First Time Rebuilding Carbs [1984 Honda CM450E] - Questions about float needles

I am about to put the carbs back on today finally. I wanted to ask if you guys have any pointers or tips to put the carbs back on since it was such a pain to take off - I can only imagine it being worse to put it back in. I saw a video of a guy pushing the air box boots deeper into the air box then fitting the carb in and shifted the boots back into place by pushing it from the air box (and a little help of silicone WD40). I was wondering how well this method will work? Any other ways to do this without being a pain in the ass?
 
I'm in a similar boat with the airbox boots on my CB900F, and it can be a PITA. Jim or Frank will have more tips for you as they've worked extensively on your model (or similar).
 
I removed the 3 bolts that fasten airbox to frame (1 left, 1 right, and 1 rear-top) and moved the entire airbox with its boots (which were glued/rubber-cemented in place by Honda when new) rearward to be out of the way of the back end of the carbs rack for my rack removal and re-installation.
The less bending those airbox boots are exposed to, the less chance they'll tear, split, break, etc... because the ONLY way to replace them is buying an entire good used airbox with good boots and that possibility is declining as time passes. The boots were never offered as a seperate part from the airbox.
Pamper your boots - treat them with as much care as you can !
 
Before you go to all the trouble of mounting those babies. Did you check them for leaks and the proper function of the accelerator pump circuit? If you replaced the fuel valves with non OEM parts they are usually a different float height setting than stock. Checking the float height is also recommended if they were replaced with aftermarket pieces.
  1. Test them for leaks with a gas bottle or tank to confirm they are gas tight and no overflow issues?
  2. Test the accelerator pump circuit to confirm you getting a solid spray of liquid from the brass nozzles on both carbs into the carb throats?
Failure to test them first is a ticket to installing and removing them again and again! I like to use isopropyl alcohol as a test liquid, since it is less stinky and easier to handle than gasoline.
 
kbongos said:
I described my method in post #33 . I never ever ever want to dislodge my rear boots from my air box ever again.
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I remember you mentioning removing the boots on the engine then taking the carbs out, I actually chose to take the advice to replace my boots so I am thinking, would it be easier to put the boots on the carb first then slide it in? Though I do worry it will dislodge the gaskets on the engine side of the boot.
 
Flyin900 said:
Before you go to all the trouble of mounting those babies did you.If you replaced the fuel valves with non OEM parts they are usually a different float height setting than stock, so checking the float height is also recommended if they were replaced with aftermarket pieces.
  1. Test them for leaks with a gas bottle or tank to confirm they are gas tight and no overflow issues?
  2. Test the accelerator pump circuit to confirm you getting a solid spray of liquid from the brass nozzles on both carbs into the carb throats?
Failure to test them first is a ticket to installing and removing them again and again! I like to use isopropyl alcohol as a test liquid, since it is less stinky and easier to handle than gasoline.
Click to expand...
Checked the float heights using the homemade gauge that LDR recommend and it was correct thankfully (15.5 mm). I tested the floats to see if they float and both passed and did not have any bubbles coming out when submerged in gasoline. the way i checked if the original overflow leak was gone was filling up the float bowl (separated from the carb) with gasoline an see if it continued to leak after replacing the drain screws and it did not. Originally it did leak when I tested with the old screws when i did the exact same test. Let me know if this is an inaccurate way of checking, ill try whatever you guys recommend if i have the tools for it. Double checked again for any visible cracks in the stand/overflow pipe and did not see anything.

For the accelerator pump, I’ll check how I can test that but how do you reccomend?
 
TomatoThePotato said:
I remember you mentioning removing the boots on the engine then taking the carbs out, I actually chose to take the advice to replace my boots so I am thinking, would it be easier to put the boots on the carb first then slide it in? Though I do worry it will dislodge the gaskets on the engine side of the boot.
Click to expand...
 
Remove the left side of the top engine mount so the cables can slide in easily.
Install the cables onto the carbs before installing the carbs to engine.
I leave the insulators in place on the engine. I used to fight and finagle the air box boots into place after carbs were in and tight. Now I've taken to doing it the Honda way of moving the air box back, no tire removal though.
 
LongDistanceRider said:
Remove the left side of the top engine mount so the cables can slide in easily.
Install the cables onto the carbs before installing the carbs to engine.
I leave the insulators in place on the engine. I used to fight and finagle the air box boots into place after carbs were in and tight. Now I've taken to doing it the Honda way of moving the air box back, no tire removal though.
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In that case, I’ll install the new insulators first.

I was speaking with boosted and he even suggested to go the extra step of checking all the cables work correctly and fully close before installing the carbs so I will do that as well.

My airbox is still pushed back from the time I removed the carb, so I’ll work with its current position. LDR, I would like to thank you and all of you guys for all the assistance, its all been super helpful.
 
The order I would suggest trying would be to attach the back boots to the air box first, those I recall were troublesome due to odd square fitting and the boots having trouble fitting on there without some large deformations to be worked out. Once those are in place I like to leave the small ones that go to cylinders last(off), where you put the carbs in place with into back boots loose so you can push them around. Get carb cables hooked up in the process, possibly before pushing into place as it makes cable access easier. Then carbs can be set into back boots and hold in place, but with clamps loose give you room to push back and to the side to slip front ones onto carb. Once both front ones on carb, bolt them to cylinders, then tighten clamps and put back on the top bracket(s) removed from frame above.
 
TomatoThePotato said:
Checked the float heights using the homemade gauge that LDR recommend and it was correct thankfully (15.5 mm). I tested the floats to see if they float and both passed and did not have any bubbles coming out when submerged in gasoline. the way i checked if the original overflow leak was gone was filling up the float bowl (separated from the carb) with gasoline an see if it continued to leak after replacing the drain screws and it did not. Originally it did leak when I tested with the old screws when i did the exact same test. Let me know if this is an inaccurate way of checking, ill try whatever you guys recommend if i have the tools for it. Double checked again for any visible cracks in the stand/overflow pipe and did not see anything.

For the accelerator pump, I’ll check how I can test that but how do you reccomend?
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So you want to be sure the fuel valves are sealing the fuel inlet since you have had the carbs apart, so even if they were working well previously, it is good to check them now. Did you replace the fuel valves, or just clean and reuse the old ones which is quite acceptable?

To check both the sealing/leaking and the accelerator pump circuit you need to improvise a gas bottle or alcohol bottle set up, or your gas tank. I have seen a plastic pop bottle used in a pinch. With the carbs upright on your work area you need to feed the liquid into the fuel hose input and fill the float bowls and let it sit for 20-30 min and look for overflow out those tubes on the bottom of the bowls. If it leaks then there is either an issue with the tube you repaired which is unlikely since to tested it after the fix, so the fuel valves aren't sealing the input of fuel 100%.

Once you confirm they are not leaking and gas tight to need to use the bellcrank that the throttle cables attach to and manually twist it quite a few times to get the liquid to spray from the two tiny brass nozzles in the back of the carbs (air box side). You should have a strong stream shoot from the back to almost the front of the carb body that is equal strength on both carb sides. If you not getting this then there is an issue with something plugged or not assembled or sealed correctly on the carb with the accelerator pump mechanism.

When both of these items test good your good to go and install them. ;)
 
Flyin900 said:
So you want to be sure the fuel valves are sealing the fuel inlet since you have had the carbs apart, so even if they were working well previously, it is good to check them now. Did you replace the fuel valves, or just clean and reuse the old ones which is quite acceptable?

To check both the sealing/leaking and the accelerator pump circuit you need to improvise a gas bottle or alcohol bottle set up, or your gas tank. I have seen a plastic pop bottle used in a pinch. With the carbs upright on your work area you need to feed the liquid into the fuel hose input and fill the float bowls and let it sit for 20-30 min and look for overflow out those tubes on the bottom of the bowls. If it leaks then there is either an issue with the tube you repaired which is unlikely since to tested it after the fix, so the fuel valves aren't sealing the input of fuel 100%.

Once you confirm they are not leaking and gas tight to need to use the bellcrank that the throttle cables attach to and manually twist it quite a few times to get the liquid to spray from the two tiny brass nozzles in the back of the carbs (air box side). You should have a strong stream shoot from the back to almost the front of the carb body that is equal strength on both carb sides. If you not getting this then there is an issue with something plugged or not assembled or sealed correctly on the carb with the accelerator pump mechanism.

When both of these items test good your good to go and install them. ;)
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This might just be a brain fart at the moment but I am not exactly sure what you mean by the fuel valves. Do you mean the air cut off valves that are on the side of each carburetor? I’ve did not replace anything in the carburetor except for the float bowl gasket and drain screws from what I remember. Everything else I cleaned and reused.
 
TomatoThePotato said:
This might just be a brain fart at the moment but I am not exactly sure what you mean by the fuel valves. Do you mean the air cut off valves that are on the side of each carburetor? I’ve did not replace anything in the carburetor except for the float bowl gasket and drain screws from what I remember. Everything else I cleaned and reused.
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He's referring to the float needles
 
LongDistanceRider said:
He's referring to the float needles
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Oh in that case, yes I kept the original ones, and the float height was 15.5mm. No resistance when I pushed the tiny rod in the back of the needle either. I just cleaned them lightly as someone previously mentioned that they looked fairly clean.
 
Flyin900 said:
To check both the sealing/leaking and the accelerator pump circuit you need to improvise a gas bottle or alcohol bottle set up, or your gas tank. I have seen a plastic pop bottle used in a pinch. With the carbs upright on your work area you need to feed the liquid into the fuel hose input and fill the float bowls and let it sit for 20-30 min and look for overflow out those tubes on the bottom of the bowls. If it leaks then there is either an issue with the tube you repaired which is unlikely since to tested it after the fix, so the fuel valves aren't sealing the input of fuel 100%.
Click to expand...
quick question, if i fill the carbs with gasoline while its disconnected from the engine, will it not overflow through the overflow pickup pipe regardless? Or should i wait for the excess fuel to drain then see if there is a leak?
 
As long as the carbs are oriented as they would be on the bike, the float needles (valves) should work the same regardless the fuel source. If you have any leakage, it's a sign you'd have leakage when they're mounted on the engine as well. And if there is a crack in one of the overflow tubes that you couldn't see while they were apart, it will show itself.
 
TomatoThePotato said:
quick question, if i fill the carbs with gasoline while its disconnected from the engine, will it not overflow through the overflow pickup pipe regardless? Or should i wait for the excess fuel to drain then see if there is a leak?
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Holding the carb in their normal position with a fuel source connected will fill the float bowls allowing you to see if there's any leak.
Once confirmed no leaks the open the drain screws to drain them and install away.
 
Will be filling the carbs with fuel and doing these tests later today (following the lovely detailed procedure flyin900 wrote, thanks!) will probably just hook my fuel tank and open the petcock and keep an eye on it for 30 mins while i also remove the old engine side boots and try to fit airbox boot as one of em came off during removal - probably also inspect if they have any tears or anything just in case.
LongDistanceRider said:
Install the cables onto the carbs before installing the carbs to engine.
I leave the insulators in place on the engine. I used to fight and finagle the air box boots into place after carbs were in and tight. Now I've taken to doing it the Honda way of moving the air box back, no tire removal though.
Click to expand...
Ill try this first, if it doesn’t work, I’ll then try this—>
kbongos said:
The order I would suggest trying would be to attach the back boots to the air box first, those I recall were troublesome due to odd square fitting and the boots having trouble fitting on there without some large deformations to be worked out. Once those are in place I like to leave the small ones that go to cylinders last(off), where you put the carbs in place with into back boots loose so you can push them around. Get carb cables hooked up in the process, possibly before pushing into place as it makes cable access easier. Then carbs can be set into back boots and hold in place, but with clamps loose give you room to push back and to the side to slip front ones onto carb. Once both front ones on carb, bolt them to cylinders, then tighten clamps and put back on the top bracket(s) removed from frame above.
Click to expand...

I also saw that my title is now ‘well known member’, I don’t know if this is done automatically by a bot or its because I have asked so many small questions, but hey I appreciate the title and also the hand holding along the way 😂
 
TomatoThePotato said:
I also saw that my title is now ‘well known member’, I don’t know if this is done automatically by a bot or its because I have asked so many small questions, but hey I appreciate the title and also the hand holding along the way 😂
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It's the result of reaching 50 total posts, the software does it automatically. The 'hand-holding' is why we're here, we enjoy helping members and doing our part to perpetuate the life of vintage Honda twins (and vintage Hondas in general). (y)
 
Doing the test right right now, it seems that the accelerator pump housing area is leaking. I think it might be because i didn’t tighten down all the way. I tightened them and redoing the test again. If tightening doesn’t fix it, what do you guys reccomend?
 
There is a small O ring that is also in an area where the float bowl gasket resides on that float bowl, its easy to miss or not install it. That will then leak around that edge and the accelerator pump will not work.
 
Flyin900 said:
There is a small O ring that is also in an area where the float bowl gasket resides on that float bowl, its easy to miss or not install it. That will then leak around that edge and the accelerator pump will not work.
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false alarm, i didnt tighten the gas line correctly and I noticed the fuel trailed from the gas inlet on the carb. Tested it for another 30 minutes and no leaks at all. Will do the next test now. Panicked a bit for a second.
 
TomatoThePotato said:
i didnt tighten the gas line correctly
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If you have to tighten the fuel line it means you're not using the right fuel line. Honda 5.5mm fuel line is a little pricey but well worth it, it fits perfectly and really doesn't even need a clamp which is why Honda put those little /lightweight spring clips on them from the factory.
 
Flyin900 said:
Once you confirm they are not leaking and gas tight to need to use the bellcrank that the throttle cables attach to and manually twist it quite a few times to get the liquid to spray from the two tiny brass nozzles in the back of the carbs (air box side).
Click to expand...
E54BEAEF-EE58-4B33-B65F-6DC8319E7DEB.jpegso I’m cranking the bellcrank that attaches to the throttle cable and it is spraying gas in burst quite nucely, i cant send vids he but ill send a photo of its burst. However it looks like the accel rod is leaking from somewhere, it could be that o ring flyin mentioned but its leaking from the boot of the rod. I did replace the boot with a new one but could it be that its not sitting well?
 
Last edited:
If you missed the O ring that goes on the float bowl as pictured. It is missing from this pic.


P1090658.JPG
 
Flyin900 said:
If you missed the O ring that goes on the float bowl as pictured. It is missing from this pic.


View attachment 29434
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Thank you so much, I thought this wasnt the issue because it wasn’t leaking from there during the leak test, however started leaking when I did the accel pump test. I opened up the float bowel, changed the O-ring and it solved the issue. THANK YOUUU
 
Alright, I am on the last and mighty step, trying to put it in position, I’ve got the cables on and ive learned to not mess with the boots since it took a while to install it back correctly seated. Currently carbs are in this position, any recommendations how to get it in?7C6D2978-7372-4594-83D3-B29B4E338CAE.jpeg
 
Push the carbs down some and wiggle them around to get them centered up on the insulators.
The carbs will snap into place, the insulators bottom out against the carbs. I've had to use a pry bar at times to get them fully seated.
Might help to pull that left upper engine mount plate off to give the cables more movement room.
 
TomatoThePotato said:
Thank you so much, I thought this wasnt the issue because it wasn’t leaking from there during the leak test, however started leaking when I did the accel pump test. I opened up the float bowel, changed the O-ring and it solved the issue. THANK YOUUU
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So you did this rebuild yourself and are in the home stretch. You learned some valuable carb lessons and the value of testing first before installation :)
 
alright so I tried wiggling them down as LDR mentioned and at one point was SO CLOSE but the airbox boot popped off so I took the carb out to inspect the boot for any damage - luckily, we’re good.
LongDistanceRider said:
Remove the left side of the top engine mount so the cables can slide in easily.
Install the cables onto the carbs before installing the carbs to engine.
I leave the insulators in place on the engine. I used to fight and finagle the air box boots into place after carbs were in and tight. Now I've taken to doing it the Honda way of moving the air box back, no tire removal though.
Click to expand...
So I have removed the side bolt of the airbox, but I kept the rear bolt loose just because the nut on that bolt looks like a paint put back on. In order to put that rear bolt on, will I have to remove the rear tire and fender? Currently the bolt is just loose enough that i can move the air-box slightly back. The more I think about it, the more i dont mind remove that rear bolt entirely though I want to make sure i dont have to disassemble a bunch of things to put that bolt back on with the nut. The bolt i am wondering about is this one. 03A176F2-F5BE-407D-9FA4-7DA57DE25120.jpeg

LongDistanceRider said:
Push the carbs down some and wiggle them around to get them centered up on the insulators.
The carbs will snap into place, the insulators bottom out against the carbs. I've had to use a pry bar at times to get them fully seated.
Might help to pull that left upper engine mount plate off to give the cables more movement room.
Click to expand...
wheres a good spot to use the pry bar that wont damage the carbs? Was worried about prying it because ive been trying to be super careful with it since i almost stripped some of the jets. Also i saw those engine mounts but I am hesitant to remove them, however I think I’ll try removing all 3 bolts. I’ll check the manual and online if theres a torque spec but if anyone knows off the top of the head so i can use a reference, thatd be great.

kbongos said:
Then carbs can be set into back boots and hold in place, but with clamps loose give you room to push back and to the side to slip front ones onto carb. Once both front ones on carb, bolt them to cylinders, then tighten clamps and put back on the top bracket(s) removed from frame above.
Click to expand...
i have not tried putting it in the airbox side first, so ill give this a shot.

I gave up on it last night and called it a day since my back was aching at this point (im too young for back problems 😭), but I was happy to accomplish the tests and getting the cables on. Im gonna come back today stronger though and hopefully give yall the good news tonight.
 
Really hoping someone is available this late (1:15 am here), i got the carbs in but the engine side is not in as much as it was before but i dont know how much it is off by. The airbox seats are perfectly in. Ill send a pic, you can see where the clean metal starts and the dirt metal ends. Its in deep hut i dont know if it is deep enough since it doesn’t line up with the original location. Srry if i sound erratic right now, on so much caffeine to keep me awake for hours230DBD99-306D-4BAD-BE87-2B5316809353.jpeg
 
Okay so, i havent moved the engine boot side any further, however i noticed my airbox was over inserted so I had corrected that, now I am just thinking, should I just push the carb into the engine ports? I keep checking if something is blocking cuz it doesnt want to budge. Ill attach images03370009-C8FA-40D1-A1BA-8DCA0E2E6C69.jpeg2FF2B3F5-6F47-4337-98B8-8BE7C40E91B7.jpeg3004037E-E467-44B6-A3FA-6488D0E71DF2.jpeg34F20460-E34B-4407-9ECD-1430E1C1D19F.jpeg
 
I think im gonna use a blow dryer to warm up the rubber (no open tubes or openings to the engine are currently exposed) and warm up the rubber to see if that will help
 
Ladies and gentlemen… the bike is now running!!! I couldnt do any carb syncs or do WOT but i pulled the choke and blip the throttle and it worked really well and it sounded REALLY NICE, NO HICCUPS OR ANYTHING. I am dead tired right now and I also do not want to piss off the neighbors, so I will carb sync tmr and inspect for any issues.
 
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