gas tank upgrade

biscuits

biscuits

Member
Joined
Jun 28, 2025
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Location
Guelph Ontario Canada
Im sure this subject has been discussed a few times, but I cannot find the threads. Feel free to direct me there if necessary.
What I am looking for is larger gas tank for 82 cm450e. Most of the guys I ride with have much larger tanks, and on long runs, they are annoyed that I have to stop and fuel up every 100 kms or so. Ideally, a larger tank, 5 gallons, that will require the least amount of retrofitting and frame work and/or adjustments.
thanks in advance, folks
 
That tank design is pretty standard - it might be worth measuring a CB750 tank to see if the core triangle is consistent or just requires a new rear mount (which often requires some seat mods).

That said, you should be getting about 200km per tank as a “bad” fuel mileage number.
 
EzPete said:
That tank design is pretty standard - it might be worth measuring a CB750 tank to see if the core triangle is consistent or just requires a new rear mount (which often requires some seat mods).

That said, you should be getting about 200km per tank as a “bad” fuel mileage number.
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Yeah, that seems like really bad gas mileage, er, kilometerage...
 
You currently have the 2nd largest tank for these models at 3.4 gallons on which .6 is the reserve.
So 100km = 62 miles. W/o reserve used you're getting @22mpg which is horrendous. You should be in the 50+ mpg.
 
I know there is something wrong with the carbs besides not being sync's properly , also I just discovered the front brakes have been dragging... That explains the gas mileage, or lack thereof.
It sounds as though I ought to be ok with this thank, though I would a little fuel in those long back roads where gas stations are few and far between. I can carry fuel in Gerry cans too, sacrifice some space.
So, the cb750 tank is bigger than 3.4? Is it worth the trouble? I don't mind a little modification, just not looking to reframe the engine for a few more kms on the tank
 
biscuits said:
The 100 is the point at which I switch to reserve, I know, way too soon. is 200 per tank before hitting the reserve?
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I don't know how many miles you should get before switching to Reserve, but I do know if you just ride the bike until it stops flowing fuel in the On position and THEN switch to reserve as the owner's manual suggests, your mileage from the On position will be easier to calculate.
 
For me, and just my humble opinion, I'd get the thing running correctly before evaluating whether you want to customize with a bigger tank. A dragging brake is a relatively easy (and necessary) fix. Syncing the carbs too, and figuring out where else you might be losing fuel. I don't know these bikes but I imagine you should be up around 160-180km on a tank without running issues.
 
biscuits said:
The 100 is the point at which I switch to reserve, I know, way too soon. is 200 per tank before hitting the reserve?
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On a KM basis, you should be at least around 200 before needing reserve.

The CB750 tank is about 3 liters larger, but may impinge on steering or require some fabrication for sure.
 
LongDistanceRider said:
1981 CM400E tank is 3.8 gallons
I typically hit reserve at 150-180 miles with my 3.8 gallon tank. .8 gallon reserve.
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I have a CB450SC Nighthawk and 200 kilometers is easy without going to reserve but close. You have a serious running issue that the brakes maybe a factor, yet I suspect you have other issues.
The Canadian gallon is 16% larger than a US gallon. The US is 3.78 liters per gallon and a Canadian gallon is 4.5 litres.
 
biscuits said:
I know there is something wrong with the carbs besides not being sync's properly , also I just discovered the front brakes have been dragging... That explains the gas mileage, or lack thereof.
It sounds as though I ought to be ok with this thank, though I would a little fuel in those long back roads where gas stations are few and far between. I can carry fuel in Gerry cans too, sacrifice some space.
So, the cb750 tank is bigger than 3.4? Is it worth the trouble? I don't mind a little modification, just not looking to reframe the engine for a few more kms on the tank
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I would try to figure out why your mileage is so bad before I worried about capacity. My 7.5 liter v8 is not far behind you.
 
biscuits said:
I'm working on it. I'm taking the carbs off this week to see if there is anything visible. Anything I should be looking for?
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Plug condition would be my first starting point. It seems like you'd really be able to feel it in engine performance with fuel efficiency that poor - might as well check everything at this point - compression, timing, clutch condition. I wouldn't pull the carbs until I'd ruled out all the other possibilities - they less you have to wrangle those boots and insulators, the better.
 
Performance is slightly more than adequate, I still slide back a bit on the seat under good throttle, if that's a thing, the plugs are new last year, but i will check them,. I have a guy going over it all with me on friday, as well as tyres and brakes. She is running rich, the missus followed me home last week, said I stank like an old gas station.
Compression and timing arent all that out, the clutch... it works well except under extreme duress with a full load.
I will double check and make sure I am on the right track. I am on the brink of ordering two Makunis, I am making sure the bike will give me many years, not months, of pleasure first.
 
biscuits said:
Performance is slightly more than adequate, I still slide back a bit on the seat under good throttle, if that's a thing, the plugs are new last year, but i will check them,. I have a guy going over it all with me on friday, as well as tyres and brakes. She is running rich, the missus followed me home last week, said I stank like an old gas station.
Compression and timing arent all that out, the clutch... it works well except under extreme duress with a full load.
I will double check and make sure I am on the right track. I am on the brink of ordering two Makunis, I am making sure the bike will give me many years, not months, of pleasure first.
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The Mikunis will be way more work than you’d want, with absolutely limited to no gain.

If you’re actually running super rich, the plugs will show it.
 
Flyin900 said:
The Canadian gallon is 16% larger than a US gallon. The US is 3.78 liters per gallon and a Canadian gallon is 4.5 litres.
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as a metric dude...
1779308826144.png

I recall some people here on Brazil sticking the CBX750F tanks on the CB400/450s with small modifications. But then again our CBs already had the more "square-y" tank. I also can't remember if the side panels looked good, probably not.
After a good look at the plugs, first thing I'd do is check the float level.
 
Stick with your original carbs. The Mikuni's sound great until you've installed and have to buy more pieces to get them working close to the originals.
I rebuilt my carbs in 2014 before the road trip and haven't need to go back in since. Avg. fuel mileage is low 60's, highest recorded was once at almost 72mpg.
 
Well, after having a really good look, I found that the front brake was way too wound up. To the point that even pushing the bike with the handle bars the wheel dipped.
It seems to be freewheeling a little easier now.
I do still have a stinky gas smell from the muffler. It's burning..., more aptly, chucking out way too much from the exhaust pipe. (Yes, only one; I went two into one ) The gas smell has always been there, also a contributor to the short mileage, surely.
Is there a quick thing I can do to relieve that issue before taking off the carbs for open heart surgery??
 
Being as you have the model that has a single air cleaner under the seat, is it possible that you have a towel or other item under the seat partially blocking the air cleaner intake?
 
Have you followed the FSM procedure for adjusting the front brake? That will be your best bet. At least you don't need to worry about arcing the shoes!

Looking at your profile picture, is your bike carrying lots of luggage on those rides? The added wind resistance is certainly not helping your mileage.
 
stl360+450 said:
Have you followed the FSM procedure for adjusting the front brake? That will be your best bet. At least you don't need to worry about arcing the shoes!

Looking at your profile picture, is your bike carrying lots of luggage on those rides? The added wind resistance is certainly not helping your mileage.
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She sucks gas empty and full. granted that the first real test was a 1000 kilometer trip with all the gear. She doesn't have the gear on right now, but next month I'm going New Brunswick a d wanna make sure she ticking right
 
I was with my mechanic buddy, he sync'd the carbs, said they were way out. He said that help the mileage somewhat. The brakes dragging IS the problem, more aptly the cable. It does not return, it's quite rotten somewhere.
Anyway, riding home after the tune up, I almost flew off the back of the seat, I was not prepared for pep in her step...wow! Definitely up close to the origanl 47 hp
 
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