Should I Run a Single Muffler or Duals? - VFR700

Hey guys, on my 86 VFR700 I'm trying to decide between cutting off the stock mufflers and bolting on 2 new slip-on mufflers or just buy one muffler and use the money I save to have a 4-2-1 pipe built. (Or reuse the stock collectors and just fab a 2 to 1 section)

I know a single muffler has more than enough flow to handle the job and it's a bit more modern looking. I've heard both set ups and they both sound really good. A single is a bit lighter weight, but weight is not a big deal for me.

So it's mostly down to looks. What do you guys prefer looks wise?

 

I like my 4-2-1 with the Yoshimura it has on it. Looks great, sounds great, and as stated it saves weight. Mine seems to be mounted quite a bit higher than other 2nd gens I have seen though (bought the bike with it previously installed.) If you make your own pipe you should fab it so that it exits at a nice high angle IMHO. You could do the same with dual mufflers too I suppose. Kind of like the RC51 exhausts that use the passenger foot peg mounts. That'd be pretty sweet.

 

You will have to rejet going 4-2-1, just keep that in mind.

 

Enlarge the mains or raise the needles? I wouldn't think that carb adjustment is necessary with exhaust changes, only with intake changes.

Btw, wouldn't the dual muffler be way less restrictive than the single setup? So if the single pipe did need carb adjustment, I'm sure the dual setup would need it as well.

 

I'd like to get a set of the factory hard saddle bags, but I doubt I'd ever find any. So mounting the cans a bit higher is a definate option. They look good a bit higher.

Could you post a pic of your exhaust?

 

I kmow both setups sound good, but does anyone know if the there is a difference in sound volume?
I know on a car that single pipes are quieter than duals when using the exact same muffler. Would the dual pipes on the bike be louder at high rpms? I'm not real sure on this one.

 

personally of all the different ones I've heard the supertrapp slipons sounds the best. and you can add or remove discs for sound and adjust flow.

 

Supertrapps are very expensive, so are not an option. The supertrapps were unique in that they were the only dual setup that didn't use chambered mufflers (that I know of). It's a good sound, definitely.

I'm gonna try and gets some quotes of having a simple 4-1 or 2-1 section fabricated. Who knows, every shop around Houston might say $400 and up and my decision will be made for me.

 

I haven't done it since I have the original mufflers on my bikes but they say the 6-7k flat spot becomes more pronounced with a 4-2-1 setup than with original.

 

An update:
I got a qoute from a local motorcycle exhaust shop here in Houston to reuse the stock collectors on each side and fabricate a 2 to 1 pipe for $200. A new Delkevic muffler is about $170, so it's not too bad for $370 dollars. It's just a tad more than buying 2 new mufflers and slipping them on the stock pipes.

Then, just last night, fate intervened. I bid and won an eBay auction for a yoshimura 4-1 setup. It's a little rough, but only $230 shipped.



I'll sand and paint the pipes and run that muffler for now. Later on I can replace it with a shiny new can. I might even look into ceramic coating the pipes that shiny chrome looking coating for even better looks.

I basically hit the rare parts motherload this week. I also got a seat cowl and a center stand. I'm hoping the stand can be made to work around the new exhaust. I'll have to wait and see.

 

Does you setup look like mine with the short can behind the foot pegs or do you have the yoshimira with the longer can that has a mounting strap around the muffler?

 

That's almost the exact setup that I have on my 86 vfr750, I have a K&N filter and a yosh 4-1 pipe (pic attached). The jets are all original - would anyone suggest re-jetting? If so what should I go with?

I'm taking them off some time this winter to clean and re-sync. Now's the time to do it if I'm going to do it at all.... there has ALWAYS been a lag at JUUUST before 8k RPM.

TIA!!!!!

 

I read about that before but could never figure out what TYPE of washer to use. Here's a pic stolen from the interwebs that I _THINK_ outlines what you're referring to:

What do you use to keep them from sliding around? Please understand that I know enough about carbs to take them off and clean them, and their basic operation, but the exact tuning is always been a bit of a black art to me ;-)

 

I think there's another thread on this topic (and likely others as well: http://vfrworld.com/forums/showthread.php/35967-1987-VFR700F2-Exhaust).

I'll browse a couple other topics and fiddle with some torn spares with needles before I get working on the actual bike (bought a grab-bag of RC24 carb parts a year ago on eBay - best $50 I ever spent. Too bad the seller removed them from the plenum).

 

[Reposting this which was originally placed between posts #12 and #13]

".....JUUUST before 8k RPM."

Try putting a small washer or two (.020") under the top of the slide needle. :glee:


No black art for tuning simple street bikes: just a few back-to-back experiments--based upon readily understood technical principals-- to find best settings for any bike. Black art is finding best compromises between competing requirements.

 

Once you get the slides out, go to the hardware store and look through the smallest stainless steel flat washers. The ID needs to be big enough to slide the needle through and the OD needs to be small enough to fit inside the diaphram. The picture you have is correct. Drop the washer into the diaphram and center it up. Then drop the needle down over it. Then the spring pushes down on the needle to hold it semi firmly in place.

(BTW, there is a limit on how many washers can actually fit. The needles have the spring above to allow them to move around slightly and self center themselves. Too many washers and the needles can't self center and they get sticky and wear the sides out. Not good at all. So limit yourself to 1 or 2 washers if they are thick. 3 washers if they are thin.)

The needle is tapered and as the diapram moves up and down based on engine load and RPM, etc... the gap around the needle and the hole it goes into (the NEEDLE JET) changes. Fuel gets sucked up through this needle gap. Adding a washer or 2 lifts the needle which means the gap is a tiny bit larger through out the range equating to a slightly richer fuel mixture through out the range. Make sense?

Shimming the needle up higher typically effects the middle rpm range and is usually done when you have a less restrictive exhaust.

On the intake side, when you add flow by removing restrictions (gauze filter, airbox holes added, etc...) you tend to run lean on the top end of the RPM range. So you need to add fuel to the upper RPM range. This involves enlarging the main jets. You can either remove your current jets, verify they have not been drilled out, note the jet size, order new jets slightly larger, then install them. This takes time and money as you wait for your new jets to arrive.

The alternative is quicker and cheaper. Remove your current jets, verify they have not been drilled out, note the jet size and use a chart to convert to Wire size. Then choose the next larger wire size, go to tool store and buy a precision drill bit in that new size. Drill out old jets carefully by hand, remove jet size number on side of jet and install them.

I played around with this stuff a lot of my previous bike. It's a bit trial and error. I chose not to modify my main jets on my VFR so I made sure to use a paper filter and stock airbox/snorkle.

My Yoshi exhaust has a 1.5" outlet which is exactly the same surface area as the stock twin 1" outlets so I don't think my exhaust requires any carb adjusting. Maybe a tiny bit since the factory settings are very lean. I already readjusted the pilot screws a bit richer (2 complete turns out) to make it crank and idle better.

My bike runs extremely well, but on the freeway, cruising at 5500rpm, if I go part throttle to half throttle the bike takes off. If I twist any further (half to full throttle) I can feel the power just drop away until I hit about 7K rpm. Then it takes off. So the next time I have the carbs out I will add one small washer under each needle and see if that helps, hurts or does nothing. I doubt it will hurt anything except maybe fuel mileage, doubtful though. If it helps, then I may later try 2 washers under each needle.

I'd like to have my bike dynoed to verify the fuel mixtures under load, but I haven't found any dyno places locally than can do this on older bikes.

 

Ok - for those reading, this explained a LOT for me regarding throttle position and when I'm experiencing my "lag" (scroll to about 15:30, but it's all worth watching): https://www.youtube.com/watch?v=y836ZPjvoMI

 

I'd definetly go bigger on the main jets. Maybe 2 jet sizes or more. If you have 118's then shoot for around 122-124. If you choose to drill, the closest drill size would be an #55 which is a 133 jet size. Most tool specialists carry individual precision drill bits for about a $1 each. I'd also add one washer under each needle.

As I mentioned earlier, your exhaust should be just like mine with a 1.5" outlet. That's equal to the factory outlet size. Although, the factory mufflers were chambered, whereas ours are straight through. So that probably increases exhaust flow a little more than stock thereby creating a need for that extra washer? I'm guessing so.


Here is a quick reference for:

Jet size - Drill bit wire size
110------------57
119------------56
132------------55
140------------54



I mention verifying what jets you have currently. Sometimes people will drill out jets and leave the number on the side. That's a no-no. It will just confuse people later on. A quick way to verify they are still stock size is to take a cleaned jet with you to the tool store. The blunt end of a 57 drill bit should fit into the jet, but an 56 should NOT fit. If it does, your 118 jets are not 118's. Keep trying drill bits until you figure out the size the jets have been drilled to. Write down the size so you don't forget and then remove the stock numbers on the jet.

 

He is incorrect about how the needle and main jets work at 6:30. As the tapered needle moves up and down the small gap around the hole it goes into (the NEEDLE JET, the top of the main jet tube) is smaller than the main jet size (screwed into the base of the tube). So that small gap determines how much fuel gets sucked out. Then once the diaphram and needle go up further that needle gap gets larger than the main jet size at which point the jet is the limiting factor. I don't know exactly how high the diaphram needs to be for the main jet to became the smaller oriface, but at high load, high rpm when the diaphram is lifted all the way, the main jet is definetly the smaller restriction.

 

Test results... inconclusive. =)

The spares box had a mixxed bag of diaphragms and some are the keen notched ones with a c-clip, the others are standard (that's eBay, right? You rolls the dice and you takes your chances).



I wrote down stamp on the mains before, they are still labelled 118. BUT - since this bike was a tweaked race bike it will be anyone's guess what I see when the diaphragm covers come off. I'll measure the opening anyhow - thanks for the reference!!! If the needles are notched I'll have to research what the "standard" height is and check the difference. One worry is that I have a 750 and _IF_ any of the sets I bought were from a 700, (and I don't have the manuals for the 700) I can't trust these as an example.

This is getting fun. :torn: