Is is acceptable/common to stagger the pilots or turns in/out on the air jets?

M

maxco

New member
Joined
Sep 30, 2009
Messages
348
Age
57
Location
coloraDO
I have tried to distill my question to this. I have a new to me 2001 mountain max. I have been in and thru the carbs religiously many, many, many, times. After many tests and runs and unfruitful trips to the mountains....the center cylinder afterfires. I believe this to be the correct term, and condition. Afterfire to my understanding is when un-combusted fuel builds up in the exhaust pipe and then ignites. It will start, and run, but at idle to 1/8 maybe 1/4 it will run for a second then puff like a persistent smoker cough. not loud, no big bang just a whoof, with a little more velocity. it clears up when it goes past into 1/2 throttle. So pilots and air screw are in play here in my opinion. Why the center cylinder? The center exhaust pipe is significantly hotter, and plug always looks wet when pulled.

I have searched thru the site, and tried to do all my homework. the reeds are in great shape, plugs are new, carbs are clean, i swapped floats from one bowl to the next. checked the needles and clips cleaned the air screw passages specifically. No change

It just seems to be too rich at idle in the center cylinder with the same setting across the board. How common is this, and is there something else I should be looking for?

My thought is to go for another 1/2 turn on the air screw then 3/4 if that does not work maybe downsize that pilot only. Thoughts?:o|


2001 Mountain Max (redhead)
Ride Altitude 10,000ft
air screws 2 1/4 across the board
pilots 60 (recently dropped from 62.5 did not do anything for the afterfire)
mains 136.3
needles 4th e clip 2 shims down
jet nozzles 1st Q-4
jet nozzles 2-3 Q-2
 
is it triples piped? try changing the needle and seat and look at the reeds. almost sounds like weak spark not producing complete combustion, try new plug caps as well.
 
It is a Tripple pipe slp pipes. Staggs65 I'm a little confused. My clymer manual for these Tripple models calls the screw on the bottom of the carbs pilot air screws, indicating turning out is more air flow to pilot circuit. What am I missing?
 
Last edited:
Just like staggs said. The more you turn the pilot screw out the more fuel the pilot circuit will have. 2 turns out from litley seated is richer than 1 1/2 turns out. A way to remember is if the pilot screw is before the slide it adjust air, if it is after the slide it adjusts fuel.
 
Ok so is it ok to have the screws set at different turns out? Or should that be telling me I have another problem?
 
i would think it points to something else acting up. if every thing is working how its supposed to all cyls should be the same. turning the screws out different amounts might just be band-aiding another problem. what ever it is probably isn't very serious, so I would set them to factory and start looking else where.
 
theres a few things i would suggest trying to eliminate an otherwise underlying problem.

first would be to move the needle from the center carb to your choice of the other two carbs and see if the problem follows the needle. i have see needles deteriorate on the tips and cause exactly your issue.

next thing i would do is replace the o-ring on the needle valve seat. it may look good, but it just may be leaking enough at idle to cause your problem, yet not enough to overfill the bowl and run out the overflow. you want a 7mm id 1.5mm thick o-ring or you can order oems.

lastly, i would inspect closely the washer, o-ring, spring and the fuel screw itself. swap these around as a set between the carbs and see what happens. those springs can corrode and sack, the o-rings can wear, and you can even install them incorrectly. order is o-ring/washer/spring/screw. a sacked spring will give you a different "feel" of lightly seated causing that carb to be richer or leaner.

clymer manuals are more for reference and are consistently inaccurate in comparison to the factory literature.
 
Thanks a lot for the help. it is what makes this site the best!
I have a clarification question. I am looking at the fishe for OEM parts, I am a little turned around then you say needle valve seat O ring. I do not see an O ring as part of the Needle jet, jet nozzle assembly. are you referring to the O ring that goes around the float pin/screen assembly #8F2-14147-00-00 or something else? the way you describe it it sounds like it would be a part of the float assembly. A part # would help.
I have replacements for the pilot screw spring, washer, and o ring. I will replace all of them today, I will switch needles today.

Thanks for all your time and patience.
 
In honest response to Yammy I have never re-set float heights, but the machine is in amazingly pristine condition. I had wondered about but having not set them before did not want to break something that might not be broke. So I swapped floats from one bowl to the next. no difference. But I will verify they are the same today since I paln on pulling the cabs off again
 
Last edited:
8F2-14147-00-00. it goes around the seat. the seat is the brass fitting that the needle valve supported by the float tang sit in. its the part of the carb thats held in place with a phillips screw. if there is little to no resistance when removing the seat, most likely the o-ring is worn. i gave you the size. you can pick up a metric o-ring kit just about anywhere. napa, fastenal, autozone, etc. you can get an entire kit for about 2 rings from the dealer but you probably wont go through them like i do. the bigger rings in the kit are good for windshield securing, placing under the kill switch, etc.

i assumed you had confirmed the float height by your statement about religion and carbs. may be time to learn.
 
So I am back to can you stagger the pilot and or the air screw?

I went thru and changed out the o rings on the float seat, replaced the spring and O ring on the pilot screw. Checked the float heights. Fired her back up and still backfiring. ;( So missed something. I got a laser/thermometer and started checking the pipe temps. The center pipe was hotter about 100 deg, but that was not the odd thing. I was using my hand to sense heat before at the pipe midpoint. With the laser I checked at the manifold. PTO was twice as hot as center and mag.
So assumption kills...... Lean condition on PTO re-jetted 62.5 across the board, and went up one main jet size on the PTO. Started her up, and backfire disappeared after running a while. :)
The 1st cylinder is still running hotter at idle then the other 2. Not as bad, but still hotter. Should you richen up the pilot screw or increase pilot size on that one cylinder?
So she is much happier now. I will still have to run her on the hill and get plug tests to check needles. Thanks for all the help.
 
Last edited:
You must log in or register to reply here.


Back
Top