Jetting & Airbox Mods With Vance & Hines Pipes;

[JungleJustice]

So, I have a set of the street V&H pipes on the way and I have heard of guys who simply drill additional holes in the top plate of the airbox on the GS 1100 - saw one set up like that on an E like mine recently...

What is best; is there a jet-kit that is a better option? I have a standard motor and standard carbs (for now)!

[tkent02]

The intake to the airbox is not the biggest restriction, I had one where the two intake holes were joined into one large oval, it flowed slightly more air than the stock box. Try running it with the airbox lid off to see what you think. Mostly it just sounds louder. Changing only the pipe won't require too much of a jet change.

[JungleJustice]

Thanks. Something does not jibe for me here (and forgive the seemingly stupid question); I come at this with a good amount of experience with fully-programmable, stand-alone engine management systems and modifications however, mostly to street and race cars!

With the pipes, you're increasing airflow - right - and yes - more out would dictate a requirement for more in then? In terms of fueling though, it runs counter then to provide more airflow (via airbox mods), when the real need would seem to be for more FUEL - no? It would seem that jetting would be the way to go, or should I be thinking in terms of an "air" jet versus a "fuel" jet?

[tkent02]

If you increase airflow, you must increase fuel flow as well, the problem with these CV carbs is that the intake restiction is very carefully controlled, once it is changed it is very hard to get the engine to run correctly in different conditions, and especially to compensate correctly for changes in elevations which CV carbs are designed to do. If you ride mostly at one elevation you can get fairly good results with a DynoJet kit, perhaps not as smooth at low power as stock, perhaps not as good gas mileage, but hopefully a bit more power on top. Even with the kit a lot of trial and error is required to get it as close to perfect as it can be.

[GS-ESW]

V&H pipe and airbox mod.

Hey there Jungle Justice, GS-ESW here,
I'm the guy who parked next to you last week, with the same old sweet ride. Glad to see you've joined the Resource. As per our extensive conversation, you have addressed all the subjects we talked about. Cool. My Vance and Hines pipe is #V12001. I paid $310.21 for it last year. The included directions say to remove the air-box lid. I did the drill-out thing instead, to have more control for fine tuning the lid-free idea.
Good luck, and congratulations on obtaining this beast of a relic.
1980 GS-1100-E, is the beginning of the Hyper-Bike. Previously, there were only Super-Bikes.

[JungleJustice]

Hey Eric! Cool - thanks for all of the info and pointers...! (Followed your suggestions to the letter - got my Progressive rear coil-overs on order. I have the V&H pipes on order, the GS1000S clutch-cable on order and I installed the choke cable by the way - works perfectly now)!

So, yeah - not second-guessing you here - just trying to clarify something; V&H pipes = more air flowing through the "pump" (and with it - the airbox-lid drilled or removed entirely = more air moved...).

Fine. I have that most basic of premise down; my questions then becomes - fuel? Where does the extra fuel come from if you're not re-jetting?

[GS-ESW]

Vance & Hines pipes no need to up the Jets...

I am no expert on the subject, but I just know what I did, and that it works perfectly. I put the pipe on, and drilled many holes in the airbox lid. I believe V&H did all the engineering, to allow the stock jets to remain. I go ten miles an hour faster in each gear, at around four to five thousand on the tach. I think there is way less back-pressure due to the 4-into-1, and this may effectively increase gas flow; I do know the holes in the airbox lid increase air flow. I used to run K&N pods on all my previous GS-1000's, and with any header at all, rejetting was mandatory. They often fowled plugs in bad rain, or mountain elevation changes. I dig the "works all the time" nature of the airbox. The true reason for no rejetting, is a cosmic mystery. You will be very happy with how the bike responds. I have found no deadspots in the entire RPM range. Excellent product.
Good luck, Sir Jungle Justice. GS-ESW

[JungleJustice]

Thanks again Eric!

Any motorcycle rolling-road dynos in the Seattle-area? (I can tell you where all of the car-chassis dynos are...)!

I'd like to get the mixtures checked under various load and rpm scenarios.

[drhach]

Fine. I have that most basic of premise down; my questions then becomes - fuel? Where does the extra fuel come from if you're not re-jetting?
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I don't think you're missing anything. More air means more fuel needed (jetting). The A/F ratio must remain the same. I think TKent's comment was, "minimal" jetting, not "no" jetting.

[tkent02]

I go ten miles an hour faster in each gear, at around four to five thousand on the tach.

Um, OK.

[Big T]

CV carbs are like no other "engine management system". They are picky and mean

Your best approach would be to install your pipe and start with the plug chops. A Dynojet or Factory jet kit may be needed, mostly for the adjustable needle.

I don't know anyone up there with a dyno, but that's going to add up some serious $$$ to your tuning costs. I'd bet South Sound BMW has one. Or Seattle Ducati

[GS-ESW]

switching to a 4-into-1 from stock pipes.

My previous statement about going ten miles an hour faster, in each gear at around four to five thousand on the tach., is simply a reference to the end result. It is not meant to be anything more than an observation. I always guage how fast I'm going by the tach.,as well as the speedo; this is in case my speedo cable breaks, and a cop is behind me. I have replaced stock dual pipes many times on many GS-1000's. Each time I noticed this general speed increase from the old pipes. It may not be of any help to anyone's pipe switching knowledge base, and I hope that mister tkent02 isn't too offended by my absolute disregard for technical correctness. Um, OK?
Now to Jungle Justice, I was going on memory about the included instructions. I put the pipe on last May, and thought I only kept the reciept. Your point about needing more gas had me looking all over for those instrucions. Well, I found them in the shop. You should be getting them too, if you ordered the same pipe. The instructions say to remove the stock airbox lid, and increase the main jet to a 122.5. The pilot jet should be raised to a 47.5.
I picked up my 1980 GS-1100-E two years ago. It came with a crappy MAC 4-into-1 pipe. The guy I bought it from told me that he didn't have to rejet it for the MAC. When I put my Vance & Hines on, I drilled out the airbox lid, and gave it a test run to see if I really had to rejet it like the instructions said. That was one year, and seven thousand miles ago. I get 37 miles to the gallon, driving hard most of the time. The bike runs so well, I see no reason to open up the carbs. Sorry I forgot about these details, but it has been a year, and I am apparently mostly an idiot. My intent is only to help, and I hope this does just that.
Good luck, GS-ESW

[JungleJustice]

Eric, while your comments are directed mainly at another respondent, I feel obligated to comment - only to say that your knowledge is VERY much appreciated, your openness and willingness to share is EXTREMELY refreshing (in the face of the eminent sniping that I see on so many of the other forums that I frequent) - and - you are a nice-nice guy!

Thanks SO much for the time that you spent with me on Saturday and for sharing all of your trial and error! You are truly passionate - no wait - rabid when it comes to the GS moniker (and you have the scars to show for it...) I'm the new kid on the block and I was not looking to cause waves!

We all understand (including Eric) that the relationship between the engine rpms in a given gear remains a constant variable in relation to wheel-speed - REGARDLESS of an increase or decrease in horsepower (within reason - for a motor that is running relatively well and where no changes were affected to chain and sprocket ratios...)!

I am sure that Eric was simply referring to the increased feel of torque (experienced in the all-knowing butt-dyno) and the commensurate lower effort that it takes for the bike to power forward at a constant rpm. Eric understands that the engine and the rear wheel are both still turning at the same relational speed that they were before - regardless of any minor increases or decreases in horsepower or torque!

What tkent02 missed in my initial comments and questions was that I DO posses a very fundamental understanding of air/fuel ratios! (I've literally spent hundreds of hours on the dyno tuning fully-programmable stand-alone engine management systems these past 7-8 years)! My question remains: unless there is something that I missed, how does addressing the need for more air on the inlet (to accommodate the increased air-flow on the exhaust side of things with the V&H pipe), address your now OVERALL increased need for fuel to keep the AFRs within the optimal ranges - without going with larger fuel-jets to increase the fuel supply to meet the increased air-flow and so on...!?

[chef1366]

I'm with Tom with the above statement.


Put in a 47.5 pilot jet
117.5 main jet
Shim the jet needle 1-2 washers
2.5 - 3 turns out on the idle mixture screws
Air box lid removed.

[JungleJustice]

The stock-stock 1980 GS1100e pipes are for sale BTW - 200 bucks.