Topic: CB650 idling issues and other small problems

[ballinchestr]

Apologies in advance for beginner post. I just bought my first bike, a 1981 CB650C. I'm new to motorcycling, but not new to engines. I just changed the oil, filter, and replaced the battery. The bike has trouble idling. when it is cold, it will not idle unless the choke is pulled out, or I give it some throttle, and until its warm, its a little sluggish. Also, fuel leaks from the carburetors when I idle it after riding it. This also sometimes happens simply when the fuel is turned on. I drained the carbs and turned on the fuel, only to have it overflow again after refilling the bowls. I hooked up a sync tool to see if they were out of sync, but they seemed okay in the few moments I looked at the gauges. I also ran some seafoam through it, but it had trouble starting afterwards.

Also, the previous owner must have misplaced some of the vacuum bolts for the sync tool (I don't know what they're called). Two were missing, one replaced with some other bolt of the same thread size, and another with a hose fitting and a small section of hose, plugged at the end. If there were a leak in any of these vacuum ports would it affect performance? If so, how can I find replacements for these bolts?

[ballinchestr]

Thanks for the info. Where can I find bolts for the sync ports? They look like 5mm, but can any bolt seal it or should all the bolts have o rings?

I'll look at the carbs when I get the chance. I'm assuming that adjusting the float height requires pulling the carbs?

[ballinchestr]

The threads were the right size, so I sealed up all four sync ports. I tried to start the bike but it wouldn't fire. I opened the drains, and there was almost no fuel in carbs 3 and 4. I then removed the carbs and opened all the bowls. Here's what I saw. https://i.imgur.com/FJmkF8T.jpg According to the carb cleaning guide, aren't I missing all 4 passage plugs? Also how do I adjust the float height? More pics.https://imgur.com/a/C9KbpgF

[ballinchestr]

Okay so the idle issue is definitely because all four slow speed jets are very clogged. I can't push guitar string through any of them. They are pressed in. What's the best way to go about unclogging them? I read that some people take the jets out somehow, and some people drill them open. If I were to drill through, what's the diameter of the slow jet?

 Suggestions?

[kkelley515]

Were you ever able to resolve the issues you were having? I've also recently acquired a 1981 CB650C, which the PO had used a few times as a dirt bike (really?) and otherwise left in a shed for the last ten years. I've spent the last seven weeks rebuilding the top end and carburetor, only to have the carb leak with some idling issues after reassembling the whole thing.

From what I can tell, there is no adjustment for the float height on this model. I'm fairly certain that the fuel leak is due to one of the float valves not closing (the valves are new, and the seats were polished during the rebuild), and it might just be sticking. In my case the fuel was leaking out of the overflow somewhere, but also back into the air box.

[ballinchestr]

Sorry for not replying to this thread, I've been in college. I thought I would get my bike running good during winter break so I can start riding right as summer starts, and I've hit a major roadblock.

Kkelley515, I fixed the fuel leak problem by thoroughly cleaning the float needles and the inlet valves they insert into. I did this with carb cleaner and a Q-tip. If your valves are new, I don't really know what to tell you, but I always had luck with just slapping the carbs with a screwdriver handle if they stuck like that.

However, the pressed in slow speed jets are still 100% gummed up, and nothing can flow through them whatsoever. I read on this forum somewhere about tapping #2-56 threads into the jet bodies and pulling them out with a threaded rod. I tried this today, and failed. Despite carefully tapping the holes, I pulled the threads out of two of the jets, and gave up after that out of frustration. I fear I will not be able to remove and clean the jets at all, and I am already looking at replacement carburetors.

 If nobody has other ideas for 'last ditch' methods for removing the jets, how should I begin looking for carburetors for the bike? I don't know where to find them, and I would love to know if any newer models are compatible with the bike, as I am done dealing with these P.O.S. pressed in jets. I realize that they stopped making them like that after 1981. The bike is a 1981 CB650c.

[Hutch]

Sorry for not replying to this thread, I've been in college. I thought I would get my bike running good during winter break so I can start riding right as summer starts, and I've hit a major roadblock.

Kkelley515, I fixed the fuel leak problem by thoroughly cleaning the float needles and the inlet valves they insert into. I did this with carb cleaner and a Q-tip. If your valves are new, I don't really know what to tell you, but I always had luck with just slapping the carbs with a screwdriver handle if they stuck like that.

However, the pressed in slow speed jets are still 100% gummed up, and nothing can flow through them whatsoever. I read on this forum somewhere about tapping #2-56 threads into the jet bodies and pulling them out with a threaded rod. I tried this today, and failed. Despite carefully tapping the holes, I pulled the threads out of two of the jets, and gave up after that out of frustration. I fear I will not be able to remove and clean the jets at all, and I am already looking at replacement carburetors.

 If nobody has other ideas for 'last ditch' methods for removing the jets, how should I begin looking for carburetors for the bike? I don't know where to find them, and I would love to know if any newer models are compatible with the bike, as I am done dealing with these P.O.S. pressed in jets. I realize that they stopped making them like that after 1981. The bike is a 1981 CB650c.

 

First advise, as long as the carbs aren't damaged, try puling the jets again. Look into ZX600C (1st gen Ninja carbs) or mid-80's GPZ550.  I believe you'll need the boots from those carbs as well for them to work.

[ballinchestr]

Before you ditch your carbs, pull them off the bike and immerse them in an Ultrasonic cleaner. Using a proper solution to dissolve carb varnish in these machines will do wonders. You can always use the machine for other projects and tasks as you go along too.

I've thought about this, but I've heard others with this problem only overcoming it by removing the jets before putting them in an ultrasonic cleaner, and leaving them in for the cleaning was unsuccessful. I no longer have a strategy for removing the jets and I don't know how I will get the slow circuit clear besides replacing all 4 carb bodies with ones with removable slow jets.

Before I give up I'm gonna drill+tap the jets with a #4-40 tap and try it again. Hopefully thatll have enough bite to pull the jets. At least since they're clogged to $%!# I wont get any shavings into the circuit! I'm gonna soak them in PB for the time being.

[TurtleSnifferII]

Were you ever able to resolve the issues you were having? I've also recently acquired a 1981 CB650C, which the PO had used a few times as a dirt bike (really?)

Interesting, the previous buffoon who I got my 1980 CB650C used it as a dirt bike and off roading as well. It was a mess that took two years to sort out.

[pmanning]

I have an '81 CB650 that had sat unused for 10 years before I bought it.  Unlike my 750 I found it. to be a much more cold natured engine.  Full choke to start and extended warm up period. It also leaked from the carbs though I removed the float bowls and carefully cleaned jets and passage ways - several times; replaced needle valves, even replaced a float.  Ultimately it turned out the leak was from the inlet "T" tubes between carbs 1&2 and 3&4.  The o-rings had dried and hardened during that extended period of disuse.  Replacing the o-rings solved the fuel leak problem.

[Hutch]

I'm gonna soak them in PB for the time being.

PB is for rust, not varnish and will likely do little to clear clogged fuel circuits. There are specific carb varnish solutions on the market, and they do work well whether a component is free or installed. An ultrasonic Cleaner also works where other methods don’t, even on installed components. Sure, best if the jets are free of the body, but you might just get them cleared without ditching your carbs. Or drilling.

Agreed, PB won't remove varnish, I prefer xylene.  For a soak, I prefer 4 gallons of white vinegar with 1.5 cups of salt per gallon, it soak for 5 full days. Much easier on the metal than simple green or pinesol.  I prefer Barryman's as a carb cleaner, works much better than the other commonly available carb cleaners.  Did you download a copy of the carb cleaning manual?

[Hutch]

For a soak, I prefer 4 gallons of white vinegar with 1.5 cups of salt per gallon, it soak for 5 full days. Much easier on the metal than simple green or pinesol.

Soaking carburetors in vinegar and salt is a surefire way to destroy them. That is an acid-based solution and these cast aluminum bodies will get eaten away promptly. Simple Green is a cleanser, Pinesol too is VERY caustic to aluminum castings and the pH of it will turn aluminum a very dark grey quickly and permanently. Spend the money on proper aluminum-appropriate solutions and task specific cleansers for the best results. Leave the res of the DIY kitchen recipes for the dolts on YT. 

Any carb soak you could recommend that would work with just a soak, always looking for a better way.  I've ready mixed reviews on the HF ultrasonic cleaner, and a proper ultrasonic is cost prohibitive.

[ballinchestr]

I'm gonna soak them in PB for the time being.

PB is for rust, not varnish and will likely do little to clear clogged fuel circuits. There are specific carb varnish solutions on the market, and they do work well whether a component is free or installed. An ultrasonic Cleaner also works where other methods don’t, even on installed components. Sure, best if the jets are free of the body, but you might just get them cleared without ditching your carbs. Or drilling.

Agreed, PB won't remove varnish, I prefer xylene.  For a soak, I prefer 4 gallons of white vinegar with 1.5 cups of salt per gallon, it soak for 5 full days. Much easier on the metal than simple green or pinesol.  I prefer Barryman's as a carb cleaner, works much better than the other commonly available carb cleaners.  Did you download a copy of the carb cleaning manual?

Sorry, I should have specified, im only soaking the slow speed jets with PB, so I can hopefully break them free. I did this by filling just the holes where the jets are pressed with PB. After about 4 hours, none had made it through the jets so they're still very much clogged. Since the #2-56 threads I tapped got pulled out, I don't see any other way to remove the jets and save these carb bodies other than drilling and tapping to a larger diameter and trying to pull them again via the same method.

[onepieceatatime]

I think I have a set or 2 of '81 cb650 carbs. I have no idea what condition they are in, as they were on my parts bikes, but I'll see if I can find them this weekend.

[ballinchestr]

Progress!

I drilled and tapped one of the jets to #4-40 and tried the same method. The first try, the nut stripped out and it stopped working, but I tried again and pulled on the bolt as I did, and the jet came right out! No damage to the circuit either, so tomorrow / later tonight I'll try my luck at the other three jets.

A couple of questions though. I want to get new jets because the insides of this one are pretty chewed up. Would it be best to tap the channel and install the newer screw-in jets, or carefully tap new jets to press in like before?
Also, there's a lot of brass chips in the channel, how do I ensure that I remove all of them?

That jet probably hasn't been taken out since it was pressed in in 1981!
Couple of pics.
https://i.imgur.com/n0WT0DK.jpg
https://i.imgur.com/kVgCaBX.jpg

[ballinchestr]

Success!

 I pulled all four slow speed jets without any more fuss. Now I just gotta clean the circuits and put in new ones. I also found the original cause of clogging., The PO had put off installing new bowl gaskets, and instead smeared gasket maker on the existing ones. Little bits of that dried up gunk must have clogged the slow jets. I already have a new set of gaskets so I just have to thoroughly clean the bowls and carb bodies. Things are looking up!