Exhaust Issue? Or Not?

[jfroman]

The other night I had the bike warming up in the driveway and as I walked around the back of the bike and my first exhaust pipe I could feel the exhaust hitting my pant leg with some force. When I walked to the next exhaust pipe the pressure was significantly lower.

 

I took my hand and moved it closer to my right hand exhaust pipe and around 10"-12" I got a hard "thump""thump""thump" from the exhaust hitting my hand. When I did the same thing with my left exhaust pipe I had to get between 4"-6" to get the same sound/pressure.

 

Is this something I should be concerned with? The bike is running great, getting 36.8 MPG on a foothill ride, and starts right away.

 

Thanks!

[Squidley]

Unless you are hearing something odd, or testing the temps of the pipes with a thermal gun and one is much cooler, I wouldn't be overly concerned. The mileage is right in line, actually pretty fair, so unless it's stumbling, I'd just enjoy the ride

[ACE50]

MPG are a little low. When's last time you did a carb sych?

[jfroman]

I purchased the bike two months ago and have only changed the fuel filter because I had an issue with it starting right away. I ride quite a bit during the week, just around town and my first two fill ups I got 34.49MPG and 34.96 MPG.

MPG are a little low. When's last time you did a carb sych?

[Squidley]

MPG are a little low. When's last time you did a carb sych?

 

Gotta remember he's in California, lots of blended gas for emissions out there, which usually doesn't equate to good MPG's. I personally have not seen an RSTD get anything better than 38 mpg, not saying it doesn't happen, but from all I have ridden them and folks that I know who own them mid 30's is about average...

 

[ACE50]

Gotta remember he's in California, lots of blended gas for emissions out there, which usually doesn't equate to good MPG's. I personally have not seen an RSTD get anything better than 38 mpg, not saying it doesn't happen, but from all I have ridden them and folks that I know who own them mid 30's is about average...

 

I get 39 to 42 all the time and runs like a banshee.

 

Check the carb synch.

[billmac]

I hang around the 45 mpg. not a lot of freeway miles usually 60 mph and below. have got up to 52 at 55-40mph.

[Hucklecatt]

It's funny, but sometimes simply having the bike on a sidestand will influence the floats and the side to side performance at cold idle warmup. You might try holding the bike upright and shaking it just a bit to see if there is a noticeable change..

 

- BUT -

 

As carefully as possible, check header temp at warmup time. A cold header pipe will reveal a lot. I would guess that your idle circuit would benefit from adjustment. Do this before you perform a carb synch.

 

- AND -

 

ABSOUTELY get a carb synch. Not hard - a long (12") standard screwdriver and a synch device to do so.

[Squidley]

I get 39 to 42 all the time and runs like a banshee.

 

Check the carb synch.

 

Thats cool, I rode one of the Hosuston members '05 for 6 months that was adjusted perfect and the best I ever got with it was 35 mpg and that was babying it.

[ACE50]

Thats cool, I rode one of the Hosuston members '05 for 6 months that was adjusted perfect and the best I ever got with it was 35 mpg and that was babying it.

 

What do you mean 'adjusted perfect'? Completely stock measurements or slightly mod'd?

 

I haven't seen a stock bike that couldn't be tuned better than a stock set-up.

As in, every bike I've owned.

[Squidley]

What do you mean 'adjusted perfect'? Completely stock measurements or slightly mod'd?

 

I haven't seen a stock bike that couldn't be tuned better than a stock set-up.

As in, every bike I've owned.

 

Bike had no mods on it, completely stock. Floats adjusted per the manual as well as the proper air/fuel mix screw set. I'm not doubting you get that kind of mileage, just stating that myself and several other RSTD bikes I personally know of just dont pull that 40 mpg. You could have great fuel where your at and that makes a good difference if your running more pure gasoline.....

[ACE50]

I get the same crap ethanol gas here. Maybe diff in altitude or riding style? Some tweaks can be done to get it to run better with a few more MPG. Stock is not necessarily best. Yamaha has to meet certain standards to sell these things.

[V7Goose]

Your symptoms are consistent with one or more pilot jets being somewhat plugged and/or carbs out of sync. If one or more cylinders are not getting full idle fuel for a hard burn, then the explosive force into the pipe when the valve opens will be less. In this case, the temp of the exhaust gas will also be noticeable cooler than the other one for the first few minutes because the pipes will not be heating evenly. The fingertip test on the cold header in the first 30 seconds of starting is also a good indication of this problem.

 

If all the headers are heating up quickly, then I'd suspect more of a sync issue.

Goose

[jfroman]

I ran the bike this morning but didn't see this post first. Can you explain the fingertip test a bit more? Should I just put my finger on the header side that I suspect is having the issue and see if it gets hot?

 

Thanks

 

Your symptoms are consistent with one or more pilot jets being somewhat plugged and/or carbs out of sync. If one or more cylinders are not getting full idle fuel for a hard burn, then the explosive force into the pipe when the valve opens will be less. In this case, the temp of the exhaust gas will also be noticeable cooler than the other one for the first few minutes because the pipes will not be heating evenly. The fingertip test on the cold header in the first 30 seconds of starting is also a good indication of this problem.

 

If all the headers are heating up quickly, then I'd suspect more of a sync issue.

Goose

[V7Goose]

This is discussed in many old threads. The test is simple, but you only have about 30 seconds to do it on a cold engine. As soon as it starts, reach UNDER each header with your finger to feel the pipe temp right next to the head. The pipes will begin heating immediately, and within one minute they will be hot enough to burn, so be quick. It is important that you do this test on the real header pipes, not the chrome shield, that is why you reach under the pipes.

 

It is also best to be able to do this test WITHOUT using the "choke", as that add adds extra fuel to the starting circuit and can mask plugged jets.

 

If any cylinder is not getting full fuel or spark at idle, it will stay cool MUCH longer than the others, so this is the quickest and most simple test to verify clean pilot jets on all four carbs.

Goose

[jfroman]

Thanks for the information. I started the bike this morning and felt all the pipes right next to the heads. They all warmed up quickly, the back two were the quickest followed by the front two not far behind. By 1 minute they were all burning my finger. I filled up today and got 36MPG with most of my driving around town and not on the freeway.

This is discussed in many old threads. The test is simple, but you only have about 30 seconds to do it on a cold engine. As soon as it starts, reach UNDER each header with your finger to feel the pipe temp right next to the head. The pipes will begin heating immediately, and within one minute they will be hot enough to burn, so be quick. It is important that you do this test on the real header pipes, not the chrome shield, that is why you reach under the pipes.

 

It is also best to be able to do this test WITHOUT using the "choke", as that add adds extra fuel to the starting circuit and can mask plugged jets.

 

If any cylinder is not getting full fuel or spark at idle, it will stay cool MUCH longer than the others, so this is the quickest and most simple test to verify clean pilot jets on all four carbs.

Goose