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Discussion Starter #1
Hi all,

Need some help with my 93 Vulcan 750. I've always been in awe of the vast amount of experience and knowledge on forums, and I've gotten as far as I have on this bike by being a lurker here, but I need some direct help now if anyone can spare it. I bought it from someone who didn't know a lot about working on bikes, but was gung-ho about doing so anyway. I keep finding little time bombs from him.

I've got it running at this point, but it runs absurdly rich. As in, gas vapor out the exhaust rich. I've meticulously cleaned the carbs, the floats are set right (and verified to be right with tube from the drain screw). The fuel petcock seems to be functioning normally (I've primed it several times with my mouth, I can see gas flowing until at some point it just stops, no gas leaking out anywhere). Gas is getting into the engine in excess, somehow, but I can't figure it out. I'm getting miserable mileage (like... 20ish miles per gallon), and the plugs are fouling within 20 miles or so. The bike starts to skip, once I brush the plugs off with a stiff bristle brush, it's back to running normally. The first time I did an oil change, there was a large liquid volume, and the oil smelled like gas. The main jet holders were smashed and holes in the side were closed off from that when I got the bike, and the coaster enricher diaphragms were garbage. Replaced those both in hopes it would make a difference, but it doesn't seem to have. I'm not averse to rebuilding the petcock, but it doesn't seem like it needs it right now (I've seen that as advice to cure a rich condition many times while lurking).

The bike is marbled, has stock exhaust, has the stock jets (unless they have been drilled).

I'm tearing my hair out with this problem, please help!
 

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Discussion Starter #2
The main jet holders were smashed and holes in the side were closed off from that when I got the bike
This is what I am referring to here. I am at a loss as to how the PO accomplished this devastation, so if you have a suggestion to fix something that it would have taken an idiot to do... he fits the bill.

(New jet holders shown with old destroyed ones)
 

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Pull the vacuum line from the petcock and let it sit with the petcock on, engine off. Check over time to see if the vacuum port of the petcock gets wet with gas. Leak through the vacuum port only affects front cylinder.

Wow, those jets are really hammered. Do the centers look to have been drilled out at all? Just wondering if someone drilled the jets while still in the carb, and drilled a carb passage too?. Or how they got bent like that. Compare centers of new vs. old jets. What are the numbers on the new jets? Stock is 138 main and 38 pilot.

Did you elongate the emulsion holes to open them, or were they like that already?

Assuming the float height is correct, and the petcock is not leaking through the vacuum port, for now I'm left wondering why it's flooding so bad.

Is the carb body cracked? Maybe check close around where the jets are.

A float filling with gas should show up in the float height check, unless float height was checked immediately after assembly when the float was still dry. Same with a stuck float, unless it stuck after the float height was checked.

Do you think there's any chance a float is stuck now? Re-check float height? It's a somewhat fine line from low to high levels.

Sounds like it's in both carbs? Affecting all the plugs? Have you gone back into the carbs to check? Make sure the tips of the needles are ok and the floats don't have gas in them .... Remove float and shake it as soon as the carb comes off.
 

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Discussion Starter #5
Pull the vacuum line from the petcock and let it sit with the petcock on, engine off. Check over time to see if the vacuum port of the petcock gets wet with gas. Leak through the vacuum port only affects front cylinder.
I'll give this a try for the sake of giving it a try, but I don't think it's going to be my issue since I'm getting plug fouling in both cylinders. (Who knows though, I may have multiple issues. Front cylinder is definitely fouling worse)

Wow, those jets are really hammered. Do the centers look to have been drilled out at all? Just wondering if someone drilled the jets while still in the carb, and drilled a carb passage too?. Or how they got bent like that. Compare centers of new vs. old jets. What are the numbers on the new jets? Stock is 138 main and 38 pilot.

Did you elongate the emulsion holes to open them, or were they like that already?
I haven't picked up new jets, just the new holders. The jets themselves looked pretty unmolested, a little bit of screwdriver damage is all. The jets in the bike are 132 main, 38 pilot. I've seen 132, 135, and 138 all listed as stock size for the bike, since I'm already running way rich and on the smallest "stock" jet, I'll probably leave these at 132 if I replace them just for the sake of replacing them. The main jet holders are exactly as I found them when I pulled them from the bike. They looked way too damaged to be reused so I just replaced them without trying to fix. I can't see any kind of excessive damage on the inside of where the main jet holder sits that could have been caused by an errant drill bit.

Assuming the float height is correct, and the petcock is not leaking through the vacuum port, for now I'm left wondering why it's flooding so bad.

Is the carb body cracked? Maybe check close around where the jets are.
Yeah, you and me both. I've been banging my head off the wall on this for weeks now. The top of one of the carb float chambers does have a small crack, but it holds liquid without drips unless I pry the crack open by pulling on the carb on either side (and even then, it barely seeps). I was very concerned about it for a quick minute, then I noticed that it's right near the vent port anyway, so it should be dry on the inside against it as it is. I definitely do think that crack is a problem, but I don't think it's contributing to my rich symptoms.

A float filling with gas should show up in the float height check, unless float height was checked immediately after assembly when the float was still dry. Same with a stuck float, unless it stuck after the float height was checked.

Do you think there's any chance a float is stuck now? Re-check float height? It's a somewhat fine line from low to high levels.
I'll recheck today to be sure, but they were sitting right where I wanted them before (per the service manual)

Sounds like it's in both carbs? Affecting all the plugs? Have you gone back into the carbs to check? Make sure the tips of the needles are ok and the floats don't have gas in them .... Remove float and shake it as soon as the carb comes off.
Tips of the needles are ok, no ridges or lines. They look good and smooth with no dimpling or rounded point. I've had the carbs off several times now and never noticed gas in them.

Thank you so much for responding, I appreciate the advice on where to look for this. I'm pretty much totally stymied at this point. It really weirded me out when, with the choke off, fuel mix screws ALL the way in, and throttle shut, this bike would run. Gas is coming from somewhere it shouldn't for sure, but I can't figure it out.
 

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Discussion Starter #6
I can't imagine any other way the holders got so smashed like that unless the PO was in there plinkin' around where he OBVIOUSLY ought not to have been

New jets aren't too expensive, Your Keihin-Mikuni Jets Store-Pjmotorsports.Com ships pretty quick, too

I've had good experiences with them in picking up my enricher diaphragms. I'll either pick up from them, or I'll just add them in to a Partzilla order I have brewing for another bike so I only have to pay one shipping charge (price is about the same).

I'm with you though on "how the heck did he do that??". If he managed to do that to them while they were in the carbs, very good chance he hurt the carbs. Part of me is honestly tempted to just go pick up a new rack of carbs for the bike. There is a cycle recycling place nearby that sells them for about $75 each. I'd have to clean them up again, but if he's damaged these carbs internally, it's the only way I'd get my issue fixed.
 

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I'm wondering if someone stuck the smaller jets in there trying to correct the flooding.

I keep thinking someone tried a custom hack and did it to both carbs. Which would mean you need a couple of carbs. Longshot for both carbs to flood the same way.
 

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I'm wondering if someone stuck the smaller jets in there trying to correct the flooding.

I keep thinking someone tried a custom hack and did it to both carbs. Which would mean you need a couple of carbs. Longshot for both carbs to flood the same way.
The more I read, the more I think I should just hit the reset button and buy a set of salvage carbs from that yard near me. If they are $75, it's probably worth my time alone if cleaning and popping them in fixes this. Especially since that one carb has a hairline crack in the float bowl. Sure it probably isn't related to this, but it's definitely not right, and replacement is the only real fix for that anyway.

On a slightly different tack, can anyone think of anyway this could be related to anything but the carbs (and petcock)? Compression is good on the bike, 160 psig in both cylinders, so I don't think I have fluids moving where they shouldn't be, just way too much gas. I don't have a ton of experience with Vulcans, just what I've read here and what I've fixed on the bike, so I'm just seeing if there was anything else out there I should look at. (Seems like definitely carb to me, but you never know).
 

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Sounds like there's really a lot of fuel pouring in, and seems like more than the usual culprits can do.

If there's a crack (or the wrong spot drilled) between the float chamber and the venturi, it will pull all the fuel it can. Somehow the the bowl got cracked, and the jet holders bent/holes reamed ... Did the previous owner exhibit signs of unresolved anger? Maybe the carbs got thrown across a garage. :hitanykey

It's kinda baffling where all this fuel is coming from. Have you examined the needles on the slides? Way too many shims on those or somehow jacked up too high all the time? Not even sure that could cause this.

$75 isn't a bad price, ebay usually has pairs around $100-120+. Not sure what Pinwall over in Akron asks for a set. If you get to choose, I'd look for the cleanest looking set, no molested screws, etc.

You have tiny jets, enough to be lean on a normal carb setup, and it's still more than pig rich. 138/38 is the norm for stock everywhere except really high altitudes, like the Rockies, Himalayas, etc. I'm earshaved with 138/38 jetting, and have no trouble when I'm on Spruce Knob at 5000'. (except my ears closing up)

You're compression is good, so there's no intake valves leaking, and it does run.
 

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FREEBIRDS MC CENTRAL NY
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are the holes the jet emulsifiers (jet holders)fit into elongated?

Sent from my LGL34C using Tapatalk
 

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Have you verified the collar isn't busted up and seating on the new emulsion tubes of the jet?
 

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Maybe breakthrough!

Have you verified the collar isn't busted up and seating on the new emulsion tubes of the jet?
One1, I think you led me to the right thinking that has me going the right way. I pulled the trigger and went and picked up a set of carbs from the local salvage yard. $79.50 after tax, and they look like carbs off a salvage bike, but nothing is bent, everything is there, and maybe most encouraging of all, the plugs are still in place over the idle mix screws. After my PO experience with the last set, that's a great thing to see. The new carbs came with 132 main jets and 38 pilots, just like the other set I have.

Upon disassembly, one of the things I noticed right away was that the main jet holders do not screw in in such a way that all threads are covered. There are probably 3-4 threads still out. I noticed this same thing when I put my new jet holders in the old carbs. They seemed to "bottom out" before being visually all the way in. Rather than force them in, I stopped turning. Thinking back, I don't remember that same condition on the carbs as they came off the bike. I don't remember seeing a few threads. Putting the pieces together, I think this is what happened.

For whatever reason, PO took these carbs apart. Probably to "clean" them. When he went to reinstall the main jet holders, he got to where they were actually installed and figured the threads were tight and instead of stopping, CRANKED down on them with a ratchet or something. This caused the main jet holders to crush, and in all likelihood, it has busted that collar like One1 asked about. There is probably at the very least a significant crack through there that's allowing fuel to flow completely unmetered from the jet bowl to the engine.

I wouldn't be surprised if he also put them in a vise, leading to the crack at the top of the one float chamber.

This is all contingent on me being right that those main jet holders are NOT supposed to thread down the whole way but should seat with a few threads left so the main jet draws from the indentation in the cover.

If this is the right train of thought, it explains why both cylinders are fouling ("hack done to both" very close to reality!), it explains how those emulsion tubes came to be crushed, and it explains how I'm flowing SO much gas. It also makes me feel pretty ok about myself, because even though I spent a small amount of money needlessly on new emulsion tubes, I really didn't do too bad about throwing parts at it.

At this point I have the new set disassembled, the first carb body is soaking in the Berryman's. After it's done I'll take to scrubbing it and soak the other, then the bits and pieces. I'll keep parts mated to the carb they came off of as much as I can, but so long as the old carb bodies come off, and the new go on, I should be in good shape. I definitely won't get it fired up tonight, but there's a chance I'll get the new carbs in tomorrow. I'm pretty excited to see what happens, so I'll be gunning for Friday at the latest (I'm too stinkin' good at getting those carbs in and out at this point, it doesn't take me long at all).
 

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So the jet holders were over-torqued and bent, and broke that collar.

Tried to find a pic but didn't find any with the correct angle.



 

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So the jet holders were over-torqued and bent, and broke that collar.

Tried to find a pic but didn't find any with the correct angle.



That's exactly what I'm saying. I won't be able to say for sure that's what's going on until I verify it's running right, but I'll do what I can in the post-mortem to get some decent pictures.


I wish I would have realized this right from the get go. It would have saved me a bunch of forehead shaped dents in my wall, and time. I just didn't have the experience with Vulcan carbs to realize until I saw both my old carbs with new tubes showing threads, and unmolested carbs showing threads.
 

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Should run great with clean, unmolested carbs. You're on your way now.

I always tell people, don't over-tighten ... jets, bowl screws, brake bleeders .... etc.

I lost a set of keys today, drove another 30 miles just to look for them, no luck. Going to try the forehead to drywall routine now.
 

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MY RICH CONDITION IS FINALLY SOLVED!

The new carb bodies did it. I ended up switching almost all the guts from the damaged set over and just using the new carb bodies. That's all that was needed it turns out. I took a look down the emulsion tube hole, but I wasn't able to see any cracking or anything, but that is definitely what was going on. I still have some tuning to do, but now I can do so without risk of washing down my cylinder walls and gouging them. I'll have to do an oil change too before I ride too far since I've got my some gas in my oil. Maybe anyway, I sniffed at the oil fill area after letting it idle for a while (no white vapor! no white vapor!!), and I couldn't smell gas in the sump, so I'm wondering if it's volatile enough that I can burn it off with a little bit of riding.

I wouldn't have been able to bring myself to buy new carb bodies if ya'll here weren't as mystified by that behavior as I was, so you definitely helped me out. I feel vindicated now in not being able to get those old carbs to run right. There was simply no way they ever would. Those things were shot!

I need to renew my Vermont registration on the bike, and once I do, it will be street legal again and ready for some more riding!

Now time to hunt down some left handed drill bits... I have an exhaust bolt seized and broken off in the cylinder head of my Suzuki GS1000 that I need to bore out.
 

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SWEET. good to hear.now stop holding out and put up some pics of that 1000

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