Thread: Carb oddities....
07-11-2009, 05:48 PM #1
I have always noticed (even after a rebuild) that there is really no difference in power from about 2/3 throttle on up. Just a bunch more induction noise.
I can actually hold my top speed, and RPM at close to 2/3 throttle.
Both plates open fully, and at the same time. I have read somewhere about a 7/8 throttle lean condition burning engines up. I obviously don't want that to happen!
I have read, and adhered to the many different "carb tuning" posts around the forum.
Or is this just something that commonly happens?
07-12-2009, 07:25 AM #2
07-12-2009, 09:59 AM #3
- Join Date
- Jun 2008
- Ontario, Canada
Yes, have the same issue with my xl760. Im going to play around with different jet sizes and high speed settings, hopefully it will change the full throttle issue
07-12-2009, 11:05 AM #4
Well, I am not going to be able to tweak with it much until I get my Tiny Tach...
07-12-2009, 02:30 PM #5
From 2/3 to wfo, do your RPM's go up? If so, how much?
By the way you said it, your R's are maxed at 2/3, correct?
This makes me think that either you don't have the power to turn the impeller higher, or maybe ...well lets see where we are here first.
07-12-2009, 03:53 PM #6
No more speed, or RPM's. Just more carb noise....
It holds at 68-6900 RPMs at WOT on the dream-o-tach. Keep in mind this is a twin, not a triple.
I screwed around with the lows, and the highs when I went out today, and I think I got it pretty close. Now the "no power difference" is from 3/4 throttle, and up so it's not as broad as it was before.
Right now, the lows are 2 turns out, and the highs are 1 1/2 turns out.
The lows WERE at 2 1/2 turns out. It runs much better, but it still gets a bog when you pin it open after idling for a minute.
I am noticing that the more I take it out, the faster is seems to get.
07-12-2009, 04:01 PM #7
My next reply was going to be about the carbs.
How is your jetting? The bog makes me think either the high needle needs to be out a bit more, of maybe you are too fat with it. I am leaning to too fat, as it is better with the screws in like you did.
I hate trying to diagnose without being there...
I myself believe that if you have any mixture screw out more than 1.5-1.75 turns, you need to go up a jet size. Mixture screws are for fine tuning, not for making up large" gaps" in jetting.
Did you do any plug chops? Mine are a nice medium cinnamon color on the insulator.
07-12-2009, 04:07 PM #8
The jetting is bone stock (whatever that is). I know about the remote diagnosis. I hate it, too. I wish I lived up around everyone who knows more about the carb stuff. I did rebuild the carbs at the end of last summer. Genuine Mikuni.
I tried to do a plug chop, but all I had with me was one of those ratty portable spark plug sockets, and couldn't get the damn things loose.
You know, the crappy, pot metal socket with the piece of L bracket that comes with it?
07-12-2009, 04:59 PM #9
Gotta love those s/p sockets......good for throwing when you are made is what they are for.
I would love to be able to help you with the jetting, but I am just a bit too far away. That and some people don't agree with my methods and results. Like when I say I run 195psi on pump and the engines lives on and on.....
07-12-2009, 05:04 PM #10
After shes warm and your at idle if you crack open the throttle what happens.
Im no expert far from it but on my 99 I started out runing decent if I just open up the throttle and bypast the low speed circuit in the carbs if I stayed in the high speed circuit I ran good but if I tried to run at 1/4 throttle is would spit and pop.
I saw no signs of being lean on top as rpm stayed steady or increased.
So it seemed to be rich on the low speed and also a little on the high speed circuits.
Put the seat in the van and turned the lows in 1/8th turn or so ran fuel through the carbs for a minuit and opened the throttle about 1/4 throttle.
She spit and Poped but not as much so went another 1/8th turn ran fuel through carbs for a minuit and opened throttle to 1/4 throttle, this time we had no spit and no pop just crisp acceleration.
No hesitation on take of now no hesitation from 1/4 throttle 1/2 throttle or 3/4 throttle power falls of at about 7/8 throttle
Ran off some gas with the seat of pipes screaming in delight then let her sit and cool of a whille (need to add dual cooling)
Put more gas in her and went back out mostly just did high speed runs and 0-6? blasts.
I did address the high speed screws before parking her I did turn in the highs twice aprox 1/4 turn and picked up rpm both times.
There may be more adjustment to the highs but its close.
You need to try pumping the primer at WOT to see if shes rich or lean it sounds like you may need more fuel up top.
What does your tach tell you at WOT
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