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Message started by spacepirates on 01/10/12 at 07:19:07

Title: Carb help on another bike
Post by spacepirates on 01/10/12 at 07:19:07

In a previous post I mentioned I picked up a 1985 Honda Sabre, fresh out of sitting in a garage for years.

I've started getting in back into running shape but ran into a carb issue that I can't quite pin down.

I took the carbs off the bike to clean them and after that was all said and done I put them back together (mostly) and checked float valve operation by putting gas in the fuel line and manually opening/closing the float with my hand (i got burned bad by this on another bike, leaked gas into the oil... not pretty). so after that checks out, i put the carbs back in the bike (which is a pain with four carbs, by the way). I start the bike, which starts up easily enough, but i notice the fuel level dropping waaaaay too fast. I have a clear fuel hose running into the carbs for now (the tank is off the bike) and it drops about an inch every few seconds, maybe going through 1/4 cup of gas a minute. it might also be important that the bike won't idle without choke out, and dies if you rev it.

pull the plugs, and one is soaked! pop the carbs off, check the floats and gaskets again... everything checks out.

what could make a carb that seems sealed and in sound condition drip fuel like it is it's job when the engine is running?

i think my next diagnostic steps are going to be swap the float valve and float from the presumably leaky carb into another one and see if the problem travels with those parts. otherwise, i'm not sure what else i can do.

thoughts? bad float valve? dirt/particles messing up the seat? some overflow channel being activated?

You might ask yourself why I've come here rather than go to the bike's forum, and i would say, first off, everyone here is sooo much cooler ;) and more knowledgeable ;) and what's that you say? something brown on my nose? oh, well i guess it is also because this bike doesn't have a forum, which leaves me feeling sad and alone :'(

Title: Re: Carb help on another bike
Post by Boule’tard on 01/10/12 at 07:32:38

Check the air vent(s) on that carb that's dripping.

Title: Re: Carb help on another bike
Post by RidgeRunner13 on 01/10/12 at 07:36:36

It's almost impossible to tell if a needle is properly seating by holdng the float with your hand. Too easy to apply more pressure than the float would.
If you want to check them before reinstalling, put the float bowl on & attach the carb to a fuel supply. Hold the carb in the same position that it would be on the bike & turn the fuel on. If it leaks you have a bad needle & seat. 8-)
There is always the chance that something in the tank (rust?) will break loose & cause a needle & seat to leak, or clog a jet or a passage. Sometimes it just takes more than one cleaning to get everything. :-/

Title: Re: Carb help on another bike
Post by spacepirates on 01/10/12 at 07:44:01

0B303D3E3C0B2C37373C2B686A590 wrote:

This is the third time I've had the carbs off the bike, and if I'm reading your post correctly, I think I do exactly what you say. I fully assemble the carbs, then put a supply of fuel into them and let them sit over night to see if anything leaks (i mark on the clear fuel line the initial level, and see if it dropped a day later).

I'll try and clean them (again) while I swap the float parts. for all i know there is one stubborn piece of dust that is causing me hours of torment...

Good thought on the float pressure. I hadn't thought of that, though now that you say it I definitely agree that anything by hand is going to have much more pressure than just the buoyancy of the float.

Boule, to be honest, i haven't gone through the air vents on the carb. how would those being clogged cause excess fuel into the throat of the engine? despite tearing apart a dozen carbs recently, I'm not versed in the actual workings of them, just in how to clean them, jet them, and put them back together (sometimes i even put them together correctly!).

Title: Re: Carb help on another bike
Post by Boule’tard on 01/10/12 at 07:55:00

1112030107120B1003160711620 wrote:

Boule, to be honest, i haven't gone through the air vents on the carb. how would those being clogged cause excess fuel into the throat of the engine?

The floats need atmospheric air pressure in order to float properly. A clogged vent will cause abnormal high air pressure above them, mucking up their ability to float at the right level. I saw this problem on a gs500..only two carbs, but the principle should still hold.

Also, we assume you have checked the floats for any pinholes and are sure they are not getting waterlogged.

Title: Re: Carb help on another bike
Post by spacepirates on 01/10/12 at 07:58:18

Ah, gotcha. I'll have to double check those vents.

The floats are plastic, and my "pinhole test" consists of me shaking the float next to my ear to listen if anything is sloshing around in it, which didn't yield any results.

Title: Re: Carb help on another bike
Post by RidgeRunner13 on 01/10/12 at 08:07:18

Ever noticed how your bike runs different with a full tank of gas than just before you go to reserve? That is the difference in fuel pressure. With a gravity feed fuel system a carb that may not leak with just a little pressure may flood with the correct pressure supplied.
I prefer to put a longer fuel line on my tank so I can rest the carb on the floor while checking. This applies more fuel pressure to the carb. If you're worried about making a mess, set the carb(s) in a drain pan. 8-)

It sounds like you have a pretty good grasp of what to do. Just clean anything that looks like it could be a passageway & you can't go wrong. ;D

Title: Re: Carb help on another bike
Post by spacepirates on 01/10/12 at 08:30:53

6E55585B596E495252594E0D0F3C0 wrote:

This is exactly how I found out I had a leaky petcock on my XS750. I was so excited I had everything back together. Took it out for a few miles spin, finally filled up the gas tank, woke up the next morning to find a puddle :-/

I've been using a wash bottle to squirt fuel down the line into the carbs, and the nozzle is large enough I can make a seal and pressurize the line a little by squeezing the bottle harder. that and the tank stays off when the carbs were back on the bike, before I'm pretty sure the carbs are good to go.

wash bottle:
http://www.usplastic.com/catalog/images/products/labware/80148p.jpg

just picked up a carb cleaning wire kit too, so that should help a bit.

Title: Re: Carb help on another bike
Post by verslagen1 on 01/10/12 at 09:00:03

One of the SOHC4 forum guys might be familiar with your bike.
They tend to be brand loyal.

Take a clear line and run it from the drain up.
turn on the fuel and see where the fuel comes up to.
shouldn't rise above the bowl gasket.

are the float valves rubberised?

Title: Re: Carb help on another bike
Post by Serowbot on 01/10/12 at 09:12:13

Check the function of the slide in the particular carb that leads to the wet cylinder...
Also, check under the main jet, that the brass tube the main screws in to, is secured in place... Usually, with tiny brass pins,.. or maybe screwed in place...

Title: Re: Carb help on another bike
Post by spacepirates on 01/10/12 at 09:54:22

647760617E7375777C23120 wrote:

I'll scope out the SOHC4 forums. Didn't even know they existed...

The float bowl in question doesn't actually sit flat in this v4 design. the float bowl is at a 45 degree angle or so from level, meaning the gasket is offset from level. I'll try the clear tubing, but the lower lip of the bowl is very close to the lowest point of the bowl itself (i think). I can't imagine the fuel level *not* being above the bowl, but i'll check.

Serow, I'll double check the jets. if i recall correctly, the main jet screws into the brass tube which screws into the carb. i guess it could have come loose or not been tightened enough.... but then i'd only have myself to blame :-[

Title: Re: Carb help on another bike
Post by spacepirates on 01/12/12 at 20:48:16

Am I going crazy? Did I just see a post appear and disappear made by Boofer about someone on Motorcycle Forums?

Cause I checked it out, and there are a few posts about mid eighties sabres being restored, but most of that is cosmetic stuff (seats, turn signals, misc small items needing replaced). sadly (for me, not for them, i guess) there isn't anything about the carbs (yet).

however, seeing as how i didn't even know such a vast repository of motorcycling knowledge existed in the first place, the exploratory journey there is worth it on its own.

Doubly sadly, I haven't been able to get back into the bike yet. I took a look at my "fuel line feeding into a car that is off the bike" setup yesterday and the entire two feet of fuel line had gone dry. definitely a leak somewhere. This weekend I hope to do a full-scale clean on it. I purchased an extra can of spray on carb cleaner (no air compressor to use yet) and rubber gloves. hopefully one more go-through in an all out attempt to be as clean as possible yields some promising results.

on the other hand, i did just get new calipers in for one of my other bikes.... hm... toss up...

Title: Re: Carb help on another bike
Post by spacepirates on 01/16/12 at 11:05:24

re-cleaned the carbs, blasted any thing i saw with cleaner and picked up a carb cleaning tool to wire out the jets.

put everything back on yesterday, but spent most of my time getting a new carb put on my savage. if this week is warm enough this week or this weekend I'll try out the Sabre again.

Of course, I still need a title for it, but that won't stop me from a little joy ride ::)