carb problems after boring

[undergroundart]

I had a 28mm carb bored to 29.5 and now I cant get the quad to run. with the choke on it ll fire but turns off as soon as you close the choke. im thinking maybe I need to go way up on my pilot. anyone ever have an issue after boring? quad started and ran great before.

 

[Blaaster]

Was it offset bored or just bored straight through.

The action of the Venturi on moving air will have been changed, which will result in the air passing over the jets is now slower.

You may need to increase the jet sizes to compensate.

Do some Googling and research the correct way to bore a carb out, it is simply not a matter of enlarging the hole out!

 

[undergroundart]

shoot well that's not good news

 

[jus_me]

I think you will be fine but you are certainly going to have to play with the jetting. Richening things up. You are lean now hence why she runs with the choke on.

What type/make carb is it?

I would start with the pilot and or needle, Do only one change at a time so you can keep track of which way you are going and if it gets worse or better. Kinda hard for it to get worse but at least she is running with the choke on.

Also make sure there are no left over pieces of metal stuck in any orifice of the carb anywhere..

 

[undergroundart]

cleaned and blew it out twice. it runs with the choke on but not for long, and it idles super fast. its a keihin pwk. ive gone up 2 sizes on the main, and up and down on the needle. played with the air screw and idle still no luck. first race is next weekend so I just ordered another carb off ebay to make sure we re ok incase I cant get this one figured out

 

[Blaster8821]

I had a 28mm carb bored to 29.5 and now I cant get the quad to run. with the choke on it ll fire but turns off as soon as you close the choke. im thinking maybe I need to go way up on my pilot. anyone ever have an issue after boring? quad started and ran great before.

I had the same thing done to the stock 26mm Blaster carb and found out it was bored out a little to big making it suck air past the slide totally ruined the carb.

 

[jus_me]

The main only affects 3/4 to full throttle. I am betting you need a larger pilot for sure. A high idle also indicates its lean. I would go up 2 sizes on the pilot and see what happens.

 

[Awk08]

this will tell you what pilot you need............
http://www.blasterforum.com/threads/adjusting-your-airscrew-pilot-jet.51060/

 

[blasterkid1998]

I had the same thing done to the stock 26mm Blaster carb and found out it was bored out a little to big making it suck air past the slide totally ruined the carb.

then the carb was bored too far the stocker can only be bored to 27.5 or it will suck past the slide causing jetting nightmares.

I had a 28mm carb bored to 29.5 and now I cant get the quad to run. with the choke on it ll fire but turns off as soon as you close the choke. im thinking maybe I need to go way up on my pilot. anyone ever have an issue after boring? quad started and ran great before.

and undergroundart my guess is the pilot will need to be enlarged. most of the time ive only experienced the need to readjust the air screw but a pilot jet change may be necessary with your application

 

[speedyslyder]

and it is on a cr80 engine??

 

[undergroundart]

cr85, and I think im gonna need a different cable. I looking into the carb and the slide sits pretty high up. even with the idle cable adjustment all the way closed. gonna rig up something tomorrow to the carb like a string and get the slide close to the bottom and see if it ll run. it always did idle a lil fast best the cable was too short to allow for adjustment, but it was acceptable. boring it out bigger would only make the space from the slide to the bottom of the carb larger

 

[speedyslyder]

cr85 it is then
i dont remember all the things you have done for more power
but ....anyhoot

 

[jus_me]

cr85, and I think im gonna need a different cable. I looking into the carbnd the slide sits pretty high up. even with the idle cable adjustment all the way closed. gonna rig up something tomorrow to the carb like a string and get the slide close to the bottom and see if it ll run. it always did idle a lil fast best the cable was too short to allow for adjustment, but it was acceptable. boring it out bigger would only make the space from the slide to the bottom of the carb larger

Its the little things like that that are over looked and make all the difference. what throttle cable are you using? Blaster or the cr?

 

[undergroundart]

right. im using a blaster cable. I just cut about 3/8 off of the metal tube on the cable where it goes into the carb. should have only done like a 1/4. I now have the slide resting on the bottom of the carb, but to do so I had to extend the idle part of the cable all the way out. once again I really don't have much adjustment available, but it should run as is. it s midnight and raining out. ha test run will have to wait for tomorrow. Hybrid problems.

 

[undergroundart]

then the carb was bored too far the stocker can only be bored to 27.5 or it will suck past the slide causing jetting nightmares.

and undergroundart my guess is the pilot will need to be enlarged. most of the time ive only experienced the need to readjust the air screw but a pilot jet change may be necessary with your application

hey blaster kid, good thing we didn't try to go a full 30. a hair bigger and there would be gaps on the side of the slide.

 

[blasterkid1998]

hey blaster kid, good thing we didn't try to go a full 30. a hair bigger and there would be gaps on the side of the slide.

i took it as far as i was comfortable with which was just right at 29.5mm

 

[Blaaster]

The problem may lie in the way the carb was bored, boring is not just a matter of enlarging the hole!

When boring carbs you must offset the bore to the top so you do not disturb the floor of the venturi. Otherwise it may never idle properly again due to airspeed issues.

 

[blasterkid1998]

The problem may lie in the way the carb was bored, boring is not just a matter of enlarging the hole!

When boring carbs you must offset the bore to the top so you do not disturb the floor of the venturi. Otherwise it may never idle properly again due to airspeed issues.

i would tend to disagree since i have bored dozens of carbs and never expirenced such issues.

 

[undergroundart]

Update. got the carb pretty close to tuned. one size up on main and screw turned half a turn out was the key. also went up 2 sizes on the main. quad runs fast. my boy was right behind a 300ex built for nationals while practicing today. a few lil things and we ll be ready for the first race on sat. thnks everyone

 

[jus_me]

No pilot change ?