Rear carburetor

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97vs800
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Rear carburetor

Post by 97vs800 »

Ok. So I tried everything to get around removing my rear carburetor to no avail.I removed it and sure enough, it was nasty looking and the pilot jet was stopped up. I stripped and dipped and cleaned it. And after fighting with it for a couple of hours I got it reinstalled and my loss of power and popping at about 1/4 throttle went away. But still had a small bit of power loss that was driving me insane. So I decided to re sync for the second time. Problem was, I couldn't get the idle to go down. The idle adjust would drop it only a minuscule amount. But I had to remove my throttle cable from the rear carb obviously and I'm thinking i routed the cables wrong. Anyone have some high definition pictures of beneath the seat i could study on? Also i didn't mark my adjusters on the rear carb and wander if anyone has any tips on where to set it at. I know all of the adjustments for syncing are on the front carb, but I'd imagine the rear adjuster has to be in a certain range to be able to be adjusted from the front(if the cable was loose in the rear you would run out of adjustment from the front before sync ever happened). Any help would be great, especially some pics.

Lechy
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Re: Rear carburetor

Post by Lechy »

Sounds like you have the cable on the rear carb too short, a bastid to slacken with the carb in place but doable.
Also, do you have a little slack on the twist grip before engaging the cable. have you seated he cables in the splitter on the front air box correctly?


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WintrSol
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Re: Rear carburetor

Post by WintrSol »

No photos, but there are routing diagrams in the service manual.
For a good idle sync, there has to be free rotation in the throttle grip, which can be created at the grip end of the cable. You can't have too much, as adjusting the sync can reduce the slack as you go. Of course, if the cable is binding from routing, this all goes out the window. Also, the splitter can be the source - if, when you removed the cable from the carb, the cable jumped out of its slot in the splitter, you can have problems. It's a PITA to address, as the tank has to come off, but it is far easier to sync with it off, anyway, and use an aux tank to feed the fuel pump.
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rikkie
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Re: Rear carburetor

Post by rikkie »

i can u help with a video how to do it

69intruder
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Re: Rear carburetor

Post by 69intruder »

Thanks , Also I want to toss the fuel pump and run gravity feed only. Anyone tried this? I'm going to order the high pressure plastic fuel line that you heat to fit onto the fittings. Much thinner diameter than the rubber lines but I want to route it so I don't need the pump. None of my old Harleys used a pump and they ran just fine so I'm thinking I should be ok trying this.

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Re: Rear carburetor

Post by Lechy »

The fuel pump is to supply to the front carb which sits quite high in the tank tunnel.
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Re: Rear carburetor

Post by navigator »

69intruder wrote:
Sun Feb 04, 2024 8:58 pm
Thanks , Also I want to toss the fuel pump and run gravity feed only. Anyone tried this? I'm going to order the high pressure plastic fuel line that you heat to fit onto the fittings. Much thinner diameter than the rubber lines but I want to route it so I don't need the pump. None of my old Harleys used a pump and they ran just fine so I'm thinking I should be ok trying this.
What Lechy says, the front carb will starve for fuel without the pump.

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hillsy v2
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Re: Rear carburetor

Post by hillsy v2 »

If you really want to do away with the electric pump another option is a vacuum fuel pump - similar to what they run on outboards. The carb'd versions of the Hyosungs ran them as well - I had a GT650 with the vacuum pump and it worked well.

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69intruder
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Re: Rear carburetor

Post by 69intruder »

Thanks for the suggestion. My idea is to put a TEE right at the petcock then feed both carbs from the TEE. I'm going to do some flow tests this week on a hard incline to check flow. I believe its possible because even if the frt carb losses some flow at low tank fuel levels the rear carb will always have plenty keeping the beast alive until I can fill up. Of course this all test to see how reliable I can get the bike before heading out into the unknown. I plan on carrying fuel lines and a spare pump if I stay with the pump system. I also need the schematic for the pump internal electrical. Its not in the factory manual or any other place I can find. I need to know this to understand how the system operates. Comes to it I may buy the cheapest pump I can find then tear it apart to get the info I need. I'm afraid the real reason for the pump is to keep some pressure in the lines during heat soak when the engine is turned off hot. Stops the fuel from boiling in the fuel lines.

I want to change the rear diff before going too. I just don't quite understand one thing in the swap is the spacer they speak of machining?

69intruder
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Re: Rear carburetor

Post by 69intruder »

WOW sorry I got confused and started posting in this thread. My posts above were intended for the thread I started for a fuel pump circuit diagram.

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hillsy v2
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Re: Rear carburetor

Post by hillsy v2 »

69intruder wrote:
Mon Feb 05, 2024 7:25 pm
Thanks for the suggestion. My idea is to put a TEE right at the petcock then feed both carbs from the TEE. I'm going to do some flow tests this week on a hard incline to check flow. I believe its possible because even if the frt carb losses some flow at low tank fuel levels the rear carb will always have plenty keeping the beast alive until I can fill up. Of course this all test to see how reliable I can get the bike before heading out into the unknown. I plan on carrying fuel lines and a spare pump if I stay with the pump system. I also need the schematic for the pump internal electrical. Its not in the factory manual or any other place I can find. I need to know this to understand how the system operates. Comes to it I may buy the cheapest pump I can find then tear it apart to get the info I need. I'm afraid the real reason for the pump is to keep some pressure in the lines during heat soak when the engine is turned off hot. Stops the fuel from boiling in the fuel lines.
The bike should run without the fuel pump with a full tank - but for how long I have no idea. Relying on running it on 1 cylinder to get to a gas station is a pretty bad idea all round. Cheap electric pumps are cheap pumps. You might get lucky but most cheap ones have a pretty limited lifespan. They all work on electric breaker points. I'd seriously look at the vacuum option if you want to do away with the electric pump. The pump won't hold pretty much any pressure in the lines when it's off so the idea it stops the fuel from boiling is doubtful.

69intruder
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Re: Rear carburetor

Post by 69intruder »

With the bike not running there is no flow to either carb, the pump must stop it. I opened both bowl dumps, nothing unless its running. I'm going to TEE off the petcock today the n do some testing. I live near a very steep mountain road and a few miles long so I can't imagine any better test site. Some body must know how these pumps are wired someplace on the net.

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Herb
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Re: Rear carburetor

Post by Herb »

Not sure about the 800 but the front cyl on the 1400 will only run about 30 miles without the pump. I was curious and plumbed around the pump. riding real easy I got to 30 miles before it quit completely.

I am not familiar with the 800 pump circuit but the 1400 has a relay that is triggered by the ignition box when the engine is cranking or running.

looking at the wiring diagram it appears that there is an internal relay that is activated by the signal from the ign box and from the start switch. This is a safety issue to shut off the fuel pump in a crash situation.

I am not sure if the signal from the ign box is a power or a ground but the 1400 ign box provides a ground to operate the relay. You can check the signal by reading for a ground on the black yellow wire out of the pump and cranking the engine. If it is a ground then grounding the B/Y wire will turn on the pump as soon as the key is turned on.

Both the 800 and the 1400 have an internal switch that shuts the pump off when it reaches a set pressure.

Easy fix if the pump is bad, buy a low pressure electric fuel pump, use the hot and ground wires to wire it in.

The pump on my 99 1400 is original, and has about 250,000 miles on it. The relay went bad so I jumperd the wires around it and it comes on when the key is turned on.
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