Carburetor heat riser


Information and questions on GL1500 Goldwings (1988-2000)
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zamboni920
Posts: 250
Joined: Sun Aug 14, 2011 5:15 am
Location: Stavanger, Norway
Motorcycle: 1996 GL1500 SE with Hannigan 2+2 sidecar

Carburetor heat riser

Postby zamboni920 » Thu Jun 07, 2012 8:18 pm



Does anyone know exactly what the purpose of the heat riser is?
I can only assume it is there to warm fuel/fuel bowls.
It is the first internal combustion engine I have seen with a set-up like this, not counting diesels wich sometimes have a fuel pre-warmer.
Is it neccessary?
What effect would it have on engine running if it was eliminated?
Most older, carburated car engines have , or wants to have, a spacer to minimize heat build-up in carbs.
Even if it is needed, wouldn't it be more practical to mount it to engine, under carbs, rather than to carbs themselves?
Wondering if there is a modification possibility here.....just for fun.



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Sempai
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Motorcycle: '94 GL1500SE
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Re: Carburetor heat riser

Postby Sempai » Fri Jun 08, 2012 6:53 am

Hmm, not exactly sure what you're referring to on the GL1500 carbs, but the heat riser on gasoline engines, as I recall, was designed to heat the air entering the airbox during cold startup. Was pretty lame, in my opinion, but auto manufacturers used them for years. It was nothing but a flexible, metal tube that ran from right on top of the exhaust manifold (was not plumbed into the manifold, just drew in air from around it) up into the airbox or the snorkel were fresh air was sucked in. I seem to remember working on cars with these worthless bits of tech on them...they ran equally well, or equally bad, with or without the riser tube!
Keep the rubber side down.

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virgilmobile
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Re: Carburetor heat riser

Postby virgilmobile » Fri Jun 08, 2012 9:35 am

Fuel when is atomized it will chill a surface.
Ask any pilot how to cool beer in flight.
You want the fuel temperature stable and warm.Not boiling(thermal isolator use)
When the fuel is cooled,it condenses and we all know that a engine doesn't run on raw gas.It runs on gas vapors down into the micron level.
So to ensure that the fuel won't condense in the long travel to the valves,the Honda gl1500 and many cars heat the bottom of the runner or intake manifold with antifreeze from the cooling system.

This is necessary because of the distance from the carb to the valves.When the carb is close,like the 1100,or 1200 or valkryie,it isn't necessary.

I had a Mustang that the hoses were bypassed and when it was very cool out,the bottom of the carb body would actually frost up.

And truth be known...I personally think the carb setup on the 1500 sucks.I think it's a botched conglomerate of hoses and valves to satisfy the EPA requirements.
In my 88 configuration,I don't believe it will ever rival the performance of my 1200.
Even tho it's bigger,the 1200 will out accelerate it any day.
Now the 1500 pulls like a truck compared to the 1200 but the pucker factor just isn't there.
I'm really looking into a fuel injection conversion,maybe a CV slide injector system and a ECU .

peppilepew
Posts: 387
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Location: Plaistow, New Hampshire
Motorcycle: 2000 Gl1500 Se
2012 GL1800 Level 3

Re: Carburetor heat riser

Postby peppilepew » Tue Jun 26, 2012 6:35 am

virgilmobile wrote:Fuel when is atomized it will chill a surface.
Ask any pilot how to cool beer in flight.
You want the fuel temperature stable and warm.Not boiling(thermal isolator use)
When the fuel is cooled,it condenses and we all know that a engine doesn't run on raw gas.It runs on gas vapors down into the micron level.
So to ensure that the fuel won't condense in the long travel to the valves,the Honda gl1500 and many cars heat the bottom of the runner or intake manifold with antifreeze from the cooling system.

This is necessary because of the distance from the carb to the valves.When the carb is close,like the 1100,or 1200 or valkryie,it isn't necessary.

I had a Mustang that the hoses were bypassed and when it was very cool out,the bottom of the carb body would actually frost up.

And truth be known...I personally think the carb setup on the 1500 sucks.I think it's a botched conglomerate of hoses and valves to satisfy the EPA requirements.
In my 88 configuration,I don't believe it will ever rival the performance of my 1200.
Even tho it's bigger,the 1200 will out accelerate it any day.
Now the 1500 pulls like a truck compared to the 1200 but the pucker factor just isn't there.
I'm really looking into a fuel injection conversion,maybe a CV slide injector system and a ECU .


I agree. The carbs are a problem on 1500's. I cleaned my 1200 carbs and she ran smooth as silk. This 2000 model i now have just doesn't run as smooth or as consistent. It runs better at altitude. I would rather have Fuel injection. The trouble is I like the 1500 better than the 1800. As for the injection mod a single throttle body setup for both banks would work. 1 O2 sensor, coolant temp sensor, throttle position sensor and a programmable ECM. The ECM wouldn't need to be all that complicated to do the job since there are no emission tests for bikes that I am aware of.




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