Carb probs...worn carb?


11 replies to this topic
  • miguelitro

Posted October 17, 2005 - 08:33 AM

#1

At the first race of the second half of the season no less :lol:
Flag dropped, bike fired 1st kick dust free to the end of the bomb run and then bwaaaaa... bike dies.
continues to do this through out the race every time i get past half throttle, especially with high load on the motor. Happens perhaps 5 times per 25 mile lap :lol:
Happens 50 feet befor checker flag and allowed my roomate to beat me by about 3 seconds(you try pushing a pig through sand after 75 miles of dez :banghead: )
still i finished :banghead:

Another racer came up to me said is your bike dying at the top end and popping excessivly? if so your carb may be worn out. Any thoughts on this?
Thanks for any help. The carb is gonna get a thorough cleaning this week and a test ride next weekend for the race on the 29th.
Hopefully that solves the problem but if it doesnt its either an edelbrock for me or ttrying to dig up another stock carb which i never really complained about...thats my :lol:

but at least i finished the race and as don87xr600 said a finish is a win points and a pin...
Mike

  • jim1234

Posted October 17, 2005 - 09:30 AM

#2

I doubt your carb is worn out. Maybe the needle and seat are worn out and sticking. Is the fuel tank screen clean. The way you describe it, it's a lean out problem. I would check the basics, needle and seat ( no burs and operates smoothly) float level . I would pull the fuel petcock and make sure no debris is in the valve or tank . and pull you fuel line off and look through it. You'll find it , it's just going to take the time to look at it.

  • miguelitro

Posted October 17, 2005 - 10:29 AM

#3

well read, it is definatly a lean out prob!
I am also sceptical of the "worn-carb" diagnosis but when told this by an expert class dez racer who happens to ride a BRP it is worth checking into.
The biggest pain about this problem is i need to run the bike WFO in high gear to have it happen which means almost an hour of driving just to have it happen or not happen.
Thanks Jim for the imput
Mike

  • qadsan

Posted October 17, 2005 - 11:00 AM

#4

It's been a while since I've looked at the service manual, but as I recall, all the moving parts have wear limits on them so all you have to do is mic them out to see if they're still in spec or not. It should be fairly easy to tell if your carb is worn out or not.

If all looks good, then maybe the float bowl is running out of fuel. Make sure your fuel supply is good (no kinks in the line, clean petcock filter, good fuel supply, no water or particulate in the fuel, etc). Check your float level and document it. Then adjust it no more than a couple mm's so there's more fuel in the bowl, which will also slightly enrichen your mixture circuits and see if this helps.

I had a similar problem a ways back in that I originally thought I was banging off the rev limiter, but the problem intermittently happened at an RPM lower than the ceiling and then my bike had a couple instances where it was hard to start, which clued me into something else. I found my auto-decompressor mechanism was failing and causing my bike to intermittently loose power at hgiher RPM. Getting rid of the auto-decomp mechanism resolved my issue completely, so keep that in mind after you've looked at everything else.

  • Shawn_Mc

Posted October 17, 2005 - 11:04 AM

#5

I almost hate to suggest this, but check the tank vent...it might be clogged and its simply sucking the bowl dry.

You could pull the bowl off or even just the fuel line and watch it flow for a minute or two...it may run to just a trickle and youve found your problem...

  • miguelitro

Posted October 17, 2005 - 11:07 AM

#6

sure hope its not the auto decomp...
the rest is all stuff that will be looked at.

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  • jim1234

Posted October 17, 2005 - 11:10 AM

#7

I agree with the tank vent also, My buddies quad quit running at Glamis . I pulled the tank vent off , and it was pinched. Cut out bad section and no more problems . The rider crashed alot but the quad ran.

  • miguelitro

Posted October 17, 2005 - 11:23 AM

#8

i've got one of those dry break style vents that come off the side of the tank and go straight down, not off the cap but i though of that as well and checked it by pouring gas out of it and it came out full stream...
list to check so far-top to bottom...
fuel tank screen
hose from tank to carb
carb tolertences
carb vent tubes
float level and flow
a good clean and overall fuel system inspection
if not all those-then
cam inspection, esp. auto decomp mechanism

any other help appreciated as i have a race in 2 weeks and need to make up the points i lost yesterday....
Thanks

  • miguelitro

Posted October 24, 2005 - 11:19 AM

#9

I had a similar problem a ways back in that I originally thought I was banging off the rev limiter, but the problem intermittently happened at an RPM lower than the ceiling and then my bike had a couple instances where it was hard to start, which clued me into something else. I found my auto-decompressor mechanism was failing and causing my bike to intermittently loose power at hgiher RPM. Getting rid of the auto-decomp mechanism resolved my issue completely, so keep that in mind after you've looked at everything else.[/QUOTE]

Cleaned up every thing and it FEELS like its hitting the rev limiter so now i'm worried :banghead: about that auto decomp....
i'll be removing it regardless as i dont feel i need it, sure hope that helps...
Mike

  • jonova

Posted October 25, 2005 - 07:02 AM

#10

Go to www.bajacycles.com, Rudi will line you out with a magic carb that won't give you trouble.

  • wr450fyamaha

Posted October 25, 2005 - 08:38 AM

#11

now way is your carb worn out.....it just doesnt happen. i would have to say your tank vent is clogged and you build up negative pressure to the point that it just doesnt suck gas any more. it sounds like it has an extremely small opening that allows for some fuel flow but not enough to sustain half throttle with high load.......full throttle would use more gas but generally the bike would be vibrating way more allowing for more air to flow around the clog.

  • miguelitro

Posted October 26, 2005 - 12:53 PM

#12

Jonova- you from down here in SD? I've met rudi acoupla times, real nice guy, and friends with some of the guys i ride with from time to time.
As of now I'm not taking out the auto decomp for this weekend's race, just not enough time. Eff it I'll just go out to finish... and hope to salvage a few points outta the deal, heck I'll be happy running #5 next year insted of #1 well not happy...
Wr450- an intelligent post for once Thanks!!! i've checked that over and over and no difference oh well. Carbs do wear out. The needle and needle jet especially will oval out. the slide will also wear over time. i ride alot and ride hard so yes its possible but again thanks for the reply.
I'm hoping that I can finish this weekend, get a new cam valves, springs etc, get the head cleaned up and back together for tha team race in acouple more weeks. Other wise I'll be riding my roomate's CR450F and i really dont like that bike at all. I'd rather have a 250 smoker, actually i keep thinking about getting one....
Mike





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