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Post by crash and burn on Oct 21, 2008 3:42:15 GMT -5
I'm sure this has been touched on before but I can't seem to find any post that are helpful to the situation I've got. I've already had the bike catch on fire once(sitting at traffic light 200' away from the fire station I work at none the less. Very embarassing!) due to this issue. The problem I keep having is that no matter what I seem to do gas is flowing right through the carb out the overflow and on to ground. I replaced the needle and seat and have taken the carb completly apart(no left over parts when I put it back together I double checked)and cleaned it and installed a fuel filter so stays that way. Tapping on the carb fixes the problem for a little while but after 5 miles or so it starts doing it again. ANY help or advice would be great I'm at a total loss here and very frusterated! Btw the carb is a stock '79 model
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pcnsd
Full Member
Posts: 113
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Post by pcnsd on Oct 21, 2008 20:53:19 GMT -5
The only common issue left is fuel level in the bowl. Are the floats undamaged, free moving and set at the correct height?
PC
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Post by crash and burn on Oct 21, 2008 21:53:44 GMT -5
The float is good I test floated it when I had the carb apart, the float pin is brand new and the float level is set to spec. Anything else I should look for?
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Post by crash and burn on Oct 23, 2008 14:15:43 GMT -5
No other advice? Oh well looks like I'm just gonna have to keep carrying an extinguisher till I can save up enough cash to replace the carb.
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Post by chew652 on Oct 23, 2008 14:21:04 GMT -5
Junk in the tank getting caught between the needle and seat? Does the needle valve stop the flow of fuel when held up manually?
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Post by solo2racr on Oct 23, 2008 14:21:52 GMT -5
From what you have described, you have covered all the bases. Just go back and double check everything.
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Post by crash and burn on Oct 23, 2008 16:27:26 GMT -5
I went thru cleaned and rechecked everthing today and I'm still having the same issue so I'm just gonna replace the carb with a 36 or 38mm mikuni. Thanks for the help guys.
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Post by phoebeisis on Oct 23, 2008 18:17:03 GMT -5
Is the float getting stuck on something- maybe there is a bit of play in something and the float can actually brush up against something and get stuck. Isn't there a little spring in there somewhere- tiny spring, not spring shaped of course- that tends to push the float down. It is sorta hooked on the float, or over that tab on the float??
Sorry to be so vague-you do still have that spring,right? If you don't have it, the float will get stuck up. My memory is a bit vague, but.... I think the spring kinda attaches near the tab and near the float needle.
Charlie
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Post by solo2racr on Oct 23, 2008 19:34:50 GMT -5
The only things that I have seen springy on a needle and seat are a spring loaded plunger in the center of the needle and a retainer that clips around the seat to hold the needle in the seat. I have never seen anything that will push the float back down. That aside, I was also thinking that the float may be sticking on it pivot. If everything is in good condition and assembled correctly, there is no good reason for it to dribble fuel out the overflow.
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Post by phoebeisis on Oct 23, 2008 20:28:50 GMT -5
solo2racer- I must be thinking of the retainer.It has been years since I looked in the float bowl
I vote for the float sticking also-little play in it, it can manage to get stuck.
I wouldn't give up on this carb yet; the stock carbs actually start better,and get better MPG than the aftermarket carbs- when they are working right. They usually have better throttle response also.
Charlie
Charlie
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Post by crash and burn on Oct 24, 2008 1:40:07 GMT -5
The pivot pin for the float is brand new and the float itself is clean and burr free but I never thought to check the inside edge of the bosses that it mounts to. I'll try polishing the mating surfaces and see if that helps.
Personaly I think the stock carb is an over-engineered P.I.T.A. compared to alot of the dirt bike and sport bike carbs I've worked on, but I'm kinda broke right now so I'm gonna try to keep it working till I can afford to replace it.
Thanks for the help we may have finaly made a break tru here.
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Post by crash and burn on Oct 24, 2008 21:06:31 GMT -5
I took the float out and polished the mating surfaces and that seems to have fixed the problem.
Thanks guys
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Post by phoebeisis on Oct 25, 2008 8:41:01 GMT -5
Great! If the problem stays away for several weeks,you are home free.
Yeah, it is overly complicated. Years ago I spent 100's of hours on those freakin' SR500 carbs. I would usually end up buying a VM36 from White Bros, but then I got better at fooling with them, I started to like them. There main problem is the idle circuit passages are absolutly tiny, and they plug.Once they plug they become really hard to start and to keep running( the start circuit also can plug, but it has huge holes).
The 3 expensive diaphragms are kinda optional-I think it can live without them.They are what make it a PITA to rebuild.One is antibackfire-one is for the accel pump, and one might be to prevent the accel pump from pumping when the motor isn't running.
Charlie
Charlie
Charlie
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Post by davedunsboro on Oct 25, 2008 8:53:57 GMT -5
One little thing that I've had heaps of success with is using a 5 or 6 mm taper tap(they go to a point & the flutes carry through)& If you put one into the seat & twist it smoothly it sort of recuts the seat that the needle sits in (most times you can reuse the needle that you have as that is the problem anyway-crud on the seat) I also use guitar string cutoffs for rodding/rehming out all the other orifices, jets & holes etc Cheers Dave.
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Post by miker on Oct 28, 2008 14:37:55 GMT -5
Dang, guitar strings... got a zillion around, what a great idea! Thanks Dave.
miker
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