It STARTS!!! But Then dies.

[jchristy456]

ok gang. I feel like i'm hitting the home stretch. So here's what i've got so far. I have spark. And i have started the bike. I started it several times yesterday.(11/18/13) After i started it (with the choke on) it would fire up and once i turned off the choke off it would slowly die. I would have to keep rev'ing it so it would stay alive. I came back today to start it and it wouldn't start at all. I pulled the plugs out and they were kind of black. One of my co-workers (a GM guy) suggested soaking the tips in a bit of gas. That really cleaned them up. It fired up again for a brief moment and the once i stopped nursing the throttle it of course died shortly after. I have a 77 motor and i'm still a bit confused on exactly what kind of carbs they are but i have attached a picture of the carbs i'm running. I have rebuilt the carbs myself and i pretty much put them back together the way i took them apart(same settings and all). Any threads you guys think i should read up on please feel free to throw them at me. And any first hand experience you guys feel like sharing would be killer. I have been doing some reading and i have a few ideas but i know this post will probably help me a little more.

p.s. I'm running a HH PMA
and a full pamco system

 

[neanderthal]

how long do you let it warm up before turning the choke off? The carb sync and adjustment of the idle mixture may be a problem. Setting the idle when the bike has warmed up sufficiently, with choke off, is also very important. i feel if you run carbs more they smooth themselves out, stock pipes?

 

[XSLeo]

Those are the stock 76-77 carb set. www.amckayltd.com/carbguide.pdf will help with rebuild your carbs.
When you did your carbs did you buy carb kits? If so you wasted money. Mikuni built these carb in many versions for many applications. Rebuild kits fit some, but very seldom the XS650. The gaskets and the float valves are about all the kits provide that is usable. Best to tear down, clean, inspect what you have then buy just the parts you need.
If you did replace the needles and jets from the kits, I hope you still have the stock parts. You will need to put the stock needles back in. On the jets you may need the stock ones but only testing will reveal this.
It's all in the carb guide.
Leo

 

[jchristy456]

Jake,

So far ive ran the bike a total of 2 mins. haha it hasn't really been running really. I also am runing pandemonium Hot rod pipes. So its a much shorter pipe and i know this with def effect the way the carbs will behave. I'm not quite sure how though. (i'm such a rookie)

XSLeo: I did buy one rebuild kit. It was from Mike's XS I did also change one needle on one side. I dont think i still have the old one. Do you suggest buying the part for the carbs from Mikuni? or is getting the indivial parts from mikes better? Thanks for the link I have some homework tonight!

 

[yamahammer]

Definitely keep things consistent between cylinders, no new needle on one side and not the other for example. If you're new to it just get in there and make mistakes, experience is the best teacher.

You're right about the open pipes, an exhaust system is an important piece of the breathing process for an engine. It's matched to the cam and the jetting very closely. Eliminating your mufflers most likely means that the engine doesn't extract exhaust gases as effectively as stock, or draw the fresh charge in as readily, changing jetting requirements.

I would ensure that your charging system is working as it should, one reason for shutting off as you describe could be that your battery is slowly dipping below the threshold where it can fire the mixture. Stock coils are weak as it is, but when you say full pamco system you might mean that you have fresh coils as well. When deviating from the stock set-up, whether it be the exhaust, charging system, ignition, etc.... you create variables which need to be compensated for, and invite the chance for improper installation or adjustment.

 

[neanderthal]

Definitely keep things consistent between cylinders, no new needle on one side and not the other for example. If you're new to it just get in there and make mistakes, experience is the best teacher.

You're right about the open pipes, an exhaust system is an important piece of the breathing process for an engine. It's matched to the cam and the jetting very closely. Eliminating your mufflers most likely means that the engine doesn't extract exhaust gases as effectively as stock, or draw the fresh charge in as readily, changing jetting requirements.

I would ensure that your charging system is working as it should, one reason for shutting off as you describe could be that your battery is slowly dipping below the threshold where it can fire the mixture. Stock coils are weak as it is, but when you say full pamco system you might mean that you have fresh coils as well. When deviating from the stock set-up, whether it be the exhaust, charging system, ignition, etc.... you create variables which need to be compensated for, and invite the chance for improper installation or adjustment.

there seems to multiple problems here, id start buy running the bike with the choke on longer and see if it dies. in fact dont touch the choke until it starts to rev high on its own, then come back here with the results. it should still idle with custom pipes, itll just run rough and you may not be able to ride it or itll bog down when giving it gas depending on the pipes. but since its only ran for about two minutes i assume the bike hasnt moved under its own power yet.

 

[angus67]

how did you know wich rebiuld kit to buy if you didnt know what carbs you had?
Im guessing your not a young guy, becuase you called your self a rookie, not a newb.
I strongly suggest you get a real in hand manual, and read thoughouly the carb guide as linked to above.

 

[jchristy456]

UPDATE: I had the bike running long enough to put it in gear and ride around the warehouse. It started several times. But its def still not running like it should. I started it with the choke on. then once it started i turned off the choke and feather'd the throttle to keep it going.

Jake, I start it with the choke on and it revs really high but pretty much stays running. I havent really kept the choke on "that long". How long do you think i should leave it on?

Angus, I didn't really? hahaha I looked on mikes and just read all of the descriptions on their website and bought kit that was in the correct year range. In the previous post XSleo revealed that they are stock 76-77 carbs. BUT are they BS38? 34? i have no idea still. Also if any of you have carb trouble http://www.amckayltd.com/carbguide.pdf <--- this is the place to be!

 

[XSLeo]

All the carb sets from 70-79 were BS38's. They made changes every two years. Some major, some not.
I have a set of 76-77 carbs and those look just like these.
When tuning carbs it's best to start at stock, test, adjust, test. Each adjustment is one change. Just make one change at a time.
We can suggest a starting point other than stock if we know any mods to the bike.
Exhaust, air filters are biggies when it comes to carb tuning. What air filters are you using?
Changes to the intake and exhaust change the air flow through the engine.
If just the exhaust or intake was changed one up on the pilots and mains may be enough. If both are changed it may need two up on the pilots and two or three up on the mains.
The carb guide has a section on "Tuning for Mods" read through this. It tells how to test and using the test results explains the adjustments needed to correct issues.
Mike's has parts that will work in your carbs. They are not genuine Mikuni parts. Mikuni parts are better. There are parts sellers that have them. Sudco, Jets R Us, Niche Cycle. Are just a few.
Start by getting the stock needle and needle jets. These are required. There isn't much options on these. The needles are 4M1, Needle jets are Z-8. as stock. Pilot jets are 25, mains 122.5.
An assortment of pilots, 27.5, 30. Mains 125, 127.5, 130, maybe even 132.5.
These will give you enough to tune your carbs.
If you have a local independent shop around that works on dirt bikes, atv's, snowmobiles and such often have gently used jets a bit cheaper than brand new. If you talk nice they may let you try several sizes and buy back the ones you don't use.
There are several near me that have big boxes of jets. Even big boxes of carbs.
Leo

 

[jchristy456]

ok so I looked at my carb rebuild kit receipt. It bough this thing off of ebay. (i'm an idiot) WEll you live and you learn. I will be purchasing the correct components asap and installing them asap. I will keep you guys posted. XSLeo you're a man of much knowledge and its a privilege being able to interact with you.

 

[5twins]

Jets and needles have numbers stamped on them to denote their size. You have to check what you've got in your carbs to see if they match one to the other. Especially check any new stuff you put in from that rebuild kit. There's a good chance the sizes are wrong on those. But I'm thinking the bike would still idle with a wrong needle in place. I'd say you may not have gotten the pilot (idle) circuits completely clear and clean. Sometimes it takes several tries to accomplish this. You not only have to clean the pilot jet but also the passageway leading from it into the carb's main bore.

 

[jchristy456]

here's a pic of the the ol' girl

 

[bonesaw]

My xs400 did the same shit.so did my 650,Sounds like the carbs honestly.rebuilt em and left some grease in them or something.ive cleaned my carbs and ran them and had to take them off to clean em again.it sucks but if u pop the acorn but off the chain adjustment makes life a lot easier.plus if u clean em again your only down a few bucks for cleaner rather then beating yourself in the head trying to figure it out.

 

[bonesaw]

here's a shot of my old lady

 

[jchristy456]

Bonesaw,

Yeah bought all new stock jets and needles and i'm going to give the carbs another cleaning for sure. Its a pain for sure but it'll be worth it in the end. I like your taste my man. you got that big wheel in the front! Looking real nice!

 

[XSLeo]

www.amckayltd.com/carbguide.pdf will help on the carb cleaning.
Leo

 

[jchristy456]

soo here is my current carb set up. as you can see i had to cut out part of the rubber lip on the filter mount. I'm still waiting for the right needles and jets to get to me in the mail. as we all know this is the hardest part for the entire experience of building a motorcycle. If you guys have any suggestions for me i'm all ears.

Thanks fellas!

 

[5twins]

If you're cutting rubber lips on filters, that's telling me you have the cheapo junk pods. You'll never get the carbs tuned right using them.

 

[jchristy456]

yeah mikes XS said it would work fine but you would have to trim the rubber. so i did. I know its less than ideal but its working. I will get better ones in the future but for now i'm just trying to get the bike running and on that note upon further investigation my cam chain tensioner was waaaaaaaaaaay to tight. so i think that contributed to the roughness in running as well.

 

[5twins]

Yes, that will put a strain on the motor (DAMHIK, lol).