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Hey folks: Just spent a crazy weekend at TT's getting the bike ready for April 30th and the season. I am about 70% there. The bike is pulling really good upto 7k-9k rpm (of course where I want it to be). Under load it feels like she is just starving for fuel. I did several spark plug chops and BOTH plugs showed the bike was running real lean. I think it is fuel management. I ajusted floats to about 26mm, running 110 jets (yeah 110)... still same result. Before I start breaking down the carbs again, I thougt I would see if I missed something. Tim gave me some needle spacers I was going to install, bring down the floats to about 24mm, check for vacum leaks, clean carbs really well again. Any other suggestions?

Pete C.



Yeller'
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Discussion Starter #3
Champ. We checked and timed it to spot on specs.

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Pete,
If BOTH plugs are looking the same then it's rarely a carb problem (assuming the main jets are large enough). By problem I mean malfunction....still possible the jets are too small.

Typically if you do a plug run, and run the bike WOT up to 9,000 and it pulls well, you should be close to right. Usually a bike will run worse under accleration if there is any serious problem.

I've found when you are kind of lost in the tuning process and have a hunch about something...then go to an extreme to test your hunch. Throw some 130's in there and see if it gets worse or better.

And "real lean" would be a very light gray color on the outer ring...or even blistered insulator. If you are running street fuel it can be kind of hard to read plugs on unleaded fuel.

And it's a stock CB right? If so...then it is going to start running out of balls at 9,000 or so I'd think. Remember...it's only a 350, if you are used to modern bikes it's not going to feel real fast.

Vacume leak is doubtful, unless it's the same leak on both sides. Fuel starvation is very easy to diagnose...the engine will cough, practically die...then pick back up....shut down...pick back up. It's a very dramatic symptom, not something subtle.

I'd try going way up in jet size and see what happens....if it's better but too rich...then start going back down again. If it's worse or the same then you know it's something else. Usually if accleration under WOT is good...and problems start arising at high rpm load it points to an ignition issue of some sort...weak coil etc.
JohnnyB
 

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Discussion Starter #5
JB. Thanks. It is stock CB. I'll pick up some 130s and put them in to see what happens. It was also real cold yesterday. Running the engine in 35 degree weather for only a 5 to 10 minutes at a time. I don't know how much that had to do with it... if at all. I am running street/unleaded fuel. The plugs were white, but no blisters. It was really choppy like you suggested once I got to a certain range... I would have the throttle wide open and no acceleration or increase in RPM....

Thanks for the advice.

Yeller'
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Ask not what the wanker can do for you, but what you can do for your wanker!

Edited by - Pete Casper on Apr 08 2007 9:29:52 PM
 

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110 doesnt seem out of the range. but it shouldnt be running real lean on them. mine runs a tad on the rich side of things with 110's in it. but im leaving it that way. like is it running waay lean? maybe try some air filters. shove a potato in your muffler. they do drop off at about 9500. when you say bring it down, you mean raising the float? measuring with the carb inverted and the float tang just touching the needle end is the position you want to measure at. so the needle is closed. more gas in the bowl will mean less air enters the motor because it wont have to use so much vacuum to pickup the gas. it will suck more gas in. just dont get yourself confused. if you raise the float level, less vacuum is needed, and it will richen. but its important to check this with the needle closed. hence the doing it with the carb off and upside down, when the needle is dropped all of the way in.

if im wrong about any of this, someone please speak up.

jc


aaron, send my wheel.
 

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Discussion Starter #7
Joe C. Exactly, that is how I was measuring the floats. TT showed me that one.

By the way, for as much crap as I give Tim. He really helped me out this weekend... he is a true wanker.

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yes, that cold will make it run lean. very lean. no choke, no airbox, etc...sure. do what jb said. hes right on. they do start to fall off at about 9-9500.





jc


aaron, send my wheel.
 

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ok, i just wanted to make sure. sometimes people do things back-asswards.



jc


aaron, send my wheel.

Edited by - joe c on Apr 08 2007 9:33:37 PM
 

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i doubt it is the float level...on both carbs...probabley the mains (assuming you are wide open...check that too). like Dr, b said; go fat (130s) and back up.
parks
how exactly is it mis-behaving?


Edited by - parks61 on Apr 08 2007 9:35:36 PM
 

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you could always post a pic of the plug for us. that might help. chris always told me its not lean til you see aluminum dust on it.

(thats a joke, dont try it)

jc


aaron, send my wheel.
 

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Discussion Starter #12
Joe, not a bad idea about posting a pic. I get one up in the next few days. I gotta go be a family guy now.

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i have also bumped my idle jets up one size too. to 68's or 70's i think. just to add. that richens the total mix a tad too id bet. but really i dont know how much a difference it makes @ wot. probably just makes it start a little easier.



jc


aaron, send my wheel.
 

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Discussion Starter #14
JB - Okay, I am going to run 130s. If problem still arises, I will change the coils to see what happens (I have an extra set). (one thing at a time to eliminate issues). If coils change does not work, then look again at timming...(I will likely do that first since it is easy enough).

I forgot to state, that I did put different intake manifolds on, and used good hose clamps, which helped a bit, but did not solve the issue of not pulling at higher RPM while at WOT (wide open throttle = WOT, i take it). Joe, I threw TT's old K&N monster air filters on and that helped a little, but did not solve the issue... again, these things lead me to believe it is fuel managment....but I am a true rookie when it comes to these bikes.

I will get as running as best I can for the April 30th. I think that will be as much a tech day for me as a track day. (I will have the BMW as a back up but I really want to use the cb to get seat time).
So, if you hear me short shift...it ain't on purpose!

Yeller'
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Ask not what the wanker can do for you, but what you can do for your wanker!
 

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My 175 has got this weird thing going where it won't rev past about 9,000 without filters....but will rev clean to 13,000 with them on...and it's not a jetting issue....tried that. Just one of them weird intake length things.
Just have to eliminate things one at a time.

JohnnyB
 

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that is wierd johnny. but hey...if you're getting 13000 without dirty air, it's a good thing. how many cc.s you running this year?
parks

another edit...gota stop trying to type so fast, being special 'n all.



Edited by - parks61 on Apr 09 2007 5:03:24 PM

Edited by - parks61 on Apr 09 2007 5:05:44 PM
 

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Parks,
I'm at 209cc (57mm bore x 41mm stroke). Which I ran for all of last season. Prior to that it was 56mm x 41mm for a bit over 200cc.

Problem is rebuilds, 57mm is now the "stock" bore...so if I need to freshen up the top end I have two ways I can go. One is just go oversize 0.25mm and be illegal at about 211cc ( 1cc over the limit), or come up with a new set of liners and bore to "stock" bore again. Going with the new liners route is probably cheaper since I wouldn't have to buy new pistons ($300).
I figure on getting at least two seasons out of a top end, so I shouldn't have to worry about it this year.

The change to 57mm from 56 is a pain...larger liners required, boring of the cases etc. The 56mm engine is very durable, cylinder walls are only about .080" thick so they dump heat into the cylinder block very quickly. But, the new thicker liners do allow boring out another 3mm or so for 230 - 235cc...for whenever I want to move up to 250gp.

Yes I think it would be quite competitive at 235cc in 250gp.
JohnnyB

PS. Zack ran a high 1:32 on Mary's bike which is a 56mm 202cc engine.



Edited by - jbranson on Apr 09 2007 7:58:42 PM
 
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