Carb Problems! or Maybe Not

[boy1der]

About a month ago I started restoring my Dads 79 XS11SF. It's been parked in a barn for over six years. After scraping the bird crap off it, I started the process of rebuilding. I've repaired most everything from brake systems to body work to gear fixes. I can not begin to tell you how helpful this site has been! But on to the problem. Everything has gone well except the carb work. I'm way beyond triple cleaning. Here's what I've done.

1. Had the gas tank treated and sealed by the local radiator shop.
2. Removed and stripped carbs. Cleaned many times. put in new float valves.
3. New plugs ngk brand 6es or something like that.
4. Cleaned K&N Indiv. Filters
5. Applied the diphram coating fix, as listed in the tech forum.
6. Repaired and tested petcocks and Octopus
7. Replaced all feul lines and have verified the route with this site and clymers manual.

With that said here's the setup
1. Accell Super Coils and Wires (put on the bike back when it ran)
2. 4in1 kerker exhaust
3. Indiv. K&N Filters
4. Jets= 180 air; stock needle, needle jet, and pilot jet; 150 mains
5. My needle is set in the middle slot.

Here's the symptoms
Bike idles well both on and off choke. The transition from idle to mid kills the engine. If I crack the throttle she dies right at 1700rpm. If I ease the throttle she can reach 2500 but only for a moment then spits sputters and dies. I felt it was lean, so to test I let the bike warm up and then spray some starting fluid on the filters and crack the throttle. She runs like a champ ful rev no hesitation but only for a moment. I need your help...... what to do next?

[Mike Hart]

The starter fluid trick sure seems to confirm that you aren't getting fuel.

Where is your float height? Is there a way you can confirm the bowls are getting 'full' of fuel?

When you cleaned the carbs, did you blast out the various fuel/air passages with compressed air?

[boy1der]

Yes, on blowing out the carbs. I even used the little toothpick tool and cleaned the holes in the needle jet and pilot jet.

I plan on checking the float level tonight.

The problem is how! The best I can tell is measure using a reference points as the clymers indicates. and then fill the bowls, cut off the gas supply then drain each bowl 1 at a time and measure the volume of fluid. try to get them the same.

Any idea how much I should have?

Would you agree with this method?

[ratbyk]

Carbs

I concure with Ken that your problem is float height related. The primary or main curcuit consists of the main jet, needle, piston and diaphram. After all of that cleaning I doubt that the main curcuit in all 4 carbs is plugged. Reset your float level higher. Remember you set this with the carbs turned upside down. Measure from the main carburetor body- the surface that the float bowl would contact- to the bottom of the floats (now the top while inverted). The floats should be in a "relaxed" situation. Resting gently on the springs inside the needle valves.
Stock float height calls for:1.012" plus or minus .004" or 25.7 mm plus or minus 1.0 mm.
To make my Ratbyk run the way I like I have been increasing my float height steadily. Finally at 1 3/16 it started to "sing" and come "alive". I have settled on this height as ideal for my bike.
Hope this helps.
Ken/Sooke
78E Ratbyk

[skids]

I think you should ease it up to the highest rpm that it will hold, let it run as long as you can and then throttle it up a little till it dies and then check the plugs to see it they are wet or no carbon at all. (too rick or too lean). Gee, you really need a color tune tool right now.

[boy1der]

Ok I set the float height to stock on all carbs. Very little change. Moved jet needles down two slots to its richest setting and my throttle came alive. I now have throttle response and a good idle. Sounds great, but one problem. After I’ve raise the rpm’s for a few moments it acts like it runs out of fuel. This is more prominent when I slowly raise the rpm’s. Do you think my float bowls are set to lean now? I even ran the cycle on prime and it still did the same. HELP. Also just found out that my mains are actually 147.5.

[ratbyk]

Carb Problems

I had a similar problem. That is why I kept raising my float level. One small step at a time until I reached 1 3/16" It then was alive everywhere in the RPM range.
My mains are much smaller than yours though at 137.5. 137.5 is the stock main jet size. If you have 147.5's then someone has put bigger jets in.
For your reference my carbs are:
Mains-137.5
Pilots-45
Air-210
Needles-5GZ6
Float level-1 3/16"

It really is a sweet runner.
Ken/Sooke
78E Ratbyk.

[CA.XSer]

Also just found out that my mains are actually 147.5.

My 79SF had Kerker 4-1 with stock air box and 137.5 mains. I now have a 4-2 Jardine with K & N filter in stock air box with 142.5 mains and it is running rich. I belive you are way to big on mains. I would go no bigger than 142.5.

[boy1der]

Ok I still have the same problem! My needles are set on richest setting.(which is the only way I was able to get any throttle response at all) It starts and idles well and has fair throttle response upto 2500rpm after that spit, sputter, die. If I slowly raise or crack the throttle theres no difference spit sputter die. So I tried to idle, spray filters with starting fluid and she again runs like a champ. I can drop and raise rpms with no hesitation at all.but only until the fluid goes dry. I thought maybe it was the slides so I tested them (pushed them up plugged the hole and they very very slowly drop) Also noticed during the spit sputter die process slides were moving under load.

HELP HELP HELP!

[ratbyk]

Carb Problems

Raise your float levels. As the slides go up the vacuum in the carb throat falls off and it is not strong enough to draw fuel any longer from being too low in the bowl.
Ken/Sooke
78E Ratbyk

[boy1der]

ratbyk

Sorry if this sounds like a stupid question, but by raising the float levels do you meen that with the carbs upside down my float top should be greater or less than 1"?

[ratbyk]

Carb Problems

Slightly more than one inch. Stock is 1.012" plus or minus 0.04". In metric it is 25.7 mm plus or minus 1.0 mm.
On my bike I had to go to 1 3/16" to make it run right.
Yours with the larger 147.5 mains may not have to be as great.
Ken/Sooke
78E Ratbyk

[Geezer]

The stock pilot jets cannot flow enough to feed an engine with those modifications. The pilot jets control the mixture between idle and 1/4 throttle.

Be careful replacing those jets. The new pilot jets that I bought at my local Yamaha dealer were of a different design than the ones in my carbs and ran way too rich. If it weren’t for the fact that I only had one new jet, it might have taken me a while to figure it out. The way it was, it was the only carb with a new jet and the first thing I suspected.

Look down the end that goes into the carb on the jets and if the new ones seem huge, they're the new style and won't work right in your carbs.

Geezer

[harvdog42]

Make sure the petcocks on the tank are clean and not blocking fuel flow.

Jim

[ratbyk]

Carb Problems

After thinking some more about your probem I think you really need to raise your float level. If it will start and run at idle but will not rev up. It indicates not enough fuel. Especially if it will rev when you hit it with starter fluid and provide extra fuel.
If you have the floats set at the stock height of 1.012. Then I would reset them to 7/8 of an inch. This will raise the fuel level in the bowls by an 1/8".
Your problem is not enough fuel not too much fuel. The previous post about the pilot jets is true and valid but not in this case. You are not getting enough not too much.
Ken/Sooke
78E Ratbyk