Sputtering

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Alright guys I have a 74 with73 carbs and 2in 1 exhaust with 4in. K&N filters. I changed my main and pilot jets to 145 and 45. The bike screams 1st through fourth but when i hit 5th and roll on the throttle above 4500rpms it sputters and loses speed. If i down shift to fourth i can crank it out to about 6000rpms before it sputters. and sugestions. I have the needle on the third notch.

xsjohn · Posted: April 2, 2008, 8:26 pm Post subject: Re: Sputtering

Considering all else is correct......

ain jets probably to big....or the pods are too small or both.........I have had some real delimas with some of my customers and the small pods...would do the same thing as you describe until they were removed and replaced with the ovals....if mine I would take the pods off and see what happens.....if nothing then maybe the main jet....if it just gets somewhat better then it is both...145 is pretty big...betting it is both......and droping the needle one notch from factory is a bunch too.... maybe forcing you to overjet to keep it from starving at moderate throttle.........all a best guess you know..????.......

If someone said what would you try.....

140MJ
bigger pods (or no pod for the test)
factory needle position

And see what happens.......then cuss me out for being an idiot......and have to think elevation too.....

xsjohn

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

I checked my plugs and their black as a coal diggers ass so i dropped my needle all the way and adjusted my idel screw 1 1/2 any thing more and it backfires like crazy.ran great on bottom end but still sputtered out at 4500 rpms in 5th.

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

I have had the same sputtering mid-range problem before -
Believe it or not - I think mine was too rich on the low end (idle circuit) and too lean on the high end (sputter).

Try this for a test: When you hit the sputter at 4500 rpm - pull out your choke halfway - if it smoothes out - you know you are too lean on the high end and too rich on the idle circuit. If it gets worse - you know you are too rich all the way around.

Some of these carbs don't fall in to the way too lean idle circuit from the factory. I would guess the older ones really aren't too lean from the factory since the epa hadn't started to bust our chops as much in 74.

I have an '81 with 34's. I have two sets of carbs. One set that will NOT tolerate 45 idle jets(must have stock 42.5 or it's too rich) - and one set that takes 45's just fine. (mine are 34's so adjust for your older carbs -ideas the same)

If the choke helped it to stop sputtering at 4500 - (Too lean high end)
try stock idle jets - and going back to notch 3 on the needle.

If it didn't - (too rich all around)
Check floats are perfectly set so that fuel isn't spilling over - Also check your needles and jet for wear - or even your diaphram for a tear. Also try leaning out your Main Jet - and going back to stock on idle jet.

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Thanks I'll give it a shot

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

Your '73 carbs should have had a #130 main as stock and the needle set in the 4th slot. A 145 is probably way too big and something like a 135 would probably be more "in the ballpark". There's also that 2-1. They can be difficult to tune for and sometimes require reducers at the head and collector.

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

What does the idel mixture screw do.?
add air or add fuel? I'm pretty mechanically inclined but dont't have a diagram of the carb that explaines all this.

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

In the case of our particular carbs - It adds fuel to the air in the throat of the carb. The more you screw it in - clockwise- the less fuel or leaner it is. The more you turn it out - counter clockwise - the more fuel you add or richer it becomes.
If you want the whole story - fuel in the bowl is drawn up throu the main jet into a little hole that leads to the pilot jet (where it mixes with some air) and goes to the mixture screw that is over a hole (just above the butterfly) in the throat (mouth?) of the carb on the engine side.

See rough picture attached.

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Thanks Jimdi that helps alot.

I took the carbs back off the bike and found looking at the old jets they were already 135. So whoever had them before me had already moved them up from 130. I guess my 145 was overkill. I put the 135's back in with 45 pilots and put the needle on the third position. I haven't put them back on the bike yet so if anyone has somemore suggestions please let me know.ALSO how hard is it to change the valve seals?

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Alright I've got the carbs on and the appear to be running alot leaner now how do you sync these things

xsjohn · Posted: April 5, 2008, 7:40 pm Post subject: Re: Sputtering

Setting carb balance….raise the idol to about 1800 or 2000……lift one plug wire and see how far down it drops on the tack……put it back on and wait a moment so the engine clears up good and pull the other side……

The balance screw between the carb……to increase the left you barely turn it counter clockwise……to increase the right turn it barely clockwise…..

I forget if you even have the sync in the center......

xsjohn

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

If you have '73 carbs then they should have 2 individual throttle cables. To sync them, you have to insure each cable has exactly the same amount of freeplay. You can use the "dead cylinder" method as John mentioned to set equal idle speeds, then set the cable freeplay to match. Any time you adjust idle speed on just one carb, you will throw the sync off. Adjusting the idle speed adds or subtracts freeplay in the cable.

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

IS there a balance screw on 73 carbs? all i see is mixture adjust screws.

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

No sync screw or linkage between carbs. You have to set and match the cable freeplay so each butterfly begins to open at the same time. This syncs them.

jayel · Posted: April 6, 2008, 2:18 pm Post subject: Re: Sputtering

you can set them with a piece of cellophane off a cig. pack as you open the throttle both butterflies should have the same amount of drag at the same opening I just make a mark with a ink pen on the grip and the handle bar clamp, open throttle 1/8 inch cello slides on carb 1, set carb 2 so cello slides when your marks line up, carbs do have to be out of the intakes when you do this but it won't change after you put them back on, just do equal adjustment to both cables after setting them this way

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Thanks guys all of you input was used and needed! I adjusted my carbs and went on a hard ride pulled the plugs and...................

They were Tan plus it ran better than ever before.
Has anyone tryed the IRADIUM plugs if so do they work?

jayel · Posted: April 6, 2008, 9:10 pm Post subject: Re: Sputtering

what plugs are you running now?

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

bp6es

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

sorry,
NGK BP6ES I tried the 7 and the 8's the 6 just seams to run better.

jayel · Posted: April 6, 2008, 10:20 pm Post subject: Re: Sputtering

6's are fairly hot for these motors if your bike is a 74 it should run 8's C models and later ran 7's so if your running clean (tan) on 6's I would think you're still rich on the mixture, what kind of gas milage are you getting? it's better to run a cold plug and foul one once in awhile than a hot plug and hole a piston, just my opinion, lol

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

jayel -- what does a set of VM34 Miks do to spark-plug heat range? Should I go hotter?

jayel · Posted: April 7, 2008, 10:56 am Post subject: Re: Sputtering

whole different ballgame there you have to read the plugs and jet accordily your best bet would be to talk to someone that has run them mike morse at 650central would be the go to guy

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

John's got me running Autolite 63's with his Needle Kit. As per his suggestion - I am at 135 mj & aj - and 45 idle jet.

Plugs are a dark tan on the tip of the electrode.

Engine runs great.

xsjohn · Posted: April 7, 2008, 12:30 pm Post subject: Re: Sputtering

Here isa color chart I found........my buddies XS1100 gets the tan to dark tan to almost a brown......my XS650 always seems to read in shades of grey........the Autolite runs good and is only $1.50 at autozone......I use antisieze ..........

www.dansmc.com/Spark_P...talog.html

The Autolite 63 is the same as the BP7ES.......
The Autolite 64 is the same as the BP6ES.......

xsjohn

anaged to find the best free email and best free email software program this weekend......Thunderbird and Gmail work great together and you can drag anddrop images right where where you want them and position them don't have to attach....... xsneedles @ gmail.com is my new one......

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