97 TB 250
Has been running fine and still runs fine but has gotten hard to start cold
engine is bored .80 over (don't ask that is another story)
pulled and cleaned carb (didn't appear to be any dirt in it)
Changed spark plug and color seemed OK
made sure there was nothing in the block

Before it would start on the first pull with little effort and normally without the choke

Now it may pop on first pull but if you don't grab and feather the throttle it will stall and be difficult to start or
it may just be difficult from the get go and you have to play with the throttle to get it to start

I have also checked the compression which was 115 after 4 pulls I think it was around 50 or so on the 1st pull

any suggestions

 

Yep sounds like you need to re-build the top end. The minimum psi is 115. How long ago did you re-build and what piston are you using?

 

There is about 10-15 hours of not too hard riding on it

When it was fresh it only had 120 compression

Once we get it started it runs great and starts fine until it sits and cools down

wiesco piston

 

That 120 compression sounds low to me, you may have an air leak somewhere or it wasn't honed and bored right..You could also have a blown gasket somewhere that would fall under an airleak.What kind of head and head gasket did you use for re-assembly, also base gasket? I ask this to make sure you used special gaskets that were bigger to compensate for the over bore. Also, the Polaris base gasket is much better than aftermarket.

 

You say it is hard to start cold? Well did you try the simple thing first like raising the needle clip. It may be to rich to start but when everything is hot it is more lean and this can make it start better.Just a suggestion to start with. I have seen the 250's run fine with 115 compression. That actually is not bad. When you get arount the 100 psi mark then things get difficult. Stock psi is around 130-135psi. It could be something as simple as just adjusting the jetting,needle,or airscrew.

 

I hope you dont mind me jumping in here...
I'm just putting together a 96 trailblazer...
and its .030 over bored and i'm getting 115 psi on the 6th to 8th cycle...
and i'm just breaking it in!!!
Now NCScambler has me worried.... what have i done wrong not to get 130 or more....
As far as the air leak goes.... this particular trailblazer has NO reed valves
so i'm assuming he's referring to above the piston... on the bottom stoke..
(BTW your site is quite informative!)
Soo i'm going to have to devise something to check with his 'Simple Green' detergent spray
or something...
Anyway.... I also have found that this 250 runs relatively fine after starting, but getting there
is a bitch... It seems to flood to easy....
So... to TOMANYTOYS..... how do you find out how to make it simple by just
adjusting the jetting,needle,or airscrew?
thanx

 

I also seem to be flooding
When it wont start the plug is soaked
so maybe I have over jetted it and it is now showing up with the warmer weather
we are going to rejet it tonight and see what happens
I beleive we went from a 140 to a 160 after the boring


Air leaks could be in the bottom end and would cause a lot of trouble
A torn crank seal is what caused ours to go from stock bore eventully to .80 over after some bad machine work

 

Most of the time if it is hard to start,you have to use the choke till it warms up,Or it takes along time to smoothen out then it is all in the carb.You have to start with a big enough main jet to supply enough fuel when full open throttle. You start with the biggest main you can then back off about 2-3 sizes. When the main is to big it will sputter when full throttle. Then you back off on the main.It should smoothen out when open full throttle. The pilot jet and jet needle controll your idle, 1/4 to about half throttle. With the mods that you have the pilot jet should not have changed. The needle and airscrew has tons to do with your cold start. If you are running rich you need to raise the needle clip 1 to 2 positions. Your airscrew should be about 1 1/2 turns out counterclockwise from seated position. You can then adjust 1/2 turn out at a time. The airscrew will not change anything over 3 full turns. A plug check is the key to see if you are right on,lean or rich. So you are flooding easily? Raise the clip 1 position and set the airscrew 1 1/2 turns out. Start it and go on a short ride. Drive at a consistant speed where your throttle is about 1/4 open. If it sputters then you are still rich. It should be smooth at 1/4 throttle. If it is smooth then ride a little longer till it gets nice and hot. Stop and pull the plug. The plug should be tan,or chocolate brown. If it is black then you are rich,if it is grey then your lean. It takes some time to get it right but it is not hard.

ASDFASD,
What mods do you have other than the bore job?

 

asdfasdfasdfqwer, calm down a little. The 115 psi munimum is for a stock engine, stock bore, stock head. I would think that scramblazer should have more than 120psi, but I could be wrong. 2Many has his bored and would have a closer baseline than I could go by. Maybe I jumped in too fast withou thinking here, but since he has starting problems, I was assuming it was compression related. Now, when a motor is bored you will lose some compression, so if you are confident that the engine is together good, run it, but if you are unsure, I would do a leakdown test to find out if there are any airleaks anywhere. Airleaks can occur and do occur often in the oil seals in the crankcase, between the crankcases themselves, the carb to intake boot, or the airbox. An airleak will destroy an engine quickly and is recognized by a high idle that falls slowly. WD-40 is good to check for airleaks on a cool engine also. Now for the jetting probs, 2 Many is right on, I will also add to check the choke adjustment as the cable can wear and stretch and the choke being out of adjustment can cause alot of problems and jetting mis-interpretation. Scramblazer 400, the main jet will have nothing to do with cranking, that is controlled by the piulot and air screw setting. Now you said it runs fine until it sits and cools, that tells me you may be running too lean, because a rich motor will get worse as it warms up. Also where is the pop coming from that you mentioned? The carb or the pipe?? If it is the carb, you are definately too lean.. the pipe, too rich.

 

well its not flooding in fact it is exactly the opposite
we changed the needle and had it running
after shutting it off it would not restart checking the plug there is gas getting in the cylinder

so off comes the carb again

BTW we change the clutch primary spring from a green the a brown and what a difference that made while it was running