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  #1  
Old 10-24-2008, 09:35 AM
LegendJet LegendJet is offline
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Question carb help needed...these things are picky

I have been working on a 1978 yamaha xs1100 and before i started working on it after market exhaust had been put on it, 4 into 2 no cross over. I know it was running lean becasue it was starving itself of fuel at about 5K rpm. and i could get it to higher rpm it just takes longer. now i put pod filters on, and bumped the main jets up from 137.5(stock) to 145. That was even worse, then it would not climb above 4K rpm, i mean it would not go. I thought maybe it was rich even though no black smoke. i yanked them back off and replaced the 145 jets with 142.5. It ran even worse now. Next i tried raising the jet needle 1 notch and it ran worse, had no power and sputters like crazy and the plugs are white...I dont know the symptoms of something running rich or lean. this is a learning process and any help would be much appriciated. thanks!!
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  #2  
Old 10-24-2008, 09:57 AM
planedick planedick is offline
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Read the plugs

White plugs means extremely lean. Go bigger on the mains. Leave the needle in the middle position. Go big on the main and get the WOT part first then adjust the needle for the best mid range and finally the idle jets for best idle and transition to mains. Keep reading the plugs as it's the best way to see what the changes did.
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  #3  
Old 10-24-2008, 10:00 AM
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GARTHXS GARTHXS is offline
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carb tuning

there is a link for cv carb tuning somewhere on the site, that was helpful to me , I would put the needles back to the center notch go back to stock main jets and just go one size up for the pilot jets , for tuning start with setting the pilot screws out 1 1/4 turns from lightly seated , see if you can start it and then sync, check plug color adjust pilot/mix as needed , then sync again .

also get a manual you will need it
also search for spark plug color online here.

and good luck!
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Old 10-24-2008, 10:01 AM
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GARTHXS GARTHXS is offline
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Thumbs up dang, you beat me to it planedick

I agree with planedick
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Old 10-24-2008, 10:03 AM
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Quote:
Originally Posted by garthxs View Post
also get a manual you will need it
Here's the XS manual if you need it.
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Old 10-24-2008, 10:36 AM
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bikerphil bikerphil is offline
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Try setting your float heights 1 to 1.5 mm lower (with carbs upside down). This will raise the floats for more fuel (right side up). Always have the needle clips in the center position. Start with your idle mixture screws about 2 turns out from lightly seated. Don't tighten these screws down too much as the tips will break off and get stuck in the carb body. Make sure this hasn't happened already.
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Old 10-24-2008, 02:50 PM
LegendJet LegendJet is offline
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OK I'm going to set the needle back to the center notch, keep the 142.5 main, and set the float 1mm lower (upside down). I can't actually rev the engine up to the higher RPM range. It just will not go, not even in neutral. I can't redline the thing. I am going to make these adjustments and check timing. I should be able to get it to idle right anyways. Thanks!!
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  #8  
Old 10-24-2008, 04:12 PM
randy randy is offline
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LegendJet;

With a 4-into2 exhaust, I run 140 mains, 24mm floats and stock pilots and she runs fine, all the way up. Could you have vacuum leaks, are your carbs synched properly? Is your air filter clogged?
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  #9  
Old 10-24-2008, 06:43 PM
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TopCatGr58 TopCatGr58 is offline
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Quote:
Originally Posted by LegendJet View Post
I have been working on a 1978 yamaha xs1100 now i put pod filters on, and bumped the main jets up from 137.5(stock) to 145. That was even worse, then it would not climb above 4K rpm, i mean it would not go.

Hey Legend,

Glad you got signed on and such. Now folks, you all missed the most important part of his description, see the bolded text above!

With the 4-2 pipes and Indy filters, the large mains was the right choice especially for white plugs. BUT, the type of Indy filters have messed you up!
You probably got the inexpensive EMGO type, K&N clones, but if you look at the mounting ring, you'll see a prominent rubber LIP on the inside, and they are known to restrict the airflow for the inlet bell ports and can actually CHOKE the carbs/engine!! That's why there are several tech suggestions/MODS for the intakes to put on velocity stack type mounts for these pod filters to open up those inlet bell ports, helps to straighten out the airflow going into the carbs from more distant positioned filters.

So, first to show that the filters are your problem, just take them off, and you can do a quick test run without them, as long as you are running on a fairly clean road/area without a bunch of dust, and you'll probably find that it will run up to redline fairly quickly! Keep the other settings as previously suggested, slide needle on middle notch, the larger 145 jets, pilot jet/idle screws set to 1.5 turns out from GENTLE seat...careful, tips easily wedge and then break OFF!!

Once you see that it has power, then find a way to do the velocity stack mod, either with your OEM airbox intake boots, or with parts from LOWES like I did!
T.C.
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  #10  
Old 10-24-2008, 09:53 PM
LegendJet LegendJet is offline
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I used the airbox velocity stacks and attached them to the filters. Your right, i got the EMGO filters. I saw the post that someone made on here. Also, i figured out another problem...I felt really stupid about this one cause its happened before and I knew it. One of my vacuum lines slipped off of the intake boot and I didn't see it...yeah I fixed that problem and it runs better, but I need to adjust the float level to 24mm and put the needle back in the center notch. Once again, thanks for getting me up and running on here!!!
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It seemed like a good idea at the time....

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  #11  
Old 10-25-2008, 09:45 AM
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dbeardslee dbeardslee is offline
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Might check the vent on the gas cap as well. If it's clogged it can cause it to starve for fuel at higher rpms. JAT
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  #12  
Old 10-25-2008, 04:43 PM
LegendJet LegendJet is offline
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ok so no matter what I do It will not reach above 5K rpm. I made all the changes except i put 147.5 main jets in becasue my 145 mains have mysteriously disappeared....i checked the timing and it was right. I'm thinking the ignition module may be at fault...anybody have any other ideas??????
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It seemed like a good idea at the time....

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  #13  
Old 10-25-2008, 04:54 PM
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bikerphil bikerphil is offline
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If your plugs are still white, you gotta give that engine more fuel. With the carbs upside down, lower the floats another 1-2mm. I've worked on some of these carbs before where I had to adjust the float level 3-4 times before I got it right. BTW, what are your float hights set at now?
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79F - owned since '89 - FJ fork mod, solo seat mod, Dyna 3Ω's, 14MM M/C (168K miles)
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  #14  
Old 10-25-2008, 05:10 PM
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TopCatGr58 TopCatGr58 is offline
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Okay Legend,

Not getting over 5K with adapted velocity stacks on the Pods, plenty of fuel.

Have you verified that the vacuum slides are actually sliding vs. being stuck?

Also, take the left timing cover off, and inspect the vacuum advance plate, make sure it moves easily, the weights move, etc., IF stuck, then it's not providing any timing advance, and that, too, will hinder attaining the higher rpms. Max timing advance should occur at ~5400rpm. The vacuum advance module is more of a device to smooth the engine during cruising and for fuel economy, not really involved with heavy throttle input, actually should RETARD the timing to the more powerful range of advance vs. Xsively advanced when very little throttle is applied....sounds strange but it's true!

You can check to see if it's actually firing on all 4 with some spritzes of water on the pipes after you have warmed it up, should sizzle on each one, but if only drips on some....then could be other problems and only getting power out of 2 cylinders...most common and usually electrical....but if 1 cylinder is affected, then more likely carb problem. 1-2 and 3-4 are paired with carb commonality, 1-4 and 2-3 for electrical/igntion problems.
T.C.
T.C.
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  #15  
Old 10-25-2008, 07:14 PM
LegendJet LegendJet is offline
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the plugs are black now. I tried running it at about the highest steady rpm i could achieve, 4K rpm, and i had black plugs and i ran at about 2K rpm...same thing.the advance moves freely , i attacked a vacume pump to the advance and rode around and then applied 5.9 inches in Hg according to the clymer manual for full advance, which actualy retards it you're right, and it has a tiny bit more pep but still nothing above 5K.
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