Newb With Questions

Rambo814

Rambo814

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Hey guys, I just picked up a Special II on 4/12 for $300 (hope I didn't pay too much). I was told that it ran on one cylinder but when my dad and I looked at it, it was firing on both. After looking at it I see the petcock has been replaced with a non-vacuum type. So, my questions are as follows:

1) Would the different style petcock cause an issue? (the vacuum port on the right hand carb is capped)

2) Any suggestions as to why it would only run on one cylinder and the other kick in at about 3/4 throttle? (the plugs, wires, and coils were supposedly changed already)

3) Where in the world can I find a good quality carb rebuild kit that comes with more than just a float boal gasket and jets?

Thanks in advance for all of your help, suggestions, and advice.
 
You got a hell of a deal especially since it runs.

First petcock no issue just make sure both vacuum ports are capped. I actually think its an upgrade as the vac petcock is a pain in the ass.

Second sounds like ur carbs aren't balanced one is pulling all the vacuum which means fuel and air with it. Once the rpms get high enough they both pull so much vacuum the second cylinder finally gets fuel.

Mikesxs.net is the general go to for parts like that.

Pics?
 
Thanks for the quick response, brownv1. I'm glad to hear I got such a good deal. I was really hoping the petcock would be the fix-all, but oh well. The carbs not being balanced is a very good possibility since the other owner took the carbs off to clean them and now the choke will not stay engaged, obviously indicating he didn't exactly know what all he was doing. I saw on pjmotorsports.com that older Kawi's had BS34's on them as well, are these any where near the same?
 
On one cylinder not running at idle is dirty idle circuits.
Mikuni CV carbs like on your bike have been used on many bikes, Rebuild kits come with parts that fit most bikes but not very often don't have the right parts for your bike. Your best bet is to get just the parts you need. Often just jets you need to rejet to match non stock air cleaners and exhaust.
The float bowl gaskets are very robust and can be reused several times unless a PO used gasket sealer on them. Take your carbs apart, clean and inspect the parts. You may just need the clean and reassemble to get them to work.
On the idle circuits there are some ver tiny holes in the carb by the throttle plates. When you have them off to clean, open the throttle and look for these holes. Now using spray carb cleaner and the straw spray cleaner in the pilot jet, cleaner should come out all those tiny holes. If not, get the tie off a loaf of bread, peal off about 1/2 inch of the cover, thuis leaves a very thin soft wire. Use this carefully to probe those tiny holes, be carefull not to over do this and damage the holes. Spray more cleaner, repeat as needed to get spray out those holes.
Now remove the air mix screws, spray the cleaner in the hole they come out. The spray should come out the tiny holes as well as the pilot jet.
A bit of probing in the hole the screws came out and in the hole whre the pilots screw into can help, as before be careful not to damage the holes where things go.
Also in the float bowl there is an enrichener jet and passage that lets fuel flow from the float bowl through the jet up to the enrichener. Down in the bowl you will see a hole going into the body of the float bowl. This hole leads to the jet. There is a passage that comes up from the jet to the top of the float bowl.
Use the carb cleaner and straw to spray cleaner into the hole in the float bowl and see if it comes out the top, spray the other way too. See if cleaner comes out the hole. If not use you bread tie to carefully probe the hole and passage.
Leo
 
Ok. Just double checking what was supposed to be done on this bike before I got it until I get the carb kits ordered. Are the Haynes manuals very accurate? It said across the coils there is supposed to be 4 ohms resistance and through the coil and plug wire it is supposed to be 9 kiloohms. I checked it today at 61 degrees Fahrenheit or 16 degrees Celsius, and got 2.9 ohms and around 19 kiloohms. Wtf?
 
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bc, I actually got the readings from the setups that are shown in the Haynes manual. I was able to get the 9 kiloohms WITHOUT the plug wire attached, but according to the Haynes manual, that would mean that the plug wire would have to have very little or no resistance at all, which we all know is impossible.
 
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That's 9 kilo not kila. Any way the points coils are about 4 ohms on the primary, the TCI coils are around 2.5. So depending on what your ignition is your coil is ok. What ignition does your bike have?
Leo
 
Oops. I guess I'm just a hillbilly who types like he talks. :) That is good info to know, Leo. My coils ARE good, then. I have the TCI ignition and was worried that I was only getting about 2.8 ohms on the primary rather than 4.
 
Sometimes I get a bit anal about nomenclature. Using the right terms is a small pet peeve of mine.
Leo
 
Yes, sounds like good coils. Remember ambient temperature can also effect that reading; mine read like 3.2 Ohms but they're fine.
 
Its cool, Leo. I'm usually the same way. I guess that one just slipped by. It's hard to talk technically when technically you're not using the correct terms.
 
Ok guys. What type of carbs SHOULD be on my frickin bike? I see XSLeo says CV but I've seen other places they are BS. My carb rebuild kit is on its way from Sirius and just to make sure all of my parts are there and all of them go back where they should I was looking at buying the Sudco Mikuni Tuning Manual. http://www.mikesxs.net/product/35-0665.html Is this manual worth me buying? The manual says it only covers the VM, TM, TMX, TMS, HS, HSR,BN and RS models. So you don't have to go back and find it, my bike is a 1980 XS400 G Special II.
 
CV is a description of how the carb works. It is a Constant Velocity type carb. It uses intake vacumm to control the lift of the slide. The BS is a Model description of the carb.
The stock carbs on the XS400 are a BS34. The BS is the model, the 34 is the diameter of the slide.
The Sudco book is a good book from what I hear but It doesn't cover the stock carbs. If you are running non stock carbs such as the VM series of carbs, then it will be a good thing to have.
It may help you understand how a carb funtions better, in that it maybe worth it.
Leo
 
Thanks for clearing that up for me Leo. I guess I still don't understand the concept behind using the vacuum. Anyways, I finally started taking my carbs apart and noticed the slides are pretty crappy. most of the brass coating is cracked and it looks like someone has polished some of it off. How important is it to have nice, smooth, brass coated slides in my carbs. Also, I had asked the question about using a non-vacuum type petcock and brownv1 said it would actually be an upgrade. But, before tearing the carbs off I had the bike running good with the petcock valve only opened part way. When I opened the valve the whole way the RPM's picked up and revving the engine was very tricky. Should I rebuild the old vacuum petcock and put it back on?
 
The vacumm petcock, if it funtions right is nice, you don't have to worry about shutting the fuel off. They only let fuel flow when the engine is running.
Now when this stops happening they become not so nice. Taking them apart, cleaning, inspecting the parts, replacing bad parts, reassembling can restore proper function.
Sometimes just unhooking the vaccum line and using the prime to run then using the on as off works too.
With the petcock partly open and it runs well, then full on it runs poorly has nothing to do with the petcock, you need to check the float height and that the float valve is clean and stops the fuel flow.
With the petcock partly on the fuel flow is restricted enough so a bad float adjustment can't flood the carbs with too much fuel. When you fully open the petcocks and your floats let in too much fuel, flooding the carb.
Rebuild the petcock and use it. That's up to you. You do need the fix the float issue.
Leo
 
Awesome! Thank you so much for the info, Leo. I am soaking my carbs in vinegar and getting ready to boil them tonight. Once everything is nice and clean I am going to check float heights, install new jets, and re-assemble. Which brings me to my next 2 questions. The first being "how nice do the vacuum slides have to be?" As stated in my earlier post they are pretty ugly. Also, I noticed that the one has 2 locating tabs on the actual diaphragm, is this from a different carb? And the second question, "a lot of my diaphragm cover and fuel bowl screws are stripped out, is there really any warrant to replace them with stainless screws?" Thanks so much, guys!
 
As long as they slide up and down in the bores they will be fine. You can clean them by using a sprau carb cleaner, spray it on a rag and wipe the slides down. Don't just spray it on the slides. Getting it on the diaphrams can hurt them. I wouldn't sand them, this could remove too much metal and let too much air flow around the slide instead of under it.
As far as two tabs on the diaphram, I've never seen that. On the one with two tabs, is that the only difference? When you install the slides the angled on the bottom should point to the air filter end of carb. Use the tab that does that.
 

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