Stumped experts: BRP Carb touched, won't start


26 replies to this topic
  • Zapp22

Posted April 28, 2007 - 11:26 AM

#1

OK this has turned into a grand mystery.
call me stooopid, but see if you can figure this one out. its gotta be simple

I had a fine-running BRP, except for "popcorn" on hard decel. Rode it all over southern new mexico, having a blast. would start on the first kick Cold or Hot. Lovely....

So I get back home and one day decide to bump up the Pilot jet to cure the backpop. Pulled the carb, flipped it over and unscrewed the 62 pilot, put in a 68 pilot. While doing this the float assembly fell out. i put it back in.
Reassembled the bike

Tried for a couple of days to get it to start. It will backfire in the can but not start no matter the mix-screw setting.
Put the 62 back in just to see.
Tried for a week everything I could think of to get it to start. Finally in utter frustration took to the honda shop... the one here is the best I've ever seen.
Best Service Manager I've ever seen in Motorcycleland.
Left it with them

A week went by with no calls.
I went down there today to see what's up. Found them stumped. Completely baffled. They have no clue why it won't start. Swapped out spark plugs, checked valves, checked compression, consulted the stars, grabbed voodoo doll, kicked it a million times.
Same thing.... huge, flamethrowing backfires so loud it wakes the dead, but will not start.

ok, so something simple changed. Bike started and ran super. Especially easy to start. Now it won't start. Has good spark, has good specs, SEEMS to have fuel if its backfiring that impressively.

What happened? What causes a spot-on PERFECT backfire... just one per kick [well its usually about the third or fourth kick that lights her off...] ?????

Did something ELSE fall out of that carburetor? I have a symptom-theory that the fuel is not emulsifying correctly. its sucking a lotta fuel in, pushing the vapors into the can. the fuel residue in the cylinder "flames" without firing, and when the exhaust valve opens it lights off the buildup of vapors in the exhaust pipe. But why is the carb not carbing ??? :excuseme:
:applause:

  • roadrunner81

Posted April 28, 2007 - 12:25 PM

#2

Are you sure the float is set properly, gravity feed so set level when float barely hits sprung part of needle assy.

  • needsprayer

Posted April 28, 2007 - 01:41 PM

#3

You say you pulled the carb. Do you put anything in the cylinder side boot while it was out?

  • jbird710

Posted April 28, 2007 - 04:44 PM

#4

Just some basic stuff you've probably aready covered:

You said the float assembly fell out, did the float needle fall out also? If so, did you check to make sure it was clean before putting it back in?

Are you sure the little wire piece on the needle is properly connected to the floats?

Any chance you have the floats in upside down (seen people do this)?

As mentioned before, any chance anything got up in the boot on the cylinder head side when you had the carb off?

Any chance something (a little piece of dirt, etc.) might have fallen into the carb while reassembling? (boot between air box and carb)

Good luck and let us know what you find; might help out someone else. :applause:

  • Billahjack

Posted April 28, 2007 - 06:17 PM

#5

Did you check that the float valve is shutting off when the bowl is full? Does your bike smell like gas when you are trying to start it? Is it leaking any gas from the vent tubes? With your air filter off and your gas petcock on, is gas pooling in the intake tract?

I would also check to see that you are getting fuel flow by loosening the float bowl drain screw with the fuel petcock on.

Turn the carb idle screw in 1.5-2 turns in so you can start it easier.

Try with the choke, then without. If you think its flooded, then hold the throttle wide open and kick it through a few times.

If fuel is flowing, then I would try putting the old pilot jet back in.

  • jetski701

Posted April 28, 2007 - 07:15 PM

#6

I'm having similar problems after having my carb off for two months. I have to put a 180 jet to get it to start,from a 170. All it would do is backfire after a few kicks. I can't get it to rev out, it backfires and sputters about 4000 rpm, and will not get past this to clean out even on a free rev. I didn't have my carb apart before the symptom occured, but took it apart and found nothing. I did notice fuel on the outside of the diaphram, on the small housing on the side of the carb. I'm not sure what the function of this is, to know if it is normal or has a hole in it? My plug reading is good if I ride it in the low rpm's, and seems to have normal power until it hits what feels like the rev limiter! Possible same problem?

  • Billahjack

Posted April 28, 2007 - 08:10 PM

#7

Sounds like bad gas. Drain it and use it in your car or lawnmower. Drain the float bowl also.

  • steed2

Posted April 29, 2007 - 03:19 AM

#8

its a problem with the float assembly.......its flooding it so I would guess the needle is installed improperly or not even there? you never mentioned that the dealer checked the carb? I find even after a good cleaning of a carburator you should tap the float bowl with a scewdriver handle the first time you turn on the petcock. Also if your needle has a grain of sand on it it will flood you bike, And we all know how much a fourstoke hates to be flooded ....especially with these bike they dont take much to flood. Go back and check the float assembly and clean it . IF YOUR STORY IS TRUE THEN THAT IS THE ONLY THING THAT COULD BE CAUSING THIS .
Good luck and dont worry youll figure it out. Ohh and one more thing ....its NOT bad gas ......gasoline doesnt go bad in a couple of hours!!

  • Zapp22

Posted April 29, 2007 - 04:50 AM

#9

ok i'll try to answer all.

it looked/looks to me like there's only one way for that float-attached needle thing to go in. its shape is keyed. I originally didn't get it set right, but the result of that was no gas at all in the bowl. now the bowl fills exactly right, no overflow, and its pulling gas in ... as is evidenced by that cannon going off every fourth kick or so :excuseme:

the original pilot has been back in now for a week or so... that's how I took it to the 'experts'. it started on first kick with this setup for the past year and a half [oh woe is me... why did i listen to all those BRP'ers saying go bigger on the pilot???]

is there some tiny almost-invisible little part associated with that needle thing? something that could have fallen out without notice? i just do not remember such from previous jetting on it way back when I first got the bike.

as to choke-on, off, turns of the screw, etc.... every possible combination has been tried innumerable times by four different people now and not even a "chuff".... no hint of starting, just the regular cannonfire. Actually, the cannon is comforting because it is so consistent/reliable.... its telling me something but I cannot decipher.....:applause:

Did you check that the float valve is shutting off when the bowl is full? Does your bike smell like gas when you are trying to start it? Is it leaking any gas from the vent tubes? With your air filter off and your gas petcock on, is gas pooling in the intake tract?

I would also check to see that you are getting fuel flow by loosening the float bowl drain screw with the fuel petcock on.

Turn the carb idle screw in 1.5-2 turns in so you can start it easier.

Try with the choke, then without. If you think its flooded, then hold the throttle wide open and kick it through a few times.

If fuel is flowing, then I would try putting the old pilot jet back in.



  • Zapp22

Posted April 29, 2007 - 04:52 AM

#10

steeed I bet you come out right on this one. its got to be that....
I plan to get with them at opening on tuesday and suggest we pull that float off and compare everything to "standard"....

its a problem with the float assembly.......its flooding it so I would guess the needle is installed improperly or not even there? you never mentioned that the dealer checked the carb? I find even after a good cleaning of a carburator you should tap the float bowl with a scewdriver handle the first time you turn on the petcock. Also if your needle has a grain of sand on it it will flood you bike, And we all know how much a fourstoke hates to be flooded ....especially with these bike they dont take much to flood. Go back and check the float assembly and clean it . IF YOUR STORY IS TRUE THEN THAT IS THE ONLY THING THAT COULD BE CAUSING THIS .
Good luck and dont worry youll figure it out. Ohh and one more thing ....its NOT bad gas ......gasoline doesnt go bad in a couple of hours!!



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  • Zapp22

Posted April 29, 2007 - 04:58 AM

#11

I'm having similar problems after having my carb off for two months. I have to put a 180 jet to get it to start,from a 170. All it would do is backfire after a few kicks. I can't get it to rev out, it backfires and sputters about 4000 rpm, and will not get past this to clean out even on a free rev. I didn't have my carb apart before the symptom occured, but took it apart and found nothing. I did notice fuel on the outside of the diaphram, on the small housing on the side of the carb. I'm not sure what the function of this is, to know if it is normal or has a hole in it? My plug reading is good if I ride it in the low rpm's, and seems to have normal power until it hits what feels like the rev limiter! Possible same problem?


your case isn't similar... you're getting started!!

its obvious from this post that I'm no expert, but I don't think your mainjet change has anything to do with starting the bike. its not in play.
sounds to me like you're too big on the mainjet, cause right around 4000 is where you really are dependent on that mainjet/mix being RIGHT. if it were mine I would back up to a 175.

  • steed2

Posted April 29, 2007 - 05:06 AM

#12

for sure ....cause if you think about it .....thats the only thing ...it ran before and now it doesnt .... I bet its something simple ...by the way try this ..
1. turn the petcock to the off position
2. Hold the decompressor and the kill switch and kick the bastard over 15-20 times. {maybe more}
3. remove the plug check if its wet if soo clean it or even better install a new plug.
4 reinstall and try to start it..... DO NOT TURN THE FUEL ON!!
5. IF IT STARTS AND RUNS then TURN THE FUEL ON .....I BET IT STALL,S OUT A COUPLE SECONDS AFTER YOU TURN THE FUEL ON.
GOOD LUCK

bY THE WAY LET ME KNOW WHAT HAPPENS.

  • jetski701

Posted April 29, 2007 - 06:18 AM

#13

your case isn't similar... you're getting started!!

its obvious from this post that I'm no expert, but I don't think your mainjet change has anything to do with starting the bike. its not in play.
sounds to me like you're too big on the mainjet, cause right around 4000 is where you really are dependent on that mainjet/mix being RIGHT. if it were mine I would back up to a 175.


Have you tried to change the main jet to a bigger one? I'm telling you I had the same symptoms as you until I put a larger main jet, then it started, but will not rev out. If I put the smaller main, which just like you, it ran before on this combo, It won't start, and will just backfire. I've went from 160 to 185 main, and up on the needle and then down, with the same results. with a big jet, it starts! I'm thinking the air valve on the left side of the carb might be leaking on mine, but I don't know much about it. I'm wandering if anybody knows the function of this valve, and what would happen if the rubber had a pinhole in it?

  • steed2

Posted April 29, 2007 - 07:39 AM

#14

all that air valve does is enrichen the pilot circuit on decelleration. It helps to get rid of the backfire on decel but it also softens engine braking .

  • Zapp22

Posted April 30, 2007 - 03:58 AM

#15

is it possible to mess up the slide somehow? overnight, I was remembering that I opened the topside checking the slide movement... if you poke at that thing will it get out of position? I'm thinking the answer is no because its spring loaded... returns to 'rest'. anyway... grasping at straws.

also after thinking on it a lot more, my 'hope' that the carb-float-needle issue is the problem is bogus.... you should have caught it! ALL that assembly does is allow the bowl to fill properly, and it is filling properly... not too much, not too little, cuts off just right. So I'm still stumped.

there's not a tiny o-ring or such associated with the pilot jet is there? something that could have dropped out unnoticed?

  • jbird710

Posted April 30, 2007 - 06:34 AM

#16

Unless you pulled the slide out and put it back in backward (not sure this is possible), it should be ok. It is possible to bump the slide needle to one side so it won't seat properly, but this should be apparent by looking through the carb. Where in Texas are you?

  • XR650L_Dave

Posted April 30, 2007 - 07:59 AM

#17

Here's a great way to check suspected float issues-

drain the carb, fuel off.

Put a clear hose on the drain nipple, and elevate the hose.

open the drain screw, and turn on the petcock.

The level the fuel assumes in the clear line will be the same as the level in the float bowl.


Dave

  • creeky

Posted April 30, 2007 - 08:11 AM

#18

Here's a great way to check suspected float issues-

drain the carb, fuel off.

Put a clear hose on the drain nipple, and elevate the hose.

open the drain screw, and turn on the petcock.

The level the fuel assumes in the clear line will be the same as the level in the float bowl.


Dave


Excellent!

  • Zapp22

Posted April 30, 2007 - 09:50 AM

#19

Unless you pulled the slide out and put it back in backward (not sure this is possible), it should be ok. It is possible to bump the slide needle to one side so it won't seat properly, but this should be apparent by looking through the carb. Where in Texas are you?



I am in New Braunfels, near Gruene hall. bike is at i35 North honda, new B also.

this is a real brain racker.... the bottom line is i really didn't do much. sure caused a LOAD of trouble ... just pulled the carb, unscrewed pilot, screwed in new pilot, replaced the float contraption which fell out, put back on bike. no worky. reversed back to the old pilot and put on bike. no worky. :applause:

  • jbird710

Posted April 30, 2007 - 11:26 AM

#20

If I slow kick mine through the compression stroke, it will backfire on the second or third kick. But it starts fine. I'm no expert, but you've got me stumped also. If I weren't down by Galveston, I'd like to see exactly what's happenin'. I know you said you only replaced the carb jet. There's no chance your timing chain is loose enough that it could have jumped a tooth is there?





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