki km 100


the filter fills with air,i first thought it was needle and seat or floats but i have checked that extensively and that is not the problem either.

    * 21 hours ago
    * - 3 days left to answer.

Additional Details
thanx for all the suggestions so far, here is more info..... it is 95 to 100 degrees F it does run.the tank has a new liner petcock flows freely.fuel line flows freely both before and after the filter. the filter media appears to be brass.the gas cap flows freely. the vents at the carb are also flowing freely.,i am stumped the carb is very clean as is the tank. it still happens with new filter.if it is vapor lock what can i do? i cant see that it can be anything else. will the gas mixture affect the engine heat,possibly causing lock?the engine is air cooled 2 stroke. i am currently running 4 oz of oil to 1 gal.... thanx again i really gotta get this bike going as my son is disapointed but wont say so,so all help and suggestions are greatly appreciated!

superchuck_a11 · Accepted Answer

This is God's Way of punishing you for BUYING A 30 Year Old Bike for a lil kid to ride!!
ahhaahah

your thrashing WAY to hard 
>>Print these out and go fix them one by one take you about 2 hours total 
STOP THRASHING

UR details in a nut shell
GAS DELIVERY ISSUES >> Tank to Carb
Tank > Cap > Petcock > Hoses > Filter > Float-Seat/Tip 

Tank
you have OLD BIKE with old bike issues in gas tank , you fixed them by cleaning /sealing the tank
 >> you used a common gas tank sealer from auto parts store or moto shop right ?
not something from work/hardware store/walmart?
not likely culprit

Gas Cap 
flows freely 
you cannot tell that except by removing the gas cap LEAVING IT OFF and riding it 4 hours > 
if it runs that long your 5 minutes of hard riding with cap on issue >>> is the cap
>>RIDE until it has issue >> remove cap > continue riding  for EXTENDED PERIOD
<i would suggest a towel or something for his protection if you want grand-kids
WHEN ISSIES DEVELOPS > take bike into closed area so you can HEAR small noises >>hurry in there HURRY>> listen for WHOOSh when you remove cap > a faulty cap will AIR LOCK the gas tank
Also check > redo the Gas Cap VENT HOSE and any connections kinks etc 
very likely culprit > old stopped up Cap Vent

new petcock
re-check it to see if it flows fuel >> unplug line observe fuel flow into container >> take it out and re-double-triple check the in-tank debris screen on petcock
AFTER RIDIG AND ISSUE develops recheck 
new not equal to GOOD/proper function
very possible culprit >debris screen

Gas line is all new
GAS hose ONLY >>>not vacuum line or hydraulic line >> get them yourself to make sure
not likely culprit
GAS LINE ROUTING 
make sure it is all down hill >GRAVITY feeds gas to carb that is why fuel filter has air pocket but still delivers fuel
Maybe culprit
http://www.powersportrider.com/cgi-bin/zcatjpg       gas line on pg 556
Fuel filter 
WHY is gas dirty still ?? 
your running a 1930's style SINTERED BRASS filter >> WHY >>go get a BRAND NEW PAPER ONE >> DO IT even if the other one FLOWS or BLOWS >>NEW FILTER TODAY
>> DO IT they are 2 dollars
run bike until issues develops >> REMOVE FUEL FILTER FROM BIKE 100% out > re-run
very possible culprit
http://www.powersportrider.com/cgi-bin/zcatjpg     filter off this page  530 and surrounding pages


Float Set/Tip
Does the bike TIP have rubber on it? If so that is a VITON TIP invented in the 40’s
Anyway AFTER ISSUE DEVELOPS REMOVE GAS LINE FROM CARB >> then remove float bowl 
> is there gas in the float bowl?
When  bowl is of and line is connected > observe flow out of carb 
Not likely culprit unless it is stuck shut >> it IS 30 years old huh? An VEY HARD or still soft?


Mechanical Issues you mentioned
Vapor Lock after 5 minutes ?
no i doubt it
something would have to HEAT THE FUEL > in the tank>line>or carb to VERY HOT (above 200 degrees) to get it to INSTA liquid to Vapor (aka Vapor Lock) WHILE IT IS IN THE FUEL LINE OR CARB

4 oz oil to 1 gal of gas >> go ahead and say your ratio much more helpful 
mix 32 :1 yea you can go 4000ballizzioln to one with space oil but hey 
WHAT ARE YOU RUNNING FOR OIL??
most important question on oil ratio >>what type/brand/ratio 
PRE_MIX oil or oil injected
Oil in the Gas Raises the VAPOR point even higher you know
>>so your needing more HEAT to Insta Vapor the fuel

100 degrees outside?? 
no problem the fuel is only 100 degrees also 

Both of these have same FIX 
>>MEASURE TEMP OF FUEL WHEN IT IS HAVING PROBLEM > no temp gauge use your hand on Tank ETC >>>> if your hands burns there is your problem
No way in hell after only 5 mins riding but hey check it anyway

STOP THRASHING CARB Performance FOR FUEL INTO CARB  DELIVERY 
until you have verified you have GAS IN THE FLOAT BOWL after issue develops

I would Replace the filter FISRT before any other work  
ride >>issue develops??
 >> GAS CAP removal > leave off
ride
Issues develops still 
>> remove tank 100% off  bike > put it on bench >leave it on bench 
Get SOMETHING as a temp tank and go ride
http://www.powersportrider.com/cgi-bin/zcatjpg   page 907 is some test tanks you can use 

If you still have issue with GAS IN FLOAT BOWL after removing TANK AND ALL HOSES >> then check out your hose pivot into carb > and you can concentrate effort on carb end of issue

Email me

Anonymous · Answer

is the petcock a diaphragm type or a regular on /off / reserve type? some petcocks have a vacuum hose that attaches to the carb, ind you may not be getting enough fuel through it if it is not attached.if it is on prime,it will fill the carburetor enough to start, but not flow enough to keep the bowl full when riding.your filter my not flow well enough to keep the bowl full. is there a filter inside the tank,above the petcock? it may be restricting flow if it has debris or liner material on it. try it without the in line filter,see if that helps. I would bet that's your problem.

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im almost sure it is gonna be a vapor lock problem,so how do i correct that?

2 Answers