Mad Mos Still Sta..Sta..Stutters!

[XSPastor]

Hey Ray,

Last time I did the carbs, I just set the mixture screws at 1 3/4 turns out and set the sync. It runs great and the plugs look good so I never messed with it anymore. I suspect the mixture screws could be fine tuned... Yeah, I always use two fans when I'm sync'ing.

I've enjoyed reading all your posts over the past 5 months since I bought my bike and joined this forum. Thanks for all the great advice you give. It is truly appreciated. I've always done all of the wrenching on my vehicles, but am new to this model of bike. Having people like you and all the other thoughtful folks on this site who have years of experience with this bike is AWESOME!

Tim

[planedick]

Synch, tune, synch

Just like Divr Ray said I think is the best way. Nothing like being able to idle slow enough to hear each cyl fire reliabely. Not that it's the best rpm for idle, but being able to idle that slow shows good settings.

[Da-Bubble]

Mad Mos Still Sta..Sta..Stutters!

Ok I thought for sure that the MikesXS coils were gonna solve my problem. As I was taking the old ones off, the PO (POS) had squashed a bullet connector then just electrical taped it together. It literally fell apart in my hands. I was so thrilled when I found that I thought, "All this carb hell for nothing. This thing is gonna run so smooooth".......

BUT NO!!! It has a low speed sputter / pop going on. What would you guys check first. Once it's pat 3-4k rpms it pulls smooth and strong. I had been messing with my idle mixture screws before this. I think they were about 2 turns out. Can they cause this?

I also synched the carbs (prior to the new coils) using a homemade vacumm gage tool per the tech tips. With all 4 synched they were only pulling about 7lbs. I've seen some of you guys' pictures with them pulling 30lbs. Should mine be pulling more vacumm?

I spent 6-months redoing my bike and I just hate that I can't fix these freaking carbs! Please help!

[bikerphil]

carbs

I was having same problem today with my Standard. I tweeked the idle mixture screws until the plugs were a dk. brown color. Seems like mine runs best when a little on the rich side. I'd ride the bike for a few miles, then let it idle for 3-4 minutes, shut it off, then read the plugs. Brush off the plugs, tweek the screws, then off for another test ride. I repeated this process 3 times until I got it dialed in. Runs great thru all ranges. HTH.

[TopCatGr58]

Hey Da-Bubble,

How about a recap of what you've done, what mods you have on the bike?? What size Pilot and main jets, float levels?

But it does sound a bit lean on the pilot circuit side. But if you have to turn the screws out more than 3 turns, then you may need to go up 1 size on the pilot jets....but you could try tweeking the float level...raising it ~.5mm (right side up) to slightly richen it up before having to invest in new pilot jets.....if you reach the 3 turns out and it just doesn't quite get rid of all of the stumble.
T.C.

[bikerphil]

idle mixture screws

If you like to tweek your idle mixture screws, this tool is great, best carb tool I ever bought....



It's a Motion Pro available at JCW.

[Da-Bubble]

My bike is a 79 Special with Kerker 4-1 with a drilled baffle and air box.

When I first bought the bike and cleaned the carbs it had the same problem, low speed stutter. I took it to a local shop and he got it running good. Fast forward six months...after I finished the overhaul it ran fine for about a month until it started missing. I pulled the carbs and decided to clean/check everything. The joker at the bike shop had told me it had a needle screw tip broken off in one of the carbs and that was the problem. He didn't say that instead of replacing the screw he just ground it down to a semi blunt tip to make it work! He also took out the new bigger Mikuni 145 mains and 45 pilots that I had purchased according to the rejetting chart. When I pulled the carbs, he'd put back my 137.5 mains and carb 1 had my new 45 pilot but 2,3,4 had the old 42.5 pilots back in them. Needles to say I am not too happy with his $220 repair job! Oh and he'd also duct taped over the hole in the bottom of the airbox...so that's why I closed it off with a metal plate when I redid the bike.

Ok. When I put them back together, I couldn't find the larger jets so I just replaced the 45 pilot with a 42.5 to match the rest. I know this is a little lean for my setup but it still should run shouldn't it? I set the floats with digital calipers to 24mm from the gasket surface.

[TopCatGr58]

Well,

I'm running the leaner pilots, but mine is an 81, and so the pilots get their own supply directly from the bowl! Yours have to sip thru the tunnel and the mains, and I would think that since you have the leaner mains, that it could affect how lean your 42.5's are as well!?!?

Can you get your larger jets that you purchased back from that "mechanic"....he should have returned all of the parts removed from the carbs with them!

Yeah, your floats are a little high for your year, but with those lean jets....just don't know?

Hopefully Prom had some other words of wisdom in his PM he sent/ tried to send. Remember, you need to click on the SENT folder, and delete the copies there as well, you're only allowed 100 messages in ALL folders combined!!

T.C.

[Da-Bubble]

The Hack Mechanic gave me back the jets in a ziplock but I can't find them.

Did Prom send me a PM? I cleaned out my inbox and sent so I should be able to receive now.

[Axel]

Synch

Synch with a Morgan Cartune II and color tune with a colortune plug from Morgan as well . They are a british outfit with good shipping .

http://www.carbtune.com/carbdtls.html

http://www.xs11.com/tips/maintenance/maint34.shtml


There is no substitute .

[Da-Bubble]

So sick of this bike.

I am almost ready to sell this POS. I cannot get the carbs tuned right. I am a mechanically inclined person. Heck, I customized this whole bike in my garage but I cannot figure out the carbs!!!

One more time for all you Gurus...I have a Kerker with drilled baffle and drilled air box so I jetted with 45 pilots and 145 mains. I bought a seperate tach to use while syncing the carbs. I made the vacuum gauge sync tool and got them all reading the same vacuum. I then TRIED to do the pilot circuit tuning by ear/tach per Ken Talbot but I could not hear or see an increase in RPMs when playing with two of the four idle screws so they are back to 1.5 turns out. I just cleaned the carbs and set the float heights to 23mm across the board. I have not pulled the plugs after this latest fiasco but it is running WORSE THAN EVER. I EFFING HATE THIS BIKE!!!!

[Ken Talbot]

Re: So sick of this bike.

Originally posted by Da-Bubble
I could not hear or see an increase in RPMs when playing with two of the four idle screws so they are back to 1.5 turns out.

Sounds like two broken pilot screws, and/or two pilot circuits that are still plugged. Sorry...

[Da-Bubble]

Nope!

All four screws are in good shape and all four holes flow carb cleaner nicely......next!

[TopCatGr58]

Hey Da-Bubble,

Aside from what Ken said, I want to be sure that these are 79SF carbs?? You have the float height at 23mm?? Stock is 25.7 +/- 1.0mm.

Drilled airbox doesn't contribute to that much leaning out of the mixture. I ran 4-1 pipes on mine with stock jets for years....before I knew what I was doing, and didn't burn up any pistons, had power to redline!

I hate to ask, but can you be a bit more specific on desribing the STUTTER, is it in first gear, at what rpm are you trying to launch the bike? Before you stated that after 3-4K rpm, it ran great, does it still, can you take it to redline without any problems in most of the gears??? IF so, then the mains are probably okay, but you may still have problems with the pilot circuit, checking the plugs would be helpful also.

And to make sure, you do have the caps on the pilot jet towers IF these are 79 carbs vs. 80-81's?? Hang in there, we'll get you right, just may take some more tinkering!
T.C.

[dbeardslee]

Da-Bubble - I was getting almost exactly the same read on my plugs. Wound up being one of the petcocks. Spring was too stiff. It worked OK with a full tank of gas, but as soon as it got down past half a tank there was no longer enough pressure to push the gas through. It would sputter and get real cranky at low RPM's, then at higher RPM's I guess the vacuum became sufficient and it would take off. I can't figure out why that made the plugs foul, but it did. As #1 and #2 share a gas line, it might be worth running in the prime position and see if they still foul.