Carb Rebuild?

So im pretty new to riding and fixing bikes scene, my question is how do i know if i would have to rebuild my carb vs cleaning? I just pulled my carbs off and have not yet opend them up, what are some things i need to look for? Anything will help, thanks!

1980 Yamaha Maxim 650

 

Read xj4evers carb cleaning under supporting vendors pages.

MN

 

If you have never rebuilt them its probably time to do so. If you know they were rebuilt recently then you can get away with a cleaning. Rebuilding carbs primarly is replacing the normal wear items like needle/seats gaskets and seals. Most of our XJs have suffered from years of neglect, carb parts suffer from old age also. Replace them if you don't know their condition.

 

You can gamble and just clean them, put it together, and see how it does. You just might have to pull them apart all over again if you realize those parts are holding you back at the end of the process. If you have the gumption to put up with that, then kudos. It'll be a good lesson in cause-and-effect of those little parts when you see what performance difference it makes.

On the other hand, you might get lucky and spend less money and do less work and come out fine.

Crapshoot. Pick your odds.

 

Pull the Carbs.
Stand them on-end.

Put some Marvel Mystery Oil on the Throttle Shafts.
Work the Linkage.
If the MMO goes through the Shaft Seals quickly, ... replace the Seals.
If the MMO does not drain, ... Leave the rack together and just CLEAN the Carbs.

Do one at a time.
Remove the Bowl.
Remove the Float Hinge Pin.
Lift the Float and Needle clear.
Observe how Needle attached to Float.
Remove MAIN Jet.
Remove Washer.
Remove PILOT Jet.
Remove FLOAT VALVE SEAT.
::: Use Caurtion ... Dont Break Float Hinge Pillar :::

Clean Bowl and Lower Orifices to Enrichment Well.
Clean all Jets and Parts.
Clean Body and all nooks and crannies.

Remove TOP
Remove Spring.
Remove Rubber Diaphragm and Piston --> Observe Alignment Tab.
Note TUBE where Diaphragm Needle extends into.

Invert Carb.
Knock-out TUBE from Body.
Clean TUBE and ALL 16 - 20 Holes.

Scrub Diaphragm Bore with ScotchBrite Gray.
Thoroughly Clean Bore and all exposed surfaces
Remove Plate from inside Diaphragm Compartment if equipped.
FLUSH Jets.
Clean and condition all parts.

Remove Pilot Screw.
Collect Screw, Spring, Tiny Flat Washer, Tiny O-ring.
Clean.
Flush.

Clean Piston
Clean Rubber Diaphragm / Inspect for integrity.

Once everything is thoroughly cleaned and flushed; re-assemble

Replace TUBE
Secure with Main Jet and Washer.

Install Diaphragm and Piston Assy.
Line-up Tab.
Refit Top-end Parts.

Refit Bottom-end Parts.

Do 2, 3, and 4.

 

Take them apart as recommended. Clean and INSPECT, carefully, all the parts. Replace rubber parts; replace other parts as necessary.

Don't assume, or "shotgun" it-- LOOK. Carefully inspect the parts; you'll be able to tell what needs to be replaced.

DO NOT submerge the carb bodies in anything unless you plan to tear them down all the way (remove butterflies and throttle shafts) to replace the throttle shaft seals.

Proceed carefully, meticulously and don't hurry. Make sure you have a clean, well-lighted work area; and keep the parts from each carb together, don't inter-mingle them. The more thorough and careful you are, the less likely you'll have to do this over and over (usually about 5 times for the average shortcutter.)

 

Thanks for all the advice everyone I went ahead pulled them apart, inspected and cleaned them. All the part were in good condition, after a good scrub I assembled and my bike started!! Hasn't started since i bought it

 

Having Clean and Tuned-up Carbs is a major contributing factor to really enjoying riding a motorcycle.

Having a bike perform to its utmost will bring a smile to your face.

 

I found an '82 XJ750 Maxim with only 5500 miles and I have been reading all of the past posts I can about carb cleaning and rebuilding. After removing the carbs from my bike seven times and each time finding and fixing or adjusting something else, I am so close to a good running bike that I haven't lost hope......yet.

My remaining problem is that the bike will only start with the idle adjustment screw turned "in" a bit then, obviously, it revs high until I turn it down again. Then it'll start just fine when warm. No amount of throttle or choke will coax it to life when it's cold (first start of the day).

I have cleaned EVERYTHING and replaced and adjusted the float valves. I bench synched the carbs using the "paper clip" method detailed in another string. I also checked the float bowl fuel level and it's good (amazingly, the drain screws didn't put too much of a fight!). The other seals and gaskets, etc. are in fine shape and don't need replacing. The boots are not cracked.

There is a local shop that does a carb synch for $125 so I'm wondering if you think that'll help solve this starting problem. I know I could get the synch kit for myself for a lot less and teach myself something in the process but summer is quickly fading here in Central Vermont and I want to get riding.

I seem to remember a warning about fast idling mentioned in one of the carb cleaning and rebuilding posts but I can't seem to find it again.

Any thoughts? Thanks.

 

There's a small hole in the bottom of the float bowl opposite the drain plug that seems like it should lead to the enrichment fuel circuit and the very small pickup tube. I tried to clean the passage, got some junk out, and tried to see if air passed through but got nothing. Does this hole feed fuel to the enrichment circuit? If so, how the heck do you get it open? Could this lead to a hard start issue?