Tell Me If This Makes Sense

[bdholsin]

While riding my '83 I notice that at above 45 MPH I get a little "stuttering" while the choke is off. If I put the choke on it goes away. When I rebuilt the carbs last year I stepped the mains up one size.

Would it make sense that the choke is putting more fuel into the cylinders and smoothing out the stutter? In other words, am I running a bit lean with these 135 mains and should step up to 140 or 145 size mains?

 

[angus67]

is that just cruising at 45? if so, one up your pilots. When your bike 'stutters' whack the throttle wide open. if it runs like a bat outta hell, its your pilots. im running 140's with 46 pilots, but i have 6th over pistons.

 

[bdholsin]

Thanks angus. It seems to pop up at 45 MPH and continues up through 70 MPH. I'm thinking an order to mikes may be on the horizon.

 

[angus67]

just read your signature. what pods do you have? what exhaust do you have?if your pipes are mostly wide open, my sugestion should help. if you are running those crap cone pods, you could be blocking the air jet in the throat.

 

[bdholsin]

I have the "performance" pods from mikes. My exhaust is stock with the exception of the wrap that I just put on a couple weeks ago.

I think I'll try stepping the jets up. I'll order two sizes and see what one more step gets me before trying the second size.

 

[XSLeo]

There is a section of the carb guide that deals with tuning, Have you read it?
Leo

 

[5twins]

While many other bikes out there can get away with just larger mains for mods, these 650s aren't like that. They pretty much always require larger mains AND pilots.

 

[Derek]

I have the "performance" pods from mikes. My exhaust is stock with the exception of the wrap that I just put on a couple weeks ago.

I think I'll try stepping the jets up. I'll order two sizes and see what one more step gets me before trying the second size.

Ditch the pods for a short run and see how it does. Those pods have been known to block the ports on the carb intakes which allow proper vacuum for the slides to lift.

~ Derek

 

[5twins]

Actually, they cause a rich condition and also contribute to a phenomenon known as "slide flutter". Blocking the main and pilot air ports means less air to those circuits which means richer running. Partially blocking the port to the slide causes the "flutter". It gets some air, just not enough for proper lift. It tries, fails, tries, fails, etc.

 

[Derek]

Actually, they cause a rich condition and also contribute to a phenomenon known as "slide flutter". Blocking the main and pilot air ports means less air to those circuits which means richer running. Partially blocking the port to the slide causes the "flutter". It gets some air, just not enough for proper lift. It tries, fails, tries, fails, etc.

Thanks for the correction, 5Twins.

~ Derek

 

[Morgue13]

I agree with stepping up the pilot

I might have some you can trow in to try it before you buy it but then again they are pretty cheap

 

[Morgue13]

whats your needle clip set at?

 

[angus67]

wow. i basically said all that in one post.

 

[bdholsin]

There is a section of the carb guide that deals with tuning, Have you read it?
Leo

Yep. I have it and have read it. The carb guide (or bible as we should be calling it) is a great place to start. Sometimes it just helps to think "outloud" here on the forum and see if the thought process is correct sometimes.

 

[bdholsin]

Ditch the pods for a short run and see how it does. Those pods have been known to block the ports on the carb intakes which allow proper vacuum for the slides to lift.

~ Derek

Not a bad idea. Once the roads dry out a little (light rain last night) I'll go for a spin.

 

[bdholsin]

Morgue13 - My needles don't have clips. If I'm not mistaken, those are for Canadian models. Mine is a US model. Thanks for the offer for the larger jets. I placed my order with mikes two nights ago though. As you said, they aren't cost prohibitive so I just ordered two sizes larger for the mains and pilots.

To be clear, the bike isn't running all that bad. It's just a sputter or hiccup. I've checked my mileage and I'm getting over 44 MPG which is waaaaay better than my '08 F-150 at a whopping 14 or 15 MPG. The bike is saving me money...however, I'm spending that money on parts. Ha!

 

[XSLeo]

On my pretty much stock 81, patched up air filters with foam, I get about 59 mpg.
On my 75 with Mike's 750 kit, 1.5 headers, emgo shorty megaphone muffs, Uni-Filtes on BS34 carbs, not quite finished tuning, I get about 55 mpg. After I finish the carbs it may loose a few mpg.
With the Uni-Filters on the BS38's it ran a bit strionger and got just a bit over 50 mpg.
At 44 mpg it seems a bit low, should be around 50 or more.
Leo

 

[5twins]

A bike that's jetted too lean can suffer from poor mileage the same as one jetted too rich. When too lean, the motor is struggling and you end up working it harder so you use more gas.

 

[Morgue13]

Morgue13 - My needles don't have clips. If I'm not mistaken, those are for Canadian models. Mine is a US model.

ahh the emission control units yeah those were on later years dont know about the canadian vs us models though

I never acually come across a set of the emission control models at my shop