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GreatDays
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20 Posts
Discussion Starter #1
Hi -- I just bought a used 1993 Vulcan 750 in pretty decent cosmetic shape for the year, and 25k miles. The bike is un-modified -- 100% stock.

When I start it, it starts fine on the choke -- but when I open the throttle it dies, sometimes right away, sometimes it bogs and stays running if the choke's on and I let go of the throttle. If the choke's off the bike won't start and if I turn the choke off after the bike's warmed up it dies.

I made sure the battery is good and have flushed out the gas tank and cleaned the petcock and installed clear fuel filters just to make sure the bike's getting fuel -- it certainly is getting gas.

I pulled and cleaned the side front air screens -- they were not very dirty.
I pulled and cleaned the plugs and made sure they were getting good spark -- they are.

So it gets fuel; it does spark; it's getting air; and it actually starts right up with the choke on.

I checked to make sure the idle adjuster knob was set correctly.
To make sure the CV carbs were working -- I loosened the carb boots leading to the airbox and twisted the throttle. I noted 2 things:

1) the butterfly in each carb opens correctly
2) and with the engine running (choke on), the throttle slide does move upward when I open the throttle -- so both the butterfly and carb slides are opening correctly.

Why is this turkey doing this?
 

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If only it had 6th gear..
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1,100 Posts
Sounds like you might have partially clogged jets. Where did you put your fuel filters? Not a lot of room in there.
Some have had success with loosening the bowl drains on the carbs and spraying carb cleaner up into them to back flush them.

Do you get good flow out of the petcock outlets? I think the 93 might have a PRI position on the petcock. If it does, lets run it on that for test purposes to bypass relying on the vacuum operated valve.
 

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GreatDays
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20 Posts
Discussion Starter #3 (Edited)
Sounds like you might have partially clogged jets. Where did you put your fuel filters? Not a lot of room in there.
Some have had success with loosening the bowl drains on the carbs and spraying carb cleaner up into them to back flush them.

Do you get good flow out of the petcock outlets? I think the 93 might have a PRI position on the petcock. If it does, lets run it on that for test purposes to bypass relying on the vacuum operated valve.
Thanks for your help! Very much appreciate it.

I put the clear see-through fuel filters side-by-side, temporarily, they stick out too far for normal use but I had to do it to eliminate fuel flow as the issue -- not the issue. These see-through inline filters are the flat 'flying-saucer' looking ones -- and both fill up about the same amount with gas. I'll redo the gas lines later after I solve this problem.

The '93 750 I have has 'On/Res/Off' -- I'm very surprised -- this is the very first vacuum petcock I've seen that had an 'Off' -- it's bizarre. If the factory thought "we need an 'Off' choice on the petcock for the 1 in ten million chance the diaphragm fails to shut off the gas flow' -- if they thought that they would have just re-designed for a better vacuum-actuated petcock. The 'Off' is handled by the diaphragm -- it is redundant to have a 2nd 'Off' selection on the petcock lever. I've seen quite a few vacuum petcocks from the 'big 4' manufacturers and they ALL had 'Pri' on them.

So the vacuum is working and gas is flowing fine. I guess there's a chance the gas inlet to each carb is obstructed -- but then why would it start even with the choke on?

I will pull the 'bowls' but here's the thing -- there are no 'bowls' on these CV carbs! The bottom of the carb is just flat -- I want to do your suggestion, should I remove the bottom of the carb -- and can it be done with carbs still on the bike?
 

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Premium Member
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306 Posts
On the bottom of both carbs there should be a drain plug, it screws counterclockwise to open and drain the carbs. Do you have these?
 

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If only it had 6th gear..
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1,100 Posts
Yeah that's right, mine has allen head bolts that will drain. You're right, the 'bowl' is actually up higher where the float is. What you're draining or opening is the jet chamber. To get to the floats, carb removal is needed but it doesn't sound like that's your problem (unless one/both are out of adjustment, not filling enough and starving the engine for fuel.
Another question: When it bogs, does it seem like both cylinders are dying or that it's a partial loss (sputter)? Trying to determine if one carb or both are affected.
 

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Old Truck Junkie
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4,133 Posts
You are not getting enough fuel to the cylinder. When you open the throttle more air flows more fuel is needed. The jets and small fuel holes are clogged. There is a small bowl where the jets are. It has two small bolts that hold it in place. It is not easy but it can be done. Remove it and spray the jet and into the jets with berryman B-12. I would also spray into the fuel lines let it set a few minutes and resarts engine. This is the best that can be done without removing carbs. You may try seafoam in the fuel tank also.
 

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Linkmeister Supreme
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7,960 Posts
I think the 93 might have a PRI position on the petcock. If it does, lets run it on that for test purposes to bypass relying on the vacuum operated valve.
The prime (PRI) position was only found on petcocks for the model years from 1985-88. :)
However the petcock from any year can be substituted for any other year.
 

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If only it had 6th gear..
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1,100 Posts
The prime (PRI) position was only found on petcocks for the model years from 1985-88. :)
However the petcock from any year can be substituted for any other year.
Thanks man. :smiley_th I bought one for my 2000 that i found on ebay and it has the 'pri' position but I didn't know what year it came from. I sort of wish it had the off position also, for draining the carbs at storage time but I'll just pop the vacuum line off and plug it to run it dry.. or of course use the drain outs:doh:. (Always seem to forget about those).
 

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Premium Member
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812 Posts
Before you do any mechanical how about a good dose of SeaFoam? That stuff is great and it may clean out your jets. Just a thought
 

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GreatDays
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20 Posts
Discussion Starter #10
Thanks everyone for the great recommendations. By the way -- yesterday I had loosened and removed the clamps from the back of the carb where the rubber airbox boots connect so the carbs could get extra air, I did that because yesterday the plugs were fouled with gas. Now that didn't change anything, loosening the rubber airbox boots at the carbs. But the carbs are flowing lots of air.

I've never used SeaFoam for the gas tank so I bought a can -- I put 2 ounces in 1 gallon of gas which is twice the recommended mixture and sloshed the tank around.



I started it as usual with the choke on and let her run on the choke for awhile (5 minutes) then switched her off and cut some weeds out of my front hedgerow for 25 minute.

Came back to the bike and started her up -- no change, I have to start the bike with the choke on and as soon as I try to rev it, the engine dies, and likewise if I try to turn the choke off it dies (and I have checked that the idle adjust is set OK).

So I put 2 more ounces of Sea Foam in the tank and sloshed it around, and started it up on the choke and let it run (it runs around 1200 to 1500 rpm on the choke) this time for 10 minutes. I wanted the Sea Foam to work into the carbs.

At the end of the 10 minutes all of a sudden the RPMs suddenly started to climb!

Good ole' Sea Foam apparently!

So the revs kept climbing and I went to the bike and NOW she responds correctly to the throttle -- when I open the throttle she revs UP and doesn't die!

Okay so after 5 minutes of "could this be true, lets try revving it again, yep it still revs!" joyfulness I got bold and started to take the choke off -- the motor stayed running!

So finally after 4x the recommended Sea Foam concentration the bike's revving at idle with NO CHOKE ON. Now the rubber airbox boots are still loose so the motor's pulling lots of air still.

I drove the bike around the block tears in his eyes I guess :smiley_th with the choke off at least at the beginning. To keep it running around the block sometimes I had to turn the choke on though.


Only running on 1 cylinder consistently.
Back home I pulled the spark plugs.

The front plugs are still fouled with gas. The rear plugs look great -- dry and tan-colored.

So I put the clamps back on to attach the rubber airbox boots to the carbs.
I started her up -- now with less air getting into the carbs (rubber boots are back on and tight) the bike won't start without the choke and dies if I take the choke off.

Any suggestions? I feel great about the Sea Foam, thanks dudes there is a light at the end of the tunnel
 

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Premium Member
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306 Posts
Possible you've got an spark problem with the front cylinders since both plugs fire at the same time. I think i would pull both front plugs and then check and compare the color of the spark you get on the plugs verses the rear spark colors you get, could be a coil is going bad on you and just some times working,, just my thoughts. You might want to also check cylinder heads to feel if one is running warmer or colder than another. NOTE SELF: gotta get the temp plug in for my digital meter that reads temps!
 

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GreatDays
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20 Posts
Discussion Starter #12
Thanks -- I was thinking spark plugs too, as I am still using the old plugs that came in the bike.

I just got back from buying 4 new spark plugs. I'll gap them and first check for spark on all 4 plugs, then if the spark looks healthy, I'll install them and see how she runs.

I'm about 98% sure though that I'm going to pull the carbs off tomorrow for cleaning. The fact that the Sea Foam got the bike to go from dying when the throttle is opened a hair -- to being able to test-ride it around the block-- that pretty much proves that the carbs responded favorably to the Sea Foam and thus must be clogged as has been mentioned and as I've suspected.
 

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Premium Member
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306 Posts
Yeppers... the Seafoam made a believer out of this ridder. If your thinking about pulling the carbs you might want to check the plastic fuel inlets on each carb to see if they are cracked before pulling the carbs off, mine were cracking before i pulled the carbs off. Let us know how things turn out! :)
 

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Premium Member
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4,765 Posts
Since the Sea Foam got it running better, I would try soaking the carbs in Sea Foam while on the bike before I pulled them off.

Here's how to do it: Turn the petcock to OFF, pull the fuel lines off, open the drain screw on the bottom side of each carb, and catch the fuel so it doesn't get all over the bike. Replace the drain screws and pour Sea Foam (a used syringe from the veterinarian works well) into the fuel line until the carb is full. Let sit for at least a day, drain the Sea Foam (can be reused) add 4-5 ounces of Sea Foam to a tank of fresh gas and ride it like you stole it.

Adding 8 ounces of SF to a fresh tank of gas and running it 'till it's used up may remove the varnish. Repeat if needed. If that doesn't fix things, you probably need to remove and clean them.
 

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GreatDays
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20 Posts
Discussion Starter #15
I found the vn750 shop manual which had the factory procedure for removing the 2 carburetors. I followed the pre-removal steps.

IT WAS STILL A NIGHTMARE GETTING THE CARBS OUT.

Kawasaki really blew it with this design. Carburetor work comes up often enough that they should have re-thought the air collector positioning and removal. The compromises the design teams made back then are such that I do not ever want to have to pull carbs on a Vulcan again.

It's a double whammy:
1) first, you have to remove WAY too many unrelated parts to get at the carbs

2) second, I still don't know how I ever got the carbs out of there. I went beyond what the factory recommended and removed EVERYTHING out that I could between the 'V' in the middle of the 2 cyclinders and I still had to fight to get the carbs out, and I'm still not sure how I actually got them free.

If I had a 'spotter' watching the carbs on the other side of the bike when they came free, perhaps I would actually know how I got them out.

THESE FUGGERS BETTER BE REAL STINKIN DIRTY INSIDE.

I mean I better find The Lost Temple, The Lost Ark of the Covenant, the Secret to Getting Laid at Any Age and Jimmy Hoffa inside these two mofo carbs today.

If these 2 carbs are spotless and I discover I didn't even need to remove them for cleaning -- there's only ONE way I can think of to take my mind of the torment of that.....................with a big............
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SLEDGE HAMMER re-injure my big toe.

 

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Chucklehead
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1,050 Posts
Just like teen-age sex ..... the first time is the worst because you have no clue what you're doing. Trust me, take your time, it gets better and easier. I would suggest soaking the jets for a day or two and blowing them out after, usually where Jimmy Hoffa hides.
 

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Premium Member
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306 Posts
Lots of posts here on the carbs just [email protected]@K around. Yes i had my carbs off 6 times as in that many days to! Just count it up as an acheivement, you did it! Good luck on the carbs hope ya find that Tim Leary ( that old '60's Hippy professor) is hidding in there some where too. Keep the post coming we want to know how your doing !
 

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If only it had 6th gear..
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1,100 Posts
"I mean I better find The Lost Temple, The Lost Ark of the Covenant, the Secret to Getting Laid at Any Age and Jimmy Hoffa inside these two mofo carbs today."
Lmao! Well I certainly hope it was worth it. I gutted and jetted mine so the airbox is gone making it easier (somewhat). Member- Ceal just kicks his out when he needs to work on them ha ha.
 

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GreatDays
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20 Posts
Discussion Starter #20 (Edited)
"I mean I better find The Lost Temple, The Lost Ark of the Covenant, the Secret to Getting Laid at Any Age and Jimmy Hoffa inside these two mofo carbs today."
Lmao! Well I certainly hope it was worth it. I gutted and jetted mine so the airbox is gone making it easier (somewhat). Member- Ceal just kicks his out when he needs to work on them ha ha.
I was kicking on them. Despite the admonishment of the factory shop manual that "the carbs come out the right side of the bike" they weren't so I thought "okay they meant LEFT side, they reversed 'right' and 'left' in the translation for the shop manual, SURELY they meant 'carbs come out the LEFT side of the engine'

I'm kicking on them. Every time I had my right foot on there, sitting on a stool, grabbing the frame rails from the side for leverage, my 9th grade midwest high school shop teacher was yelling at me "YOU JUST FLUNKED SHOP CLASS BOY DONT BE KICKIN ON THEM CARBS"



I finally realized they were not coming out the left side, so I kicked from the other side.

What finally did it was despite the factory manual saying "leave the front manifold on the engine, take the rear manifold off with the rear carb" I had to remove BOTH manifold boots off the engine and the carbs and put them aside, and it was still a war getting them out of there.


Here's what I found

- the 'bowls' had very little sediment
- the pilot jets were both solidly clogged
- but the mains were 3/4 open

That explains why, after the massive Sea Foam concentration (4x the recommend Sea Foam-to-gas mixture) the bike was revving at all -- the Sea Foam probably cleared the mains. I saw some funny lubricant-shiny-looking stains on the many side holes of the main jet/needle jet emulsion tube -- that was the Sea Foam I reckon.

But the bike would still die without the choke on -- the reason for that was the pilots were clogged bigtime.

I fully separated the 2 carbs and disassembled all the bits. I put the non-plastic and rubber bits in two separate 1-gallon cans of Berrymans carb cleaner overnight, one per carb so as not to mix up the bits.

Then I cleaned the empty carb bodies and the center 'joinder' piece the carbs mount to with

- a toothbrush
- a brass toothbrush
- gasoline
- carb cleaner aerosol with a red plastic straw for spraying into the jets
- 100psi airgun

Later on Monday afternoon I'll retrieve the small bits from the Berrymans and reassemble and reinstall the carbs, I hope they go ON much easier than they came off, will post with the result, thanks for your advice on this.
 
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