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Discussion Starter · #1 ·
Hey all!

So I've been riding my '83 CM450A for a few weeks just about daily on my couple-mile commute and am getting increasingly frustrated with how poorly it is running. The idle is very erratic, there's a dead area when the throttle's about 1/4 open, once it gets up to temp it is constantly popping/coughing from the carbs, and I find myself having to constantly open and close the choke to keep it from stalling at red lights.

I'm planning on tearing down the carbs again this weekend to give them another thorough cleaning... last time 'round I wasn't able to get the pilot jets out since they're pretty well stripped, but I thought the 24hr chem-dip soak I gave it would be enough, but based on how its running it seems like there are still some pilot issues. This time I'm removing and probably replacing the pilot jets no matter what it takes just to make certain that I know everything with that circuit is 100% clean and clear.

One of the unknowns that I'm working with that's making things more difficult to deal with is that the bike's stock airbox, filter, and exhaust were all replaced with after market parts somewhere along the line. Instead of the oem twin exhaust it has a two-into-one pipe and the airbox & filter were replaced with a pair of pods at some point. I have no idea if the bike was properly rejetted to compensate for the new parts when they were installed so I'm trying to avoid wasting time troubleshooting the carbs setup if the jets aren't correct.

I was thinking that it might be worthwhile to buy and drop in an original air box and filter setup and ditch the pods so there's only one variable that I have to compensate for when I'm trying to get the carbs running well after getting them properly cleaned. My logic is that by restoring it back to the oem air parts I'll be able to install the stock sized jets knowing they are correct, then tune the mixture and idle settings from there without worrying about the jets. ...this is all assuming that recleaning the carbs this weekend doesn't end up fixing the problem.

Is this a good way to simplify and fix these issues or am I overthinking it? Say that the jets that are currently in the bike are not correct for the pods and two-into-one exhaust, is it worth it to try and adjust the carb settings to get it running well, or is that going to make it too far out of wack to bother? Same question if I do put in the oem air parts and jets but keep the current exhaust as-is, would that be worth my time tuning or is the exhaust enough to take it too far out of spec to run well on the stock jets?

I'm determined to get this bike running as perfectly as possible so I'm very happy to get any advice or suggestions you care to offer to help get it there...
Thanks for the help once again!
-Joe
 

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Honda spent a lot of time and money to ensure the engine performed across the widest possible power band, it's unlikely some guy in his garage can throw on a pair of cheap pods and generic mufflers and achieve better results. One thing for sure is that at one point it did run properly in stock configuration.

This is an interesting thread on pods. A Pod Filter Thread for Geeto.....
 

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"if I do put in the oem air parts and jets but keep the current exhaust as-is, would that be worth my time" Yes, but you should also fix your vacuum leak. That is why you are having an erractic idle, popping, stalling, and need to put the choke on at stop lights. It might be the rubber boots between the carbs and head, or one of the small O-rings, or other rubber seals in the carbs.
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Restoring the original intake is definitely the fastest and easiest way to improve your performance. At least that way you would know that is not the problem.

You should have the VB24 carbs with a 38 slow jet and only one main jet, that being 120. If you have the earlier carbs with 2 main jets we can match it up and go from there.

http://www.hondatwins.net/forums/63...1654-carb-information-years-jetting-more.html

I suspect you're familiar with the sticky on rebuilding VB carbs but just in case:

http://www.hondatwins.net/forums/63-fuel-supply-carburation/24191-rebuilding-vbulletin-carbs.html

Let us know what you find when you open them up.
 

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Discussion Starter · #5 ·
Honda spent a lot of time and money to ensure the engine performed across the widest possible power band, it's unlikely some guy in his garage can throw on a pair of cheap pods and generic mufflers and achieve better results. One thing for sure is that at one point it did run properly in stock configuration.

This is an interesting thread on pods. A Pod Filter Thread for Geeto.....
That is exactly what I was thinking... plus I didn't get a 450 Hondamatic for performance. This is a city commuter, with an occasional weekend casual joyride from time to time. Even if the pods did increase performance by some small amount I'd take the reassurance that things are setup correctly and reliably than whatever gain they'd give me. Especially since it'd be lost in the torque converter anyway. Thanks for the link as well!

-Joe
 

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Discussion Starter · #6 ·
"if I do put in the oem air parts and jets but keep the current exhaust as-is, would that be worth my time" Yes, but you should also fix your vacuum leak. That is why you are having an erractic idle, popping, stalling, and need to put the choke on at stop lights. It might be the rubber boots between the carbs and head, or one of the small O-rings, or other rubber seals in the carbs.
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Yeah... that's what I was afraid of. I have a basket case Suzuki GS500 that had a vacuum leak that was a bitch to track down and solve....mostly because of the pain that reassembling that bike tends to be. This one ought to be a lot easier, we'll see what happens when I open it up tomorrow. Thanks for the the insight, good chance there's an o-ring missing in there somewhere.

-Joe
 

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Discussion Starter · #7 ·
Restoring the original intake is definitely the fastest and easiest way to improve your performance. At least that way you would know that is not the problem.

You should have the VB24 carbs with a 38 slow jet and only one main jet, that being 120. If you have the earlier carbs with 2 main jets we can match it up and go from there.

http://www.hondatwins.net/forums/63...1654-carb-information-years-jetting-more.html

I suspect you're familiar with the sticky on rebuilding VB carbs but just in case:

http://www.hondatwins.net/forums/63-fuel-supply-carburation/24191-rebuilding-vbulletin-carbs.html

Let us know what you find when you open them up.
Thanks, thats the kind of info that I was definitely looking for. I have read through the VB rebuild thread but didn't find it until after I put everything back together after the rebuild I did a few weeks ago. This time through I'm going to follow that to the absolute letter.

Other than ebay is there a good recommendation for a source for the stock airbox? I'm going to do the rebuild this weekend and see if I can find and fix a vacuum leak as suggested by another poster...hopefully get it running well enough to make due until I can order the parts I need to ditch the pods.

If the weather holds out I'll hopefully get into them tomorrow and will post the results.

Thanks!
-Joe
 

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You might find a salvage yard that has one. Otherwise e-bay is the best bet I know of.
 

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With all the cafe projects going on there should be some air boxes available.
Well, maybe not since most cafe projects start with a sawz-all.
 

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Hey all!

So I've been riding my '83 CM450A for a few weeks just about daily on my couple-mile commute and am getting increasingly frustrated with how poorly it is running. The idle is very erratic, there's a dead area when the throttle's about 1/4 open, once it gets up to temp it is constantly popping/coughing from the carbs, and I find myself having to constantly open and close the choke to keep it from stalling at red lights.

I'm planning on tearing down the carbs again this weekend to give them another thorough cleaning... last time 'round I wasn't able to get the pilot jets out since they're pretty well stripped, but I thought the 24hr chem-dip soak I gave it would be enough, but based on how its running it seems like there are still some pilot issues. This time I'm removing and probably replacing the pilot jets no matter what it takes just to make certain that I know everything with that circuit is 100% clean and clear.

One of the unknowns that I'm working with that's making things more difficult to deal with is that the bike's stock airbox, filter, and exhaust were all replaced with after market parts somewhere along the line. Instead of the oem twin exhaust it has a two-into-one pipe and the airbox & filter were replaced with a pair of pods at some point. I have no idea if the bike was properly rejetted to compensate for the new parts when they were installed so I'm trying to avoid wasting time troubleshooting the carbs setup if the jets aren't correct.

I was thinking that it might be worthwhile to buy and drop in an original air box and filter setup and ditch the pods so there's only one variable that I have to compensate for when I'm trying to get the carbs running well after getting them properly cleaned. My logic is that by restoring it back to the oem air parts I'll be able to install the stock sized jets knowing they are correct, then tune the mixture and idle settings from there without worrying about the jets. ...this is all assuming that recleaning the carbs this weekend doesn't end up fixing the problem.

Is this a good way to simplify and fix these issues or am I overthinking it? Say that the jets that are currently in the bike are not correct for the pods and two-into-one exhaust, is it worth it to try and adjust the carb settings to get it running well, or is that going to make it too far out of wack to bother? Same question if I do put in the oem air parts and jets but keep the current exhaust as-is, would that be worth my time tuning or is the exhaust enough to take it too far out of spec to run well on the stock jets?

I'm determined to get this bike running as perfectly as possible so I'm very happy to get any advice or suggestions you care to offer to help get it there...
Thanks for the help once again!
-Joe
The ENTIRE intake & exhaust systems have been computer designed to work optimally on each engine, for around 40 years now...From the airbox intake boot to the tip of the exhaust. And they've been jetted to run on the lean side, in order to meet emissions regulations. So changing anything -can- cause drivability problems. In addition, you NEED to find fuel that has NO alcohol in it. I had dozens of customers who bought new bikes & went across the street & filled up with 'premium'....only to return later with their bikes popping & farting, pipes turning blue....adding alcohol to fuel leans out your already lean running engine. Not to mention alcohol attacks some rubbers, plastics, & metals. Any & all new units we sold, Hondas, Suzukis, Yamahas, from singles to Goldwings, all were prone to misfire on ethanol containing fuel.

Sent from my Moto G (5) Plus using Tapatalk
 

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The lean run condition and ethanol fuel are the primary reason we have been recommending that the Primary main jet be increased one size.
 

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Discussion Starter · #13 ·
Alright, I wasn't able to touch the bike until today thanks to real life getting in the way. I did, however, get a stock airbox from ebay that is complete and looks to be in near new shape so I'm going to install that tomorrow.... hopefully.

Tonight I tore down the carbs and found that they are the VB24E version that per the model year carb identification thread on here are found on the 1982 CM450A, not the 1983 model that I have. Is there enough of a difference between these bikes for this to matter? Should I stop here and try to source a set of 1983 carbs, or can I get away with proceeding with these without causing much of a problem?

The previous owner told me that it was running just fine before sitting and I'm inclined to believe him given that everything else he told me about this bike has been dead on accurate so I'm hoping that I can just rebuild these, put them on with the stock airbox, and proceed with tuning and jetting them as if it were a '82 bike. If the only difference between 82 and 83 is that the carbs on the 83 deleted the 2nd main jet, but everything else is the same it should be fine, right?

I'm probably overthinking this again, but since my time to work on it is limited and I have to do all my work on the sidewalk in front of my house instead of a garage I want to make sure I'm wasting as little time and money here as possible.

Also, since I most likely have an air leak going on as well is it worth it to buy the stock or reproduction band clamps to secure the carbs on the intake boots and airbox connection tubes, or are standard hose clamps good enough?

Thanks again for your help all... feels like I'm getting pretty close to getting this thing back in action!
-Joe
 

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Hi Jim, when you say upping the main jet 1 size. In my case starting with a 72, do I go to a 71 or 70? I didn't know if by steps they are in increments of 1 or 2. Thanks Scott.
 

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Keihin jets are numbered small to large, so from 72 you'd go to 75 since that's the next available one.
 

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Ok, I have set of auto jet resizing bits. They are smaller the # larger the hole. It's odd because the jet is a 72 and the #72 bit I have fits it perfectly, but to up size I have to start with the #71 bit in my kit and go lower in number to go bigger with the hole. I will just try one bit at a time and see what happens.
 

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Discussion Starter · #19 ·
Alright, so good news... I was able to finally get some time to work on the bike again this past Sunday and after installing the stock airbox and filter, cleaning the carbs, replacing the mixture screws, and swapping the jets for the stock sizes it is now running beautifully!

Of course getting the stock airbox into the frame was a total pain in the ass since I didn't realize I had to remove the rear wheel until after wasting way too much time fighting it and after reassembling everything one of the float needles got stuck open which made the fuel overflow... but once that was remedied the bike started right up and was immediately running noticeably better. Once it was up to temp I dialed in the idle speed and mixture screws a bit then went for a ride and noticed instantly how much better it was running. Much more power, and super snappy throttle response, no more coughing or erratic idle issues, no backfires or stalling, and its now running so buttery smooth it feels like an entirely different bike. I didn't realize just how poorly it was running until experiencing it running well.

It also seems to have a much better sound with the stock air box instead of the pods.

For what its worth, here's the specs on what is installed now... hopefully this'll help someone else out down the line searching through this forum:

1983 Hondamatic CM450A
VB24E carb from 1982 model installed
108 & 75 main jets
38 slow jet
stock airbox and filter
both mixture screws are 2 1/2 turns out

The game changer in getting it running properly was replacing the crap pod air filters with a stock airbox and filter and getting a new set of mixture screws installed, the old ones had no o-rings or springs which was causing air leaks and the screws were rattling around, not holding their settings.

Many thanks to everyone who helped me figure things out, I really appreciate your insights and advice!
-Joe
 
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