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Message started by Brandon4d on 06/04/22 at 19:46:22

Title: 80 MPH Chug
Post by Brandon4d on 06/04/22 at 19:46:22

Ideas on where to start.

2008 S40. Never really did highway cruising but I have latley and the bikes not acting right. 0-70 bike seems good to go, no issues at all. The only issue I've seen is it won't start with the choke out at all. The choke has to be pushed in or "off" to start the bike. Outside of that, accelerates great, runs great.

75ish to 80 it starts chugging on the highway, lunging almost. It's so bad that I have to either get off the highway or off to the side. If I slow down its great. Sometimes if there is a strong headwind, same thing even at 70 mph. I normally pull in the clutch, go to neutral and cost to a stop. Today it was doing it on the highway and I attempted to "ride it out" as I got off the highway and it was backfiring like crazy.

Mods:
Cone filter - K&N RC-1250

155 main

Can't remember the other jet size.

Exhaust - VooDoo Industries VC403 Chrome Universal Cafe Style Exhaust Pipe

Aftermarket Petcock - 5LP-24500-01-00 Fuel Valve Petcock Assembly Replacement Compatible with YAMAHA 2005,2004,2003,2002,2001 YFM660R RAPTOR 660# 5LP-24500-01-00

Location:
Las Vegas

Title: Re: 80 MPH Chug
Post by justin_o_guy2 on 06/04/22 at 19:52:57

Stock petcock?

Title: Re: 80 MPH Chug
Post by Brandon4d on 06/04/22 at 19:54:26

No, aftermarket. Updated post, sorry should have put that in there. ;D

Title: Re: 80 MPH Chug
Post by justin_o_guy2 on 06/04/22 at 20:04:35

Well,, aftermarket can be better or not. If it's a 12 dollar Chinese knockoff it probably has skinny lines and doesn't deliver fuel as well as the bike wants.
Have you ever run the bike at 75 or more and it ran well?
After the new petcock?
You will get more help when you take the time to talk about your history with the bike.

Title: Re: 80 MPH Chug
Post by Brandon4d on 06/04/22 at 20:18:02

Never ran it at highway spoeds with the original petcock as it was faulty. I'll have to possibly try a new petcock. Do you think that specifically could be an issue ast those speeds and those speeds only?

5-6 months of 60 mph or under with the current setup, no problems. Never did highway driving.

Title: Re: 80 MPH Chug
Post by justin_o_guy2 on 06/04/22 at 20:57:35

High speed uses the most fuel per minute.
I'm not asking more questions.

Title: Re: 80 MPH Chug
Post by verslagen1 on 06/04/22 at 21:38:49

Yeah the 'chug' is a fuel problem.
1st cause has been eliminated by upgrading to the raptor petcock.

Do you have a fuel filter on it? That's the 2nd likely cause.

Did you remove the plastic shield from the new petcock when you installed it?

The new petcock has a screen... check that and there's a screen above the float valve, check that too.

Last thing I can think of is the float level.

Title: Re: 80 MPH Chug
Post by Brandon4d on 06/04/22 at 22:01:21

No inline filter, but I'll be pulling the petcock in the A.M and checking the all other above. Thanks!! I'll reply either way!

Title: Re: 80 MPH Chug
Post by Serowbot on 06/05/22 at 06:03:51

It could also be a clogged tank vent. Some vent in the cap, some vent via tube to a canister.

Title: Re: 80 MPH Chug
Post by ohiomoto on 06/05/22 at 11:06:07

1. These bikes are not very inspiring over 75 mph.

2. Some cone filters block the air ports on the rear of the carb. It has also been proven (on a dyno) that some pod filters actually breathe worse than the stock airbox so there is no guarantee that the pod filter is a "performance mod".*

3. Same with the pipe, it may or may not be an improvement.

4. My bike would hardly go 70-75 with a 155 main in there. It's just too rich for a mostly stock motor. I reduced my main jet to 147.5 and it will go 85 before it gets soft. That's with a dyna pipe and me on the bike (I'm 6'3" tall and probably close to 270 with my helmet and a small bag with my lunch and water in it.)

*I'm not sure where I saw the blog or video but I remember the bike had a red tank and a RYCA supplied filter. If I can find it I'll add a link here.

Title: Re: 80 MPH Chug
Post by DragBikeMike on 06/07/22 at 02:42:55

Hey Brandon, what did you find?

You can check for sufficient fuel flow by removing your float bowl, placing a suitable container under the carb, and turning on your petcock. You need to determine how much fuel the system will flow in one-minute.

You need about 6 ounces per minute to support 35 horsepower.

You want to perform this test through the normal flow circuit. In other words, through the petcock, fuel hose, and needle & seat. To verify that the tank is properly vented, your gas cap must be installed while you are doing the test. If it doesn't flow at least 6 ounces per minute, something is wrong.

Your carb will look like this picture with the float bowl removed. See the little tang circled in yellow. That tang adjusts float drop. If you aren't flowing at least 6 ounces per minute, and none of the components are obstructed, try adjusting your float drop to allow the needle to open a little more. See if that increases fuel flow. Make sure the system will deliver at least 6 ounces per minute.

Good luck.

Title: Re: 80 MPH Chug
Post by Brandon4d on 06/21/22 at 20:05:09

Well, not much help to my own post. The tank did have debris in it and I cleaned it all out. I ended up getting the VM36 carb and slapping that on. I've had to many problems with the stock carb and couldn't ever get it dialed in and or stop it from leaking at the seals etc. So far the VM36 is has kept me cruising above 80mph without a hiccup.

All I can say is my jetting on the stock carb seemed great according to the spark plug. I guess this mystery will be chalked up to a bad float possibly?!?!

But if you want to entertained for thr day.....just know I ruined a new tire with my bobber fender and clearance hahah!
[img][/img]

Title: Re: 80 MPH Chug
Post by TheSneeze on 06/21/22 at 21:38:08

Fine line between hugging it and rubbing it.