Triumphrat

Loxpump · 09-05-2006

I hate to even ask this question, but here it goes. I have a stock 2002 Bonneville. All I have done engine mod wise is to remove the AI. I have a set of Emgo megaphone mufflers on the way which from what I have heard will require some jet changes. I not looking for any performance increase with the less restricted mufflers just better/more sound.
My question is:
The jets in the carbs, control the air/fuel mixture. My engine isn't getting more air in, because the air box is still controlling that, right? The exhaust air is just leaving easier. Why should the mixture have to change? Isn't the exhaust valves closed when the intake valve opens and lets the air/fuel mixture into the combustion chamber? I have heard that it's better to be a little rich than too lean but I don't want to run richer than I have to. I do plan on eliminating the air box latter this winter and it will need changes then for sure. I guess I would like to do the jetting once and not twice.

kliff · 09-05-2006

Quote:

On 2006-09-05 13:23, Loxpump wrote:
I hate to even ask this question, but here it goes. I have a stock 2002 Bonneville. All I have done engine mod wise is to remove the AI. I have a set of Emgo megaphone mufflers on the way which from what I have heard will require some jet changes. I not looking for any performance increase with the less restricted mufflers just better/more sound.
My question is:
The jets in the carbs, control the air/fuel mixture. My engine isn't getting more air in, because the air box is still controlling that, right? The exhaust air is just leaving easier. Why should the mixture have to change? Isn't the exhaust valves closed when the intake valve opens and lets the air/fuel mixture into the combustion chamber? I have heard that it's better to be a little rich than too lean but I don't want to run richer than I have to. I do plan on eliminating the air box latter this winter and it will need changes then for sure. I guess I would like to do the jetting once and not twice.

because most every 4 stroke engine made, including the Bonnies, has what is called "cam overlap," a period of time when both intake and exhaust valves are open. This occurs so the exhaust, which you just improved, can start the intake flow, by "scavenging the combustion chamber." Therefore it is actually sucking some of your intake mixture out of the exhaust. Even tho you may NOT have improved the intake path, it WILL be operating more efficiently, supplying MORE air, due to the improved scavenging.....it's gonna NEED more fuel to go with that air.

Geoff · 09-05-2006

ok, scientific. well, no. Triumph itself will provide richer jets when you buy their TOR, or performance muffler.
If only adding the mufflers did not require a richer mix, would the notoriously cheep manufacturer provide them?
If the emgoes are louder and more flow thru than TOR (which they are) would they not require an even richer mix?
Geoff

Loxpump · 09-05-2006

I'm not doubting that the Emgo's and TOR's require jetting changes regardless or who made the pipes. It's the amount of restricted air flow that would determine that. I'm buying the mufflers from an individual not a manufacturer, so I'm not getting jets included. I can get that info/jet size needed from my dealer. The explanation from Kliff makes sense to me. I knew I could get an answer. Thanks.

ohiorider · 09-05-2006

Pg 10 provides several jetting combinations depending on how you're configuring your bike. In general, the Jenks book provides a lot of info in less than a dozen pages. Have fun!

J E N K S L I N K

Bob

[ This message was edited by: ohiorider on 2006-09-06 07:44 ]

kliff · 09-05-2006

Quote:

On 2006-09-05 14:11, Loxpump wrote:
I'm not doubting that the Emgo's and TOR's require jetting changes regardless or who made the pipes. It's the amount of restricted air flow that would determine that. I'm buying the mufflers from an individual not a manufacturer, so I'm not getting jets included. I can get that info/jet size needed from my dealer. The explanation from Kliff makes sense to me. I knew I could get an answer. Thanks.

Glad to do it man.....wish I could be of more help with selection, but the "Jenks link" provided by Bob will most definitely be of use to you.