E: Engine Blind jetting

[Bill Thomas]

If you want an Exhaust to make a road Twin FLY !!.

 

[Martyn Goodwin]

I also increased the main from a 210 to a 220 in the Amal Mk1. Always wear earplugs, to muffle the complaints of other riders about the noise of my bike. LOL

Martyn

 

[nkt267]

I also increased the main from a 210 to a 220 in the Amal Mk1. Always wear earplugs, to muffle the complaints of other riders about the noise of my bike. LOL
View attachment 22574
Martyn

I just turn my hearing aids off, sounds fine.

 

[Bill Thomas]

I do wonder why people glare at my Bike, Sounds Super to me !. Cheers Bill.

 

[davidd]

It is very difficult to get the exhaust to work correctly. It starts at the exhaust port, which is a bad design. It is very restrictive, which makes the Vincent not very sensitive to jetting changes. I asked Marty Dickerson once what jetting he used at Bonneville compared to what he used at Daytona (4000' difference) and he said he used the same jetting because it did not make any difference. When Carleton had his head flowed the first thing he found on the dyno was that changing a jet one step could get him more than a horsepower. That never happened before the head work. Before when you changed the jet it could get you a different color plug, but there were never any big spikes in HP.

The Vincent does amazingly well with big straight pipes. These are very lazy about evacuating the combustion chamber. The exhaust charge in a two inch pipe leaves with a snail's pace, but that seems to be OK with the exhaust port so restricted. The engine makes very good power low down.

If you are trying to compete with others, the only thing you can do is to increase the RPM's, otherwise, they walk away from you. You can cut the 2" pipes back to 28" or you can go to a smaller diameter and add a few inches (1-3/4" = 31"). These are just targets and they have to be tuned in. Irving said you could pick a short pulse to tune in on and then double it and that would work. I believe this is how he came up with the lengths used on the racers. I was unable to do that. My doubled straight pipe made the bike slower. This work was so expensive and time consuming that I could not do a lot of it.

Steve Hamel's 2" pipes are about the same 28" length and Steve has done a ton of dyno work. I believe this bike showed 124 BHP on the dyno.

I was revving my bike to 7000 rpm on the dyno. I suspect Steve was also as he told me that he could run up to 9000.

It is always interesting to see what the experiments of others yield.

David

 

[Cyborg]

I did a set of Mikuni slides awhile back. Decided that the guide pin slot center plane was perpendicular to the center line of the cut away and was on center of the slide. Worked out where the bottom plane of the guide slot was compare to the center of the slide, that became my rotation stop. Then measured where the cut away plane crossed the end of slide plane. Measured how far down the current cut was from the end and how much more I needed to be to make a 3 from a 2.5. Trigged out how much I needed to angle the sine plate such that a flat cut would cross the end at the same point. Zeroed on the high point at center of the slide and took very shallow cuts. Deburred with a swiss file and checked by sliding an imperial drill under the cut way, just a light drag and no lift. Unfortunately the clamping ever so lightly distorted the slides from round so I gave a few gentle taps with a raw hide while I held them in my hand. Then they slid down the bores under their own weight. If I were to do this again I would make a holding that retained them either through the needle hole or a finger on the back side.
Reason I did it was, Mikuni VM28 round slides only go to 2.5 cut away. Mikuni would make me 3's on special order at $40 a slide, minimum order 10 slides.
Showed all this to Dave Matson one evening at our monthly section meet. He looked at me and said "I just mark them with a pencil and file 'em."
Steven

View attachment 22567View attachment 22568View attachment 22566

You could use something like this to hold delicate parts. https://www.belmontmetals.com/product/117-f-47-c-low-melting-alloy/ or you could just fill the inside of the slide and use your current method

 

[vibrac]

To come back to my struggles that started this thread I chanced my local reputation (such as it is) again. (my wife said she could hear it all around my 2 mile circuit) The bottom end is clean and when I trick it into a high rev band she goes better than ever before. Now I have fitted an air lever I can see mid range just gets worse when I go richer so I think its lower the needle and try a no 5 slide unfortunately I will have to do that on the day and use up the first run in embarrassment if I get it wrong.

 

[ClassicBiker]

You could use something like this to hold delicate parts. https://www.belmontmetals.com/product/117-f-47-c-low-melting-alloy/ or you could just fill the inside of the slide and use your current method

It never dawned on me to make a filler plug to prevent distortion.

New tool the box that one. Thank you.
Steven

 

[Bill Thomas]

It is very difficult to get the exhaust to work correctly. It starts at the exhaust port, which is a bad design. It is very restrictive, which makes the Vincent not very sensitive to jetting changes. I asked Marty Dickerson once what jetting he used at Bonneville compared to what he used at Daytona (4000' difference) and he said he used the same jetting because it did not make any difference. When Carleton had his head flowed the first thing he found on the dyno was that changing a jet one step could get him more than a horsepower. That never happened before the head work. Before when you changed the jet it could get you a different color plug, but there were never any big spikes in HP.

The Vincent does amazingly well with big straight pipes. These are very lazy about evacuating the combustion chamber. The exhaust charge in a two inch pipe leaves with a snail's pace, but that seems to be OK with the exhaust port so restricted. The engine makes very good power low down.

If you are trying to compete with others, the only thing you can do is to increase the RPM's, otherwise, they walk away from you. You can cut the 2" pipes back to 28" or you can go to a smaller diameter and add a few inches (1-3/4" = 31"). These are just targets and they have to be tuned in. Irving said you could pick a short pulse to tune in on and then double it and that would work. I believe this is how he came up with the lengths used on the racers. I was unable to do that. My doubled straight pipe made the bike slower. This work was so expensive and time consuming that I could not do a lot of it.
View attachment 22576
Steve Hamel's 2" pipes are about the same 28" length and Steve has done a ton of dyno work. I believe this bike showed 124 BHP on the dyno.

I was revving my bike to 7000 rpm on the dyno. I suspect Steve was also as he told me that he could run up to 9000.

It is always interesting to see what the experiments of others yield.

David

For me the 2 into 1 With a big end pipe was far better that L/ning pipes. I tried 2" and 1.5/8 ".
Ron Gardner of Carb' Fame, Told me he thought his carb's worked better with 2 into 1.
Job to do that with a Comet !!. Cheers Bill.

 

[Bill Thomas]

To come back to my struggles that started this thread I chanced my local reputation (such as it is) again. (my wife said she could hear it all around my 2 mile circuit) The bottom end is clean and when I trick it into a high rev band she goes better than ever before. Now I have fitted an air lever I can see mid range just gets worse when I go richer so I think its lower the needle and try a no 5 slide unfortunately I will have to do that on the day and use up the first run in embarrassment if I get it wrong.

There was a Quote the other day from USA," IT's THE SLIDE " !!. Cheers Bill.