Carburetors from the grave


I've spent years acquiring mechanical survival skills from various areas . Although an experienced motorcycle mechanic my skills have come from such widely diverse areas as organic chemistry , cabinet making and restoration , wooden boats , aircraft and antique vehicles of many descriptions and eras .
Every spring a seemingly endless parade of carburetor cleaning would come through the door . Most were just plugged pilot jets and general cleaning . That is not what I want to talk about here . Every once in a while a bank of or a single carburetor would come through the door that would be a challenge even for my talents .
Just getting the carburetor(s) off can be a unique task . Snap-On made a now obscure radiator hose removal tool about 16” long that has a curious double bend at the pointed tip that is like nothing I've found since . It' is with out a doubt the best thing I've found for removal and installation .
Once on the bench I solidly support the carburetors as best I can and find a 3/16 to 5/16” punch or drift and not so lightly tap on each screw I'll be removing . Occasionally I'll find one or all of the screw slots ruined by previous attempts to disassemble . I'll tap all the burrs and damage back into the center of the screw head . The final few blows on the screw head are straight down on the screw . This has the effect of waking up the threads . If your father or grandfather wasn't a cabinet maker this may not make sense but it's the best description I can give you .
If you don't know what value a hand impact tool is to a motorcycle mechanic stop right here and do the prerequisite reading . I don't think even the weekend cycle mechanic can survive without one . Apex makes P1 , P2 and P3 Phillips head , 3/8” drive bits . The P1 is most often found in 1/4” drive .
Take the correct bit and a short , disposable 3/8” drive extension (disposable because you are going to be pounding on female end ) and center it on the screw head lined up with the now mangled screw slots . Drive the bit solidly into the slots reforming them as you drive it in . Likely you will be able to remove the extension and have the bit stick in the screw head . This isn't always the case but is the best case . Insert the hand impact into the bit and turn counter clockwise to load the impact driver . It's not unusual for the screw to turn and be easily removed at this point but most will not . Again solidly supported ,and in some cases supported directly under the screw to prevent casting breakage, take a firm grip on the hand impact holding pressure counter clock wise and hit the impact driver with a hammer . A number of things can happen at this point . Ideally the screw turns . If not the slots are completely destroyed and the bit removes them completely . If not the screw head snaps off . If not you didn't hit it hard enough . If not you hit it too hard and broke the casting .

If the screw turned , success .
If you didn't hit it hard enough , try again . This is an acquired talent and takes a bit of feel to get right .
If you hit it too hard and broke the casting you are a hammer mechanic Like I once was and need professional help .
If the screw head snapped off either you were not able to wake up the threads or didn't take the time to . Again seek professional help because repairing or replacing threads this small , with this little margin to work with is best solved by saving the original threads . That little bit of mechanical wonder is for another time .
As good as these reformed screws look do not be tempted to reuse them . Replace all of them .Preferably with socket head cap screws .
In most cases the carburetors will not have to be removed from the rails and I don't recommend it for a variety of reasons but alignment is the primary reason . In the severe case where a deceleration valve (typical Honda) needs to be removed or the carburetor bodies are so fouled that removal is looking like an option , stop . Find the smallest roll pin you can at the local nut and bolt and get it as long as you can . Find the correct drill bit (should be close to 1/16”) and drill from the cylinder head side of the rail into the carburetor body using a drill stop or piece of tubing to prevent the drill from going in too deep . Most carburetor castings are not full flush with the rail so drilling as near the outside of the area in contact with the rail will ensure that you bite into metal and not void . A change in resistance to the drill and a change in chip color and consistency will let you know that you have gotten through . Now drive the pin into the hole and trim it leaving about 1/4” . As above use the hand impact and appropriate bit to remove the screws while solidly supporting the carburetors.
Finally we're inside the carburetors and can't believe that anything like this could possibly happen just because of old fuel . After having removed all the rubber parts that could be damaged by solvents I give these special cases a very special bath . I'm fortunate enough to have a supply of moderately used transmission fluid that doesn't smell like a house fire but if you don't when was the last time you did a fluid and filter change on the daily driver ? The bath consists of transmission fluid and acetone . Mix it any way you like . For the initial bath I don't use much acetone . Some time later remove the carburetors , drain and rinse . I have a safety clean solution but there are others available . This first dip is just that a dip to soften up the deposits . Remove from the chem dip and rinse .
On the bench we have a still ugly set of carburetors with floats , needle valves and seats , with jets still installed . First things first . The hinge pin for the float has to come out . Don't hesitate , grab the micro torch the first time . I have turned several small C-clamps into tools to remove these occasionally obstinate items from their fragile supports but in most cases a small amount of heat from a micro torch or ha hot soldering iron will get them to move . Again , solidly supported use a pin pinch to attempt to get the pin to move . Some , not all , are easier to remove from one side so experiment tapping the pin back an forth gently until enough is exposed that you can grab it and pull it out . I can't emphasize enough just how fragile these posts that the pin is pressed into are .
All I can say about jet removal is fill the slot . I mean fill the flat blade screwdriver slot completely.
Some main jets are hex head but most are slotted . I have made screwdrivers from drill blanks for most common slots . These are not the common screwdriver shape but a blade shaped on the end of the drill stock with no taper . I want the flat of the diameter to rest on the upper surface of the jet and the blade to nearly touch the bottom of the slot . The handles are 1” aluminum or brass round stock and the shaft of the driver pressed into the handle . I want solid tools I can hit repeatedly with a small hammer while turning . Again start with heat first not as a last resort . Here is where I use a 50/50 mix of clean transmission fluid and acetone alternating with heat . Finally insert the bit into the jet . It should be sized so that it is between a slip and light press fit . While tapping the driver with a small ball peen hammer apply steady counter clockwise pressure . If the jet doesn't move with moderate pressure apply heat and 50/50 mix over a period of time . Patience is the key here . If the slot in the brass gives up it probably isn't your fault , some previous maniacal manic mechanic has probably destroyed the jet prior to your efforts . At this point all you can do is resort to a careful drilling and extractor . If you don't understand this part find someone who does .
All to often the novice will attempt to make up for other causes of flooding by bending the tab down onto the needle valve so far that no fuel will leak but also no fuel will flow . A general rule of thumb is if when upside down and the float adjustment tab is just resting on the needle valve adjust so that the float arm is parallel with the float bowl to carb body parting line . This only works if the floats have not been previously mangled .
Soaked , heavy or soggy floats .
even Nitrile floats have their service limits and susceptibility to modern fuels and alcohol content . If a float is suspect place it in a jar with fuel and compare it with the other three or a known good float . The difference will be obvious .
Worn needle valve . Seems obvious , replace .
The damage from constant contact with a needle seat will show as a definite ring around the Nitrile rubber tip . This just won't work . However in most cases the best cleaning agent for even the most green and ugly needle valve is simply your fingers and a bit of mineral spirits . The problem with this repair is its only half of the sealing element .
Dirty , worn or damaged needle valve seat . Simple enough ,replace .
Simple yes but not always the cause . A needle valve seat can be brought back to life with a little ingenuity . Remove the needle valve and leave the seat in the carb body for now . Find a drill bit whose shank , not drill , just fits in the seat . Cut the shank off the drill and chuck it up in a drill motor . Go over to a grinding wheel and attempt to reproduce the angle of the needle valve Viton/Nitrile tip on the exposed end . Finish this pointed down onto the side of the wheel . The reason for this is we are building a make shift valve seat cutter and using the grind marks as cutting teeth . Turn the shank around and do the same to the other end only this time the angle should be around 15 to 20 degrees . Those of you that have ground valve seats get busy as I explain the rest . Take a q-Tip and a bit of scotchbrite and either by hand or in a well controlled cordless drill and clean the valve seat . By hand take a few turns with the 15 degree end of the shank in the seat and observe the results . If you can see a definite bright ring all the way around the seat you're done . If more work is needed it may help to stick a bit of fuel line over the shank and use that to turn the shank . If that doesn't work by all means get out the fine valve grinding compound and use the drill motor . The seat was wasted anyway all you can do now is waste time . Do the same with the other end of the shank and attempt to establish the seat . This takes very little pressure and happens usually very quickly . Problem is after all this you may still have the problem and the needle and seat despite initial observations were not the cause .
The often over looked needle valve seat O-ring . Ignore this if your needle valve seat screws into the carburetor body . Oh this one still gets me on occasion even though I have the McMasters part # written on the toolbox (this for most BS34's )
Buna-N Shore A: 70 -35° to +250°F 9262K627 $2.94 per Pack of 100
Viton® Fluoroelastomer Shore A: 75 -40° to +400°F 9263K565 4.26 per Pack of 25
Sorry BTK in particular and Kawasaki in general but when I can get them at these prices you can not compete .
When you can undo the needle valve seat retaining screw and plate and the seat falls out it's pretty obvious that the fuel isn't getting past your needle and seat . It's going around the seat . Replace the O-rings and be happy . Don't cut them on installation , use a bit of grease and they should press in firmly . Verify that this is your dimension and install away .
Testing your repair .
After a carb clean of any kind I place an auxiliary fuel source at least three feet over the carbs and tip , bump , vibrate , shake and last but not least reproduce their on the side stand angle for several hours under that fuel to verify that there are no further leaks or overflow . As little room as we get to install these things I know I don't want to do it twice .
If a clean idle can't be established with the idle mixture screws less than 3 3/4 turns out from seat go up a pilot size . Put another way , you should see lean misfire anywhere from 3/4 to 1 1/4 turns from seat and rich misfire no further out than 4 turns . The sweet spot ideally is between 1 3/4 to 2 3/4 turns . Once again for those of you under the influence of cleaning solvent vapors , midnight microwave mystery meat burritos , exhaust fumes and or liquid libation , please , PLEASE , adjust the valves first . All will be right with the world if you do and if you don't gawd almighty will kill a kitten .


I was sitting in a parking lot waiting for my sister to come out of an appointment and had nothing else better to do . I'll be more than happy to edit in response to any reasonable input .


Been Around the Block
Re: Carburetors from the grave

Thanks for this write up Kop. Will be using it this weekend...


'hacking is learning'
Lol, big ol' braindump right there. Very helpful though, rebuilding a rack of BS30's this week.


Been Around the Block
Re: Carburetors from the grave

Quick question: bearing grease is fine for use on O rings and gaskets, right?


As long as it is NOT a clay base grease . In other words most any clear grease .



Been Around the Block
Interesting info about the needle valve seat. I know for dirt bike carbs they cost a packet to replace. Lucky I keep all my old parts, will try out some drill shanks.


Been Around the Block
Resurrecting another older thread... oh well. Great info.

It was just the other day that I was remarking about how totally useful the handheld impact drive/tool is to anyone working on older bikes (or anything else for that matter). I need to get a good one and this reading has pushed to do it.

Thanks for the wise words shared!



Okay it's spring and the mating sent of the neglected carburetors is in the air.
Rather than a bump I'll add some useful information as well.

The whole point of this is why pay MoCo prices for O-rings when McMaster Carr and others will sell you 100 for the price of a single with the MoCo part number on it.

So ...


Carb O-Ring 4.0mm I.D. x 1.0mm thick-pk/25 9263K284 3.87 McMaster
Carb O-Ring 7.5mm I.D. x 1.5mm thick-pk/25 9263K568 8.04 McMaster, N1.50X007.5
Carb O-Ring 2.65mm I.D. x 1.15 mm thick-pk/25 18-4632 K&L
Carb O-Ring 5.7mm I.D. x 1.3mm thick-pk/25 18-4602 K&L
Carb O-Ring 3.7mm I.D. x 1.8 mm thick-pk/25 3799N18 3.95 McMaster (note: 3.75 ID AND Buna-N)
Carb O-Ring 4.8mm I.D. x 1.9mm thick-pk/10 9263K638 6.73 McMaster
Carb O-Ring 2.4mm I.D. x 1.6mm thick-pk/25 9263K131 4.74 McMaster
Carb O-Ring 10.2mm I.D. x 1.4mm thick-pk/25 18-4637 K&L
Carb O-Ring 6.6mm I.D. x 1.5mm thick-pk/25 9263K567 7.30 McMaster (note: 6.5mm ID) N1.50X006.5
Carb O-Ring 2.7mm I.D. x 2.0mm thick-pk/25 18-4639 K&L OR 9452K13-pk/100 McMaster (note: .101" x .702 ID AND Buna-N)
Carb Passage Rubber Plug for Suzuki & Yamaha-pk/4 18-4689 K&L


Carb O-Ring 2.8mm I.D. x 1.9mm thick-pk/10 9263K636 McMaster $6.73, N1.90X002.8
Carb O-Ring 5.7mm I.D. x 1.3mm thick-pk/25 18-4602 K&L
Carb O-Ring 4.47mm I.D. x 1.78mm thick-pk/100 9464K13 McMaster $6.30
Carb O-Ring 3.2mm I.D. x 1.1mm thick-pk/25 18-4604 K&L
Carb O-Ring 4.2mm I.D. x 1.1mm thick-pk/25 18-4609 K&L
Carb O-Ring 5.0mm I.D. x 1.3mm thick-pk/25 18-4613 K&L
Carb O-Ring 2.8mm I.D. x 1.3mm thick-pk/25 18-4617 K&L
Carb O-Ring 2.8mm I.D. x 1.2mm thick-pk/25 18-4619 K&L
Carb O-Ring 5.8mm I.D. x 1.9mm thick- pk/25 18-4622 K&L ,N1.90X005.8
Carb O-Ring 6.9mm I.D. x 1.3mm thick-pk/25 18-4623 K&L
Carb O-Ring 4.8mm I.D. x 1.9mm thick-pk/25 9263K638 6.73 McMaster, N1.90X004.8
Carb Passage Rubber Plug for GL1000 -pk/4 18-4688 K&L
Carb Passage Rubber Plug for CB750K-pk/4 18-4690 K&L
Mixture Screw Washers, 1mm x 3mm x 5mm-pk/50 18-0055 K&L

I hope this helps. I'll work on the oddball and JIS another time.

I'm sure you all deserve it but won't appreciate it immediately. I ran a single shingle shop with a leaky roof and a dirt floor for several years. I had to think pennies before dollars. So if anyone can find additional sources for the above PLEASE, please do . I'm just offering yet another way for the low budget wrench to complete a dream.


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