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Discussion Starter #1
I have a good, strong compression engine. It has the Bore-Tech ignition system dialed in.
I have rebuilt carbs twice in 3 years. Cam chain timing and tension is set. It runs pretty good
but I have to have idle slide screws all the way in to keep it idling. Runs strong tho with no stumble.
I have noticed that when i shut off gas petcock while running, it will run up from like 1000 rpms to
4000 and even hits 5000 rpms before it dies. What's up? that is the way it should run all the time.
Is it a float problem? I have each bowl half full of gas when i remove them (not when i let it die of
starvation). new fuel hoses and 120 jets with the needle on the center groove. Any ideas?
 

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Sensei
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That is normal...all engines will rev as they lean out...But it's not good for the engine.
Kill the engine then shut off fuel.... Drain the bowls afterwards if you want them empty....
 

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Humor me, I am curious, why would you shut off thr petcock while the engine is running anyway?
Is this when riding or to clear the bowls of fuel when stopped to store the bike, or...........?

Are you saying that the idle screws are the idle slow run jet needle screws, or the throttle stop screws which operate the lowest position of teh butterfly?

The needle jet would have the effect of cutting all the fuel feed to the slow run when screwed in which would seem to me to effectivly stop the engine from idleing.

However the throttle stop would open the butterfly up and allow more air in, and therefor speed the engine up.

Can you be a little more specific with your description please.
 

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Nige, The later SL's used 24mm slide types not CV carbs.....No butterfly....

arstrans: Good compression would be 170+ PSI....What are your readings?
Low compression bikes need higher idle settings because they don't "pull" as much (enough) fuel/air mix in through the smaller circuits.....
 

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Thanks Steve I didnt know that :oops:
Still would the same apply to the throttle stops on the slide, giving the same result?
 

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Sensei
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nigelrharris03 said:
Thanks Steve I didnt know that :oops:
Still would the same apply to the throttle stops on the slide, giving the same result?
Yes, but I believe he has less than ideal compression or short valve open timing.... See my previous post.....
 

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Discussion Starter #7
Thanks for the replies. I have not checked compression with the engine warm yet. I will do that next. The slides are only open about 1/8" when idling. Guess I shouldn't shut gas off to empty carbs. The compression cold is 150 on each cyl. It's hard to do alone when you have to kick er over. I will dO that tomorrow warm.
 

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Discussion Starter #8
Compression warm on my engine is 150 on right and 153 on left. It was a bugger
to hold my push-on compression test in hole, hold throttle open and kick at same
time lol. I guess I could of wired throttle open. Anyway, that should be sufficent
compression. Guess I am going to take my carbs off again. Something is screwy
in there.
 

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your compression should be 170+...Honda calls for a rebuild at 150
 

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Discussion Starter #10
Yea, it is a little weak on compression but I found out the culprit to my problems today.
I had the carb slides in the wrong carbs. I guess when I did my rebuild recently, i took everything
apart. Runs great now! Sweet!!! They only go in with the bevel facing the air cleaner side.
DUH!!!!!
 

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yep that'd do it!

glad to hear you sorted it out.

those carbs are better than the CV carbs anyhow in my opinion
 

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Discussion Starter #12
Oh are they? I have a off idle stumble still when warm. Would raising the needle a notch
help that. Idles real good but stumbles a bit when reving it up. about 2000 rpms.
 

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your direct pull slides are not RPM sensitive like CV carbs but rather throttle position sensitive.

If you pay close attention you should find that (assuming your 2000 RPM stumble is carb related and not electrical) that the rpm where your stumble is changes based on how quickly you roll on the throttle.

if the stumble is always ay 2k rpms regardless of throttle position, then you may want to look at your ignition advancer.
 

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in that case it sounds like you are a little lean somewhere. to identify where you'll need to figure out at what throttle position the stumble is, there is a technique we use for tuning the Mikuni VM carbs I'd recommend...

get a sharpie or nail polish, or touch up paint and put a small dot on your throttle grip and a corresponding dot on the throttle housing...this is your full closed mark

then rotate the throttle all the way to WFO and put another dot on the throttle housing that aligns with the dot on the grip. this is your full open mark

measure the distance between the two dots on the throttle housing and put a 3rd dot at the exact middle...this is your 1/2 throttle mark

then measure the distance between 1/2 and full closed and put a 4th dot in the middle...this is your 1/4 throttle

then repeat for 3/4 throttle


once you have all 5 dots on the throttle housing and the dot on the throttle warm the bike up and take it out for a ride.

roll on the throttle slowly till you feel the stumble (usually most noticible ini 5th gear but try it in all gears to get a better feel for where it is) take note of what position your throttle is in relative to the index marks you made.

this will identify which circuit is lean

closed to 1/8 is idle mixture or pilot

1/8 to 1/4 is pilot or slide cutaway

1/4 to 3/4 is needles

3/4 to WFO is mains.
 

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mostly yes, any carb that has direct throttle valve (slide) acutation.

the fuel circuits and overlap points vary slighty but are mostly the same. there are exceptions, like the Lectron carbs they use for drag racing; which are basically on/off switches
 
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