Carb'd bike woes | GTAMotorcycle.com

Carb'd bike woes

Rob Star

Rob Star

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Background:

Dad inherited a bike from a passing relative. 2003 Honda Shadow 750. The bike has been sitting for the past five years. When we first tried to start it, It barely idled, and would want to stall every time you twist the throttle.

What Ive done thus far:

Pulled the carbs, took off the bowls, pulled the jets, cleaned them with small wires, and blew all the ports and the likes clear of dirt and debris with compressed air, I even cleaned the jets I removed in an ultra sonic tank. There seemed to be no adjustment on these carbs in terms of jetting. The jets simply screwed back into their spots in the bowl, and bottomed out once threaded in. I may be missing something important here but I followed a few you tube vids to a T.

Ive also changed the oil, flushed the coolant, changed plugs and wires, lots of spark on all four plugs. New gas, new gas filter, and I double checked the vacuum hoses all having to do with removing and reinstalling the carbs. .

What the bike is doing now:

It starts, but like before, it wants to stall when you give it gas. Sometimes it almost seems like the bike is idling on one cylinder. It sounds like its catching and missing. Thats kind of what it "sounds like" until I noticed something after investigation possible ignition problems.

The rear bank exhaust is HOT, like real hot, the pipe is turning gold. While the front bank is normal. Confirmed this by pointing a temp gun at the headers.

This is leading me to believe that the rear bank is running super lean, and its hitting fuel cut when I give it gas, explaining the stalling.

So, any suggestions on what to check on the carbs? Again, I dont "see" any kind of jetting adjustment

Is there a place in town I can just bring the carbs to and have them checked out?

Thanks in advance for any insight.
 
Do we have a service manual and a parts diagram for this carburetor?
re the exhaust temp question and general poor running, would be good to do a compression test to see if one cylinder has a problem.
 
I do have the service manual, but its not showing me what I want to know, I think it may just be an owners manual with maintenance section. Im having trouble downloading anything without going thru a massive explosion of spam websites and downloading fake links.

I do have a compression tester, I'll bring it up north with me when I go up to see dad in a couple weeks time. In the mean time I decided to pull the carbs again, I have them with me back in TO now.
 
Hey that looks like it might be it. Thank you kindly......Im going to give it a read now.
 
I immediately see something I missed on the carbs. Theres a plug covering an adjustable screw, Im supposed to use a drill according to the instructions and take the plug out which has access to this adjustable "pilot screw" Ill investigate further, thank you kindly.
 
(y) say thank you for the service manual trials :LOL:

... your carburetors have electric heaters in them ;) what could possibly go wrong with that.
Memorize that book and you should be good to go.


Somebody beat you to it and tried to make it run more rich, does it have stock or loud exhaust? That sealed screw is to show that the pollution control and fuel conservation measures have not been defeated :LOL:

... Is just as likely you need to make the adjustment to the size of the hole or the shape of the main needle jet anyway.
 
1) You can't clean jets, it doesn't work. Replace them they're cheap
2) Jets aren't adjustable. They screw in. That's that. You adjust flow through the main jets by raising and lowering the needle. You adjust the flow through the pilot jet by adjusting the air or idle screw.

By your description it sounds like you're lean. What do the plugs look like? Does it run better with the choke on? How 'bout with the choke on on the rear cylinder only?
 
The bike DOES run better with the choke on, (I think) unfortunately, the choke operates both carbs as an assembly.

EDIT: actually Im not sure whether it runs better with the choke on or off, I wasnt paying attention to be honest, but I dont remember putting the choke back in after running it. I was concerned with the heat on the rear bank and stopped running it.

I think I DO need an adjustment on the flow on the rear bank. Thank you for clearing that up for me.
 
Trials said:
(y) say thank you for the service manual trials :LOL:

... your carburetors have electric heaters in them ;) what could possibly go wrong with that.
Memorize that book and you should be good to go.


Somebody beat you to it and tried to make it run more rich, does it have stock or loud exhaust? That sealed screw is to show that the pollution control and fuel conservation measures have not been defeated :LOL:

... Is just as likely you need to make the adjustment to the size of the hole or the shape of the main needle jet anyway.
Click to expand...

Thank you for the service manual Trials :)

The bike is completely stock, the previous owner was a 70 year old man, who only rode the bike a few times a year, and always had it serviced at Honda
 
I'll add Ive never owned a carbed bike since I was a child with dirt bikes. I come from a world of laptops and wide bands, working on one is a bit foreign
 
Bike doesn't have a choke as such it has a fuel enrichment circuit. Bottom line is it don't work by closing off air it works by adding fuel.

Your CV type carburetors are from the era when they were trying to make a carburetor that runs as lean as possible, so it's a good bet that was just a little bit too lean to run good once it got a bit gunked up and old and tired. Problem still might be a lazy cylinder, that would produce the exact symptom you described in the first post.
 
I got the compression tester in my tool kit now, will definitely check that when I go up to work on the bike again. Thanks again.
 
I think you need to completely disassemble the carbs again -- take out every jet you can -- and put all the parts in a hot solvent-bath ultrasonic tank for a few hours. Fine wire is fine to run through the jets and bleeds (don't score them or make them bigger). Compressed air through the bleeds, emulsion tubes and jet orifices is critical.

Check the rubbers that connect the carbs to their respective heads; check them for cracks or breaks or poor sealing.

Also check your timing; high EGTs can be caused by retarded timing.
 
I recently started a Hawk that sat outside under a tarp for 5 years. Fuel stabilizer was added to the tank but I don't know if it was actually run through the carbs. In any case, if it ran fine before going into storage, worst case scenario is that the carbs just need cleaning if any varnish built up, but you shouldn't need to change any of the settings. You didn't say that you checked/changed the air filter. Mice seem to love building nests in those.
 
Blackfin said:
I think you need to completely disassemble the carbs again -- take out every jet you can -- and put all the parts in a hot solvent-bath ultrasonic tank for a few hours. Fine wire is fine to run through the jets and bleeds (don't score them or make them bigger). Compressed air through the bleeds, emulsion tubes and jet orifices is critical.

Check the rubbers that connect the carbs to their respective heads; check them for cracks or breaks or poor sealing.

Also check your timing; high EGTs can be caused by retarded timing.
Click to expand...

Ya see, the problem with trying to clean jets, ramming wire through them or ultrasonic spa or some witches brew or what ever, is you don't know if you have got them 100% clean (YEAH you can tell me you can look down a 30 thou diameter pilot jet and tell me it's 100% clean, but I'm not going to believe you) and if you don't know that they 100% clean that size number stamped on the jet/bleed/emulsion tube goes out the window.
If you stuff something into the jet, you'll scratch the sides (they're soft brass) and ruin the laminar flow. Same end result.
They MIGHT work, but you CANNOT tune with cleaned jets. DOES NOT WORK.

You can clean needles, but they do wear out. Same with the slides.
... and no you cannot EVER repair the diaphragm on the slide of a CV carb.
... and a lot of the jets (read all) offered on Amazon/Ali express are knock offs and aren't sized correctly. I have some that won't even screw into the jet holder. I think Keyster kits are now using third party jets too.
Buy jets from Sudco or Winner's Circle (who gets them from Sudco)
 
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